BIOCHEMICAL INVESTIGATION OF
RENAL FUNCTIONS &
DISORDERS/RENAL FUNCTION
TEST
PRESENTED BY: OLOYEDE OLUWADAMILOLA G.
OUTLINE
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Introduction
Functional Anatomy of the Kidney
Functions of the Kidney
Disorders of the Kidney
Renal Function Tests
INTRODUCTION
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The kidneys are a pair of bean-shaped or ovoid organs about the size of a clenched
fist.
They are lie retroperitoneally against the posterior abdominal wall on each side of
the vertebral column at level T12-L3 vertebrae.
During life, the kidneys are reddish brown and measure approximately 10 cm in
length, 5cm in width and 5.5cm in thickness. Weight is 150g.
Each kidney has a vertical cleft at the concave medial margin. This is the Renal hilum.
The renal hilum is the entrance to a space within the kidney, the Renal Sinus.
Structures that serve the kidneys (vessels, nerves, ureter) enter and exit the renal
sinus via the renal hilum.
INTRODUCTION
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Arterial supply: Renal arteries arising from the abdominal aorta
Venous drainage: Renal veins
The kidneys receive about 20% of the cardiac output under normal conditions.
The kidneys have 2 regions:
○ Renal cortex
○ Renal medulla
The renal medulla contains 8-10 renal pyramids
FUNCTIONAL ANATOMY OF THE
KIDNEYS
NEPHRON
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The nephron is the functional unit of the kidney.
Each kidney contains about 1 million nephrons.
The kidneys cannot regenerate nephrons. Therefore, with renal injury, disease or normal
aging, the number of nephrons gradually decreases.
Types:
a. Cortical nephrons
b. Juxtamedullary nephrons
NEPHRON
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Each nephron is made up of 5 main functional segments:
a. Glomeruli
b. Proximal Convoluted Tubules
c. Loops of Henle
d. Distal Convoluted Tubules
e. Collecting Ducts
GLOMERULI
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The glomeruli, located in the cortex of the kidney, are invaginated and surround a
capillary network of blood vessels derived from the afferent arterioles, and draining into
the efferent arterioles.
The glomerular capillaries are covered by epithelial cells, and the total glomerulus is
encased in the Bowman’s capsule.
Small molecules and water are passively filtered during the passage of blood through
these capillaries, the ultrafiltrate passing through the vessel walls and the glomerular
membranes into the glomerular spaces (Bowman’s capsule).
GLOMERULI
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The filtration barrier is has a structure to restrict the filtration of large proteins into the
Bowman’s capsule.
The filtration barrier consists of 3 parts:
○ The fenestrations of the capillary endothelium, which blocks blood cells and
platelets
○ The thick, combined basal laminae, or Glomerular Basement Membrane, which
restricts large proteins and some organic anions
○ The filtration slit diaphragms between pedicels, which restrict some small proteins
and organic anions
PROXIMAL CONVOLUTED TUBULE
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The proximal tubules are also located in the cortex and receive filtrate from the
glomerular spaces.
It is the most metabolically active part of the nephron.
The cells of the PCT have abundant mitochondria and are specialized for both
reabsorption and secretion.
Extremely high permeability to water
Na-K ATPase Pump on basolateral membrane
Major function: Reabsorption of all organic nutrients (glucose, amino acids), all proteins,
most water and electrolytes( Na, K, Cl, HCO-, H2O); secretion of organic anions and
cations, H+, and NH4+
Convolution of the proximal tubules increases the tubular length and therefore contact
between the luminal fluid and the proximal tubular cells.
LOOPS OF HENLE
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The loop of Henle consists of 3 limbs:
○ Thin Descending,
○ Thin Ascending &
○ Thick Ascending
Thin Descending Limb: Consists of thin epithelial cells with low metabolic activity. Highly
permeable to water.
Thick Ascending Limb: Consists of thick epithelial cells with high metabolic activity.
Impermeable to water (important for urine concentration).
