(05&2/3) Lactation

Question 1

(1)

(Milk Synthesis)

Milk is a mixture of proteins, carbohydrates, fats and ions in water.

Question 2

(2)

(Milk Precursors)

1. composition of milk depends on what two things?
2. major substrates exrtracted from the blood by mammary cells are what?
3. Species may differ considerably in which precursors they use and how they use them, thus both biosynthetic pathways and the final product may vary across species.

For example: monogastrics use what as the main precursor for fatty acid production within the mammary gland?

Ruminants have lower levels of glucose than other species and what they have is largely made from what rather than absorbed as glucose from the intestine?

Answer 2

1. amount and type of precursors taken up by gland

tranformation these undergo during milk synthesis

2. glucose, amino acids, fatty acids and minerals

(ruminants also use acetate and beta-hydroxybutyrate)

3. glucose

propionate (but they do have circulating acetate so they use this as the main precursor for fatty acid production and preserve the glucose for production of lactose.)

(there is a chart on 245 with a bunch of info you probably don’t need to know… but maybe should check it out)

Question 3

(3)

(milk synthesis)

(carbohydrate)

1. major sugar in milk is what?

what is it?

2. lactosed in synthesize in mammary gland from what?

in the cow this is made where?

Answer 3

1. lactose

glucose + galactose

2. glucose supplied by bloodstream

made in the liver by gluconeogenesis (In a high producing cow 60-85% of the glucose produced may be used by the mammary gland)

Question 4

(4)

(carbohydrates cont)

1. Lactose is synthesized from glucose by what?
2. the lactose synth complex is attached to what?

undergoes dramatic up-reguation when?

3. Glucose and UDP-galactose (uridine diphosphate-galactose) enter the golgi and, under the influence of the lactose synthetase complex, form what?
4. golgi permeable to glucose and galactose (monos), how about for lactose (di)?

It also draws water into golgi vesicle how?

Answer 4

1. lactose synthetase complex (2 proteins - galactosyltransferase and a-lactalbumin)
2. internal wall of the Golgi membrane (final synthesis of lactose occurs here)

at lactation onset

3. lactose and UDP (look at pic)
4. impermeable

active as major osmotically active component of milk

(This osmotic action of lactose accounts for milk volume (since in domestic species milk is mostly water).)

Question 5

(5)

(Protein)

1. milk crude protein consists of what?

what represent >90% of protein in most species? synth where?

an exception is what?

2. These newly assembled proteins have what that causes them to be inserted into the lumen of the ER?

from here they are transported to where?

3. in the golgi, the casein is combined with calcium and phosphate to form what?

Answer 5

1. the caseins (there are several), α-lactalbumin, β-lactoglobin, serum albumin, lactoferrin, lysozyme, immunoglobulins and nonprotein nitrogen compounds (mainly urea)

Casein, α-lactalbumin and β-lactoglobin; mammary alveolar epithelium

human where they represent <50%, (human milk containing high quantities of lactoferrin and nonprotein nitrogens.)

2. leader sequence of 15-30 AA

golgi apparatus

3. colloidal casein micelles

(The micelles and other proteins are co-secreted with lactose from the Golgi vesicles.)

Question 6

(6)

(Lipid)

1. What comprise 97-98% of lipids present in milk?

remainder mostly what?

2. milk fatty acids range from what to what?

those under C16 synthsized where?

those over derived from what?

3. precursors for lipid formation in ruminants are what?
4. in non-ruminants the major blood borne precursors are what?

Answer 6

1 triglycerides

phospholipids

2. C4 to C18

mammary alveolar epi cells

blood borne lipids

3. acetate, b-hydroxybutyrate, and triglycerides contained in VLDL and chylomicrons
4. glucose and triacylglycerides

Question 7

(7)

(Cellular Secretion of Milk Constituents)

(5 pathways for secretion of components into milk)

(pathway 1)

1. Proteins, lactose, salts (mainly calcium phosphate) and other non-fat components of milk are packaged into what where?
2. These vesicles bud off from the Golgi and move to the apex of the cell. At the apical surface (i.e. adjacent the lumen of the alveolus) the membrane surrounding the secretory vesicle fuses with the plasma membrane of the cell and the contents are released into the alveolar lumen.

this is a process of what?

Answer 7

1. secretory vesicles in the Golgi

(The presence of the lactose also draws water into the vesicles)

2. exocytosis

Question 8

(8)

(Cellular Secretion of Milk Constituents)

(5 pathways for secretion of components into milk)

(pathway 2)

1 Lipid droplets form near the ER and are transported to where for secretion?

2. 2. Lipid droplets form near the ER and are transported to the apical membrane for secretion. Here there is lots of spare membrane left over after secretion of the lactose/protein/mineral/water by exocytosis from the Golgi secretory vesicle. This membrane forms what?
3. The fat globule tents the apex of the cell and the membrane “pinches off” beneath it ⇨ the globule is secreted into the alveolar lumen - this process called what?
4. The membrane around each droplet of fat does what?
5. After lactose, fat and secretory proteins the next major component of milk to be secreted are the minerals that contribute to what?
6. Calcium and phosphate are secreted in the what with what?

Answer 8

1. the apical membrane
2. the milk fat globule membrane

3 reverse pinocytosis

4. prevents them from coalescing (and the membrane itself provides a useful source of phospholipids to the offspring.)
5. the ash content
6. Golgi vesicles with proteins and lactose –> by pathway 1 (exocytosis) as part of the casein micelle

Question 9

(9)

(Cellular Secretion of Milk Constituents)

(5 pathways for secretion of components into milk)

(pathway 3)

1. Other salts may be pumped into the cell at its base and some may then diffuse passively into the alveolus. The apical plasma membrane is permeable to what?

impermeable to what?

2. The cell membranes are also permeable to many pharmacological agents - concentrations can occur in milk (e.g. systemically administered antibiotics). This diffusion and pumping across basal and apical membranes is termed what?

Answer 9

1. monovalent ions (sodium, chloride and potassium) and glucose

divalent cations and disaccharides

2. transmembrane transport

Question 10

(10)

(Cellular Secretion of Milk Constituents)

(5 pathways for secretion of components into milk)

(pathway 4)

1. What is a mechanism for proteins that are not synthesized in the alveolar epithelial cell to enter the milk?

this includes what?

2. In this process the protein interacts with a specific receptor at the basal membrane of the cell. The protein-receptor complex is internalized and transported across the cell to the apical membrane where the protein (and sometimes part or all of the receptor) are released into the alveolar lumen.

Answer 10

1. transcytosis

ecretory immunoglobulin (IgA), hormones such as insulin and prolactin, growth factors such as IGF-1 and serum albumin

Question 11

(11)

(Cellular Secretion of Milk Constituents)

(5 pathways for secretion of components into milk)

(pathway 5)

1. The final pathway is what?

2 During lactation tight junctions form between adjacent mammary epithelial cells which serve to separate what?

3. During a normal lactation white blood cells appear to be able to pass into the alveolar lumen via this route without opening it to other substances.
4. during pregnancy what happens to these tight junctions?

Answer 11

1. paracellular transport
2. he interstitial spaces and the alveolar lumen (effectively closing the paracellular transport pathway)
3. ight junctions open and large proteins and other constituents can be transported via this route.

Question 12

Answer 12