Renal Physiology

1
Renal Physiology

• D. C. Mikulecky
• Faculty Mentoring Program
• Virginia Commonwealth Univ.

2
FUNCTIONS OF THE KIDNEY

• Water balance
• Electrolyte balance
• Plasma volume
• Acid-base balance
• Osmolarity balance
• Excretion
• Hormone secretion

3
THE URINARY SYSTEM

• Kidneys
• Blood supply Renal arteries and veins
• Ureter
• Urinary bladder
• Urethra

4
THE NEPHRON IS THE FUNCTIONAL UNIT OF THE KIDNEY
Bowmans Capsule
Proximal Convoluted Tubule
Distal Convoluted Tubule
Peritubular Capillaries
Cortex
Glomerulus
Medulla
Collecting Duct
Artery
Loop of Henle
Vein
5
THREE BASIC RENAL PROCESSES

• Glomerular Filtration Filtering of blood into
  tubule forming the primitive urine
• Tubular Reabsorption Absorption of substances
  needed by body from tubule to blood
• Tubular Secretion Secretion of substances to be
  eliminated from the body into the tubule from the
  blood

6
BASIC RENAL PROCESSES
Efferent Arteriole
Afferent Arteriole
Glomerulus
GF
TR
Kidney Tubule
Peritubular Capillary
TA
Urine Excreted
7
Glomerular Filtration

• First step in urine formation
• 180 liters/day filtered
• Entire plasma volume filtered 65 times/day
• Proteins not filtered

8
Forces Involved inGlomerular Filtration

Glomerular Capillary Blood Pressure
55
-
Plasma Colloid Osmotic Pressure
30
-
Bowmans Capsule Hydrostatic Pressure
15
Net Filtration Pressure

10
9
Tubular Reabsorption

• Water 99 reabsorbed
• Sodium 99.5 reabsorbed
• Urea 50 reabsobed
• Phenol 0 reabsorbed

10
Tubular Reabsorption

• By passive diffusion
• By primary active transport Sodium
• By secondary active transport Sugars and Amino
  Acids

11
Tubular Reabsorption is a Function of the
Epithelial Cells Making up the Tubule
Plasma
Lumen
Cells
12
Sodium Reabsorption
PUMP Na/K ATPase
Plasma
Sodium
Lumen
Cells
Potassium
Chloride
Water
13
Rennin-Angiotensin-Aldosterone System

• Stimulates Sodium Reabsorption in distal and
  collecting tubules
• Naturetic peptide inhibits
• In absence of Aldosterone, 20mg of sodium/day may
  be excreted
• Aldosterone can cause 99.5 retention

14
Rennin-Angiotensin-Aldosterone System
Fall in NaCl, extracellular fluid volume,
arterial blood pressure
Helps Correct
Adrenal Cortex
Juxtaglomerular Apparatus
Lungs
Renin
Liver

Converting Enzyme
Angiotensin
Angiotensin
Angiotensin
Aldosterone
Increased Sodium Reabsorption
15
DIURETICS

• ACE Inhibitors (Angiotensin Converting Enzyme)
  Cause loss of salt---gt water follows
• Atrial Naturetic Peptide (ANP) also inhibits
  sodium reabsorption
• Osmotic diuretics Are not reabsorbed

16
Glucose and Amino Acids are reabsorbed by
secondary active transport

• They are actively transported across the apical
  cell membranes of the epithelial cells
• Their active transport depends on the sodium
  gradient across this membrane
• All other steps are passive

17
GLUCOSE REABSORPTION HAS A TUBULAR MAXIMUM
Glucose Reabsorbed mg/min
Excreted
Filtered
Reabsorbed
Renal threshold (300mg/100 ml)
Plasma Concentration of Glucose
18
Tubular Secretion

• Protons (acid/base balance)
• Potassium
• Organic ions

19
Potassium Secretion
PUMP Na/K ATPase
Plasma
Sodium
Lumen
Cells
Potassium
Chloride
Water
20
DUAL CONTROL OF ALDOSTERONE SECRETION
Fall in sodium ECF Volume Blood Pressure
Increased Plasma Potassium
Increased Aldosterone secretion
Increased Tubular Potassium Secretion
Increased Tubular Sodium Reabsorption
Increased Urinary Potassium Secretion
Fall in Urinary Sodium Excretion
21
Reabsorption in Proximal Tubule (Summary)

• Glucose and Amino Acids
• 67 of Filtered Sodium
• Other Electrolytes
• 65 of Filtered Water
• 50 of Filtered Urea
• All Filtered Potassium

22
Secretion in Proximal Tubule (Summary)

• Variable Proton secretion for acid/base
  regulation
• Organic Ion secretion

23
Reabsorption in Distal Tubule (Summary)

• Variable Sodium controlled by Aldosterone
• Chloride follows passively
• Variable water controlled by vasopressin

24
Secretion in Distal Tubule (Summary)

• Variable Proton for acid/base regulation
• Variable Potassium controlled by aldosterone

25
Collecting Duct (Summary)

• Variable water reabsorption controlled by
  vasopressin
• Variable Proton secretion for acid/base balance

26
REGULATION OF URINE CONCENTRATION

• Medullary countercurrent system
• Vasopressin

27
Medullary countercurrent system

• Osmotic gradient established by long loops of
  Henle
• Descending limb
• Ascending limb

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Descending limb

• Highly permeable to water
• No active sodium transport

29
Ascending limb

• Actively pumps sodium out of tubule to
  surrounding interstitial fluid
• Impermeable to water

30
COUNTERCURRENT MAKESTHE OSMOTIC GRADIENT
From Proximal Tubule
To Distal Tubule
Cortex Medulla
300 450 600 750 900 1050 1200 1200
100 250 400 550 700 850 1000 1000
300 450 600 750 900 1050 1200 1200
Active Sodium Transport
Passive Water Transport
Long Loop of Henle
31
THE OSMOTIC GRADIENT CONCENTRATES THE URINE WHEN
VASOPRESSIN (ANTI DIURETIC HORMONE ADH) IS
PRESENT
From Distal Tubule
Interstitial Fluid
Cortex Medulla
300 400 550 700 850 1000 1100 1200
300 450 600 750 900 1050 1200 1200
Collecting Duct
Pores Open
Passive Water Flow
32
WHEN VASOPRESSIN (ANTI DIURETIC HORMONE ADH) IS
ABSENT A DILUTE URINE IS PRODUCE
From Distal Tubule
Interstitial Fluid
Cortex Medulla
100 100 100 100 100 100 100 100
300 450 600 750 900 1050 1200 1200
Collecting Duct
Pores Closed
No Water Flow Out of Duct
33
Renal Failure

• Acute Sudden onset, rapid reduction in urine
  output - usually reversible
• Chronic Progressive, not reversible
• Up to 75 function can be lost before it is
  noticeable

34
THE URINARY BLADDER STORES THE URINE

• Gravity and peristaltic contractions propel the
  urine along the ureter
• Parasympathetic stimulation contracts the bladder
  and micturition results if the sphincters
  (internal and external urethral sphincters) relax
• The external sphincter is under voluntary control

35
Reflex and Voluntary Control of Micturition

• Bladder filling reflexively contracts the bladder
• Internal Sphincter mechanically opens

• Stretch receptors in bladder send inhibitory
  impulses to external sphincter
• Voluntary signals from cortex can override the
  reflex or allow it to take place