Following body systems of chicken are discussed briefly in this article,
i) Skeleton
ii) Digestive system
iii) Respiratory system
iv) Reproductive system
v) Urinary system
vi) Muscular system
vii) Vascular system
viii) Lymphatic system
Lets discuss one by one.
Skeleton
Bones of chicken are light in weight with many containing large medullary cavities. Some of the bones are pneumatic. We are going to discuss axial skeleton first. It consists of skull and 40-60 vertebrae. Vertebrae are divided into Cervical (14), Thoracic (7), Lumbar & Sacral (14) and coccygeal (6) vertebrae. Some vertebrae are hollow and are in direct contact with respiratory system. Last vertebrae is called 'pygostyle' and it resembles a plowshare. Pubic bones are directed posteriorly in birds and pubis symphysis is absent. Appendicular skeleton consists of pectoral girdle, pelvic girdle, forelimbs and hindlimbs. Scapula, coracoids and clavicle are the bones of shoulder girdle. Forelimbs consist of humerus, radius (thinner than ulna), ulna. two carpals (radial and ulnar), metacarpus, and 3 digits. Femur, tibia, fibula, metatarsus and 4 digits constitute the hind limbs while tarsals are absent. Medullary bone is present in femur, tibia and some other bones of female where it serves as a source of calcium for egg formation but most of the calcium for egg shell comes from feed directly. Shanks of chicken reach at maximum length at 16-20 weeks and maximum body size is attained at 40-60 weeks of age.
Digestive System
It starts from mouth and ends at cloaca. Slivary glands of chicken can secrete 12ml saliva in 24 hours. Lips, teeth,soft palate and cheeks are absent and teeth function is performed by beak and gizzard. Beak also acts as a weapon of defense. Base of tongue contains taste buds. Taste buds are also present in pharynx but they are lesser as compared to that of mammals. Edges and the tip of the tongue contains touch cells but they are not concentrated. Poultry accepts or rejects feed from impulses received from tactile cells.Cleft palate is long narrow slit-like and oropharyngeal glands are small. Epiglottis is also absent.True pharynx is also absent. Esophagus is present and it has a diverticulum called crop which stores, softens and mixes the food.Pigeon crop milk is produced by male or female during the brooding season 10-16 days. Proventriculus is glandular and is called true stomach. Gizzard is an organ of mastication. Meckle's diverticulum is a remnant at mid point of gut, it is called yolk stalk. Small intestine is 1.5 meter in adults. Intestinal juice contains protease, maltase, sucrase, lactase and other enzymes. Large intestine is 10cm long in adult bird and is twice in diameter as compared to the small intestine. Cecum is absent in parrots and many pigeons. Ceca are two in number and 6 inches long in chicken. Accessory organs of digestive system include liver, pancrease and gall bladder. Liver is bilobed and the ratio of liver weight to body weight in adult chicken is 1:37. Liver produces 100 ml bile per day at the rate of 0.58 ml/g weight of the liver. Gall bladder is 2.9 cm long and contains 2.5 ml bile. Gall bladder is absent in Humming bird and in some genera of pigeons and parrots. Two bile ducts are present in chicken. Hepatic bile duct comes from liver and cystic bile duct comes from gall bladder. Pancrease is pink or pale yellow in color. It is rich in Langerhan islands and pancreatic juice contains amylase, lipase and trypsin.
Respiratory system
Physiologically, expiration is active phase of breathing while in mammals, inspiration is active process. Respiratory system consists of nasal cavity, larynx, trachea, syrinx, bronchi, lungs, air sacs and pneumatic bones. Syrinx is true organ of voice and it is located in the thoracic cavity where trachea divides. Domestic chicken have 9 air sacs, 4 paired (abdominal and thoracic) and one unpaired (inter-clavicular). Epiglottis and Diaphragm are absent.
Reproductive system
Male has two testicles which may yellow or black, vas deferens, cloaca and phallus which is rudimentary copulatory organ. Semen in one ejaculate can be up to 1 ml.
Female reproductive system is divided into ovary and oviduct. Ovary is made by a large number of visible oocytes. Only left ovary is functional in chicken. Oviduct is 45-50 cm (1.5 feet) long and is divided into 5 parts. Infundibulum is funnel shaped part which picks up yolk from the ovary. 15-20 minutes are required for yolk to pass through infundibulum. Magnum secrets albumin. Only the thick viscous white around yolk is added in this part. Egg stays for 3 hours in this part. Isthmus lays down more albumen and also the shell layers. Egg spends 1 to 1.25 hours here. Uterus has uterine glands which deposit shell around the egg. Egg stays for 20-21 hours in the uterus.Vagina is the last part of oviduct. It is a passage to the cloaca. Female stores sperms in crypts of vagina.
Urinary system
Two kidneys are present which are very dark in color and divide into 3 divisions often incorrectly referred as lobules.Urinary bladder and urethra are absent. Ureters excrete urine.Urine is excreted as white pasty material along with feces.
Muscular system
Muscle fibers in chicken do not increase in number but they increase in size by enlargement. The ability of broilers to gain weight rapidly is a result of fat deposition in fat cells rather than increase in the growth of skeleton or muscle fibers. Active muscles like those of legs are red and breast muscles are white. Ileotrochanteric and ambiens muscles have no equivalent in mammals. Gastrocnemius muscle has 3 parts.
Vascular system
Blood constitutes 12% body weight of the newly hatched chick and 6-9% body weight of adult chicken. Heart is heavier than that of mammals. Fossa ovalis fails to persist. Heart rate is 300 pulsations per minute. Systolic blood pressure is 75 to 175 mmHg and diastolic blood pressure is 140 to 160 mmHg. Arteries and veins bear plaques of cartilages at the level of semi-lunar valves.
Lymphatic system
Lymphatic system consists of lymphatic vessels and lymphoid organs. Regular lymph nodes are absent in chicken. Primary lymphoid tissue consists of thymus and bursa of fabricius. Thymus is paired organ lying in the neck near jugular vein and consists of 4-7 lobes. It attains its maximum size in 4 to 17 weeks of age. Bursa of fabricius is spherical in shape. It appears on 5th day of embryonic life. It reaches its maximum size in 3-6 weeks. Secondary lymphoid tissue includes spleen, bone marrow and lymphoid mural nodules. Spleen is an oval structure present on right side to the junction of proventriculus and gizzard. It consists of red pulp and white pulp as in mammals. Spleen is reservoir of erythrocytes. Bone marrow cells can produce antibodies. Lymphoid mural nodules are the collections of small lymphoid tissues within or near the lymph vessels. There are scattered masses of lymphoid tissues in the body too. These include those present along digestive tract (GALT) and in the lungs (BALT).
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