Difference between revisions of "Mammary Gland - Anatomy & Physiology"

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== Introduction ==
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== Introduction ==
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[[Image:Cow teat 4.jpg|thumb|right|250px|Dissection of a Teat of the Bovine Udder,Courtesy of Andrew Crook, Copyright RVC 2008]]
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[[Image:Suspensory structure of udder.gif|thumb|right|250px|Suspensory apparatus of the udder]]
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[[Image:Udder lymphatics.gif|thumb|right|250px|Lymphatic drainage of the udder, Copyright DeLaval 2008]]
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[[Image:Active Mammary Gland.jpg|right|thumb|150px|<small><center> The Active Mammary Gland.  Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center></small>]]
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[[Image:Active Mammary Gland high power.jpg|right|thumb|150px|<small><center> The Active Mammary Gland at High Power.  Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center></small>]]
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[[Image:Mammary Gland myoepithelial cells.jpg|right|thumb|150px|<small><center> Mammary Myoepithelial Cells.  Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center></small>]]
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[[Image:Mammary Gland lactiferous duct.jpg|right|thumb|150px|<small><center> Section of the Mammary Gland showing a Lactiferous Duct.  Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))</center></small>]]
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[[Image:Mammary Gland teat canal keratin plug.jpg|right|thumb|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>]]
  
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[[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>]]
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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.
  
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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) ==
  
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== Development of the Mammary Gland (prenatal mammogenesis) ==
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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.
  
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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.
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== Structure ==
  
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== Structure ==
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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.
  
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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.  
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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.
  
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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.  
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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.
  
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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.
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=== Suspensory Apparatus ===
  
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=== Suspensory Apparatus  ===
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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.
  
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In species with large udders, especially in dairy cattle, there is a&nbsp; 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.
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== Blood Supply ==
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=== Arteries ===
  
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== Blood Supply ==
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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.
  
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=== Arteries  ===
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=== Veins ===
  
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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'''.  
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'''Thoracic mammary complexes''' drain into '''cranial superficial epigastric veins''' and open into the '''cranial epigastric vein'''. It drains into the '''internal thoracic vein'''.
  
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=== Veins  ===
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'''Abdominal and inguinal mammary complexes''' drain into '''caudal superficial epigastric veins''' and open into the '''external pudendal vein'''.
  
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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'''.
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== Innervation ==
  
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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.<br>
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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.
  
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== Innervation  ==
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== Lymphatics ==
  
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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.  
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The '''inguinal mammary glands''' contain a superficial inguinal lymph node and the '''thoracic mammary glands''' contain an axillary lymph node.
  
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== Lymphatics  ==
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=== Lymphatic drainage in the cow ===
  
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The more caudal mammary glands drain to the&nbsp; '''superficial inguinal lymph node''' and the more cranial mammary glands to the axillary or sternal lymph nodes.  
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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.
  
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=== Lymphatic drainage in the cow  ===
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== Histology ==
  
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The '''afferent lymphatic ducts''' pass dorsocaudally to reach the '''superficial inguinal''' (mammary) lymph nodes at the dorsocaudal side of the udder. These are&nbsp; 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.&nbsp;
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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.
  
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== Histology  ==
+
== Species Differences ==
  
−
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.
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'''Position and Morphology'''
  
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== Species Differences  ==
 
  
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'''Position and Morphology'''
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{| style="width:75%; height:200px" border="1"
  
