Human Anatomy and Physiology Secretory functions of the alimentary tract.
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Transcript of Human Anatomy and Physiology Secretory functions of the alimentary tract.
![Page 1: Human Anatomy and Physiology Secretory functions of the alimentary tract.](https://reader036.fdocuments.in/reader036/viewer/2022081420/56649e585503460f94b519b4/html5/thumbnails/1.jpg)
Human Anatomy and Physiology
Secretory functions of the alimentary tract
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Secretion from tract
Daily volume (liters)
pH
Saliva 1.0 6 – 7
Gastric secretion 1.5 1.0 – 3.5
Pancreatic secretion 1.0 8.0 – 8.3
Bile 1.0 7.8
Small intestine secretion 2.0 7.5 – 8.0
Large intestine secretion 0.2 7.5 – 8.0
TOTAL 6.7
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Phases of digestion
Cephalic: before food enters the stomach
Gastric: events in the stomach Intestinal: events in the intestine
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Saliva
Parotid, submandibular, sublingual Secretions initiated in cephalic phase by parasympathetic
influence Composition
99.5% water, 0.5% protein and electrolytes Protein: amylase, mucus, lysozyme
Functions Water: softens food Amylase: polysaccharide breakdown Mucus: lubrication Lysozyme: kills bacteria
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Esophageal secretion
Mucus Provides lubrication for swallowing Transit time is about 10 seconds
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Gastric secretions
1. HCl By parietal cells
A. Cephalic phase HCl secreted
B. Gastric phase Breakdown proteins to peptides More distention = more HCl release Protein + HCl = gastrin release Gastrin increase HCl release Beneficial positive feedback
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Gastric secretions 2. Pepsinogen - gastric phase
Stored in chief cells as zymogen granules
pepsinogen pepsin
HCl HCO3
affectnullified
stomach small intestine
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Gastric secretions C. Intestinal phase
Inhibits gastric secretions - 3 mechanisms Decrease parasympathetic stimulation Local reflex action Release of secretin, GIP and cholecystokinin
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Gastric secretions 3. Mucus
Goblets cells Functions
Prevents mechanical injury Self digestion against pepsin Neutralizes HCl
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Inhibitors of gastric motility 1. Gastric inhibitory peptide (GIP)
Released from duodenal mucosa Stimulus is fat and sugars in duodenum Decreases gastric motility and secretions
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Inhibitors of gastric motility 2. Secretin
Released from duodenal mucosa Stimulus is high acidity in duodenum Decreases gastric motility Increases pancreas secretions
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Inhibitors of gastric motility 3. Cholecystokinin
Released from duodenal mucosa Stimulus is presence of lipid and protein Decreases gastric motility Increases pancreas secretions
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Pancreas Location and anatomy (acinar and duct cells)
Ductcells
Acinarcells
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Acinar cell secretions
Proteolytic enzymes (trypsin, chymotrypsin carboxypeptidase) Peptides
Lipase Fatty acids and monoglycerides
Amylase Disaccharides: Lactose and maltose
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Duct epithelial cell secretion Bicarbonate ions
Function: neutralizes stomach acidity
Ductcells
Acinarcells
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Hormones effecting pancreatic secretion
1. Secretin Secreted by duodenal mucosa In response to high [H+] Increases bicarbonate secretion
2. Cholecystokinin Secreted by duodenal mucosa In response to fat and protein Increases total amount of enzymes secreted
3. Acetylcholine Released from parasympathetic influence
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Liver Bile
Bile salts, bicarbonate, lecithin, water
Functions Bile salt and water: emulsifies lipid Lecithin: prevent reaggregration of emulsification Bicarbonate: neutralizes gastric HCl
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Hormone effecting bile release
Cholecystokinin Released into blood by presence of fats (and
protein) in duodenum Causes gall bladder release of bile Causes Sphincter of Oddi to relax
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Small intestine secretions
Crypts of Lieberkühn Mucus (Brunner’s glands) and aqueous salt
Functions Lubrication and protection
from stomach acid Aid in enzyme breakdown
of chyme
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Large intestine secretions
Crypts of Lieberkühn without villi secretes mucus
Functions Protection against abrasion Holds feces together Protection against bacterial
activity