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Mammary Gland - Anatomy & Physiology

2011-03-21T10:48:50Z

Dhogg:

== Introduction ==

[[Image:Cow teat 4.jpg|thumb|right|250px|Dissection of a Teat of the Bovine Udder,Courtesy of Andrew Crook, Copyright RVC 2008]] [[Image:Suspensory structure of udder.gif|thumb|right|250px|Suspensory apparatus of the udder]] [[Image:Udder lymphatics.gif|thumb|right|250px|Lymphatic drainage of the udder, Copyright DeLaval 2008]] [[Image:Active Mammary Gland.jpg|thumb|right|150px|<center> The Active Mammary Gland. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]] [[Image:Active Mammary Gland high power.jpg|thumb|right|150px|<center> The Active Mammary Gland at High Power. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]] [[Image:Mammary Gland myoepithelial cells.jpg|thumb|right|150px|<center> Mammary Myoepithelial Cells. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]] [[Image:Mammary Gland lactiferous duct.jpg|thumb|right|150px|<center> Section of the Mammary Gland showing a Lactiferous Duct. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]] [[Image:Mammary Gland teat canal keratin plug.jpg|thumb|right|150px|<center> Cross Section through the Teat Canal of the Mammary Gland showing a Keratin Plug. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]]

The mammary gland is a modified sweat gland that nourishes the young. It consists of the '''mamma''' and the '''teat'''. Undeveloped in both the male and female at birth, the female mammary gland begins to develop as a secondary sex characteristic at puberty. With the birth of the first young, and first lactation, the mammary gland attains its full size and function. When suckling by the young stops, milk production ceases and the gland regresses. Shortly before the next and subsequent parturitions, the gland is stimulated by hormonal changes to produce milk.

== Development of the Mammary Gland (prenatal mammogenesis) ==

An ectodermal thickening developes along the ventral body wall extending from the thoracic to inguinal region - this is the '''mammary ridge'''. Cells aggregate, multiply and differentiate to form a chain of condensed '''mammary buds'''. Most mammary buds regress but those that remain each develops into a '''mammary gland'''. A mammary gland is the secretory and duct system associated with one teat. Mammary buds grow into overlying mesenchyme, and '''primary epidermal sprouts''' grow out of the bud apex. The epidermal sprout branches extensively and develops a complete '''duct system'''. Mammary adipose tissue is derived from mesoderm. This is required for complete mammary development and is absent in the male. As a result, mammary development in the male is halted at the epidermal sprout stage.

== Structure ==

The '''mamma (pleural = mammae) ''' is the glandular structure associated with a '''papilla '''(teat) and may contain one or more duct systems. The '''udder''' is a term designating all the mammae in the ruminant and the mare (sometimes also used for the sow). The '''lobes''' are the internal compartments of the mamma, separated by adipose tissue. The lobes are divided into '''lobules''', consisting of connective tissue containing '''alveoli''', which are clusters of milk secreting cells. The '''lactiferous ducts''' are large ducts conveying milk from the alveoli to the '''lactiferous sinus'''. The openings of the lactiferous ducts convey milk formed in the alveolus to the gland sinus.

The '''lactiferous sinus''' (milk sinus) is the milk storage cavity within the teat and glandular body. The '''gland sinus''' is part of the milk sinus within the glandular body and the '''teat sinus''' is part of the milk sinus within the teat.

The '''teat''' is the projecting part of the mammary gland containing part of the milk sinus. The '''papillary duct '''(teat canal) is the canal leading from the teat sinus to the teat opening and may be single or multiple. The '''ostium '''(teat opening) is the opening of the papillary duct and the exit point for milk or entrance point for bacteria. The '''sphincter''' consists of muscular fibres surrounding the teat opening that prevent milk flow except during suckling or milking.

=== Suspensory Apparatus ===

In species with large udders, especially in dairy cattle, there is a  suspensory apparatus, which is organised into the lateral and medial laminae suspending the mammary gland from the ventral aspect of the trunk by their attachment to the pubic symphysis. The '''lateral lamina''' consists of collagen fibres from the fascia of the pubic symphysis and the edge of the superficial inguinal ring. The '''medial lamina''' consists of elastic fibres from the tunica flava ventral to the pubic symphysis The '''intermammary groove''' divides the left and right rows of mammae.

== Blood Supply ==

=== Arteries ===

The main blood supply to the inguinal mammary glands is from the '''external pudendal artery'''. This arises indirectly from the external iliac artery via the deep femoral artery. The external pudendal artery passes through the inguinal canal. In species which also have '''thoracic and abdominal mammary glands''' (bitch, queen, sow) additional blood supply is derived from the '''internal thoracic artery''' and its branches - cranial superficial epigastric arteries as well as from '''lateral thoracic''' and '''intercostal arteries'''.

=== Veins ===

In most species'''thoracic and cranial abdominal mammary glands '''drain via '''cranial superficial epigastric veins''' into the '''internal thoracic vein'''. '''Caudal abdominal and inguinal mammary glands '''drain via '''caudal superficial epigastric veins''' into the '''external pudendal vein'''.

In cattle a venous ring is formed between the base of the udder and the abdominal wall. During the first pregnancy, an anastamosis develops between cranial and caudal superficial epigastric veins forming the '''subcutaneous abdominal vein''' (milk vein). As a result some drainage from venous ring passes in a cranial direction via this vessel, which then drains deeply through the abdominal wall (milk well) into the internal thoracic vein. Other drainage passes to the external pudendal veins or to perineal veins. 

== Innervation ==

Somatic innervation is via the ventral rami of the spinal nerves. In the cow, the ventral branches of L1 and L2 ('''iliohypogastric and ilioinguinal''') supply the skin of the cranial glands. Mammary branches of the '''pudendal nerve''' supply the caudal aspect of the udder. There is sympathetic innervation to the blood vessels and teat sphincter smooth muscle. Mammary glands also have major influence from endocrine hormones.

== Lymphatics ==

The more caudal mammary glands drain to the  '''superficial inguinal lymph node''' and the more cranial mammary glands to the axillary or sternal lymph nodes.

=== Lymphatic drainage in the cow ===

The '''afferent lymphatic ducts''' pass dorsocaudally to reach the '''superficial inguinal''' (mammary) lymph nodes at the dorsocaudal side of the udder. These are  usually palpable large, kidney-shaped nodes between the caudal side of the udder base and the thigh. The '''efferent lymphatic ducts''' pass into the abdomen through the inguinal canal to empty into the deep inguinal node. 

== Histology ==

Secretory tissue is arranged into '''lobes''', each consisting of many '''lobules'''. Each lobule contains groups of '''alveoli''' (secretory compound tubuloalveolar cells) surrounded by a network of blood vessels and connective tissue stroma. The alveolar lumen is filled with milk during lactation. '''Myoepithelial cells''' lie between alveolar epithelial cells and the basement membrane. These contract under the influence of oxytocin to release milk to the exterior. Lobes and lobules are drained by lactiferous ducts into the '''gland sinus''', which is continuous with the '''teat sinus'''. The epithelium lining the lactiferous ducts and the sinus is two-layered cuboidal. A '''teat canal''' connects the teat sinus to the exterior. The lining is stratified squamous epithelium. Circular smooth muscle in the wall of the canal forms a '''sphincter'''. Between milkings, the narrow lumen of the teat canal is filled with a soft keratin plug to prevent bacteria entering the teat sinus and prevent milk leakage.

== Species Differences ==

'''Position and Morphology'''

 

{| border="1" style="width: 75%; height: 200px;"
|-
! Species
! '''Primates'''
! '''Elephant'''
! '''Goat and Sheep'''
! '''Guinea Pig'''
! '''Cow'''
! '''Mare'''
! '''Rat'''
! '''Dog'''
! '''Sow'''
! '''Cat'''
|-
| '''Number of Mammae/teats'''
| 2
| 2
| 2
| 2
| 4
| 4 (2 teats)
| ~10
| ~10
| 8-18
| 8
|-
| '''Position'''
| Pectoral
| Pectoral
| Inguinal
| Inguinal
| Inguinal
| Inguinal
| Abdominal,Ventral
| Thoracoabdominoinguinal
| Thoracoabdominoinguinal
| Thoracoabdominal
|-
| '''Teat Ducts'''
| 10-20
| Several
| 1
| 1
| 1
| 2
| 1
| 8-22
| 2
| 4-8
|}

 Click here for more information on the [[Cow Mammary Gland - Anatomy & Physiology|cow]], [[Small Ruminant Mammary Gland - Anatomy & Physiology|small ruminant]], [[Sow Mammary Gland - Anatomy & Physiology|sow]], [[Mare Mammary Gland - Anatomy & Physiology|mare]] and [[Carnivore Mammary Gland - Anatomy & Physiology|carnivore]].

== Links ==

Test yourself with '''[[Reproductive System Flashcards - Anatomy & Physiology|Reproductive System Flashcards]].'''

