ENTER

ANIMAL PHYSIOLOGY: monogastric

digestive tractBy: Eko Widodo

Pre-test

1. Write an assay of not less than 300 words on what you know and understand about

monogastric digestive physiology (in10 minutes)

DIGESTIVE SYSTEM ALIMENTARY

ORGANSASSESORY ORGANS

ResponsibilityUp-take

+

digestion

absorption

FEED

Mouth ~> cloaca

mouth

pharinx

oesophagus

stomachSmall intestines

Large intestinescloaca

TongeTeathSalivary gland Liverpancreas

Animals Capacity (l)

Stomach Small intestine

Cecum Colon rectum

Dogs 63 23 1 13

Pigs 29 33 6 32

Horse 9 30 16 45

Cattle 71 18 3 8

Sheep & Goat

67 21 2 10

anatomy

– the physiology of digestion and nutrition, including: anatomical views and digestive parts

identification the process of digestion and absorption factors affecting digestibility of feeds

Digestion and Absorption:

The process of digestion includes:– The prehension of food or feed– The mechanical chewing and grinding– Mixing with digestive acids and enzymes to

chemically break down the foodstuffsThe process of absorption includes:

– Transport of the digested foods across the intestinal mucosa to the blood or lymph system

The General Mechanical Process:

Mastication - chewingDeglutition - swallowingRegurgitation - movement of digesta in

reverse order from the stomach to mouth

Defecation - voiding the fecal, or waste, materials from the body

Animal Diet Types:

Species may be divided into dietary preference groups:– Herbivores consume plant materials,

examples are horses and cattle– Carnivores consume flesh of other

animals, examples are dogs and cats– Omnivores consume both plants and

flesh, examples include the primates

Differing Digestive Tracts:

Farm animal species have a variety of digestive systems– Ruminants have four distinct stomach areas

examples include bovine, ovine and caprine

– Nonruminants (also termed monogastrics) display considerable variety hogs, dogs, and cats have a single, simple

stomach poultry have a two part stomach horses have a large, functional cecum

Nonruminant Digestive System:

Mouth - prehension and chewing of food; some carbohydrate enzyme activity

Esophagus - route of food from mouth to stomach

Stomach - addition of hydrochloric acid and protein digesting enzymes, mixing and holding

Nonruminant Digestive System:

Small intestine - primary site of digestion and absorption

Large intestine - major site of water absorption and preparation of digesta for excretion

Nonruminant Variations:Poultry

– Mouth: no teeth for chewing– Esophagus: a “crop” is contained within the

esophagus for food holding and moistening– Stomach: divided into proventriculus (glandular

area) and ventriculus (crushing area) – small intestine: primary site for enzymatic

digestion– Large intestine: short and exiting into the cloaca;

two large ceca with limited function

Nonruminant Variations:

Horse– Large intestine differences:

cecum is very large (may contain 50% of digesta)

cecum provides some nutrients to the horse via microbial fermentation

Ruminant Digestive System:

Many parts of the tract are similar to nonruminant monogastric description

Significant differences include:– Mouth contains no upper incisors– Stomach is divided into four major parts

rumen reticulum omasum abomasum

Ruminant Digestive System:

Rumen– Largest digestive area of the compound

stomach– Majority of fermentation of feedstuffs

occurs here– Majority of absorption of byproducts of

fermentation - volatile fatty acids or “VFA’s”

Ruminant Digestive System:

Reticulum– Receives feed from esophagus– Initiates mixing, regurgitation, and

eructation– Environment for fermentation of feedstuffs

Ruminant Digestive System:

Omasum– Third area of the stomach receives the

digesta outflow of the rumen/reticulum– Some water absorption and further

subdivision of feed particles may occur

Ruminant Digestive System:

Abomasum– The fourth and final stomach compartment,

but very similar in function to the pig stomach

– Acid and enzyme stomach– Final holding and mixing area before the

small intestine

Ruminant Digestive System:

Selected terms:– Regurgitation - controlled reverse movement

of coarse feedstuffs from reticulum/rumen via esophagus to mouth for rechewing

– Eructation - expulsion of accumulated fermentation gases from rumen via esophagus

– Rumination - refers to the processing of feedstuffs in the reticulum/rumen, to include fermentation, regurgitation, eructation

Chemistry of Digestion:

Digestion involves enzymes and acids produced by the host animal or microbes working in symbiosis with the host– Enzymes break specific chemical bonds in feeds– Domestic animals produce enzymes to digest

nonfibrous carbohydrates, fats, and proteins– Only microbes have enzyme systems to digest

fibrous carbohydrates, such as cellulose

Digestion of Carbohydrates:

General carbohydrate digesting enzyme (amylase) in the mouth begins digestion; little amylase is found in horses and none in ruminants

Carbohydrate digesting enzymes (amylase) from the pancreas, and intestinal mucosa (sucrase, maltase, lactase) complete carbohydrate digestion

Digestion of Proteins:

Protein digesting enzyme (pepsin) and hydrochloric acid in the stomach begin significant digestion

Protein digesting enzymes (e.g. trypsin) from the pancreas and intestinal mucosa complete digestion in the small intestine

Young nursing animals – rennin coagulates milk allowing more complete digestion

Digestion of Fat:

Fat digesting enzyme (lipase) in the stomach begins digestion

Fat digesting enzymes from the pancreas (lipase) and intestinal mucosa complete digestion in the small intestine

To assist in fat digestion, bile from the liver emulsifies fat into smaller droplets in the small intestine

Factors Affecting Digestibility:

Rate of passage - in general, increased rate of passage of digesta through the tract reduces digestibility, factors increasing rate of passage include:– Increased level of feeding/intake (ruminants)– Finer processing (such as grinding) of feed

Note: grinding grain usually increases digestibility but grinding hay decreases digestibility

stomach

Divided into cardia (entrance), fundus (body) and pylorus (termination)

Cardiac gland region

This is not necessarily in the cardia which is usually non glandular. This mucosa contains glands which produce mucus.

