AQA BIOL1 3.1.5 Heart and Heart disease

Describe how thrombosis occurs.

An atheroma can rupture the endothelium, damaging the arterial wall and leaving a rough surface. Platelets and fibrin accumulate at the site of damage and form a blood clot, which is called thrombosis.

Coronary heart disease

Any condition that interferes with the coronary arteries that supply the heart muscle.

Describe the formation of an aneurysm.

Atheroma plaques narrow arteries causing high blood pressure. They also damage and weaken arteries. When blood travels through a weakened artery at high blood pressure, it may bulge forming a balloon-like swelling called an aneurysm.

Diastole

Atria and ventricles relax

Atrial systole

Atrial contraction

Describe the cardiac cycle including the stimulation of the heart beat, pressure and volume changes and associated valve movements.

Atrial systole The sino-atrial node sends electrical impulses across the atria causing atrial contraction. The non-conducting tissue between the atria and the ventricles prevents impulses from reaching the ventricles. The volume of the atria decreases and the pressure increases. The atrioventricular valves open because the pressure in the atria is greater than the pressure in the ventricles as they are relaxed. The atrioventricular node delays the electrical impulses as the blood flows into the ventricles causing a slight increase in their volume and pressure. Semilunar valves are closed as the the arterial pressure is higher than the ventricular pressure. Ventricular systole The atrioventricular node sends a wave of electrical impulses down the bundle of His. Purkyne fibres carry impulses to all parts of the ventricular walls causing the ventricles to contract simultaneously. The ventricular volume decreases and pressure increases. The atrioventricular valves close as the pressure in the atria is lower (as they are relaxed) than the pressure in the ventricles. Semilunar valves open as the pressure in the ventricles exceeds the arterial pressure. Blood flows from the ventricles into the aorta and pulmonary artery. Diastole Atria and ventricles relax. Semilunar valves close as the pressure in the ventricles is lower than the arterial pressure. Blood flows into the atria from the vena cava and pulmonary vein. Atrioventricular valves open as the pressure in the atria exceeds the pressure in the ventricles, causing blood to passively flow from the atria into the ventricles.

When do the atrioventricular valves open and close?

Atrioventricular valves open when the atrial pressure exceeds the ventricular pressure. AV valves close when the ventricular pressure exceeds the atrial pressure.

How do pressure changes determine the flow of blood?

Blood always flows from a high pressure to a low pressure.

Angina

Chest pains caused by an inadequate supply of blood (and therefore oxygen and glucose) to the heart muscle.

Low density lipoprotein (LDL)

Cholesterol attached to a protein so that it can be transported in the blood. LDLs transport cholesterol from the liver to other body tissues, raising the blood cholesterol levels. Increased concentration of LDLs increases risk of heart disease.

Describe the main structure of the human heart

Consists of four chambers, two main arteries, two main veins and valves. Atria are the smaller chambers on the top with thin walls. The right atrium receives blood from the vena cava and the left atrium receives blood from the pulmonary vein. Ventricles, are the larger chambers on the bottom which contain larger muscular walls to provide the strength needed for contractions that pump blood up into the arteries. The right ventricle pumps blood into the pulmonary artery and the left ventricle pumps blood into the aorta. Atrioventricular valves between the atria and ventricles prevent back flow of blood from the ventricles into the atria. Semilunar valves in the arteries prevent back flow of blood from the arteries into the ventricles.

Describe the double circulatory system

Consists of pulmonary circulation and systemic circulation. Pulmonary circulation: Deoxygenated blood travels to the lungs through the pulmonary artery. The blood is oxygenated, and returns to the heart through the pulmonary vein. Systematic circulation: Oxygenated blood pumped from the aorta travels to the rest of the body. The body cells use the oxygen for respiration, causing the blood to become deoxygenated. Deoxygenated blood is then returned to the heart through the vena cava.

Myogenic contraction

Contraction initiated by the muscle itself.