[[Category:Female_Reproduction]] [[Category:Integumentary_System_-_Anatomy_&_Physiology]] [[Category:A&P_Done]] [[Category:David_Hogg_reviewed]]

Mammary Gland - Anatomy & Physiology

2011-03-20T13:41:43Z

Dhogg:

Mammary Gland - Anatomy & Physiology

2011-03-20T13:23:03Z

Dhogg:

== Introduction ==

[[Image:Cow teat 4.jpg|thumb|right|250px|Dissection of a Teat of the Bovine Udder,Courtesy of Andrew Crook, Copyright RVC 2008]] [[Image:Suspensory structure of udder.gif|thumb|right|250px|Suspensory apparatus of the udder]] [[Image:Udder lymphatics.gif|thumb|right|250px|Lymphatic drainage of the udder, Copyright DeLaval 2008]] [[Image:Active Mammary Gland.jpg|thumb|right|150px|<center> The Active Mammary Gland. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]] [[Image:Active Mammary Gland high power.jpg|thumb|right|150px|<center> The Active Mammary Gland at High Power. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]] [[Image:Mammary Gland myoepithelial cells.jpg|thumb|right|150px|<center> Mammary Myoepithelial Cells. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]] [[Image:Mammary Gland lactiferous duct.jpg|thumb|right|150px|<center> Section of the Mammary Gland showing a Lactiferous Duct. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]] [[Image:Mammary Gland teat canal keratin plug.jpg|thumb|right|150px|<center> Cross Section through the Teat Canal of the Mammary Gland showing a Keratin Plug. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]]

The mammary gland is a modified sweat gland that nourishes the young. It consists of the '''mamma''' and the '''teat'''. Undeveloped in both the male and female at birth, the female mammary gland begins to develop as a secondary sex characteristic at puberty. With the birth of the first young, and first lactation, the mammary gland attains its full size and function. When suckling by the young stops, milk production ceases and the gland regresses. Shortly before the next and subsequent parturitions, the gland is stimulated by hormonal changes to produce milk.

== Development of the Mammary Gland (prenatal mammogenesis) ==

An ectodermal thickening developes along the ventral body wall extending from the thoracic to inguinal region - this is the '''mammary ridge'''. Cells aggregate, multiply and differentiate to form a chain of condensed '''mammary buds'''. Most mammary buds regress but those that remain each develops into a '''mammary gland'''. A mammary gland is the secretory and duct system associated with one teat. Mammary buds grow into overlying mesenchyme, and '''primary epidermal sprouts''' grow out of the bud apex. The epidermal sprout branches extensively and develops a complete '''duct system'''. Mammary adipose tissue is derived from mesoderm. This is required for complete mammary development and is absent in the male. As a result, mammary development in the male is halted at the epidermal sprout stage.

== Structure ==

The '''mamma (pleural = mammae) ''' is the glandular structure associated with a '''papilla '''(teat) and may contain one or more duct systems. The '''udder''' is a term designating all the mammae in the ruminant and the mare (sometimes also used for the sow). The '''lobes''' are the internal compartments of the mamma, separated by adipose tissue. The lobes are divided into '''lobules''', consisting of connective tissue containing '''alveoli''', which are clusters of milk secreting cells. The '''lactiferous ducts''' are large ducts conveying milk from the alveoli to the '''lactiferous sinus'''. The openings of the lactiferous ducts convey milk formed in the alveolus to the gland sinus.

The '''lactiferous sinus''' (milk sinus) is the milk storage cavity within the teat and glandular body. The '''gland sinus''' is part of the milk sinus within the glandular body and the '''teat sinus''' is part of the milk sinus within the teat.

The '''teat''' is the projecting part of the mammary gland containing part of the milk sinus. The '''papillary duct '''(teat canal) is the canal leading from the teat sinus to the teat opening and may be single or multiple. The '''ostium '''(teat opening) is the opening of the papillary duct and the exit point for milk or entrance point for bacteria. The '''sphincter''' consists of muscular fibres surrounding the teat opening that prevent milk flow except during suckling or milking.

=== Suspensory Apparatus ===

In species with large udders, especially in dairy cattle there is a  suspensory apparatus, which is organised into the lateral and medial laminae, which suspend the mammary gland from the ventral aspect of the trunk by their attachment to the pubic symphysis. The '''lateral lamina''' consists of collagen fibres from the fascia of the pubic symphysis and the edge of the superficial inguinal ring. The '''medial lamina''' consists of elastic fibres from the tunica flava ventral to the pubic symphysis The '''intermammary groove''' divides the left and right rows of mammae.

== Blood Supply ==

=== Arteries ===

In species with '''inguinal mammary glands''' (cow, ewe, goat, mare), the main blood supply is from the '''external pudendal artery'''. This arises indirectly from the external iliac artery via the femoral artery. The external pudendal artery passes through the inguinal canal. In species which also have '''thoracic and abdominal mammary glands''' (bitch, queen, sow) additional blood supply is derived from the '''internal thoracic artery''' and its branches -  cranial superficial epigastric arteries.

=== Veins ===

In most species'''thoracic and cranial abdominal mammary glands '''drain via '''cranial superficial epigastric veins''' into the '''internal thoracic vein'''. '''Caudal abdominal and inguinal mammary glands '''drain via '''caudal superficial epigastric veins''' into the '''external pudendal vein'''.I

Additionally in cattle during the first pregnancy an anastamosis develops between cranial and caudal superficial epigastric veins forming the '''subcutaneous abdominal vein''' (milk vein). As a result some venous drainage from the bovine udder passes in a cranial direction via this vessel, which then drains deeply through the abdominal wall (milk well) into the internal thoracic vein 

== Innervation ==

Somatic innervation is via the ventral rami of the spinal nerves. In the cow, the ventral branches of L1 and L2 ('''iliohypogastric and ilioinguinal''') supply the skin of the cranial glands. Mammary branches of the '''pudendal nerve''' supply the caudal aspect of the udder. There is sympathetic innervation to the blood vessels and teat sphincter smooth muscle. Mammary glands also have major influence from endocrine hormones.

== Lymphatics ==

The more caudal mammary glands drain to the  '''superficial inguinal lymph node''' and the more cranial mammary glands to the axillary lymph nodes.

=== Lymphatic drainage in the cow ===

The '''afferent lymphatic ducts''' pass dorsocaudally to reach the '''superficial inguinal''' (mammary) lymph nodes at the dorsocaudal side of the udder. These are  usually palpable large, kidney-shaped nodes between the caudal side of the udder base and the thigh. The '''efferent lymphatic ducts''' pass into the abdomen through the inguinal canal to empty into the deep inguinal node. 

== Histology ==

Secretory tissue is arranged into '''lobes''', each consisting of many '''lobules'''. Each lobule contains groups of '''alveoli''' (secretory compound tubuloalveolar cells) surrounded by a network of blood vessels and connective tissue stroma. The alveolar lumen is filled with milk during lactation. '''Myoepithelial cells''' lie between alveolar epithelial cells and the basement membrane. These contract under the influence of oxytocin to release milk to the exterior. Lobes and lobules are drained by lactiferous ducts into the '''gland sinus''', which is continuous with the '''teat sinus'''. The epithelium lining the lactiferous ducts and the sinus is two-layered cuboidal. A '''teat canal''' connects the teat sinus to the exterior. The lining is stratified squamous epithelium. Circular smooth muscle in the wall of the canal forms a '''sphincter'''. Between milkings, the narrow lumen of the teat canal is filled with a soft keratin plug to prevent bacteria entering the teat sinus and prevent milk leakage.

== Species Differences ==

'''Position and Morphology'''

 

{| border="1" style="width: 75%; height: 200px;"
|-
! Species
! '''Primates'''
! '''Elephant'''
! '''Goat and Sheep'''
! '''Guinea Pig'''
! '''Cow'''
! '''Mare'''
! '''Rat'''
! '''Dog'''
! '''Sow'''
! '''Cat'''
|-
| '''Number of Mammae/teats'''
| 2
| 2
| 2
| 2
| 4
| 4 (2 teats)
| ~10
| ~10
| 8-18
| 8
|-
| '''Position'''
| Pectoral
| Pectoral
| Inguinal
| Inguinal
| Inguinal
| Inguinal
| Abdominal,Ventral
| Thoracoabdominoinguinal
| Thoracoabdominoinguinal
| Thoracoabdominal
|-
| '''Teat Ducts'''
| 10-20
| Several
| 1
| 1
| 1
| 2
| 1
| 8-22
| 2
| 4-8
|}

 Click here for more information on the [[Cow Mammary Gland - Anatomy & Physiology|cow]], [[Small Ruminant Mammary Gland - Anatomy & Physiology|small ruminant]], [[Sow Mammary Gland - Anatomy & Physiology|sow]], [[Mare Mammary Gland - Anatomy & Physiology|mare]] and [[Carnivore Mammary Gland - Anatomy & Physiology|carnivore]].

== Links ==

Test yourself with '''[[Reproductive System Flashcards - Anatomy & Physiology|Reproductive System Flashcards]].'''

[[Category:Female_Reproduction]] [[Category:Integumentary_System_-_Anatomy_&_Physiology]] [[Category:A&P_Done]] [[Category:David_Hogg_reviewing]]

Mammary Gland - Anatomy & Physiology

2011-03-17T16:12:21Z

Dhogg:

== Introduction ==

[[Image:Cow teat 4.jpg|thumb|right|250px|Dissection of a Teat of the Bovine Udder,Courtesy of Andrew Crook, Copyright RVC 2008]] [[Image:Suspensory structure of udder.gif|thumb|right|250px|Suspensory apparatus of the udder]] [[Image:Udder lymphatics.gif|thumb|right|250px|Lymphatic drainage of the udder, Copyright DeLaval 2008]] [[Image:Active Mammary Gland.jpg|thumb|right|150px|<center> The Active Mammary Gland. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]] [[Image:Active Mammary Gland high power.jpg|thumb|right|150px|<center> The Active Mammary Gland at High Power. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]] [[Image:Mammary Gland myoepithelial cells.jpg|thumb|right|150px|<center> Mammary Myoepithelial Cells. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]] [[Image:Mammary Gland lactiferous duct.jpg|thumb|right|150px|<center> Section of the Mammary Gland showing a Lactiferous Duct. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]] [[Image:Mammary Gland teat canal keratin plug.jpg|thumb|right|150px|<center> Cross Section through the Teat Canal of the Mammary Gland showing a Keratin Plug. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]]

The mammary gland is a modified sweat gland that nourishes the young. It consists of the '''mamma''' and the '''teat'''. Undeveloped in both the male and female at birth, the female mammary gland begins to develop as a secondary sex characteristic at puberty. With the birth of the first young, and first lactation, the mammary gland attains its full size and function. When suckling by the young stops, milk production ceases and the gland regresses. Shortly before the next and subsequent parturitions, the gland is stimulated by hormonal changes to produce milk.

