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Organs of the Digestive System

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1 Organs of the Digestive System
For student copy

2 The Mouth aka oral or buccal cavity cheeks form lateral walls
internally covered by mucous membrane: nonkeratinized, stratified sq epith wall of cheeks: buccinator muscle then subq & skin lips or labia surround opening inner surface of each lip attached to its gum by a midline fold of mucous membrane called a labial frenulum “small bridle”


4 Mouth - 2 vestibule: space between buccal mucosa & teeth
oral cavity proper: space that extends from gums & teeth  fauces: opening between oral cavity & pharynx hard palate: anterior portion of roof of mouth maxillae & palatine bones form bony partition between oral & nasal cavities covered by mucous membrane

5 MOUTH - 3 soft palate: forms posterior portion of roof of mouth
muscular partition between oropharynx & nasopharynx uvula : hangs from free border of soft palate when swallowing soft palate & uvula drawn superiorly preventing food & liquids from entering nasal cavity


7 Salivary Glands release saliva into oral cavity 4 sets:
Parotid glands (“near ear”) between masseter & skin parotid duct secretes saliva into vestibule opposite 2nd molar Submandibular glands floor of mouth/ enter just lateral to lingual frenulum Sublingual glands under tongue lesser Sublingual glands: floor of mouth

8 Salivary Glands

9 Saliva 99.5% water 0.5% solutes: ions urea & uric acid mucus Ig A
lysozyme (bacteriostatic enzyme) salivary amylase: digestive enzyme acts on starch

10 Salivation controlled by ANS average adult secretes 1000 – 1500 mL/day
parasympathetic stimulation promotes continuous secretion  keeps mouth moist & lubricates tongue & lips during speech saliva is then swallowed moistening esophagus  most water is reabsorbed sympathetic stimulation dominates if stressed  mouth dry dehydration: secretion stops to conserve water

11 Mumps inflammation & enlargement of parotid glands
pain, malaise, fever swelling on affected side

12 Tongue skeletal muscles covered by mucous membrane forming floor of oral cavity median septum separates tongue into symmetric ½ s (attaches to hyoid bone) lingulum frenulum limits movement posteriorly if abnl short: “tongue-tied” each ½ composed of extrinsic & intrinsic muscles extrinsic: origins out of tongue/ insert to CT in tongue: move tongue side-to-side/ anchor tongue intrinsic: origin & insertion in tongue: alter shape & size of tongue for speech & swallowing


14 Tongue - 2 dorsum (upper surface) & lateral surfaces covered with papillae projections of lamina propria covered with keratinized epithelium some contain taste buds others touch receptors all increase friction between tongue/food lingual glands secrete mucous & a watery serous fluid that contains enzyme lingual lipase: acts on triglycerides

15 Taste Buds most on tongue, few on soft palate, pharynx, & epiglottis
each taste bud has 3 types epith cells: supporting cells surround ~50 receptor cells gustatory receptor cells single microvillus basal cells

16 Taste Buds - 2 each taste bud has 3 types epith cells:
supporting cells surround ~50 receptor cells gustatory receptor cells single microvillus from each = gustatory hair extends thru a taste pore (opening in taste bud) basal cells stem edge of taste bud produce supporting cells that then develop into gustatory cells (each lasts ~10 days)



19 Teeth dentes in alveolar processes of mandible & maxillae
covered by gingivae: “gums” lined by peridontal ligament: anchors tooth to socket parts of a tooth: Crown Root Neck

20 Crown of Tooth visible portion, above level of gums
interior made of dentin: calcified CT gives shape & rigidity to tooth harder than bone covered by enamel Ca++ phosphate & carbonate hardest substance in body protects tooth from: wear & tear of chewing acids that could dissolve dentin

21 Pulp Cavity w/in dentin
pulp: CT with blood, lymph & nerve supply to tooth extension thru roots = root canals  base for vessels/nerve to enter/exit tooth

22 Root of Tooth below gums covered by cementum


24 2 Dentitions Deciduous teeth Secondary teeth baby or primary teeth
~6 mos  24/mo  20 total lost age Secondary teeth 32 begin to erupt ~ 6  adult



27 Digestion in the Mouth mastication: chewing
MECHANICAL Digestion in the Mouth mastication: chewing food manipulated by tongue/ground by teeth & mixed with saliva bite of food reduced to soft, flexible, easily swallowed mass = bolus CHEMICAL Salivary amylase initiates breakdown of starch into di- & trisaccharides, shorter polymers only monosaccharides can be absorbed 2. Lingual lipase becomes activated in acid pH of stomach

