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