Human Circulatory System

Learning outcomes
• At the end of this topic, you should be able to
Explain the importance of the circulatory system in
linking all systems of the organism together
Describe the structure and function of the heart in
moving blood around the body
Describe the structure and function of the blood
vessels
Describe the structure and function of the blood in
supporting life

Lesson outline
1. What is a circulatory system?
2. Characteristics of our circulatory system
3. The heart
4. The blood vessels
5. The blood
6. Health problems in the circulatory system

• Circulatory system =
– A type of transport system, transporting
substances around the body via the blood
• Transport system =
– Transports substances around the body
– Can be via blood or lymph

2. Characteristics of our
circulatory system

A. Why do we need a circulatory system?
B. What are circulatory systems like?
C. How is our circulatory system special?

• Thinking time:
– How are substances transported in simple,
unicellular organisms?
– We are complex, multicellular organisms
Pg 139

– All cells need to
• Receive oxygen and nutrients
• Remove waste products
– Relying on diffusion alone to transport substances
to all cells in multicellular organisms is
• Not good enough
• Not fast enough
Pg 139

– Cells in multicellular organisms are organized into
systems
• E.g. Digestive system
• Cells  Tissues  Organs  Systems
– A transport system is needed to carry substances
from 1 part of the body to another
Pg 139

– Circulatory systems need
1. A transport fluid/medium
2. A pump to move the fluid along
3. A system of vessels in which the fluid moves
= Heart = Blood vessels = Blood
Pg 139

– Our circulatory system consists of
1. The heart
2. Arteries
3. Arterioles
4. Blood capillaries
5. Venules
6. Veins The blood vessels (more later)
Pg 152

– Open circulatory systems
• Blood (transport fluid) leaves blood vessels and comes
into contact with body tissue
• Found in arthropods e.g. insects, spiders and crabs
• Nutrients obtained directly from blood surrounding
organs
• BUT, movement of blood is slow and poorly controlled
• AND, blood supply is not regular or guaranteed, so
organisms can only grow to limited size
Pg 151

– Closed circulatory systems
• Blood does not leave blood vessels or come into
contact with body tissues
• Found in humans and all vertebrates (with backbone)
• Better control of movement of blood (pump)
• Regular and guaranteed supply of blood (pump)
Pg 151

– The transport system in mammals is divided into
• Blood system carries blood
• Lymphatic system carries lymph
Pg 139

– Double circulation
• In all mammals
• The blood passes through the
heart twice in 1 complete circuit
Pg 155, 156

– Pulmonary circulation
• Blood from heart to lungs and back
• Pulmonary arteries: Heart  lungs
• Pulmonary veins: Lungs  heart,
oxygenated blood
– Systemic circulation
• Blood from heart to rest of body
• Arteries: Heart  rest of body
(except lungs), oxygenated blood
• Veins: Body  Heart, deoxygenated blood
Lungs
Round
the
body
Pg 155, 156
LR

3. The Heart
A. Structure and Function of the heart
B. The Path blood takes through the heart
C. The Cardiac Cycle
D. Blood Pressure

3. The Heart
A. Structure and Function of the Heart
– Size: About the same as a clenched fist
– Shape: Roughly conical
– Location: Behind the chest bone
Between the two lungs
• Inside pericardium (double
membrane with fluid in between)
Function: helps to reduce friction
when heart is beating
Pg 157

3. The Heart
– You need to
be able to
label:
Semi-lunar valve
Semi-lunar valve
Pg 157, 158

3. The Heart
– 4 chambers
– 2 on each side
• Function: double circulation
– Upper chambers: atria
(singular: atrium)
– Lower chambers: ventricles
– Dividing wall: median septum
• Function: prevent mixing of oxygenated and
deoxygenated blood
Pg 157

3. The Heart
– Atria (Singular: atrium)
• Blood moves from atria to ventricles
• Relatively thinner muscular walls
• Function: Forces blood
into ventricles
Pg 157

