lecture 3

• the udder is a large heavy structure (40-60 lbs empty plus 50-60 lbs of milk); easily weigh more than 100 lbs
• the udder is a composite unit made of 4 teats, each with their own individual gland
• the median suspensory ligament goes down the center of the bovine udder, separating the left and right halves
• the connective tissue septum separates the front and rear halves of the bovine udder
• a supernumerary teat is an extra teat that is fairly common but does not produce milk
• support structures from outer to inner: skin, lateral suspensory ligament, medial suspensory ligament, intermammary groove, internal connective tissues (loose connective tissue, lamellar plates)
• the skin does not provide any organization in the udder
• the lateral suspensory ligament is outside the udder, just beneath the skin
• the median suspensory ligament goes down the middle of the udder and creates the intermammary groove (cleft between halves)
• internal connective tissue consists of loose connective tissue (fore quarter attachment of udder to skin) and the lamellar plates (connected to suspensory ligaments)
• the lateral suspensory ligament holds everything in, pulls towards the midline
• the medial suspensory ligament holds the udder up (balanced in all 4 directions)
• the medial suspensory ligament is the most important
• compass cow/pendulous udder: if ligaments weaken, the udder will break away; pendulous; makes more susceptible to injury and mastitis and makes it hard to milk with a milking unit
• the medial suspensory ligament is mainly elastic tissue because it is attached to the abdominal wall and it needs to be able to flex as the animal moves to prevent tearing; MOST IMPORTANT
• the lateral suspensory ligament is made of fibrous tissue because it needs to maintain shape and is attached to the pelvis
• the median suspensory ligament supports weight, while the lateral suspensory ligament and lamellar plate support shape
• median and lateral suspensory ligaments and the lamellar plates meet, forming a sling to support mammary tissues
• the individual quarters/glands are comprised of parenchymal and stromal tissues
• stromal tissues are supportive tissues (ligaments)
• parenchyma tissues are functional tissues (milk-making)
• quarters are separate and mostly independent; all have their own milk supply and can function separately
• starting from the bottom and moving up: teat, annular ring, gland cistern, ducts, secretory tissues
• the teat starting from the bottom up: apex, streak/teat canal, Furstenberg's rosette, cistern, annular ring, and then glands
• the streak/teat canal is surrounded by a sphincter of smooth muscle that keeps the canals closed to prevent milk leaking out and prevent pathogens from coming in
• Furstenberg's rosette is a sensitive folding of tissue filled with immune cells (plasma and lymphocytes) that act as the first line of defense for entering bacteria
• keratin plugs may form in non-lactating cows to protect the teat from bacteria entering; ear-wax consistency; length of streak canal
• moving into the quarter from bottom up: annular ring, gland cistern, terminal ducts, secretory tissues
• the gland cistern is where all ducts converge; main milk accumulation area; made of epithelial cells; relatively small in volume (100-400 mL), but a cow produces 5-6 liters per quarter for each milking (milked 2x day)
• the rest of the milk resides in secretory tissues if it is not in the gland cistern
• ducts carry milk from secretory tissues to cistern; branch upward from cistern in a tree-like fashion; smaller and smaller closer to milk secreting tissues; made of stratified epithelial cells
• the rear quarters are larger than the fore quarters; make 60% of milk vs fore 40%
• the mammary gland extends higher in rear quarters because it reaches the body cavity later (abdominal wall slopes up toward rear)
• if you study milk production in the quarters, you must account for difference in front/rear yields
• duct (gross and microscopic)- vessel that carries milk from parenchyma/alveoli to gland cistern
• lobe- group of lobules surrounded by connective tissue
• lobule- group of 150-250 alveoli
• alveolus- single sphere of mammary epithelial cells that synthesize and secrete milk into an open lumen; functional unit of the mammary gland
• the alveolus contain a single layer of secretory epithelial cells surrounded by myoepithelial cells that squeeze milk (smooth muscle); this is hormone (oxytocin) driven; all enveloped by a capillary bed (blood vessels to supply nutrients)
• the capillary bed in alveolus circulates 400-500 gallons of blood per 1 gallon of milk that is produced