regulation of cardiovascular system Flashcards
Which 4 factors affect venous volume distribution?
- Peripheral Venous Tone
- Gravity
- Skeletal Muscle Pump
- Breathing
What determines the stroke volume?
The amount of blood returning to the heart
What is central venous pressure?
blood pressure in the vena cava, near the right atrium
What does central venous pressure determine?
The amount of blood flowing back to the heart
How is blood flow altered?
Mainly by the arterioles and changing vessel radius
What does the constriction of veins determine?
Its compliance and venous return
What does the constriction of arterioles determine?
Blood flow to the organs they serve, mean arterial blood pressure and the distribution of blood to organs
What is the extent of vascular constriction determined by?
By the pattern of organisation of innervation to particular vascular beds - the number of adrenoreceptors will affect the blood flow to an organ
What are the 3 ways of regulating blood flow?
- Local Mechanisms - intrinsic to the smooth muscle itself or closely associated
- Hormones
- Autonomic Nervous System - innervates arterioles and veins to produce constriction or dilation
Hormones and ANS are extrinsic and local is intrinsic
What is the primary function of extrinsic factors?
To regulate arterial blood pressure by altering systemic vascular resistance
What is autoregulation?
The intrinsic capacity to compensate for changes in perfusion pressure by changing vascular resistance β this is an example of a local mechanism regulating blood flow
What would happen in the absence of autoregulation if blood pressure fell?
The resistance will increase and flow will decrease
What happens during autoregulation if pressure falls?
There will be a gradual decrease in resistance and hence a gradual increase in flow
What are the two theories suggesting how autoregulation occurs?
Myogenic Theory = smooth muscle fibres respond to stretch and as pressure rises, the muscle fibres start contracting to keep flow constant
Metabolic Theory = if the vessels supplying a particular vascular bed contract, the flow to the vascular bed decreases and the vascular bed produces more metabolites - as more metabolites are produced, it feeds back on the vessel thatβs supplying the bed and causes vasodilation and hence allows more flow to the vascular bed and the metabolites which triggered this response are washed away
How can autoregulation be affected by injury?
When a vessel is injured, platelets aggregate and they release serotonin which is a powerful vasoconstrictor which will constrict the injured vessel
Give examples of substances released from the endothelium that can regulate blood flow
Nitric Oxide - vasodilation
Prostacyclin (vasodilator)
Thromboxane A2 (vasoconstrictor)
Endothelins - potent vasoconstrictors
Give examples of hormones that can affect blood flow
Kinins
- Have complex interactions with the Renin-Angiotensin System
- Tend to relax vascular smooth muscle
ANP (Atrial Natriuretic Peptide)
- Circulating peptides that are secreted from the cardiac atria
- As the atria stretch they release more ANP which causes vasodilation
Circulating Vasoconstrictors
- Vasopressin
- Angiotensin II
- Noradrenaline
What is the structure of parasympathetic nerved and what does this mean?
Have a long preganglionic fibre and a short postganglionic fibre - the parasympathetic ganglion will be right beside the sinoatrial node
What are the SNS and PNS important for (heart)?
Sympathetic - generally controls the flow
Parasympathetic - important in regulating heart rate
Which vessels have sympathetic innervation and which donβt?
They innervate all vessels except capillaries (and precapillary sphincters and some metarterioles)
Is the distribution of sympathetic nerves even and what does this mean?
No- more sympathetic nerve fibres innervate vessels supplying the kidney, gut, spleen and skin and fewer innervate the skeletal muscle and the brain so there is more potential to constrict the blood going to these places so that we can divert blood to the organs that we need more
Where does noradrenaline bind and what does it do?
To alpha 1 adrenergic receptors to cause constriction
Where does adrenaline bind and what does it do?
To smooth muscle beta-2-adrenoreceptors to cause vasodilation in some organs
However the effect is very concentration-dependent. At high concentrations, adrenaline can bind to alpha adrenoreceptors which can override the vasodilatory effects of the beta-2-adrenoreceptor stimulation and produce vasoconstriction
Where is the vasomotor centre located and what does it consist of?
Is located bilaterally in the reticular substance of the medulla and the lower third of the pons
The VMC consists of a:
- Vasoconstrictor Area (Pressor)
- Vasodilator Area (Depressor)
- Cardioregulatory Inhibitory Area