BIOLOGY FORM 5 CHAPTER 1: 1.2 CIRCULATORY SYSTEM

BIOLOGY FORM 5
chapter 1 - Transport
1.2 Circulatory System

Learning Objectives
 1.2 Synthesising the concept of circulatory
system

Function of a circulatory system:
To provide rapid mass flow of
materials:
Blood
flow
Vein
from one part
of the body
to another
over distances where
diffusion would be too slow

On reaching their destination,
materials must be able to:
pass through the walls of the circulatory
system into the organs or tissues

BLOOD
What percent of the
human body is blood?
How much blood do we
contain?
On average 4-6 liters
8%

COMPOSITION OF BLOOD
 Blood consists of a :
Liquid component:
PLASMA
Solid component:
BLOOD CELLS

Blood is:
a liquid tissue made up of several types
of cell which are bathed in plasma
Whole Blood
Sample
Sample Placed in
Centrifuge
Blood Sample
That Has Been
Centrifuged
Plasma
Platelets
White
blood cells
Red blood
cells

Platelets
White blood cells
Red blood cells
plasma
Percentage by volume of:

What is ‘serum’?
plasma without fibrinogen

Plasma can be separated from the
blood cells. How?
Centrifugation
plasma

Plasma is a clear, yellow
fluid
Percentage of water
in plasma :
Substances dissolved in
plasma:
 Glucose
 Amino acids
 Vitamins
 Minerals
 Lactic acid
Layering of blood
components in a
centrifuged blood
sample.
90%
 Hormones
 Urea
 Respiratory gases
 Antibodies
 Proteins
10%

Question:
Name the liquid component of blood and list
TWO substances dissolved in it. (3)
Amino acids
Glucose
[any two from
previous list.
FOOD is wrong]
PLASMA

Function of plasma:
to provide a medium through which continual
exchange between cells and blood takes place
Blood flow
Body cells

Erytrocytes
Red blood cells
Platelets
Thrombocytes
Leucocytes
White blood cells
Three types of blood cells:

Red blood cells (RBC) are formed
in the red bone marrow of the:
Ribs
Sternum
Vertebrae

RBC are:
 very small and numerous
 disc-shaped (BICONCAVE)
without a nucleus
 contain the red pigment HAEMOGLOBIN
 function of RBC:
to transport oxygen & some carbon dioxide

About 2 million RBC per second are
made but production is faster at high
altitude. Why?
There is not so much oxygen in the air.

RBC
small biconcave discs
  surface area
  efficiency for diffusion
of O2 & CO2
lack a nucleus when
mature
very thin cells: efficient
diffusion of gases
across surface

RBC are flexible & elastic:
to squeeze through narrow capillaries
Cardiac muscle
and capillary
Erythrocytes in single file
– capillary is so narrow

RBC make up about half the
volume of blood
i.e. blood has an enormous oxygen-
carrying capacity
Erythrocytes
(45% of total blood)
Plasma
(55% of total blood)
Leucocytes & Platelets
(< 1% of total blood)

haemoglobin:
 the oxygen-carrying protein pigment
 combines reversibly with O2
RBC: packed with haemoglobin
Haem
Haemoglobin

Hb + O2 :
- in areas of high O2
concentration
Hb releases the O2 :
- in regions of low
O2 concentration
Oxyhaemoglobin
LOADING
UNLOADING

RBC lack mitochondria. Give two
advantages of this.
1. more room for carrying haemoglobin
2. respire anaerobically : do not use up
any of the O2 they carry

RBC contain the enzyme:
plays a role in CO2
transport
carbonic
anhydrase

Average life span of a RBC: 120 days
 the old and worn out RBC are broken down
in the:
liver
spleen

What forms from the
haemoglobin broken down?
 IRON part: stored in liver
 The rest of the haemoglobin molecule forms
BILE PIGMENTS
 bile pigments are
excreted in bile
Gall bladder
stores bile

Red blood cells are
adapted to carry oxygen:
1. biconcave disc shape offers maximum
surface area for oxygen uptake
2. haemoglobin has a high AFFINITY for oxygen
and combines with it, forming
OXYHAEMOGLOBIN
3. no nucleus = more space for haemoglobin
4. being small makes it possible for oxygen to
enter and leave the RBC quickly

