The Digestive System Chapter 23 Anatomy of the Digestive System – Part 3.
Digestive System Part 3
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Transcript of Digestive System Part 3
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Small Intestine• Duodenum:
smallest section– Stomach empties
here• Jejunum: middle
section• Ileum: final section– Joins large intestine
at ileocecal sphincter
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Small Intestine• 21 feet of small intestine with added
structures to increase surface area– Almost all absorption occurs here
• Circular folds: folds in the mucosa to splash chyme and enhance absorption
• Villi: fingerlike projections that contain capillaries, arteries, veins, all to move absorbed substances quickly
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Small Intestine• Microvilli:
smaller projections on the villi to further increase surface area and absorption
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Small Intestine• Intestinal glands: in mucosa that
secrete intestinal juice– Clear, yellowish liquid quickly
reabsorbed– pH 7.6 with water and mucous– Enzymes for Chemical Digestion:• Maltase, sucrose, lactase: disac. To monosa.• Peptidases: peptides to amino acids• Ribonuclease, dioxyribonuclease: nucleic
acids
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Small Intestine• Mechanical Digestion: – Segmentation: Concentration of chyme
and juice that sloshes between areas of contraction of the muscularis
– Perstalsis: moves the chyme steadily through intestines
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Absorption in Small Intestine• Passage of digested substances and
nutrients from the lumen to into the blood or lymph
• 90% of all absorption takes place here
• Substances absorbed by diffusion, osmosis, and active transport
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Absorption in Small Intestine• Carbohydrates absorbed as
monosaccharides• Proteins absorbed as amino acids • Lipids absorbed as monoglycerides
and fatty acids• Water —9 liters enter daily and 8
are reabsorbed
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Large Intestine• Main functions:– Completion of
absorption– Manufacture certain
vitamins– Formation of feces– Elimination of feces
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Large Intestine• Cecum: pouch after ileocecal sphincter• Colon: ascending, transverse, descending,
sigmoid– Surface area increased by pouch-like divisions: haustra
• Rectum: last part, stores waste– Last inch is anal canal
• Anus: opening to exterior– Two sphincters: internal anal sphincter
(involuntary), external anal sphincter (voluntary)
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Chemical Digestion of Lrg. Intestine
• No enzymes• Bacteria ferment remaining
carbohydrates– Release hydrogen, carbon dioxide, and
methane • Vitamins K and some B’s are made
and absorbed
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Mechanical Digestion of Lrg. Intestine
• Haustral churning: walls contract when haustra fill to a certain level
• Peristalsis: slower than other areas• Mass peristalsis: strong muscular
wave that pushes waste into the rectum
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Absorption & Feces Formation• Chyme in the colon for 3-10 hrs.
becomes rather solid: feces– Water, epithelial cells from mucosa,
bacteria, undigested food
• All but 100mL of the 1L of water is absorbed
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Defecation• Emptying of the rectum• Diarrhea: not enough water is
absorbed because chyme travels too quickly through intestine– Can cause dehydration
• Constipation: feces remains in colon too long, almost all the water is absorbed
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Digestive System Attachments• Peritoneum & serosa: secrete slippery fluid to
glide organs over each other – Outermost layer of GI tract
• Visceral peritoneum: covers some organs in abdominal cavity
• Parietal peritoneum: the walls of the abdominal cavity
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Digestive System Attachments• Mesentery: binds small intestine to
posterior abdominal wall• Mesacolon: binds large intestine to
posterior abdominal wall• Falciform ligament: attaches liver to
the anterior abdominal wall and diaphragm
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Digestive Disorders• Ulcers: lesions in a membrane– Peptic —from gastric juice– Gastric —in stomach– Esophageal —in esophagus– Duodenal —in small intestine
• Appendicitis: inflammation of appendix
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Digestive Disorders• Cirrhosis: scarred liver due to chronic
inflammation• Colitis: inflammation of colon and
rectum• Hernia: protrusion of an organ through a
membrane or cavity wall