3. The Heart
– Ventricles
• Blood moves from ventricles out of the heart
• Relatively thicker muscular walls
• Function: Left ventricle
(pumps blood around
body) is thicker than right
(pumps blood to lungs)
Pg 157

3. The Heart
– 2 sides separated by median septum
– Left side: Oxygenated blood
– Right side:
Deoxygenated blood
• ‘Hole in the heart’
Pg 157

3. The Heart
– Blood passes from
the atria to ventricles
via the valves
• Flaps of tissue
• Function: Prevent
backflow of blood
• So that blood flow is
unidirectional
Pg 158

3. The Heart
– Valves: 2 types in the heart
1. Atrioventricular
= tricuspid [3 cusps] (right)
+ bicuspid [2]/mitral (left)
2. Semilunar
(half-moon, see )
Pg 158

3. The Heart
– Valves have
chordae tendinae
• Cord-like tendons
• Function: To prevent
valves from inverting
Pg 158

3. The Heart
– Label the parts of the
heart in your handout
– You will need to refer
to it as we go through
this section
Pg 158

3. The Heart
1. We will start in the
right atrium
• This receives
de-oxygenated blood
from the rest of the
body (except lungs)
• Via the superior and
inferior vena cava
Pg 158

3. The Heart
1. The right atrium
contracts
• Tricuspid valves open
3. De-oxygenated blood
flows into the right
ventricle
Pg 158

3. The Heart
4. The right ventricle
contracts
• Tricuspid valves close
• Semilunar valves open
• Closing and opening:
due to blood pressure
5. The right ventricle
relaxes
• Semilunar valves close
Pg 158

3. The Heart
6. Meanwhile, blood
leaves for the lungs
• Right ventricle walls
thinner than left
• Less force needed to
pump blood to lungs
• Via pulmonary artery
• Blood travels more
slowly than in aorta
Pg 158

3. The Heart
– Why is it good that
blood travels more
slowly in the
pulmonary artery
than in the aorta?
Pg 158

3. The Heart
7. Blood from the lungs
returns to the left
atrium
• Oxygenated blood
• Via the pulmonary
veins
Pg 158

3. The Heart
8. The left atrium
contracts
• Bicuspid valves open
9. Oxygenated blood
flows into the left
ventricle
Pg 158

3. The Heart
10.The left ventricle
contracts
• Bicuspid valves close
• Semilunar valves open
11.The left ventricle
relaxes
• Semilunar valves close
Pg 158

3. The Heart
12.Blood leaves for the
rest of the body
• Via the aorta
• Thicker walls; more
force needed to pump
blood
– Coronary arteries
• Branch off from aorta
• Bring O2 and nutrients
to heart muscles
Pg 158

3. The Heart
– As blood travels
along the aorta
• Other arteries will
branch off
• Bring O2 and nutrients
to other tissues
Pg 158

3. The Heart
– Steps 1 -6:
• Right side of heart
• De-oxygenated blood
– Steps 7-12:
• Left side of heart
• Oxygenated blood
Pg 158

3. The Heart
– Steps 1-6 and 7-12
• Are happening
simultaneously
• Left and right atria
contract together
• Then left and right
ventricles contract
together
Pg 158

3. The Heart
C. The Cardiac
Cycle
Pg 159

3. The Heart
– There are 4 stages
• Corresponding to steps in the path of blood through
the heart
• Occurs in left and right sides simultaneously
• Stage 1: (Step 1 / 7)
• Stage 2: (Steps 2 and 3 / 8 and 9)
• Stage 3: (Step 4 / 10)
• Stage 4: (Step 5 and 6 / 11 and 12)
– Stage 4 returns the heart to Stage 1
Pg 159

3. The Heart
1. Both atria and ventricles relaxed
– Blood flows into atria
• Right side: from vena cavae
• Left side: from pulmonary veins
Pg 159

3. The Heart
2. Atria contract; blood goes into ventricles
– Atrioventricular (Tricuspid & bicuspid) valves are
already open
• Pressure in ventricles < pressure in atria
Pg 159

