Physiology Quiz 6 (Cardiovascular) Flashcards
Ectopic center
Area of cardiac muscle which normally does not perform pacemaker function that suddenly takes up pacemaker function
Common source of arrhythmia
Automaticity
Ability to fire action potential with no outside influence acting upon it (all heart structures have this property)
Causes of ectopic center
- Localized ionic imbalance
- high level of vagal tone to heart
- ischemia to area of the heart
Vasovagal response
Sudden increase in parasympathetic tone to heart (Ach), often caused by sudden, intense emotional shock; causes syncope
Ischemia
Decreased blood flow
Hypoxia
Decreased oxygen
How Ach acts on heart
Decreases HR
Decreases inotropic state
Hemodynamics
Application of physics to blood flow in the cardiovascular system
Equation for blood flow to an area
Q=P/R
Q= flow
P= pressure (mmHg)
R= resistance to blood flow
Resistance to blood flow equation
R= 8(nu)(length of pathway)/pi(radius to the 4th power)
Poiseuille’s law
Q=P(radius to 4th power)(Pi)/8(nu)L
Pascals law
Relates the effects of gravity on perfusion of blood to regions as well as development of edema
Starling-landis relationship
(Graph with hydrostatic pressure and oncotic pressure lines criss-crossing)
Relates oncotic and hydrostatic pressures along capillary length
Hydrostatic pressure drops the entire length due to…
Resistance to flow in capillary
Cause of current sink
Area becomes hypoxic
Charge approaches 0
-not producing ATP
-decreased energy for sodium potassium pump
-sodium leaks in and pump does not pump potassium out, so charge becomes more positive
Becomes current sink
What happens when a current sink forms?
Will start initiating spikes
Becomes new pacemaker
Does a current sink give a coordinated contraction ?
No
What pathology can cause a current sink
Atherosclerosis
Atrial flutter
Faster than normal contraction of atria; regular pattern
Atrial fibrillation
Aria beat irregularly and out of coordination with ventricles
Examples of abnormal centers of pacemaker functions
Atrial fibrillation
Atrial flutter
Paroxysmal ventricular tachycardia
What typically proceeds paroxysmal ventricular tachycardia?
Premature ventricular contraction
Paroxysmal ventricular tachycardia
a rapid heartbeat of sudden onset and termination caused by a quick succession of discharges from an ectopic site in a ventricle
What happens with ventricular fibrillation
Mass, uncoordinated contraction of ventricle; no blood pumped to system
Typically fatal in about 5 min
Re-entry phenomenon
Causes impulse in a cardiac contractile cell to go back up toward SA node and cancels out impulse; causes SA node to lose influence
What must you have for re-entry phenomenon to occur
Slowed conduction
Unilateral block
Oncotic pressure
Osmotic pressure of blood due to plasma proteins
Hydrostatic pressure
Pressure within blood vessel due to pumping of heart
Where hydrostatic pressure is greater than oncotic pressure, where will fluid flow?
Capillary–> tissue
Where oncotic pressure is greater than hydrostatic, where will fluid flow?
Tissue–> capillary
Edema
Change in relative levels of pressure in system that cause net gain of fluid in tissue
What increases edema
Increased hydrostatic pressure (standing, pregnancy, renal disease, congestive heart failure)
Decreased oncotic pressure(starvation, liver dysfunction)
Increased blood volume
What will shift the hydrostatic line upward
Congestive heart failure
Renal disease
Pregnancy
What will shift the oncotic pressure line downward?
Chronic starvation
Liver dysfunction
How much atrial pressure provides adequate perfusion for brain?
80-100 mmHg
Venous return
Blood returned to heart
Venous system is responsible for
Returning blood to heart
Qualities of venous system that help maintain venous return
Skeletal muscle pump
Venous valves
Thoracoabdominal pump
Skeletal muscle pump
Mechanism by which blood is forced back toward the heart when skeletal muscle contracts
Venous valves
One way valves that permit flow only in one direction
Vericose veins
When valves are damaged, blood is allowed to flow back to muscle
-happens in pregnancy
Eg. Hemoroids
Toracoabdominal pump
Blood is pulled to the heart by negative pressure in chest caused by breathing
Positive pressure in abdomen pushes blood toward thoracic cavity
-most influential during exercise
Factors to consider for how BP in CV system is regulated/influenced
Cardiac output
Total peripheral resistance (diameter)
Distensibility of vessels- influences, but will not control BP
Viscosity of blood-influences, but will not control BP
Blood volume available
Factors that act rapidly
Cardiac output
Total peripheral resistance
Factors that are slow acting
Changes in blood volume
Cardiac output
Amount of blood propelled by heart into systemic circulation per minute
Total peripheral resistance
Resistance to blood flow into systemic circulation
Blood volume
Total volume of blood in cardiovascular system
What are blood volume changes mediated by
Hormones
What % of body weight is blood?
