Download File - Mrs Jones A

(a) Explain the need for transport systems in
multicellular animals in terms of size, level of
activity and surface area:volume ratio;
Why many animals have a heart and
circulation.
Small organisms such as flatworms
Do not need a
circulatory
system
because:
They have a large
surface area to
volume ratio so
sufficient oxygen can
diffuse in across the
entire surface
They are thin enough and small
enough for sufficient materials to
diffuse to and from every cell
Why many animals have a heart and
circulation.
• In large organisms diffusion is too slow to move
materials – oxygen, food etc. - throughout the
body fast enough and in sufficient quantities to
support high metabolic rates.
• Have mass flow transport system – fluid, i.e. blood
made to move around body
• Blood made to move by pressure – generated by
heart/ pumped
• The heart and circulatory system have one
purpose: to move substances around the body!
Size:
• Many layers of cells
• Oxygen/nutrients diffusing in will no longer be able
to reach the inside, used up by outer layers
Surface area:volume ratio
• As an organism gets larger its surface area to
volume ration gets smaller, so the surface area is
not sufficient to supply all the oxygen/nutrients
needed by the internal cells
Level of activity
• Animals need energy from food
• Releasing energy from food requires oxygen
• If an animal is very active they need a good supply
of oxygen/nutrients for movement
• Mammals have greater energy requirements as they
need to keep warm
Common Features of a mass transport
system
• Suitable transport medium to carry oxygen/nutrients around the
body = BLOOD
• A means of moving the substances fast enough to supply the
needs of organism/ means of maintaining a concentration
gradient. A pump to create pressure that will push the fluid
around the body =HEART
• System of vessels: usually tubes, following a specific route,
widespread and branching to carry the transport medium =
ARTERIES< VEINS< CAPILLARIES
• A way of making sure the substances move in the right direction=
VALVES
• Exchange surfaces that enable oxygen and nutrients to enter the
blood (WHERE?) and leave it again when needed
• TWO circuits: one to pick up oxygen, other to deliver it to
tissues
(b) explain the meaning of the terms single
circulatory system and double circulatory
system, with reference to the circulatory
systems of fish and mammals;
(c) explain the meaning of the terms open
circulatory system and closed circulatory system,
with reference to the circulatory systems of
insects and fish;
• Closed: a circulatory system in which the blood is
always within blood vessels
• Single: a circulatory system in which the blood
flows through the heart once in each circulation
of the body; on from the lungs or gills to the rest
of the body, without first returning to the heart.
• Double: a circulatory system in which the blood
flows through the heart twice in each circulation
of the body there are 2 circuits, the systemic
circulation and the pulmonary circulation, the
blood returns to the heart after being oxygenated
before flowing to other parts of the body
Closed circulatory systems:
•
•
•
•
A closed circulatory system is one in which the
blood is always within blood vessels
In vertebrates blood retained in blood vessels;
blood vessels + heart = circulatory system
This allows generation of higher pressure so
blood travels faster – increases efficiency
Heart  arteries arterioles  capillaries (large
number; site of exchange between blood and
cells)  venules  veins  heart
Valves – in heart and veins – ensure one way flow
Animals with closed circulatory systems
have:
• Single circulatory systems
• Double circulatory systems
• Single circulatory system: fish
• Ventricle of heart pumps deoxygenated blood
to the gills
• Gas exchange takes place at the gills:
diffusion of carbon dioxide from blood into
water, diffusion of oxygen from water into
blood
• Blood flows around body and returns to the
atrium of the heart
ONE FLOW OF BLOOD THROUGH THE HEART!
Double circulatory systems: birds, mammals: In double
circulation blood flows through heart TWICE
Heart  lungs  heart  extra pressure ‘boost’ to increase
pressure in systemic circulation, so flow is faster  rapid delivery
of materials  allows support of higher metabolic rate
What are the advantages of a double
circulatory system?
• Oxygenated/ deoxygenated blood cannot mix
• Tissues receive as much oxygen as possible
• Fully oxygenated blood is delivered as quickly as
possible to body tissues under high pressure
• Blood passing through capillaries is at low
pressure (resistance), allows gas exchange to
take place
• Because oxygenated blood returns to the heart,
it can be pumped at high pressure to the body
Open circulatory system
A circulatory system in which the blood is not
contained within vessels for at least part of its
journey around the body
•Insects have an OPEN circulatory system. WATCH
Insect blood, properly called haemolymph, flows freely through the
body cavity and makes direct contact with organs and tissues.
Blood is pumped by a muscular organ like a heart and flows out of heart
in arteries into the body cavity called haemocoel (blood space)
Pumps by peristalsis
The insect circulation system does not carry oxygen, so the blood does
not contain red blood cells as ours does. Haemolymph is usually green
or yellow
Why don’t all animals have an open
circulatory system?
•
•
•
•
•
Works for insects because they are small
Blood does not need to travel far
Do not rely on blood to carry oxygen/carbon dioxide
In an open system there is low pressure
This would not be sufficient to supply the needs of muscles in
a large active organism
(d) describe, with the aid of diagrams and
photographs, the external and internal structure of
the mammalian heart; (HSW: Collection and
presentation of qualitative (descriptive) data: Make
measurements and annotated drawings during a
heart dissection;)
(e) explain, with the aid of diagrams, the differences
in the thickness of the walls of the different
chambers of the heart in terms of their functions;
vena cava
(superior)
pulmonary
artery
pulmonary
veins
right atrium
right ventricle
vena cava
(inferior)
aorta
pulmonary artery
pulmonary veins
left atrium
atrioventricular
valve /bicuspid
valve
semilunar
valve
left ventricle
Figure 1 Vertical section of the heart showing direction of blood flow.
The mammals’ heart is
made almost entirely of
muscle.
It’s called CARDIAC
MUSCLE (myogenic)
The mammals’ heart is
divided in 4 chambers:
RIGHT ATRIUM
RIGHT VENTRICLE
LEFT ATRIUM
LEFT VENTRICLE
The two sides are
divided by a SEPTUM to
prevent blood mixing
The walls of the 4 chambers are
made of muscle fibre.
ATRIA don’t need to generate
a huge force
Thin walls
VENTRICLES need to push
the blood to the lungs (right)
and to the rest of the body
(left)
Thick walls (especially the left
one)
Within the heart there are many
valves (made of connective tissue)
to prevent blood back-flow.
TRICUSPID VALVE
(between right atrium-ventricle)
BICUSPID or MITRAL VALVE
(between left atrium-ventricle)
SEMILUNAR VALVES
(halfmoon shaped valves in Aorta and
Pulmonary arteries)
Attached to the cardiac muscle via
TENDONS: tedinous cords
Attach valves to walls of heart and
prevent valves from inverting
(control blood flow)
Coronary arteries
• Surface of the heart
• Oxygenated blood for the heart to use
• What are the consequences of them
becoming blocked?
What are the sounds
made by?
• Lub= closing of atrio
ventricular valves when
ventricles contract
• Dub= closing of
semilunar valves when
ventricles relax
• Atrioventricular valves
snap shut so seem
louder than semilunar
as blood accumulates in
the pockets to close
them
(f) describe the cardiac cycle, with reference to
the action of the valves in the heart;
(g) describe how heart action is coordinated
with reference to the sinoatrial node (SAN), the
atrioventricular node (AVN) and the Purkyne
tissue;
The cardiac cycle: Takes 0.8 seconds!
The cardiac cycle is the sequence of events in one complete heartbeat.
Each pump or beat of the heart consists of two parts or phases diastole and systole.
Systole is when the heart is contracting and forcing blood out to lungs
and around the body
Diastole is when the heart is relaxing and full of blood
Blood flows
into the 2
atria
DIASTOLE
Filling phase
The atria
contract,
pushing the
blood into the
ventricles
ATRIAL
SYSTOLE
The ventricles
contract, forcing
blood into the
aorta and the
pulmonary artery
The blood
flows along
the arteries
and the
whole cycle
starts again
VENTRICULAR
SYSTOLE
Cardiac cycle
• The 2 ventricles contract simultaneously from
the bottom upwards
• The atria contract a fraction of a second
before the ventricles: right before left
• This sequencing of contractions PLUS valves
ensures the flow of blood in one direction
Why does blood move?
• HYDROSTATIC PRESSURE: The pressure exerted or
transmitted by the fluid. What causes this in the heart
• Blood will only move when there are pressure
differences. Initial pressure caused by systole contraction
• Ventricle contracts: volume decreases: pressure
increases: if pressure is higher than in arteries/veins:
blood moves OUT
• Ventricle relaxes: volume increases: pressure decreases:
blood moves IN from atria with higher pressure
• This is an example of a Mass Flow system: bulk
movement of materials due to pressure differences
Cardiac cycle: follow using heart
diagram
• The cardiac cycle is alternating periods of contraction
(systole), during which the heart is pumping blood, and
relaxation (diastole), during which the heart's chambers
are filling with blood.
