Functions of kidney

An illustrative presentation Functions of Kidney for Medical, Dental, Pharmacology & Biotechnology students to facilitate easy- learning.

1. Functions of kidney
Dr. Rohini C Sane
Glomerular filtration

2. Nephron as the functional unit of kidney
•Nephronis the functional unit of the kidney.
•Each Kidney is composed of approximately one million nephrons.
•Nephronis made of a renal capsuleand renal tubule.
•The renal capsule contains a thin walled sac-like structure called the Bowman's
capsuleinto which the afferent arterioles from renal artery form a capillary
network called glomerulus.
•Each renaltubuleconsists of Proximal convoluted tubule (PCT) which dips into
the renal medulla to form the Loop of Henle. The tubule reenters the renal
cortex to form the Distal convoluted tubule (DCT). Several DCTs merge to form
a Collectingduct.
•Several Collecting tubules join and open into renalpelvis. The juxtaglomerular
apparatuspresent between the DCT and afferent arterioles secretes renin.

3. Diagrammatic representation of Nephron
The glomerulus has a semipermeable membrane through which substances (except cells
and large molecular size plasma proteins) are filtered into Bowman ‘s capsule at a rate
( 120ml/minute).This is known as Glomerular filtration rate(GFR).

4. Functions of components of Nephron of kidney
❖Proximal convoluted tubules(PCT):80% salt and water are absorbed from glomerular
filtrate in proximal convoluted tubule. All filtered glucose and amino acids are reabsorbed in
here. Low molecular weight proteins ,urea ,potassium , magnesium and calcium are
reabsorbed to varying extent.
❖Loop of Henle:
▪The descending loop of Henle is highly permeable to water .Passive reabsorption of water
occurs leaving highly concentrated urine at the bottom of loop.
▪The ascending loop of Henle (diluting segment) is relatively impermeable to passage of
water but actively absorbs Na
+
and Cl
-
ions.
❖Distal convoluted tubule(DCT): a small fraction of filtered sodium ,chloride and water is
reabsorbed in DCT , which responds to ADH ,so that its water permeability is high in the
presence of hormone and low in its absence.
❖Collecting tubule :ADH controls the water permeability of the collecting tubule throughout
its length.

5. Functions of kidney

6. Functions of kidney
❖Functions of kidney :
1.Excretion of metabolite waste products:the end products of protein and nucleic acid
metabolism and metabolites of xenobiotics are eliminated from the body. (effect on
blood pressure and heart) e.g. urea, creatinine, creatine , uric acid , sulphate and
phosphates
2.Maintain fluid and electrolyte homoeostasis:the kidney is largely responsible for the
regulation of water, electrolyte ,acid -base balance(maintenance of pH) in the body e.g.
glucose , amino acids etc.
3.Endocrine Function:The kidneys also function as Endocrine organs by producing
hormones:
a)Renin
b)Erythropoietin (effect on RBC synthesis)
c)1,25 Dihydroxycholecalciferol= Calcitriol (activation of Vitamin D –effects on bones)
d)Prostaglandins (PGA
2PGE
2,PGF
2)
e)Bradykinin and Kallidin
4. Participates metabolism by retaining substances vital to body:The kidneys reabsorb and
retain several substances of biochemical importance in the body . e.g. Glucose ,amino acids .

7. Structure and Functions of kidney

8. TheFormationofurine
•Three steps of formation of urine:
1.Glomerular filtration
2.Tubular reabsorption
3.Tubular secretion

9. Glomerular filtration: various ways
Complete
reabsorption
Partial reabsorption
by diffusion
No reabsorption and
no secretion
Secretion
Reference D.N. Baron
Schematic diagram

