11 CMH HUMAN AND SOCIAL BIOLOGY THE CIRCULATORY SYSTEM

The Limitation of Simple Diffusion Very small organisms obtain their oxygen and nutrients by diffusion from the outside. When the volume of an organism is large, the surface area ratio to its volume becomes smaller.

Simple diffusion cannot cope and a transport system is needed. Human have a large volume in relation to their body surface. Sufficient oxygen cannot diffuse quickly to supply all body organs.

Purpose of a Circulatory System Transport substances from one part of the body to another. Removal of waste from body parts. Substances include: Oxygen Nutrients Carbon dioxide Urea Heat

Parts of The Circulatory System The Heart Blood Blood Components

The Heart The human heart consists almost entirely of cardiac muscle tissue. This specialized muscle can contract about 70 times per minute without tiring easily. External view Internal view

Questions Why does man need a circulatory system while a bacterium does not? What is heart muscle called? Give the name of two useful substances and two waste substances that the circulatory system transport.

Flow of Blood Through The Heart blood from all over the body enters the right atrium. Blood from upper body parts is taken by superior vena cava Blood from lower body parts by the inferior vena cava. This blood lacks oxygen. The body cells have Used the oxygen for respiration (deoxygenated).

When right atrium contracts, blood is forced through the tricuspid valve to the right ventricle. Tricuspid valve close to prevent back flow of blood to right atrium The right ventricle contracts and force blood. Pulmonary artery take Blood to both lungs.

Blood becomes oxygen rich in lungs (oxygenated). Oxygenated blood then enters the left atrium by the pulmonary vein. Blood is then force through the bicuspid valve into left ventricle. Left ventricle then contract and force blood to aorta.

The cardiac Cycle This is the complete sequence of events during one beat of the heart. Contractions of the heart chambers are called systole. When the chamber relax it is called diastole.

Diastole - when all the muscles of the heart relax and blood flows into the heart. Atria systole – when muscles of the atria contract and force blood into the ventricles. Ventricular systole – when the muscles of the ventricle contracts and force blood out of the human heart

Types Of Circulation There are two types Blood passes through the heart twice on its way around the body once. Pulmonary Circulation This is the passage of blood around from the heart to the lungs and back to the heart. Systemic Circulation This is the passage of blood around the rest of the body, and its return to the heart.

Blood Vessels Arteries Has thick, muscular and elastic walls. Has no valves. Blood under high pressure and moves in spurts. All arteries carry oxygenated blood except the pulmonary artery.

All arteries carry blood away from the heart.

Vein Has thin walls. Has valves to prevent back flow of blood. Blood is under low pressure. All veins carry deoxygenated blood except the pulmonary vein. All veins carry blood towards the heart.

The Blood Red Blood cell Also called erythrocytes Are the most numerous calls in the blood Red blood cells have no nuclei.

They are made in bone marrow. Vitamin b12 is needed to make red blood cell

After 120 days the red blood cells are destroy in the liver and spleen. Red blood cells transport oxygen round the body. Oxygen from the alveoli combines with haemoglobin to form oxyhaemoglobin. Haemoglobin can also combine with carbon dioxide for transport. It has a bi-concave shape.

The bi-concave shape of the red blood cell increase its surface area. This increase the amount of oxygen it transport.

Questions List the components of the blood. What is the advantage of the red blood cell bi- concave shape? Which type of circulation allows blood to move between the heart and lungs?

White Blood Cell Also called leucocytes Have a nucleus White blood cells destroys bacteria Two types phagocytes and lymphocytes Phagocytes engulf microorganisms in a process called phagocytosis. Lymphocytes produce antibodies which kill microorganisms.

Plasma The liquid part of the blood. It is 90% water and 10% solutes. Transport nutrients from the small intestine. Carries nitrogenous waste from cells to the kidneys. Carries hormones from endocrine gland to the organ where it is needed. Help blood carry heat around the body

Platelets Platelets have no nuclei. Platelets are colourless and help in blood clotting at wounds.

Blood Clotting When you get a cut bleeding does not continue for very long. A lump of blood clumps over the wound and seals it, preventing further bleeding. Also prevents entry of micro- organisms.

A clot consists of a mesh of fibers. This trap blood cells and platelets at the wound.

Mechanism of Blood Clotting Platelets and damaged blood vessels release the protein thromboplastin. Thromboplastin then turns the protein prothrombin into thrombin. 3. Thrombin acts on fibrinogen and turns it into fibrin.

4. The fibrin forms the fibres in the clot. 5 4. The fibrin forms the fibres in the clot. 5. Red blood cells and platelets become trapped in the fibres forming the clot. NB Prothrombin, essential for clotting, is made in the liver. Vitamin K help to make prothrombin.

The Pacemaker The heart does not need to be told to contract by the brain. In the wall of the right atrium are some specialized cardiac muscle cells. The cells act as the heart’s pacemaker. These cells send out pulses of electricity that instruct the atria and then the ventricles to contract.

Pulse rate The pumping of the heart causes the surges of blood in arteries. This is detected as the pulse where an artery lies above a bone near the surface of the body. The beating pulse can be seen at the temple and wrist.

Blood Pressure Blood in the blood vessels is under pressure. This is the pressure needed to pump blood round all parts of the body. The pressure is the force exerted on the walls of arteries.

Circulatory diseases Heart attack When blood stops flowing to part of the heart muscle. Because a blockage occurs in one of the coronary arteries. When this happens, the muscles does not get the oxygen it needs to keep it working. It stops contracting, and parts of it may die. In severe cases, the whole heart stops beating. This is cause cardiac arrest.

The person will have no pulse, and they rapidly become unconscious. Without immediate treatment, they will die.

Atherosclerosis This is when fats with high cholesterol build up in the arteries The fat laid down on the walls of the arteries and reduces their internal diameter. This causes high blood pressure (hypertension). This blockage is called thrombosis

Arteriosclerosis This is when the walls of the arteries harden and become less elastic. This also increases blood pressure and so hypertension. The nicotine in cigarette smoke also increases the risk of arteriosclerosis.