Functions of White Blood Cells (Leucocytes)  
The main function of white blood cells is to protect body against diseases and infections.  
Therefore, they are responsible for body defense. They perform this function by;  
(i)  
Engulfing and destroying pathogens, a process called phagocytosis.  
Producing substances that neutralize toxins produced by pathogens.  
(ii)  
(iii) Causing clumping together of foreign materials in the body.  
(iv) Killing infected body cells.  
Figure 5.5: Phagocytosis in the White Blood Cell  
Adaptations of White Blood Cells or Leucocytes  
(i)  
(ii)  
They have no definite shape for easy fighting against pathogens.  
They have large nuclei which control of the production of antibodies.  
(iii) Their cytoplasm contains enzymes which digest the pathogens.  
(iv) Their cell membranes have a sensitive surface to enable the cell to detect foreign  
bodies and destroy them.  
Effects of HIV/AIDS on White Blood Cells  
HIV is the short form of Human Immunodeficiency Virus. HIV causes Acquired  
Immunodeficiency Syndrome (AIDS).  
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When a person is infected by HIV, it attacks a white blood cells called T-helper cells.  
These cells are essential for body immunity.  
▪
HIV enters the human body and fuses with the CD4 found on the cell membrane of  
the T-helper cell. Then, the HIV destroys T-helper cells resulting in the reduction of  
of T-helper cells and CD4.  
▪
This results in lowering of body immunity as there are only a few white blood cells to  
fight against pathogens. When the body gets attacked by diseases frequently and a  
person suffers AIDS.  
Figure 5.6: HIV attacking T-helper  
HIV destroys T-helper cells in the following ways  
(i) It reproduces inside the T-helper cell, and then ruptures the cell's membrane and  
the new viruses are released.  
(ii) It alters the T-helper cells so that when it responds to an infection, it kills itself  
instead of dividing to form new cells.  
(iii) It marks T-helper cells as targets for destruction by other cells in the immune  
system.  
(iv) It causes the fusion of many helper-T cells to form a giant cell. Such a cell can  
survive but it cannot perform normal T-helper cell functions.  
Thus, HIV lowers the immunity of the body making it vulnerable to opportunistic  
infections.  
(d) Platelets  
Platelets are also called thrombocytes. They are small fragments of cells produced in  
the bone marrow.  
▪
▪
They are produced by fragmentation of large cells in the red bone marrow.  
They do not have nuclei and cannot reproduce.  
Function of platelets  
(i) They play an important role in clotting blood.  
Importance of Clotting Blood  
(i) The clot prevents further blood loss.  
(ii) It prevents entry of bacteria which might otherwise cause infection.  
BLOOD GROUPS  
Grouping of human blood is done by using ABO blood grouping system and rhesus factor.  
(a) The ABO blood grouping system  
In ABO system, the blood groups are determined by the presence or absence of antigen  
A and antigen B on the surface membrane of the red blood cell (RBC) as well as the  
presence or absence of antibody  
a
and antibody  
b
in the blood plasma. There are four  
major human blood groups which are; Blood group A, B, AB and O.  
▪
▪
▪
▪
A person with Blood Group A has the antigen A and antibody ‘b’.  
A person with Blood Group B has the antigen B and antibodies ‘a’.  
A person with Blood Group AB has both antigens A and B and no antibodies.  
A person with Blood Group O has no antigens and has both antibodies ‘a’ and ‘b’.  
Table 5.3: Blood Groups according to ABO system:  
Blood group  
Antigen on the membrane of RBC  
Antibody in the plasma.  
A
B
A
B
b
a
AB  
O
A and B  
None  
None  
a and b  
(b) Rhesus Factor (Rh)  
This factor is named after the Rhesus monkey in which it was first observed. In addition  
to the A and B antigens, there is another antigen in the red blood cells called Rhesus  
antigen or Rhesus factor (Rh) or antigen D. The antigen was discovered in the red  
blood cells of monkeys but it is also present in humans.  
▪
When the Rhesus factor is present on the red blood cell membrane, a person is said  
to be Rhesus positive (Rh+) and if it is absent, the person is Rhesus negative (Rh–).  
The person’s blood with Rhesus antigen gives blood the positive sign. e.g. A+, B+,  
AB+ and O+ while the person’s blood lacking Rhesus antigen gives blood the  
negative sign. e.g. A-, B-, AB- and O-.  
▪
BLOOD TRANSFUSION  
Blood transfusion is the transfer of blood from the donor to the recipient. The donor is  
the person who gives blood and recipient is the person who receives blood. Blood  
transfusion is done to replace blood when the recipient has a blood disorder or has lost a  
lot of blood due to surgery or accident.  
