Control of Vasculature and Pressure Flashcards
What are extrinsic influences on vascular function?
- influences on blood flow are neural and hormonal means of regulation
- these central mechanisms are critical for maintaining constant blood pressure and regulating distribution of blood flow to organs and tissues
What are intrinsic influences on vascular function?
- refer to local effectors which exert local influences
- these local mechanisms are important in regulating the distribution at the organ and tissue level
Extrinsic neural control - In terms of the cardiovascular control centre in the medulla oblongata, explain the effect of the PNS and SNS on heart rate
PNS - release of acetylcholine, binds muscarinic receptors on pacemaker cells, rate of depolarisation decreases, decrease
SNS - release of noradrenaline, binds to beta adrenergic receptors, this increases the rate of depolarisation of pacemaker cells increasing heart rate and also affects the myocardium by increasing sarcomere length and increasing contractile force
Explain the affect that the SNS has on the vasculature
Noradrenaline release from SNS helps to maintain myogenic tone.
It is released from post-ganglionic neurons and binds to alpha1 receptors leading to vasoconstriction.
What reinforces the affect that adrenaline has on vasculature?
Release of adrenaline from the adrenal medulla
Binds to alpha1 receptors and causes vasoconstriction
What receptors can adrenaline bind to?
Noradenaline?
Adrenaline = alpha1, beta1, beta2 Noradrenaline = alpha 1, beta1
Alpha1 - vasoconstriction of vascular beds
Beta1 - cardiac contractility and HR
Beta2 - vasodilation in the heart, liver and skeletal muscle arterioles
What does the PNS do to the vasculature?
It causes vasodilation in select vascular beds: salivary glands, pancreas, intestines
What local factors affect vascular tone?
Local hormones
Nitric oxide
Sympathetic nerves releasing noradrenaline
What does histamine do to vascular tone?
It increases vascular permeability.
Leads to NO release which causes vasodilation.
What is the difference is metabolic and reactive hyperaemia?
Metabolic - (increase in blood flow to a particular tissue) important in cardiac and skeletal muscle increased metabolism enhances production of substances which cause vasodilation of arteries
Reactive - (reduced blood flow to a tissue) if local blood flow is cut off, metabolites accumulate and cause vasodilation. When blood flow is resumed, it is enhanced until the metabolites wash out.
Explain the principle of cutaneous circulation
Thermoregulation
- Arteriovenous anatomises are muscular vessels found in skin extremities.
- Blood flow is regulated by thermoreceptors and the SNS
- Cold temperature causes increase in vasocontriction to shunt blood away from the venule (increase in sympathetic discharge)
- Hot temperature causes a decrease in sympathetic discharge and allows blood to enter the dermal venous plexus
What are 3 things that determine blood pressure?
- Stroke Volume and Heart Rate
- Total Peripheral Resistance
- Central venous pressure and blood volume
How does the baroreceptor reflex work?
Baroreceptors contain fine nerve ending sensitive to stretch - located in the aortic arch and carotid sinus
The thin wall of the carotid sinus allows small changes in pressure to be detected.
A decrease in pressure causes a decrease in firing of nerve endings.
Explain what happens to blood pressure when a patient gets off the dental chair. Why do they not fall down?
Gravity causes pooling pf blood in lower limbs. This decreases central venous pressure and stoke volume.
The fall in blood pressure is too small to be seen as the heart detects it and corrects the shortfall by increasing sympathetic drive by increasing heart rate and total peripheral resistance.
How is plasma osmolarity controlled?
If there is a decrease in plasma osmolarity, receptors detect this and insert aquaporins in the loop of Henle. This increases water reabsorption.