10. TheFormationofurine

11. Endocrine Functions of the kidney
Renin: a proteolytic enzyme produced in the juxtaglomerular apparatus of the kidney . It
stimulates the formation of Angiotensin II which in turn leads to Aldosterone production.
Angiotensin II and Aldosterone are the hormones involved in the regulation of electrolyte
balance . Angiotensin II is a powerful vasoconstrictor, that increases blood pressure and
causes contraction of smooth muscles.
Erythropoietin: a peptide hormone stimulates erythropoiesis in bone marrow (hemoglobin
synthesis) .
1,25 Dihydroxycholecalciferol(Calcitriol): 1-hydroxylation occurs in kidney to form the
biochemically active form of vitamin D (Calcitriol). It regulates calcium absorption from the
gut and homeostasis.
Prostaglandins (PGA
2PGE
2,PGF
2):are produced by renal medulla induce relaxation of
smooth muscles, vasodilatation, decrease in renal pressure, increase in renal blood flow and
excretion of sodium.
Bradykinin and Kallidin:peptide hormones produced by the kidney. They are a powerful
vasodilators that influence reabsorption of sodium and water. Bradykinin stimulates synthesis
of renal Prostaglandins.Kinins also play a role in blood coagulation increase renal blood flow
and exhibit antihypertensive effect .
❖Kidney possess receptors for hormones parathyroid hormone and ADH.
❖Kidney possess sites of inactivation of hormones such as insulin ,glucagon.

12. Glomerular filtration

13. Glomerular filtration

14. Glomerularfiltration
❖Glomerular filtration:
➢Glomerular filtration is Passive process that results in the formation of ultrafiltrate of
blood .This process occurs when blood is perfused through Bowman’s capsule .
➢Volume of blood passing through the kidneys= 1200ml/every minute(650ml plasma)
: the renal flow blood .
➢Glomerular filtration rate (GFR ): 120 -125 ml blood (one tenth)filtered by the
Glomerulus of kidneys every minute.
➢With normal Glomerular filtration rate (GFR)of 120 -125 ml/ minute , 175 -180 L of
the Glomerular filtrate is formed per day in an adult ,out of which only 1.5 L is
excreted as urine.Thus more than 99% of Glomerular filtrate is reabsorbed by the
kidneys.
➢All the (unbound) constituents of plasma ,with molecular weight less than 68000
Dalton are passed into filtrate . Therefore the Glomerular filtrate is almost similar in
composition to plasma . It is a proteinfreeand cellfreefiltrate of whole blood but
contains essentialmetabolitessuch as glucose and amino acids as well as waste
products(urea , uric acid and creatinine).Albuminuriais considered as earliest
manifestation of kidney dysfunction.

15. Factors affecting Glomerular filtration
❖Factors affecting Glomerular filtration:
A.Renal blood flow
B.Passage of macromolecules is based on their Shape ,charge and size of molecules
to be filtered : anionic derivatives ,globular molecules of molecular weight >
68000 Dalton are retained . The sieves of glomeruli are such that hemoglobin
(molecular weight 67000) is filtered and passed into urine , while albumin is
retained in the blood .Therefore ,the earliest manifestation of abnormal renal
function is appearance of albumin in urine.
C.Molecules less than 5KD such as glucose ,creatinine , urea and electrolytes are
freely filtered by glomeruli.
D.The low molecular weight proteins are freely filtered by glomeruli ,reabsorbed
and catabolized by renal tubular cells.
E.The normal urinary protein excretion < 150 mg /24 hr.(made up of mostly Tamm
horsefallglycoprotein) .

16. Tests for measuring Glomerular filtration
1.Creatinine clearance Test
2.Urea clearance Tests

17. Glomerular filtration rate (GFR )
❖A decease in the renal function is due to the loss of functional nephrons , rather
than a decease in the function of individual nephron .
❖Glomerular filtration rate (GFR) : providesthe most useful index for the assessment
of the severity of renal damage.
❖Glomerular filtration rate (GFR) is the product of filtration rate in single nephron
and number of nephrons in both kidneys .
❖FactorsaffectingGlomerular filtration rate (GFR):
1.Age( kidney function decline with age e.g. at 70 yr. of age , GFR < 60 ml/min in 25%
elders)
2.Sex
3.body size
4.Protein intake
5.Pregnancy
❖Normal Glomerular filtration rate (GFR )= 120-130ml/mt/1.73 M
2
❖Substantial kidney damage occurs before GFR is deceased .

