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Anatomy and Physiology, Sixth Edition

Rod R. SeeleyIdaho State UniversityTrent D. StephensIdaho State UniversityPhilip TatePhoenix College

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

*See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes.

Chapter 24Chapter 24

Lecture OutlineLecture Outline**

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Chapter 24

Digestive System

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Digestive System Anatomy• Digestive tract

– Alimentary tract or canal– GI tract

• Accessory organs– Primarily glands

• Regions– Mouth or oral cavity– Pharynx– Esophagus– Stomach– Small intestine– Large intestine– Anus

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Functions• Ingestion: Introduction of food into stomach• Mastication: Chewing• Propulsion

– Deglutition: Swallowing

– Peristalsis: Moves material through digestive tract

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Functions

• Mixing: Segmental contraction that occurs in small intestine• Secretion: Lubricate, liquefy, digest• Digestion: Mechanical and chemical• Absorption: Movement from tract into circulation or lymph• Elimination: Waste products removed from body

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Digestive Tract Histology

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Digestive System Regulation

• Nervous regulation– Involves enteric

nervous system• Types of neurons:

sensory, motor, interneurons

– Coordinates peristalsis and regulates local reflexes

• Chemical regulation– Production of hormones

• Gastrin, secretin

– Production of paracrine chemicals

• Histamine

• Help local reflexes in ENS control digestive environments as pH levels

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Peritoneum and Mesenteries

• Peritoneum– Visceral: Covers organs

– Parietal: Covers interior surface of body wall

– Retroperitoneal: Behind peritoneum as kidneys, pancreas, duodenum

• Mesenteries– Routes which vessels and

nerves pass from body wall to organs

– Greater omentum

– Lesser omentum

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Oral Cavity

• Mouth or oral cavity– Vestibule: Space between

lips or cheeks and alveolar processes

– Oral cavity proper

• Lips (labia) and cheeks• Palate: Oral cavity roof

– Hard and soft

• Palatine tonsils• Tongue: Involved in

speech, taste, mastication, swallowing

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Teeth

• Two sets– Primary, deciduous,

milk: Childhood

– Permanent or secondary: Adult (32)

• Types– Incisors, canine,

premolar and molars

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Teeth

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Salivary Glands

• Produce saliva– Prevents bacterial

infection

– Lubrication

– Contains salivary amylase

• Breaks down starch

• Three pairs– Parotid: Largest

– Submandibular

– Sublingual: Smallest

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Pharynx and Esophagus

• Pharynx– Nasopharynx

– Oropharynx: Transmits food normally

– Laryngopharynx: Transmits food normally

• Esophagus– Transports food from

pharynx to stomach– Passes through

esophageal hiatus (opening) of diaphragm and ends at stomach

• Hiatal hernia

– Sphincters• Upper• Lower

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Deglutition (Swallowing)

• Three phases– Voluntary

• Bolus of food moved by tongue from oral cavity to pharynx

– PharyngealReflex: Upper esophageal sphincter relaxes, elevated

pharynx opens the esophagus, food pushed into esophagus

– Esophageal• Reflex: Epiglottis is tipped posteriorly, larynx

elevated to prevent food from passing into larynx

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Phases of Deglutition (Swallowing)

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Stomach Anatomy

• Openings– Gastroesophageal: To

esophagus

– Pyloric: To duodenum

• Regions– Cardiac

– Fundus

– Body

– Pyloric

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Stomach Histology

• Layers– Serosa or visceral

peritoneum: Outermost

– Muscularis: Three layers• Outer longitudinal

• Middle circular

• Inner oblique

– Submucosa

– Mucosa

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Stomach Histology

• Rugae: Folds in stomach when empty

• Gastric pits: Openings for gastric glands– Contain cells

• Surface mucous: Mucus• Mucous neck: Mucus • Parietal: Hydrochloric

acid and intrinsic factor • Chief: Pepsinogen • Endocrine: Regulatory

hormones

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Hydrochloric Acid Production

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Phases of Gastric Secretion

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Movements in Stomach

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Small Intestine• Site of greatest amount of

digestion and absorption• Divisions

– Duodenum– Jejunum– Ileum: Peyer’s patches or

lymph nodules

• Modifications– Circular folds or plicae

circulares, villi, lacteal, microvilli

• Cells of mucosa– Absorptive, goblet, granular,

endocrine

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Small Intestine Secretions

• Mucus – Protects against digestive enzymes and stomach acids

• Digestive enzymes– Disaccharidases: Break down disaccharides to

monosaccharides– Peptidases: Hydrolyze peptide bonds– Nucleases: Break down nucleic acids