Deoxygenated
blood:
Deep red-purple
Oxygenated
blood: Bright red

Red blood cell production
 5-6 million RBC in tiny drop of human blood
 5 liters of blood in body = 25 trillion RBC
produce ~3 million RBC every second in
bone marrow to replace cells lost
each RBC 250,000 molecules
hemoglobin
each Hb molecule carries 4 O2
each RBC carries 1 million O2

Shape Biconcave Disk
No nuclei
Transports oxygen & carbon dioxide to
and from tissues
5-6 million/mm3
Has haemoglobin (a pigment)
Produced in the bone marrow
Life span 120 days
Produces enzyme carbonic anhydrase
I THINK MAP

Structure and Composition of the blood
Blood
45% blood cells and platelets
Red blood cells White blood cells Platelets
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)

98% transported as oxyhaemoglobin
2% transported as gas dissolved in plasma
Reversible reaction
Determined by
concentration of
oxygen, the pH of
blood etc.
Haemoglobin Oxyhaemoglobin
O₂ from lungs
O₂ to body tissues

air sac in
the lung
oxygen
1 as blood flows through the
lungs the haemoglobin in the
red cells picks up oxygen
2 Haemoglobin and
oxygen join to make
oxyhaemoglobin
3 when the blood flows
past cells with very little
oxygen in them the
oxyhaemoglobin breaks
down
oxygen diffuses into the cells of the
body
oxygen is used for respiration
4 the haemoglobin in
the red cells goes back
to the lungs to pick up
more oxygen

Carbon monoxide & haemoglobin
Result:
 O2 does not combine
with Hb & so it is not
transported
Hb + CO
 Hb combines with any CO available in
preference to O2
[a relatively stable compound
carboxyhaemoglobin]
HbCO
RBC do not carry oxygen to the cells Result:
The strength of the bond with CO is 10 times that of the bond with 02

Carbon dioxide is transported in three ways:
1) 7% dissolved as a gas in the plasma (7%)
3) Reacts with water to form bicarbonate ions (70%)
2) Bind to Haemoglobin to produce carbaminohaemoglobin (23%)

H+ released:
 combine with haemoglobin
 and make it less able to carry O2
CO2 has this effect because when it
dissolves it forms a weak acid:
How does CO2 make Hb release O2?

Transport of carbon dioxide
CO2 must not be allowed to accumulate in the
body
it forms an acid in solution that could lead to
fatal changes in blood pH
BECAUSE
Carbonic acid

Carbonic anhydrase in RBC
catalyses reaction to form H2CO3

CO2 forms at the lungs & is exhaled
AT ACTIVE TISSUES AT LUNGS

 In tissue :
CO2
plasma
+ H2O H+ + HCO3
-
enzyme

 In lungs:
CO2 + H2O H+ + HCO3
-
plasma
enzyme

WHITE BLOOD CELLS (WBC)
 have a nucleus
 larger than RBC
 are less numerous
than RBC
 some live for
months
 most just a few
days

Agranulocytes
Has no granules in
the cytoplasm
Granulocytes
Has granules in the
cytoplasm
LymphocyteMonocyteNeutrophilBasophilEosinophil
Produced in the
bone marrow
Colourless
Have nuclei

Lecuocytes can be divided:
Granulocytes Agranulocytes
Lymphocyte
Neutrophil
Basophil
Eosinophil
Monocyte
Lobed nucleus
Oval or bean-shaped nucleus
72% of total WBC
count
28%

All WBC are capable of a:
crawling movement called amoeboid
movement

Neutrophils:
70% of WBCs
Function
 Phagocytise & destroy
bacteria
Lobed
nucleus
First cells to
respond to
infection

Eosinophils:
1.5% of WBCs but numbers
increase with allergic
conditions
Function:
Secrete antihistamine
Eosin-staining
granules

Basophils:
0.5% of all white blood cells
granules stain blue with basic dyes
such as methylene blue
Function:
produce:
 heparin (anti-clotting protein)
 histamine (involved in inflammation)

Monocytes:
spend 30- 40 hours in
the blood then enter the
tissues where they
become macrophages
macrophages:
are phagocytic

Phagocytes are adapted to
engulf bacteria by having:
 an irregular shape
 a lobed nucleus
Phagocytes can
squeeze out of
capillaries.

What is ‘inflammation’?
 phagocytes move to an infected area to attack the
microbes
 when this happens the area becomes:
 red
 swollen
 hot
INFLAMMATION
 pus may form
Pus = accumulation of WBC
+ microbes

Lymphocytes:
 produced in:
 thymus gland
 lymphoid tissues
from cells which
originate in the bone
marrow

Lymphocytes:
are rounded
have a small quantity of cytoplasm
Considering the shape of the
lymphocyte, do you expect amoeboid
movement to be extensive or limited?
Limited

are found in:
Lymphocytes:
blood
lymph
body tissues
two types occur:
 T cells
 B cells
life span varies from:
 a matter of days
 to many years
involved in
immune reactions

Lymphocytes are produced in the
bone marrow :
 and then move into
the lymph nodes

Lymphocytes produce antibodies
in response to antigens
 antibodies are :
 proteins
 specific
antigen: material
foreign to the body e.g.
a bacterium or virus

Antibodies begin the process of
destruction of the microbe and
phagocytes finish the job

Immunity is
 a natural resistance to infection due to
antibodies

Question:
White blood cells fight microbes. The number
of white blood cells increases to eliminate the
pathogens. Phagocytes engulf and digest
harmful bacteria while lymphocytes produce
antibodies.
Briefly explain why the
presence of a large number
of white blood cells in a
blood sample, is an
indication of the presence of
an infectious disease. (3)

Platelets:
irregularly shaped
Cell fragments without
nuclei
life span:
 5-9 days before
destruction in liver &
spleen

Platelets are formed from:
special cells (megakaryocytes) in the
bone marrow

Function of Platelets:
start the clotting process
Break in
Capillary
Wall
Clumping
of Platelets Clot forms
Fibrin
fibres

How does clotting take place?
A clot begins to form when platelets
are damaged. Platelets release a
substance (thromboplastin /
thrombokinase).
Skin is cut.
A series of chemical reactions
occur that ends up by producing
a meshwork of FIBRIN.
1 2
3

HAEMOPHILIA
is an inherited disease where a person’s
blood takes a very long time to clot
Blood clot formation needs a clotting
factor: missing in haemophiliacs.

Practical work to include the microscopic
examination of stained
blood films and the identification of cells.
LymphocyteNeutrophils
Platelets Erythrocytes Monocyte

Difference between RBC AND WBC

characteristics RBC WBC
1. SHAPE a) Erythrocytes are
biconcave disc serves to:
• Increase surface area to
volume ratio
• Increase diffusion rate of
gaseous exchange
b) No nucleus to gives space
for great quantities of
haemoglobin
•Leucocytes have nuclei
•Not have haemoglobin
•Larger than erythrocytes
•Do not have fixed shaped
2.FUNCTION •Has haem group
•Contains iron atom
•For the site of oxygen
binding
•When the partial pressure of
o2 is high,
•Haemoglobin will combine
with o2 to form
•OXYHAEMOGLOBIN
•Responsible for the defense
of organism against disease
•If pathogen invade the body,
number of leucocytes will
increase

LIFESPAN 120 days
Destroyed by phagocytes
(WBC) in the liver and
spleen(limpa)
A few days by phagocytosis
process
MANUFACT
URED IN
Bone marrow
Rate: 2 million/ second
Bone marrow(granulocytes)
•But may migrate to thymus
gland or lymph node
•For their growth and
development stage
•Lymphatic system (
agranucolytes)
3. DIAMETER 8 micrometer
Thickness: 2 micrometer
15 micro meter
4.Number of
blood
cell/mm3
5 million/mm3 6000-10000/mm3
(Ration: 1WBC:700RBC)

FUNCTIONS OF THE BLOOD
TRANSPORT
PROTECTION
HOMEOSTASIS

1. Transport of O2 and CO2
 oxygen is transported from the lungs to all
body cells as oxyhaemoglobin
 CO2 is carried from the body cells to the
lungs in three ways:
1. mostly as hydrogen carbonate in plasma
(85%)
2. combined with haemoglobin (10-20%)
3. as dissolved carbon dioxide in plasma (5%)

2. Distribution of digestive products
Digested food
absorbed from the
intestines
the liver through the
hepatic portal vein
whole body

