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Circulatory System - Part 3
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The circulatory system is divided into 3 parts:
Circulatory System
Blood
Blood Vessels
HeartHeart
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Heart is made of cardiac muscle
This type of muscle is branching and has ability to contract without being stimulated by a nerve (myogenic)
Heart Muscle
skeletal
smooth
cardiac
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Histology of Cardiac Muscle
intercalated discs
nucleus
capillary
red blood cell
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While these cells can contract on their own, a steady heart beat is maintained by specialized structures in heart
Heart MuscleHeart is made of cardiac muscle
This type of muscle is branching and has ability to contract without being stimulated by a nerve (myogenic)
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Sinoatrial (SA) node is a neuromuscular mass in right atrium that sets heart’s tempoContraction is sensed by atrioventricular (AV) node, which conducts signal to Purkinje fibres
Nelson Biology 11 animation
SA nodeAV node
Purkinje fibres
Heart Rate
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Stimulation by sympathetic nerves increases heart rate, while parasympathetic stimulation slows heart rate
Secretion of adrenaline speeds up heart rate
SA node is influenced by both autonomic nervous system and endocrine system
Heart Rate
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Sound of a heart beat is sometimes described as a “lubb-dubb” and is caused by closing of heart valves
Heart Beat
After atria contract atrioventricular valves close, causing “lubb” soundAfter ventricles contract semilunar valves slam shut, causing “dubb” soundMitral valve viewed from left atrium Aortic valve viewed from aorta
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Blood pressure is a measure of force exerted on arteries as blood moves away from heart
Blood pressure readings therefore consist of both values
Blood Pressure
Blood pressure : systolic pressurediastolic pressure
First atria contract, filling ventricles with blood (diastolic pressure) and then ventricles contract with much greater force (systolic pressure)
“Normal” blood pressure varies with age and is about 120/80 for young adults (units of measure are mm Hg)Blood pressure readings above 140/90 are considered high