CV VII Flashcards
What are two examples of local control of arteriolar resistance
- Myogenic autoregulation
- Paracrines
Myogenic autoregulation
Ability of vascular smooth muscle in arterioles to constrict in response to stretch (stretch activated channels)
- maintain regular blood flow
- prevent damage from pressure
What stretches smooth muscle of arterioles and causes constriction (Myogenic autoregulation)
- increased tension due to increased blood flow
What stretch activated channels do arterioles have
TRP channels
Lead to mechanodepolarization
What do paracrines do to alter vascular smooth muscle
Local control of blood flow is important in individual tissues regulating their own blood supplies
Metabolism related paracrine signalling molecules
Decrease O2, increase CO2, NO, H+, lactate, adenosine
Non-metabolism related paracrine signalling molecules?
Kinins and histamine (inflammation), serotonin
What is the main determinant (>60%) of resistance in majority of arterioles
Sympathetic NS
How do sympathetic neurons innervate arterioles
Tonically control arteriolar diameter through activation or deactivation of alpha 1 adrenergic receptors
What does increased release of norepinephrine onto a receptors do to arteriolar diameter
As AP signal rate increases, blood vessel constricts
What does decreased norepinephrine release onto a receptors do to arteriole diameter
As AP signal rate decrease, blood vessel dilates
What is the secondary muscle involving sympathetic control of vascular smooth muscle
Release of epinephrine from adrenal medulla
What does epinephrine had a low affinity and a high affinity for
What does it depend on
Low affinity for alpha receptors which lead to vasoconstriction
High affinity for B2 adrenergic receptors which lead to vasodilation
- depends on relative amount of each receptor
What is an example of the body selectively alters blood flow to organs
Skeletal muscle receives ~20% of cardiac output at rest, but can increase as high as 85% during strenuous exercise
What does regional amount of blood flow depend on at rest
Number and size of arteries feeding the organ
How do arterioles all receive blood at the same time
Final ones that feed into capillaries are arranged in parallel
What does the total blood flow through all the arterioles equals
The cardiac output
What does flow for each arteriole depend on
The resistance
If arteriole constricts resistance increases and blood flow decreases
How does arterioles take path of least resistance
Diverts away from high resistance arterioles towards low resistance ones
What is blood flow in 4 equal vessels where all are same size with same resistance
Equal blood flow
Total flow in equals total flow out
What does the CNS coordinate in cardiovascular function
Coordinates reflex control of blood pressure and distribution of blood to tissues
What’s the main integrating centre of cardiovascular function in CNS
Medullary cardiovascular control center (CVCC)
What is CVCC
Main output region where parasympathetic and sympathetic outputs go to CV tissues and can change HR, SV, level of resistance
What is primary function of CVCC
Ensures adequate blood flow to brain and heart by maintaining sufficient mean arterial pressure at all times
How does CVCC work
Receives input from sensory receptors and other brain regions and has ability to alter function in a few organs or tissues
E.g., thremoregulatory centres in hypothalamus altering skin blood flow
Baroreceptor reflex from CVCC
Primary reflex pathway for homeostatic control of mean arterial blood pressure
Ensures adequate pressure to pump blood to brain
What are baroreceptors
Tonically active stretch sensitive mechanoreceptors that are situated on aorta and carotid artery
When do baroreceptors increase firing rate
When increase in BP and they sense stretch in artery walls
When do baroreceptors cause decrease in firing rate
Decreased BP
How quickly does baroreceptor reflex happen
Very rapidly, within a few heart beats
Local control of constricted arteriole causes
Increased resistance -> increased TPR
Increase TPR x same CO = increase MAP
Increase MAP -> baroreceptors fire -> baroreceptor reflex
Reflex -> decrease CO x increase TPR = MAP restored to normal
Why does CO fall from 5L/min to 3L/min when stand up out of bed
Blood rapidly flows to lower extremities
How long does it take baroreceptors to be activated after standing in morning
Two heart beats activation increases CO and peripheral resistance to increase MAP
Why does baroreceptor reflex not work after extended bed rest
Unable to return MAP due to loss of blood volume
