18. Peripheral Control Of Hemodynamic Function Flashcards
What does Starling’s law describe?
The greater the muscle fibres of the heart are stretched, the greater force they will contract with. Increased stretch due to increased preload
Why is the Starling mechanism necessary?
To equalise the R and L ventricle output in the case of increased preload
How is stroke volume determined?
By the central venous pressure
Why does fainting occur?
Due to a low CVP caused by blood pooling in the feet. Less preload means a lower force of contraction, so SV drops, therefore arterial pressure drops
Where does the baroreceptor reflex originate?
What does it respond to?
Initiated by stretch receptors in walls of major arteries (aorta, carotid artery)
Responds to a change in arterial BP
Why is constant hypertension bad?
Blood vessels will remodel to compensate, walls thicken. Elastic fibres begin to break. Also impairs SV (increased afterload in ventricles)
How do diuretics help treat hypertension?
Reduce overall blood volume so heart doesn’t have to pump such a large volume of blood
What is the most likely method to change blood pressure?
Through the resistance arteries, the arterioles. Account for 60% of total peripheral resistance because long and narrow
How is vascular tone controlled intrinsically?
Myogenic response - myocytes depolarise when stretched
Endothelial secretions - amounts governed by shear stress on wall
Vasoactive metabolites - blood flow diverted to areas with metabolites
Temperature - sympathetic vasoconstrictor fibres cause dilation with heat
How is vascular tone extrinsically controlled?
Vasomotor nerves - S vasoconstrictors and vasodilators, PS vasodilators
Vasomotor hormones
Which form of control more affects vascular tone?
Extrinsic - overrides intrinsic to meet the needs of the body
