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
Digestive Tract Histology
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
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
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
Teeth
� Two sets
� Primary, deciduous,
milk: Childhood
� Permanent or
secondary: Adult (32)
� Types
� Incisors, canine,
premolar and molars
Tooth structure:
Salivary Glands
� Produce saliva
� Prevents bacterial
infection
� Lubrication
� Contains salivary
amylase
� Breaks down starch
� Three pairs
� Parotid: Largest
� Submandibular
� Sublingual: Smallest
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
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
Phases of Deglutition
(Swallowing)
Functions� Ingestion: Introduction of food into stomach
� Mastication: Chewing
� Propulsion
� Deglutition: Swallowing
� Peristalsis: Moves material through digestive tract
Stomach Anatomy:
� Openings
� Gastroesophageal:
To esophagus
� Pyloric: To
duodenum
� Regions
� Cardiac
� Fundus
� Body
� Pyloric
Stomach Histology:
� Layers
� Serosa or visceral
peritoneum:
Outermost
� Muscularis: Three
layers
� Outer longitudinal
� Middle circular
� Inner oblique
� Submucosa
� Mucosa
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
Hydrochloric Acid Production
Phases of Gastric
Secretion
Movements in Stomach
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
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
Duodenum and Pancreas
Duodenum Anatomy and
Histology
Liver
� Lobes
� Major: Left and right
� Minor: Caudate and
quadrate
� Ducts
� Common hepatic
� Cystic
� From gallbladder
� Common bile
� Joins pancreatic duct at
hepatopancreatic ampulla
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
Blood and Bile Flow
Duct System
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
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
Bicarbonate Ion Production
Gastric hormones:
Movement in small intestine:
� 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
Large Intestine:
� Extends from ileocecal junction to anus
� Consists of cecum, colon, rectum, anal canal
� Movements sluggish (18-24 hours)
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
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
Histology of Large Intestine
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
Reflexes in
Colon and
Rectum:
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
Figure 24.20a, b
Liver Histology
portal
triad
3. Architecture of the Hepatic
ParenchymaThe hepatic lobule is the structural unit of the liver.
Central vein
Portal vein
Bile duct
Sinusoids
Liver cells (Hepatocytes)Hepatic arteryPortal area
Bile
� Bile acid
� Phospholipids
� Cholesterol
� Bilirubin
� Waste products
� Electrolytes
� Mucin
…each day around 600 ml of bile is produced…
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
Exocrine Pancreas –Enzymes
� Trypsinogen
� Chymotrysinogen
� Carboxypeptidases
� Pro-elastase
� Phospholipase
� pancreatic lipase
� Pancreatic amylase
Bicarbonate Ion Production
Lipoproteins
� Types
� Chylomicrons
� Enter lymph
� VLDL
� LDL
� Transports cholesterol
to cells
� HDL
� Transports cholesterol
from cells to liver
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
Effects of Aging
� Decrease in mucus layer, connective tissue,
muscles and secretions
� Increased susceptibility to infections and toxic
agents
� Ulcerations and cancers