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Cardiac Output (CO)
- Volume of blood pumped per min by each ventricle
- CO = SV(Stroke volume) x HR
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Regulation of Cardiac Rate
Without neuronal influences from the sympathetic/parasympathetic nervous systems, the heart beats according to the rhythm set by SA node
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Regulation of Cardiac Rate
Autonomic effect:
- Sympathetic and parasympathetic nerve fibers to the heart modify the rate of spontaneous depolarization
- Innervate the SA node
- NE and Epi stimulate
- ACh depresses
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Regulation of Cardiac Rate
Cardiac control center (medulla)
Coordinates activity of autonomic innervation
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Regulation of Stroke Volume
3 variables
- EDV- (increase in EDV increases SV)
- Total peripheral resistance (TPR)
- Contractility
- A change in any of these 3 will change the SV
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EDV (End diastolic volume)
Volume of blood in the ventricles at the end of diastole
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Total peripheral resistance (TPR)
Frictional resistance or impedance to blood flow in the arteries
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Contractility
Strength of ventricular contraction
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End diastolic volume
- Workload on the heart prior to contraction (preload)
- SV directly proportional to preload
- Increase in EDV results in an increase in SV
- SV directly proportional to contractility
- Strength of contraction varies directly with EDV
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Ejection fraction
- EF = SV divided by EDV
- Normally is 60% if below than this the heart is failing
- Clinical diagnostic tool
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TPR(Total peripheral resistance)
- Impedance to the ejection of blood from ventricles into arteries
- Pressure in arteries before ventricle contracts is a function of TPR
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SV inversely(opposite) proportional to TPR
Greater the TPR, the lower the SV
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Frank-Starling Law of the Heart
- Relationship between EDV, contraction strength and SV
- Just the right amount of actin and myosin, to make the greatest amount of contraction
- Explains how the heart can adjust to rise in TPR
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Extrinsic Control of Contractility
- Strength of contraction at any given fiber length
- Depends upon sympathoadrenal system
- NE and Epi produce an increase in contractile strength
- Parasympathetic stimulation- does not directly influence contraction strength
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Venous Return (the return of blood via veins)
- veins have thinner walls
- 2/3 blood volume is in veins
- EDV, SV, CO affect venous return
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Skeletal muscle pump
Aid venous return
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Blood Volume
- 2/3 of total body Water within the cells
- 1/3 total body water ( 80% interstitial fluid, 20% blood plasma)
- Maintained by constant balance between water loss and gain
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Causes of Edema- excessive accumulation of tissue fluid
- High arterial pressure
- Venous obstruction
- Leakage of plasma proteins into interstitial fluid
- Decreased plasma protein
- Obstruction of lymphatic drainage
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Regulation of Blood volume by the Kidneys
- Volume of urine excreted can be varied by changes in reabsorption of filtrate
- Adjusted according to needs of body by action of hormones
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Regulation of Blood Volume can be influenced by:
- ADH
- Aldosterone
- Renin-Angiotension-Aldosterone System
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Resistance
Influenced by the length of vessel, viscosity(thickness) of the blood and radius of the vessel
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Extrinsic Regulation of Blood Flow
Controlled by autonomic nervous system and endocrine system
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Sympathoadrenal system
Increases CO & TPR
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Parasympathetic nervous system
Promotes vasodilation to the digestive tract, external genitalia, and salivary glands
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Aerobic requirements of the Heart
Survival requires that the heart and brain receieve adequate blood supply at all times
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Coronary arteries supply enormous # of____
capillaries
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Systole contracts the coronary_____
blood vessels
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Diastole increases blood flow to the ____ ____
heart muscle
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Coronary blood flow
Coronary blood flow is the flow of blood through the coronary vessels of the heart to supply oxygen to the heart muscle
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Sympathetic nervous system
- Vasoconstriction of coronary arteries at rest (alpha receptors)
- Vasodilation of the coronary arteries during activity (beta receptors)
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Blood flow through skeletal muscles
- Sympathetic: Vasoconstrict at rest
- Parasympathetic/Sympathetic: Vasodilate during activity
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Circulatory changes during exercise
- Vascular resistance decreases to skeletal muscles
- Blood flow to skeletal muscles increases
- SV and CO increase-blood flow to brain stays the same
- HR increases to maximum of 190 beats/min-ejection fraction increases due to increased contractility
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Vascular resistance:
- Decreases to skeletal muscle
- Increases to GI tract and skin
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Cerebral circulation
Cerebral blood flow is not normally influenced by sympathetic nerve activity
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Thermoregulation
- Blood flow through the skin is adjusted to maintain deep-body temperatures at about 37C
- Occurs due to: Vasoconstriction/vasodilation arteries
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Bradykinin
Sweat glands secrete bradykinin which increases blood flow to skin and sweat glands
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Blood Pressure
- Is the pressure of arterial blood, regulated by blood volume, TPR, and cardiac rate
- Negative feedback
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Blood Pressure
3 most important variables are:
- HR
- SV
- TPR
- Increase in each of these will result in an increase in BP
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BP can be regulated by:
- Kidney (SV)- amount of water to reabsorb
- Sympathoadrenal system (HR + TPR + SV)
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Auscultation: Listening through stethoscope
Art of listening
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Laminar flow:
- Normal blood flow
- Blood in the central axial stream moves faster than blood flowing closer to artery wall
- Smooth and silent
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Turbulent flow and vibrations(of blood flow) produced in the artery when cuff is:
Greater than diastolic pressure and lower than systolic pressure
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Blood pressure cuff is inflated above____
systolic pressure
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As cuff pressure is lowered, the blood will flow only when_____ _____ is _____ cuff pressure, producing the sounds of Korotkoff.
systolic pressure; above
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Korotkoff sounds will be heard until cuff pressure equals_____ _____, causing sounds to disappear.
diastolic pressure
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Average arterial BP
120/80 mm Hg
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Average pulmonary BP
22/8 mm Hg
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Pulse Pressure
- The expansion of the artery in response to the volume of blood ejected by the left ventricle
- PP= systolic pressure - diastolic pressure
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MAP (mean arterial pressure)
- Represents the average arterial pressure during the cardiac cycle
- Is closer to diastolic presure, as the perois of diastole is longer than the period of systole
- MAP = diastolic pressure + 1/3( pp)
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Hypertension (HTN)
- Blood pressure in excess of normal range for age and gender
- High BP
- > 140/90 mm Hg
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Primary or essential hypertension
- Is the result of a complex or poorly understood process
- Naturally run high
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Secondary hypertension
Is a result of a known disease process
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Dangers of Hypertension
- Silent killer
- Atherosclerosis
- Congestive heart failure
- Damage cerebral blood vessels- cerebral vascular accident (stroke)
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Congestive Heart failure
- CO is insufficient to maintain the blood flow required by the body
- Increase venous volume and pressure
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Congestive heart failure is caused by:
- MI (most common cause)
- Congenital defects
- Hypertension
- Aortic valve stenosis
- Disturbances in electrolyte concentrations
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Congestive heart failure is treated with medications:
- Digitalis
- vasodilators
- diuretics
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