18. Conditions associated with decreased Glomerular filtration rate (GFR )
❖Decreased GFR observed in:
a.Blood pressure < 60 mm
b.Renal calculi*
c.Enlarged prostrate *
d.Old age
*causes for obstruction to the renal flow

19. EstimatedGlomerular filtration rate (eGFR )

20. Calculation of Estimated Glomerular filtration rate (eGFR )
Cockcroft–Gault equation for EstimatedGlomerular filtration rate (eGFR ) :
Ccr= (140 –age in years) x weight in kg /72 xserum creatinine
( x 0.85 in female) assuming that they have 15 % less muscle mass.
❖Estimated Glomerular filtration rate (eGFR )in ml /min / 1.73 m
2
: 186 x (serum
creatinine/88.4) –1.154 x (age) –0.203 x 0.742 (if female)
❖Estimated Glomerular filtration rate (using both equations) can be used for staging
patients with chronic kidney disease neither in healthy individuals nor in children
and obese . –Modification of Diet in Renal Disease –MDRD
•Estimated Glomerular filtration rate (eGFR ) eliminates the need for timed urine
collection.
•It allows a technique of estimating creatinine clearance and thereby GFR using
serum creatinine levels.
•Accuracy of serum creatinineestimation is a major deciding factor in both
equations.

21. Normal composition of urine
Constituents of urineUrinary ConcentrationFactors affecting urinary excretion
Calcium 100-250mg/dl
Chloride 170-250meq/dl
Creatine 100 mg/dl
Creatinine 0.8 -2 g /dl( 1-2g/day) GFR, tubular secretion ,age ,sex ,muscle mass
17-ketosteroids
(adult male)
8 -20 mg/dl
17 ketosteroids
(adult female)
5 -15 mg/dl
Oxalic acid 20 –40 mg/dl
Phosphorous 0.5 -1.5 g/dl
Urea 15-40 g/dl (15-30 g/ day)Dietary proteins , protein catabolism , blood flow
Uric acid 200-500mg/dl (0.5-0.8 g/ day)Purine catabolism, tubular excretion

22. Normal daily excretion of solutes
Compound Total daily urinary excretion under normal dietary intake
Sodium 100 –200 mmols 2–4 g
Potassium 50 –70mmols 1.5 –2 g
Magnesium 4–8 mmols 0.1 –0.2 g
Calcium 1.2 –3.7 mmols 0.1 –0.3 g
Phosphate 20 –50 mmols 0.7 –1.6 g
Chloride 100–250 mmols 110 -125 mEq
Bicarbonate 0––50 mmols
Sulphate (inorganic) 40 –120 mequ 0.6 –1.8 g
Sulphate (organic) 0. 06–0.2 g
urea 15 –30 g 6–18 g
Creatinine 1 –2g 0.3–0.8 g
Uric acid 0.5–0.8 g 0. 08 –0.2 g
Ammonia 30 –75 mequ 0. 04 –1 g
Amino acids 0. 08 –0.15 g

23. Common Biochemical tests to assess kidney functions
Compound Blood levels
under normal
dietary intake
Factors affecting urinary excretion
Sodium 135 –142
mmols/L
State of hydration, dietary sodium , renal
functions
Potassium 3.5-5.5
mmols/L
Dietary potassium , acid base balance ,
renal functions
Calcium 9-11 mg/dL Dietary Calcium ,Calcitonin ,PTH ,renal
functions , vitamin D metabolism

24. Glomerular Dysfunctions of Kidney
❖In Glomerular Dysfunctions of Kidney
1.Urine volume decreases
2.Specific gravity increases
3.Blood Urea increases (urea clearance decreases)
4.Serum creatinine increases (creatinine clearance decreases)
5.Inulin clearance decreases
6.PDH clearance decreases
7.Proteinuria (positive test for Protein in urine)
8.Serum phosphate increases

