RP5: Regulation of Tubular Reabsorption Flashcards
What are the local control mechanisms for tubular reabsorption?
➢ Tubuloglomerular Feedback Response (TGF)
➢ Glomerulotubular Balance (GTB)
➢ Pressure natriuresis/diuresis
What is the tubuloglomerular feedback response (TGF)?
Autoregulation of GFR.
➢ Keeps GFR constant
➢ Afferent and Efferent arteriolar resistance related to flow rate of NaCl by macula densa
➢ Example: GFR increase-increased NaCl to macula densa- TGF response decreases GFR
What is the glomerular tubule balance (GTB)?
Autoregulation
of PT reabsorption rate
➢ PT reabsorption rate related to tubular load
➢ As tubular LOAD increases, rate of REABSORPTION increases.
➢ Depends on changes in peritubular capillary and renal interstitial fluid Starling’s forces.
➢ Example: GFR increase-GT balance increases PT Na+/H20 reabsorption to maintain Na+/H20 balance
What do TGF and GTB together prevent?
prevent overloading of the distal tubule segment when GFR increases due to pressure changes or other disturbances
What does pressure natriuresis ensure?
assure that large changes in salt and water intake accommodated with only minor changes in ECF volume, CO, and MAP
What are the systemic control hormones that regulatetubular reabsorption?
aldosterone
angiotensin II
antidiuretic hormone (ADH)
atrial natriuetic peptide (ANP)
What is the local effector response of aldosterone?
➢ Stimulates Na+ Reabsorption
➢ Stimulates K+ Secretion
➢ Stimulates H+ Secretion
(α-Intercalated cells)
What is the systemic effector response for aldosterone?
➢ increase Na+
➢ decrease K+
➢ increase ECF pH
What controls the release of aldosterone?
Increase release of aldosterone
- increased Ang II
- increased K+
- increased H+
Decrease the release of aldosterone
- increased ANP
- increased Na (weak inhibitor)
What is the mechanistic explanation for why aldsterone has a slow onset and long duration response?
- slow onset since it takes 2 hours to change gene expression
- long duration since steroid hormones don’t like water so they are bound to proteins which increases their half-life
When is ANP secreted?
volume increases
What is aldosterone a regulator of?
ECF Osmolarity
What is angiotensin II a regulator of?
ECF volume, ECF osmolarity, and TPR
What is the local effector response for angiotensin II?
➢ Stimulates aldosterone production and secretion from Zona Glomerulosa.
➢ Directly increases Na+
reabsorption
➢ Increases H+ secretion
➢ Constricts efferent arterioles; increase GFR
➢ Constricts systemic arterioles
➢ Increases thirst
➢ Increases ADH Secretion
What is the systemic effector response for angiotensin II?
- increase ECF volume
- increase TPR
- increase MAP
- increase pH
What controls renin secretion which in turn controls angiotensin II secretion?
Increases renin/angiotensin II
- decreased MAP
- decreased blood volume
- decreased renal blood flow
- increased sympathetic activity
- decreased NaCl delivery to macular densa (TGF)
Decreases renin/angiotensin II
- increased ANP
What is ADH a regulator of?
ECF Volume and Osmolarity
What is the local effector response for ADH?
increased H2O Reabsorption in Distal nephron
What is the systemic effector response for ADH?
increased ECF volume
decreased ECF Osmolarity
increased MAP
What is the mechanism of ADH?
➢ Activation of Gαs Protein linked
receptor
➢ Increases the synthesis and insertion of AQP-2 into luminal membrane.
Where does ADH have effects in the nephron?
Late Distal Tubule
Collecting Duct
Where does aldosterone have effect in the nephron?
principal cell
alpha intercalated
Where does angiotensin II have effect in the nephron?
Prox tubule
TAL of Henle
distal tubule
collecting duct
What controls the secretion of ADH?
Increased secretion of ADH
- increase ECF osmolarity
- decreased blood volume
- decresead blood pressure
- nausea
- hypoxia
- nicotine and morphine
- angiotensin II
- ecstasy
Decreased secretion of ADH
- ethanol
- cold
What does atrial natriuretic peptide (ANP) regulate?
ECF volume
- only hormone we discussed that decreases blood pressure
What controls the secretion of ANP?
Increased secretion of ANP
- cardiac atria stretching due to blood volume increase
Decreased secretion of ANP
- decreased blood volume
What is the local effector response for ANP?
➢ Directly inhibits Na+ and H2O reabsorption in PT
➢ Increases GFR (dilates afferent, constricts efferent arterioles).
➢ Inhibits renin release and aldosterone formation.
➢ Helps to minimize blood volume expansion (CHF).
What is the systemic effector response to ANP?
- decreased ECF osmolarity
- decreased blood volume
Where does ANP have an effect in the nephron?
proximal tubule
What is aldosterone escape?
the sodium excretion returns to normal even though MAP is high
What causes aldosterone escape?
- increasing ANP
- increasing pressure natriuresis
Which disease is characterized by hyperaldosteronism?
Conn’s syndrome
What does the sympathetic nervous system regulate in the renal system?
ECF Volume and MAP
What is the local effector response of the sympathetic nervous system?
➢ Constricts arterioles
➢ Stimulates renin release.
➢ increases RAA and increases REA (Decreases GFR and
renal blood flow)
➢ Directly stimulates Na+ reabsorption via α receptors on tubule epithelial cells in PT and TAL.
What is the systemic effector response for the sympathetic nervous system?
- increased ECF volume
- increased TPR
- increased MAP
What increases the response of the sympathetic nervous system?
- decreased MAP
- increased stress
What is the effect of aldosterone?
↑ NaCl, H2O reabsorption
↑ K+ secretion
↑H+ secretion
What is the effect of angiotensin II?
↑ NaCl
↑ H2O reabsorption
↑ H+ secretion
What is the effect of ADH?
↑ H2O reabsorption
What is the effect of ANP?
↓ NaCl reabsorption
