Circulatory System OBJECTIVES:
Discuss the need for transport systems within a living organism;
Observe and draw the structure of the phloem and xylem in the stem and root of a plant;
State the function of the xylem and phloem vessels;
Relate the structure of the circulatory system in humans to their function;
Identify blood groups A, B, AB and O;
Describe the consequences that are likely to result from incorrect matching of blood groups;
Explain the possible causes of hypertension and heart attack;
The need for transport systems In single cell (Unicellular) organisms, all parts of the cell are able to effectively exchange materials with their environment by the process of diffusion. In multicellular organisms (plants and animals), many cells are a long distance away from the supply of oxygen or food. Cell to cell diffusion of substances will not be efficient. Without a method of transport, these cells would die because of lack of food and oxygen.
The Circulatory System is made up of organs such as the heart and blood vessels. The heart is the pump and the blood vessels, the tubes that take blood around the body.
THE HEART The heart is made up of a special type of muscle called cardiac muscle. The heart is divided into 4 chambers.
The two upper chambers are called atria (they receive blood) and the two lower chambers are called ventricles (they pump blood).
The right and left sides of the heart are separated by a septum; this keeps the blood from mixing. Between each atria and ventricle is a valve that shuts when blood passes through it, so the blood continues to flow through the heart and doesn’t flow backwards. Blood then flows into the arteries.
Study the diagram of the heart carefully and learn the parts.
DIAGRAM OF THE HEART
Flowchart of blood through the heart: Deoxygenated blood from the body (Pulmonary Artery) Oxygenated Blood from lungs (Pulmonary vein) To Body (Aorta)
Left Ventricle
Right Atrium
Right Ventricle
To lungs
Left Atrium
CIRCULATION Blood is pumped continuously around the body, transporting substances to and from all body tissues. These tissues must be supplied with oxygen and glucose, and be relieved of waste substances produced by the body’s chemical reactions.
There are TWO circulations: The Pulmonary and the Systematic Pulmonary Circulation – Deoxygenated blood from the body enters the heart on the right side of the heart and is pumped to the lungs for gaseous exchange. The blood becomes oxygenated and returns to the heart to the left side. Systematic Circulation – Oxygenated blood is pumped to the Aorta, which takes blood to every body organ and its tissues. Respiration and other processes occur and the blood receives carbon dioxide and becomes deoxygenated blood. This deoxygenated blood is taken back to the heart. The pulmonary artery is the only artery that carries deoxygenated blood. The pulmonary vein is the only vein in the body that carries oxygenated blood.
Blood enters the heart through veins and leaves the heart through arteries. The heart has its own blood vessels to get it food etc., called the coronary veins and coronary arteries. If a coronary artery becomes blocked then the heart muscle are starved of oxygen and the person suffers a heart attack.
THE BLOOD VESSELS The blood vessels are tubes through which the blood travels around the body. There are three types of blood vessels; the artery, vein and capillary. BLOOD VESSELS Artery
DESCRIPTION
FUNCTION
Thick muscular and elastic walls Transports blood away from the heart The thick walls withstand the great pressure which the blood leaves the heart The elasticity of the walls allows the artery to stretch as blood rushes through, therefore
preventing it from bursting Thin walls which contain less Transports blood to the heart muscle and elastic fibres One-way valves prevent the back flow of blood Wider tube than in arteries Contain one-way valves Capillaries Walls are one cell thick One-cell thick walls allow rapid exchange of materials between the blood and the cells of the Very fragile body The blood passes through at a constant and even pressure to prevent damage to the capillaries Blood flows from artery to capillary to vein Vein
THE BLOOD The blood consists of plasma, platelets, red blood cells and white blood cells. Plasma Plasma is pale yellow and the blood cells and platelets are suspended in it. The plasma is about 90% water. It contains dissolved substances such as digested food molecules, hormones, vitamins and mineral salts. Red blood cells Red blood cells are also known as erythrocytes. These cells are red because they contain a red pigment called haemoglobin. This combines with oxygen and so is important in the transport of oxygen to the cells in the body. Red blood cells are shaped like a biconcave disc. Unlike other living cells they do not have a nucleus. Red blood cells are made in the bone marrow at the ends of the large limb bones. They have a life span of up to 120 days after which they are destroyed or broken down in the liver. There are many more red blood cells in the blood than there are white blood cells. White blood cells White blood cells are larger than red cells and have a nucleus. There is one white blood cell for about every 300 red blood cells. The main function of white blood cells is to defend the body against invading organisms, whether harmful or not. There are two main types of white blood cells:
Phagocytes – The phagocytes destroy invading organisms, such as bacteria, by flowing around them and engulfing them. They then digest the organisms inside them.
Lymphocytes – All cells have chemicals on their surface which identify which body they come from. The chemicals are known as antigens. When lymphocytes find antigens in the body that they do not recognize, they release chemicals called antibodies. The antibodies will destroy the invading cells. Lymphocytes are also able to convert toxins (poisons), released into the blood stream by invading cells, into less toxic substances.
