Lecture 35 4/9/24 Flashcards
Which types of control mechanisms are in place around tubular reabsorption?
-nervous
-hormonal
-local
What is an important feature of tubular reabsorption?
reabsorption of some solutes can be regulated independently of others, esp. through hormonal control systems
What is glomerulotubular balance?
intrinsic ability of the tubules to increase their reabsorption rate in response to increased tubular load
Why does the percentage of GFR reabsorbed in the proximal tubule remain constant when filtered load increases?
because rate of reabsorption also increases
Besides the proximal tubule, which other segment of the nephron also sees a degree of glomerulotubular balance?
Loop of Henle
What is the overall goal of glomerulotubular balance?
prevent overloading of the distal tubular segments when GFR increases
Why is it important that glomerulotubular balance and tubuloglomerular feedback work together?
they both work to prevent changes in GFR from dramatically changing urine output
What percent of water and solutes is normally reabsorbed?
99%
What is the normal rate of peritubular capillary reabsorption?
124 ml/min
Which two determinants of peritubular capillary reabsorption are directly influenced by renal hemodynamic changes?
-hydrostatic pressure of the peritubular capillaries
-colloid osmotic pressure of the peritubular capillaries
How is peritubular capillary hydrostatic pressure influenced by arterial pressure?
increases in arterial pressure tend to raise peritubular capillary hydrostatic pressure and decrease reabsorption rate
How is peritubular capillary hydrostatic pressure influenced by afferent and efferent arteriole resistance?
increased resistance of the afferent or efferent arterioles reduces peritubular capillary hydrostatic pressure and increases reabsorption rate
Which factors influence the peritubular capillary oncotic pressure?
-systemic plasma colloid osmotic pressure
-filtration fraction
What are the characteristics of filtration fraction?
-the higher the filtration fraction, the greater the fraction of plasma filtered through glomerulus
-protein in the plasma left behind is more concentrated
What is filtration fraction?
GFR/RPF
How does angiotensin II raise filtration fraction?
by decreasing RPF
How do changes in the peritubular capillary physical forces influence tubular reabsorption?
by changing the physical forces in the renal interstitium
What is the net movement of water and solutes with the normal, high rate of peritubular capillary reabsorption?
net movement into the peritubular capillaries, with little back leak into the tubule lumen
What happens when peritubular capillary reabsorption is reduced?
-increased interstitial fluid hydrostatic pressure
-tendency for greater amounts of solute and water to leak back into tubular lumen
-reduced rate of net reabsorption
What is pressure natriuresis?
increased sodium excretion with increased arterial pressure
What is pressure diuresis?
increased water excretion with increased arterial pressure
Why does urine output increase when systemic blood pressure increases?
-increased GFR
-slight increase in peritubular capillary and hydrostatic pressure
-decreased angiotensin II formation
-internalization of Na transporter
What is the site of action for aldosterone?
collecting tubule and duct
What are the effects of aldosterone?
-increased NaCl and H2O reabsorption
-increased K+ and H+ secretion
What are the sites of action for angiotensin II?
-proximal tubule
-thick ascending LOH/distal tubule
-collecting tubule
What are the effects of angiotensin II?
-increased NaCl and H2O reabsorption
-increased H+ secretion
What is the site of action for ADH?
distal tubule/collecting tubule and duct
What is the effect of ADH?
increased H2O reabsorption
What is the site of action for atrial natriuretic peptide?
distal tubule/collecting tubule and duct
What is the effect of atrial natriuretic peptide?
decreased NaCl reabsorption
What are the sites of action for parathyroid hormone?
-proximal tubule
-thick ascending LOH/distal tubule
What are the effects of parathyroid hormone?
-decreased PO4- reabsorption
-increased Ca++ reabsorption
Which mechanisms are used by aldosterone?
-stimulation of Na+/K+ pump
-insertion of epithelial sodium channels
What are the most important stimuli for aldosterone?
-increased extracellular potassium conc.
-increased angiotensin II levels
How does aldosterone act on principal cells?
-stimulates Na+/K+ pump
-increases Na+ permeability while K+ diffuses out
How does aldosterone act on alpha intercalated cells?
stimulates H+ ATPase pumps to increase H+ secretion
How does aldosterone act on beta intercalated cells?
stimulates HCO3-/Cl- exchangers to increase HCO3- secretion and Cl- reabsorption
What would be seen on a chemistry panel that would indicate Addison’s disease/deficit of aldosterone?
-low Na+
-high K+
-Na+/K+ ratio below 27:1
What would be seen on a chemistry panel that would indicate hyperadolsteronism?
-high Na+
-low K+
When does angiotensin II formation increase?
-low blood pressure
-low extracellular fluid volume
What are the functions of angiotensin II?
-stimulates aldosterone release
-constricts efferent arterioles
-directly stimulates Na+ reabsorption
What are the angiotensin II mechanisms of action?
-stimulates Na+/K+ ATPase pump
-stimulates Na+/H+ exchanger
-stimulates Na+/HCO3- co-transporter
When is ADH released?
in response to increased extracellular osmolarity
What are the mechanisms of action for ADH?
-binds receptors that stimulate cAMP activation of protein kinase A
-stimulates movement of aquaporins to luminal membranes
-forms channels for water to enter cells
What are the two types of diabetes insipidus?
-lacking ADH secretion
-defect in renal receptors for ADH
When is atrial natriuretic peptide released?
when specific cells of the cardiac atria undergo increased stretch/experience increased blood volume
How does ANP act on the body?
-systemic vasodilation
-inhibits renin secretion and angiotensin II/aldosterone formation
-increases GFR and filtration fraction
-increases water excretion and reduces blood volume
What are the mechanisms of action for parathyroid hormone?
-increased distal tubular reabsorption of Ca2+
-decreased proximal tubular reabsorption of P
-stimulates Mg2+ reabsorption
What are the roles of the alpha adrenergic receptors in the kidney?
-alpha1-AR stimulates renal vasoconstriction
-alpha2-AR is responsible for Na+ reabsorption
What are the roles of the beta adrenergic receptors in the kidney?
-beta1-AR and beta2-AR regulate renal blood flow, GFR, Na+ and H2O reabsorption, acid-base, and renin secretion
-beta3-AR regulates renal water and solute reabsorption
What happens when the sympathetic nervous system is activated?
-constriction of renal arterioles
-reduced GFR and RPF
-increased sodium reabsorption
-increased renin release and angiotensin II formation