25. Tubular functions of Kidney

26. Tubular functions of Kidney
❖When the glomerular filtrate is formed, it contains all the crystalloids of
plasma .
❖Tubular functions of Kidney include Reabsorption or Secretion of solutes and
Reabsorption of water from glomerular filtrate in the proximal convoluted
tubule(PCT).
❖All filtered glucose and amino acids are absorbed in PCT.
❖The descending loop of Henle is highly permeable to water .Passive
reabsorption of water occurs leaving highly concentrated urine at the bottom
of loop.
❖The ascending loop of Henle (diluting segment) is relatively impermeable to
passage of water but actively absorbs Na
+
and Cl
-
ions.
❖Low molecular weight proteins ,urea ,potassium , magnesium and calcium are
reabsorbed to varying extent.

27. Biochemical Tests measuring tubular functions
1.Determination of specific gravity ,concentrating and diluting ability of
kidney
2.Determination of serum and urine osmolarity
3.Determination urine ammonia
4.Phenolsulphonaphthalein(PSP)Test

28. Renal Tubular reabsorption
❖Tubularreabsorption: is an activeprocess.
•The renal Tubules(Proximal convoluted tubule-PCT, Distal convoluted tubule -
DCT , Collecting tubules) retain water and most of the soluble constituents of
Glomerular filtrate by reabsorption(active or passive process) .
•A small fraction of filtered sodium , chloride and water is reabsorbed in the
distal tubule which responds to antidiuretics hormone (ADH) ,so that its water
permeability is high in the presence of hormone and low in its absence.
•ADH controls the water permeability of the collecting tubule throughout its
length of collecting tubule.
•The excreted urine has an entirely different composition compared to
Glomerular filtrate from which it is derived .

29. Renal threshold substances
•Renal threshold substances : there arecertainsubstances in the blood whose
excretion in urine is dependent on their blood concentration. Suchsubstances
arereferredas Renal threshold substances.
•At normal concentration in the blood , they are completely reabsorbed by
kidneys, with a result that their excretion in urine is almost negligible.
•But when the blood levels are elevated ,the tubular reabsorption capacity is
saturated ,so that excess will be excreted in urine.
•High threshold substances : they are reabsorbed efficiently by kidneys (e.g.
Glucose,Amino acids)
•Lowthreshold substances : they are not reabsorbed or reabsorbed slightly by
kidneys (e.g. Creatinine, Urea , Uric acid) .

30. Threshold value-Plasma levels of common substances excreted in urine
Substance Threshold value plasma levels
Glucose 180mg/dl
Lactate 60 mg/dl
Bicarbonate 28 mequ /L
Calcium 10mg/dl
The RenalThreshold of substance is the Plasma levels above which compound is excreted
in urine.

31. Role of proximal convoluted tubule (PCT) in Renal Tubular functions
Reabsorption in proximal convoluted tubule of
99 % water ( obligatory )
Uric acid (obligatory)
Sodium -Na ⁺ (85% reabsorption)
Chloride-Cl
-
(85% reabsorption)
Bicarbonates (85% reabsorption)
Potassium-K ⁺ (100% reabsorption)
Glucose (100% reabsorption)
Amino acids (100% reabsorption)
Urea/phosphates -PO ⁻⁴ / Calcium Ca
2+
: are partially absorbed
Secretion in proximal convoluted tubule of : H⁺,acids , bases, NH
4⁺, Diodrast, PAH

32. Role of loop of Henle in Tubular functions of kidney
Reabsorption of ions in loop of Henle include :
Sodium -Na ⁺
Chloride-Cl
-
Calcium –Ca
2+
Magnesium -Mg
2+

33. Role of distal convoluted tubule (DCT) in Tubular functions
Reabsorption in distal convoluted tubule include:
water (facultative)
Sodium -Na ⁺
Chloride-Cl
-
Secretion in proximal convoluted tubule of : H⁺,Potassium-K ⁺,NH
4⁺, Uricacid

34. Tubular reabsorption Function of kidney
❖Reabsorptionofwater:
•Morethan99% of water(187.5 liters/day) isreabsorbed by counter
current multiplication or countercurrent exchange .
•Reabsorption of water from distal convoluted tubule (DCT) and
collecting ducts is facilitated by the pituitary hormone ADH.
❖Reabsorption of sodium: by symport and antiport system.
❖Reabsorption of potassium: occurs in the proximal convoluted
tubule (PCT).
•Reabsorption of urates: occurs in the proximal convoluted tubule
(PCT) by both active and passive transport.

35. Tubular Functions of kidney

36. Renal Tubular reabsorption of water
•More than 99% of water entering in RenalTubulesisreabsorbed .
❖Reabsorption of water in the PCT :
1.About 80% of water is reabsorbed .
2.Water is reabsorbed by passive transport as a solvent for actively reabsorbed sodium,
chloride , bicarbonate ions and glucose (obligatory Reabsorption –water has to move
along with solutes to maintain osmalality).
3.Tubular filtrate is isosmotic with plasma.
❖Reabsorption of water in the descending limb :
1.Tubular filtrate is hyperosmotic with plasma.
2.Water without solute is lost . This is termed as counter current multiplication .
3.Counter current multiplication :
a.Functions in absence of antidiuretic hormone( ADH)
b.is an active process that creates high medullary osmality in the Renal medulla and
produces dilute urine .
❖Reabsorption of water in the ascending limb :
a.sodium chloride is lost without water .
b.Tubular filtrate is hypoosmotic with plasma.

37. Flow rates of Renal Tubular reabsorption of water
Water reaches Flow rate Osmolarity
Proximal convoluted tubules 125 ml /min sodium, chloride ,
bicarbonate ions and glucose
are absorbed. Water has to
move along with solutes to
maintain osmality-
obligatoryReabsorption
Loop of Henle 25 ml/min Sodium is reabsorbed, Water
reabsorption is less. Urine is
hypotonic.
Distal tubules 16 ml/min Water reabsorbed under
influence of ADH –facultative
reabsorption
Collecting tubules 1 ml/min Urine is hypertonic.

38. Counter current mechanism of Renal Tubular reabsorption of water
❖Reabsorption of water in the DCT and the collecting duct :
1.Water without solute is reabsorbed along the gradient created by counter
current multiplication .
2.This is termed as counter current exchange .
3.Counter current exchange :
a.is facilitated by antidiuretic hormone(ADH). ADH secretion in turn, is
controlled by hypothalamic osmoreceptors. The osmolality of plasma is the
stimulus for modulating ADH secretion.
b.concentrates the urine.

39. Factors influencing ADH secretion
❖Factors influencing ADH secretion include :
•Osmotic pressure of the blood:Osmoreceptors in the hypothalamus that are
sensitive to changes in the Osmotic pressure of the blood influence the
synthesis and secretion of ADH.
•Blood volume:volume receptors in the carotid sinus and left atrium
influence ADH secretion.
•An increase in Osmotic pressure of the blood or decrease in blood volume
stimulates ADH secretion.

40. Osmoreceptors in the hypothalamus
Osmoreceptors in the hypothalamus that are sensitive to changes in the Osmotic pressure of
the blood influence the synthesis and secretion of ADH.

