Digestion and Nutrition

1. Digestion and Nutrition Chapter 34

2. Digestion • mechanical/chemical breakdown of food  nutrients  absorbed into blood • mechanical • initial, physical breakdown of food into small pieces • does not change chemical make-up of food • mouth and stomach • chemical • breakdown of food into smaller chemical units (nutrients) • changes chemical make-up of food • mostly small intestine • nutrition • refers to the properties and functions of nutrients • absorption • nutrients transported into bloodstream across inner wall of small intestine • extracellular digestion • occurs outside of cells • may be within or outside of organism’s body • if inside, then in a digestive system • most common (incl. humans) • intracellular digestion • occurs within cells • less common • single-celled organisms

3. Intracellular digestion in Paramecium

4. Digestive Systems • incomplete (sac-like) • lack separate openings for food entering and waste exiting • gastrovascular cavity An incomplete digestive system in a gastrovascular cavity

5. Fig. 34.1 Incomplete digestive tract of a planarian

6. complete (tube-within-a-tube) • found in most animals (incl. humans) • separate openings for food entering and waste exiting • invertebrate examples • earthworm • mouth  pharynx  esophagus  crop  gizzard  long intestine (w/typhlosole)  anus • insects • mouthparts  foregut midgut (w/glands)  hindgut  anus Fig. 34.2 Complete digestive tract of an earthworm

7. vertebrate examples • sharks and bony fishes • often very effective teeth • spiral valve and lengthy intestine • amphibians and reptiles • socketed teeth or fangs, Jacobson's organ • birds • beaks, feet, crop • two-part stomach • gizzard and proventriculus • mammals • teeth types • temporary and permanent • incisors, canines, premolars, molars • ruminants • animals with a 4-part stomach • rumen, reticulum, omasum, abomasum • able to digest cellulose Fig. 34.4 Dentition among mammals

8. Ruminant digestion

9. Human Digestive System • oral cavity (mouth and throat) • taste buds, tongue, lips, teeth • salivary glands • secrete saliva and amylase • pharynx • back of throat • also contains nasopharynxand larynx (contains voice box) • swallowing • hard palate, soft palate (with uvula), epiglottis, and glottis • lips seal mouth  tongue presses food against soft palate • larynx raised  bends epiglottis over glottis  forces food down esophagus Fig. 34.6 Swallowing

10. esophagus • transport tube with no digestive function • voluntary muscle at top • mostly involuntary smooth muscle • muscle contractions called peristalsis • lined with mucous • stomach • mostly mechanical breakdown • stores and mixes food • very high acidity (pH 1 or less) • rugaemucin lining • muscular valves at both ends • pyloric and cardiac sphincters • some chemical breakdown • pepsin • gastric lipase Fig. 34.7 Peristalsis in the digestive tract

11. Fig. 34.8 Anatomy of the stomach

12. small intestine • three portions, all composed of smooth muscle • duodenum  jejunum  ileum • functions • most chemical digestion • secretes and receives many digestive enzymes • all absorption • increased surface area for absorption • length • rugae • villi • finger-like projections lining the rugae • microvilli • fine hairs (cellular extensions) lining the villi • sends undigested waste material to large intestine

13. Fig. 34.9 Anatomy of the small intestine

14. large intestine (colon, bowel) • consists of several portions, mostly composed of smooth muscle • ascending colon  transverse colon  descending colon  sigmoid colon  rectum  anal canal  anus • much voluntary skeletal muscle from rectum  anus • rectum contains rectal valves to hold waste in place • ileocecalvalve • muscular valve at junction of small and large intestine • wider and shorter than small intestine • caecum • “dead end” pouch of tissue where small and large intestine meet • appendix • small extension of tissue projecting off of caecum • vestigial structure • functions • reabsorption of water • concentration of waste material (feces) • provide suitable habitat for beneficial, symbiotic bacteria

15. Fig. 34.5 The human digestive tract

16. Fig. 34.10 Some structures of the large intestine

17. three accessory organs • liver • secretes products into duodenum • many functions • detoxifies blood • stores glucose as glycogen • secretes many enzymes • produces bile • emulsification of fats • gall bladder • stores and secretes bile through the bile duct • pancreas • secretes many digestive enzymes • sodium bicarbonate and others • pancreatic ducts  duodenum • produces insulin and other hormones

18. Fig. 34.11 The liver, gall bladder, and pancreas

20. Chemistry of Digestion • mechanical breakdown • mouth (chewing) and stomach • chemical breakdown • mouth, stomach, and small intestine • hydrolysis reactions • absorption into the bloodstream • small intestine • nutrients distributed to body tissues • circulatory system • carbohydrate digestion (esp., starches and other polysaccharides) • salivary amylase  pancreatic amylase  disaccharides  maltase monosaccharides (glucose) • lipid (fat) digestion • gastric lipase  emulsification (bile)  pancreatic lipase  fatty acids/glycerol  reform as triglycerides  join w/cholesterol chylomicrons • protein digestion • proteases • pepsin in stomach  shorter peptides  pancreatic proteases (trypsin)  even smaller peptides  peptidases  individual amino acids • nucleic acid digestion • nucleases and nucleosidases • individual nucleotides absorbed into bloodstream

21. Fig. 34.12 Digestion and absorption of nutrients