• Duodenal glands – Stimulated by vagus nerve, secretin, chemical or tactile

irritation of duodenal mucosa

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Duodenum and Pancreas

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Duodenum Anatomy and Histology

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Liver

• Lobes– Major: Left and right

– Minor: Caudate and quadrate

• Ducts– Common hepatic

– Cystic• From gallbladder

– Common bile• Joins pancreatic duct at

hepatopancreatic ampulla

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Functions of the Liver• Bile production

– Salts emulsify fats, contain pigments as bilirubin

• Storage– Glycogen, fat, vitamins, copper and iron

• Nutrient interconversion• Detoxification

– Hepatocytes remove ammonia and convert to urea

• Phagocytosis– Kupffer cells phagocytize worn-out and dying red and white blood

cells, some bacteria

• Synthesis– Albumins, fibrinogen, globulins, heparin, clotting factors

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Blood and Bile Flow

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Duct System

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Gallbladder

• Bile is stored and concentrated

• Stimulated by cholecystokinin and vegal stimulation

• Dumps into small intestine

• Production of gallstones possible– Drastic dieting with rapid weight loss

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Pancreas

• Anatomy– Endocrine

• Pancreatic islets produce insulin and glucagon

– Exocrine• Acini produce digestive

enzymes

– Regions: Head, body, tail

• Secretions– Pancreatic juice

(exocrine)• Trypsin• Chymotrypsin• Carboxypeptidase• Pancreatic amylase• Pancreatic lipases• Enzymes that reduce

DNA and ribonucleic acid

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Bicarbonate Ion Production

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Pancreatic Secretion Control

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Large Intestine

• Extends from ileocecal junction to anus

• Consists of cecum, colon, rectum, anal canal

• Movements sluggish (18-24 hours)

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Large Intestine

• Cecum– Blind sac, vermiform appendix attached

• Colon– Ascending, transverse, descending, sigmoid

• Rectum– Straight muscular tube

• Anal canal– Internal anal sphincter (smooth muscle) – External anal sphincter (skeletal muscle)

– Hemorrhoids: Vein enlargement or inflammation

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Secretions of Large Intestine

• Mucus provides protection– Parasympathetic stimulation increases rate of

goblet cell secretion

• Pumps– Exchange of bicarbonate ions for chloride ions– Exchange of sodium ions for hydrogen ions

• Bacterial actions produce gases called flatus

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Histology of Large Intestine

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Movement in Large Intestine

• Mass movements– Common after meals

• Local reflexes in enteric plexus– Gastrocolic: Initiated by stomach

– Duodenocolic: Initiated by duodenum

• Defecation reflex– Distension of the rectal wall by feces

• Defecation– Usually accompanied by voluntary movements to expel feces

through abdominal cavity pressure caused by inspiration

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Reflexes in Colon and Rectum

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Digestion, Absorption, Transport

• Digestion – Breakdown of food molecules for absorption into

circulation • Mechanical: Breaks large food particles to small

• Chemical: Breaking of covalent bonds by digestive enzymes

• Absorption and transport– Molecules are moved out of digestive tract and

into circulation for distribution throughout body

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Carbohydrates

• Consist of starches, glycogen, sucrose, lactose, glucose, fructose• Polysaccharides broken down to monosaccharides• Monosaccharides taken up by active transport or facilitated diffusion and

carried to liver • Glucose is transported to cells requiring energy

– Insulin influences rate of transport

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Lipids

• Include triglycerides, phospholipids, steroids, fat-soluble vitamins

• Emulsification breaks down large lipid droplets to small

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Lipoproteins

• Types– Chylomicrons

• Enter lymph

– VLDL

– LDL• Transports cholesterol

to cells

– HDL• Transports cholesterol

from cells to liver

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Proteins

• Pepsin breaks proteins into smaller polypeptide chains

• Proteolytic enzymes produce small peptide chains

– Dipeptides, tripeptides, amino acids

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Water and Ions

• Water– Can move in either

direction across wall of small intestine depending on osmotic gradients

• Ions– Sodium, potassium,

calcium, magnesium, phosphate are actively transported

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Effects of Aging

• Decrease in mucus layer, connective tissue, muscles and secretions

• Increased susceptibility to infections and toxic agents– Ulcerations and cancers