THE CIRCULATORY SYSTEM

Transcription

1 Functions of the circulatory system PHYSICAL EDUCATION THE CIRCULATORY SYSTEM Circulates blood through the body Transports water, oxygen and food to cells and removes wastes from the cells Helps other body systems to function (e.g. the muscular system) Helps fight disease Helps maintain correct body temperature The Circulatory system has three parts: The Heart the organ which pumps blood around the body The blood vessels the tubes through which the blood moves (arteries, capillaries, veins) The blood consists of plasma, red blood cells, white blood cells and platelets THE HEART Function The heart is a hollow muscular organ which serves as a pump to push blood around the body. It is capable of pumping blood about two meters into the air if a large artery is cut. Structure The heart is divided into four chambers A muscular wall divides it into right and left sides Each side consist of two chambers: the upper chamber is called the atrium and the lower chamber is called the ventricle Blood flows into the atrium, which pushes the blood through a valve into the ventricle. The valve ensures that blood does not flow back into the atrium

2 THE ACTION OF THE HEART (WoS pg. 37) The beating action of the heart has three stages called the cardiac cycle. Stage 1 (a) Diastole The atria and ventricles are relaxed and blood flows from the atria to the ventricles Stage 2 (b) Systole The atria contracts expelling blood into the ventricle and filling it which then cause the bicuspid and tricuspid valves to close Stage 3 (b) Systole The ventricles contract powerfully and pumps blood through the semilunar valves into the arteries The heartbeat is one complete cycle of the heart Heart rate (pulse) is the number of times the heart beats per minute. In a healthy adult the resting heart ate will be about 70 beats per minute Stroke volume is the amount of blood pumped by the heart in each beat Cardiac output is the amount of blood pumped out of the heart per minute. It is controlled by both heart rate and stroke volume: Heart rate x stroke volume = cardiac output The pulse The pulse can be felt and sometimes seen in the arteries just below the skin in certain parts of the body. The pulse occurs when the left ventricle contracts and forces the blood into the aorta. The new blood pushes blood already there further on. The movement of the blood in the artery is felt as the pulse. The pulse is felt on the radial artery of the inside of the wrist and on the carotid artery in the neck.

3 BLOOD FLOW AROUND THE BODY The right atrium (A) receives deoxygenated blood from the Inferior and Superior vena cavae. This blood is dark red because its oxygen has been used up. The right atrium pumps this blood through the tricuspid valve into the right ventricle (D). The right ventricle pumps deoxygenated blood through the semilunar valve into the Pulmonary artery (F) which takes the blood into the lungs where it regains oxygen and becomes bright red in colour. Oxygenated blood flows from the lungs through a large vein called the Pulmonary vein (G) to the left atrium (B) The left atrium pumps the blood through the Mitral or Bicuspid valve into the left ventricle (C) which is the most powerful part of the heart. The left ventricle pushes the blood through the semilunar valve into the Aorta which takes the blood to the rest of the body Systemic Circulation - blood being pumped from the heart to the lungs and back again Pulmonary Circulation blood being pumped from the heart to the lungs and back again

4 BLOOD VESSELS There are three types of blood vessels: Arteries carry blood away from the heart to the limbs and organs of the body have the thickest walls which are elastic to withstand the high pressure surges of blood caused by the powerful contractions of the heart contracts in between heart beats to help blood flow along the arteries carry oxygenated blood except the Pulmonary artery divide into smaller vessels called arterioles Capillaries are the thinnest blood vessels which are only one cell thick only let single cells of blood through one after the other allow oxygen and nutrients to pass from the blood into the cells and carbon dioxide and waste to pass from the cells to the blood join up again to form first venules then veins