28 Pharynx funnel-shaped tube extends from internal nares  esophagus posteriorly & to the larynx anteriorly skeletal muscle covered by mucous membranes 3 parts: Nasopharynx: functions only in respiration Oropharynx: digestive + respiratory functions Laryngopharynx: digestive & respiratory

29 Esophagus collapsable muscular tube posterior to trachea
inferior end of laryngopharynx  passes thru mediastinum  pierces diaphragm (opening called esophageal hiatus)  ends in superior portion of stomach

30 Histology of the Esophagus
mucosa: nonkeratinized stratified sq epith lamina propria Muscularis mucosae (smooth muscle) submucosa: areolar CT muscularis: upper 1/3 skeletal mid 1/3 skeletal & smooth lower 1/3 smooth

31 Ends of Esophagus muscularis thickens forming:
upper esophageal sphincter (UES) skeletal regulates movement of food from pharynx  esophagus lower esophageal sphincter (LES) smooth regulates movement of food from esophagus  stomach


33 Physiology of the Esophagus
secretes mucus & transports food  stomach No enzymes produced or secreted No absorption

34 Deglutition swallowing facilitated by secretion of saliva & mucus
involves mouth, pharynx, esophagus Voluntary stage bolus of food from oral cavity to oropharynx stimulates receptors in oropharynx  deglutition center in medulla & lower pons  effector fibers cause soft palate & uvula to move up to close off nasopharynx AND epiglottis closes off opening of larynx

35 Deglutition Involuntary Stage
2. Esophageal stage bolus enters esophagus peristalsis: progression of coordinated contractions & relaxations of circular & longitudinal layers of muscularis, pushes bolus onward


37 Stomach J-shaped enlargement of GI tract just inferior to diaphragm
connects esophagus  duodenum most distensible part of GI tract serves as a mixing chamber holding reservoir

38 Stomach Adaptations for Digestion
rugae mucus glands: secretion of H+ & Cl- pepsin gastric lipase intrinsic factor 3-layered muscularis

39 Anatomy of the Stomach

40 Histology of the Stomach
4 basic layers in stomach wall: (stomach wall is impermeable to most substances) surface mucosa = simple columnar epith that extend down into lamina propria where they form columns of secretory cells called gastric glands, channels between columns called gastric pits

41 Mechanical Digestion in Stomach
few minutes after food bolus enters stomach: gentle, rippling, peristaltic movements called mixing waves pass thru stomach q15 – 25 s macerate food mix with mucus secretions results: chyme soupy liquid  pylorus

42 Pyloric Sphincter slightly open
when chyme down to lower pylorus, each mixing wave forces ~ 3 mL chyme into duodenum = gastric emptying

43 Chemical Digestion in the Stomach
salivary amylase: continues to function while food in fundus when churning forces bolus further into stomach the acid pH inactivates it lingual lipase: acid pH activates triglycerides  fatty acids & diglycerides

44 Chemical Digestion - 2 H+ & Cl- ions secreted separately by parietal cells secretion stimulated by: parasympathetic neurons gastrin (from G cells) histamine (from mast cells in lamina propria): receptors on parietal cells = H2 receptors

45 Stomach Acid kills many microbes in food partially denatures proteins
stimulates secretion of hormones that promote flow of bile & pancreatic juice

46 Pepsin secreted by chief cells
greatest activity in low pH / inactivates in higher pH of small intestine secreted as pepsinogen: inactive form of pepsin (so will not break down proteins in chief cells severs peptide bonds breaking protein  smaller peptide fragments stomach wall protected from pepsin by alkaline mucus secreted by surface cells


48 Gastric Lipase splits short-chain triglycerides  fatty acids & monoglycerides most pH 5-6 (limited role in stomach)

49 Absorption in Stomach very little in stomach (epithelial cells impermeable to most substances) mucous cells do absorb some: water ions short-chain fatty acids aspirin alcohol

50 Stomach 2 – 4 hrs for food to exit meal mostly carbs: shortest time
protein – rich meal longer fat-laden meal longest

51 Emesis (vomiting) forcible expulsion of contents of upper GI tract (stomach +/- duodenum) strongest stimuli: irritation & distension of stomach other irritants: unpleasant sites general anesthesia dizziness drugs: morphine, digitalis derivatives


