Lecture 14 - Lactation pt.2 Flashcards
Mammary epithelium
- consumes 50% of O2 in arterial blood
- high mitochondrial density
- ATP for synthetic processes, uptake of precursors and transport into lumen - make proteins in the rough ER
- make phospholipids and triglycerides in SER
- FA synthesis in cytosol
- glycolysis in cytosol - lactose synthesized in the golgi
Where is lactose synthesized?
- in the golgi of the mammary epithelium
What does the golgi do?
- lactose synthase = glucose + galactose
- packaged into secretory vesicles
- main determinant of milk secreted
What turns on the enzymes for lactose production?
Prolactin!
What is driving total milk production?
- the total amount of lactose that can be produced
- lactose has the highest osmolarity = pulling in most water = impacting total milk volume the most
What is 98% of milk fat composed of?
- triglycerides; synthesized in smooth ER
- high in saturated fat
- FA hydrogenation in rumen
Where are free fatty acids obtained from?
- chylomicrons and VLDL OR DE NOVO FA synthesis in alveolar epithelial cells
Why can’t ruminants make FAs from glucose?
- do not have citrate lyase so ruminants are unable to make FA from glucose
- in non-ruminants citrate from TCA cycle is split by citrate lyase in presence of CoA producing Acetyl-CoA which is used for FA synthesis
Fatty acids in milk
- In adipose and liver tissue palmitic acid (C16) is the end product of FA synthesis
- Milk contains C4, C6, C8, C10 and C12 (medium chain triglycerides) bc mammary epithelial cells release FAs in various stages in the synthesis pathway
- some odd numbered and branched FAs produced by bacteria using branched AAs and propionate in GI
- desaturase in mammary gland can produce C18:1 or C16:1 FAs
Where are proteins made then packaged?
- made: Rough ER
- packaged: in the golgi secretory vesicles
Proteins made that go into milk
1) Whey proteins
2) Casein
Ions in milk
- Na, K and Cl as free ions in milk
- dependent on Na/K pump on basolateral membrane
- after lactose this is the second most important osmotic component of milk determining milk volume
- other ions include Ca2+, citrate and phosphate
What is the second most important osmotic component of milk determining milk volume after lactose?
Ions
- Na, K, and Cl as free ions in milk
What components of milk are secreted via the membrane route? How?
- H2O, urea, glucose, ions
- cross basolateral cell membrane and diffuse across apical membrane
What components of milk are secreted via the golgi route? How?
- lactose, casein, why proteins, citrate, calcium
- synthesized, packaged in secretory vesicles, fuse with apical membrane
What components of milk are secreted via the milk fat route? How?
- lipid soluble material (fat, hormones, drugs)
- portion of apical membrane surrounds the fat droplet
What components of milk are secreted via transcytosis? How?
- immunoglobins, albumin
- endocytosis/pinocytosis of components from the basolateral membrane to the cytoplasm to exocytosis
What components of milk are secreted via the paracellular route? How?
- immunoglobins
- components from interstitial fluid into milk- prior to tight jxn maturation
What is production regulated by?
- increasing milking frequency will increase production in dairy cows
- in animals that are not milked, production is regulated according consumption by offspring (mediated by pressure in the glands)
For how long does growth and differentiation of mammary tissue continue?
- until peak production at 4-6 wks after calving
Homeorhesis
orchestrated changes to meet the priorities of a physiological state
Homeostasis
maintenance of a steady state of a given physiological fxn
Adaptations of the GI tract for lactation (more water in, less water out
- expansion of the rumen-reticulum to accommodate greater intake
- increase in capacity of omasum, abomasum and SI
- increase in large intestine size for greater water absorption
- water absorption increases with lactation and excretion is minimized
- homeorhetic shifts in partitioning of nutrients toward mammary gland at onset of lactation
- expansion of GI tract with lactation to accommodate increases in dry matter intake pulled by energy expense of milk production
Will a cow have more blood in total when lactating?
yes
What happens to potassium and sodium requirements during lactation?
- they increase
- kidney adjusts to increase water reabsorption
- milk is 88% water
What does the liver do during lactation?
- central to nutrient partitioning of CHO, protein and fat
- hepatic portal circulation drains GIT and delivers absorbed nutrients
- propionate is a precursor for hepatic gluconeogenesis (glucose)
- glycogenolysis increases in early lactation (glucose)
- acetate and butyrate provide energy source and substrate for FA synthesis
- triglycerides synthesized in liver and exported to circulation
What does adipose tissue do during lactation?
- reduce uptake of glucose in early vs late lactation- insulin sensitivity to glucose lower
- mobilization of stored triglycerides priority over lipogenesis- growth hormone high early lactation
- leptin secretion drops as adipose tissue mass is reduced
What does bone do during lactation?
- structural framework, but also MINERAL RESERVE
- parathyroid hormone stimulates Ca2+ uptake in gut and mobilization from bone
- calcitonin prevents elevated Ca2+ in blood
- mobilization of calcium and phosphorous to support mammary gland demand
What is the priority of the mammary gland demands during lactation?
- glucose!
Glucose sparing mechanisms in the mammary gland
- acetate/proprionate utilization for energy
- no pathway for glucose use for lipogenesis (acetate and beta-hydroxybutyrate)
- glucose used for lactose synthesis in mammary epithelial cells
What does the mammary gland increase uptake of?
- amino acids + transporters
- making a lot of proteins in the ER - FFA and glycerol
- to make triglycerides
- de novo triglyceride synthesis from circulating SCFA (including butyrate and acetate) increases
What does muscle utilize for energy during lactation? What role does muscle play?
- FA (instead of glucose)
- provides a reservoir of AA for protein synthesis
- growth is prioritized over milk in first lactation
Periparturient energy balance
- while energy intake increases dramatically at parturition it does not keep up with milk yield
- uptake increases rapidly but output is greater
- increase comes after preparturient decline in intake
- start losing body reserves
What role does growth hormone play in lactation?
- GH stimulates the breakdown of triglycerides in adipose tissue; helping with negative energy balance
- GH is high at onset of lactation and declines with production lactation advance
- cows selected for yield have a higher GH concentration
- main effected: on lypolysis to make FA available
What happens to leptin during lactation?
- leptin produced by fat cells
- as adipose tissue accumulates, leptin increases and depresses feeding to slow fat accumulation
- acts as hypothalamus to depress intake
- leptin declines w/ mobilization of energy from adipose
In early lactation, can energy consumption match output?
no