6%
Better conditioned athletes, pregnancy ^ BV
Cardiac output and total peripheral resistance are changed by altering…
Neural activity
Cardiac output equation
CO=SV x HR
SV= stroke volume
Stroke volume
mL of blood propelled with each ventricular contraction (dependent on body size)
Ejection fraction
% of total volume in ventricle that is expelled in one beat
(Usually 60-67% @ rest)
Increases with exercise due to increased inotropic force
Increased papasympathetic tone to heart causes…
Decreased HR
Decreased inotropic state
Increased sympathetic tone to heart causes…
Increased HR
Increased inotropic state
Autonomic influence on the heart is determined by
Hypothalamus
Arterial pressure equation
AP= CO x TPR
Want to act upon TPR to change AP; mostly controlled by radius of vessels
Total peripheral resistance is under exclusive control of what autonomic system?
Sympathetic
Control of TPR occurs primarily at the level of the_____ and is mediated by ______
Arteriole; vascular smooth muscle
Only places arteriolar vascular smooth muscle is innervated by parasympathetics are
Salivary glands
External genitalia
Local control of TPR is exerted by
Metabolic byproducts
K, H, lactic acid
Intrinsic control predominates over these systems
Muscle
Heart
Extrinsic control predominates over these systems
GI
Skin
Kidneys
Blood flow received by an area is a result of what system?
Balance between local and extrinsic control
Local/intrinsic control
Metabolic byproducts
Extrinsic control
Autonomic nervous system
When is skin a priority for circulation
In hot weather (because it is a thermoregulator)
How much cardiac output does the average person have at est
5-6 L/min
What type of control will exercising muscle be under during exercise?
Intrinsic
Will be given priority over several other circulations
Kidneys receive ___% of cardiac output at rest
25
Why do kidneys receive so much cardiac output?
Needs BF for filtering Essential for controlling -pH -ionic levels -fluid balance
What control will non-exercising muscle be primarily under when exercising?
Extrinsic
Decreased tone to smooth muscle causes
Dilation
Increased tone to smooth muscle causes
Constriction
Kidney primarily under______control at all times
Extrinsic
Arterial barorecepors
Pressure receptors that monitor average level of arterial pressure and its rate of change
Where are arterial baroreceptors located?
Carotid sinus
Aortic arch
Where does info from aortic baroreceptors go?
Nucleus tractus solitarius in medulla
What does nucleus tractus solitarius do with info from arterial baroreceptors?
Compares it to set point for atrial pressure
If measured pressure is different from set point, hypothalamus alters autonomic outflow to bring pressure closer to set point
Arterial baroreceptors are (slow/fast) control
Fast
Left atrial receptors
Mechanoreceptors that monitor stretch of left atrial wall
Pressure in left atrial wall is directly proportional to
Blood volume
Decreased rate of firing of left atrial receptors is perceived as
Less blood volume
Where is info from left atrial receptors sent?
Centers like nucleus tractus solitarius in medulla and compares to normal set point for blood volume
If measured blood volume is different from set point….
Hypothalamus will change output of ADH (anti diuretic hormone)
- decreased blood volume will lad to increased release of ADH
Way does ADH do
Acts upon kidney to conserve water
Congestive heart failure
Left atrial exceptions are damaged, or set point changes
Renal sympathetic response in left atrial feedback loop is an exception to what?
Sympathetic system being divergent; this is point to point control
Renin-angiotensin
Hormone system entirely within kidney which has significant effect upon controlling BP, especially when arterial pressure drops
Looked at as a mechanism to protect renal blood flow, but also seems to be significant in protecting systemic arterial pressure
JGA stimulates release of
Renin
Renin
Enzyme produced by kidney
More released when kidney senses drop in arterial pressure at level of kidney
Angiotensinogen
Protein in blood that comes from liver
What does renin do
Acts upon angiotensinogen and produces angiotensin I
Angiotensin I
Has no physiological effects
What does angiotensin I do?
Converted to angiotensin II in lungs by converting enzyme
Angiotensin II
Most potent vasoconstrictor in body, also stimulates retention of sodium in kidney
What happens to angiotensin II
Converted to angiotensin III by enzyme in blood plasma
Angiotensin III
Same effects as angiotensin II, but better at release of aldosterone
What does angiotensin III do
Releases aldosterone
Converting enzyme inhibitors
Drug class to block converting enzyme for hypertension patients
Hypertensive patients have..
Faulty JGA
