fisiologi renal oleh: tunggul adi p., m.sc., apt. laboratorium farmasi klinik fkik unsoed
TRANSCRIPT
![Page 1: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/1.jpg)
Farmakoterapi IIRENAL DISEASE
FISIOLOGI RENALoleh: Tunggul Adi P., M.Sc., Apt.
Laboratorium Farmasi Klinik FKIK UNSOED
![Page 2: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/2.jpg)
TUJUAN PEMBELAJARAN
Mahasiswa mampu:- Menjelaskan fungsi fisiologis ginjal- Menjelaskan struktur ginjal- Menjelaskan proses filtrasi,
reabsorpsi, dan sekresi
![Page 3: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/3.jpg)
FUNGSI UTAMA GINJAL
Pengaturan volume dan osmolalitas cairan tubuh
Pengaturan keseimbangan elektrolit Pengaturan keseimbangan asam basa Ekskresi (metabolic product, foreign
substance, excess substance) Produksi dan sekresi hormon
(erythropoitin, 1,25-dihydroxy vitamin D3 (vitamin D activation), renin)
![Page 4: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/4.jpg)
Renal system – important points Kidneys have excellent
blood supply: 0.5% total body weight but ~20% of CO (cardiac output).
Kidneys process plasma portion of blood by removing substances from it, and in a few cases, by adding substances to it.
Works with cardiovascular system (and others!) in integrated manner
![Page 5: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/5.jpg)
A. Renal Vein
B. Renal Artery
C. Ureter
D. Medulla
E. Renal Pelvis
F. Cortex
1. Ascending loop of Henle
2. Descending loop of Henle
3. Peritubular capillaries
4. Proximal tubule
5. Glomerulus
6. Distal tubule
GINJAL DAN NEFRON
![Page 6: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/6.jpg)
The functional unit of the kidney: the nephron
Total of about 2.5 million in the 2 kidneys.
Each nephron consists of 2 functional components: The tubular component
(contains what will eventually become urine)
The vascular component (blood supply)
The mechanisms by which kidneys perform their functions depends upon the relationship between these two components.
Responsible for urine formation: Filtration Secretion Reabsorption
![Page 7: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/7.jpg)
Characteristics of the renal blood flow:
1, high blood flow. 1200 ml/min, or 21 percent of the cardiac output. 94% to the cortex
2, Two capillary beds
High hydrostatic pressure in glomerular capillary (about 60 mmHg) and low hydrostatic pressure in peritubular capillaries (about 13 mmHg)
Vesa Recta
![Page 8: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/8.jpg)
Functions of the Nephron
Filtration
Reabsorption
Secretion
Excretion
![Page 9: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/9.jpg)
From http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookEXCRET.html
Overview of nephron function
![Page 10: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/10.jpg)
HUMAN RENAL PHYSIOLOGY
• Four Main Processes:
– Filtration
– Reabsorbtion
– Secretion
– Excretion
![Page 11: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/11.jpg)
HUMAN RENAL PHYSIOLOGY
• Functions of the Kidney:–Filtration:
–First step in urine formation
–Bulk transport of fluid from blood to kidney tubule
» Isosmotic filtrate
» Blood cells and proteins don’t filter
–Result of hydraulic pressure
–GFR = 180 L/day
![Page 12: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/12.jpg)
HUMAN RENAL PHYSIOLOGY
• Functions of the Kidney:–Reabsorbtion:
• Process of returning filtered material to bloodstream
• 99% of what is filtered
• May involve transport protein(s)
• Normally glucose is totally reabsorbed
![Page 13: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/13.jpg)
HUMAN RENAL PHYSIOLOGY
• Functions of the Kidney:–Secretion:
–Material added to lumen of kidney from blood
–Active transport (usually) of toxins and foreign substances»Saccharine»Penicillin
![Page 14: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/14.jpg)
HUMAN RENAL PHYSIOLOGY
• Functions of the Kidney:– Excretion:
– Loss of fluid from body in form of urine:
Amount of solute excreted= amount filtered + amount secreted –
amount reabsorbed
![Page 15: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/15.jpg)
Filtration
![Page 16: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/16.jpg)
THE GLOMERULUS
![Page 17: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/17.jpg)
•Components of plasma cross the three layers of the glomerular barrier during filtration
• Capillary endothelium
• Basement membrane (net negative charge)
• Epithelium of Bowman’s Capsule (Podocytes –filtration slits allow size <60kD)
•The ability of a molecule to cross the membrane depends on size, charge, and shape
• Glomerular filtrate therefore contains all molecules not contained by the glomerular barrier - it is NOT URINE YET!