== Development of the Mammary Gland (prenatal mammogenesis) ==

An ectodermal thickening developes along the ventral body wall extending from the thoracic to inguinal region - this is the '''mammary ridge'''. Cells aggregate, multiply and differentiate to form a chain of condensed '''mammary buds'''. Most mammary buds regress but those that remain each develops into a '''mammary gland'''. A mammary gland is the secretory and duct system associated with one teat. Mammary buds grow into overlying mesenchyme, and '''primary epidermal sprouts''' grow out of the bud apex. The epidermal sprout branches extensively and develops a complete '''duct system'''. Mammary adipose tissue is derived from mesoderm. This is required for complete mammary development and is absent in the male. As a result, mammary development in the male is halted at the epidermal sprout stage.

== Structure ==

The '''mamma (pleural = mammae) ''' is the glandular structure associated with a '''papilla '''(teat)and may contain one or more duct systems. The '''udder''' is a term designating all the mammae in the ruminant and the mare (sometimes used for the sow). The '''lobes''' are the internal compartments of the mamma, separated by adipose tissue. The lobes are divided into '''lobules''', consisting of connective tissue containing '''alveoli''', which are clusters of milk secreting cells. The '''lactiferous ducts''' are large ducts conveying milk from the alveoli to the milk sinus. The openings of the lactiferous ducts convey milk formed in the alveolus to the gland sinus.

The '''milk or lactiferous sinus''' is the milk storage cavity within the teat and glandular body. The '''gland sinus''' is part of the milk sinus within the glandular body and the '''teat sinus''' is part of the milk sinus within the teat.

The '''teat''' is the projecting part of the mammary gland containing part of the milk sinus. The '''papillary duct '''(teat canal) is the canal leading from the teat sinus to the teat opening and may be single or multiple. The '''ostium '''(teat opening) is the opening of the papillary duct and the exit point for milk or entrance point for bacteria. The '''sphincter''' consists of muscular fibres surrounding the teat opening that prevent milk flow except during suckling or milking.

=== Suspensory Apparatus ===

In species with large udders, especially in dairy cattle there is a  suspensory apparatus, which is organised into the lateral and medial laminae, which suspend the mammary gland from the ventral aspect of the trunk by their attachment to the pubic symphysis. The '''lateral lamina''' consists of collagen fibres from the fascia of the pubic symphysis and the edge of the superficial inguinal ring. The '''medial lamina''' consists of elastic fibres from the tunica flava ventral to the pubic symphysis The '''intermammary groove''' divides the left and right rows of mammae.

== Blood Supply ==

=== Arteries ===

In species with '''inguinal mammary glands''' (cow, ewe, goat, mare), the main blood supply is from the '''external pudendal artery'''. This arises indirectly from the external iliac artery via the femoral artery. The external pudendal artery passes through the inguinal canal. In species which also have '''thoracic and abdominal mammary glands''' (bitch, queen, sow) additional blood supply is derived from the '''internal thoracic artery''' and its branches -  cranial superficial epigastric arteries.

=== Veins ===

In most species'''thoracic and cranial abdominal mammary glands '''drain via '''cranial superficial epigastric veins''' into the '''internal thoracic vein'''. '''Caudal abdominal and inguinal mammary glands '''drain via '''caudal superficial epigastric veins''' into the '''external pudendal vein'''.I

Additionally in cattle during the first pregnancy an anastamosis develops between cranial and caudal superficial epigastric veins forming the '''subcutaneous abdominal vein''' (milk vein). As a result some venous drainage from the bovine udder passes in a cranial direction via this vessel, which then drains deeply through the abdominal wall (milk well) into the internal thoracic vein 

== Innervation ==

Somatic innervation is via the ventral rami of the spinal nerves. In the cow, the ventral branches of L1 and L2 ('''iliohypogastric and ilioinguinal''') supply the skin of the cranial glands. Mammary branches of the '''pudendal nerve''' supply the caudal aspect of the udder. There is sympathetic innervation to the blood vessels and teat sphincter smooth muscle. Mammary glands also have major influence from endocrine hormones.

== Lymphatics ==

The more caudal mammary glands drain to the  '''superficial inguinal lymph node''' and the more cranial mammary glands to the axillary lymph nodes.

=== Lymphatic drainage in the cow ===

The '''afferent lymphatic ducts''' pass dorsocaudally to reach the '''superficial inguinal''' (mammary) lymph nodes at the dorsocaudal side of the udder. These are  usually palpable large, kidney-shaped nodes between the caudal side of the udder base and the thigh. The '''efferent lymphatic ducts''' pass into the abdomen through the inguinal canal to empty into the deep inguinal node. 

== Histology ==

Secretory tissue is arranged into '''lobes''', each consisting of many '''lobules'''. Each lobule contains groups of '''alveoli''' (secretory compound tubuloalveolar cells) surrounded by a network of blood vessels and connective tissue stroma. The alveolar lumen is filled with milk during lactation. '''Myoepithelial cells''' lie between alveolar epithelial cells and the basement membrane. These contract under the influence of oxytocin to release milk to the exterior. Lobes and lobules are drained by lactiferous ducts into the '''gland sinus''', which is continuous with the '''teat sinus'''. The epithelium lining the lactiferous ducts and the sinus is two-layered cuboidal. A '''teat canal''' connects the teat sinus to the exterior. The lining is stratified squamous epithelium. Circular smooth muscle in the wall of the canal forms a '''sphincter'''. Between milkings, the narrow lumen of the teat canal is filled with a soft keratin plug to prevent bacteria entering the teat sinus and prevent milk leakage.

== Species Differences ==

'''Position and Morphology'''

 

{| border="1" style="width: 75%; height: 200px;"
|-
! Species
! '''Primates'''
! '''Elephant'''
! '''Goat and Sheep'''
! '''Guinea Pig'''
! '''Cow'''
! '''Mare'''
! '''Rat'''
! '''Dog'''
! '''Sow'''
! '''Cat'''
|-
| '''Number of Mammae/teats'''
| 2
| 2
| 2
| 2
| 4
| 4 (2 teats)
| ~10
| ~10
| 8-18
| 8
|-
| '''Position'''
| Pectoral
| Pectoral
| Inguinal
| Inguinal
| Inguinal
| Inguinal
| Abdominal,Ventral
| Thoracoabdominoinguinal
| Thoracoabdominoinguinal
| Thoracoabdominal
|-
| '''Teat Ducts'''
| 10-20
| Several
| 1
| 1
| 1
| 2
| 1
| 8-22
| 2
| 4-8
|}

 Click here for more information on the [[Cow Mammary Gland - Anatomy & Physiology|cow]], [[Small Ruminant Mammary Gland - Anatomy & Physiology|small ruminant]], [[Sow Mammary Gland - Anatomy & Physiology|sow]], [[Mare Mammary Gland - Anatomy & Physiology|mare]] and [[Carnivore Mammary Gland - Anatomy & Physiology|carnivore]].

== Links ==

Test yourself with '''[[Reproductive System Flashcards - Anatomy & Physiology|Reproductive System Flashcards]].'''

[[Category:Female_Reproduction]] [[Category:Integumentary_System_-_Anatomy_&_Physiology]] [[Category:A&P_Done]] [[Category:David_Hogg_reviewing]]

Mammary Gland - Anatomy & Physiology

2011-03-17T15:16:11Z

Dhogg:

== Introduction ==

[[Image:Cow teat 4.jpg|thumb|right|250px|Dissection of a Teat of the Bovine Udder,Courtesy of Andrew Crook, Copyright RVC 2008]] [[Image:Suspensory structure of udder.gif|thumb|right|250px|Suspensory apparatus of the udder]] [[Image:Udder lymphatics.gif|thumb|right|250px|Lymphatic drainage of the udder, Copyright DeLaval 2008]] [[Image:Active Mammary Gland.jpg|thumb|right|150px|<center> The Active Mammary Gland. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]] [[Image:Active Mammary Gland high power.jpg|thumb|right|150px|<center> The Active Mammary Gland at High Power. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]] [[Image:Mammary Gland myoepithelial cells.jpg|thumb|right|150px|<center> Mammary Myoepithelial Cells. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]] [[Image:Mammary Gland lactiferous duct.jpg|thumb|right|150px|<center> Section of the Mammary Gland showing a Lactiferous Duct. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]] [[Image:Mammary Gland teat canal keratin plug.jpg|thumb|right|150px|<center> Cross Section through the Teat Canal of the Mammary Gland showing a Keratin Plug. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]]

The mammary gland is a modified sweat gland that nourishes the young. It consists of the '''mamma''' and the '''teat'''. Undeveloped in both the male and female at birth, the female mammary gland begins to develop as a secondary sex characteristic at puberty. With the birth of the first young, and first lactation, the mammary gland attains its full size and function. When suckling by the young stops, milk production ceases and the gland regresses. Shortly before the next and subsequent parturitions, the gland is stimulated by hormonal changes to produce milk.

== Development of the Mammary Gland (prenatal mammogenesis) ==

An ectodermal thickening developes along the ventral body wall extending from the thoracic to inguinal region - this is the '''mammary ridge'''. Cells aggregate, multiply and differentiate to form a chain of condensed '''mammary buds'''. Most mammary buds regress but those that remain each develops into a '''mammary gland'''. A mammary gland is the secretory and duct system associated with one teat. Mammary buds grow into overlying mesenchyme, and '''primary epidermal sprouts''' grow out of the bud apex. The epidermal sprout branches extensively and develops a complete '''duct system'''. Mammary adipose tissue is derived from mesoderm. This is required for complete mammary development and is absent in the male. As a result, mammary development in the male is halted at the epidermal sprout stage.

