Download Heart Physiology Notes

HEART PHYSIOLOGY
Physiology of Circulation
• Indicators of efficiency of a person’s
circulatory system can be obtained by taking
arterial pulse and blood pressure
measurements.
• These, along with respiratory rate and body
temperature, are called vital signs.
Heart Work
• Heart pumps the body’s 6 L of
blood over 1,000 times a day =
6,000 L of blood in a day
• Atria contract (Luppa), then
ventricles contract (Duppa) =
Luppa Duppa
• Atria contracts 60 beats/min
• Ventricles contract 20-40
beats/min
• Heart Rate - the number of
beats per minute
Arterial Pulse
• The alternating expansion and recoil of an
artery that occurs with each beat of the left
ventricle creates a pressure wave – a pulse –
that travels through the entire aterial system
• Normally, the pulse rate equals the heart rate
• It averages 70-76 bpm
• Affected by activity, posture, and emotions
Heart Rate
• Palpated at one of several arterial locations
close to surface
• Same spots used to stop hemorrhage, called
pressure points
• Radial
• Carotid
• Brachial
• Popliteal
• Posterior tibial
• Dorsalis pedis
• Facial
• Temporal
• Use two fingers to palpate – not thumb
• Coordinated by electrical pacemaker within
heart
The Electricity of the Heart
• Heart contains two
special batteries called
nodes
• Made of specialized
cardiac tissue that can
generate electricity –
mixture of nervous and
muscle tissue
Intrinsic Conduction System
• Nodal System – sets basic rhythm of heart
• Forces contraction rate of 75 beats/min so
heart beats as coordinated unit
• Two nodes:
• Sinoatrial node (SA Node)
• Atrioventricular node (AV Node)
• AV Bundle of His – bundle of fibers between
atria and ventricles
• Purkinje fibers – spread within muscle of
ventricle walls
SA Node (Sinoatrial)
• Located in RA near
junction of SVC
• Starts heartbeat and sets
pace = pacemaker
• Generates 70-80 action
potentials per minute
• Connects to AV node
• Tells atria to contract
AV Node (atrioventricular)
• Located on floor of RA
• Generates 40-60 beats per
minute on own
• Will usually follow rate of
SA node
• Tells ventricles to contract
• Delays signal (to let atria
finish contracting)
• Passes signal to bundle of
His, then to Purkinje fibers
Control of Heart Rate
• Cardioinhibitory Center
• ANS– parasympathetic
• Normal everyday
activity
• Vagus nerve releases
Ach to slow heart
• Acts like a break
• Decreases heart rate
• Cardioacceleratory
Center
• ANS – Sympathetic
• Fight or Flight response
• Cardiac nerve releases
norepinephrine or
epinephrine
• Increases heart rate
Electrocardiogram
• Also known as ECG
• Way to measure SA and
AV nodes
• Attach electrodes to
skin (moves thru water)
• Helps us know rhythm
and strength of
contractions
Reading the ECG
• P wave – SA node fires
telling atria to contract
called atrial
depolarization
• QRS complex – AV node
fires telling ventricles to
contract called vent.
Depolarization
• T wave – ventricular
repolarization (reset)
Bradycardia
• Slow heart rate
• Usually below 60
• Sign of large ventricle or
athletic
• Also can mean death is
near
• Characteristics on ECG?
Tachycardia
• Means fast heart rate
usually over 100
• Can mean small
ventricle or exercising
• Death can result around
220 or higher
• Characteristics on ECG?
Ventricular fibrillation
• Bad News!
• Heart has
uncoordinated
contractions
• Cannot effectively move
blood
• ECG characteristics?
• Will use a defibrillator
Atrial flutter
• Atrium is contracting
quickly
• Many atrial contractions
per ventricle contract.
• Why would this be Bad?
• ECG characteristics?
Cardiac Output
• Cardiac Output (CO) is the amount of blood
pumped out by each side of the heart in 1 min
• It is the product of heart rate (HR) and the
stroke volume (SV)
• Stroke volume is the volume of blood pumped
out by a ventricle with each heart beat
• CO = HR X SV
• CO = HR (75 beats/min) X SV (70 ml/beat)
• CO = 5,250 ml/min (average adult human)
Regulation
• Starling’s law of the heart – critical factor of
controlling stroke volume is how much the cardiac
cells are stretched before they contract
• More stretch = more contraction
• Venous return – amount of blood entering the heart
and distending its ventricles
• Anything that increases volume/speed of venous
return also increases stroke volume and strength of
contraction
• Example: a slow heartbeat allows more time for
ventricles to fill
Blood Pressure
• Blood pressure is the
pressure the blood exerts
against the inner walls of
the vessels
• Force that keeps blood
circulating evenly
• Flows along a pressure
gradient (high to low) from
large arteries to small
arterioles
Factors affecting B.P.
• BP = CO X PR where PR = Peripheral Resistance
• Peripheral Resistance – amount of friction the
blood encounters in blood vessels
• Vasoconstriction – narrowing of blood vessels.
• Effect on BP?
• Increase in BP. When would this occur?
• Baroreceptors – e.g. when lying down
• Vasodilation – dilating of blood vessels.
• Effect on BP? Decrease BP
• During fight or flight
Factors affecting B.P.
1. Neural factors: ANS –
vasodilation/vasoconstriction
2. Renal factors: kidneys – when BP high, kidneys
allow more blood to leave body in urine
3. Temp – cold = vasoconstriction, warm =
vasodilating
4. Chemicals – nicotine leads to vasoconstriction,
alcohol leads to vasodilation
5. Diet – low salt helps prevent hypertension