1. Atrial systole:
• Blood under low pressure flows into left and right atria
from pulmonary veins and vena cava
• Elastic recoil of atria walls =low pressure in atria that
helps draw blood into heart (volume increased)
• Atria fills and pressure pushes open atrioventricular
valves and blood leaks into ventricles
• Atria walls contract forcing more blood into ventricles
2. Ventricular systole:
• Ventricles contract (slight delay) from base of heart
upwards, increasing the pressure in the ventricles
• Blood is pushed out of arteries by pressure forcing
open semilunar valves
• Pressure of blood against atrioventricular valves
closes them and prevents blood flowing back into
atria
3. Diastole:
• Atria and ventricles relax
• Elastic recoil of relaxing heart walls lowers pressure in
atria and ventricles ( volume increased)
• Blood under high pressure in arteries is drawn back
towards ventricles closing the semilunar valves
• (Blood enters the coronary arteries in diastole)
Note:
Valves are opened and closed by pressure
changes between atria and ventricles
Atrial
Systole
Valves are
opened
and closed
by
pressure
changes
between
atria and
ventricles
Ventricular
Systole
Diastole
“DUB”
“LUB”
A
Atrioventricular valves close (1st louder heart sound “LUB”)
B
Semilunar valves open
C
Semilunar valves close (2nd softer heart sound “DUB”)
D
Atrioventricular valves open
What happens to hydrostatic pressure as blood moves away
from the heart?
Pressure changes in the circulatory system:
Pressure drops as distance from the heart increases. Biggest drop
in pressure is in the arteries. Fluctuations in pressure in the
arteries and arterioles, (pulse) no fluctuation in capillaries and
veins. Vessels become smaller but there are more of them. Vessels
have larger lumen so reduced resistance to blood.
Pressure changes in the circulatory system:
Explain
Explain why the wall of the left ventricle is thicker than the
wall of the left atrium
• 3 marks
• Thicker muscle generates more force
• To create a higher pressure
• To push the blood against greater resistance/friction
• As the left ventricle supplies the systemic system/ all parts
of the body
Explain how the pressure changes in the heart bring about
the closure of the atrioventricular (bicuspid) valve
• 2 marks
• Ventricular systole
• Ventricular contraction raises the ventricular pressure
• Pressure higher in ventricle than atria
• Movement/pressure from ventricular contraction of blood
pushes valve shut
Control of heartbeat
• The heart is made up of cardiac
muscle.
• Cardiac muscle is myogenic,
which means it naturally
contracts and relaxes.
• Therefore, it receives no impulse
from a nerve to make it contract.
• To ensure synchronisation of the
contractions the heart has a
mechanism of control:
Pacemaker:SAN
Heart rate is controlled automatically
What can you see happening??
Control of heartbeat
• The cardiac cycle is
initiated by a small patch
of muscle called the
Sinoatrial node (SAN) or
pacemaker.
• This node sets the
rhythm for all the other
cardiac muscle.
Control of heartbeat
• The SAN sends out an
excitation wave of electrical
activity over the atrial
muscular walls.
• The cardiac muscle
responds to this wave by
contracting at the same
speed as the SAN.
• This results in both atria
contracting simultaneously.
• This is atrial systole
Control of heartbeat
• There must be a delay between
atrial contraction and
ventricular contraction.
• For this reasons, fibres between
the two chambers do not
conduct the electrical impulse
• The impulse is conducted
through a patch of fibres in the
septum known as the atrioventricular node or AVN.
• This is the only route through:
the rest of the tissue is non
conducting
Control of heartbeat
• The AVN passes the wave
onto another set of
conducting fibres that run
down the centre of the
septum between the
ventricles called the
Bundle of His
This bundle spread into right
and left branches
(Purkyne fibres)
This causes ventricular
contraction (both) from the
apex upwards
The pathway followed by the wave of excitation
(h) interpret and explain electrocardiogram
(ECG) traces, with reference to normal and
abnormal heart activity;
What is an ECG?
• An ECG monitors the electrical activity of the
heart. The pattern is a result of the different
impulses produced at each phase of the
cardiac cycle
• Changes in polarisation of the heart are
detected as small electrical currents at the
surface of the skin
What does an ECG show?
• P wave depolarisation of the
atria that leads to atrial
contraction (atrial systole)
• PR interval time taken for
impulses to be conducted from
the SAN across the atria to the
ventricles, through the AVN
• QRS complex the wave of
depolarisation that results in
the contraction of the
ventricles (ventricular systole)
• T wave repolarisation of the
ventricles during diastole
Diagnoses
– The shape of an ECG trace can give an indication of
which part of the heart muscle is not healthy
– It can show if the heart beat is irregular=
arrhythmia
– If it is in fibrillation=uncoordinated beat
– Suffered a heart attack=myocardial infarction
– If the heart has enlarged
– Purkyne system is not conducting properly
A normal ECG trace compared with others indicating an unhealthy heart
Calculating heart rate:
• The interval between successive beats allows
the heart rate to be calculated
• Beats per minute
Using the ECG trace to measure heart rate
• The ECG trace can be used to measure heart rate.
• The squared paper passing through an ECG machine moves at
a steady 25 mm per second.
• This means that 300 of the large squares will pass through in 1
minute. One large square is equivalent to 0.2 seconds.
• Heart rate can be determined by finding the average number
of large squares between two QRS complexes. This value is
divided into 300 to give the heart rate. If four large squares
separated the QRS complexes the heart rate would be: 300 ÷ 4
= 75 beats per minute.