High density lipoprotein (HDL)

HDLs transport cholesterol from other body tissues to the liver, which is associated with a decrease in blood cholesterol levels. High concentrations of these lower the risk of heart disease.

Myocardial infarction

Heart attack. This occurs when part of the heart muscle dies because the blood supply to that area is blocked.

Describe the formation of an atheroma.

If damage occurs to the endothelium (e.g. by high blood pressure, viral infection or chemical pollutants), white blood cells enter the endothelium and absorb lipids from the blood, particularly LDLs. New muscle and fibrous cells repair the wall, forming a rough, hardened surface called a plaque. This is an atheroma.

Cholesterol

Lipid component of some cell membranes. Important to the development of atheroma.

Hypertension

Medical term for high blood pressure

Sino-atrial node (SAN)

Pacemaker of the heart: a bundle of heart muscle fibres found on the wall of the right atrium that initiates the heartbeat.

Atrioventricular node (AVN)

Part of the conducting pathway of the heart. The AVN picks up the signal from the sino-atrial node SAN, and delays it (allowing ventricles to fill) before passing it down the bundle of His.

Bundle of His

Part of the conducting pathway of the heart: a bundle of specialised heart muscle fibres (not nerves) that transmit the impulse from the AVN to the Purkyne fibres.

When do the semilunar valves open and close?

Semilunar valves open when the ventricular pressure exceeds the arterial pressure. The semilunar valves close when the arterial pressure exceeds the ventricular pressure.

Purkyne fibres

Specialised cardiac muscle fibres that initiate contraction of the ventricles. This contraction begins at the apex so that the blood is forced up into the arteries.

Why is an aneurysm dangerous?

The bursting of an aneurysm is generally fatal. It causes a haemorrhage (bleeding).

What happens to the cardiac output during exercise and why? And how are these changes implemented?

The cardiac output increases during exercise in order to provide oxygen and glucose at a faster rate to respiring muscle tissue, so that they can respire at faster rate and therefore produce ATP at a faster rate. It also means that carbon dioxide and lactate (the products of aerobic and anaerobic respiration respectively) can be carried away faster, and so can heat. This is done by increasing the heart rate and stroke volume. The heart rate is modified by the cardiovascular centre which alters the rate at which SAN sends out electrical impulses and also decreases the delay caused by the AVN. The stroke volume is increased by causing stronger contractions, pushing more blood out of the ventricles and into the arteries.

Atheroma

The fatty deposit that builds up under the endothelium (lining) of the blood vessels. As the atheroma gets thicker, the lumen of the artery gets smaller.

Why is the wall of the left ventricle thicker than the wall of the right ventricle?

The muscular walls in the left ventricle are thicker, as it needs to pump blood around the whole body. The right ventricle only needs to pump blood to the nearby lungs.

Heart rate

The number of heart beats per minute

Arteriosclerosis

The thickening and hardening of arterial walls.

Stroke volume

The volume of blood pumped during each heartbeat, measure in cm³.

What is the function of the valve tendons?

These tendons attach the atrioventricular valves to the ventricles to stop them being forced up into the atria when the ventricles contract.

Why are the walls of the atria thinner than the walls of the ventricles?

This is because their contractions don't need to be that powerful as the blood only needs to travel down a short distance to the ventricles.

How can thrombosis cause problems?

Thrombosis of an artery can cause complete blockage of an artery. Depending on the artery and its size, this could cause myocardial infarction or angina. It can also become dislodged and block smaller blood vessels further along the artery and cut off blood supply to smaller sections of the heart.

Ventricular systole

Ventricular contraction

Aneurysm

a ballooning of an artery due to a weakness in the wall.

Thrombosis

a blood clot (thrombus) lodged in a vessel.

Embolism

a clot/thrombus travelling in the bloodstream.

Atherosclerosis

a form of arteriosclerosis caused by a build-up of atheroma in the arteries.

Cardiac output =

stroke volume x heart rate