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STEP Pathology > deck_5112194 > Flashcards

deck_5112194 Flashcards

1
Q

How is the PT designed for large reabsorption?

A

The epithelial cells have microvilli (brush border) and basolateral surface is thrown into folds: both enhance surface area

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2
Q

T or F. Proximal tubular cells are reach in mitochondria which are needed to provide sufficient energy for the reabsorption

A

T. ISCHEMIA is bad here

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3
Q

What are the parts of the PT (structurally)?

A

First 2/3: proximal convoluted tubule (PCT)Remaining 1/3: proximal straight tubule (parse recta). In turn, parse recta has cortical and medullarly segments

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4
Q

What are the parts of the PT (functionally)?

A

Some differences in transporter proteins):- S1- initial short segment of PCT- S2- remaining PCT and cortical parse recta- S3- medullary parse recta

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5
Q

What are the main functions of the PT?

A

Reabsorption of filtered water, electrolytes, and organic compoundsSecretion of organic compounds including some drugs (S2, S3 segments)Hormonal function: final pathway in the synthesis of calcitriol

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6
Q

How much Na is reabsorbed in the PT?Water?K+?

A

55-65% (Na+ and water)K+- 65%

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7
Q

How much Pi is reabsorbed in the PT?Calcium?Glucose?Urea?

A

80-95%60%100%50%

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8
Q

What are some pathways of reabsorption in the PT?

A

1) transcellular (through the PT epithelium to the ISF)2) paracellular (through junctions to the ISF)

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9
Q

Passive diffusion typically requires what?

A

an electrochemical gradient of some kind

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10
Q

What is reabsorption in the tubular cells from the PT lumen driven by?

A

The electrochemical gradient created by the basolateral Na-K ATPase.

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11
Q

What does the basolateral Na-K ATPase do specifically?

A

transports 3Na+ to the ISF and 2K+ into the tubular cell

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12
Q

What things are typically coupled to Na+ as it is reabsorbed into the tubular cell via the electrochemical gradient formed by the basolateral Na-K ATPase?

A

sugars, AAs, phosphate, glucose in symport (or H+ into the tubular lumen in antiport)this is called 2ndary active transport

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13
Q

How is the K+ brought into the cell by the BL Na/K ATPase removed back to the ISF?

A

by passive transport couple to a negative ion (usually Cl-)

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14
Q

What is the basis of glomerulotubular balance?

A

The intrinsic ability of the tubules to increase their reabsorption rate in response to increased tubular load (increased tubular inflow). all segments have this capability

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15
Q

What things decrease the net reabsorption of sodium and water?

A

Arterial pressure (Pressure natriuresis): increase in peritubular capillary hydrostatic pressure reduces the net reabsorption of sodium and waterdiuretics, hypoaldosteronism

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16
Q

What hormones regulate PT reabsorption?

A

Angiotensin II: regulates NaCl and water re-absorption and H+ excretionParathyroid hormone and FGF23- regulate Pi excretion

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17
Q

Why is the PT highly susceptible to ischemia?

A

It has ATP dependence for the function of Na-K-ATPase, and Polarized (apical and basolateral) structure of PT cells is a dynamic and ATP dependent process relying on cytoskeleton. It involves the formation and maintenance of cell-cell and cell-substratum attachments and the targeted delivery of plasma membrane components to the appropriate domains.

18
Q

What are some basic potential defects in PT function?

A

-defective solute influx-leakage back from lumen-increased back flux across tight junctions from ISF-defective energy-decreased solute flux into blood from ISF-defective transporter recycling

19
Q

How is PT dysfunction classified?

A

A. Generalized: usually due to defect in energy generation, Na-K-ATPase activity, or dysfunction of cellular organelles affecting transport protein recycling B. Isolated solute transport disorders: typically due to defect in specific transport protein 2. Classification based on mode of inheritance: A. Genetic B. Acquired

20
Q

What is Familial/Hereditary Renal Glucosuria (HRG)?

A

isolated PT dysfunction that causes defect in glucose reabsorption

21
Q

What is the MOI for HRG?

A

AR (1:20000)

22
Q

What causes HRG?

