L12. Blood Pressure Control and Hypertension Flashcards
What is the major mechanism for the circulatory system for measuring its cardiac output? What are the other means?
Blood pressure is the main readout
In desperate times, it can also use readings of pH, PCO2 and PO2
How is blood pressure and cardiac output controlled?
Mainly neurally in the brainstem centres
What is the baroreceptor reflex and what does it control?
A reflex mechanism that maintains blood pressure homeostasis.
A negative feedback system
What are the sensors of the baroreceptor reflex? And how do they relay information back?
Arterial baroreceptors in the carotid sinus and aortic arch and preglomerular arterioles
They sense changes in pressure (by stretch) and convey messages to the autonomic centres of the brain. (They are continuously firing information and and CHANGE in firing is interpreted as a rise or fall of blood pressure)
Where is the brainstem cardiovascular control centre?
In the medulla of the brainstem which has processor and depressor centres in it
What is the sympathetic and parasympthathetic innervations of the medullary cardiovascular control centres?
Sympathetic: Increases HR and decreases conduction time, increases contractility (increase intracellular Ca) and increases TPR (vasoconstriction) and increases venous tone (increaes venous return)
Parasympathetic: reduces HR and increases conduction time.
The baroreceptor reflex acts as a buffer. Explain this statement
The baroreceptor reflex is set to a small range of blood pressures and any ranges outside this, the reflex is caused to act to return it to the set range.
It also smooths out the large variations in pressure
Dennervating it = loose the control
Can the baroreceptor threshold change?
Yes, it is able to reset to new pressures but takes 1-2 days of adjustment
What range does the baroreceptor become silent to the brain? Why is this so?
When pressure reaches below below 60 mmHg (very dire and low) and the silence signals to the brain that there is not enough delivery of flow.
At this point the PO2 and PCO2 levels dramatically change and these chemoreceptors take over in sensing
What are the chemoreceptors, where are they located?
Respond to very low O2 concentrations and are located in the carotid and aortic bodies just outside the arteries. And are stimulated at low Mean Arterial Pressures
What does the blood pressure distribution (among the population) look like
Unimodal but not symmetrical (tends to skew towards the upper end)
How does blood pressure distribute in the population?
Men > Women
Age > young
Large body size > smaller
How does systolic and diastolic pressure change with age?
Both increase with age
Diastolic tends to plateau out earlier (meaning that pulse pressure rises) this is due to a decreasing compliance of the arteries with age (especially atherosclerosis)
Is there dirunal variation in BP?
Yes:
Lower at night (by about 20 mmHg) with less variability
There is less sympathetic activity at night: the renin angiotensin system takes over the majority of control at night
What is the definition of hypertension?
Systolic pressure > 140 mmHg
Not necessarily disease state (operational definition)
