B1Mikeh.5 & H.6

Front 1

Atrial systole

Back 1

The cardiac cycle begins with the contraction of the wall of the atrium. This happens when the ventricle is already 70% full. The contraction of the atrium pumps move blood into the ventricle, filling it to its maximum capacity before the start of ventricular systole.

Front 2

Ventricular systole

Back 2

Contraction of the ventricle wall causes a rapid increase in pressure inside the ventricle. This causes the closure of the atrio-ventricular valve, which resulting vibrations in the valve and adjacent walls of the heart. These vibrations are the first heart sound. The pressure in the ventricle rapidly rises above the pressure in the aorta. causing the aortic (semi-lunar) valve to open. Blood can then be pumped from the ventricle into the aorta, raising the aortic blood pressure and decreasing the volume of blood in the ventricle to a minimum. While the ventricle is contracting, the atrium is relaxing and blood enters it from the pulmonary veins.

Front 3

SA node (sinoatrial node)

Back 3

A small region in the wall of the right atrium that initiates impulses and acts as the pacemaker of the heart. Impulses initiated by the SA node spread out in all directions through the walls of the atria.

Front 4

AV node (atrioventricular node)

Back 4

This node is positioned in the wall of the right atrium, close to the junction between the atria and ventricles. Impulses reach the AV node 0.03 seconds after being emitted from the SA node. Impulses are sent from the AV node along two bundles of conducting fibres that pass through the septum between the left and right ventricles to the base of heart.

Front 5

Conronary Thrombosis

Back 5

The rough inner surface of atherosclerotic arteries tends to cause blood clots to form. The formation of clots is called thrombosis. The wall of the heart is supplied with blood by the coronary arteries. If a blood clot blocks one of these arteries, part of the wall of the heart is deprived of its supply of oxygen. The cells in this part of the wall are unable to respire and so stop contracting. This is either called myocardial infraction or heart attack

Front 6

Partial Pressure

Back 6

Partial pressures are the pressures exerted by each of the gases in the mixture of gases

Front 7

Bohr Shift

Back 7

The release of oxygen by hemoglobin in respiring tissues is promoted by an effect called the Bohr shift. Hemoglobin's affinity for oxygen is reduced as the partial pressure of carbon dioxide increases. Respiring tissues have high partial pressures of carbon dioxide, so oxygen tends to dissociate. The lungs have lower partial pressures of carbon dioxide, so oxygen tends to bind to hemoglobin.

Front 8

Fetal Hemoglobin

Back 8

The hemoglobin in the red blood cells of a fetus is slightly differnet in amino acid sequence from adult hemoglobin. The figure shows that it has greater affinity for oxygen and so, in the placenta, the oxygen that dissociates from adult hemoglobin binds to fetal hemoglobin, which only releases it once it enters the tissues of the fetus.

Front 9

Binding of Carbon Dioxide to Hemoglobin

Back 9

In respiring tissues, carbon dioxide binds reversibly to hemoglobi8n, to form carbaminohemloglobin. in the lungs, carbaminohemoglobin dissociates and the carbon dioxide is released. Between 15% and 25% of carbon dioxide is carried in this way. The binding of carbon dioxide and hydrogen ions to hemoglobin lowers it affinity for oxygen. This causes the Bohr Shift.

Front 10

Lung Cancer

Back 10

Inhaling carcinogens can causes cancer of the lung. Most cases are caused by cigarette smoking. Tobacco smoke contains many different carcinogens. Atompheric pollution can also cause lung cancer. Workers in certain industries suffer and increased risk, especially mining and metal refining where the metal ores contain radioactive substances. Radon, a radioactive gas released by some rocks is estimated to cause 12% of deaths. Lung cancer is treated by removing part of the entire affected lung, with obvious consequences for gas exchange.