1. MILK COMPOSITION Leo Timms Iowa State University

2. MILK COMPOSITION Components are similar across species: - Water - Lactose (CHO) - Proteins - Lipids(fats) - Minerals - Vitamins Component % differ w/in & across species! Milk is greater than the sum of it’s parts! Emulsion of fat globules and a suspension of casein micelles (casein, Ca, P), all suspended in an aqueous phase which contains lactose, whey proteins, minerals, and salts.

3. MILK COMPOSITION Lactose, whey, minerals, salts H 2 0

4. A. Fully differentiated alveolar epithelial cells characterized by presence of numerous vacuoles (V), rounded basally positioned nuclei (N), abundant cytoplasm, and frequent occurrence of large apically located lipid droplets (F); alveolar lumen is L. B. Intermediately differentiated alveolar epithelial cells showing fewer cellular vacuoles, more irregularly shaped nuclei, and greater nuclear to cytoplasmic ratio. C. Undifferentiated alveolar epithelial cells displaying relative absence of cellular vacuoles, highly irregularly shaped nuclei, a mixture of large and small lipid droplets, and very large nuclear to cytoplasmic ratio, (X4,000).

5. ALVEOLUS

8. MILK COMPOSITION Apical membrane Basement membrane

9. MILK COMPOSITION Rat Cow Nucleus 22 22 RER 15 16 Golgi 21 19 Mito. 7 6 Lipid 1.5 5 Other 33.5 32

10. MILK COMPOSITION

11. SECRETION ROUTES Membrane route Water urea glucose ions

12. SECRETION ROUTES Golgi route Lactose casein whey prot. Citrate Ca

13. SECRETION ROUTES Fats hormones drugs Milkfat route

14. SECRETION ROUTES Transcytosis

15. SECRETION ROUTES Tight junction Paracellular: between cells Not common unless cells disrupted: mastitis!

16. SECRETION ROUTES Membrane recycling pH: 6.2-6.9 Freeze pt.? < 32F (0C)

17. MILK COMPOSITION

18. WATER Highest component except some marine mammals! Decreased viscosity so milk can be easily removed from the gland by the neonate Major source of water for neonates!!! No resorbtion in ducts

19. MILK COMPOSITION CARBOHYDRATES LACTOSE - primary milk CHO in most species - unique to milk - major osmole in milk - least variable component? - greatly impacted by mastitis 7%: species differences

20. MILK COMPOSITION CARBOHYDRATES* mg / 100ml LACTOSE 5000 (5%) Glucose 14 Galactose 12 N- acetyl glucosamine 11 Oligosaccharides

21. LACTOSE GLUCOSE is absolutely essential!!! Can’t be replaced by any other sugar! Lactose: uses 65-80% of total body glucose in high producing animals Correlation between milk production and mammary glucose uptake =.93! WHERE DOES THE GLUCOSE COME FROM? * non ruminants - sugars, digestion of starch

22. LACTOSE

24. LIVER (glycogen storage) Ruminant blood glucose levels 50% of monogas. 45 - 60% of blood glucose from propionate glucogenic amino acids, some lower GIT digestion

25. (Locks glucose in cell) ATP: not in ruminants NADPH, RIBOSE (fat synth., DNA/RNA) GLYCEROL milkfat

26. LACTOSE Disaccharide Glucose and galactose UTP + Glucose UDP- glucose + P-P UDP - glucose UDP galactose (epimerase) UDP - galactose + glucose lactose + UDP

27. LACTOSE

28. Major enzyme complex: lactose synthase Comprised of two enzymes Galactosyl transferase (widely present in many cells) (transfers sugar moeities) alpha lactalbumin (specific to the mammary gland!!!) gene expression increases w/lactogenesis must continually be made: secreted in milk

29. LACTOSE Draws in water

30. LACTOSE Milk is always isosmotic with blood!! Lactose is major osmole but can change!