Biology
Human Circulatory System
Human circulatory system
The circulatory system helps
• fight disease
• maintain body temperature
• helps body to achieve stability among all its systems
• It consists of heart, veins, arteries and blood.
• It is divided into pulmonary circulation and systemic circulation.
• In pulmonary circulation the deoxygenated blood is taken to the lungs from the heart and the oxygenated blood is returned to the heart. Pulmonary artery plays significant role in pulmonary circulation.
• In systemic circulation the oxygenated blood is sent to the rest of the body and deoxygenated blood is sent back to the heart from parts of the body. The artery aorta helps in sending oxygenated blood to the parts of the body and the veins superior vena cava and inferior vena cava helps in sending deoxygenated blood to the heart. At the body parts, capillaries (tiny blood vessels) connect the small artery branches to small veins. Capillaries provide oxygen and nutrients to the cells and receives waste products. Capillaries through small veins and then large veins send back blood to heart to start pulmonary circulation again.
Heart
The 4 chambers of the heart are left atrium, right atrium, left ventricle and right ventricle. The atriums are upper chambers and the ventricles are lower chambers. The atria receive blood from the veins and the ventricles push blood out of the heart. The deoxygenated blood returned to the right atrium is pushed to right ventricle, which pumps it to lungs through pulmonary artery. The left atrium receives the oxygenated blood from lungs is passed to left ventricle and the blood is pumped through aorta to different parts of the body.
Veins
The blood flows to the heart through veins. Veins that are closer to heart are larger. The walls of the veins are thinner than artery walls. They can hold more blood than arteries because of less pressure. The walls of veins have less smooth muscle and connective tissue.
Arteries
Arteries take the blood away from the heart. The arteries become smaller farther from heart. The 3 types of arteries are elastic arteries, muscular arteries and arterioles. Elastic arteries receive blood directly from the heart. Pulmonary artery and aorta are elastic arteries. The muscular arteries which are made of smooth muscle move blood from elastic arteries to the body. Femoral and coronary arteries are muscular arteries. Arterioles which move blood from muscular arteries to the capillaries are the smallest arteries.
Capillaries
They are blood vessels that transport blood, nutrients and oxygen to cells in your body. They are the smallest blood vessels. They connect arteries to veins.
Valves
Veins have valves which helps blood flow in the right direction. There are 4 valves in the heart. The tricuspid valve separates the right atrium from the right ventricle, the bicuspid valve separates the left atrium from left ventricle, the pulmonary valve separates the pulmonary artery from the right ventricle and the aortic valve separates the aorta and the left ventricle.
Blood
Blood is the transport system of the body. The 4 main components of blood are Plasma, Red blood cells, White blood cells and Platelets. Plasma which is about 55 percent of blood makes blood liquid and it consists of water, salts, sugar, fat and protein. Red blood cells (erythrocytes) which is about 40 to 45 percent of blood’s volume have no nucleus and contain a protein called haemoglobin that carries oxygen from the lungs to the rest of the body and returns carbon-di-oxide to the lungs. White blood cells (leukocytes) which is 1 percent of blood protect body from infection. Platelets (thrombocytes) which are cell fragments are essential for blood clotting