BLOOD CIRCULATORY SYSTEM

CIRCULATORY SYSTEM Forms the body’s transport system. Comprises of blood, blood vessels and the heart. Blood provides the fluid environment for the body. Blood vessels are tubes which carry the blood. The heart is the pump to keep the blood moving around the body.

THE BLOOD Blood is composed of 55% straw-coloured fluid called plasma and 45% is made up of cells Three main types of blood cells: Erythrocytes Red blood cells Leucocytes White blood cells Thrombocytes Platelets

RED BLOOD CELLS Most numerous of all the blood cells. No nucleus and the cytoplasm is filled with haemoglobin which carries oxygen. Bi-concave shape Their membranes allow for the exchange of oxygen. Produced in the bone marrow.

WHITE BLOOD CELLS Much larger than red blood cells. They have a nucleus. Protect against microbe entry. Fight bacteria and viruses. Remove waste materials

PLATELETS They are cell fragments formed in the bone marrow Involved in blood clotting and so prevent excess blood loss and to create a barrier against microbe entry.

FUNCTIONS OF THE BLOOD There are four main functions of blood Transportation Defence Regulation Clotting

Transportation Red blood cells carry oxygen to the cells of the body. Carbon dioxide is carried back to the lungs Nutrients such as glucose, vitamins and minerals are carried around the body. Hormones are transported around the body to their target organs. All waste materials such as urea, are carried in the blood to be removed and excreted.

Defence The white blood cells fight against disease and microbe entry. They engulf the bacteria and destroy them by a process called phagocytosis. Lymphocytes, specialised white blood cells, produce antibodies which give the body future resistance to re-infection.

Regulation The blood regulates body heat by absorbing it from the liver and muscles as it passes and transports it around the body. Blood also helps to regulate pH balance.

Clotting Platelets will clot a damaged area where blood loss has occurred. Clotting prevents excess blood loss and protects against microbe entry.

BLOOD VESSELS Blood flows around the body by the pumping action of the heart and is carried in vessels known as :- Arteries Veins Capillaries

ARTERIES Carry blood under pressure away from the heart. Thick muscular walls to withstand pressure. No valves Carry oxygenated blood, except for the pulmonary artery. Lie deeper than veins

VEINS Carry blood back to the heart under low pressure. The walls are less thick and elastic. Valves prevent backflow. Carry deoxygenated blood except for the pulmonary vein.

CAPILLARIES Smallest vessels. They join the arterioles and the venules. Only one cell thick to allow for the transfer of substances between the cells and the capillaries. Have no valves

CAPILLARY EXCHANGE The exchange of substances between tissue cells in the body and the blood in the capillaries. Oxygen, nutrients, vitamins and minerals pass into the tissue fluid to nourish the cells. Carbon dioxide and waste products pass out of the cell and back into the blood to be excreted.

Main arteries and veins of the arm

Main veins of the leg

Main veins of the leg

ARTERIES TO THE HEAD Facial artery Occipital artery Carotid artery

VEINS FROM THE HEAD External Jugular Internal Jugular

BLOOD PRESSURE The force with which blood is pumped through the vessels. The maximum (systolic) pressure is when the blood has just been pushed into the arteries. The minimum (diastolic) pressure is when the heart relaxes and blood flows into the heart from the veins.

FACTORS AFFECTING BP Anything that makes the heart beat faster will raise the blood pressure. Excitement Anger Stress Fright Pain Exercise Smoking and drugs

THE PULSE The pulse is the wave of blood as it passes through the arteries. It can be felt at positions on the body where the arteries pass close to the surface.

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