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Renal Physiology. D. C. Mikulecky Faculty Mentoring Program Virginia Commonwealth Univ. FUNCTIONS OF THE KIDNEY. Water balance Electrolyte balance Plasma volume Acid-base balance Osmolarity balance Excretion Hormone secretion. THE URINARY SYSTEM. Kidneys

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renal physiology

Renal Physiology

D. C. Mikulecky

Faculty Mentoring Program

Virginia Commonwealth Univ.

functions of the kidney
FUNCTIONS OF THE KIDNEY
  • Water balance
  • Electrolyte balance
  • Plasma volume
  • Acid-base balance
  • Osmolarity balance
  • Excretion
  • Hormone secretion
the urinary system
THE URINARY SYSTEM
  • Kidneys
  • Blood supply: Renal arteries and veins
  • Ureter
  • Urinary bladder
  • Urethra
the nephron is the functional unit of the kidney
THE NEPHRON IS THE FUNCTIONAL UNIT OF THE KIDNEY

Bowman’s

Capsule

Proximal

Convoluted

Tubule

Distal

Convoluted

Tubule

Peritubular Capillaries

Cortex

Glomerulus

Medulla

Collecting

Duct

Artery

Loop of Henle

Vein

three basic renal processes
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
basic renal processes
BASIC RENAL PROCESSES

Efferent Arteriole

Afferent

Arteriole

Glomerulus

GF

TR

Kidney

Tubule

Peritubular Capillary

TA

Urine Excreted

glomerular filtration
Glomerular Filtration
  • First step in urine formation
  • 180 liters/day filtered
  • Entire plasma volume filtered 65 times/day
  • Proteins not filtered
forces involved in glomerular filtration
Forces Involved inGlomerular Filtration

+

Glomerular Capillary

Blood Pressure

55

-

Plasma Colloid

Osmotic Pressure

30

-

Bowman’s Capsule

Hydrostatic Pressure

15

Net Filtration Pressure

+

10

tubular reabsorption
Tubular Reabsorption
  • Water: 99% reabsorbed
  • Sodium: 99.5% reabsorbed
  • Urea: 50% reabsobed
  • Phenol: 0% reabsorbed
tubular reabsorption10
Tubular Reabsorption
  • By passive diffusion
  • By primary active transport: Sodium
  • By secondary active transport: Sugars and Amino Acids
sodium reabsorption
Sodium Reabsorption

PUMP: Na/K ATPase

Plasma

Sodium

Lumen

Cells

Potassium

Chloride

Water

rennin angiotensin aldosterone system
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
rennin angiotensin aldosterone system14
Rennin-Angiotensin-Aldosterone System

Fall in NaCl, extracellular fluid volume, arterial blood pressure

Helps

Correct

Adrenal

Cortex

Juxtaglomerular

Apparatus

Lungs

Liver

Renin

+

Converting

Enzyme

Angiotensin

Angiotensin

Angiotensin

Aldosterone

Increased

Sodium

Reabsorption

diuretics
DIURETICS
  • ACE Inhibitors (Angiotensin Converting Enzyme): Cause loss of salt---> water follows
  • Atrial Naturetic Peptide (ANP) also inhibits sodium reabsorption
  • Osmotic diuretics: Are not reabsorbed
glucose and amino acids are reabsorbed by secondary active transport
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
glucose reabsorption has a tubular maximum
GLUCOSE REABSORPTION HAS A TUBULAR MAXIMUM

Glucose

Reabsorbed

mg/min

Excreted

Filtered

Reabsorbed

Renal threshold (300mg/100 ml)

Plasma Concentration of Glucose

tubular secretion
Tubular Secretion
  • Protons (acid/base balance)
  • Potassium
  • Organic ions
potassium secretion
Potassium Secretion

PUMP: Na/K ATPase

Plasma

Sodium

Lumen

Cells

Potassium

Chloride

Water

dual control of aldosterone secretion
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

reabsorption in proximal tubule summary
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
secretion in proximal tubule summary
Secretion in Proximal Tubule (Summary)
  • Variable Proton secretion for acid/base regulation
  • Organic Ion secretion
reabsorption in distal tubule summary
Reabsorption in Distal Tubule (Summary)
  • Variable Sodium controlled by Aldosterone
  • Chloride follows passively
  • Variable water controlled by vasopressin
secretion in distal tubule summary
Secretion in Distal Tubule (Summary)
  • Variable Proton for acid/base regulation
  • Variable Potassium controlled by aldosterone
collecting duct summary
Collecting Duct (Summary)
  • Variable water reabsorption controlled by vasopressin
  • Variable Proton secretion for acid/base balance
regulation of urine concentration
REGULATION OF URINE CONCENTRATION
  • Medullary countercurrent system
  • Vasopressin
medullary countercurrent system
Medullary countercurrent system
  • Osmotic gradient established by long loops of Henle
  • Descending limb
  • Ascending limb
descending limb
Descending limb
  • Highly permeable to water
  • No active sodium transport
ascending limb
Ascending limb
  • Actively pumps sodium out of tubule to surrounding interstitial fluid
  • Impermeable to water
countercurrent makes the osmotic gradient
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

the osmotic gradient concentrates the urine when vasopressin anti diuretic hormone adh is present
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

when vasopressin anti diuretic hormone adh is absent a dilute urine is produce
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

renal failure
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
the urinary bladder stores the urine
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
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

Reflex and Voluntary Control of Micturition