41. Renal Tubular reabsorption of sodium
•Tubular reabsorption of sodium occurs inProximal convoluted tubule-PCT by two
types of cotransport systems.
❖Symportsystem:which involves cotransport of sodium along with other substances
such as glucose ,amino acids and phosphates .It is catalyzed by Na
+ _
K
+
ATP ase
present in basolateral plasma membrane of the epithelial cells .
•This creates sodium gradient that accomplishes active transport of sodium out of
the cell while potassium enters the cell.
•There is passive transport of equivalent amount of chloride to maintain electrical
neutrality.
•The net effect is the reabsorption of sodium chloride along with glucose and amino
acids etc.
❖Antiportsystem: involve exchange of sodium (reabsorbed) for another cation such
as H
+
as in Na
+
-H
+.
This also achieves a net reabsorption of bicarbonate. When
hydrogen ions are to be conserved ,sodium to potassium exchange occurs .

42. Symport system for Renal Tubular reabsorption of sodium
Symportsystem:which involves cotransport of sodium along with other substances such as glucose ,amino
acids and phosphates . It is is catalyzed by Na
+
–K
+
ATP asepresent in basolateral plasma membrane of the
epithelial cells .

43. RenalTubular reabsorption of Glucose
•Normally Glucose is reabsorbed completely .
•The maximum rate at which Glucose is reabsorbed , referred as the Tubular
maximum for glucose(TmG)= 350 mg/min.
•When blood Glucose exceeds renal threshold for Glucose which is 10mmols/L
or (180mg/dl) , glucose spills over into the urine (glycosuria).
•Water is excreted as a solvent for glucose(osmotic diuresis).

44. RenalTubular reabsorption of Calcium
❖Tubular reabsorption of Calcium :
•About 90% of Calcium is reabsorbed from the glomerular filtrate.
•Regulation of calcium balance is achieved at the distal convoluted tubule .
•Factors regulating calcium reabsorption:parathyroid hormone and vitamin D.

45. RenalTubular reabsorption of Uric Acid
•Uric Acid is completely reabsorbed in Proximal convoluted tubule-PCT, by both
active and passive mediated process .
•There is an active secretion of Uric Acid in the tubules . About 85% of the
excreted Uric Acid is derived by tubular secretion.
•The drug ,probenecid is secreted by the tubules and competes with Uric Acid
for reabsorption . Since probenecid increases Uric Acid excretion ,it is
uricosuric.

46. RenalTubular reabsorption of Urea
•Urea is freely filtered by the glomerulus ,but about the 40% is reabsorbed
actively by the tubules.
•Rate of reabsorption of Urea varies inversely with tubular flow and accounts for
the elevation of blood urea when renal function is low.
•Concentration of Urea in urine = 70x concentration of Urea in plasma
•Urea forms 80% of total urinary solutes .
•Urine is roughly a 2 % solution of Urea.

47. Renal Tubular reabsorption of Potassium
•70%of potassium in glomerular filtrate is reabsorbed by Proximal convoluted
tubule-PCT.
•Net secretion of potassium at the distal tubules ,in exchange for sodium
reabsorption , under the effect of aldosterone.
•However when H
+
concertation is increased, H
+
ions are exchanged for
sodium instead of potassium.

48. Mechanism of action of diuretics :1
Diuretics Mechanism of action of diuretics Siteofaction
Mannitol Osmotic diuretics act by interfering with reabsorption
of solutes so that more water is obligatory excreted
along with the solutes .
PCT
Acetazolamide A carbonic anhydrase inhibitor-the dissociation of
H
2CO
3to H
2O and CO
2is inhibited →decreased
reabsorption of bicarbonate ,sodium and water .
PCT
Thiazide decreased reabsorption of sodium and more water is
excreted obligatorily .
DCT
Frusemide Inhibits reabsorption of chloride , sodium and water
(chances for potassium depletion) .
Ascending limp of
loop of Henle
Spironolactone
(K
+
sparing )
Aldosterone antagonist DCT

49. Mechanism of action of diuretics:2

50. Mechanism of action of diuretics:3

51. Reabsorption ,secretion and excretion of substances by kidney
Parameter Reabsorption Secretion Excretion/relative
concentration
Creatinine Nil Nil GF = URINE
Uric acid 70 % by proximal
convoluted tubules
(PCT)
by distal convoluted
tubules( DCT)
GF URINE
Urea 40 % by PCT Nil GF > URINE
Sodium ( Na ⁺) Partial Nil GF > URINE
Glucose Complete Nil GF >> URINE
Amino acids Complete Nil GF >> URINE

