Urine Concentration And Dilution/ Buffer Systems Flashcards
when there is excess body fuilds/water, how much can be excreted and the lowest concentration it is excreted in?
Up to 20 liters per day, [50 mOsm/L]
What the maximum urine conc the body/kidney can produce?
What two conditions are required for concentrated urine?
1200-1400 mOsm/L
Presence of ADH and high osmolarity of renal medullary interstitial tubule.
Why is 0.5 L/day the required amount of excretion the body needs?
The maximum urine concentration ability of the body is 1200 mOsm/L
Which is about 0.5 L/day.
what two sections of the nephron are most responcible for diluting urine? are they effecting by ADH? what’s their osmolarity?
Ascending thick limb of Henle
Keeps water, ions get reabsorbed
Osm is 100 mOsm/L
Late distal convoluted tubule
Impermeable to water only when ADH is absent
Osm is 50 mOsm/LWhich part of the nephron is responcible for most of the reabsorption of filtered electrolytes?
The proximal tubule
65%
Proximal tubule
Permeable to water
Reabsorbs electrolytes
Descending loop of Henle
Permeable to water
Not so much for sodium, chloride and urea
High [ADH] increases osmolarity to 1200 mOsm/L
Thin ascending loop of Henle
Impermeable to water
Reabsorbs NaCl
Makes tubular fluid more dilute
Urea diffuses into the ascending loop of Henle. (Recycled from Urea that diffused out of collecting ducts into the interstitium)
Thick ascending loop of Henle
Impermeable to water
Ions go from tubule to interstitiium
More tube fluid dilution
Early distal tubule
Late distal tubule/cortical collecting tubule
Early: becomes the most dilute: 50 mosm/L. Impermeable to water, ions out (interstitium).
Late: osmolarity is dependent on ADH
Urea isnt permanent
what are the volatile gases and how are they delt with?
carbon dioxide is volatile, its excreted by the lungs.
carbon dioxide can combine with water to form bicarbonate which will break into proton and carbonic acid.
catalyzed by carbonic acid
nonvolatile acids and how are they excreted?
sulfuric acid
lactic acid
salicyic acid
excreted by the kidneys
What are the major regulatory systems for [H+] in the body?
Chemical acid-base buffer systems of the body fluids
Respiratory center
Kidneys
What’s the pH of arterial and venous blood? Why are they different?
pH of arterial blood is 7.4
PH of venous blood is 7.35
Venous blood is more acidic because it has a higher concentration of CO2, which is an acid.
What is a buffer? What are the buffer systems in the body? Which is most important?
Substance that can reversibly bind H+, a weak/conjugate acid that’s used to maintain pH.
Buffer systems:
- bicarbonate buffer system
- phosphate buffer system
- proteins that act as buffers
Most important: bicarbonate buffer system
How does the bicarbonate buffer system respond when strong acids or strong bases are added?
The buffer consists of a weak acid, carbonic acid, and a bicarbonate salt. With enzyme carbonic anhydrase
Addition of a strong acid: leads to the formation of a weak acid
Addition of a strong base: formation of a weak base
How are bicorbonate concentration and pCO2 regulated?
Bicarbonate concentration is regulated by the kidneys
PCO2 is controlled by the rate of respiration
What cause metabolic acidosis and metabolic alkalosis?
A change in bicarbonate concentration
Acidosis: decrease HCO3-
Alkalosis: increase HCO3-
What causes respiratory acidosis and alkosis?
A change in pCO2
Acidosis increase in pCO2
Alkalosis is a decrease in pCO2
What is the pH of the equilibrium point between the concentration of bicarbonate and CO2?
PH of 6.1
Equal to the pKa
What is the phosphate buffer system, what is it’s purpose and where is it important?
It’s important from buffering renal tubular fluid, it lowers the pH and allows for greater amounts of H+ to be excreted
NaHPO4- collects H+ to be excreted as NaH2PO4
How can filtered bicarbonate be reabsorbed?
React with secreted hydrogen to form carbonic acid.
Breaks into CO2 and H2O,
diffuses into tubular cells where it reforms into carbonic acid and
then breaks into bicarbonate and H+,
bicarbonate gets reabsorbed. H+ gets excreted
What mechanism are there for regulation of extracellular H+?
- Kidney’s reabsorb filtered bicarbonate ions
- most done in proximal tubule
-kidneys can secrete hydrogen ions
-done by type A intercalated cell on the late distal and
collecting tubules- only site of primary active transport of H
ions, really everywhere but the thin limbs of the
Loop of Henle - down by secondary counter-transport
-Kidneys produce new bicarbonate ions
How is bicarbonate ion titration used to correct acidosis or alkalosis?
In metabolic acidosis new bicarbonate ions are added to the extracellular fluid
In metabolic alkalosis bicarbonate ions are removed from the fluid by renal excretion
What’s the lowest pH that the kidneys can create? How much nonvolatile acid needs to be excreted per day? What limits this and what overcomes that limit?
4.5
80 mEq/L need to be excreted
The amount that can be excreted is limited by the minimum urine pH of 4.5, it means the amount of H+ that needs to be excreted can’t be free in solution because the pH can’t drop too low. The phosphate and ammonia buffer systems remedy this.
The excess hydrogen is eliminated bound to phosphate of ammonia ions, this process allows from new bicarbonate ions to be excreted into the blood.
What are the causes of acidosis? What are the bodies compensatory responses?
Metabolic: decrease in bicarbonate ion
-increase in plasma bicarbonate ion by kidney
Respiratory: increase in carbon dioxide
-increased ventilation rate, lesser extent: new bicarbonate ion.
What are the causes of alkalosis? And the compensatory responses?
Increases ratio of bicarbonate ion to hydrogen ion
Caused by hyperventilation
-renal excretion of bicarbonate ion
Metabolic - rise in [bicarbonate ion]
-decrease ventihilation, increase renal bicarbonate excretion
Where is ADH formed?
ADH is formed in magnocellular neurons in the supraoptic nuclei and the paraventricular nuclei
What is the purpose of the osmoreceptor-ADH feedback mechanism? And what is the function of osmoreceptor cells?
THe mechanism controls extracellular fluid sodium concentration and osmolarity
Reads for osmolarity in body fluids and influences fluid intake and ADH release
explain the countercurrent multiplier mechanism?
- Sodium ions are actively transported out, potassium, chloride and other ions are cotransporters. Out of thick ascending limb of loop of henle into the interstituim
- Ions actively transported out of collecting ducts
- Urea is facilitated out into the medullary interstitium
- Water is diffused in small amounts into interstitium and less than ions
Gradient limit is 200 mOsm/L - bec paracellular diffusion
Descending loop of henle reach osmotic equilibrium, at 400 because of osmosis.
Fluid flow into proximal tubule - causes fluid flow into ascending limb
More ions pumped out of ascending limb. 200 gradient reached again, making the osmolarity 500
Process is repeated until the max is reached: 1200
