12.2-Monitoring the Circulatory System SBI 3U1

The Cardiac Cycle systole = contraction diastole = relaxation The SA node sends out an electrical stimulus that causes the atria to contract.

Steps in the Cardiac Cycle: 1)The sinoatrial (SA) node (a.k.a. the pacemaker) located in the R. atrium stimulates muscle cells to contract and relax rhythmically. 2)It generates an electrical signal that spreads over the atria so they contract simultaneously. 3)The signal reaches the atrioventricular (AV) node, which transmits the signal through a bundle of fibres called the bundle of His. 4)The signal is relayed to Purkinje fibres; these fibres initiate the simultaneous contraction of the ventricles.

Cardiac muscles contract involuntarily…

Heartbeat= “lub-DUB” The normal sound of the heartbeat, heard with a stethoscope. The sound is described as “lub-DUB.” These sounds are made as valves close: “lub” =closing of the atrioventricular valves “DUB” = closing of the semilunar valves

Electrocardiogram (ECG) Electrical impulses in your heart create heartbeat electrodes placed on the chest can measure the voltage changes electrocardiogram = plot of voltage measurements over time

Electrocardiogram (ECG) An ECG allows doctors to determine if the heart is generating signals of normal strength, frequency, and duration.

Irregularities in the Heart: Heart Murmur Heart Murmur : an abnormal swishing or whistling sound in the heart It is caused by blood not flowing smoothly. What causes it? valve stenosis (openings of heart valves or arteries are narrow) valve regurgitation septal defect

Blood pressure the pressure exerted by blood on the walls of the blood vessels as it travels through the body Measured using a sphygmomanometer Systolic pressure- max. pressure in arteries when ventricles contract and push blood from the heart -Phase is called “systole” Diastolic pressure- lowest pressure in arteries when the ventricles are not contracting -Phase is called “diastole”

Measuring Blood Pressure Pressure is recorded in mmHg (millimeters of mercury) Average healthy blood pressure is 120 mmHg (systolic) 80 mmHg (diastolic)

Factors that affect Blood Pressure: Genetics Cardiac output/activity Stress Body temperature Diet Medications *Note: It is normal for blood pressure to decrease when you are sleeping and increase when you are exercisng. Frequent high blood pressure is called hypertension

Ventricular Diastole: ▫ventricles relax; pressure drops and SL valves close (“dub”) ▫AV valves open ▫blood flows from atria into ventricles Ventricular Systole: ▫ventricles contract; pressure rises ▫AV valves close (“lub”), and SL valves open Blood Pressure During The Cardiac Cycle

Cardiac Output & Stroke Volume Cardiac output : the amount of blood pumped by the heart, in mL/min Stroke volume: the amount of blood pumped out of the heart with each heartbeat Heart rate and stroke volume are used to calculate cardiac output cardiac output (mL/min) heart rate (beats/min) stroke volume (mL/beat)

Cardiac Output & Stroke Volume cont’d… Average heart rate = 70 bpm Average stroke volume = 70 mL Average cardiac output [ adult at rest]: ▫4900 mL (70 beats/min × 70 mL/beat)  almost the entire volume of blood in the body (5 L) passes through the heart about once every minute *Note: males are generally higher than females Average Cardiac Output increases during periods of exercise

Cardiovascular Fitness Cardiovascular fitness is the capacity of the lungs, heart, and blood vessels to deliver oxygen to working muscles. 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.

Check Your Understanding… Why would individual C be considered to be the most fit? What factors determine this?

Why do athletes tend to have higher stroke volumes? stronger cardiac muscles resting heart rate is correspondingly lower less work done by heart muscles but they deliver the same amount of O2 to the muscles Check Your Understanding…

Homework: Read and make notes 12.1 Complete pg. 491 #13-18 Complete pg. 493 # 2, 5-7, 9, 11, 13, 14