18. Nephron physiology Flashcards by Andrew Pruett

early proximal convoluted tubule structure

it contains brush

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early proximal convoluted tubule - reasbsorbs

all glucose and aminoacids
most HCO3- , Na+ (65-80 %), CL-, PO4, K+, H2O , uric acid, lactate
ISOTONIC ABSORPTION

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early proximal convoluted tubule - secretes

secretes H+ ( Na- H+ exchange)
secretes NH3 ( as a buffer for secreted H+)
base -( Cl– base- exchange)

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early proximal convoluted tubule - reabsorbs Na+ is absorbed via

contrasport with glucose , aminoacids , phosphate and lactate
- countertransport via Na-H+ (linked with HCO3)

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early proximal convoluted tubules -hormones

2. ATII

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early proximal convoluted tubule - PTH

It inhibits Na/Po4 contrasport –> increased PO4 excretion

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early proximal convoluted tubule -ATII

stimulates Na/H+ exchange –> increased NA+ . H2O and HCO3- reabsorption –> permit contraction alkalosis

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early proximal convoluted tubule - basolateral membrane

nA+/k+ PUMP

- HCO3 channel

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early proximal convoluted tubule -carbonic anhydrase -action

in the cell –> CO2+ H2O –> H +HCO3 –> H+ in the lumen and HCO3 in the blood
in the lumen –> H+ HCO3–> CO2 +H2O –> in the cell

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late proximal convoluted tubule - action

Na+ is reabsorbed with CL-

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thin descending loop of Henle - function

passively reabsorbs H2O via medullary hypertonicity ( impermeable to Na+ ) –> concentrating segment –> makes urine hypetonic

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thick ascending loop of Henle - function

reabsorb Na + , 1 K+ and 2 CL –> K+ is goinging either to the blood ( basalateral membrane) or back to the lumen —> generates + lumen ( K+ backleaking) –> induces parcellular reabsorption of Mg2+ and Ca2+ ( to blood)
Impermeable to H2O –> urine less concentrated
Cl- is going to the blood (down the electrochemical gradient)

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thick ascending loop of Henle - H2O

Impermeable to H2O –> urine less concetrated

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thick ascending loop of Henle - basolateral membrane

Na+/K+ pump

2. K+ and CL- channel to their electrochemical gradient ( to the blood)

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propotion of Na+ reabsorption in proximal convoluted tubule and in thick ascending loop of Henle

proximal convoluted tubule –> 65-80%

- thick ascending loop of Henle –> 10-20%

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early distal convoluted tubule - function

reabsorbs Na/Cl - ( contransportation ) and Ca2+

2. makes Urine fully dilute (hypotonic)

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early distal convoluted tubule - hormones ( and action)

PTH –> increases Ca+/Na+ exchange on he basolateral membrane –> increases Ca2+ reabsorption

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early distal convoluted tubule - basolateral membrane

Na+/K+ pump
Cl channel
Na+/ Ca2+ exchanger

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propotion of Na+ reabsorption in proximal convoluted tubule and in thick ascending loop of Henle , and in early distal convoluted tubule

proximal convoluted tubule –> 65-80%
thick ascending loop of Henle –> 10-20%
early distal convoluted tubule –> 5-10%

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Collecting tubule - function

reabsorbs Na+ in exchange for secreting K+ and H+:

K+ channel to lumen
Na+ channel into cell
H+ ATPase to lumen
H+/K+ pump ) H+ to lumen , K+ into cells)
Cl/HCO3 exchanger ( CL into cells)
aquaporin (H2O) channels

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Collecting tubule - type of cells

principal cells
α-intecalated cells
β- Intercalated cells

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Collecting tubule - hormones

Aldosterone

2. ADH

Collecting tubule - aldosterone action

acts on mineralocorticoid receptor –> mRNA –> protein synthesis

principal cells —> a. increases apical (to the lumen) K+ conductase b. increases Na/K pump (basolateral)
c. increases epithelial Na + channel (ENaC) activity —> lumen negativity –> K+ secretion
α-intecalated cells –> lumen negativity –> H+ ATPase activity –> increased H+ secretion –> HCO3-? CL - ( Cl in the cell) exchanger activity ( in β -intercalated cells )

Collecting tubule - ADH action

acts at V receptror –> insertion of aquaporin (H2o channels) on apical side

Collecting tubule - function and which cells

reabsorbs Na+ in exchange for secreting K+ and H+: It also absorb H2O 1. K+ channel to lumen (principal cells ) 2. Na+ channel into cell (principal cells ) 3. H+ ATPase to lumen (α-intecalated cells) 4. H+/K+ pump ) H+ to lumen , K+ into cells) (α-intecalated cells) 5. Cl/HCO3 exchanger ( CL into cells) (β-intecalated cells) 6. aquaporin (H2O) channels (principal cells )

location of PTH action

1. early proximal convoluted tubule | 2. early ldistal convoluted tubule

location of ATII action

early proximal convoluted tubule

• What substance is secreted into the lumen of the early proximal convoluted tubule of the kidney and acts as a buffer for hydrogen (H+) ions?

