DESCRIBE THE CONSTITUENTS OF PLASMA AND EXPLAIN THEIR FUNCTIONS

Blood is a tissue consisting of several types of cells. These cells are:-
• RBC (Red Blood Cells). These are also called erythrocytes. Their basic functions are to transport oxygen to the body where it is needed and transport carbon dioxide to the lungs to be eliminated by the body.
• WBC (White Blood Cells). These are also called Leucocytes. There are various types of these WBCs such as lymphocytes, neurophils. However they all have one thing in common they are part of our immune system and are there to fight disease and infection.
• Platelets. The function of platelets is preventing our body from bleeding and upsetting the homeostasis of the body. They allow this to happen by helping to form blood clots at points of injury (externally and internally) such as a cut on the finger.

All these blood cells therefore need to be able to move freely through our bodies and reach specific destination points. This would be difficult if there was not something else present in blood, a fluid that enables movement. blood cells are relatively large molecules and would not easily move through blood vessels if they could not be carried in a fluid. This fluid is called plasma.
Plasma
Plasma is a pale yellow clear liquid, which is approximately 95% water. Plasma accounts for approximately 55% of a human’s blood volume.
So being liquid, it therefore has the ability to flow freely, through blood vessels and the blood cells can float in it and therefore move freely.
Plasma does not only help the blood cells in the blood to move freely to where they are needed, plasma also contains an array of other substances. It transports them, by carrying them in solution (dissolved) or suspension (held in the plasma) to specific areas in the body either to be used by the body or taken to be excreted by the body.
Examples of substances found in plasma are:-
Sugars, Vitamin, Minerals and Lipids
These are nutrients. Which are diffused into the bloodstream during digestion. These nutrients are in transit and are taken where needed and used or taken to be stored such as some vitamins and minerals will be taken to the liver to be stored. If there is excess of certain nutrients such as vitamins they will be taken to the kidneys to be excreted.
Carbon Dioxide
Carbon dioxide is a waste product of cellular respiration. Generally carbon dioxide is transported in just the RBCs, in the form of carbonic acid. However, if there is an excessive amount of carbon dioxide that needs to be removed from our body i.e. during exercise, plasma will carry this. It will transport it to the lungs, and this will be diffused into the lungs during gaseous exchange and exhaled into the atmosphere.
Chemicals
Such as medication, nicotine, alcohol and illegal drugs
These enter our bodies, through digestion, intravenously, and inhalation. These chemicals are not naturally found in our bodies. Sometimes chemicals can be helpful such as medication and sometimes chemicals can be harmful to us such as alcohol. Plasma transports these chemicals to where they are needed in our bodies, or will transport them to be taken out of our systems, such as alcohol will be taken to the liver to be broken down and then removed by the kidneys.
Proteins
Many important proteins which are vital for life and help to maintain homeostasis in our bodies are carried in plasma.6-8% of plasma are protein.
The majority of proteins in the blood are called serum albumin and serum globulins.
Serum albumin plays an important role of binding small molecules together in the plasma so that they can be transported in plasma to their destination. It also helps to regulate osmotic pressure. So water does not leave the plasma and hence the plasma will not be able to allow blood to move freely through the blood vessels.
Serum globulins are more specific. They too are there to bind molecules together, but are more specialised than serum albumin. There are various types of serum globulins such as alpha globulins that transport thyroxin (the hormone released from the thyroid responsible for many metabolic reactions in the body) and retinol (Fat soluble vitamin A).
Plasma also contains other hormones, and enzymes. These will readily be taken to specific places in our body to be used for their specific function.
A protein called fibrinogen is also present in plasma. Fibrinogens’ specific role is to aid clotting. It is therefore important that it remains within close proximatey to the platelets of the blood so that clotting can occur immediately. It is separated from the platelets due to plasma, but when it is needed the blood transports in to the specific area and the fibrinogen and platelets will react to form a clot.

These are just a small amount of what plasma carries, it carries practically everything the body needs and what it does not need and takes it to their specific destination. Everything it carries is usually in transit and is removed from a ‘source and deposited to a ‘sink’. Plasma is vital for transportation in the body not only does it carry substances, due to it being mainly water; it allows blood to flow freely. The Franklin Institute (2010) states “It might seem like plasma is less important than the blood cells it carries. But that would be like saying that the stream is less important than the fish that swims in it. You can't have one without the other.”