BLOOD AND LYMPHATIC SYSTEM BIOLOGY 11DM MRS. HAUGHTON

COMPOSITION AND FUNCTION OF BLOOD

TWO MAJOR PARTS OF BLOOD There are two major parts of blood. Each part is called a fraction. There are a : Solid fraction (blood cells and platelets) Liquid fraction (blood plasma)

PLASMA (FLUID OF BLOOD) For transport of dissolved substances and heat.

ERYTHROCYTES (RED BLOOD CELLS) For transport of oxygen.

CENTRIFUGATION SEPERATES BLOOD

BLOOD SMEAR

WHITE BLOOD CELLS AND PLATELETS For defence of the body.

BLOOD Blood is made up of a liquid part (plasma 55%) and a solid part (red and white cells and platelets 45%). Plasma is 90% water.

Functions of Blood There are three main functions of blood: Transport Function of Blood Cells Function of Blood Red cells contain haemoglobin that transports oxygen Plasma transports heat, hormones, cells, nutrients, gases etc. White cells defend the body against disease. Platelets help blood to clot after injury. There are three main functions of blood: Transport Homeostasis Defence

TRANSPORT Many different substances are dissolved in the blood plasma and are therefore able to travel around the body from cell to cell. The useful, waste and harmful substances mentioned in previous classes are dissolved and all are transported in the plasma. E.g. are water, oxygen, carbon dioxide, digested food, minerals, urea, toxins.

HOMEOSTASIS Homeostasis is the collective group of responses that the body makes in order to keep its internal environment constant. In this respect, the blood assists in keeping the body temperature at a constant 37°C by transporting heat around the body from muscles and the liver which make a lot of this heat. the blood in the capillaries supplying the skin carry away excess heat to the surface of the skin to be released if the body gets too hot.

DEFENCE The blood defends the body in two ways: The leucocytes or white blood cells which destroy invading organisms The platelets which clot the blood

WHITE BLOOD CELLS White blood cells defend the body in two main ways: By engulfing and breaking down the invading organism (monocytes and phagocytes) By releasing antibodies (lymphocytes) that will seek out the specific invading organism and cause it to explode, shrink or clump together.

PHAGOCYTES AND MONOCYTES These white blood cells actually engulf the invading organism in a process called phagocytosis. Digestive enzymes inside the white blood cells will then break-down the organism.

Phagocytosis

LYMPHOCYTES Lymphocytes are white blood cells that make a special substance called antibodies. Invading organisms each carry on their surfaces a “tag” called an antigen which distinguishes them from other types of germs. Therefore, there will always be a few lymphocytes that is specific for each type of germ that will enter your body. These are known as the memory cells. If you are infected with the same germ again, these cells will quickly act to destroy them so you are not sick for such a long time.

BLOOD CLOTTING Blood clotting serves two main purposes: It prevents the body from losing too much blood from a wound It keeps invading organisms from entering a wound and causing infection.

BLOOD GROUPS There are four blood groups: A, B, AB and O.

BLOOD GROUP INTERACTIONS

HYPERTENSION HYPERTENSION

Hypertension is abnormally high blood pressure. It develops because the blood flow through the arteries has been hindered. Two ways in which this may happen is arteriosclerosis and atherosclerosis.

ATHEROSCLEROSIS The gradual depositing of fatty plaques in the lumen of arteries that restricts the blood flow. This is common in obese patients.

ARTERIOSCLEROSIS ARTERIOsclerosis. Actual hardening of the elastic muscular walls of the arteries. This is more prevalent in older patients. Recall that the arteries walls must be muscular and flexible in order to expand and contract as blood pulses through them. Therefore, what is the implication of the walls hardening over time.

HYPERTENSION DAMAGES THE HEART If the blood vessels that supply the heart are blocked so that blood cannot reach the heart, then that part of the heart muscle will die and no longer assist in pumping. This damage is permanent and the person is said to have had a heart attack or to have gone into cardiac arrest.

HYPERTENSION DAMAGES THE KIDNEYS When the blood vessels are narrowed in the kidneys, this reduces the amount of fluid that can be filtered by the kidneys. Waste products will therefore build up in the body, the volume or urine produced will be less and eventually the kidneys may fail totally (renal failure).

HYPERTENSION DAMAGES THE BRAIN As blood pressure increases, the blood vessels in the brain may actually rupture (burst) causing: Stroke Bleeding in the brain An the result may be partial or total body paralysis, loss of speech or even death.

FACTORS THAT INCREASE THE LIKELIHOOD OF DEVELOPING HYPERTENSION Medical research has pointed out the following risk factors as increasing the likelihood of hypertension developing in patients: Stress Inheritance Diet Obesity Tobacco smoking High cholesterol levels Lack of exercise

BLOODTISSUE FLUIDLYMPH

TISSUE FLUID Capillaries are very thin and have pores. When blood at high pressure leaves arteries and enter capillaries, some of the fluid from blood is squeezed out of these pores. This fluid is called tissue fluid.

White blood cells are also flexible and can squeeze out with the tissue fluid. The tissue fluid then bathes or washes the cells that are near to the capillaries supplying cells with nutrients and oxygen.

N.B. Blood itself does not get to the cells to carry nutrients and oxygen, so the tissue fluid is useful in this respect.

As the cells produce waste such as carbon dioxide which diffuses into the tissue fluid, some of this returns into the capillaries at the venous end of the capillary bed. From here the waste returns to circulation. The tissue fluid that does not return to circulation passes into lymphatic vessels nearby and becomes lymph.

Lymph is a transparent, yellow fluid that carries white blood cells called lymphocytes that fight pathogens. Therefore, lymph nodes that are near to the site of an infection will swell and can be felt by a doctor, especially in the neck, armpit or groin area.

LYMPHATIC SYSTEM

TISSUE FLUID TO LYMPH The plasma and white blood cells that leak out of the blood capillaries return to the blood system by the lymphatic capillaries which lie within tissues and among the regular capillaries. The tissue fluid slowly drains into these lymphatic capillaries and is now known as lymph. Lymphatic capillaries join up to form lymph vessels then enters the blood system again by way of the veins.

LYMPHATIC SYSTEM AND LYMPH NODES The lymphatic system has no pump to make lymph flow so lymph vessels have valves. Lymph flows more slowly than blood. On its way back from the tissues to the veins, lymph flows through several lymph nodes which contain large numbers of white blood cells. Most bacteria and toxins are destroyed by these cells. Therefore, the lymph nodes will swell when there is an infection nearby.