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AP 2 LECTURE NOTES

• CARDIOVASCULAR PHYSIOLOGY

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CONDUCTION SYSTEM OF THE HEART

• Sinoatrial node SA node
• intrinsic rhythm
• 70-75 beats per minute
• Atrioventricular node AV node
• Ectopic pacemakers
• 40-60 beats per minute
• AV bundle ( bundle of His)
• Purkinje system

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ELECTROCARDIOGRAM

• graphic record of the hearts ELECTRIC ACTIVITY
• P wave, QRS complex, T wave
• P wave
• atrial depolarization
• P-R interval 0.12-.20 sec

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ELECTROCARDIOGRAM , cont.

• QRS complex
• ventricular depolarization
• (atrial repolarization)
• under .1 sec
• T wave
• ventricular repolarization
• Q-T interval under 0.38 sec
• cardiac muscle contraction occurs after
  depolarization begins

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CONTROL OF HEART RATE

• ratio of sympathetic and parasympathetic impulses
• sympathetic cause increase
• parasympathetic cause decrease
• sympathetic
• nerve- cardiac nerves
• neurotransmitters- norepinephrine and
  epinephrine
• action- excitatory

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CONTROL OF HEART RATE, cont.

• parasympathetic
• nerve- Vagus Nerve (X)
• neurotransmitter- acetylcholine
• action- inhibitory

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CARDIAC PRESSOREFLEXES

• stretch receptors(baroreceptors)
• aortic baroreceptor- location aorta
• carotid baroreceptor -location common carotid

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CARDIAC PRESSOREFLEXES, cont.

• CAROTID SINUS REFLEX
• Sensor- baroreceptors found in the carotid
  sinus
• carotid sinus found at beginning of the internal
  carotid
• and under sternocleidomastoid muscle

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CARDIAC PRESSOREFLEXES, cont.

• afferent fibers - bring information to the
  integrator
• sensory impulse from carotid baroreceptor
• travels up the Herring nerve
• joins the IX glossopharyngeal nerve
• goes to cardiac control center of the medulla
  oblongata

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Homeostasis - carotid sinus reflex

• SENSORS- barorecptors found in the carotid sinus
• INTEGRATOR- medulla oblongata cardioregulatory
  center
• EFFECTOR- SA node
• Stimulus -sudden raise in heart rate and or BP
• Result - Heart rate decreases, BP decreases

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AORTIC REFLEX

• sensors location- aortic arch
• afferent fibers
• aortic nerve joins the VAGUS nerve
• goes to cardiac control center
• integrator- medulla oblongata cardioregulatory
  center
• efferent fibers
• VAGUS nerve goes to SA node
• also causes acetylcholine to be released

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AORTIC REFLEX, cont.

• effector- SA node
• stimulus for reflex- Sudden raise in heart rate
  and or BP
• Result of stimulation- Heart rate decreases,
  blood pressure decreases
• cellular mechanism
• when K ion leave hyperpolarized cardiac muscle
  cells
• heart rate decreases

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FACTORS WHICH INFLUENCE HEART RATE

• anxiety, fear anger make heart beat faster
• exercise heart rate increases
• hormones- epinephrine increases heart rate
• when hot receptors are stimulated
• heart rate increases

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FACTORS WHICH INFLUENCE HEART RATE

• grief
• heart rate decreases
• cold receptor stimulation
• heart rate decreases
• sharp visceral pain
• heart rate decreases

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CARDIAC CYCLE

• TERMS
• DIASTOLE- relaxation
• SYSTOLE- contraction

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CARDIAC CYCLE

• ATRIAL SYSTOLE
• completes the emptying of blood from the atriums
  to ventricles
• A-V valves are open, semilunar valves are closed
• during P wave

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VENTRICULAR SYSTOLE

• isovolumetric ventricular contraction
• just before semilunar (SL) valves open
• just before ventricular systole pressure
  increases
• A-V valves close at this time
• QRS complex occurs here
• lub sound occurs here (A-V closing)
• ejection of blood into aorta and pulmonary blood
  vessels

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VENTRICULAR SYSTOLE, cont.

• SL valves open ( aortic and pulmonary)
• rapid ejection
• reduced ejection ( T wave)
• Note residual volume remains in ventricles
• In heart failure residual volume exceeds ejected

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VENTRICULAR DIASTOLE

• isovolumetric ventricular relaxation
• period in between
• SL valves closing
• AV valves opening
• dub sound occurs here (sound closing)
• passive ventricular filling
• AV valves are open

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HEART SOUNDS

• Lub dub ( 1st and 2nd sounds)
• Lub- sound of A-V valves closing
• start of systolic
• dub- sound of SL valves closing
• heart murmurs
• incomplete closing of valves
• stenosis
• narrowing or constriction of valves

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CONTROL OF CIRCULATION

• HEMODYNAMICS
• Blood flow goes from area of higher pressure to
  lower pressure
• example pressure in arterioles is 85 mmHg going
  in
• pressure at capillaries is 35 mmHg (P185mmHg and
  P2 is 35mmHg

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ARTERIAL BLOOD PRESSURE

• Arterial blood volume is DIRECTLY PROPORTIONAL
  to arterial blood pressure
• BP is affected by
• cardiac output
• peripheral resistance
• total blood volume

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CARDIAC OUTPUT(CO)

• stroke volume
• blood pumped out of ventricles each beat
• same as systolic discharge
• heart rate
• beats per minute
• CARDIAC OUTPUT (CO) SV(STROKE VOLUME) X HR
  (HEART RATE)

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CARDIAC OUTPUT(CO), cont.