In order for blood transfusion to be successful, the blood of the donor and that of the  
recipient must be compatible and mix without agglutination. Agglutination is the  
clumping of red blood cells which may lead to death of the recipient.  
Table 5.4: Compatibility of blood groups  
Donor’s blood  
Recipient’s blood group  
A
B
AB  
O
group  
A
✓
✗
✓
✗
Key:  
B
AB  
O
✗
✗
✓
✓
✗
✓
✓
✓
✓
✗
✗
✓
✓
means compatible  
means incompatible  
✗
NOTE:  
(i) People of blood group AB are called Universal recipients. They can receive blood  
from any of the blood groups because their blood has no antibodies ‘a’ and ‘b’ to  
attack any of the antigens of the incoming red blood cells. However, they can only  
donate blood to someone with blood group AB because blood group AB has both  
antigens A and B which will be attacked by the recipient’s antibodies ‘a’ and ‘b’.  
(ii) People with blood group O are called Universal donors. They can donate blood to  
people of all blood groups because blood group O does not have antigens A or B which  
can be attacked by any of the antibodies ‘a’ or ‘b’ in the recipient’s blood. However,  
they can only receive blood from someone with blood group O because the plasma  
contains both antibodies ‘a’ and ‘b’ which can attack either of the antigens A and B  
present in the donor’s blood.  
Precautions to be taken During Blood Transfusion  
(i)  
Blood from the donor must be checked for compatibility with blood from the  
recipient in terms of both ABO blood group and Rhesus factor in order to avoid  
agglutination and possible death of the recipient.  
(ii)  
The donor’s blood must be screened first before the transfusion process to ensure  
that it does not have any pathogen that can cause diseases such as hepatitis B  
syphilis and AIDS.  
(iii) Donated blood is stored in special bags in a refrigerator and an anticoagulant is  
added to prevent it from clotting.  
(iv) Transfusion should be done only when extremely necessary.  
(v)  
The blood should be taken from vein, probably in the arm.  
(vi) The donor should be given biscuits or glucose after donating to gain strength.  
(vii) Donated blood is should be stored above freezing point in a refrigerator for a  
maximum of 42 days. After that it expires and should not be used.  
(viii) The donor should be aged from 18 to 60 years old and healthy.  
Advantages of Blood Transfusion  
(i) It ensures rapid replacement of blood lost from the body. For example; during and  
after giving birth, during surgery and due to accident. Hence, it saves people’s lives.  
(ii) It is used to treat diseases or disorders such as sickle-cell anaemia.  
(iii) Since blood transfusion involves screening, a donor might have been found with  
health problems which would otherwise not be recognized until it is too late.  
Disadvantages of Blood Transfusion  
(i) Sometimes a reaction arises between the recipient blood and the transfused blood  
in such a way that the patient’s blood destroys the transfused blood. One person's  
blood cannot be exactly the same as another's.  
(ii) Transfused blood may cause infections if it is not well screened.  
(iii) It may cause death to recipients due to blood agglutination if blood is not matched  
with respect to Rhesus factor as well as the ABO system.  
BLOOD CIRCULATION IN HUMAN BEINGS  
Blood circulation is the movement of blood from the heart to all part of the body and back  
to the heart. Human beings exhibit double circulation where by the blood passes through  
the heart twice for each complete circulation. In other less complex organisms such as  
fish, the blood goes through the heart only once. This is known as single circulation.  
Pulmonary Circulation/ Pulmonary Circle  
Pulmonary Circulation is the flow of the blood between the heart and the lungs. In this  
route, a pulmonary artery carries deoxygenated blood from the right ventricle to the lungs.  
In the lungs, oxygen is oxygenated. The oxygenated blood from the lungs flows back to  
the heart through a pulmonary vein.  
Systemic Circulation  
Systemic Circulation is the movement of blood between the heart and all other parts of  
the body except the lungs. In this route, the deoxygenated blood from various parts of the  
body is brought to the right auricle by superior and inferior venacava. The oxygenated  
blood from the heart (left ventricle) is pumped to various body parts through the aorta.  
Importance of Blood Circulation  
(i) It transports useful materials like oxygen, and food nutrients to all body parts.  
(ii) It ensures that carbondioxide and other waste products from the cell are removed  
in order to prevent accumulation.  
(iii) It is important for regulation of body temperature by distributing body heat to all  
body parts.  
(iv) It transports hormones from the organ that produce them to the organs where they  
are needed. For example; insulin from the pancreas is transported to the liver for  
regulating of blood sugar level.  
