Swallowing Salivary Glands

Transcription

1 Digestion: A Closer Look Mechanical digestion Digestion and Metabolism Chemical digestion ACCESSORY ORGANS ALIMENTARY CANAL Digestive tract Salivary glands Mouth Tongue the breakdown of food by digestive enzymes Where digestion begins Pharynx Mouth Esophagus Liver Gallbladder Pancreas Involves physical processes like chewing Salivary glands Teeth Functions: Stomach Small Colon of large Eating and chewing Digestion of carbohydrates Appendix Rectum Anus Figure 22.5 Swallowing Salivary Glands NOT SWALLOWING Produce saliva Lubrication Contains amylase Enzyme that breaks down starch. Contains lysozyme SWALLOWING STARTED SWALLOWING FINISED Tongue Ball of food Pharynx Trachea (windpipe) open Epiglottis up Epiglottis down Esophageal sphincter (contracted) Adam s apple Esophagus closed Trachea closed Esophagus open Epiglottis up Trachea open Esophageal sphincter (contracted) Enzyme that kills bacteria. Figure

2 Esophagus Food moves down by peristalsis, alternating waves of muscular contraction and relaxation Esophageal sphincter (contracted) Food ball Relaxed muscles Contracted muscles Relaxed muscles Stomach Functions of the Stomach Churns food into a thick soup called chyme Secretes acid & starts protein digestion Stores food Controls movement of food into the small Mechanical or chemical digestion? Digestion in the stomach Why doesn t the stomach digest itself? Secretes gastric juice (2-3 quarts per day) Contains acid (Cl) Gives the stomach a p of 2 Unfolds dietary protein Activates the enzyme pepsin Digests protein elps kill bacteria found in food Gastric Pits It secretes mucus Protects Lubricates What causes eartburn? The backflow of stomach contents into the esophagus Acid reflux Esophageal sphincter usually prevents this Tips for decreasing heartburn: Avoid high fat meals Don t overeat What causes gastric ulcers? The bacteria elicobacter pylori. pylori is especially well-adapted for living in the stomach. It lives in the mucus It produces an enzyme that shields the bacterium from the acidity of the stomach Copyright 2009, John Wiley & Sons, Inc.

3 Leaving the Stomach Pyloric Sphincter : Small separates the stomach from the small. the strongest muscle in the GI tract. Controls how much chyme enters the small Anatomy of the small The longest part of the digestive tract (~20 ft) Function: digestion and absorption of nutrients 3 regions duodenum, jejunum, and ileum Villi and Microvilli Surface area is increased by folding Villi and microvilli provide more surface area for absorbing nutrients Digestive secretions of the pancreas The duodenum The first part of the small Receives chyme from stomach and digestive secretions from liver and pancreas Neutralizes acidic chyme Pancreatic juice secreted into duodenum contains: Bicarbonate to neutralize stomach acids Digestive enzymes Trypsin digests proteins Lipase digests fats Pancreatic amylase digests carbohydrates

4 Liver role in fat digestion Makes bile Bile is stored in the gallbladder Secretes bile into the duodenum after a meal Bile breaks down large fat globules to smaller ones = emulsification Macromolecules are digested by enzymes Protein 2 O Fat 2 O 2 O 2 O 2 O Enzyme (pepsin) Enzyme (amylase) Fatty acid Glycerol O O O O O Amino acid Sugar Enzyme (lipase) Figure 22.3 Enzymes: proteins that speed up chemical reactions Digestion is completed in the small pancreatic amylase maltase cell of intestinal glucose villus Protein trypsin peptides peptidase amino acids + Fat globules bile salts emulsification droplets lipase monoglycerides and free fatty acids p = basic p = basic p = basic chylomicron blood capillary blood capillary lymphatic capillary a. digestion b. Protein digestion c. Fat digestion Where are nutrients absorbed? Most nutrients (~90%) are absorbed in the small The rest? Stomach & large Blood goes from the to the liver Blood rich in amino acids and glucose travels from the digestive tract to the liver The liver Stores the glucose as glycogen Uses the amino acids to make proteins Copyright 2009, John Wiley & Sons, Inc.

5 The Large Intestine The colon the main part of the large Absorbs water Produces feces, the waste product of food The rectum stores feces Colon Small Rectum Anus Figure 22.14a Diseases of digestive tract: Diarrhea Rids body of pathogens, toxins Can quickly lead to dehydration Affects absorption of food, vitamins Summary of digestion Ingestion Food into mouth Digestion Mechanical digestion Chewing in mouth Churning in stomach Chemical digestion Saliva in mouth Acid and pepsin in stomach Enzymes in small Food Mouth Stomach Metabolism: breaking down and building up Macromolecule Absorption Nutrients and water in small Small Monomers Water in large Elimination Feces formed in large Elimination from anus Large Anus CO O + Rebuilding Food as Fuel Where Is the Energy in Food? Energy-releasing reactions Break down food molecules in cellular respiration Use oxygen Generate many molecules of Stored in chemical bonds between the C, and O atoms In cellular respiration, The chemical bonds between C atoms are broken and the energy is converted to The number of C, and O atoms doesn t change

6 What exactly is? Getting energy from food ADP Enzymes + Mitochondria = ighly Controlled Cellular respiration releases the energy in chemical bonds so slowly that the energy can be harvested efficiently The energy in is used to drive cellular work Two metabolic pathways produce Inside cell electrons Aerobic transferred by NAD metabolism Citric acid cycle glucose Cells use to build macromolecules pyruvate O2 In cytoplasm Doesn t require O2 (anaerobic) Provides quickly Inefficient Electron transport chain To transport molecules across the membrane mitochondrion ~100 times faster than aerobic metabolism need nearly 20X more glucose for same energy payoff Aerobic metabolism In mitochondria Requires O 2 Generates more To move the body What if there s no O2 around? Breakdown of carbohydrates (starch, glycogen) is generated from the glycolysis of glucose Made without oxygen Pyruvate Acetyl CoA O2 Aerobic Metabolism (requires O2) mitochondrion anaerobic Powers short, maximal bursts of energy Muscle action for lift and hold Sprinting is stored as glycogen in muscle cells only!

7 Does lactic acid buildup cause muscle burn? What if there s no O2 around? (glycogen) Made without oxygen Once thought that lactic acid causes muscle fatigue and muscle burn Lactic acid Pyruvate Recent experiments have refuted this idea a hotly debated topic Acetyl CoA Aerobic Metabolism (requires O2) mitochondrion Metabolism of simple sugars and fatty acids, simple sugars Aerobic exercise and Aerobic metabolism Fatty acids It takes about 10 million molecules per second to power an active muscle cell Aerobic metabolism only O2 Amino acids can also be used as fuel Uses fatty acids as fuel production dependent on oxygen availability Athletic Performance Only used as Fuel if No Carbs or Fats Digested to Strength-and- Endurance power events events Built Into Amino Acids Proteins Enzymes Body Parts Main fuel Fatty acids production Glyolysis Aerobic metab Bursts of More, slower No Yes Is oxygen used?