Processing of Glomerular Filtrate Physiology slideshow

Proximal convoluted tubule

•Well adapted for reabsorption
–High metabolism
–Higher number of mitochondria
–Large surface area (brush border)
–High capacity for active/passive transport
–High number of carrier protein on brush border
•65% of the filtered load is reabsorbed
•Concentration %ages can alter with need

Proximal convoluted tubule

•Na+
–Co transport with Glucose & amino acids (early segment)
–Co transport with Cl-(late segment)
–Counter transport with ions
•HCO3-
–Combine with H+ ions to form water and carbon dioxide
•Substances passively reabsorbed
–Water (osmosis), Cl-and urea
•Iso-osmotic to plasma
•Organic acids and bases are reabsorbed
•PAH secreted
•OSMOTIC DIURETICS

Loop of Henle

•3 segments
–Descending thin segment
–Ascending thin segment
–Ascending thick segment

•Descending limb
–Highly permeable to water
–~ 20 % filtered water is reabsorbed
–Moderately permeable to solutes (Na+& urea)
–Tubular fluid becomes hyper-osmotic

Loop of Henle

•Thin ascending limb
–Impermeable to water
–No active reabsorption of Na+
–Passive reabsorption of Na+and urea

•Thick ascending limb
–Impermeable to water and urea
–Active reabsorption of Na+, Cl-,and K+
–Paracellular reabsorption of Mg+, Ca+2, Na+& K+
–~25 % filtered load of Na+, Cl-and K+reabsorbed
–Impermeable to urea
–Tubular fluid becomes hypoosmotic

•Thick ascending limb
–Role of 1-Na+,2-Cl-,1-K+symporter
•Active reabsorption of 1 Na+, 2 Cl-and 1 K+
•Action of ’LOOP DIURETICS’
•Block 1-Na+,2-Cl-,1-K+symporter
•Furosemide (lasix)

Distal convoluted tubule

•Early distal tubule
–Resembles thick limb of loop of henle
•Late distal tubule
–Resembles cortical collecting tubule

•Early distal tubule —-diluting segment
•5% of the filtered load is reabsorbed
–Impermeable to water & urea
–~5 % filtered load of NaCl is reabsorbed
–Role of Na+-Cl-symporter
•Co-transport of Na+& Cl-into tubular cell
•Action of THIAZIDE DIURETICS
•Block Na+-Cl-symporter

Late distal & cortical collecting tubule

•Late distal & cortical collecting tubule
–Impermeable to urea
–Permeability to water controlled by ADH
–Concentration gradient for hydrogen ion secretion is 1000 times more
–Contains
•Principal cells
•Intercalated cells

•Principal cells
–Reabsorb Na+and secrete K+
–Site of action of ‘K+sparing diuretics’
•Intercalated cells
–Type A & B
–Type A —Secrete H+by H+-ATPase pump
–Reabsorb K+and HCO3-
–Type B cells function during alkalosis

Medullary collecting ducts

•Final site for urine processing
•Water permeability controlled by ADH
•Permeable to urea
•Secrete H+by H+-ATPase pump

Tubular Secretion

•Proximal tubule
–Active secretion of H+(Na+-H+counter transport)
–Organic acids and bases
•Bile salts, oxalate, urate, catecholamines
–Drugs
•Penicillin, salicylates
–Others
•Paraaminohippuric acid (PAH)

•Loop of henle (thick ascending limb)
–Active secretion of H+(Na+-H+counter transport)
•Late distal and cortical collecting tubules
–Active secretion of K+(principal cells)
–Active secretion of H+(intercalated cells)
•Medullary collecting duct
–Active secretion of H+

Regulation of Tubular Reabsorption

Regulation

•Glomerulotubular balance
•Peritubular capillary and renal interstitial physical forces
•Hormonal control
•Nervous control

Regulation of Tubular Reabsorption

•Glomerulotubular balance
–Rise in tubular reabsorption in response to rise in tubular load (rise in GFR)
–Intrinsic property of kidney
–Mostly occurs in proximal tubules
–Some in loop of henle
–Prevents overload in distal renal segments
–Buffer for spontaneous change in GFR on urine output

Glomerulotubular Balance

Peritubular capillary & renal interstitial physical forces

Regulation of Renal Reabsorption

•Reabsorption coefficient
–Hydraulic conductivity x Surface area
Reabsorption =
Kf×Net reabsorptive force
Kf= Reabsorption / Net reabsorptive force
Kf = 124/10
Kf = 12.4ml/min/mmHg

Peritubular capillary & renal interstitial physical forces

Peritubular Capillary & Renal Interstitial Physical Forces

•Peritubular capillary colloid osmotic pressure
–Increased plasma colloid osmotic pressure
–Filtration fraction
•↑fraction of plasma filtered →↑ proteins in the plasma →↑reabsorption in to peritubular capillaries

Hormonal Regulation

•WHY required
–Coordinated reabsorption and excretion of ions occur
–To prevent the change of ions when one is altered

•Aldosterone
–Secreted by zona glomerulosa
–Reabsorption of sodium and secretion of potassium and hydrogen occurs
–Principal cells of cortical collecting ducts
–Stimuli
•Increased ECF potassium and angiotensin II

•Angiotensin II
–Sodium retaining hormone
–Stimuli
•Low arterial pressure and ECF volume
–Actions
•Increase aldosterone secretion
•Constrict efferent arterioles
•Sodium reabsorption in the tubule

•ADH
–Water retaining hormone
–Increase water reabsorption in DCT and collecting tubules and ducts

•ANP
–Stretch on atrial muscles because of volume expansion and arterial pressure
–Decrease sodium and water reabsorption
–Decrease renin release
•Parathyroid hormone
–Act on distal segments and loop of Henle
–Reabsorbs calcium
–Decrease reabsorption of phosphate
–Increase reabsorption of magnesium in PCT