3. The Heart
1. Then ventricles contract (= ventricular systole)
– Blood pressure in ventricles increases
• Atrioventricular valves forced to close (‘lub’ sound)
– Blood pressure in ventricles > Blood pressure in
aorta
• Semilunar valves forced open
• Blood flows out of ventricles
Pg 159

3. The Heart
4. Ventricles relax (= ventricular diastole)
– Blood pressure in ventricles decreases
• Semilunar valves close (‘dub’ sound)
• Atrioventricular valves open again
Pg 159

3. The Heart
– Repeat stages 1-4!
– Atria and ventricles
work alternately
Pg 159

3. The Heart
C. The Cardiac Cycle – Heartbeat
– 1 Heartbeat = 1 Systole + 1 Diastole
• (ventricular contraction and relaxation respectively)
– Marked by the ‘lub’ and ‘dub’ sounds
– 0.8 seconds
– Short pause between heartbeats
– Average: 72 times/min
Pg 159

3. The Heart
C. The Cardiac Cycle – Heartbeat
– What does your heartbeat rate depend on?
– It varies with
• Age
• Size
• Health
Pg 159

3. The Heart
D. What is blood pressure?
– It is the force that blood exerts on the walls of
blood vessels
– Unit: millimetres (mm) of mercury
• mmHg
– Instrument: sphygmomanometer

3. The Heart
D. What affects blood pressure?
1. Within the body
a) Varies in different parts of the body
• In the circulatory system,
• Where is blood pressure highest?
• Where is blood pressure lowest?
b) Varies at different stages in the cardiac cycle
• In the arteries,
• When is blood pressure highest?

3. The Heart

3. The Heart
2. Between people
– Varies with
• Age
• Physical activity
• Emotion
• Environment

3. The Heart – Blood pressure
D. Pressure changes in the heart
– You need to remember the stages of the cardiac
cycle, as pressure changes are due to
• Contraction of atria/ventricles
• Opening and closing of valves
Left side –oxygenated blood
Atria Ventricle Bicuspid valve Semilunar valve
1 Relaxed Relaxed Open Closed
2 Contracts Relaxed Open Closed
3 Relaxed Contracts Closed Open
4 Relaxed Relaxed Open Closed

Pg 161

– Let’s look at the left side (oxygenated blood) first
– You can colour over the different lines in your
notes
Blue: Pressure in atrium
Green: Pressure in ventricle
Red: Pressure in aorta
Pg 161

D. Pressure changes in the LEFT side of the heart
– You must know what the different graphs look like
• You may get a question about only 1 of the graphs
• Or you may be asked to label
and describe the different
graphs
– Let’s look at the left side
(oxygenated blood) first
Pg 161

1.
– Pressure in the left atrium increases slightly when
it contracts
– This causes ventricular
pressure to also increase
slightly as blood enters
– Bicuspid valves are open
Pg 161

2.
– Pressure in the left ventricle increases sharply as it
starts to contract
– Once ventricular pressure >
atrial pressure, bicuspid
valve closes to prevent
backflow of blood
Pg 161

3.
– When ventricle pressure > aorta pressure,
semilunar valve opens
– Aorta pressure increases,
but later decreases as blood
is moved away
– Rate of increase of
ventricular pressure slows
Pg 161

1.
– Ventricle begins to relax, causing semilunar valve
to close to prevent backflow
of blood
– Atrial pressure begins to
increase as blood starts
flowing in again
Pg 161

5.
– Left ventricle remains relaxed
– Ventricular pressure
decreases further
Pg 161

6.
– Once ventricular pressure < atrial pressure,
bicuspid valves open again
Pg 161

7.
– Both left atria and ventricle are relaxed
– Blood flows into ventricle
– Ventricular pressure
gradually increases again
Pg 161

8.
– Cardiac cycle repeats itself
Pg 161

– Let’s look at the right side (de-oxygenated blood)
now
– Pattern of pressure
changes is similar
(look at your handout)
– BUT much smaller
magnitude

