Overview of the Digestive System

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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

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Functions of the Digestive System

• Ingestion
• Mechanical processing
• Chemical digestion
• Secretion
• Absorption
• Excretion

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Histology of the Digestive Tract
Mucosa Submucosa Muscularis Externa Serosa
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Mucosa (Innermost Layer)

• Epithelium
• Connective Tissue (Blood vessels, lymphatic
  vessels, lymphatic nodules)
• Smooth Muscle

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Submucosa

• Connective tissue
• Blood vessels
• Lymphatic vessels
• Nerve plexus
• May have glands and lymphatic tissue

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Muscularis Externa

• Smooth or Skeletal Muscle
• If smooth muscle, usually 2 layers (circular and
  longitudinal)

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Adventitia or Serosa

• Adventitia (organs superior to diaphragm)
• Serosa visceral peritoneum

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Small Intestine Peyers Patches
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Components of the Digestive System

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

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Oral Cavity
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Oral Cavity
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The Pharynx

• Nasopharynx
• Oropharynx
• Laryngopharynx

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The Esophagus
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The Esophagus

• Stratified squamous epithelium
• Mucous glands
• Muscularis externa skeletal muscle first third
  of length

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Peristalsis in Esophagus
LE 21-8
Muscles contract
Muscles contract, constricting passageway and
pushing bolus down
Muscles relax
Bolus of food
Muscles relax, allowing passageway to open
Muscles contract
Muscles relax
Stomach
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Stomach

• Site where food is churned into chyme
• Protein digestion begins

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Stomach
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Stomach
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Stomach Microscopic Anatomy
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Stomach Microscopic Anatomy
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The Stomach Microscopic Anatomy
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Ulcers in stomach
Helicobacter pylori
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Small Intestine Gross Anatomy

• Longest portion of the alimentary canal
• Site of most enzymatic digestion and absorption
• Three subdivisions
• Duodenum, jejunum, and ileum

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Duodenum and Related Organs
LE 21-11a
Liver
Bile
Gall- bladder
Stomach
Bile
Pancreas
Acid chyme
Intestinal enzymes
Pancreatic juice
Duodenum of small intestine
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Duodenum and Related Organs
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Enzymes in Small Intestine
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Small Intestine Microscopic Anatomy
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LE 21-11b
Lumen of intestine
Nutrient absorption
Vein with blood en route to the liver
Nutrient absorption into epithelial cells
Microvilli
Epithelial cells
Amino acids and sugars
Fatty acids and glycerol
Lumen
Muscle layers
Fats
Blood capillaries
Large circular folds
Blood
Villi
Lymph vessel
Lymph
Nutrient absorption
Epithelial cells
Villi
Intestinal wall
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Small Intestine Duodenum
Br Brunner glands V Villus G Goblet
cells Cr Intestinal glands MM Muscularis
Mucosae LP Lamina Propria
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The Small Intestine Structural Features
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Gross Anatomy of Large Intestine

• Cecum
• Appendix
• Ascending
• Transverse
• Descending
• Sigmoid colon
• Rectum
• Anus

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LE 21-12
Large intestine (colon)
Small intestine
Sphincter
End of small intestine
Rectum
Anus
Nutrient flow
Appendix
Cecum
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Gross Anatomy of Large Intestine

• Rectum descends along the inferior half of the
  sacrum
• Anal Canal the last subdivision of the large
  intestine

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Gross Anatomy of Large Intestine
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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

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Microscopic Anatomy of Large Intestine
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Teeth
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Salivary Glands
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Pancreas
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Exocrine Pancreas Histology
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Liver

• Largest gland in the body
• Performs over 500 functions
• Digestive function bile production
• Performs many metabolic functions

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Visceral Surface of the Liver
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Microscopic Anatomy of Liver
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Microscopic Anatomy of Liver
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Gallbladder

• Stores and concentrates bile
• Expels bile into duodenum
• Bile emulsifies fats

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Gallbladder
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Enzymes in Small Intestine
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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

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Mesenteries

• Superficial view of the abdominal organs

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Mesenteries

• Greater omentum and transverse colon reflected

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Mesenteries

• Sagittal section through the abdominopelvic cavity

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Segmentation

• Rhythmic local contractions of the intestine
• Mixes food with digestive juices

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Disorders of the Digestive System

• Intestinal obstruction
• Mechanical obstructions
• Adhesions, tumors, or foreign objects
• Nonmechanical obstruction
• Halt in peristalsis
• Trauma
• Intestines touched during surgery

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Disorders of the Digestive System

• Inflammatory bowel disease
• Inflammation of intestinal wall
• Crohns disease
• Ulcerative colitis
• Viral hepatitis jaundice and flu-like symptoms
• Major types A, B, C, and G
• Cystic Fibrosis and the Pancreas

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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