12 2 Monitoring the Human Circulatory System Heartbeat

12. 2 Monitoring the Human Circulatory System Heartbeat and Blood Pressure

Heartbeat • The heart is a myogenic muscle (can be activated in the absence of external nerves) • Heartbeat tempo is set by the sinoatrial (SA) node (a. k. a. as the “pacemaker”) and the atrioventricular (AV) node • The SA node causes the atria to contract, then the AV node sends impulse to the Purkinje Fibres to make the ventricles contract • The lub-dub sound caused by the AV valves and semilunar valves closing

Diagnosis of Heart Conditions • ECG (Electrocardiogram) measures electrical impulses in the heart • P wave: SA node fires and the atria contract • QRS complex: AV node fires, ventricles contract, and AV valves close, “lub” • T wave: ventricles relax and semilunar valves close, “dub”

Blood Pressure • Changes in blood pressure correlates to phases of heartbeat • Blood pressure caused by cardiac output (amount of blood) and arteriolar resistance (diameter of vessels) • Measured with sphygmomanometer • Normal blood pressure is 110 -140/7 -90 • Top number is called the systolic pressure = ventricles contracting • Bottom number is called the diastolic pressure = resting pressure in vessels

Low Blood Pressure: • If diastole is lower than 70 mm. Hg • Usually inherited, can cause fainting High Blood Pressure: • If diastole is greater than 90 mm. Hg or systole greater than 140 mm. Hg • Heredity, stress, lack of exercise, diet (salt and cholesterol), medications

Cardiac Output and Stroke Volume • Cardiac output indicates the amount of oxygen delivered to the body • Cardiac output determined by heart rate and stroke volume, or HR x SV • The average person has a stroke volume of 70 m. L and a heart rate of 70 bpm, therefore, cardiac output is 70 x 70 = 4900 m. L/min • Cardiac output depends on a person’s cardiovascular fitness

Homework • Review tomorrow’s lecture • Watch any youtube videos for clarification • Read 12. 2 and do page 491 #16 • Page 493, #1 -3, 6, 9, 1, 13