Gizzard - Anatomy & Physiology
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Introduction
The gizzard is also referred to as the muscular stomach or ventriculus. It is connected by the isthmus to the proventriculus and to the duodenum.
Structure and Function
- Mechanical reduction of tougher material through powerful muscular development
- Contacts the sternum and lower left abdominal wall
- Dorsally the abdominal air sacs separate it from the intestines and gonads
- More caudal than the proventriculus
- Roughly on the midline of the bird
- Lens shaped
- Interior elongated by cranial and caudal blind sacs
- Cranial blind sac contacts proventriculus
- Pylorus on right surface next to cranial blind sac
- Two thick masses of muscle that insert on tendonous surfaces
- In seed eating birds grit is digested to increase grinding down of food particles
- Surface covered by glistening tendonous layer
- The cranial and caudal extremities are formed by powerful red muscular tissue
- A circular aponeurosis is present connecting the cranial end of the gizzard to the isthmus and the caudal end to the duodenum
- Appears yellow due to bile reflux from the duodenum
- When the thin muscles of the gizzard contract, food passes from the gizzard into the duodenum
- When the thick muscles of the gizzard contract, food moves back into the proventriculus
Histology
- Thin, but tough mucous membrane
- Pale, thin lining raised into ridges
- 3 layers of lamina muscularis
- Cuboidal epithelium
- Tubular glands
- Cuticle of koilin a carbohydrate complex is present due to the solidifying of the glandular secretion. It is replenished as it is worn down.
- Thick keratin layer to protect muscle
Species Differences
- No gizzard in falconiformes (raptors etc.)
- No gizzard in stringiformes (owls etc.)
- No gizzard in gulls
Other Information
- Grit should be provided in seed eating birds diet. It is radiodense and marks out where the gizzard is located on radiographs.