2 renal phys review Flashcards
What are 5 major functions of the kidney?
- excretion of metabolic waste products and foreign chemicals
- regulation of arterial pressure
- secretion, metabolism, and excretion of hormones
- regulation of water, electrolyte, and acid-base balances
- gluconeogenesis
**Main Role= control volume and composition of the bodily fluids
Describe the distribution and major contents of body fluids (ICF/ECF)
- ICF
- 2/3 of total body water
- 40% of body weight
- K, PO4, protein
- ECF
- 1/3 of total body water
- 20% of body weight
- Na, Cl, HCO3
What is the average osmolarity of the body fluids?
ECF and ICF average 280-300 mOsm/L
What are the forces causing filtration by glomerular capillaries?
- Plasma
- glomerular hydrostatic pressure (60 outward)
- glomerular colloid osmotic pressure (32 inward)
- Bowman’s capsule
- hydrostatic pressure (18 into plasma)
- NO osmotic pressure (proteins not filtered)
- Ultrafiltration coefficient
- hydraulic permeability
- surface area of glomerular capillary membranes
What is the rate of plasma flow through afferent/efferent arterioles and a normal GFR?
- afferent= 700 ml/min
- GFR= 125 ml/min (~20% of efferent flow)
- efferent= 575 ml/min
How does chronic kidney disease affect filtration?
Glomeruli become sclerotic/fibrotic and unable to filter. This decreases the surface area available for filtration, decreasing the ultrafiltration coefficient
Increasing renal perfusion pressure from 100 mmHg to 130 mmHg will most likely…
Increase urine flow rate
(at normal pressure variation, renal blood flow and GFR remain fairly constan)
What are the mechanisms of GFR/RBF autoregulation?
-
myogenic mechanism (in all vessels)
- increased arterial pressure= increased stretch of vascular smooth muscle
- stretch elicits contraction, elevating vascular resistance, and maintaining blood flow/GFR
- F=P/R
- tubuloglomerular feedback (unique to kidney)
Describe the structure of the juxtaglomerular apparatus
Na sensing cells in the macula densa communicate with juxtaglomerular cells in the afferent arteriole (contrict aff art when increased NaCl delivery to MD)
Describe the mechanism of macula densa feedback
- elevated perfusion pressure, increases fluid filtration, increasing delivery of NaCl to the macula densa
- elicits increased vascular resistance of the afferent arteriole, decreasing flow
Describe the hormonal control of GFR (vasoconstrictors/dilators)
- vasoconstrictors (decrease GFR)
- NE
- epinephrine
- endothelin
- vasodilators (increase GFR)
- endothelial derived NO
- prostaglandins
- Ang II= no change because it affects both afferent and efferent arterioles (decreases GFR at pathological levels)
What are the 3 layers of the kidney’s filtration barrier?
- capillary wall (700 A fenestrations)
- basement membrane (IV collagen)
- podocytes (40x140 A slit pores)
**barrier is negatively charged (most proteins are neg and therefore are not permeable)
What are the main functions of the proximal tubule?
-
iso-osmotic reabsorption
- reabsorb 65% of Na, Cl, HCO3, and K
- reabsorb an equal amount of water!
- reabsorb essentially all the filtered glucose and AAs
- secrete organic acids, bases, and H ions
What diuretic works on the proximal tubule?
Carbonic anhydrase inhibitors (acetazolamide)
**Inhibits H secretion and HCO3- reabsorption (makes urine more basic, inhibits Na/H exchanger on apical membrane and decrease Na reabsorption)
Describe the absorption of various substances across the proximal tubule
What is the main function of the thin descending loop of Henle?
Reabsorption of water secondary to the cortical-medullary osmotic gradient
What are the main functions of the thin ascending loop of henle?
- passive reabsorption of sodium, dilution of tubular fluid
- secretion of urea
- IMPERMEABLE to water!
What are the main functions of the thick ascending loop of henle?
- reabsorbs 25% of filtered Na (Na/K/2Cl transporter)
- lumen positive potential (mostly from reabsorption of K+) drives paracellular reabsorption of Na, K, Mg, and Ca
- impermeable to water (dilutes tubular fluid)
What diuretic works on the thick ascending limb of henle?
Loop diuretics (furosemide, bumetanide, ethacrynic acid)
**inhibit Na/K/2Cl transporter, inhibiting ion reabsorption
What are the main functions of the early distal tubule?
- reabsorbs Na, Cl, Ca, and Mg
- Na/Cl symporter on apical membrane
- IMPERMEABLE to water
What diuretics work on the early distal tubule?
Thiazide diuretics
**inhibit Na and Cl reabsorption
What are the main functions of the principle cells of the late distal tubule/collecting duct?
- reabsorb Na, secrete K
- regulated by aldosterone
- water permeability regulated by ADH
What diuretics work in the principle cells (late distal tubule, collecting duct)?
- Aldosterone antagonists
- aka K sparing diuretics
- inhibit normal action of aldosterone (increasing Na+/K+ ATPase pump at the basolateral membrane and ENaC at the apical membrane)
- results in decreased reabsorption of Na
- Na channel blockers also work on this area
- amiloride, triamterene
- inhibit ENaC (K secretion, Na reabsorption)
What are the main functions of the medullary collecting duct?
- reabsorbs Na (similar to principle cells)
- ADH stimulate water reabsorption
- urea reabsorption
Where does aldosterone act? What is its function?
- primarily in the principal cells of the late distal tubule/collecting duct
- increases Na reabsorption, increases K secretion
Where does angiotensin II act? What is its function?
- primarily in the proximal tubule
- increases Na and water reabsorption, increases H secretion
Where does ADH act? What is its function?
- principle cells of the late distal tubule/collecting duct, and inner medullary collecting duct
- increases water reabsorption
Where does ANP act? What is its function?
- distal tubule and collecting duct
- decreases Na reabsorption
Where does PTH act? What is its function?
- proximal tubule, decreasing phosphate reabsorption
- thick ascending loop of henle/distal tubule, increasing Ca reabsorption
