TRANSPORT MECHANISMS; NEEDS, MATERIALS, THE COMPOSITION, STRUCTURE AND FUNCTIONS OF THE HUMAN BLOOD,LYMPH

In every living organism, there is a need for transportation of nutrients in the body. This is made possible through the blood as it carries nutrients eaten and absorbed by the organism to vital tissues and organs that need them the most.
There is a need for transport systems because in large and more complex organisms, 1. The ratio A/V diminishes and so the rate at which nutrients and other substances diffuses.
2. Substances have to move greater distances.

MATERIALS FOR TRANSPORTATION
In plants, they include water, mineral salts, manufactured food and carbon(IV) oxide.
In animals, they include digested food, vitamins, mineral salts, oxygen, carbon(IV) oxide, urea, salts, hormones, water and antibodies.

MEDIA FOR TRANSPORTATION
1. Blood and lymph in the vertebrates.
2. Cytoplasm in unicellular organisms
3. Cell sap or latex in most plants.
4. Body fluids in invertebrates.
5. Closed and open circulations.

COMPOSITION, STRUCTURE, AND FUNCTION OF HUMAN BLOOD

COMPOSITION
The blood consists of the fluid portion, called the Plasma and cellular elements which include the Red blood Cells also known as the Erythrocytes, White Blood Cells also known as the Leukocytes and the blood platelets also called Thrombocytes.

STRUCTURE AND FUNCTION
RED BLOOD CELLS
They are flat, circular and biconcave discs. They are produced in the erythrocytes bone marrow and have no nucleus. They contain a red pigment rich in iron called haemoglobin which readily combines with oxygen to form oxyhaemoglobin. the respiratory pigment, called the Haemoglobin transports oxygen in form of oxy- haemoglobin.

BLOOD PLATELETS OR THROMBOCYTES
They are square or star-like or irregular in shape. Thrombocytes are produced in the red bone marrow. They help in the clotting of blood to prevent excessive bleeding and entry of bacteria into the body through the wound.

PROCESS OF BLOOD CLOTTING
1. When the blood vessels are damaged, platelets break up releasing thrombokinase in the presence of vitamin K and calcium salts.
2. Thrombokinase converts prothrombin into thrombin.
3. Thrombin acts on fibrinogen to form insoluble fibrin which is the clot.
This fibrin seals the blood cells to prevent further bleeding.

BLOOD PLASMA
The blood plasma is the liquid portion of the blood. It contains 55% of the total volume of blood. It contains 92% water, dissolved nutrients, blood proteins, certain hormones and antibodies.
FUNCTIONS
1. Plasma transports some oxygen and Carbon(IV) Oxide.
2. It contains antibodies which destroy invading bacteria by producing chemicals.
3. Fibrinogen present in the plasma is an essential component of the clotting process.
4. It contains glucose which serves as the prime source of our cells.

GENERAL FUNCTIONS OF BLOOD
1. It transports oxygen, carbon(IV) Oxide, water, products of metabolism, food materials and hormones.
2. Some white blood cells produces antibodies that destroy or inactivate invading pathogens.
3. Clot formation by platelets prevents bleeding by sealing off wounds thereby excluding pathogens that would have entered the body through wounds.
4. Blood helps to distribute heat and also helps in controlling the body temperature

LYMPH
This is the pale watery fluid in the lymphatic system. It becomes the tissue fluid when it bathes the tissues and occupies the space between cells. The lymphatic vessels have valves to maintain a one-way flow of lymph. The contraction of muscles help to push the lymph forward.

COMPOSITION OF LYMPH
Lymph is similar to plasma but it contains only the substances filtered out through the plasma which include small molecules, waste materials, white blood cells and some hormones.

FUNCTIONS OF LYMPH
1. It returns excess tissue fluid to the blood.
2. It transports fatty acids and glycerol from the villi to the blood.
3. The lymph nodes produce some white blood cells that prevent pathogens and toxins from destroying the body.
4. It transports wastes from the cells.

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