This is the fluid part of blood. It is made up of;
a) A soluble protein
A soluble protein called fibrinogen that plays a role in blood clotting.
k) This is a watery fluid containing a variety of substances transported from one part of the body to another e.g. hormones, lipids, enzymes, urea carbon dioxide, plasma, proteins, amino acids etc.
Use of Blood plasma:
- To transport hormones from gland producing them to the target sites.
- To transport food nutrients from the gut to the other parts of the body.
- To transport antibodies to the infected parts of the body.
- To transport Urea from the liver to the Kidneys for excretion.
- To transport carbon dioxide from the body muscles to gaseous exchange system.
- To transport heat from the liver and body muscles to other body parts hence maintaining a constant body temperature range.
- To transport platelets to injured sites on the body so as to initiate blood clotting.
- To distribute salts around the body so as to maintain the body’s electrolytes balance.
CAPILLARY EXCHANGE, FORMATION OF TISSUE FLUID AND LATER LYMPH.
As blood flows from arterioles into blood capillaries. Pressure builds up in the capillaries forcing small molecules like food materials and the fluid part of blood to leave the capillaries and enter the intercellular spaces, leaving behind large molecules like proteins in plasma and cells.
Once the fluid is in the intercellular spaces of tissues, it is no longer called blood but tissue fluid.
Once formed, the tissue fluid surrounds the cells. Body cells then get their requirements e.g. glucose, oxygen, etc. from the tissue fluid and they add excretory materials to the fluid.
Some of the fluid returns in to the capillaries and the other is drained in to a system of narrow channels called lymph vessels. The fluid in these vessels is now called lymph. Lymph is therefore, tissue fluid in the lymph vessels.
THE LYMPHATIC SYSTEM
This is part of the vascular system. It forms the second type of circulation. Most of the tissue fluid as explained above goes back into the blood capillaries and the remainder enters the lymphatic system and becomes lymph fluid. The lymph fluid is transported through lymph vessels. The lymph vessels are similar to veins but they have more valves than the veins. The movement of the lymph fluid through the lymph vessels is due to the contractions of the surrounding muscles. As they contract and relax, they squeeze the lymph vessels to gain the force by which lymph moves. The walls of the lymphatic vessels have pores, which allow the entry of cell, wastes and bacteria. Before reaching the blood, lymph passes through the lymph nodes where the wastes and bacteria are removed.
The lymph joins the blood circulation via the thoracic ducts, which join the vein in the neck. The right thoracic duct drains its contents of the right side and that of the
left drains the left side. The lacteals of the ileum are also connected to the left thoracic duct.
Functions of the lymphatic system
- It transports fatty acids and glycerol from the ileum to the heart where they join the blood system.
- It carries excretory substances from tissues to the blood stream.
- It produces white blood cells, which assist in defense of the body.
- It filters out bacteria before they reach the blood stream.
- Transports hormones from glands to other body parts.
Similarities between blood system and lymphatic system
- Both have valves in their vessels.
- Both are means of transporting materials in the body
- In both a selected muscle provides a force by which substances are moved.
- Both have vessels through which materials are transported.
There are 4 main blood groups i.e.
1) Blood group A
2) Blood group B
3) Blood group AB
4) Blood group O
When one has got less blood than necessary, blood transfusion is carried out. The one who gives blood to a patient is called a donor and the one receiving is known as a recipient. Doctors have to match the blood of the donor to that of the recipient because when incompatibles blood is mixed, the red blood cells stick together (agglutinate) and blood clots. This is a fatal situation.
Agglutination is caused by the presence of proteins called antigens on the surface of cells being mixed with specific antibodies, which work against them. Blood groups are determined by the type of antigens one has in blood. This means that one having antigen A belongs to blood group A. Those with antigen B belong to blood group B. Those with antigens A and B belong to blood group AB while those without antigens belong to blood group O. Each blood produces particular antibodies, which work against particular antigens when introduced into the body. For example, blood group A produces antibody b. This means that blood group A is anti (against) blood containing antigen B (blood group B).
Antibodies are represented by small letters while antigens are represented by capital letters.
Before doctors can carry out transfusion, they carry out tests to make sure that the patient’s and donor’s blood are compatible (the recipient’s blood must not contain antibodies that act on the antigens in the donor’s blood. For example antigen A would agglutinate if mixed with blood containing antibody a. i.e. blood group B.
Table of compatibility:
1) Blood group AB can receive blood from all other blood groups because it has no antibodies and it is therefore called a universal recipient.
2) Blood group O can donate blood to all blood groups because it has no antigens and it is therefore called a universal donor.
“RHESUS FACTOR” System
Rhesus factor is a protein (antigen) ALSO found on the cell membranes of the red blood cells.
Many individuals have the Rhesus factor and are said to be rhesus positive (Rh+) while a few do not have the Rhesus factor and are said to be Rhesus negative (Rh-).
The Rhesus factor was first discovered in a Rhesus Monkey hence its name.
A person who is Rhesus factor positive can receive a successful blood donation without agglutination from a person of Rhesus positive and a person of Rhesus negative.
However, a person who is Rhesus negative can only receive a successful blood donation without agglutination from his fellow Rhesus negative person though he can be transfused with blood which is
Rhesus positive quite successfully only once and after this transfusion, his body produces antibodies against the Rhesus factor. Such antibodies attack the Rhesus factor with subsequent transfusion of Rhesus positive blood leading to agglutination.
The same concept can be applied to pregnancy in that a Rhesus positive woman can successfully carry on a pregnancy where the fetus is Rhesus positive or Rhesus negative.
A Rhesus negative woman can successfully carry a pregnancy where the fetus is only Rhesus negative; with such a woman, the first pregnancy with Rhesus positive fetus can be successful but during the pregnancy the woman’s blood produces antibodies against the Rhesus factor. Such antibodies attack the Rhesus factor if the woman gets subsequent pregnancies where the Fetus is Rhesus positive.
NB: During blood transfusion both the ABO system and the Rhesus factor system of blood groups are used together. So a person of blood group
ARh+ can receive blood from a donor of (i) A Rh+ (ii) A Rh- (iii) ORh+ (iv) ORh-