RENAL PHYSIOLOGY

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RENAL PHYSIOLOGY
DR SYED SHAHID HABIB MBBS DSDM FCPS Associate
Professor Dept. of Physiology College of Medicine
KKUH
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Renal Physiology

• Introduction
• Glomerular Filtration
• Tubular Processing
• Urine Concentrating Mechanism
• Micturition

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RENAL PHYSIOLOGYTUBULAR PROCESSINGTUBULAR
REABSORPTION SECRETION
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URINE COMPOSITION
pH usually acidic (pH 6) range 4.8 - 7.5
Colour Bright Yellow transparent
Volume 1 - 2 L per day
Glucose None
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REABSORTION PATHWAYS
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urea
inulin
gluc
Creat
Urinary Excretion Rate Filtration Rate
Reabsorption Rate Secretion Rate
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  of Filtered Load Reabsorbed
Glucose (g/day) 100
Bicarbonate (mEq/day) gt99.9
Sodium (mEq/day) 99.4
Chloride (mEq/day) 99.1
Potassium (mEq/day) 87.8
Urea (g/day) 50
Creatinine (g/day) 0
Glucose
Urea
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PROXIMAL CONVOLUTED TUBULE

• many mitochondria
• brush border
• tight junctions
• lateral intercellular spaces.

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GLUCOSE AND AMINO ACID REABSORPTION IN NEPHRON
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TUBULAR TRANSPORT MAXIMUM

• The Maximum limit/rate at which a solute can be
  transported across the tubular cells of kidneys
  is called TUBULAR TRANSPORT MAXIMUM

Tm for Glucose is 375 mg/min
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GLUCOSE REABSORPTION

• FBG60-110 mg/dl
• RBG110-200 mg/dl

Transport max 375 mg/min Renal Threshold
200mg/dl
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HYDROGEN
Na-H COUNTER TRANSPORT Luminal Membrane

• Secreted in Proximal Tubule and LOH by Counter
  Transport with Na

PCT LOH
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PCT
water Reabsoprtion 65
Na
Countertransport
H
Cl-
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SODIUM HANDLING

• Na moves by co transport or exchange from the
  tubular lumen into tubular epithelial cells
• From cells into interstitium it moves by primary
  active transport
• In DCT and CT it is under hormonal control

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SODIUM HANDLING
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Renal tubular reabsorption

• Solute reaborption in the proximal tubule is
  isosmotic (water follows solute osmotically and
  tubular fluid osmolality remains similar to that
  of plasma).
• 65 of water and sodium reabsorption occurs in
  the proximal tubule
• 100 of glucose amino acids
• Proximal tubules coarse adjustment
• Distal tubules fine adjustment (hormonal
  control).

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THIN LOOP OF HENLE

• few mitochondria
• flattened with few microvilli

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THIN DESCENDING LOOP OF HENLE

• few mitochondria
• flattened with few microvilli

Solutes
H2O
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THICK ASCENDING LOOP OF HANLE AND EARLY DCT
Many mitochondria and microvilli, but fewer than
in the proximal tubule
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ASCENDING LOOP OF HENLE
Many mitochondria and microvilli, but fewer than
in the proximal tubule
Solutes
H2O
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ECF
Lumen
Epithelial Cells
Events in Thick ALOH
Sodium potassium 2 chloride co transport
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Absorption through loop of Henle Descending
limb is water permeable and allow absorption of
15 of filtered H2O. It is impermeable to
Na-CL. Thin ascending limb is impermeable to
H2O, but permeable to Na-Cl, where they are
absorbed passively in this part . Thick
ascending limb is impermeable to H2O. Na-K-2Cl
co-transport occur in this part (25 of Na).
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HYDROGEN
ASCENDING LOOP OF HENLE
Na-H COUNTER TRANSPORT Luminal Membrane

• Secreted in Proximal Tubule and LOH by Counter
  Transport with Na

PCT LOH
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LATE DCT AND CORTICAL COLLECTING DUCT

• Mitochondria and microvilli decrease.
• Principal Cells (Na Abs and ADH related Water
  abs)
• Intercalated Cells (Acid Sec and HCO3 Transport)

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DCT AND COLLECTING DUCT
I Cell
P Cell

• Principal Cells (Water reabsortion)
• Intercalated Cells (Acid Secretion)

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Events in DCT
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Intercalated cell
Events in DCT CT
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Events in DCT CT
Aldosterone
Principal Cell
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Distal convoluted tubule and collecting ducts

• What happens here depends on hormonal control
• Aldosterone affects Na and K
• ADH facultative water reabsorption

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FACTORS AFFECTING ADH
Increase ADH Decrease ADH
?Osmolarity ?Osmolarity
? Blood volume ? Blood volume
? Blood pressure ? Blood pressure
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Clinical applications

