Structure of the Heart- Chambers
There are two seperate pumps- This is because:
- The blood has to pass through tiny capillaires in the lungs to present a large surface area so there's a very large drop in pressure and so the blood flow to the rest of the body would be very slow
- To keep oxygenated in the pump on the left side of the body separate from the deoxygenated blood in the pump on the right
The two chambers are:
Atrium- Thin walled and elastic which streches as it collects blood- only pumps a short distance to the ventricles
Ventricle- Much thicker muscular wall- has to pump a large distance to the lungs or the rest of the body. It needs to create enough pressure to pump the blood around the body (1.5m)
Between each chamber there are valves that prevent back flow of blood. These are:
The left atrioventicular (BICUSPID)- two cup shaped flaps on the left side
The right atrioventicular (TRICUSPID)- three cup-shaped flaps on the right side
Structure of the Heart- Blood Vessels
There are 4 large blood vessles that carry blood:
Aorta- Connected to the left ventricle and carries oxygenated blood to the body
Vena Cava- Connected to the right atrium and brings deoxygenated blood back from the body
Pulmonary Artery- Connected to the right venticle and carried deoxygenated blood to the lungs
Pulmonary Vein- Connected to the left atrium and brings oxygenated blood from the lungs
Supplying the heart with oxygen:
The heart muscle is supplied by its own blood vessles called the coronary arteries.
The arteries branch off the aorta shortly after it leaves the heart.
Blockage of these arteries leads to heart attacks because an area of the heart muscle is deprived of oxygen and so dies
Diagram of the heart
The Cardiac Cycle
There are two phases to the beating ofthe cardiac cycle:
- Contraction (SYSTOLE)
- Relaxation (DIASTOLE)
The direction of the blood flow through the heart is maintained by pressure changs and valves:
1) Blood enters atria and ventricles from pulmonary veins and vena cava- Atria are relaxed and fill with blood. Ventricles are relaxed
2) Atria contract, pushing blood into the ventricles. Ventricles remain relaxed
3) Blood pumped into the pulmonary arteries and the aorta. The atria relax and the ventricles contract, pushing the blood through the pulmonary arteries and aorta.
The valves and how they work
How do the valves work?
They are made up from a number of tough, but flexible fibrous tissue which are cusp shape
When the pressue is greater of the convex side of those cusps they move apart to let blood pass
When the pressure is greater on the concave side the blood collects within the bowl of the cups and pushes them together to form a tight fit that prevents the passage of blood
To prevent the valves becoming inverted the valves have string-like tendons that are attached to pillars of muscle in the ventricle wall
The valves control the blood flow-
Atrioventicular Valves- Between the atirum and ventricle. They prevent backflow of blood and ensures the blood moves in the right direction
Semi-lunar Valves- In the aorta and pulmonary artery. They prevent back flow into the ventricles.
Pocket Valves- In the veins throughout the venous system. Ensure the veins are squeezed
What is cardiac output?
Cardiac output is the volume of blood pumped by one ventricle of the heart in one minute.
It is measured in dm3min-1
It depends on two factors:
THE HEART RATE (the rate at which the heart beats)
THE STROKE VOULME (Volume of blood pumped out at each beat)
HEART RATE X STROKE VOULME
How is the Cardiac Cycle controlled
Cardiac muscle is myogenic- this means the contractions are initiated from within the muscle itself, rather than by nervous impulses
Within the wall of thr right atrium there is a distinct group of cells known as SINOATRIAL NODE (SAN). The inital stimulus for contraction orignates at the SAN and has a basic ryththm that determines the beat of the heart and is known at the pacemaker.
The sequence of events are as follows:
- A wave of electical activity spreadfs rom the SAN across both atria causing them to contract
- A layer on non-conducting tissue prevents the wave crossing to the ventricles
- The wave passes through a second group of cells called ATRIOVENTICULAR NODE (AVN)
- After a short delay the AVN conveys a wave of electical activity betweeen ventricles along a series of specialised muscle cells called the bundle of His
- The bundle of His conducts the wave through the septum to the base of the ventricles where the bundle branches into smaller fibres
- The waves is released from these fibres causing the ventricles to contract quickly at the same time from the base of the heart upwards
Diagram of how the heart stimulates contrations
Pressure and volume changes
Heart disease kills more people in the UK than any other disease.
