18. Nephron physiology Flashcards
early proximal convoluted tubule structure
it contains brush
early proximal convoluted tubule - reasbsorbs
all glucose and aminoacids
most HCO3- , Na+ (65-80 %), CL-, PO4, K+, H2O , uric acid, lactate
ISOTONIC ABSORPTION
early proximal convoluted tubule - secretes
- secretes H+ ( Na- H+ exchange)
- secretes NH3 ( as a buffer for secreted H+)
- base -( Cl– base- exchange)
early proximal convoluted tubule - reabsorbs Na+ is absorbed via
contrasport with glucose , aminoacids , phosphate and lactate
- countertransport via Na-H+ (linked with HCO3)
early proximal convoluted tubules -hormones
- pTH
2. ATII
early proximal convoluted tubule - PTH
It inhibits Na/Po4 contrasport –> increased PO4 excretion
early proximal convoluted tubule -ATII
stimulates Na/H+ exchange –> increased NA+ . H2O and HCO3- reabsorption –> permit contraction alkalosis
early proximal convoluted tubule - basolateral membrane
- nA+/k+ PUMP
- HCO3 channel
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
late proximal convoluted tubule - action
Na+ is reabsorbed with CL-
thin descending loop of Henle - function
passively reabsorbs H2O via medullary hypertonicity ( impermeable to Na+ ) –> concentrating segment –> makes urine hypetonic
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)
thick ascending loop of Henle - H2O
Impermeable to H2O –> urine less concetrated
thick ascending loop of Henle - basolateral membrane
- Na+/K+ pump
2. K+ and CL- channel to their electrochemical gradient ( to the blood)
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%
early distal convoluted tubule - function
- reabsorbs Na/Cl - ( contransportation ) and Ca2+
2. makes Urine fully dilute (hypotonic)
early distal convoluted tubule - hormones ( and action)
PTH –> increases Ca+/Na+ exchange on he basolateral membrane –> increases Ca2+ reabsorption
early distal convoluted tubule - basolateral membrane
- Na+/K+ pump
- Cl channel
- Na+/ Ca2+ exchanger
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%
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
Collecting tubule - type of cells
- principal cells
- α-intecalated cells
- β- Intercalated cells
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
- K+ channel to lumen (principal cells )
- Na+ channel into cell (principal cells )
- H+ ATPase to lumen (α-intecalated cells)
- H+/K+ pump ) H+ to lumen , K+ into cells) (α-intecalated cells)
- Cl/HCO3 exchanger ( CL into cells) (β-intecalated cells)
- aquaporin (H2O) channels (principal cells )
location of PTH action
- 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