Na-K ATPase Pump on basolateral membrane and Na-K-2Cl Co-transporter Pump on
luminal membrane
Reabsorbs Na, Cl, K, Ca, Mg, HCO3
DISTAL CONVOLUTED TUBULE
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Activity of Na-K ATPase is highest
Na-Cl Co-transporter on luminal membrane
Reabsorbs Na, Cl
First portion forms the Macula Densa in the Juxtaglomerular Apparatus. It provides
feedback control of GFR and RBF.
JUXTAGLOMERULAR APPARATUS
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The juxtaglomerular apparatus consists of the juxtaglomerular cells of the afferent
glomerular arteriole, the efferent glomerular arteriole, the extraglomerular mesangial
cells, and that small portion of the distal tubule known as the macula densa that is
located beside the renal glomerulus.
This structure has specialized cell types: the macula densa of the distal tubule, the renincontaining cells of the afferent arteriole, and the interstitial lacis cells of the glomerular
mesangium.
The juxtaglomerular apparatus functions to maintain blood pressure and to act as a
quality control mechanism to ensure proper glomerular flow rate and efficient sodium
reabsorption.
COLLECTING DUCTS
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Na-K ATPase Pump on basolateral membrane
Principal Cells: Regulated reabsorption of water & electrolytes; regulated secretion of
K+
Intercalated Cells: Reabsorption of K+ (low-K+ diet); help maintain acid-base balance
RENAL INTERSTITIUM
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In all parenchymal organs, including the kidney, the interstitium is situated in the space
between the basement membranes of the epithelial cells and of the nutritive capillaries.
The renal interstitium is defined as the intertubular, extraglomerular, extravascular
space of the kidney. It is bounded on all sides by tubular and vascular basement
membranes and is filled with cells, extracellular matrix, and interstitial fluid.
FUNCTIONS OF THE KIDNEY
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Endocrine Function
Homeostatic Function
Excretory Function
Gluconeogenesis
ENDOCRINE FUNCTION
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The kidneys produce hormone, Erythropoietin.
The main function of this hormone is stimulate the production of red blood cells
(erythrocytes)by the haematopoietic stem cells in the bone marrow.
Stimulus: Hypoxia
ENDOCRINE FUNCTION
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The kidneys also contribute to short-term arterial pressure by secreting hormones and
vasoactive substances such as RENIN.
The juxtaglomerular cells secrete renin in response to decreased renal blood flow.
Renin then activates the Renin-Angiotensin Aldosterone System (RAAS)
ENDOCRINE FUNCTION
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The kidneys produce the active form of Vitamin D, CALCITRIOL (1,25-dihydroxyvitamin
D3).
Calcitriol is essential for normal calcium deposition in the bone and calcium reabsorption
by the GIT.
EXCRETORY FUNCTION
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The kidneys are the primary means for eliminating waste products of metabolism.
These products include:
a. Urea
b. Creatinine
c. Uric acid
d. End products of haemoglobin breakdown (e.g Bilirubin)
e. Metabolites of various hormones
The kidneys also eliminate most toxins and foreign substances that are either produced
by the body or ingested, such as pesticides, drugs and food additives.
HOMEOSTATIC FUNCTION
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Kidneys regulate water and electrolyte balance by matching fluid output with intake.
The kidney helps maintain acid-base balance by eliminating excess acid in the form of
hydrogen ions or producing bicarbonate to neutralize excess acid.
Kidneys regulate blood pressure by excreting variable amounts of sodium and water, or
by secreting precursors (Renin) of vasoactive substances (Angiotensin II).
GLUCONEOGENESIS
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Kidneys synthesize glucose from amino acids, lactate and glycerol during prolonged
fasting, a process referred to as Gluconeogenesis.
The Kidney’s capacity to add glucose to the blood during prolonged periods of fasting
rivals that of the liver.
DISORDERS OF THE KIDNEY
PATHOPHYSIOLOGY OF RENAL DISORDERS
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Renal dysfunction of any kind affects all parts of the nephron to some extent, although
sometimes, either glomerular or tubular dysfunction is predominant.