53 Pancreas retroperitoneal gland: lies posterior to greater curvature of stomach 3 parts: Head: expanded portion near curve of duodenum Body: Tail: tapering portion Ducts: Pancreatic: runs length of pancreas, joins bile duct Accessory: branch of pancreatic


55 Histology of the Pancreas
exocrine portion made up of small cluster of glandular cells = acini about 99% of pancreas secrete mixture of fluid & digestive enzymes = pancreatic juice

56 Pancreatic Juice 1200 – 1500 mL/d
mostly: water, salts, sodium bicarbonate (makes pH 7.1 – 8.2), & enzymes (secreted in an inactive form): pancreatic amylase trypsin chymotrypsin carboxypeptidase elastase pancreatic lipase: #1 triglyceride-digeting enzyme ribonuclease & deoxyribonuclease


58 Liver heaviest gland in body (~1.4 kg or 3 lb)
2nd largest organ in body found inferior to diaphragm taking up most of RUQ

59 Anatomy of the Liver Ligaments:
falciform: attaches liver to anterior abdominal wall coronary: attaches liver to diaphragm ligamentum teres: remnant of umbilical vein

60 Anatomy of the Liver Lobes: left: smaller right: larger
includes inferior lobe: quadrate and a posterior lobe: caudate right: larger



63 Histology of the Liver lobules: functional unit of liver
6-sided structure made of specialized epith cells called hepatocytes arranged in branching, interconnected plates around a central vein highly permeable capillaries called sinusoids fixed macrophages in sinusoids called Kupffer cells destroy worn out RBCs, bacteria or other foreign material in venous blood that just arrived from small intestine



66 Bile secreted by hepatocytes  bile canaliculi  bile ductiles  bile periphery of lobules eventually, bile flows into larger right & left hepatic ducts  combine to form & exit liver as common hepatic duct made by hepatocytes  stored in gallbladder  small intestine function: emulsification of fats (large lipid globules  suspension of small lipid globules so can be absorbed

67 Jaundice yellowish coloration of sclera & mucous membranes due to a buildup of bilirubin formed as product of breaking down heme pigment in worn out RBCs excreted in bile 3 categories: Prehepatic excess production of bilirubin Hepatic due to congenital liver disease, cirrhosis, hepatitis Extrahepatic: blockage bile drainage by gallstones or CA of bowel or pancreas

68 Neonatal Jaundice aka physiologic jaundice
liver enzymes not always birth generally resolves in < days treated with blue lights: changes bilirubin into products that can be cleared by kidneys


70 Functions of the Liver #1
Carbohydrate Metabolism liver has important role in maintaining a normal blood glucose level if low: glycogen  glucose  increases blood levels enzymes can convert a.a. or lactic acid glucose if high: glucose  glycogen or triglycerides for short-term or long-term storage

71 Functions of the Liver #2
Lipid Metabolism Hepatocytes: store some triglycerides fatty acids broken down  ATP synthesize lipoproteins (transport fatty acids, triglycerides, steroids) synthesize cholesterol & use some to make bile salts

72 Functions of the Liver #3
Protein Metabolism Hepatocytes: deaminate a.a. (remove amine group) (rest of a.a. then used to make ATP or convert to carbs or fats) amine group  urea  excreted in kidneys synthesize most plasma proteins α & β globulins albumin prothrombin fibrinogen

73 Functions of the Liver #4
Processing of Drugs & Hormones detoxifies alcohol & drugs chemically alters & excretes steroid hormones thyroid estrogens aldosterone

74 Functions of the Liver #5
Excretion of Bilirubin absorbed by hepatocytes from aged RBCs then secreted into bile most bilirubin in bile metabolized in small intestines by bacteria  eliminated in feces

75 Functions of the Liver #6
Synthesis of Bile Salts used in small intestine for emulsification & absorption of lipids

76 Functions of the Liver #7
Storage glycogen Vitamins A, B12, D, E, & K Fe, Cu

77 Functions of the Liver # 8
Phagocytosis Kupffer cells eat aged RBCs, WBCs, & some bacteria

78 Functions of the Liver # 9
Activation of Vit D skin, liver, & kidneys all have role in synthesizing the active form of Vit D

79 Gallbladder pear-shaped sac found in a depression tucked under liver
function: store bile until fatty chyme enters duodenum bile  cystic duct  common bile duct  ampulla of Vater  duodenum parts: fundus body neck


