HUBS192 Lecture 33 - Renal Physiology: Body Water - Distribution and Regulation Flashcards
what drives and regulates body water homeostasis?
- distribution of body water
- osmolarity/tonicity of solutions
- reabsorption of water in the nephron
- changes in body osmolarity
- effects of osmotic changes in the kidney
how many percent of our total body weight (TBW) is water?
55-60%
how much of our total body weight (TBW) water is stored in the intracellular fluid (ICF)?
2/3
how much of our total body weight (TBW) water is stored in the extracellular fluid (ECF)?
1/3
how much of the water stored in the extracellular fluid (ECF) is stored as plasma?
1/5
how much of the water stored in the extracellular fluid (ECF) is stored as interstitial fluid?
4/5
what is osmolarity based on?
based on the number of osmotically active ions or solutes
what molecules determine osmolarity?
- Na+
- CI-
- H2O
how can osmolarity be estimated?
can be estimated by specific gravity (density of solutions)
what is iso-osmotic?
same osmolarity solutions
what is hypo-osmotic?
low osmolarity solutions
what is hyper-osmotic?
high osmolarity solutions
what is tonicity based on?
based on the effect of a solution on cells
what is an isotonic solution?
a solution that does not change water homeostasis between cells
what is the relationship between the composition of ECF, ICF and osmolarity?
no matter what the composition of ECF and ICF, osmolarity will always be in balance (have the same values for both ECF and ICF)
does total body water remain constant?
yes, total body water remains relatively constant
what are the 4 important places within the nephron where Na+ is reabsorbed?
1) proximal convoluted tubule (PCT)
2) the nephron loop
3) distal convoluted tubule (DCT)
4) collecting duct (CD)
where is 67% of the filtered load of Na+ reabsorbed in the nephron?
in the proximal convoluted tubule (PCT)
where is 25% of the filtered load of Na+ reabsorbed in the nephron?
in the nephron loop
where is 5% of the filtered load of Na+ reabsorbed in the nephron?
in the distal convoluted tubule
where is 3% of the filtered load of Na+ reabsorbed in the nephron?
in the collecting duct
how much percent of the filtered load of Na+ reabsorbed in the nephron is reabsorbed in the proximal convoluted tubule?
67%
how much percent of the filtered load of Na+ reabsorbed in the nephron is reabsorbed in the nephron loop?
25%
how much percent of the filtered load of Na+ reabsorbed in the nephron is reabsorbed in the distal convoluted tubule?
5%
how much percent of the filtered load of Na+ reabsorbed in the nephron is reabsorbed in the collecting duct?
3%
how much percent of the sodium excreted goes back into our system and why?
99% for blood pressure control - keep it constant
what are the 3 important places within the nephron where water is reabsorbed?
1) proximal convoluted tubule (PCT)
2) distal late part of the distal convoluted tubule (tDLH)
3) collecting duct (CD)
where is 67% of the filtered load of water reabsorbed in the nephron?
in the proximal convoluted tubule
where is 25% of the filtered load of water reabsorbed in the nephron?
in the distal late part of the distal convoluted tubule
where is 2-8% of the filtered load of water reabsorbed in the nephron?
in the collecting duct
how much percent of the filtered load of water reabsorbed in the nephron is reabsorbed in the proximal convoluted tubule?
67%
how much percent of the filtered load of water reabsorbed in the nephron is reabsorbed in the distal late part of the distal convoluted tubule?
25%
how much percent of the filtered load of water reabsorbed in the nephron is reabsorbed in the collecting duct?
2-8%
what is water reabsorption in the proximal convoluted tubule (67% of the filtered load) driven by?
driven by Na+ reabsorption
what 2 things is water reabsorption facilitated by?
1) aquaporins (trans-cellular)
2) leaky tight junctions (paracellular)
what uses the sodium gradient to reabsorb glucose?
transporters such as the sodium gluclose-cotransporter
what is the permeability of the nephron loop?
permeability is low
what are red blood cells dependant on?
dependant on an isotonic environment
what is the range of osmolarity of ICF/ECF?
275-295 mosmol/L
what is the process of regulation of total body water changes altering the plasma (ECF) osmolarity?
- detected by osmoreceptors in the hypothalamus
- stimulates the pituitary gland to secrete more/less ADH
- ADH alters the permeability of renal collecting duct (CD)
what are the 2 major stimuli for the release of ADH from the posterior pituitary gland?
1) increased ECF osmolarity
2) decreased blood volume
what are the 2 actions from the release of the ADH hormone from the posterior pituitary gland?
1) inserts water channels (aquaporins) in the luminal membrane of the collecting duct
2) increases water reabsorption in the collecting duct
what is obligatory water reabsorption?
not regulated and accounts for 92% of total water reabsorption
what is facultative water reabsorption?
regulated by ADH through tight epithelia that is only transcellular and accounts for 2-8% of total water reabsorption
