Clin Phys Week 8 E Flashcards
What is cardiac output?
Amount of blood ejected by each ventricle in each 1 minute
What is average cardiac output?
4-6L
Parasympathetic neurons regulate heart rate how
Muscarinic receptors of auto rhythmic cells
=Increased K efflux, decreased Ca influx
=Hyperpolarises cells decreases rate of depolarisation
=Decreased Heart Rate
Sympathetic neurons regulate heart rate how
Beta 1 receptors of auto rhythmic cells
=Increased Na and Ca influx
=Increases rate of depolarisation
=Increases Heart Rate
What is cardiac reserve?
The difference between maximum and resting Cardiac output
What is stroke volume governed by?
Preload, contractility, afterload
What is preload?
Left ventricular end diastolic volume. i.e. the amount of stretch of the left ventricleAmount of tension in ventricular myocardium before it contracts Increased preload increases contraction strength
What is afterload?
Total peripheral resistance = pressure overload
Determined by:
- Aortic pressure
- Volume and thickness of the ventricular cavity.
Pressure in the arteries above the semilunar valves opposes opening of valves. Therefore increased afterload causes a decrease in SV.
What is contractility?
Capacity of myocardium to respond to preload and afterload.Contraction force for a given preload.
What is the Frank-Starling Mechanism
Intrinsic regulatory mechanism. Cardiac length-contractility curve.
The greater the cardiomyocyte stretch the greater the strength of contraction. It is determined by venous return, the heart will pump all the blood that enters it out into the systemic circulation within its physiological limits. Ventricles eject as much blood as they receive, more they are stretched (increased preload), the hard they contract.
What are factors that increase contractility?
Positive Inotropic agents
eg hypercalcemina, catecholamines, glucagon,
What are factors that decrease contractility?
Negative inotropic agents
eg hyperkalemia, hypocalcemia, hypoxia
What are the effects of catecholamines on the autonomic nervous system,?
More forceful contractions
Shorter contraction duration
How:
- NE increased time of the opening of the voltage gated Ca channels
- Increase Ca from ECF
- NE increases Ca storage in SR via regulatory proteins.
- Increases availability of ICF calcium.
What happens if right ventricular output exceeds left ventricular output?
Pressure backs up and fluid accumulated in pulmonary tissues.
What happens if left ventricular output exceeds right ventricular output?
Pressure backs up and fluid accumulates in the systemic tissues
