GRADE 8
BIOLOGY
Chapter 9- Circulatory System
The circulatory system is a system of blood vessels with a pump and valves to ensure one-way flow
of blood
Circulatory systems in Mammals
Mammals have a four-chambered heart and a double circulation. This means that for every one
circuit of the body, the blood passes through the heart twice. The right side of the heart receives
deoxygenated blood from the body and pumps it to the lungs (the pulmonary circulation). The left
side of the heart receives oxygenated blood from the lungs and pumps it to the body (the systemic
circulation)
The double circulatory system in mammals
Advantages of Double Circulation:
Blood travelling through the small capillaries in the lungs loses a lot of pressure that was given to it
by the pumping of the heart, meaning it cannot travel as fast by returning the blood to the heart
after going through the lungs its pressure can be raised again before sending it to the body, meaning
cells can be supplied with the oxygen and glucose they need for respiration faster and more
frequently.
The Mammalian Heart
The heart is labelled as if it was in the chest so what is your left on a diagram is actually the right-
hand side and vice versa
The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs
The left side of the heart receives oxygenated blood from the lungs and pumps it to the body
Blood is pumped towards the heart in veins and away from the heart in arteries
The two sides of the heart are separated by a muscle wall called the septum
The heart is made of muscle tissue which are supplied with blood by the coronary arteries
Monitoring
Heart activity can be monitored by using an ECG, measuring pulse rate or listening to the sounds of
valves closing using a stethoscope
Heart rate (and pulse rate) is measured in beats per minute (bpm)
To investigate the effects of exercise on heart rate, record the pulse rate at rest for a minute
Immediately after they do some exercise, record the pulse rate every minute until it returns to the
resting rate
This experiment will show that during exercise the heart rate increases and may take several
minutes to return to normal.
Coronary Heart Disease
The coronary arteries
The heart is made of muscle cells that need their own supply of blood to deliver oxygen, glucose and
other nutrients and remove carbon dioxide and other waste products
The blood is supplied by the coronary arteries
If a coronary artery becomes partially or completely blocked by fatty deposits called ‘plaques’
(mainly formed from cholesterol), the arteries are not as elastic as they should be and therefore
cannot stretch to accommodate the blood which is being forced through them - leading to coronary
heart disease
Partial blockage of the coronary arteries creates a restricted blood flow to the cardiac muscle cells
and results in severe chest pains called angina
Complete blockage means cells in that area of the heart will not be able to respire and can no longer
contract, leading to a heart attack
Buildup of plaque in the coronary arteries
Diet, Exercise & Coronary Heart Disease
Reducing the risks of developing coronary heart disease
Quit smoking
Diet - reduce animal fats and eat more fruits and vegetables - this will reduce cholesterol levels in
the blood and help with weight loss if overweight
Exercise regularly - again, this will help with weight loss, decrease blood pressure and cholesterol
levels and help reduce stress
Identifying Structures in the Heart: Extended
Identifying Structures in the Heart: Extended
The ventricles have thicker muscle walls than the atria as they are pumping blood out of the heart
and so need to generate a higher pressure
The left ventricle has a thicker muscle wall than the right ventricle as it has to pump blood at high
pressure around the entire body, whereas the right ventricle is pumping blood at lower pressure to
the lungs
The septum separates the two sides of the heart and so prevents mixing of oxygenated and
deoxygenated blood
Structure of the heart showing the different valves
The function of valves
The basic function of all valves is to prevent blood from flowing backwards
There are two sets of valves in the heart:
The atrioventricular valves separate the atria from the ventricles
The valve on the right side of the heart is called the TRICUSPID and the valve on the left side is called
the BICUSPID
These valves are pushed open when the atria contract but when the ventricles contract they are
pushed shut to prevent blood from flowing back into the atria
The semilunar valves are found in the two blood arteries that come out of the top of the heart
They are unusual in that they are the only two arteries in the body that contain valves
These valves open when the ventricles contract so blood squeezes past them out of the heart, but
then shut to avoid blood flowing back into the heart
Functioning of the Heart:
Deoxygenated blood coming from the body flows into the right atrium via the vena cava
Once the right atrium has filled with blood the heart gives a little beat and the blood is pushed
through the tricuspid (atrioventricular) valve into the right ventricle
The walls of the ventricle contract and the blood is pushed into the pulmonary artery through the
semilunar valve which prevents blood flowing backwards into the heart
The blood travels to the lungs and moves through the capillaries past the alveoli where gas exchange
takes place (this is why there has to be low pressure on this side of the heart – blood is going directly
to capillaries which would burst under higher pressure)
Oxygen-rich blood returns to the left atrium via the pulmonary vein
It passes through the bicuspid (atrioventricular) valve into the left ventricle
The thicker muscle walls of the ventricle contract strongly to push the blood forcefully into the aorta
and all the way around the body
The semilunar valve in the aorta prevents the blood flowing back down into the heart
Explaining the Effect of Physical Activity on Heart Rate: Extended
So that sufficient blood is taken to the working muscles to provide them with enough nutrients and
oxygen for increased respiration
An increase in heart rate also allows for waste products to be removed at a faster rate
Following exercise, the heart continues to beat faster for a while to ensure that all excess waste
products are removed from muscle cells
It is also likely that muscle cells have been respiring anaerobically during exercise and so have built
up an oxygen debt
This needs to be ‘repaid’ following exercise and so the heart continues to beat faster to ensure that
extra oxygen is still being delivered to muscle cells
The extra oxygen is used to break down the lactic acid that has been built up in cells as a result of
anaerobic respiration
Arteries, Veins & Capillaries
Arteries
Carry blood at high pressure away from the heart
Carry oxygenated blood (other than the pulmonary artery)
Have thick muscular walls containing elastic fibres
Have a narrow lumen
Speed of flow is fast
Veins
Carry blood at low pressure towards the heart
Carry deoxygenated blood (other than the pulmonary vein)
Have thin walls
Have a large lumen
Contain valves
Speed of flow is slow
Capillaries
Carry blood at low pressure within tissues
Carry both oxygenated and deoxygenated blood
Have walls that are one cell thick
Have ‘leaky’ walls
Speed of flow is slow
Main Blood Vessels in the Body
Blood is carried away from the heart and towards organs in arteries
These narrow to arterioles and then capillaries as they pass through the organ
The capillaries widen to venules and finally veins as they move away from the organs
Veins carry blood back toward the heart
Components of Blood
Blood consists of red blood cells, white blood cells, platelets and plasma
Identifying Red & White Blood Cells
You need to be able to identify red and white blood cells in photomicrographs and diagrams
Red blood cells have a concave disc shape with no nucleus
White blood cells are usually round in shape with a nucleus
Blood micrograph, IGCSE & GCSE Biology revision notes
Components of Blood: Function
Plasma is important for the transport of carbon dioxide, digested food (nutrients), urea, mineral
ions, hormones and heat energy
Red blood cells transport oxygen around the body from the lungs to cells which require it for aerobic
respiration
They carry the oxygen in the form of oxyhaemoglobin
White blood cells defend the body against infection by pathogens by carrying out phagocytosis and
antibody production
Platelets are involved in helping the blood to clot
Blood Clotting
Platelets are fragments of cells which are involved in blood clotting and forming scabs where the
skin has been cut or punctured
Blood clotting prevents continued / significant blood loss from wounds
Scab formation seals the wound with an insoluble patch that prevents entry of microorganisms that
could cause infection
It remains in place until new skin has grown underneath it, sealing the skin again
White Blood Cells: Extended
Lymphocytes & Phagocytes
White blood cells are part of the body’s immune system, defending against infection by pathogenic
microorganisms
There are two main types, phagocytes and lymphocytes
Phagocytes
Carry out phagocytosis by engulfing and digesting pathogens
Phagocytosis
Phagocytes have a sensitive cell surface membrane that can detect chemicals produced by
pathogenic cells
Once they encounter the pathogenic cell, they will engulf it and release digestive enzymes to digestit
They can be easily recognised under the microscope by their multi-lobed nucleus and their granular
cytoplasm
Lymphocytes
Produce antibodies to destroy pathogenic cells and antitoxins to neutralise toxins released by
pathogens
They can easily be recognised under the microscope by their large round nucleus which takes up
nearly the whole cell and their clear, non-granular cytoplasm
