The Circulatory System
The Circulatory System
In chickens, the circulatory system consists of the heart and valves that transport nutrients, oxygen and carbon dioxide, waste products, hormones and heat. Unlike mammals, the vascular system of birds contains a renal portal system. Venous blood flows from the legs to the kidneys, then further to the posterior vena cava.
Chickens have a 4 chambered heart, like all birds. This allows for the complete separation of oxygenated and deoxygenated blood. The left side of the heart pumps blood at a higher pressure and as such the walls of the left ventricle are significantly thicker than the walls of the right ventricle.
Chickens, and all birds, have larger hearts than mammals. It is believed that their hearts are larger to keep up with the metabolic demands of flight. Avian hearts also tend to pump higher volumes of blood than mammalian hearts.
A bird's red and white blood cells are formed in the spleen. Unlike mammals, a bird's red blood cells are nucleated.
Diagram 10 shows the anatomy of the avian heart
Electrical activity in the avian heart works much like that of the electrical activity of mammalian hearts. A sinus node depolarization near the top of the right atrium causes the generation of a P wave. The P wave impulse spreads through the atria caudally towards the apex of the heart. The impulse then travels through the atrioventricular transmission system the muscles of the ventricles. Initial activation of the endocardium surrounding the apex of the left ventricle (in a downward direction) causes a small, upright deflection, or R wave. Rapid depolarization of the ventricle results in an S wave.
When blood is pumped from the heart it enters the vessels. There are four main types of blood vessels in the chicken body. The arteries carry blood away from the heart and towards the body cells. The arterioles distribute blood by vasodilation and vasoconstriction. The capillaries exchange nutrients, gases, and waste products between the blood and the body cells. The venules (small veins) and veins conduct blood back to the heart.
Some of the major arteries in the avian circulatory system are the Carotids which deliver blood to the head and brain; Brachials which take blood to the wings; Pectorals which deliver blood to the flight muscles (pectoralis); the systemic arch which is also called the aorta and delivers blood to all areas of the body except the lungs; the pulmonary arteries which deliver blood to the lungs; the celiac (or coeliac) which is the first major branch of the descending aorta and delivers blood to organs & tissues in the upper abdominal area; Renal arteries which deliver blood to the kidneys; Femorals which deliver blood to the and the caudal artery that takes blood to the tail. The posterior mesenteric delivers blood to many organs & tissues in the lower abdominal area.
Diagram 11 shows the anatomy of the major arteries
Some major veins in the avian circulatory system are: the jugular anastomosis which allows blood to flow from the right to left side when the bird's head is turned and one of the jugulars is constricted; the jugular veins which drain the head and neck; the brachial veins that drain the wings; the pectoral veins whose job is to drain the pectoral muscles and anterior thorax; the superior vena cava (or precavae) which drain the anterior regions of the body; the inferior vena cava (or postcava) that drains the posterior portion of the body; the hepatic vein which drains the liver; the hepatic portal vein that drains the digestive system; the coccygeomesenteric vein that drains the posterior digestive system & empties in the hepatic portal vein; the femoral veins drain the legs; the sciatic veins drain the hip or thigh regions; and the renal and renal portal veins drain the kidneys.
Avian blood consists of plasma that is largely water (~85%) plus lots of protein (~9-11%) and other constituents of blood such as glucose. The formed elements include red blood cells (or erythrocytes), white blood cells (or leukocytes), and thrombocytes. Chicken red bloods have nuclei. The only bones in the chicken capable of producing red blood cells are the ulna, radius, femur, tibotarsus, scapula, clavicles, pubis, and caudal vertebrae.
Avian White Blood Cells
The lymphocyte is the most numerous white blood cell. Lymphocytes are either T-lymphocytes (formed in the thymus) or B-lymphocytes (formed in the bursa of Fabricius). B-lymphocytes produce antibodies; T-lymphocytes attack infected or abnormal cells.
The heterophil is the second most numerous WBC in most birds. Heterophils are phagocytic and use their enzyme-containing granules to digest ingested materials. Heterophils are motile and can leave blood vessels to engulf foreign materials.
Monocytes are motile cells that can migrate using ameboid movements. Monocytes are also phagocytic.
