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Anatomy and Physiology, Sixth Edition
Rod R. Seeley
Idaho State University
Trent D. Stephens
Idaho State University
Philip Tate
Phoenix College
Chapter 24
Lecture Outline*
*See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes.
24-1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 24
Digestive System
24-2
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
24-3
Functions
• Ingestion: Introduction of food into stomach
• Mastication: Chewing
• Propulsion
– Deglutition: Swallowing
– Peristalsis: Moves material through digestive tract
24-4
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
24-5
Digestive Tract Histology
24-6
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
24-7
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
24-8
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
24-10
Teeth
24-11
Salivary Glands
• Produce saliva
– Prevents bacterial
infection
– Lubrication
– Contains salivary
amylase
• Breaks down starch
• Three pairs
– Parotid: Largest
– Submandibular
– Sublingual: Smallest
24-12
Pharynx and Esophagus
• Esophagus
• Pharynx
– Nasopharynx
– Oropharynx: Transmits
food normally
– Laryngopharynx:
Transmits food
normally
– Transports food from
pharynx to stomach
– Passes through
esophageal hiatus
(opening) of diaphragm
and ends at stomach
• Hiatal hernia
– Sphincters
• Upper
• Lower
24-13
Deglutition (Swallowing)
• Three phases
– Voluntary
• Bolus of food moved by tongue from oral cavity to
pharynx
– Pharyngeal
Reflex: 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
24-14
Phases of Deglutition (Swallowing)
24-15
Stomach Anatomy
• Openings
– Gastroesophageal: To
esophagus
– Pyloric: To duodenum
• Regions
–
–
–
–
Cardiac
Fundus
Body
Pyloric
24-16
Stomach Histology
• Layers
– Serosa or visceral
peritoneum: Outermost
– Muscularis: Three layers
• Outer longitudinal
• Middle circular
• Inner oblique
– Submucosa
– Mucosa
24-17
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
24-18
Hydrochloric Acid Production
24-19
Phases of Gastric Secretion
24-20
Movements in Stomach
24-21
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
24-23
Duodenum and Pancreas
24-24
Duodenum Anatomy and
Histology
24-25
Liver
• Lobes
– Major: Left and right
– Minor: Caudate and
quadrate
• Ducts
– Common hepatic
– Cystic
• From gallbladder
– Common bile
• Joins pancreatic duct at
hepatopancreatic ampulla
24-26
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
24-27
Blood and Bile Flow
24-28
Duct System
24-29
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
24-30
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
24-31
Bicarbonate Ion Production
24-32
Pancreatic Secretion Control
24-33
Large Intestine
• Extends from ileocecal junction to anus
• Consists of cecum, colon, rectum, anal canal
• Movements sluggish (18-24 hours)
24-34
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
24-35
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
24-36
Histology of Large Intestine
24-37
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
24-38
Reflexes in Colon and Rectum
24-39
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
24-40
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
24-41
Lipids
• Include triglycerides, phospholipids, steroids, fat-soluble
vitamins
• Emulsification breaks down large lipid droplets to small
24-42
Lipoproteins
• Types
– Chylomicrons
• Enter lymph
– VLDL
– LDL
• Transports cholesterol
to cells
– HDL
• Transports cholesterol
from cells to liver
24-43
Proteins
• Pepsin breaks proteins into smaller polypeptide chains
• Proteolytic enzymes produce small peptide chains
– Dipeptides, tripeptides, amino acids
24-44
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
24-45
Effects of Aging
• Decrease in mucus layer, connective tissue,
muscles and secretions
• Increased susceptibility to infections and
toxic agents
– Ulcerations and cancers
24-46