Control of Arterial Tone Flashcards
What are resistance vessels major contributors to?
Regulation of arterial blood pressure and regulation of local blood flow
What is pressure equal to?
Pressure = Flow X Resistance
What is TPR mainly determined by?
Resistance arteries
Define resistance vessels?
Arteries and arterioles that contribute most substantially to TPR.
What are arterioles made of?
1-2 layers of smooth muscle in the media layer
What are extrinsic factors?
Autonomic nerves and Humoral Stimuli
What are intrinsic factors?
Autacoids and autoregulation
Which factor controls large arteries and veins?
Extrinsic control
Which factor controls arterioles?
Both extrinsic and intrinsic control
What vessels don’t have a contractile function and why?
Capillaries and postcapillary venules due to having no smooth muscle layer
What is the effect of widespread resistance artery constriction?
Raised TPR which causes raised upstream pressure and downstream pressure falls.
What is the effect of local resistance artery constriction?
Limited effect on TPR and local downstream pressure falls
Define autoregulation.
A (nearly) constant flow in the face of changing pressure.
What is the role of autoregulation?
Stabilizes tissue perfusion, capillary pressure and therefore water movement across capillary walls.
What is the Myogenic Response?
The active change in diameter subsequent to a change in lumenal pressure.
What is myogenic contraction dependent on?
Ca2+ entry into smooth muscle
What is Hyperaemia?
Increased blood flow due to increased vasodilator metabolite production.
What is reactive hyperaemia?
Increased blood flow due to release of an obstruction.
What are autacoids?
Local vasoactive chemicals eg. histamine, bradykinin and prostaglandins
What are endothelium vasoconstrictors?
ET-1 and PGH2
What are endothelium vasodilators?
EDRFs, NO, PGI2, EDHF
What is the effect of Protein Kinase G
cGMP activation -> vascular relaxation by: K+ channel activation with hyperpolarisation and Ca2+ channel closure.
Ca2+ ATPase activity increased
Decreased Ca2+ sensitivity of contractile apparatus
What activates K+ channels directly
NO
What does K+ do?
Activates KIR channels and stimulates Na+/K+ATPase
How does ADRF act?
A paracrine fashion and activates K+ channels in vascular smooth muscle cells
Describe sympathetic adrenergic nerves.
Nerve fibres that are tonically active and mostly vasoconstrictor in effect eg. noradrenaline
Describe parasympathetic nerves.
Nerve fibres that are not tonically active eg. ACH, VIP and NO
Name a sympathetic cholinergic nerve and its function.
ACh.
Vasodilation via muscarinic receptors on endothelium (release of EDRFs)
Where does sympathetic tone originate from?
The medulla oblongata
What increases sympathetic tone?
Fall in arterial blood pressure sensed by baroreceptors and low PO2 and pH and high PCO2 sensed by chemoreceptors
What does NA act via?
Adrenoreceptors
What is pharmacomechanical coupling?
Depolarisation-independent contraction eg. PLC, PIP2 and DAG
What is electrochemical coupling?
Depolarisation-dependent contraction
