Urine Concentration And Dilution/ Buffer Systems

Question 1

when there is excess body fuilds/water, how much can be excreted and the lowest concentration it is excreted in?

Answer 1

Up to 20 liters per day, [50 mOsm/L]

Question 2

What the maximum urine conc the body/kidney can produce?

What two conditions are required for concentrated urine?

Answer 2

1200-1400 mOsm/L

Presence of ADH and high osmolarity of renal medullary interstitial tubule.

Question 3

Why is 0.5 L/day the required amount of excretion the body needs?

Answer 3

The maximum urine concentration ability of the body is 1200 mOsm/L

Which is about 0.5 L/day.

Question 4

what two sections of the nephron are most responcible for diluting urine? are they effecting by ADH? what’s their osmolarity?

Answer 4

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/L

Question 5

Which part of the nephron is responcible for most of the reabsorption of filtered electrolytes?

Answer 5

The proximal tubule

65%

Question 6

Proximal tubule

Answer 6

Permeable to water

Reabsorbs electrolytes

Question 7

Descending loop of Henle

Answer 7

Permeable to water
Not so much for sodium, chloride and urea
High [ADH] increases osmolarity to 1200 mOsm/L

Question 8

Thin ascending loop of Henle

Answer 8

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)

Question 9

Thick ascending loop of Henle

Answer 9

Impermeable to water
Ions go from tubule to interstitiium
More tube fluid dilution

Question 10

Early distal tubule

Late distal tubule/cortical collecting tubule

Answer 10

Early: becomes the most dilute: 50 mosm/L. Impermeable to water, ions out (interstitium).

Late: osmolarity is dependent on ADH
Urea isnt permanent

Question 11

what are the volatile gases and how are they delt with?

Answer 11

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

Question 12

nonvolatile acids and how are they excreted?

Answer 12

sulfuric acid
lactic acid
salicyic acid

excreted by the kidneys

Question 13

What are the major regulatory systems for [H+] in the body?

Answer 13

Chemical acid-base buffer systems of the body fluids

Respiratory center

Kidneys

Question 14

What’s the pH of arterial and venous blood? Why are they different?

Answer 14

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.

Question 15

What is a buffer? What are the buffer systems in the body? Which is most important?

Answer 15

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

Question 16

How does the bicarbonate buffer system respond when strong acids or strong bases are added?

Answer 16

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

Question 17

How are bicorbonate concentration and pCO2 regulated?

Answer 17

Bicarbonate concentration is regulated by the kidneys

PCO2 is controlled by the rate of respiration

Question 18

What cause metabolic acidosis and metabolic alkalosis?

Answer 18

A change in bicarbonate concentration

Acidosis: decrease HCO3-

Alkalosis: increase HCO3-

Question 19

What causes respiratory acidosis and alkosis?

Answer 19

A change in pCO2

Acidosis increase in pCO2

Alkalosis is a decrease in pCO2

Question 20

What is the pH of the equilibrium point between the concentration of bicarbonate and CO2?

Answer 20

PH of 6.1

Equal to the pKa

Question 21

What is the phosphate buffer system, what is it’s purpose and where is it important?

Answer 21

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

Question 22

How can filtered bicarbonate be reabsorbed?

Answer 22

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

Question 23

What mechanism are there for regulation of extracellular H+?

Answer 23

• 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

Question 24

How is bicarbonate ion titration used to correct acidosis or alkalosis?

Answer 24

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

Question 25

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?

Answer 25

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.

Question 26

What are the causes of acidosis? What are the bodies compensatory responses?

Answer 26

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.

Question 27

What are the causes of alkalosis? And the compensatory responses?

Answer 27

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

Question 28

Where is ADH formed?

Answer 28

ADH is formed in magnocellular neurons in the supraoptic nuclei and the paraventricular nuclei

Question 29

What is the purpose of the osmoreceptor-ADH feedback mechanism? And what is the function of osmoreceptor cells?

Answer 29

THe mechanism controls extracellular fluid sodium concentration and osmolarity

Reads for osmolarity in body fluids and influences fluid intake and ADH release

Question 30

explain the countercurrent multiplier mechanism?

Answer 30

1. 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
2. Ions actively transported out of collecting ducts
3. Urea is facilitated out into the medullary interstitium
4. 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