3. Transport of waste products and
toxic substances
 Liver: detoxifies toxic
substances
 Kidney: excretes
wastes

4. Transport of hormones
 from the endocrine gland that produces them
to the target organ

5. Transport of heat
chemical reactions
inside cells
heat
release heat
muscle contraction

Defence is achieved by:
1. Clotting of the
blood by platelets
and fibrinogen
3. Immunity: by
antibodies and
lymphocytes
2. Phagocytosis: by
neutrophils,
monocytes &
macrophages

 HOMEOSTASIS - keeping a constant internal
environment by:
1. keeping a constant body temperature - by
spreading warmth evenly around the body
2. regulating the amounts of various substances in
the tissues

Transport Protection Regulation
O2
CO2
Nutrient
Waste product
Hormones
Antibodies
Blood glucoseAgainst
pathogens
Phagocytosis
Producing
Antibodies
&
Body
temperature
pH
Osmotic
pressure

Arthropod blood is:
colourless
contains no haemoglobin
HAEMOLYMPH

The haemocoel is a network of blood-
filled spaces called sinuses in which the
internal organs are suspended.
Crayfish
Haemoc
oel
Sinu
s

Haemolymph – insect blood
• Nutrients such as digested food and hormones
diffuse from haemolymph into cells.
• Waste products diffuse out from cells into the
haemolymph
• Haemolymph does not transport respiratory
gases.
• Gaseous exchange via the tracheal system

The insect’s heart is a flexible tube
and runs:
1. longitudinally
through the
thorax & abdomen Heart
2. along the inside of the dorsal
body wall

13 chambers in
cockroach
Does not possess :
- valves
- musculature
Is a simple tube

A small valve-like opening
through which blood enters
the heart
The dorsal vessel is:
HEART
closed at the
posterior end
open at the
anterior end
The heart is divided
into chambers
separated by ostia
Heart

Each chamber has a pair of:
muscles
 expand & contract to facilitate the
flow of haemolymph through the
heart

1.The heart pumps blood
into an aorta: branches
into arteries.
2. These arteries open into
a series of blood spaces
collectively called the
haemocoel.
3. Blood under low pressure
moves slowly between
the tissues, gradually
percolating back into the
heart through open-ended
veins.

TYPES OF BLOOD VESSELS
Artery Vein
Capillary
Blood from
the heart.
Blood to
the heart.

Vertebrates:
arteries carry
blood away from
the heart
veins carry blood
back to the heart
O2 is carried by
haemoglobin in
red blood cells

What happens to an artery
when it enters an organ?
Branches into arterioles
and finally into capillaries.

Circulatory System
Veins
Carry blood towards the heart.
Venules
Capillaries join to form venules.
Blood Capillaries
Walls are one cell thick.
Partially permeable lining
allows substances to
diffuse quickly. Slow
movement of blood.
Heart
Relaxed state: heart is filled with
blood. Contracting heart: blood is
being pumped with great force out
to lungs and to rest of body.
Arteries
Artery carries blood away.
Arterioles
Branching of arteries.

Artery
Vein
Note the much
thinner walls in
veins.
Artery and Vein

One reason for walls of arteries being thick
and the middle layer being mainly
composed of elastic fibres.
1. To dilate but not rupture when the heart
forces blood into them at high pressure

Capillaries
 are very small - about the
diameter of a red blood cell
Endothelial cells

Capillaries are so thin that RBC
have to squeeze through

Comparison of blood vessels in
structure
Arteries Veins Capillaries
1) Walls have a
thick muscle and
elastic layer
Walls have a thin
muscle and elastic
layer
Walls are one cell
thick

2) No valves
present
Valves present to
prevent backflow
No valves
One-way flow

When body muscles
contract, they exert
pressure and
squeeze the veins
flat, helping the blood
to return to the heart.
How does blood return to the heart?

Veins contain
one-way
valves
Varicose Veins:
Damaged valves
in veins

Explain the presence of valves in leg and arm
veins. (2)
Question:
The contraction of muscles compressing
veins helps push blood up through the
leg and arm veins back to the heart.
The valves allow the blood to flow
towards the heart only.

3) Fluid and WBC
cannot pass
through wall
Fluid and WBC
cannot pass
through wall
Fluid without
proteins can pass
through wall. WBC
pass out between
cells
artery vein
capillary

Capillary beds are:
permeable to:
water, ions, small
molecules
impermeable to:
large proteins

Question:
Explain the wide lumen diameter and thin walls
in veins. (2)
Veins can store a large volume of blood inside
their wide lumen. Thin walls can easily extend to
contain the blood.

Comparison of blood vessels in
blood composition and flow
4) Flow is away
from the heart
Flow is towards
the heart
Flow is from
artery to vein
HEART

5) Oxygenated
blood except
pulmonary artery
Deoxygenated
blood except
pulmonary vein
Mixed
Pulmonary artery
Vein
Artery

Question:
List ONE function of the arterial
blood vessels (arteries). (2)
To supply oxygen to the body
cells.

6) Rapid flow Slow flow
Very slow
flow
7) High pressure Low pressure Low pressure
8) Pulse strong No pulse No pulse

arteries capillaries Veins
•Carry oxygenated
blood away from the
heart to all parts of
the body
•Except pulmonary
artery
•Sites for the
exchange of
respiratory gases,
nutrients and wastes
•Transport
deoxygenated blood
from all parts of the
body to the heart
except pulmonary
vein
•Blood pressure:
•High blood pressure
in arteries
•Lower than arteries
but higher than veins
•Lower than arteries
•Thick muscular wall
•Lumen size small
•One cell thickness
•Lumen is very small
•Thinner wall
•Lumen size is large
•No valve except
aorta
•No valve •Valve present to
prevent backflow of
blood

Artheriosclerosis
• a type of cardiovascular disease
• Caused by the buildup of cholesterol within arteries
Figure 42.18a, b
(a) Normal artery (b) Partly clogged artery
50 µm 250 µm
Smooth muscleConnective
tissue Endothelium Plaque

force exerted by circulating blood
on the walls of blood vessels
The pressure of the circulating blood decreases as
blood moves away from the heart
Blood Pressure refers to the:

Label the veins, venules, arteries,
arterioles, and capillaries
Across which vessels do materials diffuse
(cross into and out of the blood)?
Indicate where the
heart is
vein
venules
artery
arterioles
capillaries

How is blood propelled through
the human circulatory system?

The heart
• A heart is an organ
that generates
pressure to pump the
blood through out
the body

THE HEART
size of fist
weight is about 250-300 g.
is located between the
lungs behind the sternum
and above the diaphragm.

The heart is surrounded
by a tough sac:
Its main purpose is to:
 hold and lubricate the
heart
 make sure that it does
not expand too much.

Cardiac Muscle is:
the muscle of the heart
strong and thick
Cardiac muscle
composed of spontaneously contracting
cardiac muscle fibres: MYOGENIC
image of a single
human heart
muscle cell beating
Myogenic – self-exciting - contractions occur spontaneously

Cardiac muscle compared to
skeletal muscle
Cardiac muscle
 contracts more slowly
 does not fatigue as easily
Skeletal muscle

supply heart muscle
can become blocked
By-pass
graft

Damage that occurs when a coronary
artery feeding the heart is blocked
What is a heart attack?
Right coronary
artery
Aorta
Left coronary
artery
Blockage
Dead muscle
tissue

Blocking of a blood vessel by
cholesterol
Blocked coronary
artery leads to a
heart attack
Dead muscle
tissue due to
lack of oxygen

Question:
Suggest TWO ways in which a person’s lifestyle
might lead to a blockage of the coronary
arteries.
1. Lack of exercise.
2. Smoking.
3. Eating food rich in fats.
4. Excessive alcohol intake.

What happens to the blood pressure
if a blood vessel is blocked?
Normal blood flow
Abnormal
blood flow

What is a ‘stroke’?
 Interruption of oxygen supply to the brain
 Caused by:
A clot in an artery
in the brain
Breakage of an
artery in the brain
 Causes brain cells
to be deprived
of oxygen and die

The heart has four chambers
atria  Two upper chambers: atria / auricles
 Two lower chambers: ventricles
ventricles
A wall / septum separates the
two sides. Why?
To prevent mixing of deoxygenated
blood on the right side from the
oxygenated blood on the left.
RIGHT LEFT

2 advantages of having complete
separation of oxygenated and
deoxygenated blood :
1. Blood reaching the tissues has the highest
possible O2 content.
Interventricular
septum
Left
ventricle
Right ventricle

2. Respiratory gas exchange is maximised as
blood with:
 lowest O2 &
 highest CO2 content
is sent to the lungs

Four valves in the
heart:
Pulmonary
semilunar
valveAortic
semilunar
valve
Tricuspid
valve
Bicuspid / mitral
valve
Tricuspid
valve
Bicuspid
valve
Pulmonary
semilunar
valve
Aortic
semilunar
valve

Four valves in the heart
Tricuspid valve:
Prevents backflow
to right atrium
Bicuspid valve:
Prevents backflow
to left atrium
Semilunar valves:
Prevent backflow
to ventricles
RIGHT LEFT
Bicuspid valve
Tricuspid valve
Semilunar
valves

Chordae
tendineae
support
bicuspid valve
Papillary
muscles

Parts of the heart
Atria:
Receiving Chambers
Ventricles:
Pumping Chambers
Valves:
Control one way flow
Septum
Divides the Heart

Vertical section: the heart
Aorta
Pulmonary vein
Left atrium
Right atrium
Vena cava
Tricuspid
valve
Pulmonary artery
Right ventricle
Tendon Left ventricle
Semi-lunar valves
Bicuspid valve

The superior & inferior vena cava
return blood to the right atrium
Brings blood from
the upper part
of the body
Brings blood from
the lower part
of the body

Thickness of cardiac
muscle varies according to
the function of the chamber
Atria are thin walled:
deliver blood to adjacent ventricles
Ventricle walls are much
thicker and stronger:
Right ventricle
supplies blood to
the lungs (little
flow resistance)
Left ventricle wall:
thickest to supply
blood to all parts
of the body except
lungs

Right ventricle has thinner
walls than left ventricle
Right ventricle pumps blood to lungs which are
near to heart but left ventricle pumps to whole
body. Thus less pressure is needed.
Right
ventricle
Left
ventricle

Question:
Give a biological explanation for
each of the following.
Blood pressure is highest in the
arteries and lowest in the veins.
(4)
Highest blood pressure in arteries:
blood is pumped into them by
heart.
Lowest in veins: blood is far away
from heart.

The cardiac cycle [0.8s long] is:
the sequence of events which takes place during
the completion of one heartbeat
1 2 3

It takes about 0.8s (~1 min.) for blood
to make 1 complete cycle

Systole: contraction
Diastole: relaxation

Length of time spent at each
phase:
1
2
3

Sequence of events
1.Atrial diastole
Atria and ventricles are
relaxed.
Blood returning to the
heart under low pressure
in the veins, enters the
atria.

2. Atrial systole.
Atria contract / Ventricles relax
the two atria
contract
simultaneously.

3. Ventricular systole.
Ventricles contract / atria relax

3. Ventricular systole.
Closure of the AV valves during
ventricular systole produces the first
heart sound: ‘lub’.
AV valves
CLOSED

Ventricles contract
Atria relax
Atria contract
Ventricles relax
When ventricles
contract blood moves:
out of the heart
When atria contract
blood moves:
into the ventricles

4. Ventricular
diastole.
Ventricles relax.
 The high pressure developed in the aorta and
pulmonary artery:
 tends to force some blood back towards
the ventricles
 thus semilunar valves of the aorta and
pulmonary artery close.

4. Ventricular diastole.
The closing of the semilunar valves
causes the second heart sound, ‘dub’
Semilunar valves
CLOSED

Two normal heart
sounds with each
heart beat:
Sounds of heartbeat are from:
turbulence in blood flow caused by
valve closure

The events of the cardiac cycle

Cardiac muscle is able to
contract on its own:
A heart removed from a mammal
continues to beat rhythmically
for a considerable time if placed
in a well-oxygenated Ringer
solution at 37C, in the absence
of stimulation from nerves or
hormones.
Demonstration of the myogenic nature of the heart:

The heart beat originates in the
cardiac muscle: in the
Pacemaker
(sinoatrial node – SA node)
Called pacemaker because:
 each wave of excitation
begins here
 acts as the stimulus for the
next wave of excitation

Artificial
pacemaker is needed
if heartbeat is slow

The SA node generates waves of
excitation, 70-80 times/ min:
Location: wall of the right atrium near
the entrance of the superior vena cava
initiates & coordinates contraction of
the heart
is a cluster of specialised
muscle cells that produce
spontaneous electrical
signals at a regular rate

