BIOL 2050U Lecture Notes - Adrenal Medulla, Depolarization, Heart Valve

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29 Jan 2013
Sinus node is located at the top right atrium
o Also known as the "natural pacemaker" controlling heart rate
o Increases with physical activity and decreases when relaxing
o Electrical signal rapidly spreads from the Sinus node across the right atrium and
left atrium
Only one area where atria and ventricles are electrically connected
o Atrioventricular node or AV node deep in center of heart
o All electrical signals from atrium must pass through AV node in order to get to
o AV node is connected to the Bundle of His
o Branches into a right bundle (to right ventricle) and left bundle (to left ventricle)
Fibers that branch out to distant ventricular tissues are called Purkinje Fibers
Blood pressure
Baroreceptors near aorta and carotid arteries monitor blood pressure
Abnormal blood pressure → signal send to medulla
Cardiac center changes heart rate → cardiac output
Vasomotor center changes diameter of blood vessels
Shock: blood pressure too low
o Insufficient nutrients for cells with a high metabolism (heart, brain)
o Caused by excessive bleeding or extensive vasodilation
o Treated with vasoconstrictors such as epinephrine (adrenaline), atropine
o [NOTE] International name for adrenaline is now epinephrine
Regulation of the Cardiac Cycle
Heart has unique ability to beat (contract) on its own
Assisted by nerves and hormones in blood but functions without them
Impulse leaves SA node and passes through both atria → causing them to contract
From AV node impulse passes down to the Bundle of His
Bundle of His branches and spreads through both ventricles via Purkinje fibers →
ventricles contact
Cardiac output as a function of stroke volume and heart rate
The volume of blood pumped by one ventricle during one beat is called the stroke
Cardiac Output = Stroke Volume x Heart Rate (number of ventricular contractions/min)
↑Force of contraction → ↑Stroke volume → ↑Cardiac output
Regulation of heart rate → Cardiac output is influenced by several factors
Autonomic Nervous System
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