The Digestive Systems - Human Anatomy and Physiology II | BI 205, Study notes of Physiology

Download The Digestive Systems - Human Anatomy and Physiology II | BI 205 and more Study notes Physiology in PDF only on Docsity! 1 The Digestive System Karen Marshall, Associate Professor Montgomery College Takoma Park Campus 9/3/2003 2 Digestive System Functions 1) take in food 2) break food down into nutrient molecules 3) absorb molecules into the bloodstream 4) rid the body of indigestible remains 9/3/2003 3 Digestive System Organs two main groups – 1) alimentary canal ~ GI tract – 2) accessory digestive organs 2 9/3/2003 4 Alimentary Canal Organs mouth pharynx esophagus stomach small intestine large intestine anus 9/3/2003 5 Accessory Organs teeth tongue gall bladder digestive glands – pancreas – liver – salivary glands 9/3/2003 6 Digestive System Organs (fig 24.1) 5 9/3/2003 13 Chemical Digestion series of catabolic steps complex food molecules are broken down into chemical building blocks – via enzymes secreted by glands into GI tract • breakdown begins in the mouth and ends in small intestine 9/3/2003 14 Absorption passage of digested end products, vitamins, minerals & water – from GI tract to blood or lymph substances first enter the mucosal cells by active or passive transport processes major site – small intestine 9/3/2003 15 Defecation elimination of indigestible substances via anus – in the form of feces 6 9/3/2003 16 Digestive Processes (fig 24.2) 9/3/2003 17 Serous Membranes associated w/ all ventral body cavities associated w/ abdominopelvic cavity – peritoneum • most extensive – mesentery 9/3/2003 18 Peritoneum extensive serous membrane lines the abdominal cavity covers the surface of abdominal organs 7 9/3/2003 19 Peritoneum visceral – covers the external surfaces of most digestive organs – continuous w/ parietal peritoneum parietal – lines the body wall 9/3/2003 20 Peritoneal Cavity located between two peritoneum slitlike space containing fluid secreted by serous membrane lubricates the mobile digestive organs – glide easily over one another 9/3/2003 21 Mesentery double layer of peritoneum a sheet of two serous membranes – fused back to back extends to the digestive organs from body wall 10 9/3/2003 28 Structure of GI Tract Wall internal to external – mucosa – submocosa – muscularis externa – serosa 9/3/2003 29 Mucosa AKA mucous membrane innermost layer moist epithelial membrane lines lumen – mouth to anus very complex – consists of three sublayers • lining epithelium • lamina propria • muscularis mucosae 9/3/2003 30 Mucosa Sublayers 1) lining epithelium – simple columnar w/ mucus goblet cells – mucus prevents enzymatic digestion of organs 2) lamina propria – underlies epithelium – loose areolar connective tissue – capillaries nourish & absorb nutrients 11 9/3/2003 31 Mucosa Sublayers 3) muscularis mucosae – layer of smooth muscle – produces local movements • to dislodge food 9/3/2003 32 Major Functions of Mucous Membrane secretion – mucus, digestive enzymes, hormones absorption – end products of digestion into blood protection – against infectious ds 9/3/2003 33 Submucosa dense connective tissue – blood, lymphatic vessels, lymph nodes, nerve fibers rich supply of elastic fibers – help stomach regain shape after storing a large meal rich vascular supply 12 9/3/2003 34 Muscularis Externa AKA muscularis layers of smooth muscle cells – circular • inner layer • some places it thickens to form sphincters – act as valves » prevent backflow » control food passage between organs – longitudinal • outer layer 9/3/2003 35 Muscularis Externa responsible for segmentation & peristalsis – mixes & propel food 9/3/2003 36 Serosa protective layer areolar connective tissue – covered w/ mesothelium • single layer of squamous esophagus (thoracic cavity) – replaced by adventitia • connective tissue – binds the esophagus 15 9/3/2003 43 Tooth (fig 24.11) 9/3/2003 44 Fig. 24.06 9/3/2003 45 Fig. 24.04 16 9/3/2003 46 Fig. 24.07 9/3/2003 47 