Clare Hargreaves-Norris

Blood

ACCESS HEHuman Biology.

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Introduction

The circulatory system is comprised of: Blood, this fluid transports vital

substances to all areas of the body. Blood is transported in vessels known

as arteries, veins and capillaries. The heart acts as a pump to move the

blood around the body.

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Functions Of The Blood

The blood has three main functions

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1. Transportation

Red blood cells carry oxygen to the cells of the body.

Carbon dioxide is carried back to the lungs. Nutrients such as glucose, vitamins and

minerals are transported around the body. Hormones are secreted into the blood and

attach to the plasma so that they can be transported around the body to their target organs.

All waste materials such as urea are carried in the blood to be removed and excreted.

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2. Defence

Leucocytes (white blood cells) fight against disease and microbe entry.

Leucocytes engulf the bacteria and destroy them (phagocytosis).

Lymphocytes (specialised leucocytes) produce antibodies which give the body future resistance to re-infection.

Coagulation. Platelets start the clotting process to prevent excessive blood loss and to stop infection from gaining entry into the body.

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3. Regulation

The blood regulates body heat by absorbing it from the liver and muscles as it passes by, and then transports it around the body.

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Composition of blood

Blood is made from Plasma (55%) a

straw-coloured fluid Erythrocytes (red

blood cells) Leucocytes (white

blood cells) Thrombocytes

(platelets)

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Structure Function

Plasma 90% water. Remaining 10% consists of other substances:- blood proteins, - mineral salts,- nutrients, - waste material, - gases, - enzymes,- hormones, - antibodies.

Renews the cellular fluid. Maintains the pH of the blood at 7.4. Makes the blood viscous. Provides energy to the cells. Produces chemical reactions. Protects against infection.

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Structure Function

Erythrocytes (red blood cells)

Minute biconcave discs. They obtain their red colour from haemoglobin combining with oxygen to form oxyhaemoglobin. Made in the red bone marrow. They take approximately 7 days to form. They then function for approximately 4 months. They are then destroyed by the liver or spleen.

To carry oxygen around the body to the cells. To take carbon dioxide away from the cells.

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Structure Function

Leucocytes (white blood cells)

Are colourless cells, contain a nucleus, and are larger than red blood cells. There are fewer leucocytes than erythrocytes. There is approximately 1 leucocyte to every 600 erythrocytes.

To fight infection.2 main types of

leucocytes:1. Granulocytes (75%)

Neutrophils - digest bacteria & cell debris. Basophils – release histamine and heparin. Eosinophils – combat inflamation.

2. Agranulocytes (25%). Lymphocytes (23%) - produce antibodies to kill foreign proteins. Monocytes (2%) - ingest foreign proteins.

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Structure Function

Platelets (Thrombocytes).

Platelets are formed in the red bone marrow. They are tiny fragments that are even smaller than red blood cells.

They produce thrombokinase. Thrombokinase starts the ‘clotting cascade’. Clotting cascade is a chain of reactions resulting in a blood clot. This is an essential part of homeostasis to prevent blood loss.

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Blood clotting

Platelets produce a substance called thrombokinase.

This sets off a chain of reactions resulting in the laying of fibres.

The fibres cover the wound thus preventing blood loss.

When the blood clots it forms a scab.

A scab is a natural protective seal (plaster) to the area.

This process is known as the ‘Clotting Cascade’.

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Factors affecting the blood clotting process

The health and efficiency of the blood supply can be affected by:

Smoking Alcohol Poor nutrition intake Anti-coagulant drugs such as warfarin

and aspirin.