SEM_15_Reproductive system_PARTE2.docx

Mammary glands Mammary glands, like sebaceous and sweat glands, are specialised cutaneous glands. They start to develop in both sexes from two thickened strips of epidermal ectoderm, the mammary lines or mammary ridges which extend from the axillary to the inguinal regions. Local condensation of ec...

Mammary glands Mammary glands, like sebaceous and sweat glands, are specialised cutaneous glands. They start to develop in both sexes from two thickened strips of epidermal ectoderm, the mammary lines or mammary ridges which extend from the axillary to the inguinal regions. Local condensation of ectoderm and subjacent mesoderm occur at specific intervals along the mammary ridges. These thickened areas are the origin of the mammary papillae (teats o nippples), that are projections from the mammary glands from which milk flows or is ejected for the purpose of feeding young. The mammary glands of cattle, sheep, goats, horses, and camel are located in the inguinal region; those of primates and elephants, in the thoracic region; and those of pigs and carnivores spread throughout the ventral aspect of the trunk. In ruminants and horses, the mammary glands and teats are collectively known as the udder. - Location of mammary gland is described as inguinal, abdominal or thoracic. Goats and ewes, have 2 inguinal glands with 1 gland opening / teat. Mares has 2 inguinal glands and 2 gland openings/teat Cows have has 4 inguinal glands and 1 gland opening/teats. Sows have 2 inguinal pairs, 3 abdominal pairs, 2 thoracic pairs (thoracic are most productive) with 2 or 3 teat openings. Cats have 1 inguinal pair, 1 abdominal, 2 thoracic pairs (abdominal are most productive) and 3-6 mammary openings on the tip of each teat. Bitches have 1 inguinal pair, 2 abdominal pairs, 2 thoracic pairs (abdominal are most productive) and about 12 mammary openings situated on the tip of each eat. The teat or mammary papilla is formed by focal condensation and thickening of the ectoderm and subyacente mesenchyme that occur at specific intervals along the mammary ridge. The thickened surface epithelium give rise to the primary mammary buds that push into the underlying mesenchyme and branche into secondary mammary buds. The mammary buds lengthen and continue to branch as embyonic developement proceeds. The mammary bud are initially solid cords of ectodermal cells invade the underlying mesoderm but latter become canalised to form the lactiferous ducts that open onto the surface of the developing teats. Just before entering the teat, the lactiferous duct enlarges to form a gland sinus (ampulla), which serves as a reservoir for milk. The supporting connective tissue and vascular supply are provided by the associated mesenchymal cells. The number mammary buds that develop in each mammary gland/teat is species-dependent (approximately: 1 in sheep, goats and cows; 2 in mares and sows; 6 in queens; 12 in bitches). In humans, multiple lactiferous ducts open firstly into a depression called the mammary pit or inverted nipple; soon after birth the nipples become everted from the proliferation of the underlying mesoderm while the surrounding skin (areola) increases in pigmentation. https://sway.office.com/OqCVVhptwDvRDrvO#content=7AIynG0MhquZps - Most of the mammary ridge, which at first extends from the axillary region to the inguinal region, disappears shortly after it forms, remaining only a number of mammary buds that give rise to the mammary glands characteristic in each species. Among other subsidiary factors, hormones play a leading role in mammary development. Although mammary glands start to develop in all embryos irrespectively of their sex, testosterone secreted by the testes in male embryos induces atrophy of the mammary buds. This testosterone-dependent mammary inhibition displays some differences between males of different species (males of rats, mice, or horses are born with no rudimentary teats). During prenatal development, the mammary bud sinks into the fat pad precursor and expands to form a rudimentary duct system. The gland remains relatively quiescent until the onset of puberty, when terminal end buds are formed under the control of sex-related hormones (blow up of pubertal time point). During repeated oestrous cycles, the duct and alveolar framework is established. During pregnancy, under the influence of increased levels of oestrogen and progesterone, the terminal portions of the branches form the mammary gland alveoli. alveolar budding and differentiation take place to give rise to the milk producing cells. Further endocrine stimulation during pregnancy is needed to complete mammary growth and start milk segregation. Congenital supernumerary teats or polythelia is the most common mammary anomaly in newborns. At an early embryonic stage, the development of extra buds is not an unusual occurrence but most of these additional buds degenerate as development goes on. If additional buds fail to degenerate, they result in supernumerary teats. Although these teats are frequently rudimentary and imperforate, occasionally they are associated with a small amount of glandular tissue which may produce milk. Other congenital mammary anomalies in domestic animals include the congenital absence of one or more mammary glands (amastia) or incomplete canalisation of the glandular sprout (imperforate teats).