lecture 2

• gravid


  describes whether a cow is pregnant or not
• parous


  describes pregnancy post-birth (how many times a cow has birthed)
• milk

  lacteal secretion, from mammary gland, practically free from colostrum, obtained by the complete milking of one or more healthy cows
• the mammary gland is an exocrine gland, meaning it excretes the substances it synthesizes out of the body
• mammary glands are considered part of the reproductive system, as it's primary role is to nourish the neonate, which is partially achieved by providing protection through immunity
• the mammary glands only develop when needed to synthesize and secrete milk because it takes an abundance of energy and increases the chances for infection
• pregnancy associated hormones include estrogen, progesterone, prolactin; these all play a pivotal role in development of the mammary glands
• lactation is the secretion of milk from the mammary glands; is a characteristic of all mammals and their reproductive strategy; originated over 200 million years ago
• mammals are of the class mammalia (mamma); have hair and mammary glands
• there are estimated to be about 5,416 mammalian species total
• there are 3 sub-classes of mammals that are based on placental types: eutheria (placental), metatheria (marsupials), and monotremata (egg laying)
• some examples of eutheria (placental) mammals include humans, elephants, dogs, and wales
• some examples of metatheria (marsupial) mammals include wallaby, kangaroo, possum, and sugar gliders
• some examples of monotremata (egg laying) mammals include echidna and platypus
• 5 features that all mammals have in common include: hair, vertebrae, mammary glands, warm blooded, and breath air
• monotremes are egg laying mammals that drink milk for an extended period of time, but have no true teats or nipples
• platypus have rudimentary mammary glands, meaning there is no nipple and milk is instead lapped from hair next to the gland; have 100-150 paired glands that are similar to specialized sweat glands
• echidna have no nipple or teat and a more complex organization than platypus; have 2 mammary glands with many branches; milk is collected in an indentation
• marsupials have live births and have pouches for their young; mammary glands are always inside pouch, where the young suckle for an extended period of time
• marsupials have no true placenta, their gestation is usually very brief, with a large amount of growth and development occurring in the pouch where the offspring is affixed to the teat for a long time
• marsupials: 100 days postpartum, the young is still very small but has distinguishable features; 130 days, the young no longer needs to be affixed; 150 days, the young can come and go from the pouch as needed
• placenta mammals have live births, have mammary glands located in various regions, most have hair, and can nurse for short or extended periods of time depending on the young
• placental mammals include a large subset of animals with considerable variation of mammary gland number, location, and size, as well as milk composition
• since mammary glands are soft tissues and cannot fossilize, the evolution must instead be studied through our knowledge on the topic
• mammary glands are highly developed sebaceous glands, which are associated with hair follicles, have a saccular structure, secrete sebum (a lipid material), and conduct holocrine secretion
• the platypus uses holocrine secretion
• holocrine secretion is the soughing of the entire cell into the lumen to secrete the product; some milk components are secreted this way (foamy cells in goats)
• sweat glands are not associated with hair follicles, have a tubular structure with a salty secretion, and conduct merocrine secretion
• merocrine secretion is secretion of cell products where no part of the cell is removed; exocytosis; some milk components are secreted this way including milk protein
• the echidna uses merocrine secretion
• the main components in milk include water, protein, fat, carbohydrates, vitamins, minerals, and cells
• milk is the only food source available to the neonate, so it must have all necessary components for proper growth and development
• colostrum is considerably different in components than mature milk; it contains higher fat, protein, immunoglobulins/antibodies, can have additional growth factors and steroids, and is highly variable between species
• colostrum composition is influenced by species, diet, and environment
• milk is much more consistent than colostrum and it typically contains more water at the expense of other components
• colostrum transitions to milk; decreases in overall solids and antibodies, increase in lactose and water
• antibodies protect against infection, either viral or bacterial
• antibodies maintain different heavy chains; IgM forms a pentamer, IgG forms a monomer, and IgA formed a dimer
• bovine have very high levels of IgG in colostrum because there is no in-utero transfer of this heavy chain
• humans have high levels of the IgA heavy chain in colostrum because there is little to no in-utero transfer