A

mutation of SGLT2 glucose transporter which transports Na and glucose from the tubular lumen to the epithelium (where GLUT1 and 2 then transfer it to blood)types:a- decreased thresholdb- transport max is lowered0- no functional SGLT2 at all

23
Q

T or F. If glucose conc. exceeds the normal thresholds, patients with functional SGLT2 will also have glucosuria

A

T.

24
Q

What is Cystinuria?

A

A type of amino acid uria caused by mutation of the brush border transporter responsible for reabsorption of cystine, and dibasic amino acids ornithine, lysine, and arginine cysteine is not water soluble so once its conc. in urine is above 250, it forms hexagonal stones under the microscope

25
Q

What is the MOI of Cystinuria?

A

AR (1:20000)

26
Q

What are the causes of defects in phosphate reabsorption?

A

can be inherited or acquired

27
Q

What are some inherited phosphate reabsorption defects?

A
  • X-linked Hypophosphatemia (mutation of PHEX gene)-most common - Autosomal-Dominant Hypophosphatemic rickets (mutation in FGF-23 gene) - Autosomal-Recessive Hypophosphatemic rickets (several different mutations leading to increased FGF-23 or mutation in Na/Pi IIc tranporter)
28
Q

What are some acquired phosphate reabsorption defects?

A

Oncogenic Hypophosphatemic Osteomalacia (increased production of FGF-23 by some tumors: fibromas, angiosarcomas, hemangiopericytomas)

29
Q

What does mutation of PHEX gene cause in X-linked hypophosphatemic rickets?

A

increased levels of circulating factor FGF-23 (PHEX normally downregulates FGF23), that in turn, decreases activity of phosphate transporters. In this case, the transport protein (Na-Pi) has no mutation.

30
Q

What is X-linked hypophosphatemic rickets characterized by?

A

-urinary phosphate wasting, -low levels of serum phosphorus, -elevated serum alkaline phosphatase. Calcium and calcitriol are usually low-normal.

31
Q

How does X-linked hypophosphatemic rickets typically present?

A

rickets in children and osteomalacia (softening of bones) in adults

32
Q

What is Hartnup Disease? Treatment?

A

defect in neutral amino acid transporter (SLC6A19)- tryptaphan. Treatment: give supplemental nicotinamide (which is what tryptophan is converted to)

33
Q

What are the symptoms of Hartnup Disease?

A

failure to thrive, photosensitivity, intermittent ataxia, nystagmus, and tremor.F-PINT

34
Q

What causes Vitamin D-dependent rickets type 1?

A

mutation of 1α-hydroxylase leading to hypophosphatemia and rickets

35
Q

Generalized PT dysfunction is aka?

A

Fanconi Syndrome (can be inherited but most commonly acquired)

36
Q

The causes of Falcon syndrome vary. What are some examples?

A

defective binding of Na with transport proteins, defective insertion of carriers into brush border membrane, leaky membrane or “tight junctions”, inhibited or abnormal Na-K-ATPase, impaired mitochondrial energy generation

37
Q

What are some clinical manifestations of Falcon syndrome?

A
  • Polyuria and polydipsia (water follows) - Volume depletion - Cardiac arrhythmias - Proteinuria- Growth retardation- Rickets (loss of Pi)- Renal stones and nephrocalcinosis- Extra renal organ involvement depending on the underline cause
38
Q

What are some inherited causes of Fanconi Syndrome?

A

-Cystinosis-Hepatorenal tyrosinemia-Hereditary fructose intolerance-Galactosemia-Glycogen storage disease type I-Wilson disease-Oculocerebral renal (Lowe) syndrome-Dent’s disease-Mitochondrial disorders (Cytochrome c oxidase deficiency)

39
Q

What are some acquired causes of Fanconi Syndrome?

A

-drugs-heavy metals (lead, cadmium)-toxins (toluene, paraquat)-dysproteinemias (MM, light chain deposit disease)-acute tubular necrosis

40
Q

What drugs can cause Fanconi syndrome?

A

-Valproate-Ifosfamide -Cidofovir -Tenofovir -Outdated tetracyclines -Ranitidine -Cisplatin-Aminoglycosides VICTORCA

41
Q

Inherited PT disorders are mostly encountered in children

A

Acquired forms of PT dysfunctions or mild forms of inherited PT disorders occur in adults

STEP Pathology (80 decks)

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