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== Introduction ==

== Introduction ==

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.

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) ==

== 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 thus absent in the male.  As a result, mammary development in the male is halted at the epidermal sprout stage.

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 ==

== 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 '''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 '''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.

=== Suspensory Apparatus ===

=== 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.

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 ==

== Blood Supply ==

=== Arteries ===

=== 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.

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 ===

=== Veins ===

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

'''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'''.

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

== Innervation ==

== Innervation ==

There is '''sympathetic''' innervation to the blood vessels and teat sphincter smooth muscle via the '''genitofemoral nerve''' and '''somatic''' 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.

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 ==

== Lymphatics ==

=== Lymphatic drainage in the cow ===

=== Lymphatic drainage in the cow ===

The '''afferent lymphatic ducts''' pass dorsocaudal 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 '''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 ==

== 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.

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 ==

== Species Differences ==

==Links==

==Links==

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