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Unit H: Digestion. I. Digestion begins in the mouth. Two types of digestion occur here: mechanical and chemical . Mechanical digestion of all nutrient types occurs with chewing and mixing with saliva. Chemical digestion of carbohydrates (starch) occurs with the enzyme: salivary amylase.
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I. Digestion begins in the mouth • Two types of digestion occur here: mechanical and chemical. • Mechanical digestion of all nutrient types occurs with chewing and mixing with saliva. • Chemical digestion of carbohydrates (starch) occurs with the enzyme: salivary amylase.
Inside of Mouth: • Saliva is produced at three glands. It dissolves materials, lubricates for swallowing, and contains amylase. • Teeth of three types: incisors for biting,canines for tearing and premolars/molars for grinding food.
(a) Omnivore incisors (human) canine premolars molars
II. Swallowing: • The food bolus moves to back of throat. • Tongue pushes food into pharynx, swallowing reflex occurs. • Larynx is blocked by the epiglottis, food moves into esophagus. • Peristalsis moves food to stomach.
(a) Before swallowing roof of mouth food pharynx tongue epiglottis esophagus larynx
(b) During swallowing epiglottis (folds over larynx) food (enters esophagus) larynx (moves up)
III. Stomach Digestion: • Entrance to stomach is the cardiac sphincter. The stomach contains gastric juice containing HCl at a pH of 3 which dissolves most food substances. • The gastric glands makes HCl, mucus protects stomach from eating itself (ulcer). • Pepsin is made in gastric glands, first as pepsinogen which changes to pepsin when it contacts HCl. • Pepsin breaks down protein to polypeptides. • Stomach churns, causing mechanical digestion of all nutrients.
V.Pancreas secretes 6 substances: • HCO3- : bicarbonate neutralizes stomach’s acid and brings pH to aprox 8 • H2O: acts as a solvent and lubricant Digestive enzymes: 3) Trypsin: protein -> 4) Nuclease: Nucleic acids -> 5) Pancreatic amylase: Carbohydrates- 6) Lipase: Triglycerides-> polypeptides nucleotides maltose 3 fatty acids + glycerol
6 Functions of the Liver: • Converts glucose to glycogen to regulate blood sugar levels. • Synthesizes blood proteins like prothrombin, albumin and fibrinogen. • Makes bile from cholesterol and bilirubin. • Recycles old blood cells and their iron. • Produces urea from ammonia and cell wastes. • Detoxifies poisons like alcohol from the blood. Gall bladder Bile Duct
VI. Function of Bile • Bile is produced in the liver, and stored in the gall bladder. • When fat is detected in the duodenum, a hormone called CCK brings about the release of bile from the gall bladder and it is added to the duodenum. • Bile emulsifies fat (physically breaks it down into smaller droplets). • Bile can be blocked by crystals in gall bladder: gallstones.
VII. Intestine Digestion • Nutrients broken down by pancreatic enzymes finish their chemical digestion with enzymes found in the small intestine: • 1) Maltase: converts maltose to • 2) Peptidase: polypeptides to 2 glucoses Amino acids
VIII. Small Intestine specialized for Absorption • Very long (aprox 25 feet in humans) • Inner folds increase surface area • Folds lined with bumps called villi • Cells on villi posses special cell membranes called microvilli. • Mitochondria produce ATP to power the active transport of nutrients into cells.
(a) Small intestine (c) Villus (d) Cells of villi (b) Fold of intestinal lining lacteal microvilli villi capillaries arteriole intestinal gland lymph vessel fold of intestinal lining venule
(a) Small intestine fold of intestinal lining
(b) Fold of intestinal lining villi
(c) Villus lacteal capillaries intestinal gland arteriole lymph vessel venule
Villus is main absorption structure: • Amino acids, glucose, & nucleic acids are transferred to the blood capillaries here. • Fats are absorbed by the lacteal and enter the lymphatic system, later enter the blood at the subclavian vein.
IX. Large Intestine: Food enters large intestine through the ileo-caecal valve. The appendix no longer functions in humans, can get infected with bacteria.
Large Intestine Functions There are 3 parts to large intestine: Ascending colon Transverse colon Descending colon Functions: 1)Reabsorb water. 2) Get more vitamins out of your food. 3) Escherichia coli (E Coli) bacteria in the large intestine release some vitamins
Rectum • Storage of feces and final water removal. • Contains stretch receptors that tell the brain when full. Brain interprets signal, but has conscious control over the timing of defecation. • Rectum opens to anus, two sets of circular muscles called sphincters act as valves.
