Regulation Of ECF Flashcards
ECF osmolarity maintains…..while volume maintains…..
Cell size
Arterial blood pressure
Describe correction of hyper- or hyposmolarity
Hyper:
1. Stimulation of ADH secretion that will inc free water reabsorotion
2. Stimulation of thirst sensation that will inc water intake
Hypo is opposite
Describe peripheral mechanism of correction of osmolarity
Thirst is stimulated peripherally by a direct effect of dryness of mouth may be by nerve endings in mouth affecting thirst center, this also explains why thirst can be temporarily relieved by drinking before water reabsorption.
Describe conditions in change in ECF volume but not osmolarity
- Therapeutic IV injection of saline is associated with ECF volume inc (expansion) but the conc of solutes is still constant
- Hemorrhage or excess blood loss dec in volume but not osmolarity
Change in osmolarity occurs only with loss or gain of pure water
Why is the brain the most affected organ by inc osmolarity?
As the brain is enclosed in limited space (skull) so inc in osmolarity in ECF leads to brain cell shrinkage & dilatation of vessels which can rupture causing cerebral Hge
SKM can compensate for changes in osmolarity up to…..
20%
The portion of Na+ reabsorption subjected to hormonal regulation is….in……, controlled by…..
3%
late DCT & CD
Aldosterone & ANP
Na+ is NOT reabsorbed in….., while it is passively reabsorbed in……
Descending loop of Henle
Thin ascending LH
What are factors affecting Na+ urinary excretion?
- Amount of Na+ filtered controlled by regulating GFR
- The amount of Na+ reabsorbed (more IMP)
Main site for glomerulo-tubular balance is…..
PCT
List factors affecting Na+ reabsorption
- Glomerulo-tubular balance
- Peritubular capillaries physical forces
- Rate of tubular secretion of K & H
- Sympathetic renal nerve activity
- Hormones (RAAS & ANP)
Importance of glomeruli-tubular balance?
- Prevent overloading of DCT which would disturb its function
- Prevent inappropriate losses of Na+ & water in the urine
Describe action & mechanism of sympathetic renal nerve activity
It dec Na+ excretion in urine & inc its reabsorption
Mech:
1. Reduces GFR by constricting aff arterioles dec filtered load
2. Inc renin secretion, ang II, and aldosterone formation
3. Dec hydrostatic pressure in PTC thus inc Na+ reabsorption by 2&3
List actions of Ang II
- Causes VC
- Stimulates aldosterone & ADH secretion
- Stimulates thirst & salt appetite center
- Contraction of mesangial cells
- Inc Na+ reabsorption directly at PCT
Describe actions of ANP
- Inhibition of Na+ reabsorption in DCT & CD
- Inhibition of renin, aldosterone & ADH
- Increasing GFR through dilating aff arterioles & relaxing mesangial cells
Thus cause natriuresis & diuresis
GR: ADH & thirst have limited role in ECF volume regulation
Beccause it will be stimulated if volume dec by 10%. On the other hand, it is stimulated by 1% inc in osmolarity.
Mention homeostatic events that take place on changing ECF volume
If ECF volume dec, there is:
1. Dec GFR
2. Dec ANP & related peptides secretion
3. Dec discharge from high pressure & low pressure baroreceptors, inc sympathetic activation & inc thirst & ADH secretion
4. Activation of RAAS
5. Concentration of PPs which inc osmotic pressure & stimulates PCT Na+ reabsorption
Normal plasma Na is….., K is…..
135-145 mEq/L
3.5-5.5 mEq/L
Describe K reabsorption in thick ascending LH
25% of filtered K load is reabsorbed by:
1. Transcellular pathway via Na/K/2Cl cotransporter
2. Paracellular pathway due to inc luminal +ve charge
Describe role of late DCT & CD in K+ regulation with different levels in diet
- In normal & high K+ intake: K+ is secreted by principal cells. These cells posses basolateral Na+/K+ ATPase pump which creates a conc gradient that favors movement of K+ from cell to lumen
- In low K+ intake: K+ is reabsorbed by intercalated cells that posses H+/K+ ATPase that secretes H+ to lumen & reabsorb K+ in electroneutral fashion, its activity inc in K+ depletion.
List causes of hyperkalemia
- Cell lysis
- Hyperosmolarity
- Inhibition of Na/K pump (e.g. hypoxia)
- Acidosis
List causes of hypokalemia
- Stmulation of Na+/K+ pump (insulin, b-agonists)
- Alkalosis
List factors affecting K+ secretion & excretion
- Dietary K intake
- Aldosterone hormone
- Na+ reabsorption, as its amount reaching DCT inc, K secretion & excretion inc
- H+ reabsorption (compete for same transporter)
Ca reabsorption parallels that of……
Na+
The portion of Ca++ reabsorption that is subjected to hirmonal regulation is……in…..
8%
DCT
Serum phosphate is……
2.5-4.5 mg%
At the cellular level, phosphate is reabsorbed by…….
Na+-phosphate cotransporter
Compared to other electrolyte, a high portion of PO4- - is reabsorbed
15-20% of filtered load is excreted
Because un-absorbed phosphate serves as a urinary buffer for H+ (called titratable acid)
