Stress, shock, And The ANS Flashcards
(21 cards)
What does preload refer to in cardiovascular physiology?
Preload refers to the end-diastolic volume in the heart, or the amount of blood in the ventricles at the end of diastole, just before contraction.
Name at least two factors that can increase preload.
Increased atrial filling and increased venous return are two factors that can increase preload.
How does the Frank-Starling relationship describe the relationship between preload and stroke volume?
The Frank-Starling relationship
the greater the preload,
the greater the stroke volume,
as increased preload leads to greater myocardial stretch, which enhances contractility and, in turn, increases cardiac output. However, excessive preload can lead to overstretching, reducing contractility.
- What is the negative effect of excessively high preload on cardiac function?
Excessively high preload can overstretch the heart muscle, making it less effective at contracting and thereby decreasing cardiac output.
Explain the Bowditch effect in relation to heart rate.
The Bowditch effect
increase in heart rate leads to an increase in contractility and stroke volume
This occurs due to increased calcium availability and enhanced myocardial contraction.
What does the Bainbridge effect describe?
The Bainbridge effect refers to the increase in heart rate that occurs in response to increased venous return.
This is due to the stretch of the atrial muscles, which stimulates baroreceptors that initiate a sympathetic response to accelerate heart rate.
How does the sympathetic nervous system affect the heart?
The sympathetic nervous system increases heart rate (chronotropy), contractility (ionotropy), and conduction speed (dromotropy). It also enhances the heart’s ability to relax (lusitropy).
Chronotropy
How the ANS affects the heart rate
Ionotropy
How the ANS effects the contractility of the heart
Dromotropy
How the ANS affects the conduction speed between the atria and ventricles
What role does the RAAS (Renin-Angiotensin-Aldosterone System) play in the sympathetic response?
The RAAS increases blood pressure by promoting
vasoconstriction,
increasing sodium and fluid retention,
stimulating aldosterone release
which leads to increased fluid volume and blood pressure.
Outline the RAAS system
Liver releases ANGIOTENSINOGEN
Angiotensinogen is converted to ANGIOTENSIN I by RENIN (from kidneys)
Angiotensin I is converted to Angiotensin II by ACE (from lungs)
Angiotensin II stimulates release of VASOPRESSIN and ALDOSTERONE (both increase FV) and cause VASOCONSTRICTION
Increases BP
What triggers the release of renin from the kidneys in the RAAS system?
The release of renin from the kidneys is triggered by sympathetic nervous system activation, which is often in response to low blood pressure or reduced blood flow to the kidneys.
What effect does the parasympathetic nervous system have on the heart?
The parasympathetic nervous system decreases heart rate (chronotropy), decreases the speed of conduction through the AV node (dromotropy), and reduces atrial contractility (ionotropy).
Has little effect on RAAS and VENTRICULAR CONTRACTILITY
Primary action of parasympathetic innervation on Heart rate
Decreases heart rate
How does vasoconstriction in the sympathetic nervous system affect peripheral resistance and blood pressure?
Vasoconstriction increases total peripheral resistance, which in turn raises blood pressure.
Why might loop diuretics like furosemide be used in a hypervolemic patient?
Loop diuretics are used in hypervolemic patients to promote fluid loss through urination, which helps reduce fluid volume and lower blood pressure.
How does the autonomic nervous system respond to a drop in blood pressure?
The autonomic nervous system responds to a drop in blood pressure by increasing sympathetic tone and activating the RAAS, which helps increase heart rate, stroke volume, and blood pressure.
How does increased venous return affect heart rate?
Increased venous return leads to greater atrial stretch, which stimulates baroreceptors and results in an increased heart rate through the Bainbridge effect.
What does the autonomic nervous system do during a “fight or flight” response?
During a “fight or flight” response, the autonomic nervous system increases heart rate, contractility, and peripheral vasoconstriction to prepare the body for increased physical activity.
