Download M19 Lesson 11 12.2 HANDOUT

12.2 Monitoring the Human Circulatory System
Awesome Easy-to-Follow Handout for my lovely students…
Within the heart, the sinoatrial (SA) node (the pacemaker) stimulates the muscle cells to contract and relax rhythmically.
The SA node is in the right atrium. It generates an electrical signal that spreads over the atria so they contract
simultaneously. The signal then reaches the atrioventricular (AV) node, which transmits the signal through a bundle of
fibres known as the bundle of His. These relay the signal to Purkinje fibres; these fibres initiate the almost simultaneous
contraction of the ventricles.
The Heartbeat
The normal sound of the heartbeat, heard with a stethoscope, is described as “lub-DUB.” These sounds are made as valves
close:
•“lub” is the closing of the atrioventricular valves
•“DUB” is the closing of the semilunar valves
Sound variations can indicate heart problems, such as a stenosis murmur, or narrowing of a heart valve or artery.
The Electrocardiogram (ECG)
Most heart function is analyzed by measuring the electrical pulses generated by the nerve signals that stimulate
contractions. These create milliVolt charges that can be detected with electrodes on the skin. An ECG allows doctors to
determine if the heart is generating signals of normal strength, frequency, and duration.
Blood pressure
Blood pressure is the pressure that the blood exerts on the blood vessel walls as it travels through the body. Changes in
blood pressure correspond to the phases of the heartbeat.
Systolic pressure: maximum pressure in arteries when the ventricles contract and push blood through
Diastolic pressure: lowest pressure in arteries when the ventricles are not contracting
Measuring Blood Pressure
A sphygmomanometer (blood pressure cuff) placed on an artery in the arm measures blood pressure. Pressure is
recorded in mmHg (millimeters of mercury) as systolic over diastolic. The average blood pressure of a healthy young
person is below 120 mmHg and over 80 mmHg.
Blood pressure is affected by genetics, activity, stress, body temperature, diet, and medications. Continuous high blood
pressure (hypertension) can cause damage to the arteries and increase the risk of heart attack, stroke,
and kidney failure.
Cardiac Output
Cardiac output: the volume of blood pumped by the heart, expressed as mL per minute. It can indicate:
• the total level of work the body’s muscles can perform
• how easily the heart fills with blood
• the distensibility (stretchiness) of the ventricles
Heart rate and stroke volume (the amount of blood pumped out of the heart with each heartbeat) are used to calculate
cardiac output (heart rate X stroke volume).
Average heart rate = 70 bpm, stroke volume = 70 mL
Average cardiac output = 70 X 70 = 4900 mL/minute
Cardiovascular Fitness
Cardiovascular fitness is the capacity of the lungs, heart, and blood vessels to deliver oxygen to working muscles. In the
table below, individual C is considered to be the most fit. Another good indicator of cardiovascular fitness is the length of
time it takes the heart to return to its resting heart rate after strenuous exercise.
Section 12.2 Review