Functional Anatomy in Relation to Respiration and Flying, Digestion, and Egg Production | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Respiratory System

• Birds have a unique respiratory system different from mammals.
• Their trachea (windpipe) connects to the syrinx, where sound is produced.
• Air sacs play a role in sound production, and puncturing them affects the bird's ability to make sounds.
• Lungs are attached to the thoracic wall and have bronchi connecting to abdominal air sacs, serving as reservoirs for breathing.
• Air moves continuously through the system, influencing buoyancy.

Flying and Air Sacs

• Birds have thin-walled air sacs that connect bronchi to pneumatic bones, providing lightness and buoyancy.
• There are eleven air sacs from the neck to the abdomen, influencing the bird's center of gravity.
• Air sacs are lined with mucous membrane and covered by serous membrane.
• They play a crucial role in flying by contributing to the bird's overall body structure.

Digestive System

• The fowl's digestive system includes the alimentary tract and accessory organs.
• Birds lack teeth but have a horny beak for breaking up food.
• The mouth is triangular, and features like lips and cheeks are absent.
• The tongue helps move food towards the entrance of the gullet, with variations in water fowl.
• The hard palate has rows of backward-pointing papillae.
• The gullet is expandable and forms a crop for temporary food storage.
• The proventriculus, a glandular stomach, secretes acid-gastric juice for digestion.

Highlights for Layman

• Birds have a unique way of breathing and producing sounds using the syrinx.
• Air sacs contribute to the bird's ability to fly by providing buoyancy.
• Bird beaks replace teeth for breaking up food.
• The gullet is expandable, forming a crop for temporary food storage.
• The proventriculus is a glandular stomach that secretes acid for digestion.

Gizzard (Muscular Stomach)

• The gizzard is a muscular stomach in birds, distinct from the proventriculus by a constriction.
• It has two pairs of powerful muscles covered with a tough, horny lining called "pseudocuticula."
• The gizzard's condition varies based on the bird's diet, being softer with an all-mash ration.

Intestine

• The small intestine includes duodenum, jejunum, and ileum.
• The duodenum is a loop enclosing the pancreas, receiving bile and pancreatic juices.
• In birds, there's no clear distinction between jejunum and ileum.
• The large intestine is short, with blind pouches called caeca attached, and it leads to the colon.
• The cloaca, common to digestion and urogenital systems, has three parts: coprodaeum, urodaeum, and proctodaeum.

Liver and Pancreas

• The liver, the body's largest gland, has two lobes and is dark reddish-brown.
• It's closely associated with digestion, with the gall-bladder on the right lobe.
• Two ducts carry bile from the liver to the duodenum.
• The pancreas, a long, light-colored organ, secretes pancreatic juice through three ducts.
• It also produces an internal secretion from islets of Langerhans, whose function is not entirely understood.

Highlights for Layman

• The gizzard is a strong stomach in birds with a tough lining, influenced by their diet.
• The intestines have a duodenum, jejunum, ileum, and a short large intestine with caeca.
• The cloaca is a shared chamber for digestion and waste elimination.
• The liver, a major digestive organ, produces bile for digestion.
• The pancreas plays a role in digestion by secreting pancreatic juice.

Reproductive System in Birds

Male

• Organs:
  • Male reproductive organs include two testes, each connected to the cloaca through a vas deferens.
  • Testes are attached to the abdominal wall near the kidneys and are usually larger during the breeding season.
  • They appear elliptical, light yellow, with a reddish tint due to blood vessels.
• Cloaca and Copulatory Organ:
  • Cloaca has three parts separated by folds: urodaeum, proctodaeum, and a median ventral fold.
  • A small shiny projection on the fold is the rudimentary copulatory organ.
  • This organ doesn't connect to the vas deferens and is used for sorting day-old chicks.

Female

• Organs:
  • Female reproductive organs include the ovary and oviduct.
  • During embryonic development, there are two gonads, but usually, only the left one develops into a functional ovary.
• Ovary:
  • The left ovary is near the left kidney and consists of yellow vascular spheres, varying in size.
  • These spheres are ova or yolks enclosed in thin membranes, independently attached to the ovary.
  • In non-laying hens, ova are small, none more than one-fourth inch in diameter.
  • The number of ova in a normal ovary is much greater than the number of eggs produced in a hen's lifetime.

Highlights for Layman

• Male Reproductive System:
  • Two testes connected to the cloaca.
  • Testes get larger during breeding season.
  • Cloaca has a small copulatory organ used for sorting chicks.
• Female Reproductive System:
  • Female organs are the ovary and oviduct.
  • Left ovary has yellow spheres (ova) of varying sizes.
  • The number of ova in the ovary is greater than the number of eggs produced in a hen's lifetime.

Bird's Oviduct (Female Reproductive System)

Structure

• The oviduct is a twisted tube that occupies a significant part of the left abdominal cavity in laying hens.
• It hangs from the dorsal body wall, supported by a membranous ligament, and is positioned above the abdominal air sac.

Divisions

The oviduct can be divided into five functional and histologically distinct parts:

• Funnel (Infundibulum): The initial part where the egg is captured after ovulation.
• Albumen-Secreting Section (Magnum): A region where the egg's albumen (egg white) is produced.
• Isthmus: Part where shell membranes are formed around the egg.
• Shell Gland or Uterus: This is where the eggshell is formed.
• Vagina: The final part that opens into the cloaca.

Function and Size

• The oviduct, when active, can stretch up to about 30 inches.
• Muscular tissue in the oviduct helps move the egg through peristaltic contractions during its formation.

Size Variation

In non-laying hens or pullets, the oviduct is much smaller, around four to five inches in length.

Egg Retention

• The fully formed egg is typically held in the uterus for several hours before being laid.
• During this time, the egg's position can be sensed through touch or palpation from outside.

Highlights for Layman

• The oviduct is like a twisted tube in a hen's abdomen.
• It has five parts, each with a specific role in egg formation.
• The oviduct is longer and more active in laying hens, with muscles helping move the egg.
• In non-laying hens, the oviduct is much smaller.
• Fully formed eggs are held in the uterus for a few hours before being laid, and their position can be felt from the outside.