4. The Blood Vessels
• We will be looking at
1. Arteries
– Arteriole = small artery
1. Veins
– Venule = small vein
1. Capillaries
Pg 153

4. The Blood Vessels
• Function
– To transport blood
around the body
• Structure of arteries and veins
– Wall has 3 layers
• Endothelium (innermost layer, 1 cell thick)
• Middle layer (Smooth muscle + Elastic fibres)
• External layer (Connective tissue)
– Lumen
• Space enclosed by the wall
Pg 153, 154

4. The Blood Vessels - Arteries
• Definition: Blood vessels that carry blood
AWAY from the heart
• Structure
– Thick, muscular and elastic walls
– Elastic wall much thicker in
arteries near the heart
– No valves
– Lumen smaller than that of vein with same
diameter
Pg 153, 155

Questions
• What is the function of the smooth muscle?
• What is the function of the elastic tissue?
• What would happen if the arteries were less
elastic?

• Function
– To withstand immense pressure of blood as it is
forced out of the heart
– Elastic fibres enable artery wall to stretch and recoil
(Recoil = spring back)
so that blood is pushed along the artery in spurts
– Smooth muscle contracts
• Artery constricts (lumen narrower, less blood/unit time)
– Smooth muscle relaxes
• Artery dilates (lumen wider, more blood/unit time)
Pg 153, 155

Thinking question
• How does pulse come about?

• Related to heartbeat
– When you feel your pulse, you are feeling the recoil
of artery walls
– Ventricular contraction (systole)  Arteries dilate
– Ventricular relaxation (diastole)  Arteries recoil
– Helps blood to move along arteries in a series of
waves (Pulse wave)
• Heart pumping is not the only mechanism
Pg 153, 162

• Main arteries of the body
– Pulmonary artery
– Aorta/aortic arch
• Arteries to the head, neck & arms
• Dorsal aorta (continues on)
• Hepatic artery (to liver)
• Arteries to stomach & intestines
• Renal arteries (1/kidney)
• Arteries to legs
Pg 162

What can happen if there is a fault to the
veins?

4. The Blood Vessels - Veins
• Definition: Blood vessels that carry blood
BACK to the heart
• Structure
– Middle wall layer much thinner
• Less muscular
• Less elastic tissue
– Has semilunar valves
– Skeletal muscles present around the veins
– Lumen larger than that of artery with same
diameter
Pg 154, 155

Questions
• Compare and contrast arteries and veins
– In terms of wall thickness, presence of valves,
lumen diameter (Past year O level qn)
• How do these differences relate to their
functions?

• Function
– Blood flow slower and smoother
• Much lower blood pressure
– Semilunar valves
• Prevent backflow of blood
– Skeletal muscles
• Increase pressure exerted on
the veins
• Help move blood along more
quickly
Pg 154, 155

• Main veins of the body
– Pulmonary veins [to left atrium]
– Superior vena cava [from head, neck and arms to
right atrium]
– Inferior vena cava [from rest of body to right
atrium]
• Hepatic veins (from liver)
• Hepatic portal vein (from stomach and intestines, to liver)
‘Portal’ carries blood from 1 capillary network to another
• Renal veins (from kidneys)
Pg 163

4. The Blood Vessels - Capillaries
• Definition: Microscopic thin-walled blood
vessels that carry blood from an
arteriole to a venule
• Structure
– Walls have 1 layer
• Endothelium only
• 1-cell thick
• Small gaps
between cells
– Extensive network
Pg 153, 164

Questions
• Why is an extensive network of capillaries
required?
• By what mode of transport do capillaries carry
out their function?
• What is diffusion?

