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The Beating Heart
- The rate and strength of a heartbeat is under control of
the nervous system.
- The SA (sinoatrial) node stimulates muscle cells to contract
and relax. (involuntary and rhythmical)
o Known as the pacemaker because it controls the
heart rate.
o Can get a manmade pacemaker when this natural SA
node breaks down and cannot function properly.
o Located in the wall of the right atrium.
o Sends a signal to the 2 atria, which then contracts
simultaneously.
- As the 2 atria contract, the signal reaches the AV
(atrioventricular) node.
o The signal then goes through the “bundle of His” and
then “Purkinje fibres” which then initiate the
contraction of the right and left ventricles.
- The signal that is sent can be measured using an ECG
(electrocardiogram) (measuring the electrical activity of
the heart as it contracts and relaxes). Figure 8.8 page 275
Note: the closing of the AV valves during ventricle contraction produces the “lub”
sounds, and the closing of the semilunar valves during ventricular relaxation
causes the “dub” sounds of the heartbeat.
Blood Pressure
- When the blood passes through the vessels, it exerts
pressure against the vessel walls.
o When ventricles contract and force blood into the
pulmonary arteries and the aorta, the pressure
increases.
o Systolic Pressure: the max. pressure during the
ventricular contraction. (top part of the fraction)
o Diastolic Pressure: the lowest pressure before the
ventricles contract. (bottom part of the fraction)
o Pressure is measured in millimeters of mercury
(mmhg).
o Presented in a fraction: Systolic over Diastolic. A
normal reading is near 120mmHg/80mmHg.
Homework Questions pages 272 – 275 #’s 9 -11
Pathways of the Circulatory System
- 3 different pathways to carry
blood:
o Pulmonary pathway:
transports oxygen-poor
blood to the lungs.
o Systemic pathway:
transports oxygen-rich
blood from the left
ventricle to the body
tissues.
o Coronary pathway:
provides blood, matter
and energy to the cardiac muscle tissue.
Cardiovascular Disorders and Treatments
- Risk factors of cardiovascular disease:
o Smoking
o Obesity
o Insufficient exercise
- Disease can be reduced or eliminated by lifestyle changes,
medications and/or surgery.
- Arteriosclerosis occurs when the walls of the arteries
thicken (by several different factors) and lose some of
their elastic properties becoming harder, thus blood flow
is decreased and blood pressure is increased.
Treatments: (Page 279 – list and explain)
Assignment:
P. 277 #’s 12-13
Page 281 # 3, 4 , 7