Urinary S3 - Renal Control of BP, Cardiac Output & Plasma Volume Flashcards
What happens as a result of increased ECF volume? How does the kidney respond?
BP and blood volume increases
Oedema may occur
Low pressure baroreceptors would detect this and cause ADH secretion to be reduced
Therefore sodium excretion from the kidneys would increase and water would follow
Homeostasis is maintained
What is positive sodium balance? What are the effects?
When sodium excretion<intake
NA ions are retained in the ECF
ECF volume increases
What is negative sodium balance? What are the effects?
When excretion>intake
Therefore reduced ECF sodium ion content
So reduced ECF volume as water follows osmotic gradient
What happens as a result of decreased ECF volume? How does the kidney respond?
Reduced BP and blood volume
This is detected by low pressure baroreceptors
This causes increased ADH secretion
Therefore increased sodium retention by the kidneys
Therefore increased water follows sodium and emails in the body
Thirst is also triggered
Homeostasis is maintained
Where are high pressure baroreceptors found?
Carotid sinus
Aortic arch
(Aka the arterial side of the circulatory system)
Where are low pressure baroreceptors found?
Atria
Pulmonary vasculature
(Aka venous/high-compliance side of the circulatory system)
What nerves do high pressure baroreceptors use to communicate with the brainstem?
Afferent fibres of the vagus nerve
Glosopharyngeal nerve
What nerves do low pressure baroreceptors use to communicate with the brainstem?
Vagus nerve
What is the pressure difference required to cause baroreceptors to fire?
Usually 5-10% decrease in pressure of either high or low pressure baroreceptors is sufficient
What are the effects of baroreceptors impulses?
They cause:
Increased sympathetic outflow from the brainstem
Increased ADH secretion
What controls systemic BP?
Cardiac output and total peripheral resistance (CO&TPR)
How is BP controlled in the short term?
Via the baroreceptor reflex
How is BP controlled in the longer term?
Largely by the kidneys. These regulate body fluid volumes, therefore circulatory volume and cardiac output. The RAAS system has a huge effect and is controlled by the kidneys
What affects the rate of renin secretion?
> The intra-renal baroreceptor system: a drop in pressure causes juxtoglomerular cells to release renin
The rate of transport of Na and Cl ions across the macula densa: the higher the rate, the lower the rate of renin secretion
What are the effects of angiotensin II?
EXTREMELY potent vasoconstrictor acting on smooth muscle, primarily arteriolar (increasing TPR) Stimulates production and secretion of aldosterone from adrenal glands (increasing salt&water retention so blood volume so CO) Thirst (increasing blood volume so CO) ADH secretion (increasing salt&water retention so blood volume so CO)