- Half of heart diseases deaths are from coronary heart disease (CHD).
What is Coronary Heart Disease?
- It affects the pair of blood vessles, the coronary arteries, which supply the heart muscle with the glucose and oxygen that is required for respiration.
- Blood flow through these vessles may be impaired by the build up of fatty deposits known as atheroma.
- If blood flow to the heart muscle is interuppted, it can lead to myocardial infaraction- Heart attack
- Generally, heart disease can be prevented
Heart Disease- Atheroma
What is atheroma?
- Atheroma is a fatty deposit that forms within the wall of an artery
- It begins as fatty streaks that are accumulations of white blood cells that have taken up low-density lipoproteins (LDLs).
- These streaks enlarge to form atheromatous plaque. This occurs in larger arteries and are made up from deposits of cholesterol, fibres and dead muscle cells
- They bulge in the lumen of the artery, causing it to narrow so that blood flow through is reduced
Atheromas increase the risk of two dangerous conditions:
What is Thrombosis?
- If an atheroma breaks through the lining of the blood vessel is forms a rough surface that interrups the smooth flow of blood
- Resulting in the formation of a blood clot, or thrombus in a condition known as thrombosis.
- This may block the vessel reducing the supply of blood to the tissue beyond it
- The reigon deprived of blood often dies as a result of lack of oxygen, glucose and other nutrients that the blood normally provides.
- Sometimes the thrombus is carried and lodges in and blocks another artery.
Heart Disease- Aneurysm
What is Aneurysm?
Atheromas that lead to the formation of thrombus also weaken the artery walls.
Theses weakneded points swell to form a ballon-like blood filled struture called an aneurysm.
Aneurysms frequently burst, leading to haemorrhage and therefore loss of blood to the region of the body served by that artery.
A brain aneurysm is known as a cerebrovascular accident (CVA) or a stoke.
Heart Disease- Myocardial Infarction
Myocardial Infarction (Heart Attack), What is it?
- It refers to a reduced blood supply of oxygen to the muscle of the heart.
- It results from a blockage in the coronary arteries.
- If this occurs close to the junction of the coronary artery and the aorta, the heart will completely stop beating because the blood supply is cut off.
- If the blockage is further along the coronary artery, the symptons will be milder because of the smaller area of muscle will suffer oxygen deprivation.
Risk Factors- Smoking
How is smoking a risk factor for coronary heart disease?
Smokers are between 2 and 6 times more likely to suffer from heart disease than non-smokers.
It combines with haemogoblin in red blood cells to form carboxhaemogoblin. This reduces the oxygen-carrying capacity of the blood. The hard must work harder to supply the equivalent amount of oxygen. This can lead to raised blood pressure increasing the risk. During exercise a insufficant supply of oxygen may occur leading to chest pain (angina) or myocardial infarction.
Stimulates production of the hormone adrenaline, which increases heart rate and raises blood pressure. Nicotine also makes the platelets in the blood more 'sticky' and leads to a high risk of thrombosis, strokes and myocardial infarction.
Risk Factors- High Blood Pressure
High blood pressure increases the risk of heart disease because..
- The heart must work harder to pump into the higher pressure arteries and therefore more proneto failure
- High pressure within the arteries means that they are more likely to develop aneurysm and busrt causing haemorrhage
- To resist the higher presure within them, the walls of the arteries tend to become thickened and may harden restricting blood flow
Risk Factors- Blood cholesterol and Diet
High-density lipoproteins (HDLs)
They remove cholesterol from tissues and transport it to the liver for excrection. They help prorect the arteries against heart disease
Low-density lipoproteins (LDLs)
They transport cholesterol from the liver to the tissies, includuing the artery walls, which they infiltrate leading to development of atheroma and heart disease.
High levels of salt raise blood pressure
High levels of saturated fat increase low-density lipoprotein levels and hence blood cholesterol concenration.