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 Digestive System 
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Post Digestive System
1.5.3 Digestive System

The digestive system of birds has some very specialized organs and is quite different from that of monogastic mammals.

1.5.3.1 Beak

Horny, breaking up and gathering food and protection. Most birds use their lower beak, by raising and lowering the head, as a scoop for funneling food and water to the crop. Birds of prey do chop their food into small pieces and psittacines dehull or crack seeds with their beaks. Pigeons and finches are two domesticated pet birds which can suck.

1.5.3.2 Mouth parts

No teeth, lips and cheeks. The tongue is shaped like the barbed head of an arrow with the point directed forward. The barb-like projections at the back of the tongue serve the purpose of forcing the food toward the entrance to the gullet when the tongue is moved back and forth. In water fowl, the tongue is wider, softer and more flexible.

1.5.3.3 Pharynx

Common passage for food and air.

1.5.3.4 Esophagus (gullet)

Dorsal to trachea, passage way for foods.

1.5.3.5 Crop or ingluvius

An expandable organ, serves as storage site for ingested food which is awaiting digestion. It is located in the lower neck on the midline or slight]y to the left, outside of the body cavity.

Amylase enzyme which originated in the mouth, start working on starch in this organ. There are two kinds of movements in this organ. Forcing ingesta into the preventriculus. Hunger contraction began 30 to 45 minutes after eating, gradually increasing in frequency and vigor until in 5 to 6 hours they occurred in groups of 6-12 or more, separated by intervals of comparative rest of the crop. Crop is absent in geese and swans. In small passerines the crop is rudimentary while in gallinaceous birds it is very large. Besides storage food, the epithelial cells of the crop mucosa of some birds (pigeon) swell up and rupture producing a nutritious crop milk (pigeon milk) which the adults, both male and female, regurgitant to feed their young.

1.5.3.6 Proventriculu

True stomach with glandular secretions. Spindle shape, lumen is scarcely larger than that of the esophagus. Storage capacity is very limited. The stomach glands secrete gastric juice (Pepsin and hydrochloric acid). Fish-eating birds possess such potent enzymes that even bones are digested, while birds of prey, such as owls, cannot tolerate bones and regurgitate them.
1.5.3.7 Ventricle (gizzard)

oval, flattened from side to side, composed of two pairs of red, thick powerful muscles, covered internally with a crushing coarse feed. This process is aided by the presence of grit or gravel taken through the mouth.

1.5.3.8 Small Intestine - Duodenum

The first section of the small intestine, a folded loop of about 5 inches long in mature chicken, and encloses the pancreas. It termination is marked by the pancreatic and bile ducts which pour their respective juices into the intestine at very nearly the same point. Duodenum acts like a stomach of a mammal, gastric digestion is active. Pancreatic juice contains,

* (l) Trypsin - protein,
* (2) lipase - fat,
* (3) amylase carbohydrate,
* (4) bile - digestion of fat, contains amylase (the amyloytic action is smaller than pancreatic juice).

Jejunum-ileum - No line of demarcation between the two parts. They are supported by a mesentery and bounded by airsac which separate them from abdominal wall. Length about 4 feet long in mature chicken, (intestinal juice secreted enzymes included: erepsin protein, sucrose, lactose and maltose). Absorption begins in this section of small intestine. The digestion and absorptive process in the small intestine are extremely rapid; digestion and absorption can be completed in three hours.

Yolk sac diverticulum - a remnant of the yolk stalk between jejunum and Merckel's ileum, which is transformed into a lymphoepithelial tissue.

1.5.3.9 Ceca or one cecum

Two blind pouches, about 4-6 inches long in chicken function unknown. Cecum empties its contain twice daily, (usually 7 am. and pm.). Manure in the par is brown in color. Absent in pigeons, hawks, eagles and parrots,

Colon-rectum - Very short, about 5 inches. Function is to absorb water from urine and intestinal tract. No enzyme secretion or digestion takes place here.

1.5.3.10 Cloaca or Vent

A chamber common to digestive and urogenital systems. There are three openings:

Coprodaellm - stores feces Urodaeum - collects urine Protodaeum - tile exterior opening of the cloaca (vent), the duct of the bursa of Fabricius enters just cranial to protodaeum. The protodaeum turns inside out during mating of both sexes, permitting the transfer of semen.

1.5.3.11 Liver

The largest gland of the body, consists of two lobes, dark reddish-brown in color (yellow in baby chicks, due to fat deposit, replaced by blood in 3-4 weeks). The outer surface is convex and smooth. The visceral surface is irregularly concave molded to fit the adjacent organs. The right lobe is larger: On its visceral surface the gall bladder is absent in the following fowls:

* Ostrich,
* pigeon and
* guinea fowl.

1.5.3.12 Pancreas

* Long, thin, light-colored organ, occupies the space formed by the loop of the duodenum.
* Function - Secretes pancreatic juice and insulin

1.5.3.13 The PHI of intestine

Gizzard content is most acidic (PH2-3.5). Relatively alkaline in small intestine (PH5.5-6.8). However, intestinal contents never reach alkaline state.

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August 25th, 2008, 2:44 pm
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