Spectrum Biology - September 2016

Diversity in the Intestine of Different Vertebrates

Or gan isms In tes tine Fig ure

1. Cyclostomes,
   chondrichthian
   fishes and primitive
   bony fishes

They have short, nearly straight intestines

that extend from the stomach to the anus.

2. Bony fishes The intestine increases in length and begins to
   coil.


3. Amphibians
   and reptiles

The intestines are moderately long.

4. Birds and mammalsThe intestines are longer and have more
   surface area than other tetrapods. Birds have
   two caeca and mammals have a single caecum
   at the beginning of large intestine.

PharynxStomachPyloric valve Anus

Lung ductBile duct Spiral valveIntestine

Livers and Gall Bladders

 The liver manufactures bile, which is

stored by gall bladder. Bile is a fluid

containing bile salts and bile pigments.

Bile salts play an important role in the

digestion of fats, although they are not

digestive enzymes.

 The gall bladder is relatively large in

carnivores and vertebrates, in which fat is

an important part of the diet.

 It is much reduced or absent in blood

suckers, such as the lamprey and in the

animals that feed primarily on plant food,

e.g., some teleosts, many birds and rats.

Pancreas

Every vertebrate has a pancreas, however in

lamprey and lung fishes it is embedded in the

wall of intestine and is not a visible organ.

Intestines

The configuration and divisions of the small

and large intestines vary greatly among

vertebrates. Intestines are closely related to

the animal’s type of food, body size and levels

of activity.

Ruminants such as cows and sheep have a

four-chambered ‘stomach’, with three-

chambers derived from the lower part of the

oesophagus (rumen → reticulum → omasum)

and one chamber (the abomasum) that is

the true stomach.

In the mouth, grass cropped by the incisors/

horny pad is ground up by the premolars and

molars, swallowed with copious saliva and

passed to the rumen.

The fermented grass passes to the reticulum and

is formed into balls (cud), which are regurgitated

to the mouth for further chewing. The cud is then

swallowed and passed to the omasum.

In the omasum much water is reabsorbed from

the cud (a cow secretes 100-190 dm of^3

digestive juices each day). The firmed-up

remainder of the cud passes to the abomasum.

In the abomasum, normal gastric secretions

begin to digest the proteins of grass and

also of the bacteria and ciliates, including

the proteins synthesised in the rumen (see 2).

Chyme passes to the duodenum and then to

the small intestine, where digestion is completed

and the products of digestion are absorbed.

Small intestine Oesophagus

AbomasumOmasum Oesophagus

Duodenum Reticulum Rumen

2

4

5

6

3

1

Four-chambered

stomach

2

1

3

4

5

6

The rumen functions as a fermentation vat.

Cud is mixed with anaerobic cellulolytic

bacteria, which breakdown cellulose to glucose,

which in turn is fermented to organic acids.

These fatty acids are absorbed into the blood

through the rumen wall and are the major

source of energy for ruminants. The fermentation

produces carbon dioxide and methane, which

are belched out. The rumen bacteria also form

proteins from inorganic nitrogen (ammonium salts)

and B-complex vitamins are also synthesised.

The rumen also contains Protozoa (ciliates)

that feed on the bacteria.

The Digestion of Cellulose by Ruminants takes

place in six stages:

Ruminating Stomach :

An Adaptation to Digest Cellulose

Duct to swim

bladder Gall bladderStomach

Anus

PharynxPyloric cecaIntestine

Gall bladder

Pharynx

Stomach

Liver

Small intestine

Duodenum

Pylorus

Bladder

Cloaca

Oesophagus

Oesophagus

Crop

Stomach

Liver

Gizzard

Pancreas

Small

intestine

Rectum

Cloaca