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Transcript
Essentials of Anatomy and Physiology Fifth edition Seeley, Stephens and Tate Chapter 17: Cellular Metabolism Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 2.1 Processes of the Digestive System Figure 14.11 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.46 Control of Digestive Activity Mostly by reflexes via the parasympathetic division Chemical and mechanical receptors trigger reflexes Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.47a Control of Digestive Activity Stimuli include: Stretch of the organ pH of the contents Presence of breakdown products Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.47b Control of Digestive Activity Reflexes include: Activation or inhibition of glandular secretions Smooth muscle activity Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.47b Digestion and Absorption in the Stomach Proteases act on: Pepsin –protein digestion Rennin –milk protein digestion Absorption of: Water, alcohol and aspirin Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.55 Digestion in the Small Intestine Pancreatic enzymes provide… Complete digestion of starch Amylase Other carbohydrases About half protein digestion (trypsin, etc.) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.57a Digestion in the Small Intestine Pancreatic enzymes, cont… Fat digestion (lipase) Nucleic acid digestion (nucleases) Alkaline content neutralizes acidic chyme Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.57b Stimulation of the Release of Pancreatic Juice Vagus nerve Local hormones Secretin Cholecystokinin Figure 14.15 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.58 Absorption in the Small Intestine Water Products of digestion Most molecules absorbed by active transport Lipids absorbed by diffusion Nutrients transported to the liver Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.59 Nutrition Nutrient – substance used by the body for growth, maintenance, and repair Categories of nutrients Carbohydrates Lipids Proteins Vitamins Mineral Water Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.63 Cellular Metabolism “All the chemical reactions necessary to maintain life” Anabolism: a constructive process during which larger molecules are built from smaller ones Usually involves condensation AKA dehydration synthesis Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.67 Cellular Metabolism, con’t… •Carbohydrates •Monosaccharides = simple sugars •Glucose, fructose •Disaccharides = Combinations of monosaccharides, removal of water •Sucrose, lactose, maltose • Polysaccharides: usually polymers of glucose •Starch, cellulose, chitin Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.67 Cellular Metabolism, con’t… •Lipids •1 glycerol + 3 fatty acids neutral fat + 3 H2O •These are triglycerides •Further modifications produce: •Phospholipids (cell membrane) •glycolipids (cell membrane) •Lipoproteins (cell membrane, blood) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.67 Cellular Metabolism, con’t… •Proteins •Two amino acids a dipeptide + H2O •Covalent bond formed is a peptide bond •Unique to proteins •Polypeptides: 2-100 amino acids •Protein: >100 amino acids •Require additional modification to become functional Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.67 Cellular Metabolism, con’t… •Proteins •Modification occurs on four levels •Primary: string of amino acids •Secondary: helix or “pleat” structures •Tertiary: 3-D folding •Quarternary: two or more 3-D proteins that act as a functional unit •i.e., hemoglobin, collagen Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.67 Cellular Metabolism, con’t… •Proteins •Recall from Chemistry: •Proteins each have a unique 3-D shape •Shape determines function •Loss of shape leads to loss of function •“denaturing” proteins with heat, pH changes Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.67 Cellular Metabolism, con’t… •Proteins •May be structural or functional •Structural: •Play a role in cellular architecture •Collagen, fibrin, actin, myosin, etc. •Functional: •Play a role in cell metabolism •Enzymes, neurotransmitters, antibodies, etc. