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cells to systems The Gastrointestinal System (Dr brown) (11 major…
cells to systems The Gastrointestinal System (Dr brown)
6 functions of the digestive system:
Mixing and propulsion
Secretion of water, acid, buffers, and enzymes into lumen
Absorption – passing into blood or lymph
Ingestion
Defaecation – elimination of feces
Digestion:
Mechanical digestion churns food
Chemical digestion – hydrolysis
Cells of the gastric mucosa: - The gastric mucosa is protected by a layer of alkaline mucous secreted by the surface and mucous neck cells
Over view of the GI tract functions:
Mouth---bite, chew, swallow
Pharynx and oesophagus----transport
Stomach----mechanical disruption; absorption of water & alcohol
Small intestine--chemical & mechanical digestion & absorption
Large intestine----absorb electrolytes & vitamins (B and K)
Rectum and anus---defecation
11 major structures of the digestive system:
Ascending colon
Transverse colon
Ileum
Descending colon
Jejunum
Sigmoid colon
Duodenum
Rectum
stomach
Anus
1.Oesophagus
Small intestines
Large intestine
Major valves (sphincter):
Oesophagus
Upper oesophageal sphincter
Pharynx and oesophagus
Lower oesophageal sphincter
Oesophagus and stomach
Stomach
Cardiac sphincter (LOS)
Oesophagus and stomach
Pyloric sphincter
Stomach and duodenum
Small intestine
Sphincter of Oddi
Large intestine valves (sphincters):
Ileocaecal sphincter – ileum and caecum
Internal anal sphincter – involuntary smooth muscle
External anal sphincter – voluntary skeletal muscle
The small intestine:
Microvilli are microscopic folds in the apical surface of the plasma membrane on each simple columnar cell (about 200 million/mm2).
The plicae circulares,
villi, and microvilli all
contribute to increase
the surface area of the
small intestine, allowing
for maximum absorption of nutrients.
Special structural features increase surface area for digestion and absorption in the small intestine:
Circular folds (plicae circulares)
Permanent ridges of mucosa and submucosa
Cause chyme to spiral
Villi
Fingerlike projections of mucosa
Contains arteriole, venule, blood capillary, and lacteal
Microvilli
Projects of apical membrane of absorptive cells
Brush border with brush border enzymes
Brush border:
Digestive enzymes attached to the microvilli complete the digestive process of carbohydrates and proteins, called a brush border.
Give the appearance of a brush when viewed under an electron microscope.
Regulation of acid secretion:
H2 antagonists
Cimetidine
Ranitidine
Famotidine
Proton pump inhibitors
Omeprazole
Pantoprazole
Rabeprazole