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
What areas of the circulatory system detect low pressure in blood vessels
baroreceptors found in the atria, left ventricle and pulmonary veins
What is ANP and what does it do
Atrial natriuretic peptide - Mostly produced in the atria - acts at the level of the kidney to inhibit water re-uptake
What action do chemoreceptors have on control of circulation
Angina - cardiac chemoreceptors detect a fall in pH/rise in CO2 and signal pain - leads to an increase in BP
What is the hypo-defence area of the hypothalamus’ role
leads to sympathetic dilation of skeletal muscles and blood vessels
What is the role of the hypo-thermoregulatory centres
When warm - Vasodilation and sweating
When cold - Vasoconstriction and shivering
What is the role of the hypo-medial preoptic area
Sexual response
What is the role of the anterior cingulate gyrus
Bradycardia - hypotension
Drops HR and BP to avoid predation in animals who are playing dead
