Human Biology - EDEXCEL IGCSE - Internal Transport

Internal Transport

The Blood Contains…

• Plasma
• Red blood cells (erythrocytes)
• White blood cells (lymphocytes and phagocytes)
• Platelets

Sickle Cell Anaemia:

This is a disease where the genetic code for the production of haemoglobin has mutated. This causes the haemoglobin when the oxygen concentration is low, to become sickle shaped. Effects of this are:

1. The sickle cells stick together to form blockages in the capillaries causing severe pain, especially in the joints. This is known as sickle cell crisis.
2. A stroke may occur because of this as there is reduced supply of blood to the brain.
3. The sickle shape means less oxygen can be carried. They also often burst and are destroyed by the spleen at a higher rate than normal cells. This causes anaemia.

Haemophilia:

This is caused by a mutation in a gene which produces chemicals needed to form clots. This means that the person infected would often need a blood transfusion after minor injuries and would need injections of the missing clotting factor every time they are injured.

Plasma transports hormones from the glands to organs of the body, nutrients such as glucose, amino acids, proteins and lipids from the gut to cells, urea to the kidneys, carbon dioxide (90%) and heat energy from muscles and the liver to organs that produce less heat maintaining an even body temperature.

Red Blood Cells:

White Blood Cells:

White blood cells prevent diseases. Around 70% of these cells are phagocytes which produce extensions of their cytoplasm called pseudopodia to enclose the foreign organism in a vacuole. Enzymes then break them down. Phagocytes essentially consume them. 25% of these cells are lymphocytes. They are used to make antibodies which stick to the antigens on microorganisms to kill or make it easier to kill it. This is because antibodies make pathogens group together making them easier to kill. Some lymphocytes also produce memory cells which make us immune to diseases.

Platelets:

Exposure to air stimulates the platelets and damaged tissue to produce chemicals. This causes the soluble protein fibrinogen to change into an insoluble fibre of a protein called fibrin. Fibrin forms a network across the wound, trapping the red blood cells and forming a clot. This prevents further loss of blood and entry of pathogens. The clot will develop into a scab which protects the damaged tissue while the new skin grows.

Blood Groups: 
Each person either is in blood group A, B, O or AB. This is dictated by what antigens are located on your red blood cells. Blood group A will have antigen A, blood group B will have antigen B, blood group AB will have both antigen A and B and blood group O will have neither antigen. This is important for blood transfusion as you also have antibodies in the blood which cause the red blood cells with a particular antigen to agglutinate (clump together) and die. For example, if you are blood group A, you will have antibody B meaning only group A or group O blood can be transfused to you. Group O is called the universal donor as it has neither antigen A or B meaning it will never agglutinate. Group AB is  called the universal recipient as it has neither antibody A or B meaning all blood groups can be transfused to the patient.

Transplants:

Transplants are dangerous because of organ rejection. This is where the lymphocytes recognise the antigen on the new cells to be foreign and produces antibodies to destroy them. This can be prevented through tissue typing to keep the antigens as close as possible to the ones already inside the body. This can be achieved by using organs from relatives. Organ rejection can also be prevented through the use of immunosuppressive drugs which stop the immune system from damaging the foreign organ.

Heart:

How the heart works:

1. Blood enters the atria.
2. The walls of the atria contract, raising pressure and forcing open the bicuspid and tricuspid valves. 
3. When the ventricles fill with blood, the ventricles contract, raising pressure and closing the valves.
4. The ventricles continue to contract and raise pressure. This forces the semilunar valves (pulmonary valve and aortic valve) to open.
5. Blood flows into the aorta which carries blood to parts of the body and the pulmonary artery which carries blood to the lungs.
6. High pressure in the aorta and pulmonary artery closes the semilunar valves and the process restarts.

Heart attacks are caused when the coronary artery is blocked completely meaning the heart muscles will stop contracting. This blockage is usually caused by a build-up of fat called an atheroma. Many factors can make heart attacks more likely:

1. Heredity
2. Permanent high blood pressure/hypertension puts more strain on the heart muscles as it has to work harder to pump blood.
3. Diet - a diet rich in fats raises cholesterol. High cholesterol and fats create the atheroma which can block the coronary arteries.
4. Smoking - nicotine constricts blood vessels, raises blood pressure, speeds up the heart rate and increases blood cholesterol.
5. Stress - hormones released during stress constricts blood vessels, raising blood pressure.
6. Lack of exercise - regular exercise reduces blood pressure and strengthens the heart.

Heart rate:

Your heart rate increases during exercise to supply oxygen needed for the increased need for aerobic respiration to release more energy to be supplied to the muscle. This occurs as the aorta and the carotid artery detects extra carbon dioxide from the exercise and sends a signal to the medulla in the brain. The medulla sends impulses along the acceleration nerve. When carbon dioxide production slows, the medulla sends impulses along the decelerator nerve.

Arteries: 

• Used to carry food away from the heart.
• Small lumen (central cavity).
• Thick wall with thick muscle fibres and elastic tissue.

Vein:

• Used to carry blood to the heart.
• Large lumen (central cavity).
• Thin wall with little muscle fibres and elastic tissue.
• Have valves which prevent the back-flow of blood.

Capillaries:

• Carry blood through organs and between cells.
• Capillary walls are one cell thick and allow substances to diffuse in or out.

Pulse:

A pulse occurs when the aorta stretches the wall of the aorta because of high pressure. When the ventricle of the heart relaxes, the stretched section of the aorta recoils, increasing the pressure inside it and thereby creating a wave of stretching followed by constrictions along the aorta and through the arterioles. There is no pulse in veins as it is too far away for the wave to reach.

Tissue Fluid:

This surrounds the capillaries and is the liquid that leaks out of the capillaries under high pressure. It is like blood plasma except lacking in protein which is too large to pass through the capillary walls. Tissue fluid forms a pathway for diffusion of substances between the capillaries and cells.

Circulation System: