Human Circulatory System

THE CIRCULATORY SYSTEM NOTES

2021

www.scienceexamssorted.co.uk

AQA The Circulatory System Notes

1

AQA The Circulatory System Notes

Science Exams Sorted

This topic is regularly assessed in the exams, questions on this topic can range from short 1 mark/ multiple

choice questions to 6 mark questions. Before we look at the blood vessels etc let’s look at the blood itself.

The Functions of Blood

Blood is essentially a transport medium. Blood transports the following:

1.Oxygen from the lungs to all other parts of the body.

2.Carbon dioxide from all parts of the body to the lungs.

3.Nutrients such as glucose from the small intestine to all parts of the body.

4.Urea from the liver to the kidneys.

5.Hormones, antibodies and many other substances are also transported by the blood as well as it

distributing heat around the body.

The Composition of the Blood

Red blood cells – contain haemoglobin to carry oxygen to the all cells in

the body. When oxygen binds to haemoglobin it forms oxyhaemoglobin.

Phagocytes – are cells that protect the body by ingesting harmful foreign

particles, bacteria, and dead or dying cells (a process known as

phagocytosis).

Note: How can I tell phagocytes and lymphocytes apart?

Phagocytes have a multi lobbed nucleus. Lymphocytes have one large

nucleus.

Lymphocytes – eliminate an antigen, by producing/releasing antibodies

against that specific antigen. They do not ingest cells.

Platelets – clump together to form clots.

These protect the body by stopping bleeding preventing loss of blood.

Plasma: Fluid part of blood. It carries carbon dioxide, hormones and

waste e.g. Urea.

AQA The Circulatory System Notes

2

AQA The Circulatory System Notes

Science Exams Sorted

Arteries carry blood away from the heart. These vessels split up into smaller ones called arterioles, which

in turn split up into tiny blood vessels called capillaries.

Capillaries are where exchange of particles and gases takes place. These then join together to form larger

vessels called venules which join together to form veins.

Veins carry blood towards the heart (usually deoxygenated blood, except for the pulmonary vein).

Blood Vessels

Blood vessels are tubes which carry the blood around the body. There are different types of blood vessels.

Arteries

Function: Carry blood away from the heart (always oxygenated apart from the pulmonary artery which goes

to the lungs).

Structure: Have thick muscular walls.

Lumen: Have small passageways for blood

(internal lumen).

Pressure: Contain

blood

under

high

pressure.

Veins

Function: Carry blood to the heart (always de-oxygenated apart from the pulmonary vein which goes from

the lungs to the heart).

Structure: Have thin walls.

Lumen: Have larger internal lumen.

Pressure: Contain blood under low pressure.

Valves: Have valves to prevent blood flowing

backwards. This is the function of valves ??v

AQA The Circulatory System Notes

3

AQA The Circulatory System Notes

Science Exams Sorted

Capillaries

Function: Where exchange of substances takes place. Oxygen

passes through the capillary wall and into the tissues, carbon

dioxide passes from the tissues into the blood.

Structure: Microscopic – one cell thick.

Pressure: Very low blood pressure. Found in the muscles and lungs.

Differences between arteries and veins

What do I need to know?

Arteries

Veins

Carries blood away from the heart

Blood travels to the heart

Have a narrow lumen

Have a wide lumen

Has a thick muscular wall with lots of elastic fibres

Has a thin wall with few elastic fibre

Has a thick muscular layer

Has a thin muscular layer

Does not have valves

Has valves

Blood travels in pulses

Blood travels constantly

Blood is under high pressure

Blood under lower pressure

AQA The Circulatory System Notes

4

AQA The Circulatory System Notes

Science Exams Sorted

“Why is the left hand side of the heart much thicker than the wall of the right?”

Ideal answer �v: This is because the left-hand side must pump to the entire body. The thicker muscle is

able to generate a greater force to ensure a higher pressure to push blood around the body. The right-

hand side only has to pump to the lungs, a much shorter distance.

The Structure of the Heart

You will not be asked to draw a diagram of the heart. But you could be asked to label a pre-drawn diagram.

Please be aware that when you’re looking at a diagram of the heart the left-hand side of the heart is on the

right side of the page and vice versa.

Different thicknesses of each side of the heart

AQA The Circulatory System Notes

5

AQA The Circulatory System Notes

Science Exams Sorted

Stroke volume: the volume of blood pumped out of the heart with every beat. The average amount of

blood per beat is 0.07 litres.

Blood flow through the heart

I have seen this appear as questions ranging from four to six marks. I know it’s a lot of information but break

it up and use flashcards they will really help to learn and retain this. �v
??

Key:

= oxygenated blood

= deoxygenated blood

1.Blood enters the right atrium from the vena cava.

2.From right atrium, it passes the tricuspid valve to the right ventricle.

3.From the right ventricle, it is forced through the pulmonary (semilunar) valve to the pulmonary artery.

4.From the pulmonary artery it moves into the right and left pulmonary arteries to the lungs.

5.From the lungs, oxygenated blood is returned to the heart through the pulmonary veins.

6.From the pulmonary veins, blood is forced into the left atrium.

7.From the left atrium, blood is forced through the bicuspid valve into the left ventricle.

8.From the left ventricle, the blood passes the aortic (semilunar) valve into the aorta.

9.Blood is distributed to the rest of the body from the aorta.

Stroke volume

You can be asked to complete a calculation to determine stroke volume.

The equation for this calculation is:

Stroke volume =

𝐶𝑎𝑟𝑑𝐶𝐶𝑎𝑐𝑂𝑢𝑡𝑝𝑢𝑡

𝐻𝑒𝑎𝑟𝑡 𝑟𝑎𝑡𝑒

AQA The Circulatory System Notes

6

AQA The Circulatory System Notes

Science Exams Sorted

Blood pressure

When the heart contracts it pushes blood into blood vessels which creates blood pressure.

A blood pressure reading consists of two values:

Systolic value – blood pressure while the heart is squeezing.

Diastolic value – blood pressure while the heart is relaxing.

The average blood pressure for an adult is 120/80 mmHg. The first number is the systolic value and the

second number is the diastolic value.

Overview of the cardiovascular system