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.67 Cellular Metabolism, con’t… •Enzymes: •Biological catalysts •Highly specific for a substrate •Substrate: substance upon which an enzyme acts • i.e., peptidases act only on peptide bonds in small polypeptides •Produced only in presence of substrate Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.67 Cellular Metabolism, con’t… •Enzymes: •Huge protein molecules •Alter shape to conform to shape of substrate (“wrap around” effect) •Average 1500/cell (>5000 in liver cells) •Most require co-enzymes Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.67 Cellular Metabolism, con’t… •Enzymes: •Recognize substrate by shape of binding site •Serve to lower energy required for reaction to occur (activation energy) •therefore speed up reactions •Not changed or used up during reaction Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.67 Cellular Metabolism, con’t… •Co-Enzymes: •Required to activate enzymes •Facilitate enzymatic reactions •May be a metal ion (Zn++, Cu++, Fe++) •May be a vitamin •Vitamins are co-enzymes •Only function if “their” enzyme is available Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.67 Cellular Metabolism Catabolism: substances are broken down into molecules “destructive” process Large molecules broken down into smaller molecules Usually by hydrolysis “splitting with water” Adds H2O back into molecule Breaks covalent bonds Cellular Metabolism Catabolism Energy is released when bonds break Reverse of dehydration synthesis (condensation) Hydrolysis = chemical digestion Occurs simultaneously (and continuously) with anabolism Processes controlled by enzymes Cellular Energy Cellular energy is chemical energy Derived from breaking chemical bonds ~ ½ Energy is stored as ATP ~ ½ Energy is released as heat Helps maintain body temperature Enzymes control in the process Cellular Energy • All nutrient molecules are ultimately degraded or converted to glucose • Only glucose can be used to make ATP • Oxidation: cellular process of chemically breaking apart a glucose molecule to release energy Cellular Energy • Glucose oxidation occurs in 2 phases • Anerobic metabolism • Occurs in cytoplasm • Without oxygen • AKA glycolysis • Splits glucose into two 3-Carbon molecules: pyruvate Cellular Energy • Glycolysis • Process also produces 2 ATPs • In yeast, plant cells: • Pyruvate can undergo alcoholic fermentation • In bacteria, animal cells: • Pyruvate can produce lactic acid Cellular Energy • Aerobic metabolism • Uses oxygen • AKA Kreb’s Cycle or Citric Acid cycle or Tricarboxylic Acid (TCA) Cycle • Occurs in mitochondria • Makes more ATP than anerobic processes Cellular Energy • Aerobic metabolism • CO2 and H2O are waste products • CO2: • Diffuses out of cells • Dissolves in plasma • Produces HCO3- in blood • Exhaled from lungs Cellular Energy • Aerobic metabolism • H2O: • “metabolic” water • Exhaled from lungs • Final products of glucose oxidation: • CO2, H2O, ATP Cellular Energy • Aerobic metabolism • For each molecule of glucose: • 2 ATP formed in glycolysis • 36 ATP formed in TCA cycle • Energy stored in phosphate bonds • A reversible reaction Metabolic Pathways • “A particular sequence of enzymatic reactions” • Such as glycolysis, TCA cycle • Carbohydrate pathways • Carbos should comprise most of our diet (~ 50% complex carbs) • Used as a primary energy source • Produce 4kcal/gm Metabolic Pathways • Carbohydrate pathways • Excess carbs converted to energy storage forms • Glycogen (muscle, liver) • Adipose tissue (hips) • Process is anabolism Metabolic Pathways • Lipid pathways • Metabolism controlled by liver • Should comprise <30% of calories in diet • Get 9 kcal/gm (more ATP!) • Must be degraded into glycerol, fatty acids, then pyruvate • A reversible catabolic process Metabolic Pathways • Protein pathways • Proteins should comprise ~30% of diet • Get 4 kcal/gm • Catabolism is more complex • Proteins contain nitrogen Metabolic Pathways • Protein pathways • Deamination: removal of nitrogen from amino acids • Occurs in liver • Nitrogen is converted to urea » A nitrogenous waste product • Sent to kidneys for excretion Metabolic Pathways • Protein pathways • After deamination: • amino acid “skeleton” is processed • in TCA cycle • May produce CO2, H2O, ATP • May form glucose or fat Metabolic Pathways • Protein pathways • Glucose formed from amino acid skeletons may be re-converted to amino acids • “Essential” amino acids: • Body cannot make these • Must obtain in the diet Regulation of Metabolic Pathways • Enzyme “saturation” • Too much substrate for number of enzyme molecules • Reaction rate cannot increase • A single enzyme can control an entire metabolic pathway • “rate limiting” enzyme Digestive System: Disorders Ulcers: bacterial infection with H. pylori Vomiting: controlled by center in medulla oblongata Activity of tract slows in old age Fewer digestive juices Peristalsis slows Diverticulosis and cancer more common Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.92b Digestive System: Disorders IBS: irritable bowel syndrome Crohn’s disease (autoimmune) Constipation Diarrhea Colitis Colon polyps/cancers Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 14.92b