Renal 5 - Regulation of Tubular Reabsorption Flashcards
what is tubular reabsorption controlled by
local control mechanisms, nervous system and endocrine system
what are the local control mechanisms of tubular reabsorption
-tubuloglomerular feedback (TGF)
- glomerulotubular balance (GTB)
-pressure natriuresis/diuresis
what hormones control tubular reabsorption
- aldosterone
-ANG II - ADH
-ANP
-PTH
what division of the nervous system regulates tubular reabsorption
sympathetic nervous system
what does the TGF response do
autoregulation of GFR to keep it constant
what does the TGF response consist of
afferent and efferent arteriolar resistance related to flow rate of NaCl by macula densa
what does the GTB regulate
autoregulation of PT reabsorption rate related to tubular load
in GTB, as tubular load increases, the rate of reabsorption _____
increases
what does GTB depend on
changes in peritubular capillary and renal interstitial fluid starlings forces
what do TGF and GTB do together
prevent overloading of the distal tubule segment when GFR increases due to pressure changes or other disturbances
-assures homeostasis is maintained
what can small changes in MAP do to Na+ and water excretion
can cause large increases in their excretion
what do pressure natriuresis and pressure diuresis do
assure that large changes in salt and water intake only cause small changes in ECF volume, CO and MAP
what are the stimuli for aldosterone
-high [ANG II] in ECF
- high [K+] in ECF
- low blood pressure
- low Na+
what are the effector responses for aldosterone
-stimulates Na+ reabsorption
- stimulates K+ secretion
-increases H+ secretion by intercalated cells of late distal and cortical collecting tubule: excess aldosterone may cause metabolic acidosis
- increases Na+ reabsorption and K+ secretion by sweat and salivary glands
- increases Na+ absorption by intestine
what cells does aldosterone act on
principal cells
describe the response from aldosterone and why
slow onset long duration because it involves gene expression (slow onset) and circulates bound to plasma proteins so it lasts longer
what would cause a decrease in aldosterone secretion
- ANP via decreased renin secretion
- increased Na+ concentration
- high blood pressure
what does ANG II do
major regulator of Na+ and water reabsorption
what are the stimuli for renin secretion
-decreased MAP
- decreased ECF volume
- decreased filtrate flow rate to macula densa
- increased sympathetic activity
what inhibits renin secretion
increased ANP
where does ANG II action occur
in most nephron segments
what are the effector responses for ANG II
-stimulates aldosterone production and secretion from zona glomerulosa
- directly increases Na+ reabsorption
- increases H+ secretion
- constricts efferent arterioles and increases GFR
- constricts systemic arterioles, increasing TPR and MAP
what does ADH do
increases water reabsorption in the apical membrane in the late distal tubule and collecting duct
what are factors that stimulate ADH secretion
- increased ECF osmolarity
- decreased blood volume via decreased ANP
- decreased blood pressure via decreased baroreceptor activity
- nausea
-hypoxia - nicotine and morphine
-ANG II
what factors decrease ADH secretion
- decreased ECF osmolarity
- increased blood volume via increased ANP
- increased BP via increased baroreceptor activity
- ethanol
-cold
what are the mechanisms of action of ADH
- increases water permeability via activation of Galpha s protein linked receptor
- activates cAMP
-increases the synthesis and insertion of AQP-2 into apical membrane
what does ANP do
increases GFR and decreases Na+ reabsorption and increases Na+ excretion
what is the stimulus for ANP
secreted by cardiac atria in response to stretch from increased blood volume
what are the effector responses of ANP
- directly inhibits Na+ and water reabsorption in PT
- increases GFR by dilating afferent arterioles and constricting efferent arterioles
- inhibits renin release and aldosterone formation
- helps minimized blood volume expansion
what does the sympathetic nervous system do in tubular reabsorption
-decreases Na+ and water excretion by:
-constricting arterioles
-stimulates renin release
-decreases GFR and renal blood flow
- directly stimulates Na+ reabsorption via alpha receptors on tubule epithelial cells in PT and TAL
what is total body calcium and where is it stored and how much in each
- 1100 g
- 99% bones
- 0.1% ECF
- 1 % ICF
what is Ca++ critical for
-normal cell function
- neural transmission
- membrane excitability
- bone structure
- blood coagulation
- intracellular signaling
what form of calcium is most important for functions in the body
ionized
describe the renal processing of Ca++
60% of plasma calcium filtered
- 65% of filtered calcium reabsorbed in PCT
- 25-30% reabsorbed in loop of henle
- 4-9% reabsorbed in distal and collecting tubule
-1% excreted
where does PTH regulate Calcium in the nephron
in TAL and DT
what mechanism does PTH affect calcium reabsorption
only transcellular
what percentage of calcium is reabsorbed by transcellular and paracellular transport
50% each
what promotes passive paracellular movement of calcium
the +8 mV luminal charge
