Control of circulation Flashcards
What are baroreceptors and where are they found?
Stretch receptors and are found in the carotid sinus and aortic arch
What happens when the baroreceptors are stimulated by an increased blood pressure
Carotid sinus sends action potentials along the sinus nerve then the glossopharyngeal nerve fibres -
Aortic arch sends APs along vagus nerve fibres to the medulla (nucleus tractus solitarius)
Inhibitory interneurons suppress the sympathetic nervous system activity that would normally be causing tonic vasoconstriction/increased heart rate/CO which are therefore decreased.
What is meant by tonic sympathetic adrenergic constrictor input
Seen in most vessels - in normal conditions sympathetic signalling to these vessels causes consistent levels of constriction - adrenergic
What neurotransmitter causes vasodilation in pre-capillary vessels in skeletal muscle, kidneys, lungs, and heart
Acetylcholine - exception to the rule that sympathetic post-ganglia axons usually release noradrenaline
What autonomic supply does the erectile tissue/glands have and what does it cause
Parasympathetic supply by Ach causes vasodilation
What is the effect of adrenaline at the skin/viscera
Vasoconstriction
What is the effect of adrenaline at the skeletal muscle/liver
Vasodilation
What role do kinins have on circulation
Bradykinin - vasodilatory peptide
What role does angiotensin II have on circulation
Vasoconstriction - increases blood pressure - Formed by enzymes (renin) acting on precursors when BP falls (ACE in the lungs)
What effect do prostaglandins have on blood vessels
Vasodilation
What effect does histamine have on blood vessels
Released by mast cells - vasodilation, fluid accumulation by making the vessel leaky
What is the action of endothelium-derived relaxing factor
Released after Ach stimulation - Nitric oxide stimulates cGMP in muscle - this causes relaxation of smooth muscle and therefore vasodilation
What effect does viagra have on cGMP
Inhibits the action of cGMP on smooth muscle so maintains contractility - used to maintain an erection
What is the action of nitroglycerin
Increases NO levels, causing vasodilation, causing increased blood flow and increased oxygen supply - used to treat angina (the heart isn’t getting enough blood)
What is the action of the sympathetic and parasympathetic nervous systems in the cushing reflex
- Sympathetic control - due to head injury - swelling within the cranium causes intracranial pressure to rise - when it exceeds mean arterial blood pressure it becomes very hard for the blood to receive blood - compensation for this from the SNS - Causes vasoconstriction and tachycardia
- parasympathetic - baroreceptors detect the change in BP (stretched) afferent fibres to the medulla (nucleus tractus solitarius) inhibitory interneurons act to inhibit sympathetic NS action on the heart causing bradycardia
Very dangerous - High BP and Low heart rate - death