81 Gallstones If bile contains insufficient bile salts or lecithin or excessive cholesterol, the cholesterol crystallizes to form stones passing small ones can cause intermittent pain but larger ones can obstruct  severe pain/infection

82 Small Intestine site of most major events of digestion & absorption
adaptations long: ~ 10 ft in living adult/ 21 ft in dead surface area increased by circular folds villi microvilli

83 Functions of the Small Intestine
segmentations mix chyme with digestive juices & bring food particles into contact with the mucosa for absorption; peristalsis propels chyme thru completes digestion of carbs, proteins, lipids; begins & completes digestion of nucleic acids absorbs 90% of nutrients & water that pass thru

84 Anatomy of Small Intestine
3 regions Duodenum “12” width of 12 fingers Jejunum 1 m in length “empty” Ileum 2 m joins large ileocecal valve

85 Histology of Small Intestine
same 4 layers of GI tract mucosa: simple columnar epith with 6 types of cells absorptive cells goblet cells intestinal glands (crypts of Lieberkϋhn) Paneth cells Enteroendocrine cells: S, CCK, K

86 Absorptive Cells digest & absorb nutrients from chyme
apical membranes form microvilli: projections that increase surface area: form fuzzy line called brush border

87 Crypts of Lieberkϋhn intestinal glands w/in deep crevices of small intestine mucosa secrete intestinal juices

88 Paneth Cells enteroendocrine cells
secrete lysozyme: bactericidal enzyme also can act as phagocytes

89 Enteroendocrine Cells
S cells: secrete hormone secretin CCK cells: secrete hormone cholecystokinin (CCK) K cells: secrete hormone glucose-dependent insulinotropic peptide (GIP)

90 Histology of Small Intestine
Lamina Propria: areolar CT with: abundance of MALT (mucosa-associated lymphoid tissue) solitary lymphatic nodules in distal ileum Peyer’s Patches: aggregated lymphatic follicles also found in ileum


92 Histology of Small Intestine
Submucosa: Bruner’s glands in duodenum: secrete alkaline mucus that neutralizes the gastric acid in chyme

93 Structural Features that Facilitate Digestion & Absorption:
Circular folds: folds of mucosa & submucosa (~1 cm long) proximal duodenum  mid-ileum increase surface area for absorption Villi: fingerlike projections of mucosa (~,5 – 1 mm long) gives mucosa velvety appearance Microvilli: brush border


95 Lacteals the arteiole, venule, capillary bed & a lymphatic capillary (the lacteal) found w/in a villus

96 Intestinal Juice clear, yellow fluid
+ pancreatic juice makes a liquid environment for chemical digestion & absorption contains: water, alkaline mucus (pH 7.6)

97 Brush-Border Enzymes absorptive cells secrete several digestive enzymes  inserting them into the plasma membranes of microvilli lumen enzymes (from pancreatic secretions) break larger molecules into smaller ones) brush- border enzymes break them down even smaller (small enough to be absorbed) cytoplasmic enzymes finish digestion


99 Mechanical Digestion in Small Intestine
Segmentations: localized, mixing contractions, occur in portions of sm intestine distended by large vol of chyme mix chyme with digestive juices bring particles of food into contact with mucosa for absorption Do Not push chyme onward

100 Brush-Border Enzymes digest: α-dextrins maltose sucrose lactose
peptides nucleotides

101 Absorption in Small Intestine

102 Absorption of Alcohol lipid-soluble – so begins absorption in stomach where surface area for absorption much less than in small intestine longer stays in stomach the slower blood alcohol levels rise fatty acids in chyme slow gastric emptying gastric juices have enzyme alcohol dehydrogenase (breaks down alcohol): ♀ 60% less than ♂ so become intoxicated on less alcohol  chyme into small intestine absorption more rapid greater surface area


104 Large Intestine terminal portion of GI tract
~1.5 m long & 6.5 cm diameter ileocecal sphincter  anus attached to posterior abdominal wall by its mesocolon Regions: Cecum Colon Rectum Anal Canal

105 Functions of Large Intestine
haustral churning, peristalsis, & mass peristalsis bacteria convert proteins to a.a., breakdown a.a., & produce some B vitamins and vitamin K absorption of some: water, ions, vitamins forming feces defecation (emptying rectum)

