The Heart and Heart Disease

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Structure

The right side of heart pumps deoxygenated blood, the left side pumps oxygenated blood

The ventricles have thick muscular walls - need to pump blood a further distance than the aorta. The left ventricle has a thicker muscular wall than the right one - lungs are closer than the entire body

The AV valves are between the atria and ventricles. They close when the ventricles contract - pressure is greater in the ventricles than atria - to stop blood flowing back into the atria. They open when the atria contract as pressure is greater in atria than ventricles.

The semi-lunar valves are between the ventricles and the pulmonary and aorta artery. They open when the ventricles contract and close when the ventircles relax to stop blood flowing back into the ventricles

There are cords attached to the AV valves to stop them being forced into atria when ventricles contract.

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Coordination of the heart

Cardic muscles myogenic - contracts/relaxes without nerve signals

Heartbeat process:

1- SAN in right atrium is pacemaker - sends out electrical wave into atria. Atria contract.This is called ATRIAL SYSTOLE

2- Collagen tissue stops it spreading to ventricles. So go to AVN. After slight delay - to let atria fully empty - passes along bundle of his to purkyne fibres in bottom of ventricle walls

3- As travels along purkyne fibres, ventricles contract from bottom up. This is called VENTRICULAR SYSTOLE

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Equation for cardiac output

Cardiac output = stroke volume x heart rate

Stroke volume = volume of blood pumped in one heartbeat

Heart rate = number of heart beats per minute

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Cardiac Cycle

Continuous contraction + relaxation of atria and ventricles to circulate blood

Stages:

1- Atria contract, Ventricles relax - atrial systole

Volume of atria decreases so pressure inside chamber increases. This forces blood into ventricles. Ejected blood in ventricles causes slight increase in pressure and volume

2- Atria relax, Ventricles contract - ventricular systole

Volume of ventricles decreases so pressure increases. Pressure greater than in atria so AV valves close so no backflow. Pressure greater than in arteries so semi-lunar valves open and blood forced out of ventricles into arteries

3- Atria relax, Ventricles relax - diastole

Higher pressure in arteries closes the semi-lunar valves to prevent backflow.Pressure higher in veins so blood fills the atria. Pressure in ventricles slighlty lower than atria so blood passively flows from atria into ventricles without contraction. Cycle then repeats

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Atheromas

Wall of artery made of many layers, the inner layer - endothelium - usuallys smooth

Damage can occur to endothelium by high blood pressure, white blood cells + lipids clump under lining to form fatty streak

Over time, connective tissue, more WBC and lipds build up and harden to make fibrous plaque - atheroma

Atheroma partially blocks artery, reducing blood flow.

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Aneurysm

A balloon like swelling of artery - atheromas increase chance

Atheromas damage and weaken artery walls and narrowing of lumen increases blood pressure

High blood pressure can force inner layers of artery through outer elastic layer to form swelling - aneurysm

If this bursts, it causes bleeding - haemorrhage

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Thrombosis

Formation of blood clot - atheromas increase chance

If atheroma bursts through endothelium (ruptures) it damages the wall and makes rough surface

Platelets and fibrin accumulate (gather) at ruptured site and form a clot - thrombus

Blood clot thick and can block artery or reduce blood flow. If it becomes dislodged, it travels through the arteries to smaller vessels and can block them completely

Debris from rupture can damage artery endothelium elsewhere and cause more clots to form

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Myocardial Infarction

The heart muscle is supplied with blood by coronary arteries. Supplies oxygen needed for respiration

If a coronary artery is blocked - eg. by thrombus - the area supplied will be completely cut off from oxygen supply and die

This causes myocardial infarction - heart attack

Symptoms include - shortness of breath, pain in upper body and chest and sweating

If large areas of heart affected, can cause heart failure which can be fatal - cause death

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Factors which increase coronary heart disease (CHD

CHD = type of cardiovascular disease - coronary arteries blocked by atheromas

1- High blood cholesterol and poor diet

  • Cholesterol one of main substances in fatty streaks in atheromas. So high levels increase chance of CHD
  • If you have a diet with high saturated fats, you intake more cholesterol
  • High salt intake increase chance of high blood pressure

2- Smoking

  • Carbon monoxide combines with haemoglobin and reduces oxygen uptake. If heart muscle has reduced oxygen supply, can lead to myocardial infarction
  • Reduces amount of antioxidants - needed to prevent cell damage in coronary artery walls. Damage could lead to atheroma

3- High Blood Pressure

  • Can cause damage of artery walls, lead to atheromas.
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