7. Physiology of the Urinary System Part II Flashcards
Regulation of Urine Concentration and Volume Overview
1) Homeostasis
a) Urine concentration altered to maintain this equilibrium state
b) Kidneys control total solute concentration of body fluids
Countercurrent Flow (2)
1) Movement of fluids in opposite directions through adjacent channels
a) Filtrate flows in one direction through renal tubules
b) Blood in adjacent channels flows in the opposite direction
2) Accomplished by blood vessels of the vasa recta and peritubular capillarie
Osmotic gradient (3)
1) Osmotic gradient: concentration of solutes inside a solution
a) Measured in milliosmoles/liters (mOsm/L)
2) Reabsorption and secretion establishes an osmotic gradient from renal cortex to renal medulla
3) Countercurrent flow protects osmotic gradient established in the medullary interstitial space
Osmotic Characteristic of PCT (2)
1) Isosmotic: fluid inside and outside have the same osmotic concentrations
2) Filtrate entering PCT is identical to surrounding plasma
Osmotic Characteristic of Loop of Henle (4)
1) Descending loop
a) Solute concentration increases as it descends
2) Hairpin turn
a) Inner medulla
b) Increases to maximum of about 1200 mOsm/L
3) Concentration of filtrate increases because water can leave the descending limb but not salt
4) Ascending loop
a) Salt can leave but not water
b) Concentration of filtrate decreases because salt can leave but not water
c) Filtrate becomes about 100 mOsm/L as it becomes the DCT
Urea (4)
1) Also contributes to the high osmolarity of the deep medullary region
2) Concentration of urea is high in the DCT and cortex regions
3) Tubules in the cortex are impermeable to urea
4) Medullary collecting ducts are highly permeable to urea, so it diffuses out of the medullary ducts and into the interstitial fluid
5) Medulla: concentration of urea are equal inside and outside duct
Osmolarity graphic
ADH - Antidiuretic Hormone (5)
1) Produced in the hypothalamus, stored and released by posterior pituitary
2) Inhibits urine output
a) Increases the channels in the cells of the collecting ducts
b) Allows water to pass from filtrate and move into interstitial space, returned to blood circulation
3) Release of ADH connected to degree of the state of hydration
4) ADH released in dehydrated states
a) Solute concentration too high in blood
5) Dehydration causes
a) Excessive water loss
b) Sweating, vomiting, diarrhea
ADH and blood loss (3)
1) ADH released in severe blood loss
a) Hemorrhage = large amount of blood loss and severe drop in blood pressure
b) Responds by retaining up to 99% of the water from the filtrate
2) When ADH is released highly concentrated urine is released
a) As high as 1200 mOsm/L
3) When not released, dilute urine is excreted
a) As low as 65 mOsm/L
Aldosterone (2)
1) Released by the adrenal cortex under control of the RAA system
2) Places many types of ion channels inside the cells of the collecting ducts
Aldosterone - sodium-hydrogen ion channel (3)
1) Increases Na+ reabsorption by excretion of hydrogen ions
2) Na+ pumped out of filtrate, H+ pumped inside filtrate
3) Water follows salt, Na+ reabsorption also causes water reabsorption
Aldosterone - sodium-potassium pump (3)
1) Increases potassium excretion by returning Na+ to the blood
2) Na+ pumped out of filtrate, K+ pumped inside filtrate
3) Water follows salt, Na+ reabsorption also causes water reabsorption
Aldosterone can act separately
1) Release can occur apart from the RAA system
a) High K+ levels or low Na+ levels in the extracellular compartment
Aldosterone trigger and timing
1) Normal triggers for aldosterone is release through RAA system
2) Aldosterone control is slow acting (hours to days to take effect)
