Presentation on theme: "The Digestive System and Body Metabolism"— Presentation transcript:
1 The Digestive System and Body Metabolism DigestionBreakdown of ingested foodAbsorption of nutrients into the bloodMetabolismProduction of cellular energy (ATP)Constructive and degradative cellular activitiesDigestion is primarily extracellular, with the end of digestion at the pt when nutrients are absorbed into cells.Metabolism occurs within cells, involving release of chemical energy from food AND building of biological molecules.
2 Processes of the Digestive System Mechanical propulsionSecretionDigestion - mechanical and chemical breakdownAbsorptionEliminationOne way disassembly line. Several steps done by dift organs. Some overlap in function.Simpler systems are sacs, with batch processing only. One-way systems allow specialization, continuous processing, th4, constant or irregular feeding.Digestive systems have evolved to match feeding habits/ opportunities. So, bird with expandable crop to collect seeds, grind them up in safer location. Carnivores with shorter intestines, as meat is quicker to digest than plant material with cellulose. Ruminants that rechew food to break down plant fibers, get max nutrition w/ aid of microbes.
3 Mechanical Processing Teeth break down foodmolars (12)Teeth - Permanent teeth replace deciduous teeth beginning between the ages of 6 to 12A full set is 32 teeth, but some people do not have wisdom teethShape of tooth reflects type of cutting/grinding:Types: incisors, canines, premolars, molarsStructure: crown, rootTongue: skeletal muscle, moves food in mouth, tasteSaliva: Mixture of mucus and serous fluidsHelps to form a food bolusContains salivary amylase to begin starch digestionDissolves chemicals so they can be tastedSource: parotid, submandibular, sublingual salivary glandsComposition: mucin, salivary amylase, bicarbonate, lysozymePermanent teethReplace deciduous teeth beginning between the ages of 6 to 12Activities of the Pharynx and EsophagusThese organs have no digestive functionServe as passageways to the stomachVoluntary phase: tongue pushes bolus of food into pharynxInvoluntary phase/swallowing reflex: receptors in pharynx stimulated by presence of foodSoft palate rises, Larynx rises slightlyTongue pushes food further, Food enters esophagusTongue blocks off the mouthSoft palate (uvula) blocks the nasopharynxEpiglottis blocks the larynxPeristalsis moves the bolus toward the stomachThe cardioesophageal sphincter is opened when food presses against itpremolars (8)canines (4)incisors (8)lower jawupper jaw
4 Stomach Functions Acts as a storage tank for food Mechanical, chemical breakdown of protein beginsDelivers chyme to the small intestineChyme = processed foodConvolutions of interior surface allow stomach to expand.Gastric juice: specific cells secreteHydrochloric acid: produces a pH of about 2, breaks down large bits of foodIntrinsic factor; made by same cells making acid, needed to absorb Vitamin B12Mucus: protects stomach lining from acidPepsinogen: activated by acid to pepsin, begins protein breakdownRennin – works on digesting milk proteinThe only absorption that occurs in the stomach is of alcohol and aspirinNecessity of an Extremely Acid Environment in the StomachActivates pepsinogen to pepsin for protein digestionProvides a hostile environment for microorganisms
5 Propulsion in the Stomach Food must first be well mixedRippling peristalsis occurs in the lower stomachThe pylorus meters out chyme into the small intestine (30 ml at a time)The stomach empties in four to six hoursStomach contractions: blend food and propel forwardStructural adaptation: third muscularis layerDirection: from lower esophageal sphincter to pyloric sphincterChyme: result of mixing, affects hormone secretions regulating peristalsis and emptying of stomachGastric fluid is regulated by neural and hormonal factorsPresence of food or falling pH causes the release of gastrinGastrin causes stomach glands to produce protein-digesting enzymesFigure 14.15
6 Chemical Digestion in the Small Intestine Pancreatic enzymes digest starch, proteins, nucleic acids, fats; reset pH.Gall bladder -Pancreatic enzymes play the major digestive functionHelp complete digestion of starch (pancreatic amylase)Carry out about half of all protein digestion (trypsin, etc.)Responsible for fat digestion (lipase)Digest nucleic acids (nucleases)Alkaline content neutralizes acidic chymeEndocrine products of pancreasInsulinGlucagonsEnzymes from the brush borderBreak double sugars into simple sugarsComplete some protein digestionFigure 14.6
7 Propulsion in the Small Intestine Peristalsis is the major means of moving foodSegmental movementsMix chyme with digestive juicesAid in propelling foodEsophagus moves food bolus by peristalsisSmall intestine uses segmental movements to mix food, push it up agst lining for better absorption.