Once contraction has begun: it spreads
through the walls of the atria [at 1 ms-1]
Excitation spreads to the
AV node
both atria contract more
or less simultaneously

Tissues of AV node are
similar to SA node AV node supplies
the bundle of His
bundle of His:
provides the only route for the transmission of
the wave of excitation from the atria to the
ventricles
bundle of His
Location of AV node:
Base of right atrium
Function of AV node:
Connects atria & ventricles
electrically

Bundle of His consists of modified
cardiac fibres that do not contract
fibres of the bundle of His divide into
right & left bundle branches
bundle of His
bundle branches
bundle branches:
 run to the tips of the ventricles
& then spread throughout the
ventricles as Purkinje fibres

Cardiac Conduction
System includes:
1. Sinoatrial (SA)
node [pacemaker]
2. Atrioventricular
(AV) node
3. Bundle of His
5. Purkinje fibres
4. Bundle
branches

The control of heart rhythm
SA node
(pacemaker)
AV node Bundle
branches
Heart
apex
Purkinje
fibres
2
Signals are
delayed
at AV node.
1
SA node
generates
wave of signals
to contract.
Signals pass
to heart apex.
4 Signals spread
throughout
ventricles.
1 2 3 4

Question:
During exercise the heart pumps out a greater
volume of blood per minute than when the
body is at rest. List TWO ways in which the
heart can increase the volume of blood
pumped out. (4)
1. Increase in heart beat rate.
2. Each beat becomes stronger.

The
The muscle cells
initiate electrical signals
Activation of
the atria
Slow heartbeat
Fast heartbeat
can alter the rate of
these signal

The heart is controlled by the
autonomic nervous system
Sympathetic NS
heart rate
The autonomic NS:
 controls the involuntary functions of the body
 has two subdivisions which exert opposite
effects:
Parasympathetic NS
heart rate
Rest & digest

Sympathetic & Parasympathetic
fibres both end on the SA & AV nodes
Parasympathetic
Nerve
[vagus nerve]
Sympathetic Nerve
Slows heartbeat Increases heartbeat

Hormonal control
of heart rate

Adrenaline
 Secreted by: adrenal medulla
 When a person is excited, an
increase in the secretion of
adrenaline causes the heart
to beat faster
medulla
cortex
The medulla also secretes smaller amounts of the
hormone noradrenaline : has similar effects to
adrenaline
 both stimulate the heart, but adrenaline is more
effective

Heart rate increases when
there’s:
Increase in partial pressure of CO2 in
the blood
Body temperature is elevated

force exerted by circulating blood
on the walls of blood vessels
The pressure of the circulating blood decreases as
blood moves away from the heart
Blood Pressure refers to the:
Regulatory mechanism of blood pressure

Regulatory mechanism of blood
pressure
• Arterial blood pressure is highest during
ventricular systole , and lowest during
diastole

Two reasons why pressure in the RIGHT
VENTRICLE is much lower than that in the
left ventricle:
1. prevent stress on
the capillaries of the
lungs
2. give chance for
gaseous exchange
to take place

A ‘pulse’ is caused by:
ventricular systole & the elastic recoil of
the arteries as blood at high pressure is
forced through them

Blood pressure
Systolic
pressure =
pressure when
the heart
contracts.
Diastolic
pressure =
pressure
between heart
beats (when
heart relaxes)

SPHYGMOMANOMETER
Measure blood pressure.

Baroreceptors
Baroreceptors =
pressure receptors
• Normal bp is 120/80 mmHg
• 120 mmHg = systolic
pressure
• 80 mmHg = diastolic
pressure
• Blood pressure is regulated
by baroreceptors (pressure
receptors ) in the walls of the
aorta and carotid arteries.
• Baroreceptors monitor the
pressure of blood flowing to
body and brain

Measurement of blood pressure
hypertension =
(high blood pressure)
if systolic > 150
or
if diastolic > 90

The overall nervous control of
the cardiovascular system is located in
the medulla oblongata
Brain stem Spinal cord

Increase in BP
Increase in BP
stretches baroreceptors
impulse cardiovascular centre (medulla)
impulse via parasympathetic nerve heart
heartbeat slows
BP drops
 BP normal

