Digestive System

Overview

The digestive system starts at the mouth (oral cavity) and continues all the way to the cloaca where waste exits the body.
The function of the digestive system is to break food into smaller pieces so nutrients can be absorbed.
Chickens have a digestive system compromised of two distinct parts: the glandular portion and the muscular portion.

Oral Cavity

Mouth

The mouth is where food enters the digestive system.
Chickens have no lips or teeth to aid with prehension, instead they utilize a pecking motion.
No mechanical digestion occurs in the mouth of chickens.

Beak

The function of the beak is to hold, crush, or tear food.
These are elements of mechanical digestion.

Tongue

The chicken's tongue is used to distinguish food types. This is done with the help of many specialized touch receptors on the tongue.
The tongue also has taste buds, however, there are not as many as in other species.
The chicken tongue is very narrow and can be described as triangular in shape.

Esophagus

The esophagus is the tract that connects the mouth to the crop.
Its function is to transport foods and liquids to begin digestion.
The esophagus is muscular in nature and runs lateral and dorsal to the trachea.

Crop

The function of the crop is to store food temporarily before digestion.
This allows birds who fly to maintain energy as they can digest food stored in the crop as they fly to gain energy.

Proventriculus

The proventriculus is also called the glandular stomach or "true stomach".
It is where digestion really begins with chemical digestion.
Secretion of HCL, peptic enzymes, and mucus chemically break down food.

Gizzard

The gizzard is composed of thick muscular walls and has a sandpaper-like surface on the inside.
The gizzard is where some mechanical digestion occurs when strong contractions grind food into smaller portions.
The gizzard also contains small rocks and gravel which the chicken swallows to mash up the food.

Small Intestine

The small intestine is divided into three main portions or sections: the duodenum loop, the jejunum, and the ileum.
The small intestine is fixed to the dorsal abdominal wall by the mesentary.
The overall function of the small intestines is nutrient absorption.

Duodenum

The duodenum is where digestion begins as it is the initial portion of the small intestine.
It is where Chyme from the stomach is broken down and absorbed.

Jejunum

The jejunum absorbs sugars, amino acids, and fatty acids.

Ileum

The ileum absorbs any of the remaining nutrients that were not absorbed by the duodenum or the jejunum.
It also specifically absorbs B12 and bile.

Pancreas

The pancreas is located in the duodenum loop of the small intestine and its primary function is to create pancreatic juices and enzymes.
It also contains bile ducts which connects to the duodenum.

Intestinal Ceca

The intestinal ceca are where cellulose and plant nutrients that are unable to be broken down and absorbed in the small intestine, are processed.
This is due to specialized bacteria contained in the ceca.
The ceca are also where some water reabsorption occurs.

Liver

The liver is located in the anterior abdominal cavity, has four lobes and can be categorized as a gland.
The primary function of the liver is bile production.

Gall Bladder

The gallbladder stores bile that is produced in the liver.
It is then able to discharge the bile into the duodenum which aids in digestion as well as the absorption of lipids.

Large Intestine

The large intestine is also called the colon and it is where most of the water absorption occurs.
Fecal material is also stored in the colon before it is excreted.

Cloaca

The cloaca is the exit point of the urogenital and digestive system. It connects to the end of the digestive system the large intestine or colon.
Fecal material stored in the colon is excreted from the vent which is the external opening of the cloaca.

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