understanding the basic physiology of kidney, for easier understanding in CRF

6. GLOMERULAR FILTRATION RATE(GFR)
• The level of urea depends both on GFR and its
production rate.This is influenced by protein
intake and tissue catabolism.
• The creatinine level is much less dependent
but is more related to age,sex and muscle
mass.
• Serum creatinine is better guide to GFR than
urea and good way to monitor futher
deterioration in the GFR

7. 1. creatinine clearance
2. Calculated GFR
• Cockcroft-Gault equation
• Modification of diet in renal disease
(MDRD) equation
• CKD Epidemiology (CKD-EPI)
collaboration equation
U x VP
(U=Urine concentration of creatinine.
V = rate of urine flow in mL/min ,
P = plasma concentrarion of creatinine)
Normal ranges :
90-140 mL/min in men,
80-125 mL/min in female

9. TUBULAR FUNCTION
• Selective reabsorption or excretion of water
and various cations and anions to keep the
volume and electrolyte composition of body
fluid normal

10. FLUID AND ELECTROLYTE BALANCE
Water balance
• Water balance : input = output
• Direct control of water excretion in the kidneys is exercised by :
– vasopressin, or anti-diuretic hormone (ADH).
– ADH causes the insertion of water channels into the membranes of
cells lining the collecting ducts, allowing water reabsorption to occur
=> lowering osmolarity (reducing sodium concentration), helpto dilute
bodily fluids.
– To prevent osmolarity from decreasing below normal, the kidneys also
have a regulated mechanism for reabsorbing sodium in the distal
nephron. This mechanism is controlled by aldosterone,
The adrenal cortex directly
senses plasma osmolarity. When
the osmolarity increases above
normal, aldosterone secretion is
inhibited.
Activation of
Renin
angiotensin
aldosterone
system (RAAS)

12. URINE CONCENTRATION AND THE
COUNTERCURRENT SYSTEM
• The loop of Henle acts as a countercurrent
multiplier that uses energy to create
concentration gradients.
The descending limb is
water permeable. Water
flows from the filtrate to
the interstitial fluid, so
osmolality inside the limb
increases as it descends
into the renal medulla.
At the bottom, the osmolality
is higher inside the loop than
in the interstitial fluid. Thus,
as filtrate enters the
ascending limb, Na+ and Cl-
ions exit through ion
channels present in the cell
membrane.
Further up, Na+ is
actively transported
out of the filtrate and
Cl- follows. Osmolarity
is given in units of
milliosmoles per liter
(mOsm/L).

13. Sodium balance
• In addition to regulating total volume,
the osmolarity of bodily fluids is also tightly regulated.
Extreme variation in osmolarity causes cells to shrink
or swell, damaging or destroying cellular structure and
disrupting normal cellular function.
• Regulation of osmolarity is achieved by balancing the
intake and excretion of sodium with that of water
• An important concept is that regulation of osmolarity
must be integrated with regulation of volume, because
changes in water volume alone have diluting or
concentrating effects on the bodily fluids.

14. ACID-BASE BALANCE
• The kidneys have two very
important roles in maintaining the
acid-base balance:
1. to reabsorb bicarbonate from
urine
2. to excrete hydrogen ions into
urine.

16. ACID-BASE BALANCE

17. ENDOCRINE FUNCTION
• RENIN-ANGIOTENSIN SYSTEM
JUXTAGLOMERULAR APPARATUS:
• Renin converts angiotensinogen to angiotensin II
• Renin released is controlled by:
1. Pressure changes in afferent arteriole
2. Sympathetic tone
3. Chloride and osmotic concentration in distal tubule
via the macula densa
4. Local prostaglandin and nitric oxide release

19. ERYTHROPOIETIN
• Loss of renal
substance,results in
normochromic,normocytic
anaemia
• Conversely,erythropoietin
secretion is increased in
polycystic kidney,benign
renal cysts or renal cell
carcinoma

20. VITAMIN D METABOLISM

21. AUTOCRINE FUNCTION
ENDOTHELIN
• The vascular actions are mediated by 2
receptors ETA for vasocontriction and ETB
causing vasodilation.
• Function : Inhibits sodium and water
absorption by suppressing Na+/K-ATPase and
Na+/H+ antiporter activity in prox tubule
• Antagonize the action of ADH and aldosterone
in the collecting duct.

22. PROSTAGLANDIN
• COX-1 expressed in collecting duct
• COX-2 is restricted in macula densa
• COX convert arachidonic acid to prostaglandin H2
VC ,mainly
synthesized
in
glomerulus
Produced in
prox tubule
Produce in
collecting
duct,responsible
for natriuretic and
diuretic peptide
Mainly
synthesized in
the interstitial
and vascular
compartment

23. NATRIURETIC PEPTIDE
Significant role in cardiovascular and fluid
homeostasis
BNP
-Found in ventricle and
brain
-Exceed in congestive
heart failure
ANP
-Secreted from atrial
granules in response to atrial
stretch.
-Increase sodium and water
excretion and GFR
-Direct VD,reduces renin
release and aldosterone
secretion and inhibits
angiotensin II

24. NITRIC OXIDE AND THE KIDNEY
ACTIONS IN THE KIDNEY
• Regulation of renal hemodynamics
• Natriuresis by inhibiting Na+/K+-ATPase and
Na+/H+ antiporter and antagonizing ADH