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Mammary Gland - Anatomy & Physiology (view source)
Revision as of 15:16, 17 March 2011
, 15:16, 17 March 2011no edit summary
== Introduction ==
== 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|<small><center> The Active Mammary Gland. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center></small>]] [[Image:Active Mammary Gland high power.jpg|thumb|right|150px|<small><center> The Active Mammary Gland at High Power. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center></small>]] [[Image:Mammary Gland myoepithelial cells.jpg|thumb|right|150px|<small><center> Mammary Myoepithelial Cells. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center></small>]] [[Image:Mammary Gland lactiferous duct.jpg|thumb|right|150px|<small><center> Section of the Mammary Gland showing a Lactiferous Duct. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center></small>]] [[Image:Mammary Gland teat canal keratin plug.jpg|thumb|right|150px|<small><center> Cross Section through the Teat Canal of the Mammary Gland showing a Keratin Plug. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center></small>]]
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 '''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 '''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 '''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.
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 ==
=== Veins ===
=== Arteries ===
'''Thoracic mammary complexes''' drain into '''cranial superficial epigastric veins''' and open into the '''cranial epigastric vein'''. It drains into the '''internal thoracic vein'''.
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'''.
== Lymphatics ==
== 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.
=== Lymphatic drainage in the cow ===
== Lymphatics ==
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.
The '''inguinal mammary glands''' contain a superficial inguinal lymph node and the '''thoracic mammary glands''' contain an axillary lymph node.
== Histology ==
=== 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.
== Species Differences ==
== Histology ==
'''Position and Morphology'''
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'''
!Species
<br>
!'''Primates'''
!'''Elephant'''
{| border="1" style="width: 75%; height: 200px;"
!'''Goat and Sheep'''
|-
!'''Guinea Pig'''
! Species
!'''Cow'''
! '''Primates'''
!'''Mare'''
! '''Elephant'''
!'''Rat'''
! '''Goat and Sheep'''
!'''Dog'''
! '''Guinea Pig'''
!'''Sow'''
! '''Cow'''
!'''Cat'''
! '''Mare'''
|-
! '''Rat'''
| '''Number of Mammary Glands'''
! '''Dog'''
| 2
! '''Sow'''
| 2
! '''Cat'''
| 2
|-
| 2
| '''Number of Mammary Glands'''
| 4
| 2
| 4 (2 teats)
| 2
| ~10
| 2
| ~10
| 2
| 8-18
| 4
| 4 (2 teats)
| ~10
| ~10
| 8-18
| 8
| 8
|-
|-
| '''Position'''
| '''Position'''
| Pectoral
| Pectoral
| Pectoral
| Pectoral
| Inguinal
| Inguinal
| Inguinal
| Inguinal
| Inguinal
| Inguinal
| Inguinal
| Inguinal
| Abdominal,Ventral
| Abdominal,Ventral
| Thoracoabdominoinguinal
| Thoracoabdominoinguinal
| Thoracoabdominoinguinal
| Thoracoabdominoinguinal
| Thoracoabdominal
| Thoracoabdominal
|-
|-
| '''Teat Ducts'''
| '''Teat Ducts'''
| 10-20
| 10-20
| Several
| Several
| 1
| 1
| 1
| 1
| 1
| 1
| 2
| 2
| 1
| 1
| 8-22
| 8-22
| 2
| 2
| 4-8
| 4-8
|}
|}
<br> 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 ==
==Links==
Test yourself with '''[[Reproductive System Flashcards - Anatomy & Physiology|Reproductive System Flashcards]].'''
[[Category:Female Reproduction]]
[[Category:Female_Reproduction]] [[Category:Integumentary_System_-_Anatomy_&_Physiology]] [[Category:A&P_Done]] [[Category:David_Hogg_reviewing]]
[[Category:Integumentary System - Anatomy & Physiology]]
[[Category:A&P Done]]
[[Category:David Hogg reviewing]]