== Structure ==

The '''mamma (pleural = mammae) ''' is the glandular structure associated with a teat. The '''udder''' is a term designating all the mammae in the ruminant and the mare (sometimes used for the sow). The '''lobes''' are the internal compartments of the mamma, separated by adipose tissue. The lobes are divided into '''lobules''', consisting of connective tissue containing '''alveoli''', which are clusters of milk secreting cells. The '''lactiferous ducts''' are large ducts conveying milk from the alveoli to the milk sinus. The openings of the lactiferous ducts convey milk formed in the alveolus to the gland sinus.

The '''milk or lactiferous sinus''' is the milk storage cavity within the teat and glandular body. The '''gland sinus''' is part of the milk sinus within the glandular body and the '''teat sinus''' is part of the milk sinus within the teat.

The '''teat''' is the projecting part of the mammary gland containing part of the milk sinus. The '''teat canal''' is the canal leading from the teat sinus to the teat opening. The '''teat opening''' is the opening of the teat canal and the exit point for milk or entrance point for bacteria into the mammae. The '''sphincter''' consists of muscular fibres surrounding the teat opening that prevent milk flow except during suckling or milking.

=== Suspensory Apparatus ===

The suspensory apparatus is organised into the lateral and medial laminae, which suspend the mammary gland from the ventral aspect of the trunk by their attachment to the pubic symphysis. The '''lateral lamina''' consists of collagen fibres from the fascia of the pubic symphysis and the edge of the superficial inguinal ring. The '''medial lamina''' consists of elastic fibres from the tunica flava ventral to the pubic symphysis The '''intermammary groove''' divides the left and right rows of mammary complexes.

== Blood Supply ==

=== Arteries ===

In species with '''inguinal mammary glands''' (cow, ewe, goat, mare), the main blood supply is from the '''external pudendal artery'''. This arises indirectly from the external iliac artery via the femoral artery. The external pudendal artery passes through the inguinal canal. In species which also have '''thoracic mammary glands''' (bitch, queen, sow) blood supply is from the '''internal thoracic artery''' and its branches - cranial and cranial superficial epigastric arteries.

=== Veins ===

'''Thoracic mammary complexes''' drain into '''cranial superficial epigastric veins''' and open into the '''cranial epigastric vein'''. It drains into the '''internal thoracic vein'''.

'''Abdominal and inguinal mammary complexes''' drain into '''caudal superficial epigastric veins''' and open into the '''external pudendal vein'''.

== Innervation ==

There is '''sympathetic''' innervation to the blood vessels and teat sphincter smooth muscle via the '''genitofemoral nerve''' and '''somatic''' innervation via the ventral rami of the spinal nerves. In the cow, the ventral branches of L1 and L2 ('''iliohypogastric and ilioinguinal''') supply the skin of the cranial forequarters. Mammary branches of the '''pudendal nerve''' supply the caudal aspect of the udder (hindquarters). Mammary glands are, however, mainly under the influence of endocrine hormones.

== Lymphatics ==

The '''inguinal mammary glands''' contain a superficial inguinal lymph node and the '''thoracic mammary glands''' contain an axillary lymph node.

=== Lymphatic drainage in the cow ===

The '''afferent lymphatic ducts''' pass dorsocaudally to reach the mammary lymph nodes (superficial inguinal). The '''mammary (superficial inguinal) lymph nodes''' include two nodes at the dorsocaudal side of the udder, usually a palpable large, kidney-shaped node between the caudal side of the udder base and the thigh. The '''efferent lymphatic ducts''' pass into the abdomen through the inguinal canal to empty into the deep inguinal node. The '''deep inguinal lymph node''' is small and located in the dorsocaudal udder. It is too deep to be palpated.

== Histology ==

Secretory tissue is arranged into '''lobes''', each consisting of many '''lobules'''. Each lobule contains groups of '''alveoli''' (secretory compound tubuloalveolar cells) surrounded by a network of blood vessels and connective tissue stroma. The alveolar lumen is filled with milk during lactation. '''Myoepithelial cells''' lie between alveolar epithelial cells and the basement membrane. These contract under the influence of oxytocin to release milk to the exterior. Lobes and lobules are drained by lactiferous ducts into the '''gland sinus''', which is continuous with the '''teat sinus'''. The epithelium lining the lactiferous ducts and the sinus is two-layered cuboidal. A '''teat canal''' connects the teat sinus to the exterior. The lining is stratified squamous epithelium. Circular smooth muscle in the wall of the canal forms a '''sphincter'''. Between milkings, the narrow lumen of the teat canal is filled with a soft keratin plug to prevent bacteria entering the teat sinus and prevent milk leakage.

== Species Differences ==

'''Position and Morphology'''

 

{| border="1" style="width: 75%; height: 200px;"
|-
! Species
! '''Primates'''
! '''Elephant'''
! '''Goat and Sheep'''
! '''Guinea Pig'''
! '''Cow'''
! '''Mare'''
! '''Rat'''
! '''Dog'''
! '''Sow'''
! '''Cat'''
|-
| '''Number of Mammary Glands'''
| 2
| 2
| 2
| 2
| 4
| 4 (2 teats)
| ~10
| ~10
| 8-18
| 8
|-
| '''Position'''
| Pectoral
| Pectoral
| Inguinal
| Inguinal
| Inguinal
| Inguinal
| Abdominal,Ventral
| Thoracoabdominoinguinal
| Thoracoabdominoinguinal
| Thoracoabdominal
|-
| '''Teat Ducts'''
| 10-20
| Several
| 1
| 1
| 1
| 2
| 1
| 8-22
| 2
| 4-8
|}

 Click here for more information on the [[Cow Mammary Gland - Anatomy & Physiology|cow]], [[Small Ruminant Mammary Gland - Anatomy & Physiology|small ruminant]], [[Sow Mammary Gland - Anatomy & Physiology|sow]], [[Mare Mammary Gland - Anatomy & Physiology|mare]] and [[Carnivore Mammary Gland - Anatomy & Physiology|carnivore]].

== Links ==

Test yourself with '''[[Reproductive System Flashcards - Anatomy & Physiology|Reproductive System Flashcards]].'''

[[Category:Female_Reproduction]] [[Category:Integumentary_System_-_Anatomy_&_Physiology]] [[Category:A&P_Done]] [[Category:David_Hogg_reviewing]]

Category:Expert Reviewer

2011-03-01T12:10:16Z

Dhogg:

Here are the experts that are currently reviewing content for WikiVet: __NOTOC__ 

{| width="100%" style="margin:0px 0px 0px 0px; background:none;"
|-
| class="MainPageBG" style="width:50%; border:1px solid #cef2e0; background:#f5fffa; vertical-align:top; color:#000;" |
{| width="100%" cellpadding="2" cellspacing="5" style="vertical-align:top; background:#f5fffa;"
|-
!
== [[Simon Priestnall]] - [[:Category:General Pathology|General Pathology]] Reviewer ==

|-
| style="color:#000;" |
[[Image:Spriestnall.jpg|left|120px]]

Simon is a lecturer in Pathology at the [[RVC|Royal Veterinary College]], UK.
<center>[[Simon Priestnall|See Simon's Profile here]]</center>
|}

| class="MainPageBG" style="width:50%; border:1px solid #cedff2; background:#f5faff; vertical-align:top;" colspan="1" |
{| id="mp-right" width="100%" cellpadding="2" cellspacing="5" style="vertical-align:top; background:#f5faff;"
|-
!
== [[User:A.allison|Asher Allison]] - Technical Director ==

|-
| style="color:#000;" |
[[Image:Asher Allison team.jpg|right|120px]]

Asher is our main technical support and is responsible for maintaining the server, extensions, providing templates for the general design and lots of other useful stuff. As he is currently very busy with his finals, Brian is here to give a hand when necessary.
<center>[[User:A.allison|See Asher's Profile here]]</center>
|}

|}

<

Mandibular Gland - Anatomy & Physiology

2011-03-01T11:27:03Z

Dhogg: /* Links */

[[Image:Parotid & Mandibular Salivary Gland.jpg|thumb|right|250px|Mandibular Salivary Gland - Copyright Nottingham 2008]]

==Overview==

The '''mandibular gland''' produces a '''merocrine''' secretion, which means it is a mixed gland - [[Serous Salivary Gland - Anatomy & Physiology|serous]] and [[Mucous Salivary Gland - Anatomy & Physiology|mucous]] secretions.
It is generally smaller than the '''[[Parotid Gland - Anatomy & Physiology|parotid]]''' gland and is a moderately large gland in carnivores and herbivores. It is compact and located around the angle of the jaw.

The '''mandibular duct''' runs ventral to the mucous membrane of the floor of the [[Oral Cavity Overview - Anatomy & Physiology|oral cavity]], close to the '''frenulum''' of the [[Tongue - Anatomy & Physiology|tongue]]. The duct opens at the '''sublingual caruncle'''.

==Histology==

The mandibular gland is known as a '''tubulo-acinar gland'''. It consists of [[Mucous Salivary Gland - Anatomy & Physiology|mucous]] cells that stain lighter and [[Serous Salivary Gland - Anatomy & Physiology|serous]] demilunes that stain darker. '''Demilunes''' secrete into lumen by canaliculi between mucous cells.

==Innervation==

The mandibular gland is innervated by the '''facial''' nerve ([[Cranial Nerves - Anatomy & Physiology|CN VII]]) via the '''chordi tympanii''' and by the '''trigeminal''' nerve ([[Cranial Nerves - Anatomy & Physiology|CN V]]).

==Species Differences==

===Carnivores===
The mandibular gland produces mainly [[Mucous Salivary Gland - Anatomy & Physiology|mucous]] secretions in the dog and cat. It is an oval shape in the canid.

===Herbivores===
The mandibular gland in herbivores is larger and deeper.

