Physiology 2130 Study Guide - Final Guide: Common Bile Duct, Pancreatic Lipase Family, Stomach

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2 Feb 2016
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Physiology TEST 4
Gastrointestinal and Metabolism
4 processes of the digestive system:
1) digestion: mechanical and chemical breakdown of food
2) absorption: active or passive transfer of substances from lumen of the GI tract to
ECF
3) Motility: movement of material along GI tract
4) Secretion: release of substances from salivary glands, GI epithelial cells,
hepatocytes or pancreatic acinar cells into the GI tract lumen or EFG
*see book for anatomy of digestive system
Mouth:
-beginning point of digestion (mechanical breakdown) of food but no absorption
of nutrients here
-saliva secreted made of water, proteins and ions secreted by 3 exocrine glans
-major component of saliva is mucus produced by serous cells
-salivary glands are converging duct system (similar to pancrease) where multiple
ducts flow into 1 main duct
3 Salivary Glands:
1) Paratoid gland- secretes watery liquid that contains salivary amylase
2) Submandular gland- secretes thicker liquid that contains mucus and amylase
3) Sublingual gland- secretes more mucus and less amylase
Regulation of Salivary Secretions:
-Regulated by neuropathways only
-Positively regulated by both parasym and sympathetic pathways
-PSYN= major pathway to stimulate saliva secretion and initiates and sustains high
levels of saliva secretion
-SYN= cant initiate salivation, but can potentiate effects of PSYN
Mastication: the mechanical manipulation of food into a lump of food called BOLUS.
Chemical digestion also begins in the mouth with secretion of salivary amylase and
lingual lipase
3 stages of swallowing:
1) Voluntary- movement of bolus to the oropharynx
2) Pharyngeal - involuntary closure of the larynx (so doesn’t go down wind pipe)
3) Esophageal- involuntary passage of bolus into stomach
Peristalsis: movement of bolus down esophagus to stomach by progressions of
coordinated contractions and relaxations of both circular and longitudinal muscles. Under
control by medulla oblongata, and is involuntary. Secondary peristalsis initiated to move
lodged food.
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Stomach:
-acts as a reservoir for food before it enters the intestines to be absorbed
-bolus is liquefied to enhance enzymatic digestion
-2-3 L gastric juices are secreted a day (from exocrine type gland cells in stomach)
-*see anatomy of stomach in book
3 Types of Exocrine Cells in the Stomach:
1) Mucus neck cells- secretes mucus and bicarbonate
2) Chief cells- secretes pepsinogen and gastric lipase
3) Parietal cells (oxyntic)- intrinsic factor, H+ and Cl (HCl)
Enteroendocrine Cells: G Cells- secretes gastrin involved in motility and function
4 Layers of the Stomach:
1) Mucosa- first main layer, epithelium and lamina with thin layer of smooth muscle
separation from submucosa (gastric pits)
2) Submucosa- layer under mucosa made of fibrous connective tissue. Separates
mucosa from smooth muscle
3) Smooth muscle- 2 layers of smooth muscle responsible for motility (superficial
circular and deeper longitudinal)
4) Serosa- strong connective tissue, layer over smooth muscle, maintains shape and
protects
Digestion in the Stomach:
Mechanical Digestion: (Bolus to Chyme)
-gentle mixing of bolus gastric secretions generated every 15-25 seconds
-propulsion towards the pyloric sphincter
-some chime moves into duodenum, most returns to stomach for further mixing
Chemical Digestion:
-acidic gastric juices inactivate the salivary amylase and activate the lingual lipase
-production of HCl essential as pH of stomach ether activates or inactivates these
enzymes
-pepsinogen inactive protein that must contact with acid to produce active enzyme
called pepsin (responsible for beginning protein digestion in stomach)
-protein digestion begins in stomach (HCl secretion=pepsin production)
-carbohydrate digestion which began in mouth is halted
-lipid digestion begins thru activation on lingual lipase
Acid in the stomach:
-activates lingual lipase and pepsin
-inactivates salivary amylase
-kills microbes
-denatures proteins stimulates
-secretion of hormones
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Pancreas: an organ with essential endocrine and exocrine functions. Connects pancreas
to the small intestine (duodenum) by 2 ducts
Exocrine Secretions of Pancreas:
1) Bicarbonate
2) Pancreatic Amylase
3) Chymotrypsinogen to Chymotrypsin
4) Trypsinogen to trypsin
5) Procarboxypeptidase to carboxypeptidase
6) Pancreatic Lipase
Endocrine Secretions of Pancreas:
1) Insulin
2) Glucagon
3) Somatostatin
Functions of the Liver:
1) synthesis of bile salts
2) excretion of bilirubin
3) metabolism of carbohydrates, lipids and proteins
4) processing of drugs and hormones
*main type of liver cell are hepatocytes which secrete bile*
Bile Components: bile salts, cholesterol, bile pigments (bilirubin), water and ions
Gall Bladder: pear shaped sac that lies behind liver. Connected to liver by cyctic duct
forming common bile duct. The sphincter of Oddi closes off the common bile duct from
small intestine (bile moves to gall bladder for storage at these times)
Intestines:
3 regions of small intestine:
1) Duodenum- most important for digestion, 12 inches long containing many
endocrine cells and chemo and mechanoreceptors. Functions to regulate digestion
and absorption
2) Jejunum- most nutrient absorption occurs here (3 feet, large SA for ab) ability to
do so is amplified by number and length of villi and microvilli
3) Ileum- less nutrient absorption (less villi) but does absorb specific molecules like
bile. Can absorb more nutrients if necessary
4 layers of the small intestine:
1) Mucosa- single layer of epithelial cells (for absorption) at surface, connective
tissue, small blood vessels and lacteals (pick up fat)
2) Submucosa- connective tissue, submucosal plexus
3) Muscularis- longitudinal and circular smooth muscle, myenteric plexus
4) Serosa- connective tissue
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