Fundic gland region

Fundic glands are simple and tubular and contain 3 types of cells:

1. Mucus neck cells, which produce mucus

2. Parietal cells, which produce HCl

3. Peptic or zymogen cells, which produce enzymes

Pyloric gland region

These glands are lined entirely with mucus-secreting cells like those within the cardiac glands. The hormone gastrin is produced by G cells of the pyloric gland.

Gastric juice

Is the total secretory product (fluid) from the surface epithelial cells and the cardiac, fundic and pyloric glands of the stomach. It is colourless and is made up of two components; a parietal cell acid component, and an alkaline component containing pepsin, mucin and electrolytes.

Pepsin

Is synthesised in the peptic cells from the inactive precursor, pepsinogen. It begins the digestion of protein in the stomach if the pH is acid. Proteins are converted to proteoses and peptones in the stomach, and digestion of protein Is completed in the intestine.

Rennin

Is a milk clotting enzyme secreted as inactive prorennin which Is activated by the presence of acid. In adition to clotting milk rennin also exhibits proteolytic properties. It is foundin the gastric juices of calves, lambs, and young pigs.

Gastic lipase

Is present in low concentration in the gastric juice of carnivores. It can hydrolyse fats that are emulsified, such as milk fat but probably had little effect on unemulsified fats.

Hydrochloric acid

Is produced by the parietal cells of the fundic glands of the stomach of all vetebrates. HCl activates pepsin and rennin and aids pepsin in protein digestion by lowering the pH of the stomach contents.

Phases of gastric juice secretion

Cephalic phase

Presence of food in the mouth may result in the secretion of gastric juice in the stomach.

Gastric phase

When food reaches the stomach, gastric juice secretion Increases for a period up to several hours.

Intestinal phase

When products of gastric digestion reach the duodenum, intestinal gastrin is produced.

Pancreas and pancreatic secretion

The pancreas consists of exocrine and endocrine portions. The exocrine part consists of acini responsible for the production of pancreatic juice and ducts which convey the juice to the duodenum. The endocrine portion is made up of the Islets of langerhans which secrete insulin into the bloodstream.

Pancreatic juice is secreted under the influence of two hormones produced In the mucosa of the duodenum.

Secretin increases the rate of flow and hydrocarbonate concentration of the pancreatic juice.

Pancreozymin increases the amount of enzymes In the pancreatic juice. An additional factor which results in a pancreatic juice rich in enzymes Is neurogenic stimulation by the vagus nerve.

Pancreatic juice contains sodium carbonate, which neutralises acid from the stomach and Increases alkalinity of intestinal fluid, and a number of enzymes for the hydrolisis of proteins, fats and carbohydrates.

There are 3 major group of enzymes In pancreatic juice.

1. Pancreatic proteases or proteolitic enzymes in the pancreas are trypsin, chymotrypsin A, chymotrypsin B, and the carboxypeptidases.

2. Pancreatic amylase is an αamylase, probably structurally identical to salivary amylase secreted in an active state. Amylase attacks starch grains and produces dextrins and maltose. Maltase is also present in pancreatic juice and it hydrolyses maltose to glucose.

Pancreatic lipase is secreted in an active form and it hydrolyses fats into carboxylic (fatty) acids and glycerol. Pancreatic lipase is most effective after the fats have been emulsified by bile.

Bile is a greenish yellow liquid consisting largely of water, bile salts, bile pigments and cholesterol with smaller amount of fats and inorganic salts.

Intestinal secretion

Intestinal juice, called succus entericus, is produced by the intestinal glands scattered throughout the entire small intestine, and submucosal duodenal glands. Secretion of these glands is stimulated by the presence of food in the intestine. The release of intestinal juice Is also brought about by hormone called enterocrinin.

In addition to water, salts and mucus, a number of enzymes have been described In the intestinal juice. These include enterokinase (which activates trypsinogen), and the following inverting enzymes:

Maltase - hydrolyses maltose to glucose

Sucrase - sucrose to glucose and levulose

Lactase - lactose to glucose and galactose

Peptidase - peptides to amino acids

Polynucleotidase - splits nucleic acids into mononucleotides

Nucleotidase - nucleotide into nucleosides and phosphoric acid

Nucleosidase - hydrolyses nucleosides

prehension

The manner in which food is grasped. Picked up, carried to the mouth, mixed with saliva and manipulated before swallowing

deglutition

The process in which food particles are swallowed whole and pass to the crop

Passage of ingesta through the tract

Rate

The rate of feed passage through the alimentary canal is influenced by the consistency, hardness and water content of the feed and by the amount consumed.

Factors Affecting Digestibility:

Rate of passage - in general, increased rate of passage of digesta through the tract reduces digestibility, factors increasing rate of passage include:– Increased level of feeding/intake (ruminants)– Finer processing (such as grinding) of feed

Note: grinding grain usually increases digestibility but grinding hay decreases digestibility

Motility

1. Crop and esophagus

2. Proventriculus

3. Gizzard

4. Small intestine

5. Large intestine