==Links==

'''Test yourself with the [[Oral_Cavity_- Anatomy & Physiology_-_Flashcards#Salivary_Glands_Flashcards|Salivary Gland Flashcards]]'''

[[Category:Salivary Glands - Anatomy & Physiology]]
[[Category:A&P Done]]
[[Category:David_Hogg_reviewed]]

Mandibular Gland - Anatomy & Physiology

2011-03-01T11:26:20Z

Dhogg: /* Links */

David Hogg

2011-03-01T11:19:39Z

Dhogg: /* David's involvement in WikiVet */

{{UserPage
|Name=David Hogg
|Occupation= Veterinary Surgeon
|School= UK - Glasgow
|Year= 1967
|Email= dhogg@rvc.ac.uk
|Image= David_Hogg.jpg
}}

 ''David is a Consultant Lecturer in Veterinary Anatomy, who regularly works with Veterinary schools around the globe''

== David's involvement in WikiVet ==

[[:Category:David Hogg reviewing|View pages]] that David is reviewing

David has reviewed [[:Category:David Hogg reviewed|these pages]] which have the below banner on them:
{{Template:David Hogg reviewed
|date=}}

== Biography ==

David graduated from Glasgow Veterinary School in 1967 and initially entered mixed, mainly agricultural practice in Scotland.  David returned to Glasgow a year later and took a temporary position to teach veterinary anatomy. He then proceeded to teach at the Western College of Veterinary Medicine in Saskatoon, Canada in 1969. He returned to Glasgow in 1970 and spent some years teaching Veterinary Anatomy and proceeding towards his PhD in study of aspects of bone development in birds compared to mammals, which he completed in 1977. He made a move to Human Anatomy to learn about the human body, which led to a long period teaching Gross Anatomy to medical and dental students. While here he became interested in more specialized areas such as Animal Developmental Biology and the essential neuroscience instruction for students of Speech Pathology. David has worked abroad and helped to develop new Veterinary Schools in Kenya, Zambia, Zimbabwe, Trinidad and Tobago and was the Inaugural Dean of the School of Veterinary Medicine in St. George’s University, Grenada in 1998-2003.

== Research ==

David has focussed his research mainly on comparitive anatomy.  His PhD was on the bone development in birds compared to mammals and his later reserch has been into the embryonic development of bones and joints. 

== Teaching ==

David has taught all over the globe and is now teaching Veterinary Anatomy where and when required.  He now focuses his teaching predominantly in the UK.

[[Category:Expert Reviewer]]
[[Category:UK - Glasgow Graduates]]

Template:David Hogg reviewed

2011-03-01T11:17:53Z

Dhogg: Created page with "{{ambox | type = reviewed | text = This article has been expert reviewed{{#if: {{{by|Dr David Hogg}}} |  by {{#if: {{{page|}}}| [[{{{page|}}}|{{{by|[[Dav..."

{{ambox
| type = reviewed
| text = This article has been expert reviewed{{#if: {{{by|[[David Hogg|Dr David Hogg]]}}} |  by {{#if: {{{page|}}}| [[{{{page|}}}|{{{by|[[David Hogg|Dr David Hogg]]}}}]].| {{{by|[[David Hogg|Dr David Hogg]]}}} BVMS PhD MRCVS.}} | . }}{{#if: {{{by|[[David Hogg|Dr David Hogg]]}}} |Date reviewed: {{{date|}}}|}}|}}

Talk:Neurogenesis - Anatomy & Physiology

2011-03-01T11:13:01Z

Dhogg: Created page with "test for reviewing"

test for reviewing

Neurogenesis - Anatomy & Physiology

2011-03-01T11:08:18Z

Dhogg:

== Introduction ==

The nervous system develops from '''ectoderm'''. Some of the ectoderm will also develop into the ''epidermis''. Signalling factors from elsewhere in the embryo determine which parts of the ectoderm become neural tissue or epidermis. In the anterior part of the embryo, the ectoderm forms the '''neural plate''', a flat layer of ectodermal cells lying directly above the node. The morphogenic changes from this neural plate to the nervous system is split into two parts; primary and secondary neuralation.

== Neural Plate Induction ==

[[Image:WIKIVETformationofneuraltissue.jpg|thumb|right|350px|Formation of Neural Tissue - Copyright Sophie Stenner]]

Cells of the ectoderm are directed to develop into either neural ectoderm or epidermis.

=== How is this choice made? ===

Formation of the '''neural ectoderm''' is the default pathway. Therefore, in order to make epidermis, a signal from the environment must be diverting cells from going down this default pathway. This signal comes from the lateral plate mesoderm (LPM) which directs ectoderm to become epidermis. This signal is the '''secretory factor BMP-4'''. The notochord (lying along the midline) secretes an antagonist, Noggin, to the factor of the LPM (BMP-4), so that neural ectoderm is formed above the notochord. Therefore, in lateral regions, ectoderm becomes epidermis and along the midline ectoderm becomes neural ectoderm.

== Neuralation ==

=== Primary Neuralation ===

Cells of the neural plate proliferate, causing the neural plate to thicken. Cells then converge at the midline and become wedge shaped, which drives the neural plate to become long and narrow. Cells along the midline descend ventrally and contact the notochord, forming a "hinge". This forms a depression which is called the '''neural groove'''. Either side of the neural groove, ectoderm converges towards the midline. This causes elevations either side of the neural groove, called '''neural folds'''. Hinges form at the foot of each neural fold, allowing the folds to be brought together, forming a tube. The tube sinks, as non - neural ectoderm fuses above the neural tube, "zipping" the neural tube up. The non - neural ectoderm will form epidermis. Failure of the neural tube to close causes '''spina bifida''' (spinal cord protrusion) and '''exencephaly''' (brain located out of the skull).

=== Secondary Neuralation ===

Secondary neuralation occurs posteriorly, from the lumbar level onwards. The neural plate descends ventrally and medially. Cells of the neural plate condense and form a solid rod called the '''medullary cord'''. It is then made hollow by cavitations which join up to make a lumen. Tubes formed by primary and secondary neuralation fuse together to make one continuous tube called the '''neural tube'''.

== Neural Tube Development ==

[[Image:Neural tube.jpg|thumb|right|250px|Catcasillas 2010. Shh and BMP gradient in the vertebrate neural tube]]

The neural tube is one cell thick. The lumen of the neural tube enlarges as cells at the periphery of the lumen divide under mitosis. Cell division is governed by oscillations of the nucleus. When the nucleus reaches the luminal side of cell, the cell undergoes mitosis.

=== Neural Tube Regionalisation ===

The neural tube undergoes regionalisation to define the anterior as the brain, and the posterior as the [[Spinal Cord - Anatomy & Physiology|spinal cord]]. In the anterior, the neural tube swells into the three ventricles of the brain: the forebrain, midbrain, and hindbrain. This occurs as fluid is pumped into the lumen of the neural tube. Pressure is regionalised to the anterior by occlusion of the neural tube at the base of the hindbrain. The occlusion reopens after enlargement of the ventricles.

=== Formation of Cell Layers ===

The neural tube begins with the germinal layer which is a single cell layer thick. All cells have the capacity to undergo mitosis. Some cells then lose their ability to undergo mitosis, they detach from the germinal layer and move away from the lumen to exist behind the germinal layer. This produces new layers called the '''mantle and intermediate layer'''. The germinal layer is now known as the '''ventricular layer'''. Cells of the intermediate layer differentiate into one of two cells:

#'''[[PNS Structure - Anatomy & Physiology#Nerve_Fibre|Neurones]]''' - for conductance of nerve impulses.
#'''Glia''' - for insulation of electrical signals.

Glia form oligodendrocytes in the CNS, and [[PNS Structure - Anatomy & Physiology#The_Schwann_Cell|schwann cells]] in the PNS. Glial cells surround the axons furthest away form the lumen of the neural tube. Because this part is myelinated, it appears ''white'' and is called the '''marginal layer'''. Axons closer to the lumen of the neural tube, which the glial cells do not surround appear ''grey''. This layer is called the '''intermediate layer'''. The ventricular layer persists, so that the spinal cord develops with these three layers.

In the brain, further layers are added to increase complexity. This is possible because in the anterior of the embryo, neuroblasts (cells of the ventricular layer) retain their ability to undergo mitosis after leaving the ventricular layer. This difference is achieved by increased hydrostatic forces acting on the neuroblasts.

== Organisation of the Nervous System ==

=== Somatic Nervous System ===

Sensory neurones enter the central nervous system (CNS) through the '''dorsal root'''. Sensory neurones have their cell bodies in dorsal root ganglia (DRG). DRG are evenly spaced along the spinal cord. Response to the stimulus is mediated by a single motor neurone. Somatic motor neurones have their cell bodies in the CNS. They leave the CNS by the '''ventral root'''. Dorsal and ventral roots converge to form '''spinal nerves'''.

=== Autonomic Nervous System ===

Sensory neurones also enter the CNS through the dorsal root, with their nuclei in DRG. In contrast to the somatic nervous system, the motor component is in two parts; a preganglionic and postganglionic neurone. The preganglionic neurone has its cell body in the CNS. It exits via the ventral root and synapses with the postganglionic neurone. Cell bodies of the postganglionic neurone lie outside the CNS in ganglia. Ganglia of the ''sympathetic'' nervous system are near the '''spinal cord'''. Ganglia of the ''parasympathetic'' nervous system are near the '''target organ'''.

== Neural Crest ==

[[Image:Neual crest.png|thumb|right|250px|Mithril 2010 Cross section scheme of vertebrate embryo. 1 – neural crest, 2 – neural tube, 3 – dorsal somite, 4 – notochord. Both paths of the neural crest cells migation marked by arrows: red one is the dorsolateral path, blue one signs the ventromedial path.]]

