MILK COMPOSITION Leo Timms Iowa State University
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.
MILK COMPOSITION Lactose, whey, minerals, salts H 2 0
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).
ALVEOLUS
MILK COMPOSITION Apical membrane Basement membrane
MILK COMPOSITION Rat Cow Nucleus RER Golgi Mito. 7 6 Lipid Other
MILK COMPOSITION
SECRETION ROUTES Membrane route Water urea glucose ions
SECRETION ROUTES Golgi route Lactose casein whey prot. Citrate Ca
SECRETION ROUTES Fats hormones drugs Milkfat route
SECRETION ROUTES Transcytosis
SECRETION ROUTES Tight junction Paracellular: between cells Not common unless cells disrupted: mastitis!
SECRETION ROUTES Membrane recycling pH: Freeze pt.? < 32F (0C)
MILK COMPOSITION
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
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
MILK COMPOSITION CARBOHYDRATES* mg / 100ml LACTOSE 5000 (5%) Glucose 14 Galactose 12 N- acetyl glucosamine 11 Oligosaccharides
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
LACTOSE
LIVER (glycogen storage) Ruminant blood glucose levels 50% of monogas % of blood glucose from propionate glucogenic amino acids, some lower GIT digestion
(Locks glucose in cell) ATP: not in ruminants NADPH, RIBOSE (fat synth., DNA/RNA) GLYCEROL milkfat
LACTOSE Disaccharide Glucose and galactose UTP + Glucose UDP- glucose + P-P UDP - glucose UDP galactose (epimerase) UDP - galactose + glucose lactose + UDP
LACTOSE
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
LACTOSE Draws in water
LACTOSE Milk is always isosmotic with blood!! Lactose is major osmole but can change!