Lecture 1 Physiology 2nd Semester ~ InfoZone

Introduction To Gastrointestinal Physiology

n DIGESTIVE SYSTEM

n In simple terms, the digestive system is a portal for nutrients to gain access to the circulatory system.

► Foodstuffs are broken down to very simple molecules.

► Resulting sugars, amino acids, fatty acids, etc. are then transported across the GI tract lining into blood.

► The specific foodstuffs animals are able to utilize is dependent on the type of digestive system they possess.

n Three (3) basic types of digestive systems:

► Monogastric – simple stomach.

► Ruminant (cranial fermentor) – multi-compartmented stomach.

► Hind gut (caudal) fermentor – simple stomach, but very large and complex large intestine

Basic Functional Anatomy of the Digestive System

– Monogastrics

n Organs of the Digestive System
– Monogastrics

n Mouth

► Mechanical breakdown of foodstuffs by chewing (reduces particle size, increases surface area for action of enzymes).

► Saliva added as a lubricant and, in some species, contains amylase to begin starch digestion.

► Esophagus

► Tube connecting the mouth to the stomach.

n Stomach

► Enzymatic digestion of proteins begins.

► Foodstuffs reduced to liquid form.

► Liver

► Center of metabolic activity in the body.

► Major role in digestive process is to provide bile salts to small intestine (needed for digestion and absorption of fats).

n Pancreas

► Provides a potent mixture of digestive enzymes to the small intestine to help in digestion of fats, carbohydrates, and proteins.

► Small Intestine

► 3 sections – duodenum, jejunum, ileum

► Site of final stages of chemical enzymatic digestion.

► Where almost all nutrients are absorbed.

n Large Intestine

► 3 sections – cecum, colon, rectum

► Site of water absorption from G.I. tract.

► Bacterial fermentation occurs (production and absorption of volatile fatty acids).

P Somewhat limited in monogastrics

► Feces formed.

Specialized Organs in Poultry

n Beak

► No lips, no teeth, and no chewing.

► Crop

► Out-pocketing of the esophagus that provides storage for consumed food.

► Foodstuffs moistened and softened (little if any digestion).

n Proventriculus

► Glandular stomach where the first significant amount of digestive juices are added.

n Gizzard

► A muscular organ used to grind and break up food.

► May contain grit (small stones) eaten by animal.

n Cloaca

► Common chamber into which the digestive, urinary, and reproductive tracts open.

► When fecal material is excreted, the cloaca folds back at the vent allowing the rectal opening of the large intestine to push out, closing the reproductive tract opening.

Basic Functional Anatomy of the Digestive System

– Ruminants –

« Mouth, esophagus, liver, pancreas, gall bladder, small intestine, and large intestine have functions similar to monogastrics.

« Ruminants produce prodigious quantities of saliva. Published estimates for adult cows are in the range of 100 to 150 liters of saliva per day! Aside from its normal lubricating qualities, saliva serves at least two very important functions in the ruminant:

« provision of fluid for the fermentation vat

« alkaline buffering - saliva is rich in bicarbonate, which buffers the large quanitity of acid produced in the rumen and is probably critical for maintainance of rumen pH.

« Stomach

« Structure and function of the stomach is the major difference between monogastrics and ruminants.

Multi-compartmented stomach – rumen, reticulum, omasum, abomasum

n Rumen:

► Large, anaerobic fermentation vat.

n Rumen (continued):

► Houses microorganisms.

n Protozoa – 100,000 per gram of rumen fluid.

n Bacteria/fungi – 100 million per gram of rumen fluid.

► Functions of microorganisms.

n Digest roughages to make Volatile Fatty Acids (VFA’s), make microbial protein, and make vitamins K and B-complex.

► VFA’s absorbed in rumen.

► Lined with millions of papillae (short projections on wall of rumen) needed for absorption.

► “Shag carpet” appearanc

n Rumen saturated with gases and in constant motion.

n Contractions occur at a rate of 1-3 per minute.

► Serve to mix contents, aid in eructation of gases, and move fluid and fermented feedstuffs into the omasum.

n Rumination:

► Ruminants are well known for “cud chewing”.

► Rumination involves:

n Bolus of previously eaten foodstuff carried back into the mouth by reverse peristalsis.

n Fluid in bolus is squeezed out with the tongue and reswallowed.

n Bolus is rechewed and reswallowed.

► Rumination may occupy about 1/3 of a ruminant’s day

n Eructation (belching):

► Fermentation of foodstuffs in the rumen generates enormous quantities of gas.

n 30-50 liters per hour in adult cattle.

n 5-7 liters per hour in adult sheep or goats.

► Belching is how ruminants get rid of fermentation gases:

n Anything that causes a hindrance to belching can be life threatening.

n Bloating can result in death from asphyxiation.

n Reticulum:

► Contains microorganisms (like the rumen).

► Provides additional area for fermentation.

► As fermentation by microorganisms proceed and feedstuffs are digested, smaller and more dense material is pushed into the reticulum (from which it along with microbe-laden liquid is ejected into the omasum).

► Lining has a honeycomb structure.

n Catches and holds hardware consumed by animal.

n Hardware can be removed with rumen magnate.

n Omasum:

► A heavy, hard organ with a lining that has many folds (leaves).

► Function not well understood.

► Believed to produce a grinding action on foodstuffs.

► May absorb residual VFA’s and bicarbonate.

n Abomasum:

► The true, glandular stomach.

n Secretes acids and functions very similarly to monogastric stomach.

► Unique feature is that it secretes lysozyme.