52. Tubular maximum
•Tubular maximum (Tm): is used to indicate maximum capacity of kidneys to
absorb a particular substance .
•e.g. Tubular maximum for glucose (TmG) : 350 mg/min

53. Defects in Renal Tubular reabsorption
•Renal glycosuria in which glucose appears in urine despite of normal plasma
glucose levels .
•Vitamin D resistant rickets : in which phosphates reabsorption is defective .
•De Toni Fanconi syndrome:is associated with glycosuria, phosphaturia and
Renal Tubular acidosis.
•RenalAminoaciduria: as in Fanconi syndrome and cystinosis .

54. Cystinosis and Fanconi syndrome : Defects in Renal Tubular reabsorption
Cystinosis Fanconi syndrome

55. Tubular secretion in kidney
❖Tubular secretion in kidney :
❖substancesactively secretedby renal tubular cells include:
a)Endogenoussubstances( e.g. hippuric acid ,bile salts ,urates)
b)Exogenoussubstances( e.g. diuretics , salicylates ,p-amino Hippurate,
penicillin )
❖Creatinine: is secreted when plasma levels increase above normal levels .
❖Potassium: is secreted in the DCT in exchange for sodium reabsorbed.
❖Aldosteronefavors sodium reabsorptionand excretionofPotassium.
❖Primaryaldosteronism (excessive Aldosterone): there is excessive excretion
ofPotassium and retention of sodium.
❖Addison’sdisease(deficiency of Aldosterone) : sodium excretedand
Potassium retained in excess .

56. Addison’sdisease and Cushing's syndrome
Addison’sdisease(deficiency of Aldosterone)
: sodium excretedandPotassium retained in
excess .
Primaryaldosteronism (excessive
Aldosterone): there is excessive excretionof
Potassium and retention of sodium.

57. Addison’sdisease-bronze pigmentation
Addison’sdisease(deficiency of Aldosterone) : sodium excretedandPotassium
retained in excess .

58. Tubular secretory mass in kidney
•Tubular secretory mass : mass of functioning Tubular mass can be assessed
by measuring the tubular maximum for PAH(Tm PAH).
Tm = UV/P X GFR
For PAH ,the Tm is 76 mg/minute.

59. Tubular Dysfunctions of Kidney
❖In Tubular Dysfunctions of Kidney:
1.Urine volume increases
2.Urine concentration decreases
3.Specific gravity decreases
4.Serum uric acid increases (uric acid excretion decreases)
5.Acidification of urine decreases
6.Amino aciduria present
7.Serum phosphate decreases
8.Urine dilution test abnormal

60. Summary of kidney function tests in Glomerular and tubular dysfunction
Glomerular dysfunction observationTubular dysfunctionobservation
Serum urea Increased Urine concentrationdecreased
Serum creatinine IncreasedDilution test Abnormal
Serum phosphate decreasedSerumphosphate decreased
Inulin clearance decreasedUric acid excretiondecreased
Creatinine clearance decreasedBlood Uric acid Increased
Urea clearance decreasedAcidification of urineDecreased
PAH clearance decreased
Proteinuria Present Aminoaciduria Present
Urine volume Decreased Urine volume Increased 
Specific gravity Increased Specific gravity decreased

61. Biochemical parameters based on renal functions
Renal function Biochemical Parameters
Excretory function NPN –plasma levels of Urea ,Creatinine, Uric acid
Endocrine function Hemoglobin ,Serum calcium , Serum Phosphorus
Homeostasis
(acid -base balance)
Blood pH , Serum Electrolytes ( Sodium, Potassium ,chlorides) Serum
Bicarbonate, Serum Calcium and Inorganic phosphorous ,
Blood gases ( PO
2
, PCO
2)

62. Thank you
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