Control of arterial BP part 2 Flashcards
What percentage of the body weight is water?
60%
Total body fluid equation?
Intracelullar (2/3) + extracellular fluid - normally 1/3 of the total
Extracellular Body fluid volume equation?
ECFV= Plasma volume + Interstitial fluid volume ECFV= PV + IFV
What is ECFV?
The fluid that bathes the cells and acts as the go between for the blood and the body cells
What happens if plasma falls?
Compensatory mechanisms shift fluid from interstitial compartment to plasma compartment
What else is controlled if ECFV is controlled?
MAP
Blood volume
20% of body weight is?
Extracellular fluid
40% of body weight is?
Intracellular fluid
Components of extracellular fluid?
3/14th plasma
11/14th Interstitial fluid
What 2 main factors affect our bodies extracellular fluid volume ECFV?
Water excess or deficit
Na+ excess or deficit
How do our bodies control the factors that affect our extracellular fluid volume?
Hormones act as effectors to regulate the ECFV by regulating the water and salt balance in our bodies
Healthy= water input=water output
Hormones which regulate the extracellular fluid volume?
The renin-angiotensin - aldosterone system (RAAS) Natriuretic Peptides (NPs) Antidiuretic hormone (Arginine Vasopressin) - ADH
Role of RAAS?
Important role in plasma volume regulation and SVR - hence the regulation of MAP
3 components of RAAS?
Renin
Angiotensin
Aldosterone
What is renin?
Renin is released from the kidneys and stimulates formation of angiotensin 1 in the blood from angiotensinogen (produced by liver)
Angiotensin 1 conversion?
Converted to angiotensin 2 by angiotensin converting enzyme- ACE
Where is angiotensin converting enzyme produced?
Mainly by pulmonary vascular endothelium
What does angiotensin 2 do?
-Stimulate the release of aldosterone from the adrenal cortex
- Causes systemic vasoconstriction -which increase SVR
- Also stimulates thirst and ADH release
Contributes to increasing plasma volume mainly by aldosterone
What does aldosterone do?
A steroid hormone which acts on kidneys to increase sodium and water retention- increase plasma volume
What is the rate limiting step for RAAS?
Renin secretion
What is the renin angiotensin aldosterone system regulated by?
Mechanisms which stimulate renin release from the juxtaglomerular apparatus in the kidney.
What does the mechanism that regulates RAAS involve?
1) Renal artery hypotension- caused by systemic hypotension (decreases blood pressure)
2) Stimulation of renal sympathetic nerves
3) Decreased [Na+] in renal tubular fluid - sensed by macula densa (specialized cells of kidney tubules)
What are natriuretic peptides?
Peptide hormones synthesized by heart (also brain and other organs)
When are natriuretic peptides released?
In response to cardiac distension or neurohormonal stimuli
What do NPs do?
- They cause excretion of salt and water in the kidneys thereby reducing blood volume and blood pressure.
- Decrease renin release- decrease BP
- Act as vasodilators; decrease SVR and BP
- Provide a counter regulatory system for the RAAS
How many types of natriuretic peptides are released by the heart?
2
The NPs released by the heart?
1) Atrial natriuretic pepide (ANP)
2) Brian-type natriuretic peptide (BNP)
What is ANP and when is it released?
28 amino acid peptide synthesized and stored by atrial
myocytes (Atrial muscle cells)
-Released in response to atrial distension (Hypervolemic states)
What is Brian-type natriuretic peptide?
32 amino acid peptide synthesized by heart, ventricles, brain and other organs
How is BNP first synthesized?
First synthesized as prepro-BNP (
then cleaved to Pro-BNP (108)
Then finally BNP (32)
What can be measured in patients with suspected heart failure?
Serum BNP
N-terminal piece of pro-BNP (NT- proBnp)
Where is ADH synthesized and stored?
Hypothalamus and stored in posterior pituitary
What is secretion stimulated by?
1) Reduced extracellular fluid volume
2) Increased ECF osmolality (main)
What does plasma osmolality indicate?
Relative solute-water balance
What is osmolality monitored by?
Osmoreceptors in brain in close proximity to the hypothalamus
What is ADH release stimulated by?
Increased plasma osmolality?
What does ADH do?
Acts in the kidney tubules to increase water reabsorption(conserves water) antidiuresis (concentrating urine
What does antidiuresis cause?
increased ECFV and plasma volume hence cardiac output and BP
How does ADH act on blood vessels?
Causes vasoconstriction which increases SVR and blood pressure- this effect is small in normal people but for people in hypovolaemic shock it becomes important (haemmorhaging people)
How is short term moment to moment control of MAP carried out?
Baroreceptor reflex (rapid)
Long term regulation of MAP is achieved by?
Control of Blood volume by hormones
Summary of what ADH does?
Regulates ECF including plasma volume and osmolality to deal with fluid loads/deficits
Role of Renin angiotensin aldosterone system?
Important role in long term regulation of MAP
Role of natriuretic peptides?
Act as counter-regulatory to RAAS
