*Physiology 5 (lecture 5) Flashcards
What is the total body fluid made up of?
Intracellular fluid (2/3rds) and extracellular fluid (1/3rd)
What makes up the extracellular fluid?
Plasma volume + interstitial fluid volume
What happens if the plasma volume falls?
Compensatory mechanisms shifts fluid from the interstitial compartment to the plasma compartment
What are the 2 main factors that affect extracellular fluid volume?
Water excess or deficit
Na+ excess or deficit
How does the body control the extracellular fluid volume (water excess/ deficit and Na+ excess and deficit) therefore controlling MAP? (2)
Hormones act as effectors to regulate the extracellular fluid volume (including plasma volume) by regulating the water and salt balance in our bodies
Healthy people stay in a stable water and salt balance, where water input = water output
What 3 hormones/ systems regulate extracellular fluid volume?
The renin-angiotensin-aldosterone system Atrial natriuretic peptide (ANP) Antidiuretic hormone (arginine vasopressin) -ADH
What are the 3 important components of the Renin-angiotensin-aldosterone system (system helps to regulate plasma volume and TPR ad hence the regulation of MAP)?
Renin
Angiotensin
Aldosterone
Where is renin released?
What does it do?
Kidney
Stimulates the formation of angiotensin I in the blood from angiotensinogen (produced by the liver)
What happens to angiotensin I once it is produced?
It is converted to angiotensin II by angiotensin converting enzyme (ACE) which is produced in the pulmonary vascular endothelium
What does angiotensin II do?
Stimulates the release of aldosterone from the adrenal cortex Causes vasoconstriction (increases TPR and therefore BP) Causes increased ADH release and increased thirst (Increased plasma volume = increased BP)
When is renin released form the kidney?
When plasma volume drops causing a drop in blood pressure
What effects does aldosterone have?
Causes increased sodium and water reabsorption in the kidneys
Causes an increased plasma volume
Causes an increased blood pressure
What is the rate limiting step in the RAAS?
Renin secretion
What 3 factors cause renin release?
Renal artery hypotension (caused by systemic hypotension)
Stimulation of renal sympathetic nerves
Decreased [Na+] in renal tubular fluid (sensed by macula densa)
what in the renal tubules senses decreased [Na+]?
Macula densa
What synthesis and stores the atrial natriuretic peptide?
28 amino acid peptide synthesised and stored by atrial muscle cells
When is atrial natriuretic peptide released?
In response to atrial distension
Causes excretion of salt and water in the kidneys thereby reducing blood volume and blood pressure
Acts as a vasodilator
Decreases renin release
What is another name for ADH?
Vasopressin
Where is ADH synthesised and stored?
Synthesised by the hypothalmus and stored in the posterior pituitary
What stimulates secretion of ADH?
Reduced extracellular fluid volume
Increased extracellular fluid osmolarity (main stimulus)
How is plasma osmolarity monitored?
By osmoreceptors mainly in the brain in close proximity to the hypothalamus - increased plasma osmolarity will stimulate release of ADH
Where does ADH act?
In the kidney tubules to increase the reabsorption of water
This leads to an increase in extracellular and plasma volume and hence cardiac output and blood pressure
ADH also acts on blood vessels to cause vasoconstriction
What is short term moment to moment control of MAP achieved rapidly by?
Baroreceptors reflex
What is long term control of MA achieved by?
Control of blood volumes by hormones