Dental Caries AKA cavities a gradual demineralization – enamel & underlying dentin • by bacterial action decay process begins – dental plaque adhere to teeth • sugar, bacteria, & other mouth debris 9/3/2003 48 Dental Caries metabolism of trapped sugars – by bacteria produces acids • dissolve Ca salts of teeth – remaining organic matrix of tooth » susceptible to digestion by bacterial enzymes trt (tx) – plaque removal • frequent brushing & flossing 17 9/3/2003 49 Gingivitis calcification of dental plaque – gingival sulci (gums) disruption of seals between the gingavae & teeth red gums soreness swelling bleeding 9/3/2003 50 Gingivitis reversible – if calculus (tartar) is removed neglected – bacteria invasion of bone around teeth • form pockets of infection – immune system attacks • bacterial invaders & body tissues • carves deep pockets around the teeth – dissolves the bone 9/3/2003 51 Periodontal Disease AKA periodontitis ~ 80-90 % of tooth loss in adults more serious condition of gingivitis goal of trt – alleviate • bacterial infestation – reattach • surrounding tissues to teeth & bones 20 9/3/2003 58 Digestive Processes: Role of Absorption pharynx & esophagus – conduits to pass food from mouth to stomach – function • food propulsion 9/3/2003 59 Mastication AKA chewing 1) begins in mouth – w/ mechanical breakdown 2) cheeks & closed lips hold food between the teeth 3) tongue mixes food w/ saliva to soften it 4) teeth cut & grind solid food into smaller morsels 9/3/2003 60 Process of Mastication partly voluntary – put food into mouth & close jaws partly reflexive – continued jaw movements • controlled – stretch reflexes & pressure inputs » from cheek, gum & tongue receptors 21 9/3/2003 61 Deglutition AKA swallowing complicated process coordinated activity – tongue – soft palate – pharynx – esophagus – over 22 separate muscle groups 9/3/2003 62 Deglutition to send food – compacted by tongue • into a bolus – then swallowed 9/3/2003 63 Deglutition two major phases – buccal • occurs in mouth • voluntary • forces food into oropharynx – pharyngeal-esophageal • controlled by swallowing center – located in medulla & lower pons • involuntary 22 9/3/2003 64 Deglutition pharyngeal-esophageal – motor impulses from swallowing center • transmitted via cranial nerves (vagus) – to muscles of pharynx & esophagus 9/3/2003 65 Process of Deglutition buccal phase – tongue rises & presses against hard palate • forces food bolus into oropharynx – allow involuntary phase to begin – upper esophageal sphincter is contracted 9/3/2003 66 Process of Deglutition pharyngeal-esophageal phase – a) entry into respiratory passageways is prevented • uvula & larynx rise • upper esophageal sphincter is relaxed – food enters the esophagus – b) contraction of pharynx constrictor muscles • entry of food into esophagus inferiorly – contraction of upper esophageal sphincter after entry 25 9/3/2003 73 Gross Anatomy of Stomach two curvatures – greater – lesser two mesenteries – AKA omenta – extend from curvatures • lesser • greater – help hold stomach to other digestive organs & body wall 9/3/2003 74 Greater Omentum dorsal mesentery connects greater curvature (stomach) to body wall covers abdominal viscera covers the coils – small intestine – transverse colon – spleen 9/3/2003 75 Greater Omentum secures the large intestine to abdominal wall fat deposits cover & protect abdominal contents large collections of lymph nodes – “police” peritoneal cavity & intraperitoneal organs 26 9/3/2003 76 9/3/2003 77 9/3/2003 78 Lesser Omentum runs from liver to lesser curvature continuous w/ visceral peritoneum covering the stomach 27 9/3/2003 79 9/3/2003 80 Gross Anatomy of Stomach (fig 24.14) 9/3/2003 81 Fig. 24.11b 30 9/3/2003 88 Chief Cells AKA zymogenic cells produce pepsinogen – inactive form of pepsin (enzyme) function of pepsin – protein digestion (stomach) – optimally in acidic pH • 1.5-2.5 9/3/2003 89 Chief Cells stimulation – 1) activation of 1st pepsinogen molecules released