YEAR 8 SCIENCE - CIRCULATORY SYSTEM (page 129)

BLOOD

Blood is made of red blood cells, white blood cells, blood platelets and the straw-coloured fluid they all float in called plasma

Red blood cells

Red blood cells are red because they contain an iron-containing pigment called haemoglobin

Oxygen reacts with haemoglobin to form oxyhaemoglobin

Their small size and biconcave shape allow them to fit inside tiny capillaries

They have a large surface area for their size which also assists in their important oxygen transporting role

White blood cells

They contain a nucleus and are larger and fewer than red blood cells They are also referred to as the soldiers in blood as they fight off diseases Some produces chemical anti-bodies Other engulf and ‘eat’ bacteria and other foreign matter When you fall sick, the number of white blood cells increase to fight off what is

making you sick

Platelets

Platelets in the blood help it to clot and plug the damaged blood vessel. This seal prevents germs from getting in

CONNECTED PATHWAYS

The circulatory system transports oxygen and nutrients to your body’s cells and wastes such as CO2

There are interactions between blood cells, blood vessels and the heart Blood vessels called arteries transport blood from the heart Veins transport blood back to the heart Materials are exchanged between blood and cells through tiny blood vessels called

capillaries that are located between arteries and veins

ARTERIES, VEINS AND CAPILLARIES

Arteries have thick, elastic, muscular walls and carry blood under high pressure away from your heart

Veins have thinner walls and possess valves that prevent the blood from flowing backwards as they take blood to your heart

Capillaries are the most numerous and smallest vessels that penetrates almost every tissue, so no cell is very far away from one

THE HEART

TWO PUMPS IN ONE

The human heart is actually two pumps One side contains oxygenated blood and the other deoxygenated blood Veins bring ‘used’ deoxygenated blood back to the heart

All the veins join up into a larger vein called the vena cava Entering the top right chamber of the heart (the right atrium), blood is pumped into

the bottom right chamber (the right ventricle) Blood is then pumped into the lungs where it picks up oxygen and become

deoxygenated and redder in colour Carbon dioxide is lost (which you breath out) Oxygenated blood returns to the left side of the heart (into the left atrium to the left

ventricle) to be pumped out through arteries to your body tissue where it delivers oxygen and nutrients

Deoxygenated blood then returns to the right-hand side of the heart for the cycle to be repeated

FOUR CHAMBERS

The human heart has two upper and two lower chambers The two upper chambers are called the left and right atrium (plural – atria) The lower chambers are called the left and right ventricles The two sides of the heart is different… The walls of the left side are thicker and more muscular because they need to have

the power to force the blood from the heart to the rest of the body Valves (flap-like structures) are attached to the heart walls – they prevent blood

from flowing backwards and keep it going in one direction The sound you hear when listening to your heart is referred to as the ’lub-dub’ sound

The lub sound you hear when listening to your heart is due to the valves shutting between the atria and ventricles

The dub sound is due to the closing of the valves that separate the heart from the big blood vessels that lead to the lungs and the rest of the body

BLOOD PRESSURE

The force with which blood flows through the arteries is called Blood Pressure

Blood pressure can change depending on your mood as well as when the heart contracts and relaxes

Blood pressure is the highest when the heart contracts (systolic pressure)

It is the lowest when the heart relaxes (diastolic pressure)