HEART
The heart is a
muscular pump in the chest, which beats continuously, sending blood to the
lungs and the rest of the body. It is like the engine room of the body; without
the heart a person would not be able to survive. A constant supply of blood is
needed to circulate round the body to keep a person healthy.
Facts about the heart
The heart is in fact
a very strong piece of muscle, which is about the size of a clenched fist and
weighs around 350 grams in an adult (a man’s heart usually weighs more than a
woman’s). The heart lies to the left of the chest cavity between the lungs and
is protected by the sternum (breastbone).
What does the heart do?
Its job is to pump
blood round the body by way of the cardiovascular system and with each
heartbeat, blood is sent to all parts of the body, delivering oxygen and
nutrients to help a person live. The heart beats about 100,000 times a day, to
pump the equivalent of 7,000 litres a day through a 60,000 mile network of
arteries, veins and capilliaries.
When someone is
exercising or frightened by something, the heart is told by the brain to beat
faster to deliver oxygen round the body, similarly during resting or sleep, the
heart beats at a slower rate.
Structure of the heart
The heart is made up
of four chambers which are divided from each other by thick muscular walls.
Each heart chamber
has a valve, which prevents the blood from flowing back into the chamber, and
ensuring that all the blood flows in one direction. These valves contract (open
and close) at every heart beat, and send blood out from the ventricles into arteries
(singular artery).
The heart is divided
into two sides, the right and left, by a septum (wall) and each side is divided
into an atrium (left and right) and ventricle (left and right).
The function of the
atria (plural of atrium) is to receive blood into the heart (like a reservoir)
to supply the ventricles which pump the blood away from the heart.
Pumping blood
The right side of
the heart receives the dark de-oxygenated (blue) blood from the body and sends
it to the lungs through the pulmonary artery, where it is given fresh oxygen
and becomes bright red again (oxygenated). This newly oxygenated blood is sent
back to the left side of the heart which is then pumped through the aorta to
the rest of the body.
The pericardium
The heart is
contained within the pericardium, which is a strong sac protecting the heart
from other organs.
The heart wall
itself is made up of three layers, the epicardium,
myocardium and endocardium.
Like all living
tissues, these layers need to receive a constant supply of blood, and the
myocardium in particular will be damaged as a result of a heart attack.
