Chapter 5: TRANSPORT OF MATERIALS IN MAMMALS  
Mammals are complex organisms which are made up of many cells. Hence, diffusion alone  
is not enough to ensure efficient carrying out of life processes. Mammals therefore have  
an elaborated and efficient transport system called the circulatory system.  
Circulatory System is the system that permits blood to circulate and transport nutrients,  
oxygen, hormones throughout the body as well as carbon dioxide and other wastes from the  
cell of the body. Circulatory system is also called cardiovascular system.  
Components of the Circulatory System  
Circulatory system is made up or composed of the three components namely:  
(i)  
Heart (pumping organ).  
(ii)  
Blood (transporting fluid).  
(iii) Blood vessels (tubes through which blood flows).  
Therefore, transport in mammals such human involves the pumping of a red liquid called  
blood by an organ called heart. The pumped blood is distributed to all parts of the body  
by the blood vessels.  
1. THE MAMMALIAN HEART  
The mammalian heart is the organ whose function is to pump blood to the whole body via  
the blood vessels. It is located in the center of the chest cavity between the two lungs.  
The External Structure of the Mammalian Heart  
Externally, the mammalian heart consists of the following;  
(a) It is broader at the top and narrower at the bottom.  
(b) It is made up of specialized strong muscles called cardiac muscles. These muscles  
are capable of contracting and relaxing over a long period without getting tired as  
long as a person is alive. Cardiac muscles are found only in the heart.  
(c) It is enclosed by a sac or double layer of tough inelastic membranes called the  
pericardium.  
Functions of Pericardium  
(i)  
It protects the heart from mechanical injury and friction.  
It holds the heart in position to reduce friction between the heart and other  
structures.  
(ii)  
(iii)  
(iv)  
(v)  
It prevents the heart from over-expanding when it is beating very fast.  
It provides enough room for vigorous pumping of the heart.  
It secretes a fluid called pericardial fluid which lubricates the heart and allows  
for smooth movement of the heart when it beats.  
(d) Just beneath the pericardium, the wall of the heart consists of three layers:  
(i)  
The epicardium: It is the outer protective layer.  
(ii)  
The myocardium: It is the middle layer. It contains cardiac muscles that  
contract and relax during heart movement.  
(iii) The endocardium: It is the inner most layer. This layer is continuous with the  
lining of the blood vessels attached to the heart.  
(e) There are also various blood vessels attached to the heart which are:  
(i)  
Coronary artery. It supplies oxygenated blood to the heart muscles.  
Coronary vein. It carries deoxygenated blood containing waste materials away  
from the heart.  
(ii)  
Therefore, the heart has its own blood supply through coronary artery and  
coronary vein.  
(iii)  
(iv)  
The vena cava. It is the largest vein that carries deoxygenated blood from the  
rest of the body to the heart.  
The pulmonary artery. It transports deoxygenated blood from the heart to  
the lungs.  
(v)  
The pulmonary vein. It carries oxygenated blood from the lungs to the heart.  
The aorta. It is the largest artery that carries oxygenated blood from the heart  
to the rest of the body.  
(vi)  
Figure 5.1: External structure of the mammalian heart.  
The Internal Structure of the Mammalian Heart  
Internally, the mammalian heart consists of the following:  
(a) It consists of four chambers which are;  
(i) The two upper chambers are called auricles or atria (singular: atrium). They  
include right auricle and left auricle.  
(ii) The two lower chambers are called ventricles. These are right ventricle and the left  
ventricle.  
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•
•
The ventricles have thicker walls than the auricles because they have a task of  
pumping blood at a greater distance and higher speed than the auricles.  
The auricles pump blood to the ventricles while ventricles pump blood to all other  
parts of the body.  
The left ventricle is thicker than the right ventricle because the left ventricle pumps  
oxygenated blood to the rest of the body; therefore, much pressure is required to  
pump blood.  
•
The right ventricle pumps deoxygenated blood to the lungs. The lungs are close to  
the heart; therefore, it does not require much pressure to pump blood.  
(b) The heart has several valves that control the flow of blood between the auricles and  
ventricles. The valves have flaps that ensure that blood flows in one direction only.  
(i)  
Tricuspid valve. It is found between the right auricle and the right ventricle.  
(ii)  
Bicuspid valve. It is found between the left auricle and left ventricle.  
(iii) Semilunar valves. They are located at the base of the pulmonary artery and  
aorta. The valves prevent blood from flowing back into ventricles. The valves close  
when blood tries to flow back.  
