PHYSIOLOGY - Control of Blood Vessels Flashcards
What is basal vascular tone?
Basal vascular tone is a baseline level of contraction of vascular smooth muscle
What is the difference between intrinsic and extrinsic factors which influence blood vessel tone?
Intrinsic factors are factors which originate from the blood vessel itself or from the surrounding tissue, extrinsic factors originate from outside the tissue in which the blood vessel is located
List five intrinsic factors which influence blood vessel tone
Temperature
Mechanical compression
Myogenic response
Local metabolites
Autocoids
How does temperature influence blood vessel tone?
An increase in temperature will cause vasodilation to dissipate heat and a decrease in temperature will cause vasoconstriction to retain heat
How does mechanical compression influence blood vessel tone?
Mechanical compression will limit blood flow which can disrupt the signalling processes that control blood vessel tone
What are the risks of prolonged mechanical compression of blood vessels?
Ischaemia
Infarction
Give an example of physiological mechanical compression of blood vessels
The pumping action of the heart causes transient mechanical compression of the coronary blood vessels
What is the myogenic response?
The myogenic response is the change in blood vessel tone in response to changes in transmural pressure (pressure difference between the inside and outside of blood vessels)
Why does the myogenic response trigger vasoconstriction in response to increased intravascular pressure?
The myogenic response triggers vasoconstriction in response to increased intravascular pressure as a protective mechanism to prevent excess stretch of the vascular wall to prevent rupture
How do local metabolites influence blood vessel tone?
Tissue metabolism produces many by-products which stimulate vasodilation and increase blood flow and local tissue perfusion - this is known as metabolic hyperaemia
How do autocoids influence blood vessel tone?
Autocoids are vasoactive chemicals which are mainly involved in changing blood vessel tone in response to inflammation and haemostasis
List two extrinsic factors which influence blood vessel tone
Autonomic nervous system (ANS)
Hormones
How does the sympathetic nervous system influence blood vessel tone?
The sympathetic nervous system stimulates vasoconstriction
How does the parasympathetic nervous system influence blood vessel tone?
The parasympathetic nervous system stimulates vasodilation
How does adrenaline release influence blood vessel tone?
In response to the sympathetic nervous system, adrenaline will be released and bind to receptors on the vascular smooth muscle to stimulate vasoconstriction
What are baroreceptors?
Baroreceptors are sensory mechanoreceptors which detect changes in blood pressure
Where are baroreceptors located?
Carotid sinuses
Aortic arch
Describe how the baroreceptor reflex is involved in short-term regulation of blood pressure
Baroreceptors located in the carotid sinuses and aortic arch detect changes in blood pressure and transmit sensory information up CNIX and CNX to the central nervous system which stimulates the autonomic nervous system to adjust heart rate and blood vessel tone
Why is the baroreceptor reflex not useful in long term regulation of blood pressure?
The baroreceptor reflex is not useful in long term regulation of blood pressure because of the adaptability of the baroreceptors to prolonged changes in blood pressure. Baroreceptors will begin to behave as if the abnormal blood pressure is normal and aim to maintain this abnormal blood pressure.
Describe briefly how the baroreceptor reflex will respond to a decrease in blood pressure
When blood pressure decreases, there will be reduced stimulation of the baroreceptors resulting in the transmission of this sensory information to the autonomic nervous system. This will increase sympathetic nervous system activity resulting in an increase in heart rate and vasoconstriction. The sympathetic nervous system will have stimulated adrenaline release which will also increase heart rate and cause vasoconstriction. There will also be a decrease in parasympathetic nervous system activity which will further increase the heart rate
Other than the baroreceptor reflex, how does the body respond to a decrease in blood volume?
To increase blood volume and thus increase blood pressure, the body will induce the sensation of thirst and activate the renin angiotensin aldosterone system which will stimulate sodium and water reabsorption, increasing fluid retention and thus increases blood volume