Eosinophils make up about 2 to 3 % of the WBC population of healthy birds. The function of these cells is unclear.
The next page will discuss the nervous system.
Chickens have a 4 chambered heart, like all birds. This allows for the complete separation of oxygenated and deoxygenated blood. The left side of the heart pumps blood at a higher pressure and as such the walls of the left ventricle are significantly thicker than the walls of the right ventricle.
Chickens, and all birds, have larger hearts than mammals. It is believed that their hearts are larger to keep up with the metabolic demands of flight. Avian hearts also tend to pump higher volumes of blood than mammalian hearts.
A bird's red and white blood cells are formed in the spleen. Unlike mammals, a bird's red blood cells are nucleated.
Diagram 10 shows the anatomy of the avian heart
Electrical activity in the avian heart works much like that of the electrical activity of mammalian hearts. A sinus node depolarization near the top of the right atrium causes the generation of a P wave. The P wave impulse spreads through the atria caudally towards the apex of the heart. The impulse then travels through the atrioventricular transmission system the muscles of the ventricles. Initial activation of the endocardium surrounding the apex of the left ventricle (in a downward direction) causes a small, upright deflection, or R wave. Rapid depolarization of the ventricle results in an S wave.
When blood is pumped from the heart it enters the vessels. There are four main types of blood vessels in the chicken body. The arteries carry blood away from the heart and towards the body cells. The arterioles distribute blood by vasodilation and vasoconstriction. The capillaries exchange nutrients, gases, and waste products between the blood and the body cells. The venules (small veins) and veins conduct blood back to the heart.
Some of the major arteries in the avian circulatory system are the Carotids which deliver blood to the head and brain; Brachials which take blood to the wings; Pectorals which deliver blood to the flight muscles (pectoralis); the systemic arch which is also called the aorta and delivers blood to all areas of the body except the lungs; the pulmonary arteries which deliver blood to the lungs; the celiac (or coeliac) which is the first major branch of the descending aorta and delivers blood to organs & tissues in the upper abdominal area; Renal arteries which deliver blood to the kidneys; Femorals which deliver blood to the and the caudal artery that takes blood to the tail. The posterior mesenteric delivers blood to many organs & tissues in the lower abdominal area.
Diagram 11 shows the anatomy of the major arteries
Some major veins in the avian circulatory system are: the jugular anastomosis which allows blood to flow from the right to left side when the bird's head is turned and one of the jugulars is constricted; the jugular veins which drain the head and neck; the brachial veins that drain the wings; the pectoral veins whose job is to drain the pectoral muscles and anterior thorax; the superior vena cava (or precavae) which drain the anterior regions of the body; the inferior vena cava (or postcava) that drains the posterior portion of the body; the hepatic vein which drains the liver; the hepatic portal vein that drains the digestive system; the coccygeomesenteric vein that drains the posterior digestive system & empties in the hepatic portal vein; the femoral veins drain the legs; the sciatic veins drain the hip or thigh regions; and the renal and renal portal veins drain the kidneys.
Avian blood consists of plasma that is largely water (~85%) plus lots of protein (~9-11%) and other constituents of blood such as glucose. The formed elements include red blood cells (or erythrocytes), white blood cells (or leukocytes), and thrombocytes. Chicken red bloods have nuclei. The only bones in the chicken capable of producing red blood cells are the ulna, radius, femur, tibotarsus, scapula, clavicles, pubis, and caudal vertebrae.
Avian White Blood Cells
The lymphocyte is the most numerous white blood cell. Lymphocytes are either T-lymphocytes (formed in the thymus) or B-lymphocytes (formed in the bursa of Fabricius). B-lymphocytes produce antibodies; T-lymphocytes attack infected or abnormal cells.
The heterophil is the second most numerous WBC in most birds. Heterophils are phagocytic and use their enzyme-containing granules to digest ingested materials. Heterophils are motile and can leave blood vessels to engulf foreign materials.
Monocytes are motile cells that can migrate using ameboid movements. Monocytes are also phagocytic.
Eosinophils make up about 2 to 3 % of the WBC population of healthy birds. The function of these cells is unclear.
The next page will discuss the nervous system.
- Next page: The Nervous System
- Previous page: The Reproductive System