The crest neuroectoderm is the region at the junction of epidermis and neural plate. When the neural tube closes, the epidermis is brought into contact with the crest neuroectoderm. This contact causes cells of the crest neuroectoderm to undergo an epithelial to mesenchymal transition. Cells that undergo this transition break away from the neuroectoderm and are called '''neural crest cells'''. The peripheral nervous system (PNS) develops from the neural crest. The undifferentiated neural crest cells migrate away from the neural tube along "pathways". These pathways are governed by repulsive cues from the cells, as well as proliferation and survival signals. They differentiate once they reach their destination. Other non - neural tissues also develop from the neural crest. The type of tissue that neural crest forms is dependant on the origination of the cell along the anterior - posterior axis:

'''Anterior Neural Crest''' forms:

:sensory neurones and [[PNS Structure - Anatomy & Physiology#Schwann_Cells|schwann cells]]
:[[Bones - Anatomy & Physiology|bones]] of the head
:dermis of the face
:[[Cartilage - Anatomy & Physiology|cartilage]]

'''Trunk Neural Crest''' forms:

:sensory neurones of the somatic and autonomic nervous systems (ANS)
:sympathetic motor neurones of the ANS
:melanocytes

'''Posterior Neural Crest''' forms:

:parasympathetic motor neurones of the [[Alimentary System Overview - Anatomy & Physiology#Small_Intestine|gut]], which control peristalsis.

== Ectodermal Placodes ==

The ectoderm thickens in places, with cells changing from cuboidal to columnar. These regions are called '''placodes'''. Placodes may be neurogenic or non - neurogenic. Neurogenic placodes are only found in the head, forming only sensory cells. Morphogenic changes produce the following derivatives:

'''Nasal placodes''' - by partial invagination.

'''Inner Ear''' - by invagination and vesicle formation.

'''Sensory Ganglion of Cranial Nerves''' - epithelial to mesenchymal transition.

[[Category:Developmental_Biology]] [[Category:Nervous_System_-_Anatomy_&_Physiology]] [[Category:A&P_Done]] [[Category:David_Hogg_reviewing]]

Neurogenesis - Anatomy & Physiology

2011-03-01T11:07:45Z

Dhogg:

Neurogenesis - Anatomy & Physiology

2011-03-01T11:06:47Z

Dhogg:

== Introduction ==

The nervous system develops from '''ectoderm'''. Some of the ectoderm will also develop into the ''epidermis''. Signalling factors from elsewhere in the embryo determine which parts of the ectoderm become neural tissue or epidermis. In the anterior part of the embryo, the ectoderm forms the '''neural plate''', a flat layer of ectodermal cells lying directly above the node. The morphogenic changes from this neural plate to the nervous system is split into two parts; primary and secondary neuralation.

== Neural Plate Induction ==

[[Image:WIKIVETformationofneuraltissue.jpg|thumb|right|350px|Formation of Neural Tissue - Copyright Sophie Stenner]]

Cells of the ectoderm are directed to develop into either neural ectoderm or epidermis.

=== How is this choice made? ===

Formation of the '''neural ectoderm''' is the default pathway. Therefore, in order to make epidermis, a signal from the environment must be diverting cells from going down this default pathway. This signal comes from the lateral plate mesoderm (LPM) which directs ectoderm to become epidermis. This signal is the '''secretory factor BMP-4'''. The notochord (lying along the midline) secretes an antagonist, Noggin, to the factor of the LPM (BMP-4), so that neural ectoderm is formed above the notochord. Therefore, in lateral regions, ectoderm becomes epidermis and along the midline ectoderm becomes neural ectoderm.

== Neuralation ==

=== Primary Neuralation ===

Cells of the neural plate proliferate, causing the neural plate to thicken. Cells then converge at the midline and become wedge shaped, which drives the neural plate to become long and narrow. Cells along the midline descend ventrally and contact the notochord, forming a "hinge". This forms a depression which is called the '''neural groove'''. Either side of the neural groove, ectoderm converges towards the midline. This causes elevations either side of the neural groove, called '''neural folds'''. Hinges form at the foot of each neural fold, allowing the folds to be brought together, forming a tube. The tube sinks, as non - neural ectoderm fuses above the neural tube, "zipping" the neural tube up. The non - neural ectoderm will form epidermis. Failure of the neural tube to close causes '''spina bifida''' (spinal cord protrusion) and '''exencephaly''' (brain located out of the skull).

=== Secondary Neuralation ===

Secondary neuralation occurs posteriorly, from the lumbar level onwards. The neural plate descends ventrally and medially. Cells of the neural plate condense and form a solid rod called the '''medullary cord'''. It is then made hollow by cavitations which join up to make a lumen. Tubes formed by primary and secondary neuralation fuse together to make one continuous tube called the '''neural tube'''.

== Neural Tube Development ==

[[Image:Neural tube.jpg|thumb|right|250px|Catcasillas 2010. Shh and BMP gradient in the vertebrate neural tube]]

The neural tube is one cell thick. The lumen of the neural tube enlarges as cells at the periphery of the lumen divide under mitosis. Cell division is governed by oscillations of the nucleus. When the nucleus reaches the luminal side of cell, the cell undergoes mitosis.

=== Neural Tube Regionalisation ===

The neural tube undergoes regionalisation to define the anterior as the brain, and the posterior as the [[Spinal Cord - Anatomy & Physiology|spinal cord]]. In the anterior, the neural tube swells into the three ventricles of the brain: the forebrain, midbrain, and hindbrain. This occurs as fluid is pumped into the lumen of the neural tube. Pressure is regionalised to the anterior by occlusion of the neural tube at the base of the hindbrain. The occlusion reopens after enlargement of the ventricles.

=== Formation of Cell Layers ===

The neural tube begins with the germinal layer which is a single cell layer thick. All cells have the capacity to undergo mitosis. Some cells then lose their ability to undergo mitosis, they detach from the germinal layer and move away from the lumen to exist behind the germinal layer. This produces new layers called the '''mantle and intermediate layer'''. The germinal layer is now known as the '''ventricular layer'''. Cells of the intermediate layer differentiate into one of two cells:

#'''[[PNS Structure - Anatomy & Physiology#Nerve_Fibre|Neurones]]''' - for conductance of nerve impulses.
#'''Glia''' - for insulation of electrical signals.

Glia form oligodendrocytes in the CNS, and [[PNS Structure - Anatomy & Physiology#The_Schwann_Cell|schwann cells]] in the PNS. Glial cells surround the axons furthest away form the lumen of the neural tube. Because this part is myelinated, it appears ''white'' and is called the '''marginal layer'''. Axons closer to the lumen of the neural tube, which the glial cells do not surround appear ''grey''. This layer is called the '''intermediate layer'''. The ventricular layer persists, so that the spinal cord develops with these three layers.

In the brain, further layers are added to increase complexity. This is possible because in the anterior of the embryo, neuroblasts (cells of the ventricular layer) retain their ability to undergo mitosis after leaving the ventricular layer. This difference is achieved by increased hydrostatic forces acting on the neuroblasts.

== Organisation of the Nervous System ==

=== Somatic Nervous System ===

Sensory neurones enter the central nervous system (CNS) through the '''dorsal root'''. Sensory neurones have their cell bodies in dorsal root ganglia (DRG). DRG are evenly spaced along the spinal cord. Response to the stimulus is mediated by a single motor neurone. Somatic motor neurones have their cell bodies in the CNS. They leave the CNS by the '''ventral root'''. Dorsal and ventral roots converge to form '''spinal nerves'''.

=== Autonomic Nervous System ===

Sensory neurones also enter the CNS through the dorsal root, with their nuclei in DRG. In contrast to the somatic nervous system, the motor component is in two parts; a preganglionic and postganglionic neurone. The preganglionic neurone has its cell body in the CNS. It exits via the ventral root and synapses with the postganglionic neurone. Cell bodies of the postganglionic neurone lie outside the CNS in ganglia. Ganglia of the ''sympathetic'' nervous system are near the '''spinal cord'''. Ganglia of the ''parasympathetic'' nervous system are near the '''target organ'''.

== Neural Crest ==

[[Image:Neual crest.png|thumb|right|250px|Mithril 2010 Cross section scheme of vertebrate embryo. 1 – neural crest, 2 – neural tube, 3 – dorsal somite, 4 – notochord. Both paths of the neural crest cells migation marked by arrows: red one is the dorsolateral path, blue one signs the ventromedial path.]]

The neuroectoderm is the region at the junction of epidermis and neural plate. When the neural tube closes, the epidermis is brought into contact with the crest neuroectoderm. This contact causes cells of the crest neuroectoderm to undergo an epithelial to mesenchymal transition. Cells that undergo this transition break away from the neuroectoderm and are called '''neural crest cells'''. The peripheral nervous system (PNS) develops from the neural crest. The undifferentiated neural crest cells migrate away from the neural tube along "pathways". These pathways are governed by repulsive cues from the cells, as well as proliferation and survival signals. They differentiate once they reach their destination. Other non - neural tissues also develop from the neural crest. The type of tissue that neural crest forms is dependant on the origination of the cell along the anterior - posterior axis:

'''Anterior Neural Crest''' forms:

:sensory neurones and [[PNS Structure - Anatomy & Physiology#Schwann_Cells|schwann cells]]
:[[Bones - Anatomy & Physiology|bones]] of the head
:dermis of the face
:[[Cartilage - Anatomy & Physiology|cartilage]]

'''Trunk Neural Crest''' forms:

:sensory neurones of the somatic and autonomic nervous systems (ANS)
:sympathetic motor neurones of the ANS
:melanocytes

'''Posterior Neural Crest''' forms:

:parasympathetic motor neurones of the [[Alimentary System Overview - Anatomy & Physiology#Small_Intestine|gut]], which control peristalsis.

== Ectodermal Placodes ==

The ectoderm thickens in places, with cells changing from cuboidal to columnar. These regions are called '''placodes'''. Placodes may be neurogenic or non - neurogenic. Neurogenic placodes are only found in the head, forming only sensory cells. Morphogenic changes produce the following derivatives:

'''Nasal placodes''' - by partial invagination.

'''Inner Ear''' - by invagination and vesicle formation.