(c) The heart has a thick muscular wall called septum. It divides the heart into the left  
and right halves. Septum prevents mixing of oxygenated and deoxygenated blood from  
one half to the other.  
Figure 5.2: The Internal Structure of the Mammalian Heart  
The Flow of Blood Through the Heart  
The heart is an organ that pumps blood throughout the body.  
(a) The heart has two branches of venacava.  
•
•
•
The superior (anterior) vena cava which transports deoxygenated blood from the  
upper parts of the body such as head, neck and upper limbs (arms).  
The inferior (posterior) vena cava which transports deoxygenated blood from the  
lower parts of body such as the lower limbs, kidney, liver, stomach and intestines.  
The superior and inferior vena cava join to form the main vena cava that empties the  
deoxygenated blood in the right auricle.  
(b) The heart is divided into two separate pumping systems, the right side and left side.  
•
The right side of the heart receives deoxygenated blood from the vena cava and pumps  
it to the lungs where it picks up oxygen gas and releases carbon dioxide gas.  
Deoxygenated blood contains higher amounts of carbon dioxide and low amounts of  
oxygen because it comes from respiring cells.  
•
The left side of the heart receives oxygenated blood from the lungs and pumps it  
through the arteries to the rest of the body where oxygen gas is released and carbon  
dioxide gas is picked up.  
The flow of blood through the heart occurs in the following sequence:  
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Deoxygenated blood from the body enters the heart through the superior and  
inferior vena cava into the right auricle.  
As the right auricle fills up, the pressure within it rises and the tricuspid valve opens  
and allows the blood to enter the right ventricle.  
When the right ventricle is full, the increased pressure causes the muscles to  
contract and the semi lunar valve in the pulmonary artery to opens.  
The blood is then pumped through the semilunar valve into the pulmonary artery  
and carried to the lungs.  
In the lungs, blood receives oxygen to become oxygenated blood and the bicuspid  
valve closes to prevent back flow of blood.  
From the lungs, the oxygenated blood returns to the heart again through pulmonary  
vein into the left auricle. When the left auricle relaxes, the semi lunar valve opens  
and blood from the pulmonary vein flows in.  
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The oxygenated blood from the left auricle flows into the left ventricle through the  
bicuspid valve. Pressure builds up in the left ventricle as blood flows in.  
As the pressure builds in the left ventricle, the muscles of the left ventricle contract  
and the oxygenated blood is powerfully pumped through the semilunar valve into  
the aorta and distributed to all parts of the body.  
NOTE: Apart from transporting gases, the blood also transports nutrients and water  
needed in the metabolic processes of the body. The heart beats in such a way that when  
the auricles contract, the ventricles relax and vice versa.  
ADAPTATION OF THE MAMMALIAN HEART TO ITS FUNCTIONS  
(i) The heart has muscular walls which contract to pump blood.  
(ii) It has cardiac muscles which contract and relax continuously without getting tired  
to ensure continuous pumping of blood.  
(iii) It has valves (bicuspid and tricuspid valves) which prevent the back flow of blood,  
hence ensures blood flows in one direction.  
(iv) It has septum which prevents the mixing of deoxygenated blood in the right and  
oxygenated blood in the left.  
(v) It has sinoatrial node which acts as a pacemaker, setting the time and rate of  
cardiac muscle contraction.  
(vi) The pericardium produces pericardial fluid which prevents friction as the heart  
beats.  
(vii) It has coronary artery and coronary vein. The coronary artery nourishes the heart  
and supplies it with oxygen while coronary vein removes waste that would harm the  
heart if left to accumulate.  
(viii) It has connection with pulmonary artery and pulmonary vein. This enable the heart  
to pump out deoxygenated blood to the lungs and receives oxygenated blood from  
the lungs.  
(ix) It has connection with venacava and aorta which enables the heart to receive  
deoxygenated blood and pumps out oxygenated blood.  
(x)  
It has a large number of mitochondria enabling continuous supply of energy to the  
heart.  
(xi) The left ventricle has a thick muscular wall to pump blood at higher pressure to the  
distant body tissues.  
2. THE BLOOD VESSELS  
The blood vessels are channels or networks of hollow tubes that transport blood to various  
parts of the body. The blood vessels are distributed throughout the body. Mammals have  
three main types of blood vessels namely: arteries, veins and capillaries.  
ARTERIES  
The large and main artery is aorta. Arteries are located deep in the body.  
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Arteries are thick-walled, muscular and elastic vessels that transport oxygenated  
blood from the heart to all parts of the body.  
All arteries transport oxygenated blood (pinkish in colour), except the pulmonary  
artery which transports deoxygenated blood from the heart to the lungs.  
They have small and smooth lumen to enable them transport blood at high pressure.  
They have no valves with exception of the largest artery (aorta).  
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The wall of the artery consists of three layers.  
(i)  
The endothelium. This is the innermost layer of the artery which is attached to a  
basement membrane. It surrounds the lumen (the central tube of the vessel).  
The muscular layer. This is made of smooth muscle and elastic fibres. This layer  
enables the artery to contract and relax for the efficient movement of blood.  
(ii)  
(iii) The fibrous layer. This is the outermost layer is made of collagen. The fibres enable  
the artery to withstand the pressure caused by the blood coming from the heart.  
THE VEINS  
The large and main vein is the venacava. They are located just beneath the skin. Superior  
vena cava and inferior vena cava join together to form vena cava.  
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▪
▪
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Veins are blood vessels that transport deoxygenated blood from the body parts to the  
heart.  
All veins carry deoxygenated blood (reddish in colour) except pulmonary vein which  
carries oxygenated blood from the lungs to the heart.  
Veins have larger lumen and less muscular wall than arteries. Therefore, the blood  
in the veins flows at low pressure.  
All veins carry blood with less oxygen and nutrients and more waste products and  
carbondioxide except hepatic portal vein and renal vein.  
Most veins have valves to prevent back flow of blood away from the heart, because  
blood in veins moves under very low pressure.  
NOTE: Oxygenated blood is the blood rich in oxygen and deoxygenated blood is the blood  
rich in carbon dioxide.  
THE CAPILLARIES  
Capillaries are small and narrow blood vessels whose walls are thin made up of one cell  
thick. They are in direct contact with the all tissues of the body.  
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The thin walls of the capillaries are permeable to enable oxygen and nutrients to  
diffuse from the blood to the cells, carbon dioxide and other waste products to diffuse  
from the cells into the blood and white blood cells to reach sites of infection.  
Therefore, their thin walls maximize the rate of diffusion.  
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They have no valves.  
The blood flow rate is very slow because of falling pressure.  
Generally; blood flows from arteries to veins through capillaries.  
Adaptations of Blood Capillaries  
(i)  
They are numerous to increase the surface area.  
(ii)  
They are very close to the tissue for easy exchange of materials.  
(iii) They have very thin walls which allow easy diffusion of materials between blood  
and body cells.  
(iv) They have very small lumen which forces red blood cells to squeeze and hence  
oxygen diffuses into body cells.  
Table 5.1: Comparison of structure and function of arteries, veins, and capillaries.  
Structure  
Lumen  
Arteries  
Veins  
wide  
Capillaries  
irregular Have narrow  
Have narrow smooth  
lumens  
Have  
lumens  
smooth lumens  
Lack valves  
Valves  
Lack  
valves  
they  
except  
are  
Have valves at regular  
intervals  
where  
connected to the heart  
Transport blood  
Pressure  
at Transport blood at low  
pressure  
Transport blood at  
low pressure  
high pressure  
Direction  
blood flow  
Function  
of Transport blood away  
from the heart  
Transport blood towards Transport  
blood  
the heart  
within the tissues  
Transport oxygenated  
Transport deoxygenated  
Transport  
either  
or  
blood,  
except  
the blood,  
except  
the oxygenated  
pulmonary artery  
Contract and relax to  
create a pulse  
pulmonary vein  
deoxygenated blood  
Blood flow  
Blood flows smoothly  
Blood  
flows  
smoothly  
Wall layers  
Have three wall layers  
Have three wall layers  
Have one wall layer  
Wall thickness  
Have thick muscular Have  
thin,  
less Have  
one  
cell's  
walls  
muscular walls  
Not permeable  
thick walls  
Permeable  
Permeability of  
the walls  
Not permeable  
Elasticity  
walls  
of Very elastic  
Less elastic  
Not  
elastic  
(inelastic)  
Table 5.2: The Differences between Arteries and Veins  
S/N  
Arteries  
Veins  
(i)  
They have thick muscular walls and  
much elastic tissue.  
They have thin muscular walls and less  
elastic tissue.  
(ii)  
They always carry blood away from  
the heart into the body tissue.  
They have small lumen.  
They always carry blood towards the heart  
from the body tissue.  
(iii)  
(iv)  
They have large lumen.  
They are pink in colour.  
They are red in colour.  
(v)  
(vi)  
(vii)  
All arteries except the pulmonary  
artery carries oxygenated blood.  
All veins except the pulmonary vein carry  
deoxygenated blood.  
