renal transport mechanism ( dr. hardian )
TRANSCRIPT
RENAL TRANSPORT MECHANISMNaCL AND WATER REABSORPTION ALONG THE NEPHRON
OBJECTIVE
1.Explain the three processes involved in the production of urine a. filtration b. reabsorption c. secretion..2.Describe the magnitude of the processes of filtration and reab- sorption by the nephron.3.Describe the composition of normal urine.4.explain the basic transport mechanisms present in each nephron segment.5.Describe how water reabsorption is “coupled” to Na+ reabsorp tion in the proximal tubule.6.Explain how solutes, but not water , are reabsorbed by the thick ascending limb of Henle’s loop.
OBJECTIVE - COUNT.
7. Describe how Starling forces regulate solute and water reabsorption across the proximal tubule.8. Explain glomerulotubular balance and its phy- siological significance .9. Identify the major hormones that regulate NaCl and water reabsorption by its nephron segment
COMPOSITION OF URINE
SUBSTANCE CONCENTRATION
Na+ 50 - 150 meq/l K+ 20 - 70 meq/l NH4- 30 - 50 meq/l Ca++ 5 - 12 meq/l Mg++ 2 - 18 meq/l Cl - 50 - 130 meq/l PO4 20 - 40 meq/l Urea 200 – 400 mM Kreatinin 6 - 20 mM pH 5 - 7 Osmolality 500 - 800 mOsm/Kg H2O others 0
MECHANISMS OF SOLUTETRANSPORT
PASSIVE . Spontaneous , down an electrochemical gradient no energy requirement. Diffusion Facilitated diffusion ion channel Uniport Coupled transport Antiport Symport
ACTIVE Against an electrochemical gradient, requires direct input of energy Active transport Endocytosis.
Tubuler fluid
Paracellulerpathway
Transcellulerpathway
Tightjunction
Apical cellmembrane
Lateral intercellular space
blood
Na+
K+
Na+
Na+
Basolateralmembrane
CapillaryBasementmembrane
ATP
ATP
ATP
Tubular fluid
blood
Na+
X
Na+H+
HCO3
K+
Na+ATP
X
CO2 + H2O
CA
First half of proximal tubule
Tubular fluid
blood
NaCl
H2O
Na+
Cl-
organics
H2O
0rganics Na+ Cl-
organic Na+ Cl-
organics Na+ Cl-
H2O
Tubular fluid
CL-Na+
Na+ Na+ Na+
H+HbaseBase
Cl-
Cl-Na+
Cl-
H base
K+ATP
K+Cl-
blood
Second half of proximal tubule
Some organic secreted by the proximal tubule
Endogenous anions Drug
cAMP acetazolamideBile salts chlorothiazideHippurate(PAH) furosemideOxalate penicillinProstaglandins probenecidUrate salicylate(aspirin) hidrochlorthiazide bumetanide
Some organic cations secreted by the proximal tubule
Endogenous cations Drugs
Creatinine atropineDopamine isoproterenolEpinephrine cimetidineNorepinephrine morphine quinine amiloride
Tubular fluid
A-
PAHOA-
Na+
K+
Na+
Di/tri carboxylaseDi/tri carboxylase
PAH(OA-)
ATP
BLOOD
HENLE’S LOOP
-Reabsorbs approimately 20 % of filtered Na+, Cl – and K+-Ca+, HCO3- and Mg++-Exclusively in the thick ascending limb-The ascending thin limb and descending thin limb does not reabsorbs.-water is reabsorbed exclusively in the descending thin limb-The ascending limb is impermiable to water
Tubulalar fluid blood
Paracellulardiffusion
Na+2Cl-K+
Na+
K+
H+ CO2 + H2O HCO3
Cl-K+
Na+
K+ATPCA
Na+K+Ca++MG++
H2O
+
DISTAL TUBULE AND COLLECTING DUCT
•Reabsorb approximately 12 % of the filtered Na+ and Cl-•Secrete variable amount of K+ and H+•The first segment: reabsorbs Na+.Cl- and Ca++ and it’s im-•permiable to water.•The last segment of distal tubule and collecting duct: reabsorb ed Na+ and water and secrete K+(princial cell)•Intercalated cell secrete H+ and reabsorb HCO3- and K+
Tubularfluid
blood
Na+
Cl-
H2O
Na+
Cl-K+
ATP
EARLY SEGMENT OFTHE DISTAL TUBULE
Tubularfluid
blood
DISTAL TUBULE AND COLLECTING DUCT
Principal cellNa+
K+
Na+
K+ ATP
Tubularfluid
blood
H+ HCO3
Intercalated cell
CO2 + H2O
CAATP
REGULATION OF NaCL AND WATER REABSORPTION
Tubularfluid
bloodInterstitial space
Basementmembrane
1
3
2
IIcapP cap
P is
II is
1. STARLING FORCES
2. GLOMERULOTUBULAR BALANCE
3. HORMONES
4. SYMPHATIC NERVOUSN SYSTEM
HORMONES that regulate NaCl and water reabsorption
SEGMENT HORMONE EFFECTS
Prox.tubule angiotensin II NaCl H2O glucocorticoids NaCl H2OThick Asc. Aldosteron NaCl limb vasopressin NaCl
Distal Tub./ aldosteron NaCl Collecting Duct atrial natriuretic Pep. NaCl H2O prostaglandin NaCl H2O bradikynin NaCl vasopressin NaCl H2O