(v) It enables transportation of white blood cells from where they are produced to where  
there is an infection in the body to fight against diseases and infections.  
(vi) It enables transportation of platelets to the injured area hence it facilitates blood  
clotting to prevent loss of blood.  
Blood Pressure (BP)  
Blood pressure is the force exerted by the blood inside the heart due to contractions and  
relaxation of the heart muscles. Blood pressure is measured by considering the systolic  
pressure and the diastolic pressure.  
When ventricles contract and blood is pumped into the heart, it causes systolic pressure.  
On the other hand, when the auricles contract and pump blood into the ventricles, it  
causes diastolic pressure. The pressure developed during these actions can be felt in the  
arteries.  
Measurement of Blood Pressure  
Blood pressure is usually measured in an artery. It is measured in millimeters of mercury  
(mmHg). The instrument used to  
measure blood pressure is known as  
sphygmomanometer. In a healthy adult the systolic pressure is 120푚푚 표푓 푚푒푟푐푢푟푦 and  
diastolic pressure is about 80푚푚 표푓 푚푒푟푐푢푟푦. Therefore, the blood pressure is expressed  
120  
as  
⁄
푚푚퐻푔. This is the average blood pressure in normal human being.  
80  
NOTE: A blood pressure is recorded in two numbers because when the heart beats once,  
the blood pressure rises to the maximum level and then fall to a minimum level.  
The maximum blood pressure is called systolic pressure and the minimum blood  
pressure is called diastolic pressure.  
DISEASES AND DISORDERS OF THE HUMAN CIRCULATORY SYSTEM  
1. Arteriosclerosis.  
It is the hardening of arteries. It happens when there are fat depositions on the wall of  
the artery causing narrowing of the lumen of the artery. As a result, the heart has to  
pump harder in order to supply the tissues with enough blood.  
Causes of Arteriosclerosis  
(i)  
Excessive alcohol intake and smoking.  
(ii) Stress.  
(iii) Too much fat in the diet.  
(iv) Lack of exercise.  
(v) Old age.  
Effects of Arteriosclerosis  
It may result into high blood pressure (hypertension).  
(ii) Stroke.  
(i)  
(iii) It causes swelling of part of a blood vessel and rupturing of the artery walls.  
(iv) It causes total blockage of an artery, thus depriving some tissues of oxygen. This  
can cause the affected tissue to become severely damaged or to die.  
Prevention and Treatment of Arteriosclerosis  
(i)  
Avoiding excess alcohol intake and smoking.  
(ii) Reducing stress.  
(iii) Minimizing intake of fatty foods.  
(iv) Engaging in regular physical exercise.  
(v) Arteriosclerosis can be treated by medication or surgery.  
2. Sickle-cell Anaemia  
This condition is a genetic disorder which is caused by production of abnormal  
haemoglobin and malformed red blood cells. This is a health problem that makes a  
person’s red blood cells become C shaped or curved like a sickle or a crescent shape  
instead of round.  
Symptoms of Sickle-Cell Anaemia  
(i)  
Fatigue or excessive tiredness.  
(v)  
Abnormal heartbeat.  
(ii) Headaches.  
(vi)  
General body weakness.  
(iii) Dark-coloured urine.  
(iv) Abdominal pain.  
(vii) Shortness  
of  
breath  
during  
physical exercise.  
Control and Prevention  
It is difficult to prevent since it is inherited. Sickle-cell anaemia has no cure. However;  
(i)  
Sickle cell anaemia can be controlled by eating a healthy diet that is rich in  
minerals and vitamins.  
(ii) Patients should avoid doing too much physical exercise, cigarette smoking or  
climbing mountains.  
Figure 5.7: Normal and sickle shaped red blood cells  
3. Leukemia  
Leukemia is a type of blood cancer caused by the over production of white blood cells  
and less production of red blood cells.  
Causes of Leukemia  
(i) Exposure to radiation, certain chemicals such as benzene, cigarette smoking.  
(ii) Exposure to certain types of viruses.  
Symptoms of Leukemia  
(i)  
Abnormally high counts of white blood cells in the blood sample.  
(ii) Abnormal bleeding. For example; nose bleeding and bleeding even from minor cuts.  
(iii) Anaemia. The level of haemoglobin or the number of red blood cells decreases.  
(iv) Extreme body weakness.  
(v) Mouth and throat infections accompanied by fever.  
(vi) Persistent fever and night sweats.  
(vii) Bone and joint pain.  
(viii) Swelling or discomfort in the abdomen.  
(ix) Swelling of lymph nodes especially in the neck or armpit.  
(x) Loss of body weight.  