Plasma is filtered through the glomerular barrier
![Page 18: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/18.jpg)
Glomerular filtration GFR controlled by
diameters of afferent and efferent arterioles
Sympathetic vasoconstrictor nerves
ADH and RAAS also have an effect on GFR.
Autoregulation maintains blood supply and so maintains GFR. Also prevents high pressure surges damaging kidneys.
Unique system of upstream and downstream arterioles.
• Remember: high hydrostatic pressure (PGC) at glomerular capillaries is due to short, wide afferent arteriole (low R to flow) and the long, narrow efferent arteriole (high R).
![Page 19: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/19.jpg)
GFR depends on diameters of afferent and efferent arterioles
GFR GFR
Glomerulus
Afferent arteriole
Efferent arteriole
Glomerular filtrate
Aff. Art. dilatation
Eff. Art. dilatation
Eff. Art. constriction
Aff. Art. constriction
Prostaglandins, Kinins,
Dopamine (low dose), ANP, NO
Angiotensin II (low dose)
Angiotensin II blockade
Ang II (high dose), Noradrenaline (Symp nerves), Endothelin,
ADH, Prost. Blockade)
![Page 20: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/20.jpg)
Glomerular Filtration Rate (GFR)
Measure of functional capacity of the kidney
Dependent on difference in pressures between capillaries and Bowman’s space
Normal = 120 ml/min =7.2 L/h=180 L/day!! (99% of fluid filtered is reabs.)
![Page 21: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/21.jpg)
Oncotic pressure
Oncotic pressure is the component of total osmotic pressure due to colloid particles.
Water molecules cross the membrane to equalize the concentration of colloid particles on each side.
![Page 22: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/22.jpg)
Glomerular filtration rate (GFR)
Depends on the difference in hydrostatic and oncotic pressure on either side of the glomerular basement membrane
GFR
=
Kf(PGC - PBS - COPGC)
P = hydrostatic pressure
COP = colloid osmotic pressure
Kf determined by surface area and permeability of
H2O
PGC PBS
COPGC COPBS
GlomerularCapillary (GC)
Bowman’s space (BS)
![Page 23: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/23.jpg)
Reabsorption and secretion
![Page 24: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/24.jpg)
Peritubular reabsorption Peritubular capillaries
provide nutrients for tubules and retrieve the fluid the tubules reabsorb.
Oncotic P is greater than hydrostatic P in these capillaries, so therefore get reabsorption NOT filtration.
Must occur since we filter 180l/day, but only excrete 1-2l/day of urine.
Reabsorb 99% H2O, 100% glucose, 99.5% Na+ and 50% urea. Most of this occurs at proximal convoluted tubule.
![Page 25: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/25.jpg)
Reabsorption
Active Transport –requires ATP Na+, K+ ATP pumps
Passive Transport- Na+ symporters (glucose, a.a., etc) Na+ antiporters (H+) Ion channels Osmosis
![Page 26: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/26.jpg)
Renal transport systems Lots of transporter
proteins for different molecules/ions so they can be reabsorbed.
They all have maximum transport (TM) capacities where transport saturates i.e. 10mmol/l for glucose.
Over this value, you excrete the excess in urine, so can be useful sign of disease either in kidneys or other systems.
Amino acids also have a high TM value because you try and preserve as much of these useful nutrients as possible.
![Page 27: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/27.jpg)
Factors influencing Reabsorption
Saturation: Transporters can get saturated by high concentrations of a substance - failure to resorb all of it results in its loss in the urine (eg, renal threshold for glucose is about 180mg/dl).
Rate of flow of the filtrate: affects the time available for the transporters to reabsorb molecules.
![Page 28: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/28.jpg)
What is Reabsorbed Where?Proximal tubule - reabsorbs 65 % of filtered Na+ as well as Cl-, Ca2+, PO4, HCO3
-. 75-90% of H20. Glucose, carbohydrates, amino acids, and small proteins are also reabsorbed here.
Loop of Henle - reabsorbs 25% of filtered Na+.
Distal tubule - reabsorbs 8% of filtered Na+. Reabsorbs HCO3-.
Collecting duct - reabsorbs the remaining 2% of Na+ only if the hormone aldosterone is present. H20 depending on hormone ADH.
![Page 29: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/29.jpg)
![Page 30: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/30.jpg)
Secretion
Proximal tubule – uric acid, bile salts, metabolites, some drugs, some creatinine
Distal tubule – Most active secretion takes place here including organic acids, K+, H+, drugs
![Page 31: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/31.jpg)
Countercurrent exchange
The structure and transport properties of the loop of Henle in the nephron create the Countercurrent multiplier effect.
A substance to be exchanged moves across a permeable barrier in the direction from greater to lesser concentration.
Image from http://en.wikipedia.org/wiki/Countercurrent_exchange
![Page 32: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/32.jpg)
Loop of Henle Goal= make isotonic
filtrate into hypertonic urine (don’t waste H20!!)
