THE CIRCULATORY SYSTEM
It is made of
• The heart
• Blood vessels
• Valves
• Blood
The heart
Function: To pump blood around the body.
Circulation
Blood passes twice through the heart in one complete circulation. This is called double/dual
circulation. Dual circulation is made of,
• Pulmonary circuit
• Systemic circuit
Pulmonary circuit
The right ventricle pumps blood through the pulmonary circuit. The right atrium receives
blood from the vena cava. From the right atrium, the blood flows into the right ventricle.
Most of the ventricular filling is passive and the atrium contracts (diastole) to add a little
more blood to the ventricular volume just at the end of the period of filling. The right
ventricle contracts (systole) and pumps blood into the pulmonary artery, which transports
blood to the lungs. The pulmonary vein returns oxygenated blood from the lungs to the left
atrium.
Summary
Heart lungs heart
Systemic circuit
The left ventricle pumps blood through the systemic circuit.
The right atrium receives oxygenated blood from the pulmonary vein. From the left atrium
blood enters the left ventricle. Just like in the right hand side of the heart, most of the
ventricular filling is passive and the atrium contracts to add a little more blood to the
ventricular volume just at the end of the period of filling. The left ventricle is more
muscular than the right ventricle and it contracts with a large force to pump oxygenated
blood at a high pressure into the aorta to start circulation throughout the body and
eventually back to the right atrium.
Summary
Heart body heart
Differences between pulmonary and systemic circuit
Pulmonary Systemic
pressure low high
Direction of blood flow Heart to lungs to heart Heart to body cells to heart
Blood quality Low ( contains carbon dioxide High ( contains digested food
and digested food in low in high concentrations and
concentrations. oxygen)
Plan of the main blood vessels in the human body
Leave space
BLOOD VESSELS
These are tubes within which blood flows round the body. they are of three types
• Arteries
• Veins
• Capillaries
Arteries
Function
• carry oxygenated blood from the heart to body parts ( except the pulmonary artery
that carries deoxygenated blood from the heart to the lungs)
Description
• Thick muscular walls with thick elastic fibres to withstand the high pressure of blood from
the heart
• Narrow lumen
Structure
VEINS
Function
• carry deoxygenated blood from body parts to the heart ( except the pulmonary vein that
carries oxygenated blood from lungs to the heart)
Description
• thin muscular walls with thin elastic fibres
• wide lumen
• have valves
Structure
CAPILLARIES
Function
• allow exchange between blood and tissue fluid. They distribute useful substances to body
cells and remove waste material from cells
Description
• walls are one cell thick
• walls are partially permeable
Structure
PULSE
Pulse is a result of contraction and relaxation of the elastic walls of arteries due to high pressure
generated when ventricles contract.
There is no pulse in veins as blood moves at low pressure.
Pulse rate
This is the number of heart beats per minute.
Effect of exercise on pulse rate
• increases pulse rate
This happens because,
✓ the heart beats faster
✓ more blood is pumped to the muscles
✓ more glucose and oxygen are transported to the muscles
✓ respiration increases
✓ more energy is released for the exercise
CORONARY HEART DISEASE
This is disease caused by blockage/occlusion of the coronary artery which supplies the heart muscle
with oxygen and glucose. If the coronary artery is blocked the cardiac muscle suffocates and the
heart may stop beating and one suffers from heart attack.
Coronary artery may be blocked by,
✓ a fatty substance called artheroma that gets deposited in the arteries
✓ a blood clot called thrombus which forms when the surface of the
artheroma becomes rough causing platelets to initiate blood clotting
Factors contributing to heart disease
1. Fatty diet – cause risk of fat and cholesterol deposit in arteries
2. smoking – nicotine in tobacco smoke roughness the lining of arteries and promotes fat and
fibrin deposition
3. lack of exercise – exercise helps to burn fats and reduce the risk of heart attack
4. Stress – high stress levels lead to high blood pressure. High bllod pressure increases the risk
of heart attack
5. Heredity – one can be born with the tendency of heart attack
Preventative measures of heart attack
✓ Avoid smoking
✓ Avoid fatty diet
✓ Exercise regularly
✓ Avoid or deal with stress
BLOOD
Blood is made of
• Plasma
• Red blood cells( erythrocytes)
• White blood cells
• Platelets
BLOOD PLASMA
This is a pale yellow liquid made up of water (90%) and different substances dissolved in it; eg;
- Dissolved food substances;
▪ Glucose
▪ Amino acids
▪ Mineral salts
▪ Vitamins
- Blood proteins;
▪ Fibrinogen
▪ Enzymes
▪ Antibodies
▪ Hormones
▪ Albumin
- Excretory products;
▪ Urea
▪ Carbon dioxide
functions
• Transports dissolved and floating substances around the body
• Distributes heat around the body
BLOOD CELLS
1. Red Blood Cells (erythrocytes)
Characteristics
• minute, disc-like and biconcave shaped cells
• does not have a nucleus.
• Contain a red pigment called haemoglobin.
Function;
• transport oxygen around the body. Haemoglobin binds with oxygen as blood passes
through the lungs to form oxy-haemoglobin.
2. White Blood Cells
Function
• to fight against diseases- causing micro-organisms
There are two type of white blood cells;
• Phagocytes
• Lymphocytes
Phagocytes
Characteristics
• have irregularly shaped nucleus to enable them to change shape to be able to squeeze
through capillary walls
Function
These cells defend the body by a process called phagocytosis;
Phagocytosis
1) phagocyte migrates towards a pathogen
2) pathogen attaches to the phagocyte
3) phagocyte engulfs (surrounds)the pathogen
4) phagocyte releases digestive enzymes that digests pathogen
5) useful material from pathogen is absorbed and waste is excreted
Lymphocytes
Characteristics
• These have a large nucleus covering more than ¾ of the cell area.
Function;
• Produce antibodies that
o Clump pathogens for easy phagocytosis
o Neutralize toxins produced by pathogens
3. Platelets
Characteristics
• small pieces or fragments of cells produced by the red bone marrow.
• Made of cytoplasm surrounded by cell membrane
• No nucleus
• Irregularly shaped
Function
• Help in blood clotting.
Blood clotting
When a blood vessel is cut or damaged, the platelets produce some substance (enzyme) that
converts the soluble fibrinogen into fibrin which is insoluble in blood plasma;
o Fibrin fibres form a mesh which trap red blood cells and platelets which becomes a
blood clot.
o The blood clot
▪ stops the bleeding.
▪ Prevents entry of pathogens
The blood clot eventually dries and hardens to form a scab which also prevents entry of pathogens.
TRANSFER OF MATERIALS BETWEEN CAPILLARY AND TISSUE FLUID
Arterial blood pressure in the capillaries forces part of blood plasma through the capillary walls.
This fluid is not blood nor plasma, but tissue fluid. It lacks proteins and red blood cells. Tissue fluid
surrounds and bathes every living cell. It contains glucose, oxygen, amino acids, glycerol, vitamins
and minerals which diffuse into the cells
It also contains waste chemicals such as carbon dioxide, water, ammonia and used hormones which
diffuse from cells at the venous end where pressure is low. Most of the tissue fluid then passes back
into the capillary while some enter the blind ending thin walled vessels called lymphatics.