The net effect of renal disease on plasma and urine depends on the proportion of
glomeruli to tubules affected and on the number of nephrons involved.
To understand the consequences of renal disease it is good to compare what happens in
the plasma and urine when there’s is low GFR and normal tubular function and vice
versa.
REDUCED GFR WITH NORMAL TUBULAR FUNCTION
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The total amounts of urea and creatinine excreted are affected by the GFR. If the
filtration rate fails to balance that of production, plasma concentrations will rise.
Plasma concentrations rise because less than normal is filtered.
More of the reduced amount reaching the proximal tubule can be reabsorbed, and the
capacity for secretion is impaired if the filtered volume is too low to accept the ions,
further contributing to high plasma concentrations.
REDUCED GFR WITH NORMAL TUBULAR FUNCTION
PLASMA
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Uraemia & Creatininemia
Low bicarbonate concentration, with
low pH (acidosis)
Hyperkalemia
Hyperuricemia
Hyperphosphatemia
URINE
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Oliguria (reduced volume)
Low (appropriate) sodium
concentration - only if RBF is low,
stimulating aldosterone secretion
High (appropriate) urea concentration
and therefore a high osmolality - only if
ADH secretion is stimulated
REDUCED TUBULAR FUNCTION WITH NORMAL GFR
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Damage to tubular cells impairs adjustment of the composition and volume of the urine.
Impaired solute reabsorption from proximal tubules reduces isosmotic water
reabsorption.
Countercurrent multiplication may also be affected, therefore the ability of the
collecting ducts to respond to ADH is reduced. A large volume of inappropriately urine
is produced.
REDUCED TUBULAR FUNCTION WITH NORMAL GFR
PLASMA
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Normal urea and creatinine concentration (normal glomerular function)
Due to proximal tubular failure
○ Hypophosphatemia, hypomagnesaemia, hypouricaemia
Due to proximal or distal tubular failure
○ Low Bicarbonate concentration and low pH
○ Hypokalaemia
REDUCED TUBULAR FUNCTION WITH NORMAL GFR
URINE
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Due to proximal tubular failure
○ Glycosuria
○ Generalized amino aciduria
○ Phosphaturia
○ Possible tubular proteinuria
Due to proximal and/or distal tubular failure
○ Increased volume
○ Inappropriately high pH
Due to distal tubular failure
○ Inappropriately high Sodium concentration (even in RBF is low)
○ Inappropriately low Urea concentration and osmolality (even if ADH is stimulated)
CLINICAL FEATURES OF RENAL DISORDERS
UREA & CREATININE
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Plasma concentrations depend largely on glomerular function.
Urinary concentrations depend largely on tubular function.
Difference between plasma and urinary concentrations is due to tubular function.
The more the tubular function is impaired, the nearer the plasma concentrations will be
to the urinary concentration.
Urinary concentration inappropriate to the state of hydration of the body suggest
tubular damage, regardless of the degree of glomerular dysfunction.
CLINICAL FEATURES OF RENAL DISORDERS
SODIUM
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Plasma concentration is not primarily affected by renal diseases.
The urinary volume depends on the difference between volume filtered in the
glomerulus and volume reabsorbed by tubules.
WATER
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As 99% of filtered water is normally reabsorbed, a small reabsorption impairment causes
a large increase in urine volume.
Polyuria results from predominant tubular dysfunction, even though glomerular
filtration is reduced.
CLINICAL FEATURES OF RENAL DISORDERS
POTASSIUM, PHOSPHATE & URATE
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Degree of retention depends on balance between degree of glomerular retention and
loss due to reduced absorptive capacity of the proximal tubules.
Plasma concentration rises if little is filtered due to predominant glomerular
dysfunction, even though there is failure of reabsorption.
Plasma concentration is normal or even low, if tubular dysfunction predominates as the
impaired reabsorption is balanced by the glomerular retention.