'''Sensory Ganglion of Cranial Nerves''' - epithelial to mesenchymal transition.

[[Category:Developmental_Biology]] [[Category:Nervous_System_-_Anatomy_&_Physiology]] [[Category:A&P_Done]] [[Category:David_Hogg_reviewed]]

Neurogenesis - Anatomy & Physiology

2011-03-01T11:05:32Z

Dhogg: /* Ectodermal Placodes */

==Introduction==

The nervous system develops from '''ectoderm'''. Some of the ectoderm will also develop into the ''epidermis''. Signalling factors from elsewhere in the embryo determine which parts of the ectoderm become neural tissue or epidermis. In the anterior part of the embryo, the ectoderm forms the '''neural plate''', a flat layer of ectodermal cells lying directly above the node. The morphogenic changes from this neural plate to the nervous system is split into two parts; primary and secondary neuralation.

==Neural Plate Induction==
[[Image:WIKIVETformationofneuraltissue.jpg|thumb|right|350px|Formation of Neural Tissue - Copyright Sophie Stenner]]

Cells of the ectoderm are directed to develop into either neural ectoderm or epidermis.

===How is this choice made?===
Formation of the '''neural ectoderm''' is the default pathway. Therefore, in order to make epidermis, a signal from the environment must be diverting cells from going down this default pathway. This signal comes from the lateral plate mesoderm (LPM) which directs ectoderm to become epidermis. This signal is the '''secretory factor BMP-4'''. The notochord (lying along the midline) secretes an antagonist, Noggin, to the factor of the LPM (BMP-4), so that neural ectoderm is formed above the notochord. Therefore, in lateral regions, ectoderm becomes epidermis and along the midline ectoderm becomes neural ectoderm.

==Neuralation==

===Primary Neuralation===

Cells of the neural plate proliferate, causing the neural plate to thicken. Cells then converge at the midline and become wedge shaped, which drives the neural plate to become long and narrow. Cells along the midline descend ventrally and contact the notochord, forming a "hinge". This forms a depression which is called the '''neural groove'''. Either side of the neural groove, ectoderm converges towards the midline. This causes elevations either side of the neural groove, called '''neural folds'''. Hinges form at the foot of each neural fold, allowing the folds to be brought together, forming a tube. The tube sinks, as non - neural ectoderm fuses above the neural tube, "zipping" the neural tube up. The non - neural ectoderm will form epidermis. Failure of the neural tube to close causes '''spina bifida''' (spinal cord protrusion) and '''exencephaly''' (brain located out of the skull).

===Secondary Neuralation===

Secondary neuralation occurs posteriorly, from the lumbar level onwards. The neural plate descends ventrally and medially. Cells of the neural plate condense and form a solid rod called the '''medullary cord'''. It is then made hollow by cavitations which join up to make a lumen. Tubes formed by primary and secondary neuralation fuse together to make one continuous tube called the '''neural tube'''.

==Neural Tube Development==
[[Image:neural tube.jpg|right|thumb|250px|Catcasillas 2010. Shh and BMP gradient in the vertebrate neural tube]]

The neural tube is one cell thick. The lumen of the neural tube enlarges as cells at the periphery of the lumen divide under mitosis. Cell division is governed by oscillations of the nucleus. When the nucleus reaches the luminal side of cell, the cell undergoes mitosis.

===Neural Tube Regionalisation===

The neural tube undergoes regionalisation to define the anterior as the brain, and the posterior as the [[Spinal Cord - Anatomy & Physiology|spinal cord]]. In the anterior, the neural tube swells into the three ventricles of the brain: the forebrain, midbrain, and hindbrain. This occurs as fluid is pumped into the lumen of the neural tube. Pressure is regionalised to the anterior by occlusion of the neural tube at the base of the hindbrain. The occlusion reopens after enlargement of the ventricles.

===Formation of Cell Layers===

The neural tube begins with the germinal layer which is a single cell layer thick. All cells have the capacity to undergo mitosis.
Some cells then lose their ability to undergo mitosis, they detach from the germinal layer and move away from the lumen to exist behind the germinal layer. This produces new layers called the '''mantle and intermediate layer'''. The germinal layer is now known as the '''ventricular layer'''. Cells of the intermediate layer differentiate into one of two cells:

# '''[[PNS Structure - Anatomy & Physiology#Nerve Fibre|Neurones]]''' - for conductance of nerve impulses.
# '''Glia''' - for insulation of electrical signals.

Glia form oligodendrocytes in the CNS, and [[PNS Structure - Anatomy & Physiology#The Schwann Cell|schwann cells]] in the PNS. Glial cells surround the axons furthest away form the lumen of the neural tube. Because this part is myelinated, it appears ''white'' and is called the '''marginal layer'''. Axons closer to the lumen of the neural tube, which the glial cells do not surround appear ''grey''. This layer is called the '''intermediate layer'''. The ventricular layer persists, so that the spinal cord develops with these three layers.

In the brain, further layers are added to increase complexity. This is possible because in the anterior of the embryo, neuroblasts (cells of the ventricular layer) retain their ability to undergo mitosis after leaving the ventricular layer. This difference is achieved by increased hydrostatic forces acting on the neuroblasts.

==Organisation of the Nervous System==

===Somatic Nervous System===

Sensory neurones enter the central nervous system (CNS) through the '''dorsal root'''. Sensory neurones have their cell bodies in dorsal root ganglia (DRG). DRG are evenly spaced along the spinal cord. Response to the stimulus is mediated by a single motor neurone. Somatic motor neurones have their cell bodies in the CNS. They leave the CNS by the '''ventral root'''. Dorsal and ventral roots converge to form '''spinal nerves'''.

===Autonomic Nervous System===

Sensory neurones also enter the CNS through the dorsal root, with their nuclei in DRG. In contrast to the somatic nervous system, the motor component is in two parts; a preganglionic and postganglionic neurone. The preganglionic neurone has its cell body in the CNS. It exits via the ventral root and synapses with the postganglionic neurone. Cell bodies of the postganglionic neurone lie outside the CNS in ganglia. Ganglia of the ''sympathetic'' nervous system are near the '''spinal cord'''. Ganglia of the ''parasympathetic'' nervous system are near the '''target organ'''.

==Neural Crest==
[[Image:neual crest.png|right|thumb|250px|Mithril 2010 Cross section scheme of vertebrate embryo. 1 – neural crest, 2 – neural tube, 3 – dorsal somite, 4 – notochord. Both paths of the neural crest cells migation marked by arrows: red one is the dorsolateral path, blue one signs the ventromedial path.]]

The crest neuroectoderm is the region at the junction of epidermis and neural plate. When the neural tube closes, the epidermis is brought into contact with the crest neuroectoderm. This contact causes cells of the crest neuroectoderm to undergo an epithelial to mesenchymal transition. Cells that undergo this transition break away from the neuroectoderm and are called '''neural crest cells'''. The peripheral nervous system (PNS) develops from the neural crest. The undifferentiated neural crest cells migrate away from the neural tube along "pathways". These pathways are governed by repulsive cues from the cells, as well as proliferation and survival signals. They differentiate once they reach their destination. Other non - neural tissues also develop from the neural crest. The type of tissue that neural crest forms is dependant on the origination of the cell along the anterior - posterior axis:

'''Anterior Neural Crest''' forms:
:sensory neurones and [[PNS Structure - Anatomy & Physiology#Schwann Cells|schwann cells]]
:[[Bones - Anatomy & Physiology|bones]] of the head
:dermis of the face
:[[Cartilage - Anatomy & Physiology|cartilage]]

'''Trunk Neural Crest''' forms:
:sensory neurones of the somatic and autonomic nervous systems (ANS)
:sympathetic motor neurones of the ANS
:melanocytes

'''Posterior Neural Crest''' forms:
:parasympathetic motor neurones of the [[Alimentary System Overview - Anatomy & Physiology#Small Intestine|gut]], which control peristalsis.

==Ectodermal Placodes==

The ectoderm thickens in places, with cells changing from cuboidal to columnar. These regions are called '''placodes'''. Placodes may be neurogenic or non - neurogenic. Neurogenic placodes are only found in the head, forming only sensory cells. Morphogenic changes produce the following derivatives:

'''Nasal placodes''' - by partial invagination.

'''Inner Ear''' - by invagination and vesicle formation.

'''Sensory Ganglion of Cranial Nerves''' - epithelial to mesenchymal transition.

[[Category:Developmental Biology]][[Category:Nervous System - Anatomy & Physiology]]
[[Category:A&P Done]][[Category:David Hogg reviewed]]

Mammary Gland - Anatomy & Physiology

2011-03-01T11:03:40Z

Dhogg:

== Introduction ==
[[Image:Cow teat 4.jpg|thumb|right|250px|Dissection of a Teat of the Bovine Udder,Courtesy of Andrew Crook, Copyright RVC 2008]]
[[Image:Suspensory structure of udder.gif|thumb|right|250px|Suspensory apparatus of the udder]]
[[Image:Udder lymphatics.gif|thumb|right|250px|Lymphatic drainage of the udder, Copyright DeLaval 2008]]
[[Image:Active Mammary Gland.jpg|right|thumb|150px|<center> The Active Mammary Gland. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]]
[[Image:Active Mammary Gland high power.jpg|right|thumb|150px|<center> The Active Mammary Gland at High Power. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]]
[[Image:Mammary Gland myoepithelial cells.jpg|right|thumb|150px|<center> Mammary Myoepithelial Cells. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]]
[[Image:Mammary Gland lactiferous duct.jpg|right|thumb|150px|<center> Section of the Mammary Gland showing a Lactiferous Duct. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]]
[[Image:Mammary Gland teat canal keratin plug.jpg|right|thumb|150px|<center> Cross Section through the Teat Canal of the Mammary Gland showing a Keratin Plug. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center>]]

The mammary gland is a modified sweat gland that nourishes the young. It consists of the '''mamma''' and the '''teat'''. Undeveloped in both the male and female at birth, the female mammary gland begins to develop as a secondary sex characteristic at puberty. With the birth of the first young, and first lactation, the mammary gland attains its full size and function. When suckling by the young stops, milk production ceases and the gland regresses. Shortly before the next and subsequent parturitions, the gland is stimulated by hormonal changes to produce milk.