to become pepsin • by HCl present in gland – 2) pepsin catalyzes the conversion to pepsin • via positive feedback 9/3/2003 90 Parietal Cells AKA oxyntic cells secrete HCl – into stomach lumen • H ions • Cl ions secrete intrinsic factor (IF) – glycoprotein 31 9/3/2003 91 Parietal Cells function of HCl – make stomach contents extremely acidic • pH 1.5-3.5 – needed for activation & optimal activity of pepsin – kills bacteria ingested w/ foods 9/3/2003 92 Parietal Cells function of IF – required for absorption of vitamin B12 in small intestine • needed to produce mature erythrocytes – absence » pernicious anemia production of IF – only stomach function essential to life 9/3/2003 93 Stomach Mucosa produces a mucosal barrier consists of – 1) thick coat of bicarbonate rich mucus – 2) tight junctions to prevent leakage of gastric juices – 3) impermeable PM glandular cells • impermeable to HCl – 4) renewal of stomach surface epithelium • division of undifferentiated stem cells 32 9/3/2003 94 Mucosal Barrier created by four factors serve protective function prevent stomach from being destroyed by acidic gastric juice 9/3/2003 95 Microscopic Anatomy of Stomach (fig 24.15) 9/3/2003 96 Stomach Functions 1) mechanical digestion & propulsion – peristaltic waves mix food w/ gastric juice – propel food into duodenum 2) chemical digestion – proteins • begins w/ pepsin 3) absorption – few fat soluble substances • aspirin, alcohol, some drugs 35 9/3/2003 103 Villi finger-like projections of mucosa give a velvety texture consist of epithelial cells – absorptive columnar cells • enterocytes capillary bed w/ wide lymph capillary • known as lacteal – located w/in core of each villus smooth muscle w/in villus core 9/3/2003 104 Villi function – absorb digested foodstuff • through epithelial cell – into the capillary blood & lacteal – alternately shorten & lengthen (smooth muscle) • pulsates – 1) increase in amt of contact between the villus surface & contents in intestinal lumen » makes absorption more efficient – 2) milk lymph along through the lacteals 9/3/2003 105 Microvilli tiny projections of PM – absorptive cells of mucosa give a fuzzy appearance – known as brush border 36 9/3/2003 106 Microvilli function – 1) increase the absorptive surface – 2) contain enzymes called brush border enzymes • complete the final stages – CHO digestion – protein digestion 9/3/2003 107 Fig. 24.23a 9/3/2003 108 Fig. 24.23b 37 9/3/2003 109 Microscopic Anatomy of Small Intestine (fig 24.21) 9/3/2003 110 Hepatitis inflammation of the liver mostly due to viral infection – ~ 6 viruses • hepatitis A to hepatitis F nonviral causes – drug toxicity & wild mushroom poisoning transmission – enterically (HVA, HVE) • self-limiting – blood (HVB, HVC) 9/3/2003 111 Hepatitis Hepatitis C – most important liver ds • persistent or chronic liver infection – trt • combination drug therapy 40 9/3/2003 118 Gallbladder thin-walled, green sac ventral surface of liver stores bile – not immediately needed for digestion – concentrates it • absorbing some of its water & ions 9/3/2003 119 Gallstones biliary calculi crystallization of cholesterol – obstructs the flow of bile from gallbladder causes – too much cholesterol • bile major vehicle for cholesterol excretion – too few bile salts • keep cholesterol dissolved w/in bile 9/3/2003 120 Gallstones when gallbladder or duct contracts – sharp crystals cause agonizing pain • radiates to right thoracic region blockage of bile duct – prevents both bile salts & pigments from entering the intestine • accumulation of yellow bile pigments (blood) • deposited in skin (yellow color) – jaundice » blocked duct » liver ds 41 9/3/2003 121 Gallstones trt – dissolving crystals • drugs – lithotripsy • pulverization w/ ultrasound vibrations – vaporization w/ lasers – surgical removal • bile duct enlarges – assumes the bile-storing role 9/3/2003 122 Subdivisions of Large Intestine cecum appendix colon – ascending – transverse – descending – sigmoid rectum anal