• Function
– Small gaps between cells
• Allow white blood cells to squeeze through (more later)
Pg 164, 165

• Function
– Transfer of substances to tissue cells
– By diffusion
– Down concentration gradient
– Efficiency increased by
1. Extensive network
2. Narrow capillary
lumen
Pg 164

• Function
– Diffusion
• From capillaries into tissue fluid to cells
• Dissolved food substances
• Dissolved oxygen
Pg 164

• Function
– Diffusion
• From cells into tissue fluid to capillaries
• Dissolved waste products
– Transported to
excretory organs
for removal
Pg 164

• Tissue fluid/intercellular fluid/interstitial fluid
– Definition
• Diluted blood plasma containing white blood cells, small
solute molecules and ions
– Formation
• Blood plasma forced out of arterial end of capillaries
– Function
• Bathes the tissue cells, filling spaces between them
• Carries substances in solution between tissue cells and
blood capillaries
Pg 164, 165

• Tissue fluid/intercellular fluid/interstitial fluid
– Is related to lymph
• More tissue fluid is constantly leaving the capillaries
• Forcing it into lymph capillaries
• Forming lymph
– Lymph vessels
• Lymph capillaries join, forming larger and larger vessels
• Empty contents into vena cava (to right atrium)
• Contents return to blood plasma
Pg 164, 165

5. The Blood
A. Structure and composition of blood
– Plasma
– Red Blood Cells
– White Blood Cells
– Platelets
B. Blood groups
C. Functions of blood
– Transport
– Protection
– Organ transplant and tissue rejection

A. Structure and Composition of the blood
• Microscope picture of blood smear
– Different types of blood cells
– Blood is a tissue
because it
contains cells
(Cells make up a
tissue. A tissue can
contain different
kinds of cells)
Pg 140

Blood
55% plasma 45% blood cells and platelets
90% water 10% dissolved substances
Antibodies
Digested food
Mineral salts
Proteins for blood clotting
Excretory products
(Pale yellowish liquid)
Amounts kept relatively constant Pg 140

Blood
45% blood cells and platelets
Red blood cells
White blood cells
Platelets
55% plasma
Pg 141

Blood
Red blood cells White blood cells Platelets
55% plasma
= Erythrocytes = Leukocytes/leucocytes = Thrombocytes
Pg 141-143

Blood
55% plasma
- Ave 5 million/cm3
of blood (varies with gender and health)
- Produced by bone marrow
- Each cell lives about 3-4 months
- Destroyed in the ____________
- Haemoglobin broken down in the ______________
Pg 141

Blood
55% plasma
Structure
- What do you remember about its structure? (Recap: Cells, TB pg 25)
Pg 141

Blood
55% plasma
Structure
- No nucleus (Function: more space for haemoglobin)
- Haemoglobin pigment (Function: )
- Circular, flattened biconcave disc (Function: )
- Elastic, can become bell-shaped (Function: Squeeze through blood vessels)
Pg 141

Blood
55% plasma
- Larger in size than erythrocytes, but fewer in number
- Ave 5000-10000/cm3
of blood
- Colourless (no haemoglobin)
- Most are also produced by bone marrow
Pg 142

Blood
55% plasma
Structure
- Irregular in shape
- Has a nucleus
- Can move and change shape (Function: )
Pg 142

Blood
55% plasma
2 main types
- Phagocytes (different types have different names)
- Lymphocytes
- Function: To help the body fight disease
Pg 142

Blood
55% plasma
- Phagocytes
- Structure: Nuclei have lobes and cytoplasm is granular
- Function: Engulf, ingest and digest foreign particles
- Lymphocytes
- Structure: Nuclei are large and round (no lobes), cytoplasm is non-granular
- Function: Produce antibodies Pg 142

Blood
55% plasma
- Not true cells
- But classified with cells when talking about composition of blood
- Membrane-bound fragments of cytoplasm
- Produced by bone marrow
- Function: Involved in blood clotting
Pg 143

B. Blood groups
• There are 4 possible blood groups
– A
– B
– AB
– O
• It is important to know your blood group for blood
transfusions
– Needed when a lot of blood is lost due to injury or surgery
– Require compatible blood groups to be successful
Pg 143, 144

