Lecture 7 - ECF Volume Regulation 1 and 2 Flashcards
What ions are the major ECF osmoles?
Na Cl
What substance is the major ICF osmole?
K salts
How is regulation of ECF volume carried out?
By regulating body Na
Describe the total distribution of body water between: Plasma Interstitial fluid ICF
Plasma - 3L Interstitial fluid - 11L ICF - 28L (1/3 ECF, 2/3 ICF) TBW = 42L
Changes in sodium content of ECF lead to what?
Changes in ECF volume –> affects vol of blood perfusing the tissues = effective circulating volume + therefore BP So regulation of Na basically dependent on high and low P baroreceptors
What is the renal response to hypovolaemia?
inc. salt and water loss (e.g. diarrhoea, vomiting, xs sweating) –> dec. plasma volume –> dec. venous pressure –> reduced venous return –> decreased atrial pressure –> dec. end diastolic volume –> dec. stroke volume and CO –> reduced BP –> reduced carotid sinus baroreceptor inhibition of sympathetic discharge –> inc. sympathetic discharge –> increased vasoconstriction –> inc. total peripheral resistance –> inc. BP towards normal
What does the increased sympathetic discharge caused by hypovolaemia lead to in the kidneys?
Increased renal arteriolar constriction + increase in renin
What does an increase in renin lead to?
Increased angiotensin II –> reduced peritubular hydrostatic P (and oncotic pressure increases) so less Na is excreted –> inc. angiotensin II –> inc. aldosterone –> increased DCT Na reabsorption so less Na excreted
What type of cells are juxtaglomerular cells?
Specialised smooth muscle cells
What hormone do the juxtaglomerular cells release?
Renin
When do the juxtaglomerular cells release renin?
- When BP is low 2. Sympathetic nerve stimulation 3. Macula densa cells send message to JG cells via prostaglandins if low Na concentration in DCT
What are the macula densa cells?
Cells in the distal convoluted tubule that sense sodium In low BP, less blood is moving through the nephron so less salt is reabsorbed
What is the liver’s role in the RAAS?
Produces angiotensinogen
What happens when renin meets angiotensinogen?
Renin cleaves angiotensin to make it angiotensin I
What happens to angiotensin I in the RAAS?
Endothelial cells lining BVs (esp in the lungs) produce angiotensin converting enzyme which converts angiotensin I to angiotensin II
What are the actions of angiotensin II?
- Smooth muscle cells in BVs constriction (v. potent vasoconstrictor) 2. Makes kidney cells hold on to more water 3. Pituitary produces ADH –> collecting duct + increases water reabsorption 4. Adrenal gland - produces aldosterone 5. Stimulates thirst mechanism and salt appetite
What are the actions of aldosterone?
Increases tubular Na and Cl reabsorption, water retention and K excretion
Why is oncotic pressure increased in hypovolaemia and why is this beneficial?
Less water/NaCl in the arterioles therefore oncotic pressure is higher Means we can reabsorb even more of the filtrate at the PCT (75% compared with 70% in normovolaemia)
GFR remains largely unaffected until what?
There is a SUBSTANTIAL drop i MBP
What is the function of aldosterone?
Regulation of distal tubule Na reabsorption
Where are the juxtaglomerular cells located?
They are smooth muscle cells of the afferent arteriole just before it enters the glomerulus
With which cells are the JG cells closely associated?
A specialised loop of the distal tubule containing macula densa cells
What is the juxtaglomerular apparatus?
Macula densa + JG cells

How many peptides make up angiotensin I?
10