Physiology- Renal II Flashcards
Major function of nephrons
Reabsorption of NaCl and water
3 basic process involving formation of urine
Ultrafiltration of plasma by glomerulus
Reabsorption of water and solutes from ultrafiltrate
Secretion of of selected solutes into tubular fluid
What gets reabsorbed in proximal tubule
65% of filtered: Na Cl K Water Urea 90% of filtered: Bicarbonate Almost all of filtered: Glucose Amino acids Phosphate
What gets secreted at proximal tubule
Hydrogen ions Drug toxins Organic acids and bases -bile salts -oxalates -irate -catecholamines
How much NaCl is reabsorbed in loop of henle?
25%
How much water is reabsorbed in loop of henle
15%
What is loop of henle responsible for
Urinary concentrating ability
-generation of hypertonic medullary interstitium=countercurrent multiplication
What gets reabsorbed in loop of henle
NaCl
Water
Calcium
Magnesium
Major segments of loop of henle
Descending thin limb
Descending thin limb highly permeable to
Water
Descending thin limb impermeable to
NaCl
Ascending thin limb does reabsorption of
NaCl
Ascending thin limb impermeable to
Water
Ascending thick limb does reabsorption of
NaCl
Na
K
2Cl
Ascending thick limb impermeable to
Water
Which part of loop of henle is the primary target of loop diuretics
Ascending thick limb
How does loop of henle contribute to urine concentrating ability
By establishing hypertonic medullary interstitium
How is hypertonic medullary interstitium created
Reabsorption without water dilutes tubular fluid and increases osmolality of interstitial fluid surrounding thick ascending loop of henle
What is reabsorbed at distal tubule
5% NaCl
Ca
What works to reabsorbe NaCl at distal tubule
Thiazides
What is ca reabsorption stimulated by in distal tubule
Parathyroid hormone
Major divisions of collecting duct
Cortical collecting duct
Medullary collecting duct
Role of collecting duct
Regulates final composition of urine
Reabsorbs 4-5% of filtered Na
Important for regulation of salt and water balance
2 cell types in cortical collecting duct
Principal
Intercalated
Principal cells are site of action of
Aldosterone
What is reabsorbed in principal cells
Na
Cl
What is secreted in principal cells
K
What is permeability of water in principal cells dependent on
ADH
Intercalated cells responsible for regulation of
Acid base balance
What is reabsorbed at intercalated cells
K
Bicarbonate
What is secreted at intercalated cells
H
What is reabsorbed at medullary collecting duct
NaCl
Water (controlled by ADH)
Urea
What is secreted at medullary collecting duct
H
Mechanisms that control tubular reabsorption
Glomerular balance Peritubular capillary and renal interstitial fluid physical forces Pressure naturesis/diuresis Hormonal control Sympathetic nervous system
Glomerular balance
Intrinsic ability of tubules to increase their absorption rate in response to increased tubular load (increased tubular inflow)
-total rate of absorption increases as filtered load increases
Peritubular capillary and renal interstitial fluid physical forces
Hydrostatic and colloid osmotic forces govern rate of reabsorption across peritubular capillaries
Aldosterone secreted by
Adrenal cortex
What is aldosterone’s site of action
Principal cells of cortical collecting tubule
Effects of aldosterone
Increases Na and K reabsorption
Secretion of aldosterone stimulated by
Increased extracellular K concentration
Increased angiotensin II levels
-typically occur in conditions associated with Na and volume depletion or low BP
3 main effects of angiotensin II
Stimulates aldosterone secretion
Constricts efferent arterioles
Directly stimulates reabsorption in proximal tubules, loop of henle, distal tubules, and collecting ducts
Antidiuretic hormone
Increases water permeability of distal tubule, collecting tubule, and collecting duct
-helps body conserve water in times of ECF volume depletion
Atrial natriuretic peptide secreted by
Cells in cardiac atria
What stimulates release of atrial natriuretic peptide
Distension by increased plasma volume
What does atrial natriuretic peptide do?
Directly inhibits reabsorption of Na and water by renal tubules, especially collecting ducts Inhibits renin (thus, aldosterone), which indirectly inhibits Na and water reabsorption
What does activation of sympathetic nervous system decrease excretion of?
Na
Water
(By constricting renal arterioles, reducing GFR)
Sympathetic nervous system increases
Renin release Na reabsorption (low levels of stimulation) in proximal tubule, thick ascending loop of henle -does this by activating adrenergic receptors in renal tubular epithelial cells