Effects of Leukemia  
(i)  
The excess white blood cells produced causes the enlargement of the liver and the  
spleen. Tis reduces the efficiency in the functioning of these organs.  
Leukemia is painful therefore it may cause emotional distress and eventually  
death if not treated.  
(ii)  
Prevention of Leukemia  
Leukemia cannot be cured. However, it is controlled by;  
(i)  
Physical exercising.  
Avoiding smoking.  
(ii)  
(iii) Maintaining healthy eating habits.  
(iv) Avoiding harmful radiation and chemicals.  
(v)  
Frequent blood transfusions.  
(vi) Using radiotherapy and chemotherapy to kill the abnormal cancer cells.  
(vii) Transplant of the bone marrow.  
4. High Blood Pressure (Hypertension)  
High blood pressure is the rise in blood pressure above the normal levels. The blood  
pressure of a normal human being is 120/80 mmHg. The high blood pressure over  
140/90 mmHg cause hypertension and sometimes leads into heart failure.  
Causes of High Blood Pressure  
(i)  
Over-consumption of fatty foods.  
(ii) High salt intake.  
(iii) Lack of physical exercise.  
(iv) Obesity.  
(v) High emotional stress.  
(vi) Alcoholism and smoking.  
(vii) Arteriosclerosis.  
Symptoms of High Blood Pressure  
(i) Severe headache  
(ii) Feeling dizzy.  
(iii) Ringing sound in the ears.  
(iv) High blood pressure over 140/90 mmHg recorded in 3-4 consecutive days.  
(v) Failure to see clearly (misty vision).  
(vi) Breathlessness (shortness of breath).  
Effects of High Blood Pressure  
(i) Stroke. Blood supply to the brain is blocked or reduced preventing brain tissue from  
getting oxygen and nutrients.  
(ii) Bursting of the walls of blood vessels that lead into death.  
(iii) Damage of the kidney  
(iv) It may lead to heart failure i.e. the heart fails to function and it stops functioning.  
(v) It may lead to blindness (problem of seeing).  
Prevention of High Blood Pressure  
(i) Engaging in regular physical exercises.  
(ii) Avoiding alcohol and smoking.  
(iii) Eating a balanced diet with less fats to control weight  
(iv) Limiting salt intake.  
(v) Maintaining healthy weight.  
(vi) Reducing stress as much as possible.  
5. Coronary thrombosis (Heart attack)  
Coronary thrombosis occurs when there are blood clots in the blood vessels that supply  
blood to the heart (coronary arteries). This prevents blood from reaching some tissues  
of the heart. The affected tissues lack adequate amounts of oxygen and waste materials  
accumulate in the cells to toxic levels.  
Symptoms of Coronary Thrombosis  
(i) Uncomfortable pressure or sharp pain in the chest, sometimes extending to the  
neck, shoulders and arms.  
(ii) Excessive sweating.  
(iii) Dizziness and fainting.  
(iv) Nausea  
(v) Severe indigestion.  
(vi) Shortness of breath.  
Effect of Coronary Thrombosis  
(i) It can cause death of some cardiac tissue or sudden human death.  
Prevention and Treatment of Coronary Thrombosis  
(i) Doing regular physical exercise  
(ii) Avoiding sudden strenuous activity  
(iii) Avoiding alcohol and smoking  
(iv) Minimize intake of fatty foods  
(v) Minimizing intake of salt by consuming less that 5g of salt per day.  
(vi) Avoiding excessive stress.  
6. Stroke  
A stroke occurs when there is interference in the amount of blood flowing to the brain.  
Such interference can be due to blockage or rupture of an artery supplying blood to  
the brain. This causes some brain cells to lack adequate oxygen and nutrients.  
Symptoms of Stroke  
(i)  
Sudden numbness or weakness especially on one side of the body.  
Sudden confusion or trouble in understanding or speaking  
(ii)  
(iii) Unexpected poor vision in one or both eyes.  
(iv) Sudden dizziness.  
(v)  
Loss of balance.  
(vi) Trouble when walking because of lack of coordination.  
(vii) Sudden severe headaches  
Effects of a Stroke  
(i)  
Weakness or paralysis on one side of the body, leading to difficulties in movement  
and coordination.  
(ii)  
Lack of sensation on one side of the body.  
(iii) Speech or language problem.  
(iv) Loss of memory.  
(v)  
(vi) Difficulty when swallowing.  
Prevention and Treatment of a Stroke  
Behaviour changes.  
(i) Avoiding alcoholism and smoking,  
(ii) Maintaining blood pressure within the normal range.  
(iii) Exercising regularly.  
(iv) Eating a low-fat and low-salt diet