Platelets Platelets are fragment of cells formed in the bone marrow. Their main function is to help in the clotting of blood in open wounds. When a blood vessel is cut, there is bleeding. This helps to wash away dirt and any invading organisms, such as bacteria that may have entered the cut. After a short while though platelets near the wound cause the blood to produce thread-like proteins called fibrin. These form a mesh of fibres that traps the blood cells and eventually forms a blood clot. This seals the wound and prevents further bleeding, the clot dries up to form a hard protective coat called a scab, which keeps the wound clean and protects it until a new layer of skin is formed. In areas where there is a wound you will also find many white blood cells. They are attracted to the wound area to remove any foreign material that may have entered the body through the cut.
Blood groups Humans have one of four types of blood group: A, B, AB and O. the blood group of an individual is determined by the presence of antigens on the surfaces of the red blood cells and antibodies in the plasma. Blood group A B AB O
Antige n A B A and B none
Antibodies anti- B anti- A none anti- A and antiB
The antibodies in the plasma must be different from the antigens on the red blood cells; otherwise they will react and make the cell stick together. This is called clumping of agglutination.
The importance of matching blood groups If a person needs blood, they can be given a blood transfusion. People called blood donors give this extra blood and it is stored in a blood bank, at the hospital. Before the transfusion, it is very important that the blood group of the patients is matched with the blood they are being given. If the wrong kind of blood is given, the antibodies will react with the antigens, causing agglutination of the cells and possibly death to the patient.
You will see that a person with type O blood can donate blood to anyone. Therefore they are called ‘universal donors’. This is because antibodies in the recipient’s blood have no antigens in the donor blood to react with. However a person with AB blood type can receive blood from people with any blood group. So they are called ‘universal recipients’. This is possible because they do not have any antibodies in the plasma to react with antigens of the other blood types.
Diseases of the heart and circulation Hypertension Blood pressure stethoscope.
is
measured
using
a
sphygmomanometer
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Normal blood pressure for a healthy adult is about 120/80. Hypertension is the term for high blood pressure. This is when the pressure passing through the blood vessels is higher than the norm. This condition results from the hardening of arteries, where the arteries have lost their elasticity making it impossible for the artery to stretch to accommodate the blood which is being forced through it. It may also happen if the diameter of the artery becomes narrower due to the build- up of fatty deposits of cholesterol on the wall. This is called atherosclerosis. Hypertension puts greater pressure on the heart since the blood has to be pushed through a much smaller diameter.
Angina The heart keeps pumping because it gets a continuous supply of food and oxygen from the blood passing through the coronary arteries. If the coronary arteries harden, this will restrict the flow of blood to the heart muscles and result in severe chest pains called angina. Thrombosis Sometime the cholesterol build-up in an artery creates a very rough surface through which the blood passes. This can result in the formation of a blood clot which is released into the blood flow. If the blood clot is large enough, it can block the narrow passages in an artery and stop the blood flow through it. This is a condition called thrombosis. If the thrombosis occurs in the coronary artery (coronary thrombosis) this can stop the heart beating and a person has a heart attack. To start the heart beating again, it needs to be massaged or given electrical shock. In the longer term it can be treated by giving the patient a coronary bypass. This is an operation in which a piece of blood vessel is taken from the person’s leg and used to create a new passage for the flow of blood to the heart muscles, bypassing the blocked area.
TRANSPORT VESSELS IN PLANTS The xylem and the phloem are the two structures responsible for transporting material within plants. The phloem and xylem run parallel to each other and their combined structure is called the vascular bundle.
How does water move through plants Water enters a plant through its roots, which spread out into the soil. The outer cells of the roots have very fine extensions called root hairs. These greatly increase the surface area of the roots for the uptake of water. The cell membrane of the root cells acts as a partially permeable membrane and water enters the roots by osmosis. In the soil there are usually more water molecules than in the root cells, so there is a net movement of water molecules into the root hair cells. As water molecules move into these cells, there is then more water in those cells than the ones next to them, so the water will move into those cells. This process of osmosis will continue from one root cell to the next until the water reaches the xylem vessels. The water moves up the xylem vessels because of three factors: 1. Root pressure – as water enters the roots, the pressure in the roots increases. This pushes water up the xylem. 2. Capillarity (Capillary action) – Water molecules are strongly attracted to each other and also to the walls of tubes. This gives rise to the curved shape of the water surface in a tube, called
the meniscus. The narrower the tube, the higher the water molecules can climb. In the very narrow xylem vessels, water can rise to a height of about 3 metres by capillarity. 3. Transpiration – Water is lost from the leaves of plants. This results in the pull of water up the xylem vessels. This mechanism is essential for plants that exceed a height of 3 metres because capillarity is not effective.
How can transpiration be affected? The rate of transpiration (evaporation) from the leaves, and therefore the rate at which water is pulled up the xylem vessels, is affected by temperature, wind speed, humidity and surface area.
Temperature – Water evaporates more rapidly as the temperature increases, because the water molecules have more energy to move around. So they will diffuse out the stomata faster. As it gets colder the transpiration rate will slow down.
Wind speed – If it is windy, the wind will blow away or remove the water molecules near the leaves at a faster rate. So the number of water molecules near the stomata will be lower and the rate of diffusion of water molecules from the air spaces out of the stomata and into the air will be faster.
Humidity – Humidity is a measure of how many water molecules there are in the air. When the air is humid, it contains a lot of water. This will reduce the net rate of diffusion of water molecules out of the stomata into the air.
Leaf surface area – Water diffuses out of the stomata of the leaves, so if there are few leaves (reduce surface area) on the plants then there are fewer parts of the plant losing water vapour.
