17. Renal NOTES - Penguin Prof
Transcript of 17. Renal NOTES - Penguin Prof
Urinary System
Functions of the Kidney
• Regulation of extracellular fluids
• Concentrations of waste, salts, regulating pH, etc.
• Formation of urine
• Regulation of plasma volume (blood pressure)
Urine Characteristics
• The more solutes = darker urine
• Measured in specific gravity
• Measuring solutes:
• PURE water: 1.000
• Dilute urine: 1.001
• Concentrated urine: 1.035
Urine Characteristics
• Urine may become dilute due to:
• Excess drinking, diuretics, renal failure
• Urine may become concentrated due to:
• Inadequate fluid intake, fever, pyelonephritis
Abnormal solutes signal problems:
• Glucose • due to excess sugar intake
or diabetes • Proteins
• due to physical exertion, pregnancy, glomerulonephritis, hypertension
• Pus • urinary tract infection
• rbc's • bleeding in the urinary tract
• Bile pigments • liver disease (hepatitis)
Urinary System Anatomy
• Location, Size
• Hilum
• Renal capsule
• Adipose capsule
The Kidney
Kidney in cross section
Kidney Blood Supply
• Renal artery ! many vessels branching and becoming smaller in diameter ! Afferent arterioles
• Efferent arterioles ! many vessels joining and becoming larger in diameter ! renal vein.
Ureters
Tubes which run from the hilum of the kidney to the posterior aspect of the bladder.
Is it just gravity that moves urine to the bladder?
5 mm is the limit of stones which can pass on their own
Urinary Bladder
• Bladder consists of 3 layers of smooth muscle
• Mucosa is transitional epithelium.
• Empty bladder: 5 - 7.5 cm long
• Moderately full: 12.5 cm long and holds 500 ml
• Urinary bladder plasticity
Urethra
• Carries urine from the bladder to the outside of the body.
• Internal urethral sphincter: at bladder / urethra junction.
• External urethral sphincter: as urethra passes through pelvic floor
• Is this voluntary or involuntary?
urethral challenges...
Seriously...
• How much excretion?
• Obligatory water loss = 400 ml / day
• Maximum? What do you think?
• How is this regulated?
Urinary System II Renal Physiology
Meet the Nephron!
Nephron Anatomy• Functional unit of the
kidney
• Made of tubular elements and vascular elements interwoven together
• Fluid in the tubular elements is called FILTRATE, while fluid in the vascular elements is called BLOOD
• Afferent arteriole ! Glomerulus ! efferent arteriole
• is there something wrong here?
Nephron Anatomy: Vascular Elements
• Renal corpuscle
• Glomerulus + Bowman's capsule
• Proximal tubule
• Loop of Henle
• Distal tubule
• Collecting duct (not part of the nephron)
Nephron Anatomy: Tubular Elements
Nephron Physiology
Filtration
• Movement of fluid from blood to nephron lumen
• Once in the lumen, what is it? Where is it?
• Specific or non-specific?
• What drives it?
• Why does the blood get filtered?
• Haven’t we done this before?
Filtration in the Nephron
Exchange is now from one tube to another!
so there’s another gradient in play
Glomerular Filtration Rate
• (GFR) = amount of fluid filtering into Bowman's capsule per unit time
• = 115 ml/ min in women and 125 ml/ min in men
• Influenced by:
• Net filtration pressure
• Available surface area
Regulation of GFR
• Extrinsic regulation: ANS
• Intrinsic regulation: Autoregulation
• Intrinsic regulation: Tubuloglomeruler feedback
• What does this tell you?
Reabsorption
• Returning fluid from the lumen to the blood
• 180L of plasma is filtered, but 99% of that (178.2L) is reabsorbed
• WHY?
Reabsorption may be:
• Active: Primary, secondary active transport
• Passive: diffusion, leak channels, facilitated diffusion carriers
Secretion
• Transporting substances from the blood to lumen
• Depends mostly on membrane transport systems
Excretion
• Urine is very different from the filtrate entering the nephron
• What is enriched? What is removed?
Journey Through the Tubulesand TWO BIG QUESTIONS:
How can the kidneys produce urine that is hypertonic to the blood being filtered?
and
How is urine volume / osmolarity regulated as hydration levels change?
How can solutes be concentrated?Doesn’t water always follow the solute?
Sunset Cliffs at low tide
Let’s Take a Trip…
Proximal Tubule
• Filtrate coming in is isoosmotic w/ plasma (300 mOsm)
• Ion reabsorption: pumps for Na+ and K+
• Cl- ions follow Na+ through channels
• Osmosis: water reabsorption
• So... is peritubular blood isoosmotic? What’s the point?
• Regulation here?
Loop of Henle
• Reabsorption of 20% of salts and water, regardless of hydration state
• Regulation here?
• Ascending limb:
• Na+ reabsorption via pumps; Cl- follows passively.
• What about water?
Loop of Henle
Walls of the ascending limb are not permeable to water.
Descending Limb
• Impermeable to salt
• Permeable to water; water is reabsorbed via osmosis out of the descending limb in response to the hypertonic tissue fluid
• Countercurrent multiplier effect
Other Hormonal Effects