4 basic digestive processeshomepages.wmich.edu/~clinn/teaching/bios6130/lecture...biliary system 5 4...
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Animal Physiology
BIOS 6130
Organic molecules + oxygen ATP + carbon dioxide and water
4 basic digestive processes
• Motility
• Secretion• Secretion
• Digestion
• Absorption
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Categories of food
• Carbohydrates
• Proteins• Proteins
• Fats
All of these are large molecules that can’t be absorbed as is. They must be broken down into smaller molecules to be absorbed into the circulatory system.
Digestion• Carbohydrates (starch and cellulose) are
hydrolyzed into glucose molecules.
• Proteins are hydrolyzed into amino acids
• Fats are hydrolyzed into monoglycerides and free fatty acids
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Digestion of carbohydrates• Starches contain α
bonds between the glucose units.
• Cellulose contains β bonds between glucose units that are derived from plant sources.
Cellulose digestion is the result of:
• Symbiotic microorganisms that proliferate in the digestive tract
• necessary enzymes (cellulases) that catabolize cellulose
Animals can be classified according to their primary feeding methods:
• Carnivores
• HerbivoresIn cow and deer, microbes and cellulase necessary to break down cellulose, proliferate in a fermentation vat in the foregut called the rumen. The rumen is one of 4 compartments that together make up the stomach.
• Omnivores
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Vertebrate digestive tracks
that show progressive anatomicanatomic
specialization for digestion
Digestive System in humans
• Composed of digestive tract and accessory organs:
Salivary glands
Exocrine glands
Biliary system
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4 factors involved to ensure that the digestive system functions
properly:• Autonomic smooth muscle function
I t i i l i• Intrinsic nerve plexis
• Extrinsic nerves
• Gastrointestinal hormones
Nerve plexusAn interconnecting network of nerve cells
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Extrinsic nerves to the various digestive organs in the digestion system:
Sympathetic fibers
Parasympathetic fibers
Function of extrinsic innervation to the digestive organs
Modify ongoing activity in the intrinsic plexusp
Alter the level of gastrointestinal hormone secretion
Act directly on smooth muscle and glands
Gastrointestinal hormones:
Endocrine gland cells found in the mucosa of certain regions of the digestive tract
Gastrointestinal hormones are released inGastrointestinal hormones are released in response to specific local changes in luminal contents
Gastrointestinal hormones act directly on endocrine gland cells or indirectly through the enteric nervous system
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First stop:
The mouth
Salivary proteins
Amylase
MucusMucus
Lysozyme
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Swallowing
Next stop:
The esophagus
Sphincter’s of the esophagus
Pharyngeoesophageal sphincter
Gastroesophageal sphincter
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Peristalsis
Ring-like contractions of circular smooth muscle in the esophagus that moves the food
fbolus forward
Next stop:
The stomach
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The gastric digestive secretions released in the stomach lumen from
exocrine glands are:
• HCl (Released from Parietal cells)
I t i i f t (R l d f P i t l ll )
• Pepsinogen (Released from Chief cells)
• Intrinsic factor (Released from Parietal cells)
• Mucus (Released from mucous cells in walls of gastric pit and from surface epithelial cells)
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Gastric secretions released into the blood from endocrine glands in the
gastric pit include:Histamine (Released from ECL cells from oxyntic mucosa.
Causes release of HCl from parietal cells)
Gastrin (Released from G cells in pyloric gland area. Stimulates parietal, chief and ECL cells)
Somatostatin (Released from D cells in pyloric gland area. Inhibits parietal, G and ECL cells)
Two separate digestive processes take place in the stomach
Pepsin begins protein digestion
Amylase found in center of food bolus continues carbohydrate
•• No food or water is absorbed into the No food or water is absorbed into the blood from the stomach mucosa!blood from the stomach mucosa!
Amylase found in center of food bolus continues carbohydrate digestion
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Next stop:
The small intestines
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Pancreatic exocrine cells
Secrete enzymes from the acinar cells:Proteolytic enzymes
Pancreatic amylase
Pancreatic lipase
Secrete sodium bicarbonate
Pancreatic exocrine cell regulation
Secretin
Cholecystokinin (CCK)
Biliary SystemLiver
Gallbladder
Associated ducts
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Hepatic portal system
Circulation through the liver
Bile• Bile salts
• Cholesterol
• Lecithin
• Bilirubin
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Bile SaltsDerivatives of cholesterol
iBreaks up fat molecules through detergent action (emulsification)
Facilitate fat absorption (micelles)
Function:
Small Intestines
• Duodenum• Jejunum• Ileum• Ileum
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Functions of Segmentation
Mixes chyme
Exposes chyme to the absorptive surface of the p y psmall intestines mucosa
Moves the chyme slowly forward
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Next stop:
The large intestines
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Function of the colon
Water and salt absorption
S f f f iStore feces before defecation
Last stop:
The anus
How are feces eliminated form the body?
• The defecation reflex– Internal anal sphincter– External anal sphincter