== Development of the Mammary Gland (prenatal mammogenesis) ==

An ectodermal thickening developes along the ventral body wall extending from the thoracic to inguinal region - this is the '''mammary ridge'''. Cells aggregate, multiply and differentiate to form a chain of condensed '''mammary buds'''. Most mammary buds regress, those that remain and develop each give rise to a '''mammary gland'''. A mammary gland is the secretory and duct system associated with one teat. Mammary buds grow into overlying mesenchyme, and '''primary epidermal sprouts''' grow out of the bud apex. The epidermal sprout branches extensively and develops a complete '''duct system'''. Mammary adipose tissue is derived from mesoderm. This is required for complete mammary development and is absent in the male. As a result, mammary development in the male is halted at the epidermal sprout stage.

== Structure ==

The '''mamma (pleural = mammae) ''' is the glandular structure associated with a teat. The '''udder''' is a term designating all the mammae in the ruminant and the mare (sometimes used for the sow). The '''lobes''' are the internal compartments of the mamma, separated by adipose tissue. The lobes are divided into '''lobules''', consisting of connective tissue containing '''alveoli''', which are clusters of milk secreting cells. The '''lactiferous ducts''' are large ducts conveying milk from the alveoli to the milk sinus. The openings of the lactiferous ducts convey milk formed in the alveolus to the gland sinus.

The '''milk or lactiferous sinus''' is the milk storage cavity within the teat and glandular body. The '''gland sinus''' is part of the milk sinus within the glandular body and the '''teat sinus''' is part of the milk sinus within the teat.

The '''teat''' is the projecting part of the mammary gland containing part of the milk sinus. The '''teat canal''' is the canal leading from the teat sinus to the teat opening. The '''teat opening''' is the opening of the teat canal and the exit point for milk or entrance point for bacteria into the mammae. The '''sphincter''' consists of muscular fibres surrounding the teat opening that prevent milk flow except during suckling or milking.

=== Suspensory Apparatus ===

The suspensory apparatus is organised into the lateral and medial laminae, which suspend the mammary gland from the ventral aspect of the trunk by their attachment to the pubic symphysis. The '''lateral lamina''' consists of collagen fibres from the fascia of the pubic symphysis and the edge of the superficial inguinal ring. The '''medial lamina''' consists of elastic fibres from the tunica flava ventral to the pubic symphysis The '''intermammary groove''' divides the left and right rows of mammary complexes.

== Blood Supply ==
=== Arteries ===

In species with '''inguinal mammary glands''' (cow, ewe, goat, mare), the main blood supply is from the '''external pudendal artery'''. This arises indirectly from the external iliac artery via the femoral artery. The external pudendal artery passes through the inguinal canal. In species which also have '''thoracic mammary glands''' (bitch, queen, sow) blood supply is from the '''internal thoracic artery''' and its branches - cranial and cranial superficial epigastric arteries.

=== Veins ===

'''Thoracic mammary complexes''' drain into '''cranial superficial epigastric veins''' and open into the '''cranial epigastric vein'''. It drains into the '''internal thoracic vein'''.

'''Abdominal and inguinal mammary complexes''' drain into '''caudal superficial epigastric veins''' and open into the '''external pudendal vein'''.

== Innervation ==

There is '''sympathetic''' innervation to the blood vessels and teat sphincter smooth muscle via the '''genitofemoral nerve''' and '''somatic''' innervation via the ventral rami of the spinal nerves. In the cow, the ventral branches of L1 and L2 ('''iliohypogastric and ilioinguinal''') supply the skin of the cranial forequarters. Mammary branches of the '''pudendal nerve''' supply the caudal aspect of the udder (hindquarters). Mammary glands are, however, mainly under the influence of endocrine hormones.

== Lymphatics ==

The '''inguinal mammary glands''' contain a superficial inguinal lymph node and the '''thoracic mammary glands''' contain an axillary lymph node.

=== Lymphatic drainage in the cow ===

The '''afferent lymphatic ducts''' pass dorsocaudally to reach the mammary lymph nodes (superficial inguinal). The '''mammary (superficial inguinal) lymph nodes''' include two nodes at the dorsocaudal side of the udder, usually a palpable large, kidney-shaped node between the caudal side of the udder base and the thigh. The '''efferent lymphatic ducts''' pass into the abdomen through the inguinal canal to empty into the deep inguinal node. The '''deep inguinal lymph node''' is small and located in the dorsocaudal udder. It is too deep to be palpated.

== Histology ==

Secretory tissue is arranged into '''lobes''', each consisting of many '''lobules'''. Each lobule contains groups of '''alveoli''' (secretory compound tubuloalveolar cells) surrounded by a network of blood vessels and connective tissue stroma. The alveolar lumen is filled with milk during lactation. '''Myoepithelial cells''' lie between alveolar epithelial cells and the basement membrane. These contract under the influence of oxytocin to release milk to the exterior. Lobes and lobules are drained by lactiferous ducts into the '''gland sinus''', which is continuous with the '''teat sinus'''. The epithelium lining the lactiferous ducts and the sinus is two-layered cuboidal. A '''teat canal''' connects the teat sinus to the exterior. The lining is stratified squamous epithelium. Circular smooth muscle in the wall of the canal forms a '''sphincter'''. Between milkings, the narrow lumen of the teat canal is filled with a soft keratin plug to prevent bacteria entering the teat sinus and prevent milk leakage.

== Species Differences ==

'''Position and Morphology'''

{| style="width:75%; height:200px" border="1"

!Species
!'''Primates'''
!'''Elephant'''
!'''Goat and Sheep'''
!'''Guinea Pig'''
!'''Cow'''
!'''Mare'''
!'''Rat'''
!'''Dog'''
!'''Sow'''
!'''Cat'''
|-
| '''Number of Mammary Glands'''
| 2
| 2
| 2
| 2
| 4
| 4 (2 teats)
| ~10
| ~10
| 8-18
| 8
|-
| '''Position'''
| Pectoral
| Pectoral
| Inguinal
| Inguinal
| Inguinal
| Inguinal
| Abdominal,Ventral
| Thoracoabdominoinguinal
| Thoracoabdominoinguinal
| Thoracoabdominal
|-
| '''Teat Ducts'''
| 10-20
| Several
| 1
| 1
| 1
| 2
| 1
| 8-22
| 2
| 4-8
|-
|}

Click here for more information on the [[Cow Mammary Gland - Anatomy & Physiology|cow]], [[Small Ruminant Mammary Gland - Anatomy & Physiology|small ruminant]], [[Sow Mammary Gland - Anatomy & Physiology|sow]], [[Mare Mammary Gland - Anatomy & Physiology|mare]] and [[Carnivore Mammary Gland - Anatomy & Physiology|carnivore]].

==Links==

Test yourself with '''[[Reproductive_System_Flashcards_- Anatomy & Physiology|Reproductive System Flashcards]].'''

[[Category:Female Reproduction]]
[[Category:Integumentary System - Anatomy & Physiology]]
[[Category:A&P Done]]
[[Category:David Hogg reviewing]]

Category:UK - Glasgow Graduates

2011-03-01T10:58:24Z

Dhogg: Created page with "Here is a list of graduates from the Glasgow Vet school:"

Here is a list of graduates from the Glasgow Vet school:

David Hogg

2011-03-01T10:58:00Z

Dhogg:

{{UserPage
|Name=David Hogg
|Occupation= Veterinary Surgeon
|School= UK - Glasgow
|Year= 1967
|Email= dhogg@rvc.ac.uk
|Image= David_Hogg.jpg
}}

 ''David is a Consultant Lecturer in Veterinary Anatomy, who regularly works with Veterinary schools around the globe''

== David's involvement in WikiVet ==

[[:Category:David Hogg reviewing|View pages]] that David is reviewing

David has reviewed [[:Category:David Hogg reviewed|these pages]]

== Biography ==

David graduated from Glasgow Veterinary School in 1967 and initially entered mixed, mainly agricultural practice in Scotland.  David returned to Glasgow a year later and took a temporary position to teach veterinary anatomy. He then proceeded to teach at the Western College of Veterinary Medicine in Saskatoon, Canada in 1969. He returned to Glasgow in 1970 and spent some years teaching Veterinary Anatomy and proceeding towards his PhD in study of aspects of bone development in birds compared to mammals, which he completed in 1977. He made a move to Human Anatomy to learn about the human body, which led to a long period teaching Gross Anatomy to medical and dental students. While here he became interested in more specialized areas such as Animal Developmental Biology and the essential neuroscience instruction for students of Speech Pathology. David has worked abroad and helped to develop new Veterinary Schools in Kenya, Zambia, Zimbabwe, Trinidad and Tobago and was the Inaugural Dean of the School of Veterinary Medicine in St. George’s University, Grenada in 1998-2003.

== Research ==

David has focussed his research mainly on comparitive anatomy.  His PhD was on the bone development in birds compared to mammals and his later reserch has been into the embryonic development of bones and joints. 

== Teaching ==

David has taught all over the globe and is now teaching Veterinary Anatomy where and when required.  He now focuses his teaching predominantly in the UK.

[[Category:Expert Reviewer]]
[[Category:UK - Glasgow Graduates]]

User:Dhogg

2011-03-01T10:57:48Z

Dhogg:

{{UserPage
|Name=David Hogg
|Occupation= Veterinary Surgeon 
|School= UK - Glasgow
|Year= 1967
|Email=
|Image=
}}

[[David Hogg|link to David's profile]]

User:Dhogg

2011-03-01T10:57:29Z

Dhogg: