Prepared by Mr Tan Kaiyuan Hwa Chong Institution CAA 120709

Hwa Chong Institution
Hwa Chong Institution
Sec3 (IP) Biology
Sec3 Biology
Prepared by Mr Tan Kaiyuan
CAA 120709
Name: _____________________________________
Class: 3____
Date: ______________________
For the Beginners and Intermediate Learner
A comprehensive website on the circulatory system and its components. Highly
Interactive website that describes in a lot of details the structures and function of the
components of the circulatory system.
Another website with great details on the cellular components of blood as well as
information on agglutination.
Video to describe the development of atherosclerosis and myocardial infarction.
For the Adventurous Learner
A tour on blood vessel histology.
A tour of the lymphatic system.
Very detailed website on myocardial infarction: causes, prevention and cure.
Transport in Humans
9.1 The Circulatory
9.1.1 Substance
Exchange in
9.1.2 The Need for
9.1.3 Double
9.1.4 The Heart
9.1.5 The Vessels
9.2 Blood, the Fluid Tissue
9.3 The Cardiac Cycle
9.2.1 Components of Blood
a) Blood Plasma
b) Red Blood Cells
c) White Blood Cells
d) Platelets
9.2.2 Functions of Blood
a) Haemoglobin and O2 Transport
b) Phagocytosis of Foreign Bodies
c) Antibodies and ABO Blood
d) Blood Clotting
9.2.3 The Lymphatic System
9.3.1 Blood
Pressure in
the Heart
9.3.2 Blood
Pressure in
the Vessels
9.3.3 Effects of
Exercise on
Heart Rate
9.4 Heart Diseases
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
Learning Objectives
At the end of this chapter, you should be able to:
(1) *Describe the circulatory system as a system of tubes with a pump and valves to
ensure one-way flow of blood.
(2) *Describe the double circulation in terms of a low pressure circulation to the lungs
and a high pressure circulation to the body tissues and relate these differences to
the different functions of the two circuits.
(3) Describe the structure and function of the heart in terms of muscular contraction and
the working of valves.
(4) *State that heart action is initiated at the pacemaker (sino-atrial node).
(5) Outline the cardiac cycle in terms of what happens during systole and diastole with
involvement of the heart valves (Histology of the heart muscles, names of nerves
and transmitter substances are not required.)
(6) Describe the effect of exercise on heart rate and its significance.
(7) Identify the main blood vessels to and from the heart, lungs, liver and kidney.
(8) Describe the structure of arteries, veins and capillaries in relation to their functions
and be able to recognize these vessels from photomicrographs.
(9) *State the origin of blood pressure.
(10) *Describe how blood pressure is measured.
(11) *Describe how a pulse is generated.
(12) List the components of blood as red blood cells, white blood cells, platelets and
(13) Identify red and white blood cells as seen under the microscope on prepared slides,
and in diagrams and photomicrographs.
(14) State the functions of various blood components:
red blood cells – haemoglobin and oxygen transport
white blood cells – phagocytosis, antibody formation and tissue rejection
platelets – fibrinogen to fibrin, causing clotting
plasma – transport of blood cells, ions, soluble food substances, hormones,
carbon dioxide, urea, vitamins, plasma proteins
(15) Explain the role of haemoglobin in the transport of oxygen.
(16) Describe the transfer of materials between capillaries and tissue fluid
(17) Describe coronary heart disease in terms of the occlusion of coronary arteries and
analyse the possible causes (diet, stress, smoking), and state the possible
preventive measures
(18) List the different ABO blood groups and all possible combinations for the donor and
recipient in blood transfusions.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
All living things grow,
metabolise and eventually
reproduce. These life
processes require energy
and lead to changes in
biomass over time. Surely,
this energy and biomass
must come from somewhere
or is removed somehow.
We have seen in the earlier
chapter how biomass and
energy is obtained by the
ingestion of food. Such is
the role of the digestive
In order to unleash the
chemical potential energy
locked within food molecules,
respiration must take place.
Oxygen is required for
respiration and this is
respiratory system.
Respiration and many other
Accumulation of waste can
be toxic to the body and an
organism must find means of
removing it. This is the role
of the excretory system.
Figure 9.1 Overview of the cardiovascular system in humans (Homo sapiens).
Acquired from,
illustrated by Mariana Ruiz Villarreal.
Since every single body cell
grows and metabolises, they will require food and oxygen, and will need to remove metabolic
waste. While these requirements are well handled by the organ systems highlighted above, a
cell has limited accessibility to them because it is buried deep and far away from them in
remote areas of the body. Thus, the body must develop a means of delivering nutrients and
collecting waste to these remote areas. This is the role of the cardiovascular system. It is in
our interest in this chapter to understand the importance of transport. Before we look at
complex multicellular organisms, we shall first examine how transport of substances occur in
simple unicellular organisms.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
9.1.1 Substance Exchange in Unicellular Organisms
• Life processes are sustained by a continuous supply of energy and raw materials.
• Any delay in providing these key ingredients may grind life to a halt.
• Therefore, time is a crucial factor.
• Simple unicellular organisms obtain food and oxygen, and remove carbon dioxide
and wastes by simple diffusion. This is an efficient (sufficient supply to meet
demands in a short time) method for material transport in these organisms.
• Why does simple diffusion work for unicellular organisms?
• There are two primary considerations:
1) Large surface area to volume (SA/V) ratio
• Most of the metabolic processes take place within the cell’s volume (ie. in the
cytoplasm and within the organelles).
• Food and oxygen must therefore cross the cell membrane to get into the cell.
The expense of the cell membrane thus forms the surface area through which
these molecules must cross in order to get into the cell’s volume.
• Once in the cytoplasm, there molecules will have to diffuse across the volume of
the cell to the site where the metabolic reaction will take place. If a cell has a very
large volume, then the molecule will take much longer to reach its site of reaction.
• In unicellular organism, the cytoplasm bounded within the cell membrane has a
relatively small volume.
• Thus, molecules undergoing simple diffusion across the cell membrane from any
direction may very quickly reach the site of metabolic reaction within the cell.
• Hence simple diffusion is an efficient means for substance transport in unicellular
Figure 9.2 Comparing the surface area to volume
ratio of cubes of different dimensions. The
rightmost cube is composed of smaller cubes, each
with their surface area exposed by the gaps
between them. Though the effectively volume
remains the same as the middle cube, its surface
area is greatly increased. Diagram from
jpg acquired on 5th July 2009.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
2) Diffusion gradient maintained
• How fast substances diffuse across the cell membrane also depends on the
steepness of the diffusion gradient.
• In Figure 9.3, the diagrams on the left for both (a) and (b) represent solutions
with steep diffusion gradients. The concentration of dye molecules is high in one
region and low in the other.
• Molecules tend to diffuse quickly when the diffusion gradient is steep.
• There will be no net diffusion of molecules when the solution reaches equilibrium
(on the right of Figure 9.3).
• Since many unicellular organisms are capable of moving from one
microenvironment to another, they may migrate to environments where the
concentrations of food molecules and oxygen are high, and where the
concentrations of carbon dioxide and metabolic wastes are low.
• This ensures that a steep diffusion gradient is maintained.
• For unicellular organisms that cannot move about. They are usually equipped
with flagella and cilia that sweep about to circulate the liquid in their external
Figure 9.3 On the extreme left, molecules of one type is well partitioned in one region (a) or separated
from molecules of another (b). A steep diffusion gradient is thus established. As time passes (proceeds
from left to right), the diffusion gradient becomes less steep and is eventually dissipated. When the
diffusion gradient is completely dissipated, the system is said to be in a state of equilibrium (diagrams on
the right). From, acquired on 5th July 2009.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
9.1.2 The Need for Transport
• While simple diffusion may suffice for unicellular organisms, multicellular organisms
require a more efficient method for the transport of materials.
• Multicellular organisms face two key problems:
First, they have a small surface area to volume ratio.
 Solution: Increase surface area by having an internal system of channels,
sinuses or chambers.
Second, the body cells of multicellular organisms are mostly localised in fixed
positions relative to the body tissues and are unable to move about. Thus a
diffusion gradient is difficult to maintain if they are bathed in static body fluid.
 Solution: Actively circulate the body fluid to supply fluid that is rich in
oxygen and food molecules and low in waste or carbon dioxide
concentration. To do this, some form of a pump must be devised to move
the fluid.
• These solutions have thus become the key components in the circulatory system of
multicellular organism:
Heart – the muscular pump that moves the fluid.
Blood Vessels – the system of channels that services the remote parts of the
Blood – The fluid that has the capacity to carry the metabolites.
• Before we examine each of these components, let us compare and contrast the types
of circulatory systems found in vertebrate animals.
9.1.3 Double Circulation
• Unlike simpler organisms such as the jellyfish
or sponges, vertebrate animals (animals with a
backbone) have a closed circulatory system.
• Closed circulatory systems have their blood
enclosed within vessels of different sizes and
thickness at all times. That is, the blood does
not pass out of these vessels into the body
• In open circulatory systems however, blood
(known as haemolymph) moves through the
circulatory system, and into the body tissues,
bathing the organs directly with blood, before
returning back to the heart through small
• Closed circulatory systems may be further
categorised as a single circulatory system or
double circulatory system.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
• The figures below illustrate the differences between the single circulatory system and
the double circulatory system.
Figure 9.4 (Left) The single circulatory
system found in fish. (Below) The double
circulatory system found in amphibians,
reptiles, birds and mammals. Dark grey
portions represent oxygenated blood,
deoxygenated blood. Illustrated by Tan
• The
system is so-called because
a complete round through
the entire circulatory system
requires that the blood
enters two circuits.
• One circuit takes blood from the heart
to the lungs and then back to the heart. This is
known as the pulmonary circulation.
• The other circuit takes the blood from the heart to the rest of the body
and then back to the heart again. This is known as the systemic circuit.
• Blood moves from the heart to the pulmonary circuit, back to the heart, then to the
systemic circuit, and then back to the heart, and returns to the pulmonary circuit.
• In this way, the movement of blood alternates between the two circuits, and enters
the heart twice for every complete round through the whole circulatory system.
What are the advantages of a double circulation over a single circulation?
1. Blood leaving from the heart to the lungs (from the right ventricle into the lungs
via the pulmonary arteries) is at a lower pressure than blood leaving the heart
from the left ventricle. This gives sufficient time for the blood to be fully
oxygenated by oxygen taken in from the lungs before returning to the heart to be
distributed to the rest of the body.
2. Blood leaving the heart to the rest of the body (from the left ventricle to the rest of
the body via the aorta) is at high pressure, thus ensuring that oxygen is delivered
to the rest of the body quickly and allowing cells to maintain a high metabolic rate.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
9.1.4 The Heart
• The human heart is about the size of a clenched fist and is roughly conical in shape.
• It is located between the left and the right lungs, and dorsal to the sternum or chestbone.
The External Structure of the Heart
• The heart is surrounded by two layers of thin membrane which surrounds a fluid-filled
space. Collectively, this structure is known as the pericardium. As the heart beats,
the fluid serves to reduce friction that may lead to wear and tear as the heart moves
against the surrounding tissues.
• The heart is essentially a muscular bag. Contraction and relaxation of the heart
muscles (or cardiac muscles) results in the pumping of blood around the body.
• Like all other muscles, the cardiac muscles that form the heart walls must also be
supplied with blood rich in food and oxygen, to keep themselves alive and active.
• This is obtained via the coronary artery, which is a branch of the aorta.
• Blockage of the coronary artery can lead to fatal consequences as the heart muscles
are unable to obtain its supply of food and oxygen. As a result, the cardiac muscles
cannot contract. This may then lead to heart failure and death.
• Figure 9.5 illustrates the external structure of the human heart. Notice the coronary
arteries and the network of blood vessels on the surface of the left and right ventricles.
Figure 9.5 Diagram
(right) illustrating the
relative position of the
heart to the lungs in the
thorax. Diagram (above)
depicting the heart and
the associated coronary
arteries and veins. From
“Anatomy, Descriptive
and Surgical” by Henry
Gray (1862).
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
Chambers of the Heart
• The heart is longitudinally separated by a muscular wall known as the median septum
(Figure 9.6 - bottom) into two lateral halves; one on the left and the other on the right.
• Each half is further subdivided into two chambers of unequal volume by a transverse
constriction. The anterior (upper) chamber in each
halves has a smaller volume than the posterior
(lower) one.
• Thus the heart has 4 chambers in all.
• The two anterior chambers of the
heart are known as the atria
(singular: atrium) or auricles
(singular: auricle).
• The posterior (lower) two chambers
of the heart are known as the
ventricles (singular: ventricle).
Not only are their volumes larger,
the ventricles also possess walls that
are more muscular and thicker than the
• The left atrium and left ventricle contains
deoxygenated blood while the right atrium
and right ventricle contains oxygenated blood. Thus the median
septum prevents the mixing of the two types of blood.
Figure 9.6 Above: Diagram
showing the right atrium and
right ventricle with part of their
walls removed. From “Anatomy,
Descriptive and Surgical” by
Henry Gray (1862). Left:
Longitudinal section of the
human heart (ventral view).
Illustrated by Tan Kaiyuan.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
Heart valves
• Each atrium is connected to the respective ventricle via a large oval aperture (opening).
Blood passes from the atrium to the ventricle through this aperture.
• The apertures are guarded by a valve each. The valve on the right side of the heart is
known as the tricuspid valve, and that on the left side is known as the bicuspid valve.
• The tricuspid valve is so-called because it possesses three flaps, while the bicuspid
possesses only two flaps (illustrated in Figure 9.7 Right).
• The apex (tip) of the flaps point into the ventricles. This allows blood to flow only in a
single direction, from the atria into the ventricles.
• The flaps are connected by an apparatus comprising a series of tendons known as
chordae tendineae. These are in turn connected to papillary muscles projecting into the
ventricular cavity form the ventricular walls (illustrated in Figure 9.6).
• Contraction of the papillary muscles pulls on the chordae tendineae tendons, thereby
opening the flaps.
• Blood may then pass from the atria into the ventricles when the flaps open.
• As blood fills up the ventricles, building up the ventricular blood pressure, the flaps will
collapse back into their closed positions.
Figure 9.7 Left: Diagram showing the top (anterior) view of the heart. Notice the semi-lunar valves in the
pulmonary artery and the aorta. Right: Diagram depicting the top (anterior) view of the heart with the atria
removed. The tricuspid and bicuspid valves leading into the ventricles may be seen.. From “Anatomy,
Descriptive and Surgical” by Henry Gray (1862).
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
The table below summarises the form and function of the heart:
Fluid-filled Pericardium
Reduces friction when heart beats thus preventing wear and
Median septum
Prevent mixing of oxygenated and deoxygenated blood
Left ventricle more muscular
than right ventricle
Provide higher blood pressure in left ventricle to move blood
to the extremities of the body. Right ventricle to move blood
into the lungs at lower pressure than left ventricle to provide
time for diffusion of oxygen and carbon dioxide.
Heart valves point into
Semi-lunar valves in
pulmonary artery and aorta
Ensures that blood flows in a single direction; prevents
backflow of blood.
9.1.5 The Blood Vessels
Types of blood vessels
• We may identify five major
categories of blood vessels in
the human circulatory system.
• These are namely:
(1) Arteries
(2) Arterioles
(3) Capillaries
(4) Venules
(5) Veins
• The main artery leading away
from the heart to the rest of the
body is known as the aorta.
• The aorta branches repeatedly
Figure 9.8 Diagram representing blood capillaries and their
into vessels of smaller diameter
relation to arteries, arterioles, venules and veins. Image from
known as the arterioles before
each arteriole branches further
cSYS.html, accessed on 28 June 2009, and published by web
into capillaries.
owner with permission from Purves et al., Life: The Science of
• Capillaries have walls that are
Biology, 4th ed. (Sinauer Associates and WH Freeman).
only a single cell-thick. This
facilitates diffusion of nutrients, dissolved gases and waste. After passing the tissues,
capillaries reunite to form venules, which reunite to form veins.
• The two main veins that return to the heart from the upper part and the lower part of the
body are known as the superior (anterior) vena cava and the inferior (posterior) vena
cava respectively.
• In summary, blood always flow from the heart  arteries  arterioles  capillaries 
venules  veins  back to the heart.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
• Hence, the direction of flow of blood in the arteries will always be away from the heart,
while that of veins will always be towards the heart.
Structure of blood vessels
(1) Arteries
• The hollow in the centre of the vessel is known as the lumen. The lumens of arteries
are usually narrower than that of veins of similar diameters.
• Arterial walls consist of 3 layers (from interior to exterior): tunica intima, tunica media,
tunica externa (formerly tunica adventitia). (You are not required to know the names
of the 3 layers, but you must know what they comprise).
i. Tunica intima
– comprises a single layer of endothelial cells surrounded by a thin basement
ii. Tunica media
– composed of smooth muscle cells.
– Contraction of these cells causes the lumen of the artery to become narrower or
to constrict; relaxation of these cells causes the artery to become wider or to
Tunica intima
- endothelial cells
- basement membrane
Internal elastic membrane
Tunica media
- smooth muscle cells
external elastic
Tunica externa
- fibrous tissues
- connective tissues
- epithelial cells
Figure 9.9
Comparing the structure of an artery and a vein. Image taken from
th, accessed on 28 June 2009. Original image by
Fox and Stuart, Human Physiology, 4 ed. (Brown Publishers).
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CAA 120709
Hwa Chong Institution
Sec3 Biology
– Constricted
reduce the volume of
blood flowing through the
vessel per unit time (rate
of blood flow), while
dilated vessels increase
the volume of blood flow
per unit time.
– By controlling the rate of
blood flowing into an
organ, the body is able to
divert blood to where it is
needed most, and is thus
emergencies. This control
is mainly dictated by the
system to prepare the
organism for “flight or fight”
iii. Tunica externa
– Connective and
• Each layer is also separated from
membrane between the tunica
intima and the tunica media is
known as the internal elastic
lamina, and that between the
tunica media and tunica externa
is known as the external elastic
lamina (absent in some arteries).
• As the heart beats, blood rushes
through the arteries at high
pressure. The elastic membrane
allows the arteries to stretch and
recoil under this great pressure.
The recoiling force also pushes
the blood along these vessels in
spurts, resulting in what is felt as
pulses in the arteries.
Figure 9.10
A – Image of the cross-section of an
artery showing the lumen, internal elastic lamina (IEL)
and tunica intima, the tunica media, tunica externa
(tunica adventitia) and the external connective tissues
(CT), seen under a light microscope. B – Light microscope
image comparing both the thickness of the walls of an
artery and a vein. Both images obtained from
s/Lab12b/Lab12b.htm, accessed on 6th July 2009.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
(2) Veins
• Much wider lumen than artery of similar diameter.
• Also consists of 3 layers (from interior to exterior): tunica intima, tunica media,
tunica externa.
Tunica intima
– comprises a single layer of endothelial
cells surrounded by a thin basement
– continuous with semi-lunar valves at
intervals to prevent the backflow of blood.
– Blood moves at much slower rates in the
veins and tends to flow backwards
(especially when ascending up a vein
towards the heart). The semi-lunar valves
consist of flaps with their apices pointing
towards the heart. Thus they open only in
one direction (ie. towards the heart), and
closes in the other.
Tunica media
– composed of smooth muscle cells, but this layer is much thinner compared to
an artery of the same
Tunica externa
– consists of connective
and fibrous tissues
• There is also a layer of elastic
lamina between the tunica
intima and the tunica media.
The elastic lamina present in
arteries between the tunica
media and tunica externa is
absent in veins.
• Blood in the veins are also
pushed along the veins by the
contraction of skeletal muscles
that are adjacent to these veins.
This is analogous to the
except that this occurs in a
single direction due to the
presence of the semi-lunar
Figure 9.11
Scanning electron microscope image of a
capillary. Notice the red blood cell (RBC) peeking out of
the capillary. This provides a comparison between the
diameter of the capillary and the RBC. Image from
s/Lab12b/Lab12b.htm, accessed on 6th July 2009.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
(3) Capillaries
• Unlike veins and arteries where their primary function is to serve as conduits for the
transport materials, capillaries play a critical role as the surface for the exchange of
• Thus, capillary walls are only a single-cell thick. This wall layer comprises endothelial
cells resting on a thin basement membrane.
• The total cross-sectional area of a group of capillaries arising from a single arteriole is
far greater than the cross-sectional area of that arteriole. This increases the surface
area to volume ratio of the capillaries in close association with the surrounding tissues.
• Blood passing through capillaries move at a slower rate and lower blood pressure,
allowing time for diffusion of substances to take place.
Relating the Form of Blood Vessels to their Functions
• The table below compares and contrasts the form and function of the different blood
Direction of
Blood Flow
Carry blood away from
the heart
Carry blood towards the
Carry blood from
arterioles to venules
Carry oxygenated blood
(with the exception of
the pulmonary artery
and the umbilical artery)
Carry deoxygenated
blood (with the
exception of the
pulmonary vein and the
umbilical vein)
Oxygenated blood on the
end nearer to arterioles
and deoxygenated blood
on end nearer to venule
High arterial blood
Low venous blood
Blood pressure varies;
higher on the end nearer
to the arteriole and lower
on the end nearer to the
Thick, elastic muscular
Relatively thinner,
slightly muscular walls
One-cell thick walls
Absence of valves
Presence of valves
Absence of valves
Smaller lumen as
compared to a vein of
the same diameter
Larger lumen as
compared to an artery of
the same diameter
Very small lumen,
enough only red blood
cells to squeeze through
one at a time
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
• We have seen how the heart and the blood vessels are structurally adapted for their
functions. Let us now examine the third and final component of the circulatory system, that
is, blood itself.
• Blood is also known as a fluid “tissue” (NOTE: not to be confused with the term “tissue
fluid”, which we will encounter subsequently in this chapter).
• Fluid because a large percentage of it consists of water.
• Tissue because it also comprises a large percentage of living cells.
9.2.1 Components of blood
• Blood consists of a non-cellular component formed primarily by blood plasma, and a
cellular component consisting of red blood cells (or erythrocytes), white blood
cells (or leucocytes) and platelets (or thrombocytes).
• The diagram below illustrates the percentages by volume of each component of blood.
The Blood Plasma
• Blood plasma is a yellowish liquid in which blood cells are suspended.
• Dissolved in the blood plasma are many soluble substances described in the diagram
above. Listed below are examples of each category of dissolved substances:
• Soluble proteins: fribrinogen, prothrombin, antibodies etc.
• Hormones: insulin, glucagon etc.
• Electrolytes: bicarbonate ions (HCO3-), phosphate ions (PO43-), sulphate ions (SO42-),
calcium ions (Ca2+), sodium ions (Na+) etc.
• Nutrients: Glucose, amino acids, vitamins, lipids etc.
• Excretory wastes: urea, uric acid, creatinine etc.
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CAA 120709
Hwa Chong Institution
Sec3 Biology
The Cellular Components of Blood
• The table below describes the three key cellular components of blood:
Red Blood Corpuscles
Produced in bone marrows
Life-span of 3 to 4 months
Key features:
White Blood Lymphocytes
Produced in bone marrows
Short lifespan of a few days
Matures in lymph nodes
Key features:
Rounded with large round nucleus
Little granular cytoplasm
Produces antibodies
Many different types of phagocytes
(neutrophils, macrophages, mast cells)
Usually short life spans of a few days
Key features:
Platelets (Thrombocytes)
Circular, flattened, biconcave discs 
increases its SURFACE AREA TO
VOLUME RATIO for oxygen to diffuse into
the cell
Lacks a nucleus  contains MORE
Elastic and is able to change into a bell
shape to enter narrow capillaries
Contains a red pigment known as
haemoglobin, critical for the transport of
Irregularly shaped
Lobed nucleus
Granular cytoplasm
Capable of migrating around in the body
Ingests foreign bodies in bloodstream by
Not true cells; membrane-bound cytoplasmic
fragments of certain bone marrow cells.
Critical for clotting of blood
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CAA 120709
Hwa Chong Institution
Sec3 Biology
9.2.2 Functions of Blood
• We may identify three key functions of blood: transport functions, protective
functions and dissipating body heat.
A. Transport Functions
1. Nutrients
2. Hormones
3. Excretory Wastes
4. Carbon dioxide
5. Oxygen
- Nutrients absorbed from the small intestines is delivered
to all parts of the body as they diffuse across capillary
- Hormones are delivered from the glands which produce
them to many target organs in several parts of the body
and rely on blood to deliver them to their targets.
- Metabolic wastes from body tissues are removed by the
blood and delivered to kidneys for excretion.
- Carbon dioxide is first converted into hydrogencarbonate
ions and is carried in the bloodstream to the lungs. In the
lungs, the hydrogencarbonate ions are reconverted back
into carbon dioxide and removed as we exhale.
- Transported to all parts of the body from the lungs by red
blood cells.
Haemoglobin and Oxygen Transport
- Red blood cells are able to
transport oxygen because they
contain a soluble protein known
as haemoglobin. It is this
protein which gives blood its
red colour.
- Haemoglobin is a soluble
protein which comprises 4
polypeptide chains.
- Each polypeptide chain is
associated with a cofactor known
as a porphyrin ring which contains
a single iron atom.
Figure 9.12
- The iron atom is responsible for
image above represents the quaternary
haemoglobin’s ability to bind
structure of the haemoglobin protein.
This process is
Four iron ions coordinated each with a
reversible depending on the
porphyrin ring are associated with each of
concentration of oxygen (or
the four polypeptide chains. and is
partial pressure of oxygen) in the
responsible for haemoglobin’s ability to
surrounding tissues.
bind to oxygen molecules. Image taken
Binding of Oxygen
aemoglobin.png. Accessed on 13th July
- When no oxygen is bounded,
haemoglobin is a purplish red
- In this state, haemoglobin has high affinity for oxygen. That is, it has a high
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CAA 120709
Hwa Chong Institution
Sec3 Biology
“tendency” or “propensity” to bind with oxygen reversibly.
Deoxygenated blood returns from the body tissues into the lungs have low
concentration of oxygen (or low partial pressure of oxygen).
Since the lung tissues contain a high concentration of oxygen (or high partial
pressure of oxygen), haemoglobin (with its high affinity for oxygen) will bind
readily with oxygen molecules as they diffuse into the bloodstream from the
air sacs in the lungs.
Once bound with oxygen, haemoglobin turns bright red and is now known
as oxyhaemoglobin.
As oxygenated blood gets transported from the lungs to the body tissues,
where oxygen may once again be released to the body tissues that are low
in oxygen concentration.
Figure 9.13
Oxygen binding. When the surrounding tissues are high in oxygen partial
pressure, haemoglobin molecules adopt a relaxed binding structure which readily accepts oxygen
due to its high affinity for oxygen. As oxyhaemoglobin enters tissues poor in oxygen content, it
adopts a tight binding structure, which lowers its affinity for oxygen and purges oxygen into the
surrounding tissues. Adapted from
Accessed 13th July 09.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
B. Protective Functions
1. Phagocytosis by Phagocytes
- Phagocytes are mobile and migrate freely in the bloodstream. They may also
squeeze between the epithelial cells that form the capillary walls, and move
through body tissues to sites of injury or sites invaded by pathogens.
- Upon encountering a foreign particle or pathogenic organism,
phagocytes are capable of changing their shapes so as to engulf the
foreign object. This process is known as phagocytosis.
- The foreign object will then be sequestered in a vacuole within the
cytoplasm of the phagocyte. Digestive enzymes are then released
into this vacuole, destroying the pathogen.
- Some of the phagocytes may be killed in the process of combating
the invading foreign organisms. Together with the engulfed foreign
organisms, the dead phagocytes will form pus.
Vacuoles with digestive enzymes
fuse with phagocytotic vacuole.
2. Antibodies produced by Lymphocytes
- Lymphocytes secrete soluble proteins known as antibodies.
- Antibodies protect the body against the invasion of pathogens by binding to
surface proteins or surface polysaccharides on these pathogens. These
surface proteins or polysaccharides are known as antigens.
- Antibodies are also very specific in their binding to antigens. ie. Given an
antibody “X”, it will only bind to specific antigen “x”. It will not bind to antigen
“y” or otherwise.
- Once an antibody binds to the corresponding antigen found on the surface of
particular cells, these cells will then be targeted for destruction or become
inactivated by the immune system.
Interaction between Antibodies and Antigens in ABO Blood Groups
- There are two types of surface antigens found on the red blood cells of
human beings, known as antigen a and antigen b.
- A person may possess red blood cells with:
a. No antigens
b. Only antigen a
c. Only antigen b
d. Both antigen a and antigen b
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
- Present in the bloodstream are also natural antibodies not produced by the
- There are two such types of antibodies: antibody A and antibody B.
- Antibody A is specific for antigen a while antibody B is specific for antigen b.
- When the antibody binds to the specific antigen found on the surface of the
red blood cells, this causes the red blood cells to agglutinate (“clump up” by
“sticking” to each other), thus preventing them from carrying out their
function of transport.
- Thus a person possessing red blood cells with antigen a for instance, will
only have antibody B in the bloodstream. Presence of antibody A causes
his/her red blood cells to agglutinate.
- The table below summarises the antigen and antibodies found in a person:
Blood Type
Antigen on Red Blood Cells
a and b
Antibody in Bloodstream
A and B
- During blood transfusion, only the red blood cells are transfused. The blood
plasma is not introduced into the recipient and thus antibodies are excluded.
- If the patient is of blood type A, he may receive blood from a donor with
blood group A or O.
- The red blood cells from a donor with blood group A only has surface
antigen a, and thus will not bind with antibody B present in the bloodstream
of the recipient.
- Similarly, the red blood cells from a donor with blood group O has no surface
antigen and will not bind with antibody B in the bloodstream of the recipient.
- People with blood group O may thus donate blood to any other blood group
but may themselves only receive blood from another donor of blood group O.
Thus, blood group O is the “universal donor”.
- Can you explain why people with blood group AB are known as “universal
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
Figure 9.14 Blood antibodies and surface antigens of red blood cells.
Organ Transplants and Tissue Rejection
- As described above, blood protects an individual by: (1) Phagocytosis of
foreign bodies; (2) Production of antibodies; (3) Blood clotting.
- This poses a problem during organ transplant.
- An individual who have perhaps met a severe accident or contracted certain
diseases may receive a replacement organ from a donor.
- However, the protective functions of blood may recognised the donated
organ as a foreign body.
- This activates the phagocytes and also results in the production of
antibodies against the cells of the donated organ, thus destroying the organ.
- Such is the case of tissue rejection, and may be avoided only if the tissue
that was transplanted into the patient belongs to the patient himself/herself.
1. Transplanted tissue should be derived from close relative of the
recipient so as to reduce risk of tissue rejection.
2. Immunosuppressive drugs may be used to inhibit the immune
system of the recipient. However this may put the recipient at risk of
other forms of infection and the drug must also be administered
regularly to suppress the immune system.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
3. Blood Clotting by Platelets
- Blood clotting serves two protective functions.
it prevents the excessive loss of blood.
it reduces the chance of invasion into the bloodstream by pathogenic
- Platelets gather at the site of tissue damage and together with the damage
tissue secrete an enzyme known as thrombokinase.
- This enzyme performs two roles:
converts an inactive enzyme present in the bloodstream, known as
prothrombin into an active form known as thrombin.
neutralises an anti-clotting substance known as heparin in blood
plasma. Heparin ensures that blood flowing within the blood vessels
remains fluid. Thrombokinase thus inhibits the action of heparin,
allowing blood to coagulate where it is necessary.
- Thrombin in turn catalyses the conversion of a soluble protein, known as
fibrinogen, into an insoluble form known as fibrin. Fibrin proteins are
thread-like and form a mesh-like net that traps the blood cells.
- As the wound gets sealed by the mesh-like network of fibrin threads and
clotting blood, a yellowish fluid is left near the site of the wound.
- This fluid is known as serum, which is essentially the blood plasma less the
clotting factors.
C. Dissipation of Body Heat
Blood also serves to distribute heat produced from organs such as the
muscles and liver to the rest of the body.
This prevents the body from overheating.
9.2.3 The Lymphatic System
• What happens when blood passes into a capillary bed from the arterioles?
Movement of Fluid from Capillaries into Body Tissues
• The blood pressure in the arterioles is much higher than that in the capillaries.
• As blood passes from the arterioles into the capillary bed, the difference in blood
pressure forces blood plasma out of the capillaries, and into the surrounding tissues
through minute gaps or pores in the capillary walls.
• These gaps or pores are too small for the soluble proteins to pass through.
• Thus, the component of the blood plasma that enters the surrounding tissue does not
contain the blood proteins.
• This fluid bathes the surrounding cells and is known as the tissue fluid or the
interstitial fluid.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
Returning Tissue Fluid back into the Bloodstream
• The
tissues and must thus be
• This is taken care of by
the lymphatic system.
• The lymphatic system
consists of a system of
vessels (lymph vessels)
with blind ends. Along
these vessels are also
lymph nodes where
lymphocytes mature.
• Lymph is also drained
from the small intestines
from lacteals (recall
from Animal Nutrition Digestion),
proportion of fats and
• The
surrounding tissues into
these lymph vessels and
enters the lymphatic
• Once in the lymphatic
system, the fluid is then
known as lymph, which
is a clear fluid.
• The lymphatic system
services the entire body,
draining tissue fluid from
those regions. It is
directly connected to the
circulatory system via a
small opening along the
right subclavian vein.
Lymph is deposited back
into the bloodstream
from this opening.
Figure 9.15
The lymphatic system. Image from
Accessed 13th July 09.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
• Now that we are familiar with the structure and functions of the three main components of
the circulatory system, that is, the heart, the blood vessels and blood, we shall now
examine the processes involved in generating a single heartbeat.
• The cardiac cycle involves the sequence of contraction and relaxation of the atria and
ventricles that will generate a single heartbeat.
• A contraction of either the atrial or ventricular muscles is known as a systole.
• The relaxation of either the atrial or the ventricular muscles is known as a diastole.
• The cardiac cycle may be described in 3 phases:
Atrial systole / ventricles in diastole
Prior to atrial systole, blood fills into the atria passively. During atrial systole, blood
pressure within the atria increases as the right and left atria contract. The bicuspid and
the tricuspid valves (collectively known as the atrio-ventricular valves or AV valves)
open and blood is forced into the ventricles.
Figure 9.16 The cardiac cycle. Image from, published by McGraw Hill. Accessed on 13th July 09.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
Ventricular systole / atrial diastole
The atria relax, and the ventricles begin contracting. Blood pressure within the
ventricles increases. When the ventricular blood pressure exceeds that in the atria,
the AV valves close. In late ventricular systole, the semi-lunar valves in the
pulmonary artery and the aorta open, and blood is forced into the respective
Ventricular diastole / atrial still in diastole
Ventricles begin relaxing. The blood pressure in the ventricles begins to decrease
and blood begins filling the atria. When ventricular blood pressure falls lower than
the atrial blood pressure, the AV valves open.
9.3.1 Pressure changes in the heart
• The diagram below illustrates changes in blood pressure in the left atrium, left
ventricle and aorta.
• Note that the opening and closure of valves corresponds to the points where the
pressure plots for the heart chambers crosses each other.
Figure 9.17 The cardiac cycle. Image from
/5b/Cardiac_Cycle_Left_Ventricle.PNG. Accessed on
13th July 09.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
9.3.2 Pressure changes in the vessels
Figure 9.18 Blood pressure in the blood vessels.
• Blood pressure is the force of the blood acting on the walls of the blood vessels. It
may be determined using a sphygmomanometer.
• Blood pressure fluctuates in the aorta and the arteries, with the
highest value obtained during ventricular systole and lowest during
ventricular diastole.
• The difference in blood pressure during these two instances in the
arteries is known as the pulse pressure which diminishes as blood
passes into the arterioles and eventually through the capillary bed and
then the veins.
• From the arteries to the veins, blood pressure decreases, with the
sharpest decline when it enters from the arterioles into the capillary
• The lowest pressure with a value almost close to zero is found in
the vena cavae before it enters the right atrium.
• The difference in pressure from arteries to veins
determines the direction of flow of blood.
NOTE: The blood pressure in the veins is LOWER than the
associated capillaries!!! A common misconception that
people may have is that the blood pressure in the veins is
higher than the associated capillaries. If this was the case,
then blood may not flow from capillaries to the veins!!!
Figure 9.19 Sphygmomanometer.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
9.3.3 Exercise and Heart Rates
• Heart rate is usually measured as the number of times the heart beats in a minute
and may be given in the unit of beats per minute (bpm).
• This may be indirectly obtained by counting the number of pulses felt under the skin
within a minute, or more accurately determined by an electrocardiogram (see Figure
• The resting heart rate (RHR) of the average adult is measured to be about 50 bpm to
100 bpm. A fit individual tend to have lower RHR.
• The resting heart rate may fluctuate depending on the activity an individual is
engaged in. Hence, the most accurate RHR is obtained upon waking up because
even moderate activities may increase the heart rate.
• Drugs administration, or consumption of caffeine and smoking may also alter the
resting heart rate.
• As an individual increases fitness through aerobic exercises, his/her heart rate will
decrease. This is because the heart muscles get stronger with training, and are able
to deliver oxygenated blood to the rest of the body at a faster rate.
• Likewise, a reduction of fatty deposits in the blood vessels also reduces the heart rate
as blood may flow through the vessels with little resistance.
• Most heart diseases are
associated with the coronary
artery and are hence known as
coronary heart diseases.
• Coronary heart diseases result
from a constriction of the
orignates from the base of the
aorta and supplies the heart
muscles with food and oxygen)
(Figure 9.5).
• Constriction of the coronary
artery reduces the rate at
which oxygen and food is
delivered to the heart muscles
resulting in heart muscle failure.
Figure 9.20 Atherosclerotic arteries. Image acquired
from, accessed on 15th July 2009.
• Coronary heart diseases may result in two outcomes:
1. Angina pectoris – a severe, tightening pain in the chest due to lack of blood
flow to the heart muscles.
2. Myocardial infarction (Heart attack) – occurs when blood supply to the heart
is completely interrupted thus leading to the death of heart muscles. This is a
fatal condition.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
• There may be many causes to constriction of the coronary artery. Some examples
1. Atherosclerosis – where lesions in the coronary artery may lead to the
development of a thrombosis which blocks the coronary artery and reduces
blood flow.
2. Coronary vasospasm – where the smooth muscles of the coronary artery
undergoes spasm, and contract, leading to vasoconstriction, thus impeding
blood flow.
• Most coronary heart diseases are associated with atherosclerosis. We shall look at
the development of atherosclerosis in details.
Figure 9.21 Stages of endothelial dysfunction in atherosclerosis. Image acquired from on
15th July 2009.
Prepared by Mr Tan Kaiyuan
CAA 120709
Hwa Chong Institution
Sec3 Biology
Development of Atherosclerosis
• High blood pressure may lead to the development of a lesion in the arterial walls.
• Platelets, blood cells and cholesterol molecules may get trapped in the lesion.
• Arterial walls release chemical signals that attract leucocytes to the lesion.
• Leucocytes transform into macrophages that “clean up” the cholesterol.
• When macrophages absorb too much cholesterol, they expand and become foam
cells. Overtime, these foam cells multiply and develop into a plaque.
• The plaque narrows the lumen of the coronary artery.
Factors Leading to Atherosclerosis
• High cholesterol diet
• Diet consisting of saturated animal fats
• Chronic stress
• Smoking: - Nicotine increases blood pressure
- Carbon monoxide increases chance of fats depositing in arterial walls
Preventive Measures
• Balanced diet
• Using polyunsaturated plant fats as a substitute for animal fats
• Stress maangement and work-life balance
• Regular exercises to strengthen heart