Heartbeat, activated

Physiological response glycogen breakdown visual excitation histamine secretion in all allergic reactions slowing of pacemaker activity that controls the rate of the heartbeat... 

Two important concepts to keep in mind throughout this discussion are that (1) the heart can only pump what it gets and (2) a healthy heart pumps all of the blood returned to it. The SA node may generate a heartbeat and cause the ventricles to contract however, these chambers must be properly filled with blood in order for this activity to be effective. On the other hand, the volume of blood that returns to the heart per minute may vary considerably. The heart has an intrinsic ability to alter its strength of contraction in order to accommodate these changes in volume. 

Arrhythmia is defined as loss of cardiac rhythm, especially irregularity of heartbeat. This chapter covers the group of conditions caused by an abnormality in the rate, regularity, or sequence of cardiac activation. 

Arrhythmia. Any variation from the normal rhythm of the heartbeat it may be an abnormality of either the rate, regularity, or site of impulse origin or the sequence of activation. 

When an animal is confronted with a stressful situation that requires increased activity—fighting or fleeing, in the extreme case—neuronal signals from the brain trigger the release of epinephrine and norepinephrine from the adrenal medulla. Both hormones dilate the respiratory passages to facilitate the uptake of 02, increase the rate and strength of the heartbeat, and raise the blood pressure, thereby promoting the flow of 02 and fuels to the tissues (Table 23-6). 

Causing death. Death is defined as the cessation of visible signs of all movement or other activity. For example, death of daphnids is defined as the cessation of all visible signs of movement or other activity, including second antennae, abdominal legs, and heartbeat as observed through a microscope. Volume 1(10,14), Volume 2(8). 

The thinking behind the MET is very logical and easy to understand. When we engage in any physical activity, the heart beats to match demand, to pump out the amount of oxygen-can-ying blood needed. Some activities require 50 percent of an individual s maximal capacity. Others call for 60 percent. Still others may need even more. You can determine your own maximal capacity very easily. Simply subtract your age from the number 220. The result is the maximum heartbeats per minute you can achieve without harm. Obviously, we never reach that maximum output. 

Increased physical activity, especially vigorous activity that really gets the heart beating faster, lowers the resting heartbeat rate. A heart rate above 80 beats per minute at rest has been linked with an increased risk of heart disease in men and women with hypertension. And a study at the Medical University of South Carolina reported in the American Journal of Hypertension in August 2006 showed that the risk of coronary heart disease increased by 50 percent in prehypertensive individuals with resting heart rates more than 80 beats per minute. Increased physical activity can eliminate that risk. 

CARDIAC DEPRESSANTS are little used in medicine, however, some are used to slow the heartbeat in tachycardias and a number of these are often analogues or derivatives of other drugs with optimized activity for this purpose in the heart (e.g. procainamide, quinidine) - these are dealt with under antiarrhythmic agents. 

Normal growth requires potassium involvement in enzyme activities. It plays a part in making muscle protein from amino acids, assists in the storage of glucose in the hver, and cooperates with sodium in maintaining blood pressure. It helps in the synthesis of nucleic acids and signals the kidneys to eliminate wastes in the urine. Potassium works with sodium to regulate the heartbeat. 

A compound may also be toxic if it modulate.s the activity of a protein unrelated to its intended target. For example, many compounds block ion channels such as the potassium channel HERG (the human homolog of a Drosophila channel found in a mutant termed ether-a-go-go ), causing disturbances of the heartbeat. To avoid cardiac side effects, many compounds are screened for their ability to block such channels. 

Three months later, Jane is taking a walk in the Central Park on a Sunday afternoon. A sudden large noise startles her. The microbot implanted in Jane s chest detects irregular heartbeats and activates the automatic implantable cardioverter defibrillator, and makes an emergency call (911) via the Medical Implant Communication Service (MICS) interface and cellular communication. 

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