ANATOMY OF DIGESTIVE SYSTEM

The mouth (buccal cavity)

It is in the mouth or buccal cavity where food is tone, cut and nibbled & grind to smaller particles before being swallowed.

The soft part of the mouth or buccal cavity is also well supplied with relatively small mucus gland which helps to moistly and lubricate the food be4 swallowing.

Oesophagus It is more less a muscular tube w/c convey the flood from the mouth to the crop. Its size depends on the type of food eaten.

It is also provided mucus glands which affords the food to pass smoothly from the mouth to crop.

The crop In many birds, the posterior end of the oesophagus becomes enlarged into a storage chamber known as a crop. Here, food is stored until a stomach can accommodate.

In pigeons, the crop is very dev’d and it is here that “pigeon milk” is secreted to feed the young. Pigeon milk is a large substance rich in fats and proteins. The substance is mixed with food in the crop and then regurgitated into the mouth of the young bird. Crops are generally prominent in grain eaters like game birds and pigeons.

They permit the owner to gather and swallow food in a hurry way, thus shortening their exposure to their enemies.

The same thing is true with the ruminates where the rumen is the food storage chamber. The difference between crop and rumen is that; in the crop the food is not regurgitated back in the mouth fore recuing and reswallowing. Crop also permits hard seeds to be softened with mucus be4 further digestion in the stomach and intestines. No digestive gland is known exist in the walls of the crop.

Stomach The stomach of bird is divided into two distinct functional organs. There is the interior soft and glandular stomach also known as proventiculus and repostilier. Muscular stomach known as the gizzard

PROVENTRICULUS OR GLANDULAR STOMACH.

This is an organ which evolved after the evolution of birds. It is not found in reptiles. The stomach is well supplied with peptic enzymes that digest protein foods. The secretion is also highly acidic and therefore able to desolve large bones. The proventiculusare glandular stomach is more developed among meet esters that plant and seed eaters.

THE GIZZARD OR MOSCULAR STOMACH

It is a Rotarian trait. I.e. it is also found in reptiles. The gizzard is some time known as the “grinding stone”. It normally posses grits or small stones (swallowed by birds) which helps to crush or digest seeds and other plant materials and as would be expected the gizzard is more dev’d amongst seed and plant eater that meat eaters.

The following are figures which show considerable force generated by a compressive walls of gizzard as formed in different birds. Force is expressed in millimeters of mercury.

Hen has 100-150mm

Ducks has 180mm

Goose has 265-280mm

Turkey has been known to grind 12 steel niddles to pieces in 36hrs and 16 surgical linnets to pieces in 16 hrs.

A huge of sheet iron that could be only bent under a load of 36kg was flattened and partly rolled within 24hrs.

The gizzard is also found amongst carnivorous birds spp but here its function seems to act as a troupe that prevent sharp bones and undigestable things from proceeding down in digestive system such resist them may be rolled up into elongated pellet and rig agitated by mouth.

THE LIVER The liver of a bird is a to logged structure. It is the largest gland in the body and it is larger in birds than in mammals of comparable size and is also somewhat in lager in fish and insect eater than in meat and grain eaters.

Basically the liver in birds has the same function as in mammals such function are;

To store excess sugar

To manufacture bile

To synthesis certain proteins from amino acids

To excrete waste products

Stores vitamins and minerals

Dicrofy poison

Supplies quick energy to the body and by using sugar into the body

As regards the secretion of water products from the blood it is worthy to note that 60% of the uric acid, which is achieved nitrogenous pdts of birds, is found in the liver and excreted in kidney.

Together with other waste products, the kidneys pass on uric acid to the cloaca to final digestion outer the body.

PANCREAS like the liver, pancreas is larger in birds tan in mammals of comparable size. It’s also larger among fish, insects and grain eaters than meat eaters. The 1 degree function of pancreas is to produce or secrete digestive enzymes which act on all three types of food like fats, Cabohydrates and protein.

INTESTINE it is chief organ of digestion and absorption of food. In birds, the organ is not sharply differentiated into regions as in mammals.

