Overview of the Digestive System

Digestive Tract: Mouth, pharynx, and esophagus, stomach, small intestine, and large intestine (colon)

Accessory Organs:Teeth, tongue, salivary glands, pancreas, liver, and gallbladder

Functions of the Digestive System

• Ingestion• Mechanical

processing• Chemical

digestion• Secretion• Absorption• Excretion

Histology of the Digestive Tract

Mucosa

Submucosa

Muscularis Externa

Serosa

Mucosa (Innermost Layer)

• Epithelium• Connective

Tissue (Blood vessels, lymphatic vessels, lymphatic nodules)

• Smooth Muscle

Submucosa

Connective tissue

• Blood vessels

• Lymphatic vessels

• Nerve plexus

• May have glands and lymphatic tissue

Muscularis ExternaSmooth or Skeletal Muscle

If smooth muscle, usually 2 layers (circular and longitudinal)

Adventitia or Serosa

Adventitia (organs superior to diaphragm)

Serosa = visceral peritoneum

Small Intestine: Peyer’s Patches

Components of the Digestive System

GI Tract:

•Oral Cavity•Pharynx•Esophagus•Stomach•Small Intestine•Large Intestine

Oral Cavity

Oral Cavity

The Pharynx

• Nasopharynx

• Oropharynx

• Laryngopharynx

The Esophagus

The Esophagus

• Stratified squamous epithelium

• Mucous glands

• Muscularis externa – skeletal muscle first third of length

Peristalsis in EsophagusLE 21-8

Bolus offood

Muscles relax,allowingpassagewayto open

Stomach

Musclescontract,constrictingpassagewayand pushingbolus down

Musclesrelax

Muscles contract

Muscles relax

Muscles contract

Stomach

• Site where food is churned into chyme

• Protein digestion begins

Stomach

Stomach

Stomach – Microscopic Anatomy

Stomach – Microscopic Anatomy

The Stomach – Microscopic Anatomy

Ulcers in stomach

Helicobacter pylori

Small Intestine – Gross Anatomy• Longest portion of

the alimentary canal

• Site of most enzymatic digestion and absorption

• Three subdivisions• Duodenum,

jejunum, and ileum

Duodenum and Related OrgansLE 21-11a

LiverBile

Gall-bladder

Bile

Duodenum ofsmall intestine

Acid chyme

Pancreaticjuice

Intestinal enzymes

Stomach

Pancreas

Duodenum and Related Organs

Enzymes in Small Intestine

Small Intestine – Microscopic Anatomy

LE 21-11b

Veinwith blooden route tothe liver

Musclelayers

Lumen

Largecircular folds

Villi

Nutrientabsorption

Lymphvessel

Intestinal wall

Villi

Bloodcapillaries

Epithelialcells

Nutrientabsorption

Lumen of intestine

Epithelial cells

Lymph

Blood

Fats

Aminoacidsand

sugars

Fattyacidsand

glycerol

Nutrient absorptioninto epithelial cells

Microvilli

Small Intestine: Duodenum

Br = Brunner glands

V = Villus

G = Goblet cells

Cr = Intestinal glands

MM = Muscularis Mucosae

LP = Lamina Propria

The Small Intestine – Structural Features

Gross Anatomy of Large Intestine

•Cecum

•Appendix

•Ascending

•Transverse

•Descending

•Sigmoid colon

•Rectum

•Anus

LE 21-12

Largeintestine(colon)

Sphincter

Endof smallintestine

Nutrientflow

Appendix

Cecum

Anus

Rectum

Smallintestine

Gross Anatomy of Large Intestine• Rectum – descends along the inferior half of the

sacrum

• Anal Canal – the last subdivision of the large intestine

Gross Anatomy of Large Intestine

Microscopic Anatomy of Large Intestine

• Villi are absent

• Contains numerous goblet cells

• Intestinal crypts – simple tubular glands

• Lined with simple columnar epithelial tissue

• Epithelium changes at anal canal• Becomes stratified squamous epithelium

Microscopic Anatomy of Large Intestine

Teeth

Salivary Glands

Pancreas

Exocrine Pancreas: Histology

Liver

• Largest gland in the body

• Performs over 500 functions

• Digestive function – bile production

• Performs many metabolic functions

Visceral Surface of the Liver

Microscopic Anatomy of Liver

Microscopic Anatomy of Liver

Gallbladder• Stores and concentrates bile

• Expels bile into duodenum• Bile emulsifies fats

Gallbladder

Enzymes in Small Intestine

The Peritoneal Cavity and Peritoneum• Mesentery – a

double layer of peritoneum• Holds organs in

place

• Sites of fat storage

• Provides a route for circulatory vessels and nerves

Mesenteries

• Superficial view of the abdominal organs

Mesenteries

• Greater omentum and transverse colon reflected

Mesenteries

• Sagittal section through the abdominopelvic cavity

Segmentation

• Rhythmic local contractions of the intestine

• Mixes food with digestive juices

Disorders of the Digestive System

• Intestinal obstruction • Mechanical obstructions

• Adhesions, tumors, or foreign objects

• Nonmechanical obstruction • Halt in peristalsis

• Trauma

• Intestines touched during surgery

Disorders of the Digestive System

• Inflammatory bowel disease • Inflammation of intestinal wall

• Crohn’s disease

• Ulcerative colitis

• Viral hepatitis – jaundice and flu-like symptoms • Major types – A, B, C, and G

• Cystic Fibrosis and the Pancreas

The Digestive System in Later Life

• Middle age – gallstones and ulcers

• Old age – activity of digestive organs decline• Fewer digestive juices and enzymes produced

• Absorption is less efficient

• Dehydration of fecal mass leads to constipation

• Diverticulosis and cancer of digestive organs