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 What do you think would happen if your atria and ventricles contracted at the same time? Pg. 305 in my textbook Note: the pair of atria and the pair of ventricles should be functionally coordinated so that both members of the pair contract simultaneously…this permits synchronized pumping of blood into the pulmonary and systemic systems -LOOK UP AV NODAL DELAY… this used to allow for the ventricles to completely fill

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” -look at page 309 in my textbook to confirm!!

Look at page 311 in my textbook for a breakdown of the different heartbeats!!

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 -sphygmomanometer is what you see at the doctors office…it is an externally applied inflatable cuff attached to a pressure gauge…we then determine the blood pressure by placing a stethoscope over your brachial artery at the inside bend of the elbow just below the cuff…hint: no sound will be heard when blood is not flowing through the vessel OR when blood is flowing in the normal, smooth laminar flow …you will need to adjust the cuff pressure because the trick is to balance the pressure in the cuff with the pressure in the artery -systolic pressure is the maximum pressure exerted in the arteries when blood is ejected into them during systole -diastolic pressure is the minimum pressure within the arteries when blood is draining off into the rest of the vessels during diastole

Low Blood Pressure: If diastole is lower than 70mmHg Usually inherited, can cause fainting High Blood Pressure: If diastole is greater than 90 mmHg or systole greater than 140 mmHg 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 70mL and a heart rate of 70 bpm, therefore, cardiac output is 70 x 70 = 4900mL/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