A reptilian x-tic in intestines of birds is longitudinal muscle found on the outside walls of the intestines as opposed to mammals whose intestinal longitudinal muscles are found inside the walls of the intestines.

Among related spp, large birds are required to absorb more nutrients in order to survive and a longer intestine provides the necessary required volume for digestion and absorption of food. Doubling linear dimension of an object increases the volume by 8 times. Relatively the smaller intestines are found in grain eaters than in other birds. This is because grain eaters take more solid food and therefore need more space for its digestion and absorption.

CAECA The main function is absorption water and digested proteins, and particular the bacterial decomposition of crude fibrous. The undigested matter in the caeca is dark and moist and is discharged separately in a whitish dinner intestinal feeces. In domestic hen there is one caeca discharge for a bit a very intestinal defecation.

CLOACA A cavity in birds & reptiles in w/c the intestinal & urinary ducts in terminate. The cloaca is found at the end of the intestinal canal & its divided in2 3 regions.

·        Coprodacum Interior regions w/c receives excrements in the intestines.

·        Urodacum Middle region w/c receives discharges of the kidney through the ureters and of the gentle organs through the vas deferens/oviduct.

·        Proctolaeum Posterior or terminal regions and is suplied with powerful ejection muscles. It’s closed posterior by the muscular anus. Its main function is to store the excrements before final discharge.

ADAPTION OF BIRDS FOR FLIGHT

In order 2 conquer the air, birds have evolved features adapted 4 flight. The adaptations are not confined 2 birds a lone but also 2 bats, flying squirrels etc. however when it comes 2 sustained flying, birds are considered true flyers.

Features adapted 4 flight

Uniformity in body size plus architecture. In general birds have a union body size i.e. the difference btn the smallest the smallest the largest bird is considerably smaller than the difference btn the smallest & largest mammals. Example of body size uniformity.

Spp                                    wf/1                          Ratio (largest Vs smallest)

Ostrich                             144kg                              { 1:64.000}

Humming birds                2225g                            { 1:64.000}

Blue whale                        190000kg                      {1:82600000}

Plggmy shrew                   2.3g                               {1:82600000}

Weight reducing adaptation Compared the reptiles & mammals, bones, of birds are much higher. Some of the weight decreasing adaptation are as follows.

Skeleton Greatly reduced in weight compared 2 mammals or reptiles of comparable size e.g. the skeleton and all other bones of a 7kg pelican weighs 0.6kg or 9.3% of the total body weight of the bird.

A pigeon’s skeleton accounts for 4.4% body weight whereas compared to a rat, the skeleton accounts 4 5.6% of the total body weight. It reduced long tail 2 4m stunted pygostyle.

·        Bird’s hand (wings) finger bones are decreased both in size and No’s where by fingers are missing plus 2 of the remaining 3 fingers are fused.

·        Absence of teeth

·        Sternum is thin & keeled there by greatly decreased in weight.

·        Bones of birds are hollow hence greatly reduced the heavier.

Light feathers: presence of feathers has replaced the heavier scale and scutes found in reptiles.

Air sacs presence of air sacs which are branched all throughout the body& penetrating the hallow bones. The air sacs and the feathers are responsible for reducing the specific gravity of flying birds. The specific gravity of feathered duck is 0.6 compared 21.0in most vertebrates.

Excretory system Absence of urinary bladder & urethra 2 hold and discharge urine. The kidney exploit nitrogenous waste concentrated in 4m of uric acid w/c passes directly through the cloaca whose walls further absorb more H₂O. The wastes pass 2gether with those of the intestines in the form of conc white guano.

Reproductive system Birds don’t give birth to live young ones and not carry to unborn baby inside the body. Female spp of birds don’t contain one function ovary and oviduct (the left). The right ovary is normally atrophical and doesn’t develop for reproduction. Eggs are laid outside and the development of young occurs outside the body of the mother. Both ovaries and tests are atrophy during non breeding season. It has been found that sex organs of starlings weigh about 1500 times more during the breeding season compared 2 the non breeding season.

Body glands Except uropygial gland (oil gland), Glands are generally absent in birds.