5 Veins return blood from the limbs and organs to the heart are wider and have thinner walls than arteries because the blood pressure in them is thin and less than that of the arteries some have valves which prevent blood flowing backwards, away from the heart, such as in the limbs the contraction of muscles around the vein assist the return of blood to the heart carries deoxygenated blood except the Pulmonary vein BLOOD seven percent of body weight is blood blood is composed of Plasma 55% and cells 45% which consist of red cells, white cells and platelets Plasma is a pale yellow liquid contains proteins, salts, glucose, fats, antibodies, hormones, carbon dioxide and waste products Red blood cells (erythrocytes) made in the red marrow of long bones, sternum, ribs and vertebrae are very tiny and numerous (millions would fit on a pin head) give blood its colour contains Haemoglobin which is responsible for carrying oxygen from the lungs to the cells and taking carbon dioxide from the cells to the lungs Haemoglobin carrying oxygen is bright red Haemoglobin carrying carbon dioxide is dark red White blood cells (leucocytes) Are made in the bone marrow, lymph nodes and spleen are colourless and not as numerous as red blood cells three times the size of red blood cells engulf and destroy foreign particles or harmful bacteria which get into tissue or blood

6 Platelets are made in bone marrow stick to each other easily are tiny fragments of large cells helps to clot blood so that dangerous bleeding cannot occur seal holes and tears in small blood vessels FUNCTIONS OF BLOOD Blood links all the tissues and organs of our body together. Blood has four main functions Transportation Carries nutrients from our digestive system to all body cells Takes oxygen from the lungs to working muscles Removes carbon dioxide from the body s cells and takes it to the lungs Removes waste products and excess water in our kidneys Takes hormones to where they are needed Protection Carries white cells to the sites of infection Carries antibodies to destroy germs Carries platelets to damaged areas to form clots Temperature regulation Carries heat away from working muscles to skin Carries heat away from the centre of the body to skin Maintains temperature within the body Maintains the body s equilibrium Reduces the effect of lactic acid produced in the working muscles Regulates fluid balance Enables hormones and enzymes to work

7 BLOOD PRESSURE Blood pressure is the force of the blood against the walls of the blood vessels. It is measured in the large artery found above the elbow. Blood Pressure is measured in two ways Systolic pressure is measured when the left ventricle of the heart contracts Diastolic pressure is measured when the left ventricle of the heart is relaxed Blood pressure is expressed as a fraction: Systolic pressure Diastolic pressure Average blood pressure is 120 (measurements are millimeters of mercury). 80 The normal range for a healthy adult is between 100 and In arteries blood pressure is high because the arteries are narrow and a lot of blood is being forced into them from the heart. Blood pressure in veins is low because they are wider and far away from the heart. Because the pressure in veins is low, valves are needed to prevent blood from flowing backward. Factors that affect Blood Pressure Age increases blood pressure because arteries become less elastic. Exercise increases blood pressure and returns to normal after exercise. Regular exercise helps to lower resting blood pressure and prevent cardiovascular disease. Stress cause hormones to be released into the blood which increases blood pressure. Smoking increases blood pressure because nicotine reduces the efficiency of the capillaries. Diet can increase blood pressure if fat and salt intake is too high. Fatty deposits block and harden the arteries. Over Weight puts extra pressure on the circulatory system and increases blood pressure. High Blood Pressure or Hypertension is caused by blockages in the smaller blood vessels, or arteries which mean that the heart has to work harder to force blood around the body. Arteries taking blood to the heart muscle can also become blocked. Sudden activity can cause a sharp pain (called angina) or even a heart attack.

8 EFFECTS OF EXERCISE ON THE CIRCULATORY SYSTEM During Exercise Heart rate increases. When we start to exercise the hormone adrenaline is released into the bloodstream which causes the heart to beat faster Stroke volume increases. The heart contracts more forcefully which sends out a greater amount of blood with each contraction. Cardiac output increases. Blood circulation speeds up and greater amounts of oxygencarrying blood reach the working muscles. The forceful contractions of muscles forces more deoxygenated blood back to the heart more quickly. Blood flow is reduced in areas of the body not in urgent need of oxygen, e.g. the digestive system. Blood flow is increased to the areas of the body in greatest need of oxygen, e.g. skeletal muscles. Blood vessels to the skin areas become enlarged to allow excess heat from muscles and organs to be lost more easily from the skin. During very hard exercise blood vessels are reduced in size which will cause body temperature to raise very quickly and cause fatigue and overheating. Oxygen going to the muscles can be increased up to 3 times the resting amount. Blood flow can be increased up to 30 times which means that the working muscles can receive up to 90 times the amount of oxygen they receive at rest.