Intestine and Villi

The Bird Digestive System

The Bird Digestive System

Intestine and Villi

Relative Length of the Intestinal Canal

Intestinal Fold or Loop Types

Intestinal Loops and Fold Characteristics in Bird Groups

Home to discover more interesting bird facts and information at The Wonder of Birds

Continued from The Bird Digestive System

The Intestine

The intestine, or gut proper, begins at the pyloric end of the stomach and ends at the cloaca. It may be conveniently divided into

  1. The duodenum, or first loop.
  2. The ileum or narrowest and longest portion, equivalent to both the jejunum and ileum of humans.
  3. The rectum, corresponding with the human large intestine.
The transition from the ileum to the rectum is marked by a more or less circular valve (the "ileo-caecal"), so placed as to permit its contents to pass into the caeca and rectum, but to hinder their return-their passage throughout the whole intestine being aided by the peristaltic contractions of the muscular layers of its walls. An epithelium of cylindrical cells, forming a colourless, structureless and soft cuticle, lines nearly the whole of the intestine, and is perforated by numerous small pores, opening upon their interstices. In many parts these cells form very simple and sometimes tubular glands ("Lieberkuhn's"), and the greater portion of the walls is beset with the villi mentioned above. These are very numerous, and are arranged in various ways-being either uniformly and thickly spread over the surface, giving it a velvety appearance, or are longer and more sparingly distributed in lines, which may be straight or zigzag, transverse or longitudinal. Their arrangement is occasionally characteristic of different groups of birds; but it varies also in different parts of the gut. As a rule they are largest and most numerous in the duodenum, but sometimes in the rectum as well.  The structure of these small but important organs will be best understood by reference to the accompanying diagram.

Diagram of the Digestive Organs of a Bird

T. ..... Tongue
P.G. L.G. ..... Parotid and salivary glands
Tr. ..... Trachea
l.Br. r.Br. ..... left and right bronchus
Cr. .....Crop
Pr. ..... Proventriculus or glandular stomach
g. ..... Gizzard or muscular stomach
Py. ..... Pylorus
D. .....Duodenum
L. ..... Liver with gall-bladder and duct
Pa. ..... Pancreas with duct
C. ..... Caeca
R. ..... Rectum
K. ..... Kidney with Ureter opening into the middle cloacal chamber

The Villi

Each villus consists of a finger-shaped prolongation of the tissue of the submucosa, which contains a ramified central canal conveying the collected chyle into the lymphatic vessels, which are frequently connected with a lymphatic follicle for the production of white Blood-corpuscles or lymph-cells. A pair of small arteries and veins enter the villus, forming a capillary network, while fine unstriped muscles in its walls contract it and force the chyle into the lymphatic vessels. In the diagram, on one side of the villus is shown a Lieberkuhn's gland, since such are generally associated with the villi.

Diagram of an Intestinal Villus with the Central Absorbent, Ramified Canal

L.v. ..... Its duct
Sm ..... the submucous layer
A and v ..... Artery and vein ascending in the scubmucous layer
E. ..... Cylindrical cells of the epithelium of the mucous layer, which at L.G. forms a Lieberkuhn gland
Lg. and An. ..... Longitudinal and annular or circular muscular fibres
Se. ..... Serosa or outer layer of connective tissue, together with the investing peritoneal lamella Pe., which forms the mesentery M. in the diagram below.

Diagram of a Transverse Section through the Intestine

V. ..... Villi
M. ..... Mesentery with blood and lymphatic vessels.

Previous...The Bird Digestive System Next...Relative Length of the Intestinal Canal


Home to get more interesting bird facts and information at The Wonder of Birds

This page ©