Harvesting energy from food Or how food gets from to and body structures Cheese protein (a polymer of amino acids in a specific sequence) Breakdown of protein by human digestive system Amino acid monomer Amino acids Absorption of amino acids by cells lining the small intestine; transport via bloodstream to other cells Human protein Cells use amino acids from the cheese and other foods to produce new human proteins Figure 22.2-3 Digestion: A Closer Look Mechanical digestion Involves physical processes like chewing Chemical digestion the breakdown of food by enzymes ACCESSORY ORGANS Salivary glands Liver Gallbladder Pancreas ALIMENTARY Digestive tract CANAL Mouth Tongue Pharynx Esophagus Stomach Small intestine Colon of large intestine Appendix Rectum Anus Figure 22.5 Where digestion begins Mouth Salivary glands Teeth Functions: Eating and chewing Digestion of carbohydrates Mechanical or chemical digestion? Salivary Glands Produce saliva Lubrication Contains amylase Enzyme that breaks down starch. Contains lysozyme Enzyme that kills bacteria. 1
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 There s a sphincter at the bottom of the esophagus A circular muscle that closes off one end of an organ. The lower esophageal sphincter allows the bolus to drop into the 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 intestine Mechanical or chemical digestion? Digestion in the stomach Secretes gastric juice (2-3 quarts per day) Secretes acid (HCl) Gives the stomach a ph of 2 Unfolds dietary protein Activates the enzyme pepsin Digests protein Helps kill bacteria found in food Gastric Pits Why doesn t the stomach digest itself? It secretes mucus Protects Lubricates What causes Heartburn? 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 2
What causes gastric ulcers? The bacteria Helicobacter pylori H. 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 Leaving the Stomach Pyloric Sphincter : separates the stomach from the small intestine. the strongest muscle in the GI tract. Controls how much chyme enters the small intestine Copyright 2009, John Wiley & Sons, Inc. Small intestine The longest part of the digestive tract (~20 ft) Function: digestion and absorption of nutrients 3 regions duodenum, jejunum, and ileum The duodenum The first part of the small intestine Receives chyme from stomach and digestive secretions from liver and pancreas Neutralizes acidic chyme Digestive secretions of the pancreas Pancreatic juice secreted into duodenum contains: Bicarbonate to neutralize stomach acids Digestive enzymes Trypsin digests proteins Lipase digests fats Pancreatic amylase digests carbohydrates 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 3
4/17/13 Fat digestion is completed in the small intestine Bile salts emulsify fats break down large fat globules to smaller ones Then pancreatic lipase digests fats into fatty acids Which are absorbed Summary: Digestion of foods Fat globules + bile salts emulsification droplets lipase monoglycerides and free fatty acids ph = basic chylomicron lymphatic capillary c. Fat digestion Macromolecules Enzymes: proteins that speed up chemical reactions Monomers Where are nutrients absorbed? Most nutrients (~90%) are absorbed in the small intestine The rest? Stomach & large intestine Copyright 2009, John Wiley & Sons, Inc. The Large Intestine The colon Why is digestion important? the main part of the Colon large intestine Absorbs water Produces feces, the waste product of food The rectum stores feces It creates: Small intestine Rectum Anus Figure 22.14a Molecules small enough for cells to absorb Monomers (building blocks) that can be recombined into new molecules Monomers that can be metabolized to produce ATP 4
Where Is the Energy in Food? Food as Fuel Stored in chemical bonds between the C, H and O atoms Cellular respiration Breaks apart organic molecules Generates many molecules of ATP In cellular respiration, the chemical bonds between atoms are broken and the energy is converted to ATP Where is the energy in ATP? Some ways cells use energy ATP ADP To build macromolecules To transport molecules across the membrane To power muscle contraction Why is ATP a good source of energy for cells? Ways our body makes ATP It is versatile used in many types of reactions Its breakdown is easily coupled with energy-requiring reactions It provides just the right amount of energy for cellular reactions 5
Creatine phosphate (CP) and the aerobic system work together CP Stored in muscles in small amounts. Easily converted to ATP Produces instant energy for sudden movements e.g. a punch or a kick These energy systems work in different parts of the cell Fuels for making ATP Cytoplasm Mitochondria Carbs are the main energy source for glycolysis Blood glucose Aerobic respiration O 2 Fuels for making ATP If oxygen is limiting, ATP is made by glycolysis X X Lactic acid (by-product) 6
Does lactate buildup cause muscle fatigue? Once thought that lactate causes muscle fatigue and muscle burn Lactic acid isn t the culprit Muscle soreness is caused by actual muscle cell damage and inflammation Recap: the glycolysis and aerobic energy systems generates a small amount of ATP Aerobic system Requires O 2 Generates the most ATP 7