Lecture 3-Digestion and Absorption of Macronutrients: page 3

Lecture 3 page 1 2 3 4 5

Protein

Made up of 20 amino acids
Adult Requirements: 0.8 g protein/kg/d

Essential Amino Acids (not synthesized in the body)
Methionine	Threonine
Valine	Isoleucine
Phenylalanine	Leucine
Tryptophan	Lysine
Histidine
Sources of protein
Diet
Digestive Juices (35g)
Desquamated intestinal cells (30g)
Excretion: 6-12 g/d in feces

Digestion
-Intraluminal hydrolysis by proteases secreted by stomach and pancreas

-Peptidases in brush border membrane of small intestine digest protein to amino acids and di- and tripeptides that are taken up by the enterocyte

Stomach (Pepsin)

-Proteolytic enzymes contained in gastric juice

-Requires acid environment of stomach to hydrolyze protein

-Denatured by alkaline fluid (small intestine)

-Synthesized in the gastric chief cells as inactive pre-proenzymes (pepsinogen)

Pancreas

-Secretes proteases as proenzymes

-Enterokinase - an intestinal brush border enzyme that activates pancreatic proteases. Stimulated by trypsinogen contained in pancreatic juice.

Figure 3
Protein digestion and absorption in the small intestine

1. brush-border membrane peptidases
2. brush-border membrane amino acid transporters
3. brush-border membrane di- and tripeptide transporters
4. intracellular peptidases
5.basolateral-membrane amino acid carriers
6. basolateral membrane di- and tripeptide carriers

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Lecture 1:Introduction to Nutrition in Western Civilization
Lecture 2: Dietary Macronutrients, Body Fat, and Blood Lipids
Lecture 3:Digestion and Absorption of Macronutrients
Lecture 4:Basic Principles of Nutrient Metabolism
Lecture 5:Obesity
Lecture 6:Fuel Utilization During Exercise
Lecture 7:Biochemistry of Oxidant Stress in Health and Disease Antioxidants
Lecture 8:Nutrition for the 21st Century

Nutrition 101 - Natural Remedies - Weight Management - Physician Education
Vitamins & Minerals- Nutrition & Aging - Nutrition & Disease - Research