AQA AS Biolgy unit 1- Heart and Heart diseases

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HEART AND HEART DISEASE
Heart is a muscular organ that lies in the thoracic cavity behind the sternum
(breast bone).
STRUCTURE
There are four cavities called chambers. The two upper chambers are called
the right and left atria. The two lower chambers are the right and left
ventricles. The pump on the left side deals with oxygenated blood from the lungs
and pump on the right deals with deoxygenated blood from the body.
The atrium is thin walled and elastic and it stretches as it collects blood. It has a
THIN MUSCULAR WALL because it only has to pump blood to a shorter distance
VENTRICLE has a much THICKER muscular wall as it has to pump blood some
distance, either to the lungs or to the rest of the body. Thicker muscle enables it
to create enough pressure to pump blood to the extremities of the body.
We have 2 SEPARATE PUMPS because the blood has to pass through tiny
capillaries in the lungs in order to present a large surface area for gas
exchange. In doing so there is a very large drop in pressure and so the blood flow
to the rest of the body will be slow. Therefore we have a system in which the
blood is returned back into heart to increase pressure before it is distributed to
rest of the body.
VALVES
Valves are flap-like
structures that allow blood
to flow in one direction. The
valves are held open or
closed by tendons (chordae
tendinae), which are
attached at the other end to

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They PREVENT BACKFLOW of
blood into the atria when ventricles contract. There are two kinds of valves:
THE ATRIOVENTRICULAR (bicuspid) VALVES- They are located
between atria and ventricle. The valve on the left is called BICUSPID and
right is called TRICUSPID VALVE.
SEMILUNAR VALVES- they are located between the aorta and the left
ventricle (aortic valve) and between the pulmonary artery and the right
ventricle (pulmonary valve).
Vessels connecting the heart to the lungs are called pulmonary vessels.…read more

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THE CARDIAC CYCLE
The heart undergoes a sequence of events that is repeated 70 times each minute.
This is known as cardiac cycle
There are two phases to the beating of the heart: contraction (systole)
and relaxation (diastole).
Contraction occurs separately in the ventricles and
the atria.…read more

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CONTRACTION OF ATRIA (ATRIAL SYSTOLE)
CONTRACTION OF THE VENTRICLE
(VENTRICULAR SYSTOLE)…read more

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Blood
always move from a region of high pressure to low pressure
VALVES IN CONTROL OF BLOOD FLOW
ATRIOVENTRICULAR VALVES- these prevent back flow of the blood
when contraction of the ventricle means that VENTRICULAR PRESSURE
EXCEEDS ATRIAL PRESSURE.…read more

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SEMI LUNAR VALVES- these prevent backflow of the blood into
ventricles when recoil action of the elastic walls of aorta and pulmonary artery
creates a greater pressure in the vessels than ventricles
POCKET VALVES- it is in veins that occur throughout the venous system.
These ensure when the veins are squeezed (e.g. when skeletal muscles contract)
blood flows back to the heart rather than away from it.…read more

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Initial stimulus for contraction originates from here. It has a basic rhythm of
stimulation that determines the beat of the heart.…read more

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HEART DISEASE
CORONARY HEART DISEASES affects the pair of blood vessels, the coronary
arteries, which supply the heart muscle with glucose and oxygen for respiration.
ATHEROMA
They're fatty deposits that form within the wall of an artery.…read more

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THROMBOSIS
If an atheroma breaks through the lining (endothelium) of the blood vessel, it
forms a surface that interrupts the smooth flow of blood. This may result in the
formation of a blood clot or thrombus, this condition is an
THROMBOSIS.
This thrombus may block the blood vessel, reducing or preventing
the supply of the blood to tissues.…read more

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The symptoms include: milder,
because a smaller area of muscle will suffer oxygen deprivation.
RISK FACTORS ASSOCIATED WITH CORONARY HEART
DISEASE
SMOKING- carbon monoxide and nicotine reduces oxygen carrying capacity of
the blood
HIGH BLOOD PRESSURE
BLOOD CHOLESTEROL-
DIET- high levels of salt raise blood pressure and high levels of saturated fat
increase LDL
Electrocardiogram
During the cardiac cycle, the heart undergoes a series of electrical current
changes.…read more

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