Counter-current multiplier:▪ Descending loop is permeable
to Na+, Cl-, H20
▪ Ascending loop is impermeable to H20- active NaCl transport
▪ Creates concentration gradient in interstitium
▪ Urine actually leaves hypotonic but CD takes adv in making hypertonic
![Page 33: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/33.jpg)
Na+ absorption Na+ absorbed by active
transport mechanisms, NOT by TM mechanism. Basolateral ATPases establish a gradient across the tubule wall.
Proximal tubule is very permeable to Na+, so ions flow down gradient, across membranes.
Microvilli create large surface area for absorption.
Electrical gradient created also draws Cl- across.
H2O follows Na+ due to osmotic force.
Means fluid left in tubule is concentrated.
![Page 34: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/34.jpg)
Glucose handling Glucose
absorption also relies upon the Na+ gradient.
Most reabsorbed in proximal tubule.
At apical membrane, needs Na+/glucose cotransporter (SGLT)
Crosses basolateral membrane via glucose transporters (GLUT’s), which do not rely upon Na+.
![Page 35: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/35.jpg)
Amino acid handling
Preserve as much of these essential nutrients as possible. Can be absorbed by GI tract, products of protein catabolism, or
de novo synthesis of nonessential amino acids. TM values lower than that of glucose, so can excrete excess in
urine. Amino acid transporters rely upon Na+ gradient at apical
membrane, but a couple of exceptions don’t. Exit across basolateral membrane via diffusion , but again,
some exceptions rely on Na+.
![Page 36: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/36.jpg)
K+ handling K+ is major cation in cells and
balance is essential for life. Small change from 4 to 5.5
mmoles/l = hyperkalaemia = ventric. fibrillation = death.
To 3.5 mmoles/l = hyperpolarise = arrhythmias and paralysis = death.
Reabsorb K+ at proximal tubule.
Changes in K+ excretion due to changes in K+ secretion in distal tubule
Medullary trapping of K+ helps to maximise K+ excretion when K+ intake is high.
![Page 37: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/37.jpg)
K+ handling
K+ reabsorption along the proximal tubule is largely passive and follows the movement of Na+ and fluid (in collecting tubules, may also rely active transport).
K+ secretion occurs in cortical collecting tubule (principal cells), and relies upon active transport of K+ across basolateral membrane and passive exit across apical membrane into tubular fluid.
![Page 38: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/38.jpg)
Hormones Produced by the Kidney
Renin: Released from juxtaglomerular apparatus when low
blood flow or low Na+. Renin leads to production of angiotensin II, which in turn ultimately leads to retention of salt and water.
Erythropoietin: Stimulates red blood cell development in bone marrow.
Will increase when blood oxygen low and anemia (low hemoglobin).
Vitamin D3: Enzyme converts Vit D to active form 1,25(OH)2VitD.
Involved in calcium homeostasis.
![Page 39: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/39.jpg)
Renin, Angiotensin, Aldosterone:
Regulation of Salt/Water Balance
![Page 40: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/40.jpg)
Renin/AII and Regulation of GFR
GFR = Kf(PGC - PBS - COPGC)
• “flight or fright”
•- sympathetic tone
• afferent arteriolar constriction (divert cardiac output to other organs)
•-PGC
•-GFR and renal blood flow
![Page 41: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/41.jpg)
Renin/AII and Regulation of GFR
GFR = Kf(PGC - PBS - COPGC)
•Low BP sensed in afferent arteriole or low Na in distal tubule
•renin released
•renin converts angiotensinogen to Angiotensin I
•ACE converts AI to AII
•efferent > afferent arteriolar constriction
•- PGC - - GFR (this is AUTOREGULATION of GFR)
PGC-
constricts
![Page 42: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/42.jpg)
Aldosterone
Secreted by the adrenal glands in response to angiotensin II or high potassium
Acts in distal nephron to increase resorption of Na+ and Cl- and the secretion of K+ and H+
NaCl resorption causes passive retention of H2O
![Page 43: FISIOLOGI RENAL oleh: Tunggul Adi P., M.Sc., Apt. Laboratorium Farmasi Klinik FKIK UNSOED](https://reader035.vdocuments.site/reader035/viewer/2022062322/56649f0c5503460f94c1fc15/html5/thumbnails/43.jpg)
Anti-Diuretic Hormone (ADH)
Osmoreceptors in the brain (hypothalamus) sense Na+ concentration of blood.
High Na+ (blood is highly concentrated) stimulates posterior pituitary to secrete ADH.
ADH upregulates water channels on the collecting ducts of the nephrons in the kidneys.
This leads to increased water resorption and decrease in Na concentration by dilution