106 Large Intestine: Layers
Mucosa: many mucous cells mucus only secretion absorptive cells that absorb water Muscularis: external layer of longitudinal smooth muscle & internal layer of circular but here longitudinal layer in bands = teniae coli that run most of length contraction of teniae cause series of pouches = haustra (singular: haustrum) which give organ a puckered appearance


108 Cecum opening from ileum has fold of mucous membrane = ileocecal valve
hanging inferior to it is cecum (small pouch) vermiform appendix attached to cecum which is attached to mesocolon by mesoappendix

109 Appendicitis inflammation of appendix
starts with obstruction to entry of appendix chyme, tumor, foreign body Symptoms: high fever, elevated WBC’s (neutrophils), anorexia, pain McBurney’s point appendix can become edematous, gangrenous, rupture w/in 24 hrs often patient presents after rupture (much higher mortality rate)

110 Colon

111 Parts of Colon ascending colon  rt hepatic flexure  transverse colon  lt splenic flexure  descending colon  level of iliac crest where it becomes sigmoid colon (S-shaped)  projects medially to midline  terminates as rectum

112 Rectum last 20 cm of GI tract anterior to sacrum & coccyx
anal canal: last 2 – 3 cm mucous membranes arranged in longitudinal folds called anal columns: contain network of arteries & veins opening to outside body = anus: guarded by an internal anal sphincter (smooth muscle) & an external anal sphincter (skeletal muscle) normally, both closed except during elimination of feces


114 Mechanical Digestion in Large Intestine
ileocecal sphincter: controls chyme entering cecum relaxes from hormone gastrin gastroileal reflex: starts immediately after meal intensifies peristalsis in ileum which forces any chyme there  cecum: when distended ileocecal sphincter tightens

115 Mechanical Digestion in Large Intestine - 2
Haustral churning: characteristic movement in large intestine Haustra remain relaxed & become distended while they fill up Peristalsis: slower rate (3 – 12 contractions/min) than in proximal GI tract Mass Peristalsis: strong peristaltic wave begins mid-transverse colon & quickly drives forward contents  rectum

116 Chemical Digestion in Large Intestine
done by bacteria acting on chyme use fermentation on remaining carbs  gases (H2, C2, CH4) Flatulence: excessive gas convert remaining proteins  a.a.  skatole, indole (contributes to odor of feces) decompose bilirubin  simpler pigments (gives brown color to feces) produce Vitamin K & some B Vitamins

117 Occult Blood “hidden blood” (not visible) screen for colorectal cancer

118 GI Tract Homeostatic Imbalances
Colorectal Cancer: 2nd to lung ca in males & 3rd after lung & breast in females for deaths due to ca >1/4th have family hx 5 – 6% have known gene ~95% adenocarcinomas: many start as colon polyp flat, depressed lesions more likely to be malignant

119 GI Tract Homeostatic Imbalances
Hepatits inflammation of liver Causes: viruses, drugs, alcohol, chemicals Viral Hepatitis: A: hep A virus spread by fecal contamination  orally mild in children & young adults jaundice, malaise , anorexia, nausea, diarrhea, fever, chills resolves 4 – 6 wks NO lasting damage

120 GI Tract Homeostatic Imbalances
Hepatitis B Hep B virus spread thru body fluids: sexual contact, contaminated needles or transfusion equipment tears, saliva, can be present a lifetime  cirrhosis or ca of liver vaccines available Hepatitis C hep C virus similar to hep B

121 GI Tract Homeostatic Imbalances
Hepatitis D hep D virus person must already be infected with hep B to get hepD severe liver damage higher fatality rate than hep B alone Hepatitis E Hep E spread like Hep A No liver damage has high mortality in pregnant women

122 Medial Terminology Cirrhosis:
scarred liver due to chronic inflammation due to hepatitis, chemicals, parasites, or alcoholism jaundice, swelling of lower limbs, uncontrolled bleeding, increased sensitivity to drugs Dysphagia: difficulty swallowing due to inflammation, paralysis, obstruction, trauma

123 Medical Terminology Halitosis: bad breath Hernia:
protrusion of all or part of an organ thru a membrane or cavity wall hiatal hernia umbilical hernia inguinal hernia

124 Medical Terminology Nausea:
discomfort characterized by loss of appetitie & sensation of impending vomiting caused by local irritation of GI tract, some other systemic disease, brain trauma, overexertion, or 2° to meds/drugs Irritable Bowel Syndrome (IBS): involves entire GI tract stress-related abd pain or cramping ass’c with alternating diarrhea/constipation

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