canal 9/3/2003 123 Functions of Large Intestine 1) chemical digestion 2) absorption 3) propulsion 4) defecation 42 9/3/2003 124 Chemical Digestion digestion of remaining food residues – enteric bacteria production of vitamin K & some B vitamins – enteric bacteria 9/3/2003 125 Absorption not major function absorbs – most remaining water – electrolytes (mainly NaCl) – vitamins produced by bacteria 9/3/2003 126 Propulsion propels feces toward rectum – peristalsis • mass movements – long, slow moving powerful contractile waves – haustral contractions • churning – slow segmenting movements » occur ~ every 30 min 45 9/3/2003 133 Defecation aid in the process – 2) contraction of levator ani muscle (p 348) • pulls the anal canal superiorly – leaves the feces below the anus » outside the body 9/3/2003 134 Defecation Reflex 1) distension – triggers depolarization of sensory fibers 2) parasympathetic motor fibers stimulate – contraction of rectal walls – relaxation of internal anal sphincter 3) voluntary motor nerve stimulates – external anal sphincter to relax • if convenient to defecate 9/3/2003 135 Defecation delayed temporarily – conscious control • allows voluntary constriction of external sphincter 46 9/3/2003 136 Defecation if delayed – reflex contractions end w/in a few seconds – rectal walls relax – reflex initiated again • w/ next mass movement – process continues • until one chooses to defecate • urge becomes unavoidable 9/3/2003 137 Diarrhea watery stools cause – any condition that rushes food residue through the large intestine • before absorbption of remaining water – irritation of colon • bacteria prolonged diarrhea – dehydration – electolyte imbalance 9/3/2003 138 Constipation food remains in colon for extended periods – absorption of too much water • stool becomes hard – difficult to pass 47 9/3/2003 139 Constipation causes – lack of fiber in diet – improper bowel habits • failing to go – lack of exercise – emotional upset – laxative abuse 9/3/2003 140 Pancreatic Juice components – water – enzymes – electrolytes • primarily bicarbonate ions – make pancreas alkaline » neutralizes chyme entering the duodenum » provide optimum pH for intestinal & pancreatic enzymes 9/3/2003 141 Pancreatic Juice enzymes – pancreatic amylase • breakdown starch – lipase • breakdown lipids – trypsin – chymotrypsin • breakdown proteins 50 9/3/2003 148 Absorption liver – filters & processes nutrient rich blood • stores glucose as glycogen • stores fat-soluble vitamins • detoxifies blood – result » blood w/ fewer nutrients & waste materials 9/3/2003 149 Carbohydrate Absorption carriers – located close to enzymes on microvilli – combine w/ monosaccharides at end of chemical digestion • move CHOs into epithelial cells facilitated diffusion – CHOs enter capillary blood 9/3/2003 150 Carbohydrate Absorption process is coupled w/ active Na ion transport (cotransport) – glucose – galactose fructose – absorbed entirely by facilitated diffusion 51 9/3/2003 151 Protein Absorption occurs by carriers coupled to active transport of Na short chains of 2 or 3 a.a’s are actively absorbed into epithelial cells – digested to a.a. before entering capillary blood via diffusion 9/3/2003 152 Flowchart of Chemical Digestion & Absorption (fig 24.33) 9/3/2003 153 Lipid Absorption water insoluble products of fat digestion become associated w/ bile salts & lecithin – monoglycerides – free f.a.’s • form micelles – collection of fats clustered w/ bile salts – polar ends face water – non polar ends face middle » easily diffuse between microvilli & reach mucosal cell surface 52 9/3/2003 154 Lipid Absorption lipid substance leaves micelle – highly lipid soluble • moves through lipid portion of PM via simple diffusion into intestinal mucosal cells 9/3/2003 155 Fatty Acid Absorption (fig 24.36) 9/3/2003 156 Flowchart of Chemical Digestion & Absorption (fig 24.33) 55 9/3/2003 163 Fig. 24.26 9/3/2003 164 Fig. 24.27 9/3/2003 165 Fig. 24.28a (2) Seton vel testa ga eet eet 7320 24.280