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<br>
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!Species
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!'''Primates'''
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{| border="1" style="width: 75%; height: 200px;"
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!'''Elephant'''
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|-
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!'''Goat and Sheep'''
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! Species  
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!'''Guinea Pig'''
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! '''Primates'''  
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!'''Cow'''
−
! '''Elephant'''  
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!'''Mare'''
−
! '''Goat and Sheep'''  
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!'''Rat'''
−
! '''Guinea Pig'''  
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!'''Dog'''
−
! '''Cow'''  
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!'''Sow'''
−
! '''Mare'''  
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!'''Cat'''
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! '''Rat'''  
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|-  
−
! '''Dog'''  
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| '''Number of Mammary Glands'''
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! '''Sow'''  
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| 2
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! '''Cat'''
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| 2
−
|-
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| 2
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| '''Number of Mammae/teats'''  
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| 2
−
| 2  
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| 4
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| 2  
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| 4 (2 teats)
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| 2  
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| ~10
−
| 2  
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| ~10
−
| 4  
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| 8-18
−
| 4 (2 teats)  
 
−
| ~10  
 
−
| ~10  
 
−
| 8-18  
 
 
| 8
 
| 8
 
|-
 
|-
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| '''Position'''  
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| '''Position'''
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| Pectoral  
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| Pectoral
−
| Pectoral  
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| Pectoral
−
| Inguinal  
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| Inguinal
−
| Inguinal  
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| Inguinal
−
| Inguinal  
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| Inguinal
−
| Inguinal  
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| Inguinal
−
| Abdominal,Ventral  
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| Abdominal,Ventral
−
| Thoracoabdominoinguinal  
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| Thoracoabdominoinguinal
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| Thoracoabdominoinguinal  
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| Thoracoabdominoinguinal
 
| Thoracoabdominal
 
| Thoracoabdominal
 
|-
 
|-
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| '''Teat Ducts'''  
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| '''Teat Ducts'''
−
| 10-20  
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| 10-20
−
| Several  
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| Several
−
| 1  
+
| 1
−
| 1  
+
| 1
−
| 1  
+
| 1
−
| 2  
+
| 2
−
| 1  
+
| 1
−
| 8-22  
+
| 8-22
−
| 2  
+
| 2
 
| 4-8
 
| 4-8
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|-
 
|}
 
|}
  
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<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]].
 
  
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{{Template:Learning
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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]].
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|flashcards = [[Reproductive System Flashcards - Anatomy & Physiology|Mammary gland flashcards]]
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|powerpoints = [[Mammary Gland Histology resource|Histology of the mammary gland]]
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==Links==
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|videos = [[Video: Bovine teat and mammary gland potcast|Bovine teat and mammary gland potcast]]<br>[[Video: Mammary gland of the ewe|Mammary gland of the ewe]]
 
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}}
 
−
<br>
 
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{{Template:David Hogg reviewed
 
−
|date=20/03/2011}}
 
  
 +
Test yourself with '''[[Reproductive_System_Flashcards_- Anatomy & Physiology|Reproductive System Flashcards]].'''
  
−
==Webinars==
 
−
<rss max="10" highlight="none">https://www.thewebinarvet.com/urogenital-and-reprodcution/webinars/feed</rss>
 
  
−
[[Category:Female_Reproduction]] [[Category:Integumentary_System_-_Anatomy_&_Physiology]] [[Category:A&P_Done]] [[Category:David_Hogg_reviewed]]
+
[[Category:Female Reproduction]]
 +
[[Category:Integumentary System - Anatomy & Physiology]]
 +
[[Category:A&P Done]]
 +
[[Category:David Hogg reviewing]]

Revision as of 11:03, 1 March 2011

Introduction

Dissection of a Teat of the Bovine Udder,Courtesy of Andrew Crook, Copyright RVC 2008
Suspensory apparatus of the udder
Lymphatic drainage of the udder, Copyright DeLaval 2008
The Active Mammary Gland. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))
The Active Mammary Gland at High Power. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))
Mammary Myoepithelial Cells. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))
Section of the Mammary Gland showing a Lactiferous Duct. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))
Cross Section through the Teat Canal of the Mammary Gland showing a Keratin Plug. Copyright RVC 2008 (Courtesy of Tanya Hopcroft (RVC))

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


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, small ruminant, sow, mare and carnivore.

Links

Test yourself with Reproductive System Flashcards.

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