Ammonia (NH3)

• What substances are largely reabsorbed in the early proximal convoluted tubule?

All glucose and amino acids and most bicarbonate, sodium, chloride, potassium, phosphate, and water

• The reabsorption of glucose, amino acids, HCO3-, Na+, Cl-, PO43-, and H2O in the proximal tubule is ____ (isotonic/hypotonic/hypertonic).

Isotonic

• In a study, radiolabeled angiotensin II (AT II) is found in high concentrations in the early proximal convoluted tubules (PCTs). Why?

AT II stimulates Na+/H+ ion exchange, increasing sodium, water, and bicarbonate reabsorption and permitting contraction alkalosis

• A hiker high up on a mountain is delirious. What mechanism makes acetazolamide a treatment? Will his urine be acidic or alkalotic?

It is useful in altitude sickness because it blocks the uptake of bicarbonate via inhibition of carbonic anhydrase; urine will be alkalotic

• In the thin descending loop of Henle, ____ (H2O/Na+) is ____ (actively/passively) reabsorbed via medullary ____ (hyper-/iso-/hypotonicity).

Water; passively; hypertonicity (medulla is hypertonic and impermeable to Na+)

• In the loop of Henle, the thin part is ____ (impermeable/permeable) to water; the thick part is ____ (impermeable/permeable) to water.

Permeable; impermeable

• Which segment of the kidney nephron do the hormones aldosterone and antidiuretic hormone (vasopressin) act on?

The collecting tubules

• What type of cell in the collecting tubule of a nephron is responsible for sodium/potassium exchange and the reabsorption of water?

The principal cell

• A patient taking lithium loses aquaporin-linked receptor function in renal principal cells. Which hormone normally binds to these receptors?

Antidiuretic hormone (ADH) normally binds to V2 receptors on principal cells

• Early PCT fluid tonicity is measured in a patient. He is healthy and not taking medication. Is the fluid hypertonic, isotonic, or hypotonic?

Isotonic

• In the loop of Henle, the thin part makes urine ____ (hyper-/iso-/hypotonic), and the thick part makes it ____

Hypertonic; hypotonic (diluted)

• The early distal convoluted tubule ____ (concentrates/dilutes) urine, causing it to be ____ (hypertonic/isotonic/hypotonic).

Dilutes; hypotonic

• In what action does antidiuretic hormone (ADH) activity at V2 receptors result?

Insertion of aquaporin water channels on the luminal side of the collecting tubules, resulting in increased water reabsorption

• What indirectly induces the paracellular absorption of magnesium and calcium at the thick ascending loop of Henle?

Positive lumen potential generated by potassium backleak

• What is aldosterone's main action at the collecting tubules?

Acts on mineralocorticoid receptors and inserts sodium channels, thereby reabsorbing sodium and secreting potassium and hydrogen

• What percentage of nephron lumen sodium is reabsorbed in the early PCT? The thick ascending tubule? The early DCT? The collecting tubule?

65%–80%; 10%–20%; 5%–10%; 3%–5%

• How does the influence of aldosterone affect principal cells?

Increased apical K+ conductance, increased Na+/K+ pump activity, and increased ENaC channels, leading to lumen negativity and K+ loss

• How does the influence of aldosterone affect α-intercalated cells?

Increased H+ ATPase activity, leading to increased HCO3-/Cl- exchanger activity

• A patient ingests a toxin that interferes with protein synthesis. Will the kidneys be able to utilize aldosterone effectively?

No—aldosterone binding acts by increasing mRNA production and protein synthesis, so such a toxin would interfere with its function

• What is the effect of PTH on the early DCT?

Increases activity of the sodium/calcium exchanger between the blood and the DCT cells, thereby promoting calcium uptake from the lumen

• In terms of ion processing, what is the main function of α-intercalated cells?

They secrete H+ into the urine (and take up K+ from it), promoting HCO3- release into the blood (in exchange for Cl-)

• In terms of ion processing, what is the main function of β-intercalated cells?

β-intercalated cells secrete HCO3- into the urine (and take up Cl- from it), promoting H+ release into the blood

• In the early DCT, which ion diffuses from the urine into the blood as a result of transporter activity?

Chloride

• In the thick ascending tubule of Henle, which two ions diffuse from the urine into the blood down their electrochemical gradient?

Chloride and potassium

• In the collecting tubule, which ion diffuses from the urine into the blood passively?

Chloride

• Which three ions are actively taken up by the thick ascending loop of Henle?

Sodium, potassium, and chloride