Physiology - Nephron Flashcards by Joe Bloggs

What substances are reabsorbed in the Proximal Tubule?

100%

Glucose
Amino acids

67%

Water
Bicarb
NaCl
K+
Phosphate

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What side does the Na+/K+ATPase pump lie on and what does it create?

Lies on basolateral side

- Decreases Na+ intracellularly - generating a conc. gradient between tubule cells and tubular fluid

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Via what channel does glucose get reabsorbed?

SGLT2 (in proximal tubule)

- Sodium co-transporter

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What molecules are secreted by the proximal tubule?

Anions:

Hydroxide (-OH)
Formate
Oxalate
Sulfate

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What ion is taken up by the transporter which excretes anions?

Cl-

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What transporters channels are present on the basolateral surface of the PCT cells?

Na/KATPase
K+ Cl cotransporter
Glucose
Na+ HCO3- cotransporter

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What substances are taken into the blood via the paracellular route in the PCT?

- NaCl

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At what level does glucose appear in the urine?

160mg/dL

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At what level do all glucose levels become saturated?

350mg/dL

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Why is a diabetes diagnosis from urine unreleable in pregnancy?

Some glycosuria is normal in pregnancy
Serum testing needed for diagnosis
Increased GFR in pregnancy
Decreased glucose reabsorption in pregnancy

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What ion are amino acids reabsorbed with in the PCT?

Na+

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What is Hartnup disease?

No typtophan transporter in PT
Tryptophan deficiency
Skin rash resembling pellagra (plaques, desquamation)
Amino acids in urine

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What transporter excretes H+ in the PCT?

Na+/H+ cotransporter

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What reactions does Carbonic Anhydrase catalyse?

Describe the pathway of H2CO3 and how the urine is acidified and how HCO3- is taken up in blood

H2CO3 to Co2 + H2O

In Tubular fluid
Co2 and H2O can then be taken up

Can also convert CO2 + H2O to H2CO3 in the tubular cells

H2CO3 can then be converted to H+ and HCO3-

H+ enters urine via H+/Na+ antiporter

HCO3- enters blood via HCO3-/Na+ cotransporter

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Via what transporter does HCO3- enter the blood?

HCO3-/Na+ cotransporter on basolateral membrane

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What do carbonic anhydrase inhibitors do?

Alkalises urine - bicarb loss in urine, acidifies body (used in alkalosis)
Weak diuretic (block Na+ reabsorption)

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What is Type II Renal Tubular Acidosis?

Ion defect
Inability to absorb bicarb
Metabolic acidosis

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What is Fanconi syndrome?

Loss of proximal tubule functions
Impaired resorption of solutes
HCO3-, glucose, amino acids, phosphate lost
Polyuria and polydipsia (diuresis from glucose), normal serum glucose
Non anion gap acidosis (loss of HCO3-)
Hypokalemia (increased nephron flow)
Hypophosphatemia (loss of phosphate)
Amino acids in urine

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What are the 2 forms of Fanconi syndrome?

Inherited or acquired

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When and what does inherited Fanconi syndrome present with?

Infancy

Cystinosis - accumulation of cysteine (
Lysosomal storage disease

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What are acquired causes of Fanconi Syndrome?

Lead poisoning 
Multiple Myeloma 
Drugs 
- Cisplatin 
- Ifosfamide (alkylating agent)
- Valproate 
- Aminoglycoside antibiotics 
- Deferasirox (iron chelator)

Where is urea generated?

The liver and protein metabolism

Where in the nephron is urea reabsorbed?

Medullary Collecting duct

- Enters medullary interstitium

What are the 3 solutes responsible for the high osmolarity in the medulla?

Na
Cl
Urea

What is cystinuria?

- Different from cystinosis - Proximal tubule defect - Impaired reabsorption of cystine - Cystine kidney stones - +ve Sodium cyanide nitroprusside test - Stones may form staghorn calculi - Urine crystal is hexagonal

What other amino acids are poorly reabsorbed in cystinuria?

COLA - Cystine - Ornithine - Lysine - Arginine

What is the thin descending loop of Henle impermeable to?

NaCl

What is the osmolarity of the tubular fluid at each area of the nephron?

- 300 mOsm (around glomerulus and when leaving PCT) - 600 mOsm in Outer Medulla - 1200 mOsm in Inner medulla - 120 at end of TAL

Where is NaCl specifically reabsorbed?

Thick Ascending Loop of Henle

What is the pump responsible for generating the low osmolarity in the TAL?

Na+/K+/2Cl-

What causes the +ve charge in the lumen of the TAL?

- Na/KATPase brings K+ into the cell - K+ channel on apical membrane brings +ve charge into lumen - This postive charge in the lumen then drives the Na+/K+2Cl- pump (all travel into cell) - Allows Mg2+ and Ca2+ to enter the blood via the paracellular route

What channels/pumps are present on the apical membrane of the distal tubule?

- Na+/Cl- (same direction) | - Ca2+

What channels are present on the basolateral membrane of the distal tubule?

- NaKATPase - Cl- (out) - Na+(in)/Ca2+(out) cotransporter

What are the 2 cell types present in the collecting duct?

- Principal cell | - Intercalated cell (secrete H+)

What channel is important on the apical surface of the intercalated cells of the CD?

H+/ATPase

What is the channel by which sodium is reabsorbed by the principal cells in the CD?

ENaC (regulated by aldosterone)

What channels are present on the apical surface of the principal cells?

- ENaC - K+ (out) - H2O (in)

What are the main substances secreted by the CDs?

- Reabsorb Na+, H2O | - Secrete K+/H+

Describe how loops and thiazides cause hypokalemia?

Increased Na delivery to CD -> More into cell via ENaC - > Na+ can then be exchanged for K+ which is brought into the cell - > increased K+ excretion - > Contributes to hypokalemia with loops thiazides

What tranporters are increased by Aldosterone?

Principal cells - Na+/K+ATPase (basolateral) - ENaC (apical) Intercalated cells - H+ATPase

What is the overall effect of Aldosterone (what substances are increased/decreased)?

- Sodium/water resorption (increased effective circulating volume) - Increased K+ excretion - Increased H+ excretion

What is the release of aldosterone stimulated by?

- Angiotensin II - High K+ - ACTH (minor effect)

What are the 2 physiologic stimuli for ADH release?

- Major: Hyperosmolarity | - Volume loss: non-osmotic release (does not depend on osmolarity, pituitary detects low ECV, emergency)

What are the 2 receptors ADH acts on?

- V1: Vasoconstriction | - V2: Antidiuretic response

What cells contain the V2 receptors?

Principal cells (basolateral surface)

What channels are activated by ADH?

AQP-2 channel

What are the AQP channels which are always active?

- AQP-3 - AQP-4 Both on Basolateral surface

What would the urine osmolarity be in a high ADH state (parched)?

High - 1200mOsm

What would the urine osmolarity be in a low ADH state (high water intake)?

Low - 60

What is the effect of ADH on urea reabsorption?

Increases reabsorption of urea | - Maintains high osmotic gradients so ater ccn be reabsorbed in LOH

Where are the transporters located that recycle the urea?

Thin descending limb