mammary gland development and anatomy Flashcards
what is the significance of lactation
- frees neonate from dependency on other foods
- allows offspring to continue development outside the uterus
- provides for social development and bonding
- provides a natural form of contraception
how dp mammary glands develop embryolologically
- mammary glands are glands that originate from the epidermis
- they arise along two lateral lines on the ventral surface of the developing fetus
- these lines are called mammary ridges
- mammary ridges extend from the axillary region to the inguinal region
- number and position of glands depends on the species
describe the microanatomy of the mammary glands
- secretory epithelial cells surround a spherical lumen: alveolus
- myoepithelial cells surround each alveolus and the ducts
- contraction of myoepithelial cells propels the milk out of the alveoli into the ducts
what is special about the teat streak
stratified squamous epithelial cells rather than cuboidal epithelium –> bacteriostatic
how many glands will an animal have
about twice the number of normal litter size
which species have one canal per teat
cow, ewe, goat
which species have 2-3 ducts per teat
mare, sow
which species have 5-6 ducts per teat
bitch, queen
which species have 8-10 ducts per teat
primates, elephants
what are lactiferous sinuses
smaller versions of the gland sinus in teats with many ducts
what are supranumery teats
- potentially any part of the embryological mammary ridge can produce glands and teats
- ocasionally an extra teat will be seen
- will need to be removed from dairy heifers (wont be connected to a sinus, simple surgery
explain the mammary suspensory system
supported by a strong suspensory ligament divided into 2 parts:
- medial suspensory ligament arising from the symphyseal tendon (attaches the prepubic tendon to the pelvic symphysis). yellow elastic tissue
- lateral suspensory ligaments running from the symphyseal tendon and the external crus of the inguinal ring, assisted by the medial femoral fascia and then runs ventrallt over the lateral aspect of the udder inelastic connective tissue
how do mammary glands grow
- endocrine mediated
- complete development and ability to secrete milk does not occur until puberty
- birth to puberty: isometric growth (like all other tissues)
- after puberty: allometric growth
- complete and rapid growth of ducts occurs in the presence of prolactin and growth hormone
- during oestrus ducts begin to branch under the effect of oestrogen
- alveoli are formed under the influence of progesterone
- in pregnancy terminal alveoli grow into lobules due to progesterone dominance
- prolactin, adrenal cortical hormones and placental lactogen (relaxin in pigs from CL) allow the synthesis of milk
outline the hormones involved in mammary function
discuss mammogenesis during pregnancy
- placenta produces hormones during pregnancy to induce mammary growth
- levels are higher in twin than in singleton pregnancies
- placental lactogen acts in synergy with oestrogen
- placental lactogen has both prolactin and growth hormone activities
- ## produced by binucleate cells of placenta
what hormone triggers mammogenesis in the sow
relaxin as dont have placental lactogen
outline vascularisation to the mammary glands
- the local vessens running from the major arteries to the mammary glands are always called mammary arteries
- thoracic gland = branches of internal thoracic artery via intercostal perforating artery and pectoral artery
- abdomina glands = branches of the cranial and caudal superficial epigastric artery
- inguinal glands = branches of the external pudendal
discuss venous drainage from the mammary glands of the cow
- external pudendal veins into the external iliacs then caudal vena cava
- perineal veins into the internal pudendal then caudal vena cava
- superficial epigastric veins (AKA milk veins) then to internal thoracis vein then cranial vena cava
discuss innervation of the bovine mammary gland
- somatic sensory innervation (afferent) carries impulses from tactile receptors in the skin
- sympathetic motor nerve (efferent) run along blood vessels
- no parasympathetic innervation
- myoepithelial cells are not innervated
- 1st, 2nd lumbar nerve, inguinal and perineal nerves = branches
discuss lymph drainage from mammary glands
- cranial glands lead to axillary and accessory axillary LN
- caudal glands lead to superficial inguinal nodes
- lymph from middle glands drains either caudally or cranially, not a mixutre
