ECF Volume Regulation Flashcards
What is one of the most important aspects of the ECF regulated by the kidney?
Volume
Why is the distribution of TBW between the cells and the ECF determined by the number of active osmotic particles in each compartment?
H2O can freely cross all cell membranes so the body fluids are in osmotic equilibrium
What are the major ECF osmoles?
Na and Cl
What are the major ICF osmoles?
K salts
What is regulation of ECF volume regulated by?
Regulation of body Na
How is water distributer within the body?
Water= 60% TBW=42l
- ICF= 2/3= 28l
- ECF=1/3 =14l
- Plasma accounts for 3l and interstitial fluid accounts for 11l of the ECF
How do changes in Na content of the ECF affect BP?
Changes in Na+ content of the ECF will lead to changes in ECF volume and therefore will affect the volume of blood perfusing the tissues determining effective circulating volume and therefore BP.
What is regulation of Na basically dependent on?
High and low pressurebaroreceptors
Hypovolaemia?
Low ECF volume
What happens to the body in hypovolaemia?
- Increases in salt and H2O loss
- Decrease in pulse volume
- Decrease in venous pressure
- Decrease in venous return
- Decrease in atrial pressure
- Decrease in End diastolic volume
- Decrease in stroke volume
- Decrease in cardiac output
- Decrease in BP
- Decrease in carotid sinus baroreceptor inhibition of sympathetic discharge
How does the body compensate for hypovolaemia?
- Decreases carotid sinus barocreceptor inhibition of sympathetic discharge leads to increased sympathetic discharge
- Increase VC
- Increase TPR
- Increase BP towards normal
Give examples when there might be increase salt and water loss?
- Vomiting/diarrhoea
- Excess sweating
How does the renal system respond to comepensation for hypovolaemia?
- Increase ADH
- Increases renal arterial constriction
- Increases renin
- Increase angiotensin II
- Increased NaCl and H2O reabsorption in proximal tubule
- Increased aldosterone which increases NaCl and H2O reabsorption in the distal tubule
What effect does increased renin have on the proximal tubule of the kidney?
- Increases angiotensin II
- Decreases peritubular capillary hydrostatic pressure (+ the osmotic pressure)
- Increased Na reabsorption from the proximal tubule and less Na excreted
What effect does renin have on the distal tubule of the kidney?
- Increased renin
- Increased angiotensin II
- Increased aldosterone
- Increased distal tubule Na reabsorption and less Na excreted
What is the sympathetic discharhe on the kidney determined by?
Osmotic pressure
What are changes in proximal tubule Na reabsorption due to?
Changes in the rate of uptake by the peritubular capillaries
What are increases in Na reabsorption due to?
Greater reabsorptive forces in the peritubular capillaries
What is the reabsorptive range of the proximal tubule?
- 65% in volume excess
- 75% in volume deficit.
- Big range of volume just because of changes in Starling’s forces.)
Why is GFR largely unaffected by changes in ECF?
Autoregulation maintains GFR and the VC of afferent and efferent means little effect on GFR until volume depletion severe enough to cause considerable decrease in MBP.
What maintains GFR in ECF loss?
- Constriction of afferent due to sympathetic VC
- Constriction of efferent mediated by angiotensin II
What is regulation of distal tubule Na reabsorption under control of?
Adrenal cortical steroid hormone aldosterone
What hormone is very important in the long-term regulation of Na and ECF volume?
Aldosterone
What is aldosterone secretion controlled by?
Reflexes involving the kidneys themselves
What cells are present in the smooth muscle media of the afferent arteriole just before it enters the glomerulus?
Juxtaglomerular cells (JG): specialized, containing large epithelial cells with plentiful granules
What are the 2 components of the juxtaglomerular apparatus?
- Juxtaglomerular cells
- Macula densa
What are the JG cells closely associated with?
A histologically specialized loop of the distal tubule known as the macula densa
What do JG cells produce?
Renin
What is renin?
A proteolytic enzyme which acts on a large protein in the 2-globulin fraction of the plasma proteins known as angiotensinogen.
What does renin do the angiotensinogen?
Renin splits off the decapeptide angiotensin I which is then converted by enzymes in the endothelium to the active octapeptide = angiotensin II