RENAL FUNCTION TESTS
RENAL FUNCTION TESTS
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Renal function tests are a group of laboratory tests useful in investigating and evaluating
kidney function.
They include:
a. Glomerular Function Tests
b. Renal Tubular Function Tests
GLOMERULAR FUNCTION TESTS
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As glomerular function deteriorates, substances that are normally cleared by the
kidneys, such as urea and creatinine, accumulate in the plasma.
The glomerular function tests include:
a. Measurement of Plasma Concentrations of Urea and Creatinine
b. Plasma Clearance as an Assessment of GFR
c. Cystatin C
MEASUREMENT OF PLASMA CONCENTRATIONS OF
UREA & CREATININE
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Normal range of Plasma Urea Concentration is 1.0 – 15mmol/L.
Raised Plasma Urea Concentration is always accompanied with elevated Plasma
Creatinine Concentration.
The rate at which urea is reabsorbed from the collecting ducts is dependent on
○ The amount filtered by the glomerulus
○ Rate of luminal fluid flow
MEASUREMENT OF PLASMA CONCENTRATIONS OF
UREA & CREATININE
Basis
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Plasma Urea Concentration greater than 15mmol/L indicates impaired glomerular function.
Urea concentration rises when production exceeds clearance or when clearance is impaired.
In renal dysfunction caused by reduced GFR, the plasma urea concentration rises faster than
creatinine.
Causes of Increase in Plasma Urea Concentration
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High protein diet.
Absorption of amino acids and peptides from digested blood after haemorrhage into the
gastrointestinal lumen (proctitis, cancers, tumors, haemorrhoids).
Increased catabolism due to starvation, tissue damage, sepsis or steroid treatment.
MEASUREMENT OF PLASMA CONCENTRATIONS OF
UREA & CREATININE
Basis
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Plasma Urea Concentration less than 1.o mmol/L could be due to increased GFR (most
common) or decreased synthesis
Urea concentration is lowered when clearance is increased or production is reduced
Causes of less than 1.0mmol/L Plasma Urea Concentration (due to increased GFR)
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Pregnancy (commonest in young women)
Over-enthusiastic intravenous infusion (commonest in hospital patients)
Syndrome of inappropriate ADH Secretion
MEASUREMENT OF PLASMA CONCENTRATIONS OF
UREA & CREATININE
Causes of less than 1.0mmol/L Plasma Urea Concentration (due to decreased
synthesis)
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Low protein intake
Very severe liver disease (low amino acid deamination)
Use of amino acids for protein anabolism during growth, especially in children
Inborn errors of the urea cycle (rare, and usually occur in infants)
CLEARANCE AS AN ASSESSMENT OF GLOMERULAR
FILTRATION
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Clearance is the volume of plasma that could theoretically be completely cleared of a
substance in 1 minute.
Only substances freely filtered by the glomeruli and not acted on by the tubules can be
used to give true measurement of GFR.
Exogenous substances that can be used for measuring clearance include:
○ Inulin
○ Radiochromium-labelled EDTA
Endogenous substance commonly used is Creatinine
The reciprocal of plasma creatinine concentration is called Renal Index
Creatinine Clearance vs Inulin Clearance vs Urea Clearance
Creatinine Clearance vs Plasma Creatinine Concentration
CLEARANCE AS AN ASSESSMENT OF GLOMERULAR
FILTRATION
CYSTATIN C
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Plasma Cystatin C (Cys C) is an endogenous marker that may be used to replace
Creatinine
Unlike endogenous substances like Creatinine, it is neither secreted into the renal
tubules nor reabsorbed back into the bloodstream.
RENAL TUBULAR FUNCTION TEST
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Proximal Tubular Function Test
Distal Tubular Function Test
Water Deprivation Test
REFERENCES
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Clinical Biochemistry and Metabolic Medicine by Martin A Crook
Guyton and Hall Textbook of Medical Physiology by John E. Hall
Clinically Oriented Anatomy by Keith L. Moore, Arthur F. Dalley, Anne M. R. Agur