They  
are  
situated  
deep  
in  
the They are situated close to the surface of  
the skin.  
muscles.  
Most arteries do not have valves to  
prevent reflux of blood.  
Most of veins have valves to prevent the  
reflux or back flow of blood.  
(viii) Blood in the arteries flows under high  
pressure.  
Blood in veins flows under low pressure.  
3. THE BLOOD  
Blood is a specialized fluid tissue in humans and other vertebrates. It consists of four  
main components which are  
Composition of The Blood  
In vertebrates, blood is composed of four main components which are:  
(a) Plasma (or Blood plasma).  
(b) Red blood cell  
(c) White blood cell  
(d) Platelets (fragments of cells)  
Functions of Blood  
(i)  
It transports oxygen from the lungs to the body tissues where it is used for  
respiration.  
(ii)  
It transports nutrients throughout the body. When the food is digested it is passed  
into the blood which carries it to the tissues all over the body.  
(iii) It transports carbondioxide from the body tissues as to the lungs.  
(iv) It transports waste products such as urea formed in the liver to the kidneys from  
which it is excreted as urine.  
(v)  
Distribution of heat and temperature: Heat is transferred from the tissues of the  
liver and muscles where it is being produced to all parts of the body.  
(vi) Distribution of hormones: Hormones are distributed from the area of their  
production to their places of action in the body.  
(vii) It is involved in immune response to infection: The white blood cells defend the  
body against harmful bacteria. They engulf bacteria and destroy them.  
(viii) It forms blood clots that prevent excessive loss of blood upon injury.  
(a) The Plasma  
Plasma is a mild alkaline pale-yellow fluid of the blood. It consists of water, food  
nutrients, proteins, waste products, oxygen, mineral salts, antibodies, enzymes and  
hormones.  
The major functions of plasma  
(i)  
It transports nutrients from the digestive system to other parts of the body.  
It transports red blood cells containing oxygen to the tissues and carbon dioxide  
to the heart and lungs.  
(ii)  
(iii)  
(iv)  
(v)  
It transports wastes such as carbon dioxide and urea to the excretory organs.  
It transports white blood cells and antibodies to sites of infection.  
It transports hormones to the target organs.  
(vi)  
It transports mineral ions such as sodium, potassium and chlorides so as to  
ensure ionic balance in the body.  
(vii)  
It transports platelets to sites of bleeding so as to initiate blood clotting.  
(viii) It distributes heat to all parts of the body.  
(ix)  
(x)  
It regulates the pH of body fluids.  
It maintains a normal balance of body fluids.  
(b) Red Blood Cells  
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Red blood cells are also called erythrocytes. They are red, round and biconcave cells  
with no nucleus.  
In adults, red blood cells are produced in the red bone marrow while in foetus they  
are produced in the liver.  
They have a lifespan of about 120 days (four months). The old red blood cells are  
destroyed by the spleen and liver to form bile in the gall bladder and release  
haemoglobin for the formation of new cells.  
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Haemoglobin is the red pigment in erythrocytes containing iron compound that  
readily combines with oxygen to form a bright red compound called oxyhaemoglobin.  
Figure 5.3: A structure of a normal red blood cell  
Functions of Red Blood Cells (Erythrocytes)  
(i) Transport of oxygen from the lungs to various tissues of the body. In the lungs  
haemoglobin combines with oxygen to form oxyhaemoglobin. This is an unstable  
compound which releases oxygen when it reaches tissues that have a low concentration  
of oxygen.  
Haemoglobin + Oxygen  
Oxyhaemoglobin  
(ii) Transport of carbon dioxide from various tissues of the body to the lungs. In the red  
blood cells, carbon dioxide combines with haemoglobin to form  
carbaminohaemoglobin. The formed compound is transported to the lungs where  
carbon dioxide is released and removed from body.  
Haemoglobin + Carbondioxide  
Carbaminohaemoglobin  
Adaption of Red Blood Cells to their functions  
They have haemoglobin which carries oxygen.  
(i)  
(ii)  
They are many in number for effectively transport of gases. (About 5-6 million per  
1 푐푚3of blood).  
(iii) They lack nucleus to increase surface area for taking up oxygen.  
(c) White Blood Cells (Leucocytes)  
White blood cells are also called leucocytes. They are irregular shaped cells, that is,  
they change their shapes like amoeba.  
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All white blood cells have nuclei (singular: nucleus).  
They are produced in the white bone marrow and in the lymph nodes.  
They do not possess haemoglobin.  
Figure 5.4: White blood cells of different shapes