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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