B. Blood groups - Antigens
• Blood group is determined by erythrocytes
– By proteins embedded in the erythrocyte cell
membrane
– Antigens
• They are found on all red blood cells
Pg 143, 144

B. Blood groups - Antigens
• Antigens correspond to the blood groups
– Antigens are represented by capital letters
– There are only 2 antigens, A and B
– There are 4 possible combinations
-
A and B
B
A
O
AB
B
A
AntigenBlood group
Pg 143, 144

B. Blood groups - Antibodies
– Antigens are found on erythrocytes
• Other components of blood respond to these
antigens (compatibility)
– Lymphocytes produce antibodies
• Help to protect us against foreign particles
• Recognize what ‘belongs to us’
• Antibodies are part of the 10% dissolved substances in
plasma
– Antibodies react with what is foreign to cause
clumping/agglutination of foreign particles or cells
Pg 143, 144

• Antibodies
– Are represented with small letters a and b
– There are only 2 antibodies, but 4 possible
combinations
– Antibodies are able to recognize antigens of the
same letter to cause clumping/agglutination
Pg 143, 144

– People with blood group AB have no antibodies
against antigens A and B (NOT that they have no
antibodies at all)
a and b
-
a
b
-
A and B
B
A
O
AB
B
A
AntibodyAntigenBlood group
Pg 143, 144

B. Blood groups – Blood transfusions
• What about blood cells donated in blood
transfusion?
– Antibodies are able to recognize their own blood
cells as ‘self’
– Donated blood cells are ‘foreign’

a and bO
-AB
aB
bA
O (no
antigens)
AB (antigens
A and B)
B
(antigen B)
A
(antigen A)
Donor’s blood groupRecipient’s
antibodies
Recipient’s
blood
group

• How come antibodies in the donor’s blood do
not cause clumping of the recipient’s red blood
cells?
– It depends on the volume of blood
Vol of blood from donor << Total vol of blood in recipient
– Donor’s blood is greatly diluted so antibodies in the
donor’s plasma will not have an effect on
recipient’s erythrocytes
Pg 145

Question
• Mr. Tan had an accident and lost a lot of blood. He
requires a blood transfusion. His blood group is A.
Several people have come forward to offer to donate
blood to him. His wife is blood group AB, his father is
blood group B, while his brother is blood group O.
• Who can he accept blood from and why? Use the table
given to determine the answer
• If Mr. Tan’s wife had been in the accident as well, could
she have accepted blood from any of the other 2 donors?
Why?

C. Functions of the blood
• 3 functions
– Transport
– Protection
• Protection against disease-causing
organisms(phagocyctosis & blood clotting)
• Antibody production
Pg 146-150

C. Functions of the blood – 1. transport
• Transport medium – plasma
Blood
55% plasma 45% blood cells and platelets
90% water 10% dissolved substances
Antibodies
Digested food
Mineral salts
Proteins for blood clotting
Excretory products
(Pale yellowish liquid)

C. Functions of the blood – 1. transport
• Transport medium – red blood cells
– O₂ is carried by red blood cells
• Red pigment haemoglobin (NOT an enzyme) has high
affinity for O₂
• O₂ is released as blood passes tissues containing little
oxygen. It then diffuses into tissue fluid to the tissue cells
• As blood returns to lungs, haemoglobin combines with O₂
in oxygen-rich environment again
Haemoglobin Oxyhaemoglobin
O₂ from lungs
O₂ to body tissues
Pg 146-150

C. Functions of the blood – 2a. protection
• Protection against disease-causing organisms –
white blood cells
– Phagocytes
• Engulf, ingest and digest bacteria
• Can also ingest dead body cells
Pg 146-150

C. Functions of the blood – 2a. protection
• Protection against disease-causing organisms –
white blood cells
– Lymphocytes
• Produce antibodies when stimulated by bacteria entering
the bloodstream, which can
– Cause clumping/agglutination
– Cause bacterial cell membranes to rupture
– Neutralize toxins
– Make viruses unable to bind to their host cells
• Antibodies have long-term protection: they remain in the
blood long after the infection is over
Pg 146-150

