Download Digestion and Absorption Chapter 3 Objectives of Chapter Know

Digestion and Absorption Chapter 3
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Objectives of Chapter
Know each component of the digestive system and its function
Review limitations & key concerns of digestion with regards to exercise
Read pages 101-119
Know flow & key functions of food through digestive tract
Stomach
Function
o mix food with gastric juices
o digests protein
Gastric glands secrete
o HCL, Mucus, Pepsinogen
HCL acid
o kills pathogens
 iron & Ca++ absorption
o converts pepsinogen to pepsin
o inactivates hormones of plant & animal origin
o produces intrinsic factor for B12 absorption
Mucus – protects inner lining
Pepsin – denatures protein
1-4 hrs to empty (simple carbs, fiber, fats/protein) (liquids solids)
Small Intestine
“pyloric sphincter” to large intestine
Completes digestion of “chyme”, absorbs nutrients & transports remnants to large intestine
o most important absorbing organ, little absorbable material reaches distal end
Composed of
o Duodenum, Jejunum, Ileum
All absorbed nutrients are delivered to the liver via “hepatic portal vein”
o lipids enter lymphatic system which eventually delivered to bloodstream
o medium chain triglycerides via hepatic portal vein
Large Intestine
“Bowel”, cecum to anal canal – 4 ft
Reabsorbs & recycles water; electrolytes, forms & stores “feces”
“Colon” – ascending, transverse, descending, rectum, anal canal
Mucus secretion
Chyme at this point contains few nutrients
Intestinal flora – bacteria lining wall, break down molecules escaping earlier digestion
o cellulose (complex carb), bacteria synthesize Vit. K, B12, thiamine, & riboflavin
Accessory Organs
Liver Functions
o Carb. Metabolism – maintain normal “blood glucose”
o Produce lipoproteins, cholesterol, phospholipids
o Convert carbs & protein (deamination/transamination) to fat
o urea production
o Destroy damaged blood cells, kill foreign antigens, remove toxic substances
o Serve as blood reservoir, store glycogen, vitamin A, D, & minerals B12 & iron
o Produce & release bile to support digestion
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Gallbladder
o Stores bile & secretes into small intestine when stimulated by food moving into small intestine
o Bile – secreted by hepatic cells, made of cholesterol, bile salts, & electrolytes
o Aids digestive enzymes by “emulsifying” fat, which allow lipases to digest fat more effectively
Lack of bile salts result in poor lipid absorption & vitamin deficiencies
Gallstones – crystalization of bile
Pancreas
o Secretes digestive juices called “pancreatic juice” acts on carbs, fats, proteins, & nucleic acids
 Pancreatic amylase – starch to disaccharides
 Pancreatic lipase – triglycerides to fatty acids & glycerol
 Proteases – all split protein bonds
 Also release bicarbonate ions to make juice alkaline (more favorable for enzymes to
function)
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Carbohydrate Absorption
Glucose absorption rate = 50-80 g/hr.
During intense exercise = 4g/min. used or 240 g/hr.
Implications?
Fructose absorbed slower than glucose & may cause GI distress
Implications?
70% of world’s pop.  levels of “lactase”
Implications?
Monosaccharides transported to liver for processing & storage (all converted to glucose)
Fiber passed to colon – some digestion from bacteria (little); absorbs water**
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Protein Absorption
Protein digestion and absorption is very high, < 3% remain in digestive tract
Low pH facilitates protein digestion
Pre-digested proteins (amino acids) widely sold in supplement business, nice marketing technique but
not practical
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Mineral Absorption
Body doesn’t absorb minerals well
o
Iron & calcium are biggest concerns
o low pH facilitates absorption
o magnesium, zinc, & chromium also poorly absorbed
Excess fiber intake hinders absorption (iron, zinc, calcium)