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

Gizzard Anatomy - RVC 2008

• Mechanical reduction of tougher material through powerful muscular development

• Cranial to the liver and spleen (contacts the liver)

• Contacts the sternum and lower left abdominal wall

• Dorsally the abdominal air sacs separate it from the intestines and gonads

• Duodenum and pancreas lies in its caudal right surface

• 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

Gizzard Histology- Dr. Thomas Caceci

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 Diffences

• 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.

Links

Avian Alimentary Tract Flashcards