Lecture 14 - Lactation pt.2

Question 1

Mammary epithelium

Answer 1

1. consumes 50% of O2 in arterial blood
2. high mitochondrial density
   - ATP for synthetic processes, uptake of precursors and transport into lumen
3. make proteins in the rough ER
4. make phospholipids and triglycerides in SER
   - FA synthesis in cytosol
   - glycolysis in cytosol
5. lactose synthesized in the golgi

Question 2

Where is lactose synthesized?

Answer 2

• in the golgi of the mammary epithelium

Question 3

What does the golgi do?

Answer 3

• lactose synthase = glucose + galactose
• packaged into secretory vesicles
• main determinant of milk secreted

Question 4

What turns on the enzymes for lactose production?

Answer 4

Prolactin!

Question 5

What is driving total milk production?

Answer 5

• the total amount of lactose that can be produced
• lactose has the highest osmolarity = pulling in most water = impacting total milk volume the most

Question 6

What is 98% of milk fat composed of?

Answer 6

• triglycerides; synthesized in smooth ER
• high in saturated fat
• FA hydrogenation in rumen

Question 7

Where are free fatty acids obtained from?

Answer 7

• chylomicrons and VLDL OR DE NOVO FA synthesis in alveolar epithelial cells

Question 8

Why can’t ruminants make FAs from glucose?

Answer 8

• 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

Question 9

Fatty acids in milk

Answer 9

• 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

Question 10

Where are proteins made then packaged?

Answer 10

• made: Rough ER
• packaged: in the golgi secretory vesicles

Question 11

Proteins made that go into milk

Answer 11

1) Whey proteins
2) Casein

Question 12

Ions in milk

Answer 12

• 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

Question 13

What is the second most important osmotic component of milk determining milk volume after lactose?

Answer 13

Ions
- Na, K, and Cl as free ions in milk

Question 14

What components of milk are secreted via the membrane route? How?

Answer 14

• H2O, urea, glucose, ions
• cross basolateral cell membrane and diffuse across apical membrane

Question 15

What components of milk are secreted via the golgi route? How?

Answer 15

• lactose, casein, why proteins, citrate, calcium
• synthesized, packaged in secretory vesicles, fuse with apical membrane

Question 16

What components of milk are secreted via the milk fat route? How?

Answer 16

• lipid soluble material (fat, hormones, drugs)
• portion of apical membrane surrounds the fat droplet

Question 17

What components of milk are secreted via transcytosis? How?

Answer 17

• immunoglobins, albumin
• endocytosis/pinocytosis of components from the basolateral membrane to the cytoplasm to exocytosis

Question 18

What components of milk are secreted via the paracellular route? How?

Answer 18

• immunoglobins
• components from interstitial fluid into milk- prior to tight jxn maturation

Question 19

What is production regulated by?

Answer 19

• 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)

Question 20

For how long does growth and differentiation of mammary tissue continue?

Answer 20

• until peak production at 4-6 wks after calving

Question 21

Homeorhesis

Answer 21

orchestrated changes to meet the priorities of a physiological state

Question 22

Homeostasis

Answer 22

maintenance of a steady state of a given physiological fxn

Question 23

Adaptations of the GI tract for lactation (more water in, less water out

Answer 23

1. expansion of the rumen-reticulum to accommodate greater intake
2. increase in capacity of omasum, abomasum and SI
3. increase in large intestine size for greater water absorption
4. water absorption increases with lactation and excretion is minimized
5. homeorhetic shifts in partitioning of nutrients toward mammary gland at onset of lactation
6. expansion of GI tract with lactation to accommodate increases in dry matter intake pulled by energy expense of milk production

Question 24

Will a cow have more blood in total when lactating?

Answer 24

yes

Question 25

What happens to potassium and sodium requirements during lactation?

Answer 25

• they increase
• kidney adjusts to increase water reabsorption
• milk is 88% water

Question 26

What does the liver do during lactation?

Answer 26

• 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

Question 27

What does adipose tissue do during lactation?

Answer 27

• 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

Question 28

What does bone do during lactation?

Answer 28

• 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

Question 29

What is the priority of the mammary gland demands during lactation?

Answer 29

• glucose!

Question 30

Glucose sparing mechanisms in the mammary gland

Answer 30

• 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

Question 31

What does the mammary gland increase uptake of?

Answer 31

1. amino acids + transporters
   - making a lot of proteins in the ER
2. FFA and glycerol
   - to make triglycerides
   - de novo triglyceride synthesis from circulating SCFA (including butyrate and acetate) increases

Question 32

What does muscle utilize for energy during lactation? What role does muscle play?

Answer 32

• FA (instead of glucose)
• provides a reservoir of AA for protein synthesis
• growth is prioritized over milk in first lactation

Question 33

Periparturient energy balance

Answer 33

• 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

Question 34

What role does growth hormone play in lactation?

Answer 34

• 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

Question 35

What happens to leptin during lactation?

Answer 35

• 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

Question 36

In early lactation, can energy consumption match output?

Answer 36

no