• Thiazide diuretics
• Loop diuretics
• K sparring diuretics

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MEDULLARY COLLECTING DUCT
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REABSORPTION OF WATER IN DIFFERENT SEGMENTS OF
TUBULES
PART OF NEPHRON PERCENTAGE REABSORBED
Proximal tubules 65
Loop of Henle 15
Distal tubules 10
Collecting ducts 9.2
Passing into urine 0.8
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RENAL PHYSIOLOGYTUBULAR SECRETION

• DR SYED SHAHID HABIB
• MBBS, FCPS

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TUBULAR SECRETION

• Tubular Secretion may be by Passive or Active
  Mechanisms
• The most important secretory processes are for H,
  K and Organic Ions

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HYDROGEN

• Secreted in Proximal Tubule by Counter Transport
  with Na
• In DCT and CT it is secreted by Hydrogen ATP ase
• When body fluids are more acidic H secretory
  process is accelerated and Vice Versa

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HYDROGEN
Na-H COUNTER TRANSPORT Luminal Membrane

• Secreted in Proximal Tubule and LOH by Counter
  Transport with Na
• Secreted in DCT by H ATP ase Primary Active
  Transport

PCT LOH
I Cell in DCT
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RENAL PHYSIOLOGY COUNTER CURRENT MECHANISM
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COUNTER CURRENT MECHANISM

• KIDNEYS HAVE
• MECHANISMS FOR EXCRETING EXCESS WATER
• MECHANISMS FOR EXCRETING EXCESS SOLUTES

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NEPHRON TYPES

• Superficial (cortical) 85
• Capable of forming dilute urine
• Juxtamedullary 15
• Capable of forming concentrated
• (gt 300 mOsm/kg) urine

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EXCRETION LIMITS

• At least 600 mmol of solutes must be excreted
  each day
• minimum volume 600/1200 0.5L
• maximum volume 20 Liters

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EXCRETION LIMITS
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COUNTER CURRENT MECHANISM

• LOOPS OF HENLE OF JUXTA MEDULLARY NEPHRONS
  establish hyperosmolality of interstitium of
  medulla. They are called COUNTER CURRENT
  MULTIPLIERS
• VASA RECTA maintain hyperosmolality established
  by counter current multipliers. They are called
  COUNTER CURRENT EXCHANGERS

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300
200
300
300
300
Cortex
300
250
300
400
300
400
300
Medulla
500
400
500
600
500
600
400
700
600
700
800
800
800
Osmolality
1000
1000
1000
1200
1200
1200
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DISORDERS OF URINARY CONCENTRATING ABILITY

• Failure to Produce ADH "Central" Diabetes
  Insipidus.
• Inability of the Kidneys to Respond to ADH
  "Nephrogenic"
• Diabetes Insipidus.

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RENAL PHYSIOLOGYMICTURITION
DR SYED SHAHID HABIB MBBS DSDM FCPS Assistant
Professor Dept. of Physiology College of Medicine
KKUH
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MICTURITION

• It is the process by which the urinary bladder
  empties when it becomes filled
• Filling of bladder.
• Micturition reflex.
• Voluntary control.

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Physiologic Anatomy and Nervous Connections of
the Bladder

• Composed of
• Body
• Neck..post urethra (stretch receptors)
• External sphincter.
• Pelvic diaphragm.

A reservoir adult 250-400ml DETRUSOR MUSCLE
pr can rise upto 40-60 mmHg. Mucosa RUGAE
TRIGONE


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Nervous Connections of the Bladder
Urogenital diaphragm
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Micturition Reflex

• Actions of the internal urethral sphincter and
  the external urethral sphincter are regulated by
  reflex control center located in the spinal cord.
• Filling of the urinary bladder activates the
  stretch receptors, that send impulses to the
  micturition center.
• Activates parasympathetic neurons, causing
  rhythmic contraction of the detrusor muscle and
  relaxation of the internal urethral sphincter.
• Voluntary control over the external urethral
  sphincter.
• When urination occurs, descending motor tracts to
  the micturition center inhibit somatic motor
  fibers of the external urethral sphincter.

AUTONOMIC SPINAL REFLEX
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INNERVATION OF THE BLADDER
Nerves Characteristic Function
1 Pelvic nerves (parasympathetic fibers) S-2 and S-3 Both sensory and motor nerve fibers Contraction of bladder The sensory fibers detect the degree of stretch in the bladder wall
2 Pudendal Nerve somatic nerve Fibers that innervate and control the voluntary skeletal muscle of the sphincter
3 Hypogastric Nerves sympathetic innervation (L2) Stimulate mainly the blood vessels and have little to do with bladder contraction. Sensory nerve fibers of the sympathetic nerves also mediate the sensation of fullness and pain.
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CYSTOMETROGRAM