• Sample calculations of cardiac output
• average normal stroke volume 70ml
• resting pulse (heart rate) 72bpm
• CO70ml x 72bpm 5040ml per minute

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COMPARISONS

• increases in heart rate tend to make cardiac out
  put increase
• increases in stroke volume tend to make cardiac
  out put increase
• increases in cardiac out and peripheral
  resistance tend to make blood pressure higher

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STARLING LAW OF THE HEART

• the greater the stretch of the heart (large
  volume)
• the greater the strength of contraction (within
  limits)

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PERIPHERAL RESISTANCE

• arteriole runoff
• blood going from arteries to arterioles
• the greater the resistance the less the runoff
• blood viscosity
• the more RBC and the more protein the greater
  the resistance
• the greater the viscosity the higher the
  resistance

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vasomotor control mechanism

• vasomotor control center - medulla oblongata
• efferent nerves go to smooth muscle layer of
  vessels in blood reservoirs
• blood reservoirs- venous plexuses
• spleen, liver, skin
• changes in arterial oxygen or carbon dioxide
  levels triggers reflexes

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Vasomotor pressoreceptor reflexes

• STIMULUS- a sudden increase in blood pressure
• sensors- carotid and aortic baroreceptor
• inhibits vasoconstrictor centers, stimulates
  vasodilation centers
• vasodilation occurs and less blood is returned to
  heart

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Vasomotor pressoreceptor reflexes

• integrator
• activation of vasomotor center
• causes a decrease in stroke volume
• decrease cardiac output which leads to reduced BP
• END RESULT- blood pressure returns to normal

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Vasomotor pressoreceptor reflexes

• sensor- baroreceptors in carotid and aorta
• integrator- vasomotor centers- stimulation of
  vasodilation center
• effector- precapillary sphincter muscles in blood
  reservoirs capillaries

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Vasomotor pressoreceptor reflexes

• STIMULUS-a sudden drop in blood pressure
• carotid aortic baroreceptors are activated
• stimulates vasoconstrictor centers, inhibits
  vasodilation center
• venous blood volume to the heart increases
• blood volume to the heart increases
• cardiac output increases, blood pressure increases

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vasomotor pressoreceptor reflexes

• End Result- Blood pressure returns to normal
• sensor- baroreceptors in carotid and aorta
• integrator- vasomotor centers- stimulation of
  vasoconstrictor centers
• effectors- precapillary sphincter muscles in
  blood reservoirs capillaries
• note this mechanism is active during exercise

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Vasomotor chemoreceptor reflexes

• stimulus- hypercapnia (high CO2 in blood)
• some reaction to low O2 in blood
• hypoxia or decreased arterial pH
• impulses to vasoconstrictor center of medulla
  increases
• venous blood volume to the heart increases
• increases pulmonary circulation

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Vasomotor chemoreceptor reflexes

• Result oxygen levels raise and carbon dioxide
  levels decrease
• sensor chemoreceptors found in aorta and carotid
  sinus
• integrator- vasoconstriction center of medulla
• effector- more blood flow to the lungs

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Medullary ischemic reflex

• emergency mechanism
• active when oxygen is low to brain stem
• Sensors- osmotic receptors in the medulla
• integrator- vasomotor center
• effector- lungs- increase blood flow to the lung

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VENOUS RETURN TO HEART

• Respiratory pump
• decreased thoracic pressure (during inspiration)
• pulls blood into central veins
• increasing thoracic pressure (during expiration)
• pushes blood in central veins into heart
• deeper respirations increase venous return to
  heart

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VENOUS RETURN TO HEART

• skeletal muscle pump
• contraction and relaxation pumps blood upward
• note both these methods depend on the presence
  of functioning semilunar valves

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WHERE IS THE BLOOD WHEN AT REST

• 60-70 is in the veins and venules
• 10-12 is in lungs (arteries)
• 8-11 is in heart (arteries)
• 10-12 is in the systemic arteries
• 4-5 is in the capillaries

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HORMONES WHICH AFFECT THE HEART

• antidiuretic (ADH) mechanism
• decrease water lost, Blood volume increases, BP
• renin-angiotensin mechanism
• retention of Na therefore retention of water
• increase in blood volume due to aldosterone, BP

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HORMONES WHICH AFFECT THE HEART

• ANH mechanism
• causes blood volume to decrease
• increases urine sodium loss
• causes water loss ( follows osmotically
• Blood volume decreases, BP