Revision:Transport

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H.5.1 Explain the events of the cardiac cycle

Explain the events of the cardiac cycle including atrial and ventricular systole and diastole, and heart sounds.

The cardiac cycle consists of alternate contractions (systole) and relaxation (diastole). It has three stages.

Ventricular diastole is when both the right and left ventricles relax simultaneously.  Blood flows from Atria into the ventricles. The A/V valves are open, the semi-lunar valves are closed. Contractions from atria seals off vena cava and the pulmonary vein.

Ventricular systole is when the left and right atria relax while the left and right ventricles contract. The A/V valves are closed while the semi-lunar valves are open.

Diastole is when both the atria and ventricles simultaneously relax. During this time, there is high pressure in the aorta and in the pulmonary artery, the semi-lunar valves are closed, and the pressure in the ventricles has fallen. The pressure is low in the atria, so they fill with blood.

The three stages repeat over and over again. The sounds heard are lub...dup...lub...dup. These sounds are associated with heart valve closing. The first sound is the simultaneous closure of the A/V valves, which is at the start of the ventricular systole. The second sound is the closure of the Semi-Lunar valves which is during ventricular diastole. The pause is during the diastole.

H.5.2 Analyze data showing pressure and volume changes in the left atrium, left ventricle and aorta, during the cardiac cycle

H.5.3 Outline the mechanisms that control the heart beat

Outline the mechanisms that control the heart beat including SA node, AV node, and conducting fibers in the ventricular walls.

Excitation originates in the SA node. Muscle tissue conducts the excitation to both atria. At the base of the right atrium a second node, the atrio-ventricular node, conducts the excitation via fibers known as the Purkinje Fibers. In this way, the excitation is passed on to the ventricles, and they contract. As the ventricles contract, the atria relax. Then there is a period where all chambers are relaxed, and then the cycle starts again.

H.5.4 Outline atherosclerosis and the causes of coronary thrombosis

Atherosclerosis is when the arteries become full of lipids, cholesterol, and the elasticity of the arteries decreases. They become narrower and the blood flow becomes less efficient. This causes clots.

Coronary thrombosis is when there is a clot in a coronary heart vessel.

H.5.5 Discuss factors which affects rates of coronary heart disease

Chances of developing Coronary Heart diseases are due to:

• an increase in age
• smoking
• stress
• a bad diet (too much cholesterol and saturated fats)
• obesity, if body mass is too high, the tension on heart and arteries is high
• other diseases such as High blood Pressure or diabetes
• a lack of exercise
• males are more prone to Coronary Heart Disease than females.

H.5.6 Outline the way in which tissue fluid and lymph are formed in body tissues

Tissue fluid is inorganic ions, hormones, oxygen, glucose, amino acids, and fatty acids. It is similar to plasma but it lacks proteins. When pressure is high, fluid is forced out of capillaries. The fluid escapes from the plasma and forms tissue fluid. This excess liquid is collected by the lymphatic system. It has many valves to prevent backflow. Some of it moves back into the veins by diffusion, but most does not because it is dependent on a concentration gradient.

The lymph moves due to the movement of surrounding skeletal muscles. As they contract and relax, they squeeze connective tissue in which vessels lie. Wall contains holes (pores) that allow the entry of cell debris and bacteria. Before returning to the blood, the lymph passes through the lymph nodes where all the debris is filtered out by white blood cells. After it has been 'cleansed' it goes back into the blood stream as plasma.

H.5.7 Outline the transport functions of the lymphatic system

The lymphatic system helps by:

• keeping extra tissue fluid
• draining excess tissue fluid and placing it back into the circulation system
• the lymphoid tissue is part of the immune system; it defends the body against infections
• serves as a temporary reservoir for fluids and releases them gradually, thus reducing the workload of kidneys
• also absorbs fat from digestive system, moves it through lacteals then to blood stream (it is the transport medium for non-soluble substances)

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