Physiology 441

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Physiology 441
The Renal System, Chp. 14 Text Human Physiology
(Sherwood), 6th Ed.
Julie Balch Samora, MPA, MPH jbsamora_at_hsc.wvu.edu
293-3412, Room 3145
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Medullary vertical osmotic gradient

• The medullary vertical osmotic gradient and ADH
  allow the kidney to excrete urine of varying
  concentrations
• Without this osmotic gradient, we could not
  produce a concentrated urine, and would be unable
  to conserve water
• We would likewise be unable to rid the body of
  excess water w/o this system

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Distal tubule
Distal tubule
Glomerulus
Proximal tubule
Bowmans capsule
Proximal tubule
Cortex
Medulla
Loop of Henle
Collecting duct
Descending limb of loop of Henle
Other nephrons emptying into the same collecting
duct
Vasa recta
Ascending limb of loop of Henle
To renal pelvis
Fig. 14-5, p. 505
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Countercurrent Multiplication

• The loops of Henle of the juxtamedullary nephrons
  are responsible for establishing the
  concentration gradient in the renal medulla
• Descending limb is freely permeable to H2O, but
  NOT NaCl so H2O goes into IF
• Ascending Limb IMPERMEABLE to water
• The ascending limb actively transports out NaCl

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Countercurrent
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Renal Disease

• Acute sudden shutdown of kidneys may be
  reversible
• Chronic progressive, slow, insidious,
  irreversible loss of kidney fxn. Up to 75 of
  kidney tissue can be destroyed before loss of
  kidney fxn is even noticeable
• End stage renal failure when 90 of kidney fxn
  has been lost

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Consequences of Renal Failure

• Uremic toxicity retention of waste products
  body overwhelmed by toxins
• Metabolic acidosis results from the inability
  of the kidneys to adequately secrete H - leads
  to CNS depression
• Potassium retention from inadequate tubular K
  secretion altered cardiac excitability

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Consequences of Renal Failure

• Sodium imbalances from inability of kidneys to
  vary Na reabsorption
• Phosphate and calcium imbalances from impaired
  reabsorption leads to skeletal disturbances
• Loss of plasma proteins from leakiness of
  glomerular membrane leads to edema
• Inability to vary urine concentrations from
  impairment of countercurrent system

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Consequences of Renal Failure

• Hypertension from salt and fluid retention and
  excess angiotensin II
• Anemia deficiency of erythropoietin
• Depression of immune system toxic effect on
  immune system ? infxns

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Micturition

• Transmission of urine to the bladder
• Urine forced along ureters by peristalsis
• Ureters penetrate bladder obliquely, preventing
  reflux
• As bladder fills, the ureteral openings are
  compressed
• Even though urine can still enter bladder through
  compressed openings, urine cannot escape back up
  ureters

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Micturition

• Storage of urine
• The bladder wall, made of smooth muscle, can
  stretch without a concomitant build-up of
  intrabladder pressure
• Once bladder fills beyond 200-400 ml, the
  pressure rises, stretching receptors
• Internal urethral sphincter at end of bladder,
  closes off
• Bladder supplied by PNS

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Micturition

• Role of the external urethral sphincter
• Farther down the urethra is a circular layer of
  skeletal muscle
• This sphincter is supplied by a motor neuron
• Unless the motor neuron is inhibited, it fires
  continuously, keeping the external sphincter
  contracted, thereby preventing urine from leaving
  bladder

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Micturition Reflex

• When stretch receptors within the bladder wall
  are stimulated, the micturition reflex is
  initiated
• Afferent fibers from the stretch receptors
  stimulate the PNS to inhibit the motor neuron
  supplying the external urethral sphincter
• In response to PNS stimulation of the bladder, it
  contracts.

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Micturition Reflex

• As the bladder contracts, the internal urethral
  sphincter is pulled open mechanically
• Inhibition of the motor neuron supplying the
  external sphincter allows for relaxation
• Both sphincters are relaxed, bladder is
  contracting, and urine flows freely from the
  bladder through the urethra
• Entirely a spinal reflex!

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Voluntary Control of Micturition

• Must be learned
• Can override the micturition reflex
• One can delay micturition despite synaptic input
  from bladder stretch receptors
• Although internal sphincter is open, can keep the
  external sphincter contracted so no urine is
  expelled

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Review Questions

• What gives rise to the unique appearance of the
  kidney?
• What is the average GFR?

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Review Questions

• What is the role of the vasa recta?
• What is the importance of the vertical osmotic
  gradient?

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Review Questions

• What is the major force favoring glomerular
  filtration?
• A decrease in afferent arteriolar resistance will
  do what to the GFR?

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Review Questions (T/F)

• The kidney eliminates toxins such as urea, uric
  acid, glucose and creatinine
• The kidney plays a role in the bodys vitamin D
  concentration
• The kidney produces renin

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Review Questions

• What are the types of autoregulation in the
  kidney?
• Where is sodium reabsorbed?

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Review Questions (T/F)

• Most of the filtered plasma is excreted
• Glomerular filtration is a highly discriminating
  process
• The higher the BUN, the better function the
  kidneys have

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Review Questions

• What is an example of a substance that is both
  actively secreted and actively reabsorbed?
• What is the formula for FF?

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Review Questions

• If a gentlemans avg. GFR is 125 ml/min, a
  substance that is being reabsorbed would have a
  clearance rate that is ?, ?, or ? compared with
  his avg. GFR.
• What establishes the medullary vertical osmotic
  gradient via the countercurrent multiplication?

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Review Questions (T/F)

• The ascending limb of the loop of Henle of a
  juxtamedullary nephron is permeable to water.
• The glomerular capillary pressure is lower than
  capillary pressure elsewhere in the body

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Review Questions (T/F)

• Water moves by osmosis from an area of lower
  osmolarity to an area of higher osmolarity
• ADH is secreted during water excess

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Review Questions (T/F)

• The amount of glucose filtered is directly
  proportional to the plasma glucose concentration
• Upon entering the distal tubule, the tubular
  fluid is hypertonic

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Review Questions (T/F)

• Potassium is filtered and both actively
  reabsorbed and actively secreted
• Urea is filtered and actively reabsorbed
• What substance is filtered, and completely
  reabsorbed (under nrml conditions)?