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Regulation of the Heartbeat. Pacemaker A specific region of your heart muscle sets the rate at which your heart contracts. . The pacemaker located in the wall of the right atrium. (SA Node)
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Regulation of the Heartbeat • Pacemaker • A specific region of your heart muscle • sets the rate at which your heart contracts.
The pacemaker • located in the wall of the right atrium. (SA Node) • generates electrical impulses that spread rapidly over the walls of both atria, making them contract. • impulses spread to a region of the heart called the AV node (atrioventricular node).
From there, the electrical impulses spread to the ventricles, causing them to contract. • The contracting ventricles propel blood to the rest of the body.
Pacemaker ensures that the heart beats in a rhythmic cycle. • The relaxation phase, called diastole, the atria and ventricles are relaxed, allowing blood from veins to enter the heart. • The contraction phase is called systole.
The pacemaker is controlled by • the nervous system and the endocrine system. • two sets of opposing nerves by speeding it up and by slowing it down. • Hormones secreted into the blood.
EX: The hormone epinephrine, also called adrenaline, increases heart rate when the body is under stress
Measuring Blood Pressure • When the ventricles contract, they increase pressure on the blood. • The resulting force that blood exerts against the artery walls is called blood pressure. • This force drives blood through the arteries and into the capillaries. • Artery walls are elastic, which enables them to stretch in response to this force.
Blood pressure • represented by two numbers separated by a slash, such as 120/80. • measured in millimeters of mercury (mm Hg), a standard unit of liquid pressure. • The first number is referred to as systolic pressure, the highest recorded pressure in an artery when the ventricles contract (systole). • Diastolic pressure, the second number, is the lowest recorded pressure in an artery during the relaxation phase of the heartbeat (diastole).
A blood pressure of about 120/80 is the average for a healthy young adult. As a person ages, blood pressure may increase. Smoking or a fatty diet can contribute to this increase by causing arteries to become less elastic. A blood pressure above 140/90 is considered high and may lead to other cardiovascular diseases.