Endocrine System

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Heart Arrhythmia

3.10   The heart beats in a regular rhythm as the walls of the atria and ventricles alternately contract and relax. This is called the cardiac cycle. If the cardiac cycle is disrupted and the heart gets out of rhythm, a condition called arrhythmia results. Arrhythmia can lead to serious consequences, including death. When a person begins to exercise, the heart adjusts to the greater demand for oxygen by increasing its rate. If the person exercising has a heart problem or is in a weakened condition, there is a chance that as the heart rate increases, the heart will get out of rhythm. When the heart’s atria get out of synch, a person can survive because blood is still able to move through the heart. However, if the ventricles are affected, sudden death may occur because blood does not get pumped to the vital organs. To help avoid exercise-related heart-rhythm problems, always warm up first so the heart can adjust slowly. There are other causes for arrhythmia. For example, the drug cocaine can cause arrhythmia by disabling the nerves that regulate the contractions of the heart.

 What is Blood Pressure?

3.11   Blood pressure (BP) is determined by two key factors: how hard heart beats and how easily the blood flows through the arteries. The force exerted by the heart as it pumps blood into the arteries creates a pressure within them and this is called “blood pressure”. A certain level of blood pressure is thus essential to keep the blood circulating in the body. But when pressure becomes too high, it is called hypertension which is caused by constriction or narrowing of the small blood vessels.

How is Blood Pressure Measured?

3.12   The blood pressure has been traditionally measured in two figures with an instrument called “sphygmomanometer” in millimeter height of mercury rise (mmHg). Blood pressure is the result of two forces; (i) force from the heart as it beats and pumps blood into the arteries and throughout the circulatory system and (ii) the force of the arteries as they resist blood flow between heart beats when the heart is at rest. Thus during each heart beat, the heart muscle contracts to push blood around the body. The pressure produced by the heart is the highest when it contracts to push the blood on its journey through the body and this is known as systolic (higher value) pressure and indicates the activity of the heart. Then the heart muscle relaxes before its next contraction, and the pressure is at its lowest, which is known as diastolic (lower value) pressure and shows the condition of blood vessels.

3.13   Both systolic and diastolic pressures are measured when you have your BP checked. For example, universally recognised normal BP of 120/80 represents 120 mmHg of systolic pressure and 80 mmHg of diastolic pressure. Systolic pressure range can be from 80 to 300 and diastolic from 60 to 140.

 The Role of Lymphatic System

3.14   The cells of the body are bathed in a clear watery fluid called lymph. This fluid helps move materials between the capillaries and the body’s cells. Lymph is formed from water, proteins, and other nutrients that move out of the blood into the spaces between the body’s cells. This fluid must be returned to the circulatory system. A system of lymphatic vessels similar to the veins and capillaries collect the fluid and return it to the circulatory system. The lymph capillaries parallel the blood capillary system and are connected to larger lymph vessels that eventually connect to one of two ducts. These two ducts, the thoracic and the right lymphatic, open into two veins just above the heart.