8 Absorption in the Small Intestine Site of nutrient absorption into the bloodVilli = Fingerlike structures on the mucosa surfaceMicrovilli on cellsAll increase surface areaEach villus is made of many cells. Each absorptive cell has tiny microvilli (1700) on its free surface. = brush border. Result is increase about 600-fold of surface area.Note vascular connections and lymph collecting vessels (green)Most absorbed by active transport through cell membranesSubstances are transported to the liver by the hepatic portal vein or lymphFigure 14.7a
9 Absorption of Proteins and Carbohydrates Amino acids, sugars move by active transport into blood vesselsNext stop: liver, where glucose glycogenamino acids proteinExcess moleculesare converted to fatsFigure 14.13
10 Absorption of FatsLipids are absorbed into lymph system, which drains into heartEmulsified with bile saltsDigested into fatty acids, glycerolWith bile salts, diffuse into cellsReassembled into fats, exocytosisFigure 14.14
11 Food Breakdown and Absorption in the Large Intestine No digestive enzymes are producedResident bacteria digest remaining nutrientsProduce some vitamin K and BRelease gasesWater and vitamins K and B are absorbedUndigested fiber keeps materials moving and is eliminated via feces
12 Control of Digestive Activity Regulation dependent on volume and content of foodNervous system: sight, smell of food, stretch receptors in stomachHormones:Gastrin: stimulates release of gastric juiceSecretin: stimulates pancreas to secrete water and bicarbonateCholecystokinin (CCK): signals pancreas to secrete digestive enzymesChemical and mechanical receptors in organ walls trigger reflexesTable 14.1, p475. Stomach is stimulated by food entering it. Produces 3 hormones:Gastrin - stimulates release of gastric juice, stimulates small intestineHistamine - stimulates parietal cells to release HCl. pH dropsSomatostatin - inhibits secretion of gastric juice and pancreatic juice. Inhibits emptying of stomach.2-3 L of gastric juice per day, normally.Stimuli include:Stretch of the organpH of the contentsPresence of breakdown productsReflexes include:Activation or inhibition of glandular secretionsSmooth muscle activityNOTE: this is not appetite control mechanism. Separate system.Appetite stimulated by: CCK (from pancreas) , low glucose levels in blood.Suppressed by leptin (from adipose cells). Phen-fen drug.
13 Nutrition Carbohydrates: major energy source, simple or complex Lipids: cell components and energy sources, saturated or unsaturatedProteins: 20 amino acidsVitamins: fat soluble and water solubleMinerals: recommended daily allowanceFiberMajor biological polymers, made of repeated monomers. Same categories as listed on food nutrition labels. These molecules make up the vast bulk of our food, organic or otherwise.Carbs - energy, fiberLipids, energy and membsProteins - made up of amino acids.20 essential our bodies must ingest 9 of these, can make the rest.Vitamins - coenzymes. Essential to function of other enzymes, but not consumed in reaction.Minerals - specific functions. Fe in hemoglobin.Water - vital. Part of everything
14 Food Guide PyramidCarbohydrates are The body’s preferred source to produce cellular energy (ATP)Glucose (blood sugar) is the major digestive product and serves as fuel to make ATPBrain uses 65% of blood glucose. Neurons take lots of energy, prefer to use glucose.Other cells will use fats, proteins if glucose is unavailable.Caffeine stimulates enzymes which break down fats AND those which make storage fats. No net gain.Figure 14.16
15 Body Energy BalanceEnergy intake = total energy output (heat + work + energy storage)Energy intake from food oxidationEnergy outputHeat is usually about 60%Storage energy is in the form of fat or glycogenEnergy intake - combat obesity by blocking conversion of food.Olestra - fat which cannot be broken down (5 Carbon sugar with 5 fatty acids)gastric bypass surgeryartificial sweeteners - same sweetness, fewer molecules = fewer CaloriesEnergy output -maintain body temp. Heat is usly lost to environment. So if two people weigh the same, which uses more energy for body temp stability: short, wide vs tall, thin? Why?Storage energy - carbo loading before a competition is putting glycogen into muscle cells and liver.Longer term storage uses fats in adipose tissue, usly underneath skin.
16 Regulation of Food Intake Mechanisms that may regulate food intakeLevels of nutrients in the bloodHormonesBody temperaturePsychological factorsAnorexia - may involve some a transport protein for norepinephrine.neurotransmitter,BullemiaHormones : ghrelin, from stomach and brain cells, makes you feel hungry. Goes down after a meal. Increases with dieting.Leptin - secreted by fat cells. Dampens appetite center in brain. Not a candidate for weight control. Overweight people may beless sensitive to leptin.CCK - cholecystokinin - from small intestine to stimulate pancreas to release enzymes. Also signals brain to dampen appetite. Perhaps some potential as anti-obesity drug.PYY another candidate for appetite control. Dampens.
17 Basal Metabolic RateBMR– amount of heat produced by the body per unit of time at restFactors that influence BMRSurface areaGenderAge – children and adolescents have a higher BMRthyroxine from thyroid glandGive reasons why each one of these factors should influence BMR.Factors that influence BMRSurface area - loss of body heat. Surface area/volumeGender - males highe b/c of lower % BODY FAT. Adipose tissue w/ low metabolic rate.Age – children and adolescents have a higher BMR b/c of growth, not just repair of cells.thyroxine from thyroid gland.
18 Total Metabolic Rate (TMR) Total amount of kilocalories the body must consume to fuel ongoing activitiesTMR increases with an increase in body activity