Suporn Katawatin Department of Animal Science Khon Kaen University Question -

† Why do cows have four mammary glands?

† Click here Why4.doc Mammary gland

† Gland anatomy † Circulatory system † Lymphatic system † Nervous system Gross anatomy: cow model To achieve functional capacity of mammary gland, a number of supporting systems must exist

† Physical support of the mass - Suspensory system † On/off valve for intermittent removal of milk - Teat † Pathway for milk to travel from the milk synthesis site to the exit - Ducts & Cisterns † Means of actively expelling milk from the udder - Neural system † Continuous supply of substrates for milk synthesis - Blood system † Means of balancing the fluid dynamics in the tissue - Lymph system † Internal secretory tissue - Lobes/lobules/alveoli Suspensory system: Physical support of the udder mass

† median suspensory ligament „ most important part of the suspensory system in „ partially separates the left and right halves of the udder „ great tensile strength, able to stretch, allow increased weight of gland „ located at center of gravity of the udder to give balanced suspension Suspensory system

† There are seven tissues that provide support for the udder: „ Suspensory system.doc Teat : On/off valve for intermittent removal of milk

† only exit for secretion from gland and for calf to receive milk † one teat one gland † no hair, sweat glands or sebacious glands † size and shape are independent of the size, shape or milk production of the udder † average size (cow model) „ fore teats 6.6 cm long and 2.9 cm in diameter „ rear teats 5.2 cm long and 2.6 cm in diameter Supernumerary Teats

† extra teats † some open into a "normal" gland, but many do not † pseudo-teat has no streak canal, no connection internal of gland † many sows have extra, non- functional teats Streak canal (ductus papillaris)

† only orifice between internal milk secretory system and external environment † main barrier against intramammary infection † lined with keratin material, antibacterial properties † kept closed by sphincter muscles † opened when milked for an hour or more after , provides access of bacteria to inside gland † during dry period, epidermal tissue lining streak canal forms keratin plug to effectively seals off canal Teat cistern (Sinus papillaris)

† cavity within teat, continuous with gland cistern † lined with longitudinal and circular folds in mucosa, form pockets on the inner lining of the teat. † fills with milk during milk letdown, and together with milk in gland cistern removed with each sucking Click to read more on teats Teat.doc Ducts & Cisterns: Pathway for milk to travel from synthesis site to the exit

† ducts are tubing by which milk moves from alveoli to teat for milk removal † cisterns are open areas between teat and large ducts, collect milk between milkings „ allows accumulate more milk in udder between milkings or suckling by the calf „ Gland Cisterns or udder cistern opens directly into the teat cistern Click to read more on ducts & cisterns

† ducts & cisterns.doc Neural system: Means of actively expelling milk from the udder

† innervation inside udder sparse compared with other tissues † sympathetic nerves present in the tissue, associated with arteries, but do not innervate alveoli † no parasympathetic innervation, similar to other skin glands † Sensory nerves found in teats and skin, initiating milk ejection reflex † no innervation of the secretory system include Myoepithelial cells, contract in response to oxytocin † Few nerves go to interior of the udder, biopsy of gland can be done with local anesthetic to skin ภาพแสดงระบบ ประสาทที่เตานม้ Blood system: Continuous supply of substrates for milk synthesis

† All milk precursors come from blood † 400 - 500 units of blood through udder for each unit of milk synthesized; ~280 ml per sec. † 2-6 fold increase in blood flow in mammary gland starting 2-3 days prepartum † efficiency of extraction of components from blood is important † decrease in production with advancing lactation is not due to decreased blood flow, rather to loss of secretory epithelial cells through apoptosis ภาพแสดงระบบไหลเวยนเลี ือดที่มายงเตั านม้

† Diagram showing location of arteries (red) and veins (purple) leaving the body cavity through the inguinal canal (white circle). Green circle indicates location of supramammary lymph nodes. Lymph system: Means of balancing the fluid dynamics in the tissue

† large molecules, proteins, metabolites, secretory products, not return to venous drainage but are in the interstitial spaces, „ disrupt normal balance of osmotic pressure in tissue „ upsetting trans-capillary fluid exchange „ excess fluid accumulate in the interstitial spaces † Functions of lymphatics: „ Drained extracellular fluids from tissue back to blood via the lymphatic network „ contain lymphocytes and macrophages in lymph nodes, an immune response to bacteria and foreign „ transport vitamin K, lipids Udder edema

† swelling of the udder, fluid accumulates between skin and glandular tissue, and in gland † caused by an imbalance of hydrostatic and osmotic pressures, increasing fluid flow out of the capillaries into the interstitial spaces † first time calving heifers prone to udder edema † Severe edema can strain supportive structures of udder ภาพแสดงระบบน้าเหลํ ือง lymphatic system.doc Lobes/lobules/alveoli: Internal secretory tissue

† Connective tissue: parenchyma & fat pad

† Secretory tissue : secretory epithelial cells, organized into lobes, with each lobe made up of many lobules. Each lobule contains 150-220 microscopic alveoli Lobules

† fundamental growing units of mammary tissue- mammary growth † composed of a cluster of 150-220 alveoli, encapsulated by connective tissue sheath † During late pregnancy, alveolus forms within the lobules Alveoli -(acini)

† sac-like, where milk is synthesized and secreted † lumen lined by single layer of secretory epithelial cells † epithelial lining surrounded by myoepithelial cells † Outside of myoepithelial cells surrounded by basement membrane † outside alveolus, between alveoli, is capillary bed, part of the stromal tissue (connective tissue) † precursors and substrates of milk components must pass epithelial cells to be converted into milk lactose, fat, or proteins

alveoli from lactating pig

† stained material in the lumen is milk contents † several round clear areas near bottom fat of the right-hand droplets alveolus are fat droplets, ready to be secreted non-lactating cow (30 days after drying off)

† alveoli shrunk lactating † more stromal area between alveoli and ducts

† ducts not regress as Non- much as alveoli lactating during mammary gland involution Non-lactating alveoli

Lactating alveoli