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Digestive System Chapter 18.

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Presentation on theme: "Digestive System Chapter 18."— Presentation transcript:

1 Digestive System Chapter 18

2 Function Obtain resources from the external environment
Water Minerals Nutrients (Lipids, Carbohydrates, Proteins) Vitamins Break down large particles into smaller ones Transfer materials from external environment  blood  cells

3 Anatomy Fig 18.2 Digestive tract oral cavity pharynx esophagus stomach
small intestine large intestine anus Fig 18.2

4 Anatomy Fig 18.2 Accessory organs salivary glands pancreas liver
gall bladder Fig 18.2

5 Digestive Processes Motility Secretion Digestion Absorption
movement of food through the digestive system Secretion release of substances to enhance breakdown of food Digestion physical and chemical breakdown of food Absorption transfer of materials to internal environment

6 Motility Figs 18.4, 18.14 Muscle contractions of digestive tract
propulsion of food through GI tract mixing of food with digestive juices (facilitates digestion and absorption) Processes: ingestion (taking food into mouth) mastication (chewing) deglutition (swallowing) peristalsis (rhythmic movement of GI tract) segmentation (mixing in intestine) Figs 18.4, 18.14

7 Secretion Digestive juices Most food molecules too large to absorb
enzymes, bile salts, mucus, etc. released by exocrine glands into GI tract Most food molecules too large to absorb Must break bonds with enzymes (various organs) Enzyme function aided by… HCl (stomach) Bile (liver) NaHCO3 (pancreas)

8 Digestion Physical and chemical break down nutrients into absorbable unit Physical digestion (chewing, mixing) Chemical digestion (enzyme catalyzed) polysaccharides  monosaccharides proteins  amino acids fats  glycerol + fatty acids

9 Absorption Transfer of digested materials across the digestive epithelium intestinal lumen  blood or lymph

10 Gastrointestinal Tract Structure
Mucosa (lumen side) Epithelial tissue Submucosa elastic connective tissue contains lymph and blood vessels Muscularis smooth muscle Serosa outer layer of connective tissue secretes serous fluid Fig 18.3

11 Mouth Fig 18.2 Ingestion - bringing food into the body
tongue - taste buds detect chemical composition of food Mastication - chewing (physical digestion) teeth and tongue Chemical digestion - saliva moistens food amylase - breaks down starch into maltose lysozyme - antibacterial agent Fig 18.2

12 Pharynx and Esophagus Figs 18.2, 18.4
Transport food and water to stomach, secretes mucus deglutition (swallowing) reflex moves food to stomach Movement of food bolus in esophagus (and rest of GI tract) via peristalsis Figs 18.2, 18.4

13 Stomach Fig 18.5 Muscular sac-like organ
Chemical and physical digestion forms chyme Stores food, releases small amts. to small intestine takes 2-6 hours for stomach to empty inner surface lined w/ rugae Fig 18.5

14 Stomach Mucosal Cells Figs 18.7-18.9 goblet cells – mucus
Gastric Mucosal Barrier = mucus and layer of HCO3 that protects stomach epithelium parietal cells – HCl kills bacteria, denatures proteins chief cells - pepsinogen pepsinogen activated by HCl  pepsin pepsin breaks down proteins Figs

15 Small Intestine Figs 18.10-18.13 12’ long tube (20’ in cadavers)
Duodenum (1’)  Jejunem (4’)  Ileum (7’) Most chemical digestion occurs here Most absorption occurs here Large surface area Plicae – folds in mucosa Villi – fingerlike projections Capillaries, central lacteal (absorption) Microvilli ("brush border") on epithelium Figs

16 Chemical Digestion: Small Intestine
brush-border enzymes bound to epithelial cell membranes hydrolyze disaccharides, polypeptides, etc. e.g. enterokinase - activates trypsin (pancreatic enz.) Fig 18.29

17 Chemical Digestion: Pancreas
Exocrine cells secrete pancreatic juice into duodenum amylase - breaks down starch trypsinogen converted to trypsin by enterokinase breaks down polypeptides lipase - digests triglycerides many others (proteases, nucleases, etc.) NaHCO3 (alkaline) - neutralizes stomach acidity Fig 18.26

18 Chemical Digestion: Liver
secretes bile stored in gall bladder, secreted into duodenum bile salts used for lipid absorption bilirubin secretion metabolic processing of absorbed materials Nutrient-rich blood from villi flows into hepatic portal system processed by liver prior to general circulation Fig 18.22

19 Chemical Digestion Fig 18.22
degradation of waste, hormones, drugs, etc. synthesizes plasma proteins stores glycogen, fats, minerals and vitamins Fig 18.22

20 Absorption: Carbohydrates and Proteins
digested into monosaccharides and amino acids / small peptides transported into the epithelium by cotransport coupled to flow of Na+ or H+ into epithelial cells transported into blood entering hepatic portal system Figs 18.33, 18.22

21 Absorption: Lipids Figs 18.25, 18.35, and 18.36 emulsification
lipids interact w/ bile salts form emulsification droplets pancreatic lipases break emulsified fat into free fatty acids and monoglycerides absorbed by epithelium Figs 18.25, 18.35, and 18.36

22 Absorption: Lipids Fig 18.36 reform triglycerides in epithelial cells
combined w/ protein to form chylomicrons chylomicrons released via exocytosis into submucosa enter central lacteal  lymphatic system transported to blood Fig 18.36

23 Large Intestine Fig 18.17 colon, cecum, appendix, rectum (5' long)
small amount of salt and water absorbed here main function is to store undigested material (feces) 30% dry weight of feces = bacteria (E. coli) live in large intestine (produce vitamin K) Fig 18.17

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