Decrease in BP
sympathetic nerve increases stimulation
of SA node
contraction of cardiac muscles (heart)
& smooth muscles of arteries
heartbeat faster
BP increases
BP normal

As the blood flows through the blood
vessels it is “resisted” by the vessel wall:
if the vessel is:
WIDE [vasodilation]:
 resistance is very low
 blood pressure is low
NARROW [vasoconstriction]:
 resistance is high
 blood pressure is high

Regents Biology
Circulatory systems
 All animals have:
 muscular pump = heart
 tubes = blood vessels
 circulatory fluid = “blood”
open closed
hemolymph blood

Types of circulatory systems
• Open circulatory system : fluid is
circulated through an open body
chamber.
• Closed circulatory system : fluid
is circulated through blood
vessels.

Examples of Animals with an
Open Circulatory System
 clams
 Crayfish, shrimp,
lobsters (not
shown)
 insects as
exception to low
oxygen use rule
(remember the
tracheal system)

OPEN CIRCULATORY SYSTEM
Arthropoda

Closed system
• Vertebrates, annelid
worms, and a few
mollusks have a
closed circulatory
system.
• Blood is moved
through blood vessels
by the heart’s action. It
does not come in
direct contact with
body organs.

Examples of Animals with a
Closed Circulatory System
 vertebrates from
fish to mammals

Regents Biology
fish amphibian reptiles birds & mammals
A A
V
V V VV
A AAA
A
V
2 chamber 3 chamber 3 chamber 4 chamber
Closed Circulatory System
Blood only flows in blood vessels

Regents Biology
 increase body size
 fuel warm-blooded
 enable flight
 Higher energy needs
 greater need for energy,
fuel, O2, waste removal
 warm-blooded animals &
flying need 10x energy
 need to deliver 10x fuel & O2
What advantage has a 4-chambered heart?

Two-chambered heart
• The simplest
vertebrate heart is the
two-chambered heart,
seen in fishes.
• A single atrium
receives blood from
the body cells. A
ventricle sends blood
to the gills to collect
oxygen.

Three-chambered heart
• Separate atria allow
some separation of
oxygenated and
deoxygenated blood,
which was an advantage
for land organisms
(reptiles, amphibians).
• Though blood can mix in
the ventricle, mixing is
minimal. Some reptiles
have partial separation
of the ventricle.

Four-chambered heart
• The four-chambered
heart, seen in birds and
mammals, allows
complete separation of
oxygenated and
deoxygenated blood.
• Complete separation is
necessary to support a
fast metabolism found
in homeotherms.

Single
circulation
Double
circulation
FISH
BIRDS & MAMMALS
have true double
circulations

Human blood circulation:
1. It is a double circulation.
 blood passes
through the heart
twice for each
circuit of the body

Double circulation: blood passes twice
through the heart for each circuit of the body
Pulmonary circulation:
Heart-lungs-heart
Systemic circulation:
Heart-body-heart

Double circulation is
found in:
 birds
 mammals

Why is a single circulation less efficient
than a double circulation?
Drop in pressure
as blood passes
through the gills

Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates
(www.sinauer.com) and WH Freeman (www.whfreeman.com)

Comparison of Circulatory Systems

 Explain why a baby born with a hole in its
heart tires very easily.
Deoxygenated blood from the right atrium flows into
the left atrium where it mixes with oxygenated blood.
The aorta carries this mixture to the muscles. The
muscles do not receive enough oxygen.
Adult heart Foetal heart

 Draw schematic figure and compare
circulation system in fish, amphibian and
mammals
PRACTICE

A. Structure and Composition of
the bloodBlood
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

the bloodBlood
Red blood cells
White blood cells
Platelets
55% plasma

the bloodBlood
55% plasma
= Erythrocytes = Leukocytes/leucocytes = Thrombocytes

the bloodBlood
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 ______________

the bloodBlood
55% plasma
Structure
- What do you remember about its structure?

the bloodBlood
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)

the bloodBlood
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

the bloodBlood
55% plasma
Structure
- Irregular in shape
- Has a nucleus
- Can move and change shape (Function: )

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

the bloodBlood
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

the bloodBlood
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

BIOLOGY FORM 5 CHAPTER 1: 1.2 CIRCULATORY SYSTEM

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BIOLOGY FORM 5 CHAPTER 1: 1.2 CIRCULATORY SYSTEM