C. Functions of the blood – 2b. protection
• Blood clotting
– Stopping of blood flow at a wound is due to clotting
• Important to a) Seal the wound
b) Prevent entry of bacteria
– Is the 1st
line of defence
• If bacteria does enter the bloodstream, phagocytes and
lymphocytes are the 2nd
line of defence
– Involves platelets, proteins and enzymes
Pg 146-150

• Blood clotting
– A multi-step process involving enzymes
– Like in Nutrition,
• There are inactive proteins that have to be activated
• They have similar names e.g. prothrombin (enzyme)
fibrinogen (NOT an enzyme)
Pg 146-150

• Blood clotting
Platelets and
damaged tissue
Thrombokinase
Produce
Inactive
prothrombin
Active enzyme
Active
prothrombin
Converts
Soluble
fibrinogen
Insoluble fibrin
threads
Converts
Clot
Entangle red blood cells at the wound, forming
Pg 146-150

• Blood clotting
– Does not normally occur in our blood vessels
• Due to presence of heparin which prevents clotting
• Heparin is produced in the liver
– Thrombokinase released by platelets neutralizes
the effect of heparin
– Haemophilia
• Condition where ≥1 parts of the clotting process are
defective, so blood clotting cannot occur
• Haemophiliacs can lose a lot of blood from simple injuries
Pg 146-150

6. Heart Disease
• Heart disease = cardiovascular disease
– cardio = heart
– vascular = related to the vessels around the heart
• Types of heart disease
– Coronary heart disease
• includes coronary artery disease, myocardial infarction
(heart attack), thrombosis and angina
– Irregular heart beat (arrhythmias)
• Includes cardiac arrest

6. Coronary Heart Disease (CHD)
• While there are different kinds, they are all caused by
blockage or narrowing of coronary arteries
• Angina: (a feeling)
– Chest pains due to lack of oxygen to cardiac muscle
• Heart attack: (an event)
– Blood flow to parts of the heart are blocked
– Cardiac muscle does not receive oxygen and nutrients
– Cardiac muscle dies (this is irreversible)
– This can be fatal

6. Causes of CHD
• Cholesterol and saturated fats deposited on the
inner surface (endothelium) of the arteries
– Narrows the lumen
– Increases blood pressure
– Increases risk of blood clots (as inner surface of
arteries is now rough, not smooth)
• Thrombus = blood clot in the blood vessels
• Thrombosis = having a blood clot in a blood vessel
• Embolus = blood clot that is able to move within blood
vessels and cause a blockage away from the original site

6. Causes of CHD
• Atherosclerosis
– The hardening of arteries
– Due to the response of the white blood cells to fatty
deposits
– One type of arteriosclerosis (hardening of any
arteries, for many different reasons)
– There is also arteriolosclerosis (hardening of
arterioles)

6. Causes of CHD
• Blocked coronary arteries can start as early as
childhood!
– Unhealthy diet
• High in cholesterol
• High in fat
– Smoking
• Carbon monoxide and nicotine increase risk of heart
disease
– Lack of exercise

6. Causes of CHD
• Other factors can increase your risk of CHD
– Gender
– Age
– Family history
– Emotional stress
– Lifestyle

6. Risk of CHD
• Doctors assess your risk by looking at your
– Gender
– Age
– Family history
– Cholesterol level
– Blood pressure level
– Weight (or height/weight ratio)
– (See Risk Prediction chart)

6. Risk of CHD
Blood
pressure/
Cholesterol
Risk of heart
disease

Preventing CHD
• Healthy diet
– Balanced
– Low in cholesterol (LDL only, not HDL)
– Low in saturated fats
– Rich in fibre
• Stress management
• Stop smoking
• Exercise
• If already at risk
– Medication e.g. statins lower cholesterol levels

Human Circulatory System

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