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2011-02-06 17:26:06

Chapter 26 Urine formation 1
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  1. The kidneys regulate
    • Vit D3
    • erythropoiten; meduallary fibroblasts
    • glucose synthesis; gluconeogenisis rivals the liver
  2. Arcuate arteries
    • connect interlobar areteries to interlobular arterioles
    • interlobular arterioles lead to afferent arterioles
  3. Hydrostatic pressure in the renal blood capillaries
    • in the glomerular capillaries there is a high pressure to cause rapid filtration and in the peritubular capillaries there is a lower pressure that facilitates absorption
    • By adjusting the afferent and efferent resistance pressure can be adjusted correctly
  4. Connecting tubule
    • connects the distal tubule to the collecting duct
    • 8-10 connecting tubules empty into 1 collecting duct
  5. Three types of nephrons
    • subcapsular/cortical
    • intermediate
    • juxtamedullary
  6. Physical id of the trigone
    • its inner mucosa is smooth
    • the rest of the inner bladder is rugae. thick folded muscle
  7. Nerve innervation of the bladder
    • para S2-S3
    • sympathetics L2, hypogastric nerve, little to do with bladder contraction mostly stimulate the vessels
    • external sphincter is from pudendal S2-S3
  8. Stretch of the ureter
    • causes peristalsis
    • parasympathetic response
    • these peristalsis waves force urine through the normal tone of the detruser muscle which normally keeps the ureters closed
  9. vesicoureteral reflux
    • urine flows retrograde out of the bladder into the ureters
    • ureters do not pass all the way into the bladder
    • detruser muscle weakness
  10. Pain in the ureters from blockage
    • cause sympathetic reflex to the kidney to constrict the afferent arterial decreasing urine output from that kidney
    • Uretorenal reflex
    • prevents overflow and pressure from a blocked ureter
  11. Micturition waves
    • intermittent contractions that attempt to signal bladder emptying
    • start around 20-50ml and stay constant up until 300-400ml then increase rapidly
    • Receptors are mainly in the posterior urethra
    • As the bladder fills the contractions last longer and longer, the contraction are self regenerating. The contraction further increases the stretch
    • If the contractions become severe the nervous reflex inhibits the pudendal nerve and causes urination
  12. Matriculation reflex
    is completely autonomic in the spinal cord
  13. Voluntary urination
    • person voluntarily contracts there abdominal muscles, this increases bladder pressure
    • this pressure stimulates the maturation reflex and also inhibits the external sphincter tone
  14. Overflow incontinence
    • loss of stretch signals from the bladder
    • urine leaks out
    • usually caused by a crushing injury
    • Tabetic dorsalis- fibrosis of dorsal nerve roots by syphilis
  15. Autonomic bladder
    if the spinal cord is injured about the sacral level all bladder control will be reflex
  16. Uninhibited neurologic bladder
    • frequent matriculation
    • from partial damage of the spinal cord, inhibitory signals are lost so the brain keeps the sacral region excited causing matriculation with only a small amount of urine
    • over excited bladder
  17. ion concentration in the glomerulus
    freely filterd so same as plasma except no proteins
  18. filtration and absorption
    work in unison
  19. carbonic anhydrase diuretics
    if bicarb is not reabsorbed it binds Na in the urine and does not allow it to be reabsorbed
  20. Advantages of a high GFR
    • it allows kidneys to rapidly remove waste products from the body that depend on the kidney for excretion
    • allows all the body fluids to be filtered by the kidneys many times per day
    • entire plasma volume is filtered 60 times per day
    • High GFR allows the kidney to rapidly control the volume and composition of body fluids
  21. GFR is determined by
    • balance of hydrostatic and osmotic pressure
    • capillary permiability
    • Glomerular capillaries have a high pressure
  22. Normal GFR
    • 125ml/min
    • 180 L/day
  23. Normal filtration fraction of the gomerular capillaries
    • 20%
    • FF= GFR/renal plasma flow
  24. Glomerular capillary endothelium
  25. Basement membrane proteoglycans
    • heparin sulfate
    • negative change
  26. All three layers of glomerular filtration
    contain negative charges to decrease protein filtration
  27. Dextran
    polysaccharide that can be manufactured as a cation, neutral, or anion
  28. GFR=
    • K x net filtration pressure
    • filtration pressure is normally around 10 mmHg
  29. Osmotic pressure of bowmans capsule
    clinically said to be zero since no proteins are filterd
  30. Normal plasma colloid osmotic pressure
    28 mmHg
  31. Kf in DM and chronic HTN
    becomes lover over time due to thickening of the basement membrane
  32. Normal hydrostatic pressure of bowmans capsule
    • 18 mmHg
    • urinary stones lead to a higher pressure and a lower GFR
  33. What is the change in osmotic pressure as plasma flows through the glomerulus
    • flows in at 28 mmHg and in the efferent arterioles it is around 36 mmHg
    • this is due to a filtration fraction of plasma of 20% deceases the amount of plasma
  34. Two factors that influence the glamerular capillary colloid osmotic pressure
    • the arterial osmotic pressure and the filtration fraction of the plasma
    • An increase in arterial colloid osmotic pressure would decrease the GFR
  35. Blood flow and GFR
    • i higher rite of blood flow increases GFR
    • A lower rate of flow decreases GFR
  36. GFR and pressure changes
    • increased arterial pressure tends to raise glomerular hydrostatic pressure and raise GFR
    • Increased resistance eof the afferent arterial reduced hydrostatic pressure and decreases GFR
    • Constriction of the efferent arteriole increases the resistance of outflow from the glomerular capillaries. This raise in pressure increases GFR as long as the constriction does not lower renal blood flow to much
  37. Severe contraction of the efferent arterioles
    • the contraction slows renal blood flow and in turn increases the filtration fraction which increases the colloid osmotic pressure.
    • The raise in osmotic pressure exceeds the hydrostatic pressure and decreases GFR
    • The decrease in GFR; as the efferent constriction becomes severe constriction increases the protein concentration and causes the donnan effect.
    • Donnan effect; As plasma protein concentration increases the osmotic pressure increases non linearly because the proteins negative charge attracts more ions to add to the osmotic pressure
  38. Efferent arteriole contraction
    • is a biphasic effect on GFR
    • first increases then decreases
  39. Kidney O2 consumption
    • use oxygen at twice the rate if the brain but have 7 times the blood flow
    • High rate of oxygen consumption is due to ATP pumps
  40. Renal blood flow
    pressure difference = flow x resistance
  41. Most resistance in the renal blood flow
    • interlobular arterioles
    • afferent and efferent arterioles
  42. Kidney autoregulation on blood flow
    works between 75 and 160
  43. most blood flow in the kidney goes
    • to the cortex
    • only 1-2% to the medulla
  44. renal sympathetic innervation
    • T10-L1
    • Most important in reducing GFR during severe acute disturbances lasting a few minutes to a few hours such as those elicited by brain ischemia or severe hemorrhage
    • does not react to weak influence of barorecptors
  45. Hormones that reduce GFR, autocoids
    • norepinephrine, epinaphrine, sympathetic nervous system
    • endothelian ; released from damaged cells. Released during toxemia of pregnancy (preeclampsia)
  46. Angiotensin II
    • Usually released during times of decreased arterial pressure and decreased GFR
    • Maintains GFR while increasing extracellular volume
    • preferentially constricts efferent arterioles. Raises glomerular pressure and lowers blood flow
    • increases GFR but slows flow though the peritubular capillaries which in turn increases Na and water reabsorption
    • Thus increases in angiotensin II that occurs with a low sodium diet or hypovolemia helps to preserve GFR and maintain normal excretion of waste products that depend on GFR. at the same time constriction of efferent arterioles increases tubular reabsorption of Na and water helping to restore volume
  47. Endothelian derived NO
    • increases GFR by dilating arterioles
    • there is a basil level of secretion
    • Drugs that decrease NO production decrease GFR
  48. After surgery NSAIDs
    • stop production of prostoglandins and can lower GFR
    • Prostoglandins cause vasodilation and increase renal blood flow
  49. Main function of autoregulation in the kidneys
    • to maintain GFR
    • in other tissues it is to control nutrient delivery and waste excretion
    • 60-180 mmHg
  50. Two reasons changes in arterial pressure have a small effect on urine volume
    • renal autoregulation prevents large changes in GFR
    • additional adaptive mechanisms in the renal tubules allow them to increase reabsorption when GFR rises. Glomerulotubular balance
  51. Glomerulotubular balance
    an increases in GFR causes an increase in Na and water reabsorption
  52. Tubuloglomerular feedback
    • Links changes in Na at the macula densa to renal arteriolar resistance
    • Directed to stabalizing Na concentration in the tubules
    • two mechanisms; sfferent arterial feedback mechanism and efferent arteriole feedback mechanism
  53. Decrease in Na at the macula densa , tubuloglomerular feedback cont.
    • A decreased GFR slows the flow rate at the TAL allowing more time for Na reabsorption
    • decreased Na at the macula densa has two effects.
    • It decreases resistance to blood flow in the afferent arterioles increasing glomerular hydrostatic pressure increasing the GFR
    • increases renin secretion
  54. Myogenic mechanism
    • individual blood vessels resist stretching
    • respond to increased pressure and stretch by contracting
    • stretch of the vascular walls allows increased movement ov calcium ions into the cell causing contraction
  55. High protein intake on GFR / increased blood glucose
    • high protein intake increases both GFR and renal blood flow
    • Can be due to growth of the kidney
    • High amount of filtered AA causes a high absorption in the proximal tubules, this is by secondary active transport which causes an increase in Na reabsorption.
    • The increase in Na reabsorption causes less Na to be delivered to the macula densa and a release of renin. Increased GFR and blood flow through the dilated afferent vessels
    • Not only absorbs the extra AA but with increased AA breakdown there is an increase in Urea, the increase in GFR allows for an increase in Urea excretion
  56. Increased Na at macula densa
    • tubuloglomerular feedback
    • causes vasoconstriction which decreases renal blood flow and decreases GFR
  57. Urine flow rate
    =GFR - Reabsorption rate