HRE TBL 6 - Renal Physiology Part 2

Which transporter reabsorbs sodium and glucose in the early proximal tubule?

SGLT2

Which transporter reabsorbs sodium and glucose in the late proximal tubule?

SGLT1

Which transporter moves glucose across the basolateral membrane of the proximal tubule?

GLUT

Which transporter reabsorbs sodium in exchange for hydrogen in the proximal tubule?

Na⁺/H⁺ exchanger (NHE3)

Which enzyme facilitates bicarbonate reabsorption by converting CO₂ and H₂O to H₂CO₃?

Carbonic anhydrase

Which transporter is responsible for sodium reabsorption in the thick ascending limb?

Na⁺ K⁺ 2Cl⁻ cotransporter

Which channel is activated by aldosterone to reabsorb sodium in the collecting duct?

Epithelial Sodium Channel

Which transporter is responsible for potassium secretion in the collecting duct?

Renal Outer Medullary Potassium channel

Which transporter maintains intracellular sodium and potassium gradients in all nephron segments?

Na⁺/K⁺ ATPase

Which transporter secretes hydrogen ions in alpha-intercalated cells of the collecting duct?

H⁺ ATPase

Which transporter secretes hydrogen in exchange for potassium in alpha-intercalated cells?

H⁺/K⁺ ATPase

Which transport protein is involved in bicarbonate reabsorption in the proximal tubule?

Na⁺/HCO₃⁻ cotransporter

Which transporter is upregulated during acidosis for ammonium excretion?

NH₄⁺ transporter (linked to glutamine metabolism)

Which sodium transporter is involved in sodium reabsorption in the distal convoluted tubule?

Na⁺/Cl⁻ cotransporter

What is the equation for net filtration pressure (NFP)?

NFP = PGC - (PBS + πGC)

What does PGC stand for and what is its role?

Glomerular capillary hydrostatic pressure; drives filtration

What does PBS stand for and what is its role?

Bowman’s space hydrostatic pressure; opposes filtration

What does πGC stand for and what is its role?

Glomerular capillary oncotic pressure; opposes filtration

What is the normal GFR in a healthy adult?

125 mL/min

What is the typical renal plasma flow (RPF) in a healthy adult?

625 mL/min

What is the normal filtration fraction?

0.2 or 20%

How is filtration fraction calculated?

GFR divided by RPF

What does a decrease in afferent arteriole resistance do to GFR?

Increases GFR

What does a decrease in efferent arteriole resistance do to GFR?

Decreases GFR

What does an increase in afferent resistance do to renal plasma flow?

Decreases RPF

What is the site of glucose reabsorption in the nephron?

Proximal tubule

Which transporters reabsorb glucose in the proximal tubule?

SGLT2 and SGLT1

What causes glucose to appear in urine?

When plasma glucose exceeds the renal threshold

What is the consequence of osmotic diuresis caused by glucosuria?

Loss of water and sodium

What class of drugs inhibits glucose reabsorption in the proximal tubule?

SGLT2 inhibitors

What is one therapeutic benefit of SGLT2 inhibitors in diabetes?

Promote glucosuria to lower blood glucose

What happens when the tubular load of glucose exceeds the transport maximum (Tm)?

Glucose is excreted in the urine

What is the key regulator of GFR via tubuloglomerular feedback?

Macula densa

What does the macula densa sense in the nephron?

Sodium chloride concentration

What type of feedback does the macula densa use to regulate afferent arteriole tone?

Tubuloglomerular feedback

How is renal blood flow autoregulated?

Myogenic mechanism and tubuloglomerular feedback

What electrolyte is secreted in the distal nephron?

Potassium (K⁺)

Which hormone increases potassium secretion?

Aldosterone

Which cell type is responsible for potassium secretion in the collecting duct?

Principal cells

What channel allows potassium to be secreted in the collecting duct?

ROMK

Which segment reabsorbs the majority of filtered potassium?

Proximal tubule

What is the impact of increased distal sodium delivery on potassium secretion?

Increases potassium secretion

Which type of intercalated cell secretes hydrogen ions?

Alpha-intercalated cells

Which type of intercalated cell secretes bicarbonate?

Beta-intercalated cells

What is the role of the bicarbonate buffer system?

Maintains pH balance in the body

What equation describes the bicarbonate buffer system?

Henderson-Hasselbalch equation

What is the normal ratio of HCO₃⁻ to CO₂ in the blood?

20:01

How do the lungs respond to metabolic acidosis?

Increase ventilation to reduce CO₂

How do the kidneys compensate for respiratory acidosis?

Increase H⁺ excretion and HCO₃⁻ reabsorption

What are the two main physiological buffers in the nephron for H⁺?

Phosphate and ammonium

What is the renal response to respiratory alkalosis?

Decrease bicarbonate reabsorption

Where is ammonium (NH₄⁺) produced in the nephron?

Proximal tubule

How does the kidney generate new bicarbonate?

Through ammoniagenesis and H⁺ secretion

What is the definition of renal clearance?

Volume of plasma cleared of a substance per unit time

Which substance is used as the gold standard for measuring GFR?

Inulin

Why is inulin ideal for measuring GFR?

It is freely filtered and neither reabsorbed nor secreted

What is a common endogenous marker used to estimate GFR?

Creatinine

Why does creatinine slightly overestimate GFR?

Because it is also secreted by the tubule

What does it mean if clearance of a substance is greater than GFR?

The substance is filtered and secreted

What does it mean if clearance of a substance is less than GFR?

The substance is reabsorbed

What is the significance of being "freely filtered"?

Substance crosses the glomerular filtration barrier unimpeded

Which molecules are not freely filtered?

Proteins (e.g. albumin) and blood cells

How does phosphate buffer H⁺ in the nephron?

Forming H₂PO₄⁻ in the tubular fluid

What is titratable acid?

H⁺ excreted bound to phosphate

Where in the nephron does phosphate buffering primarily occur?

Distal tubule

What enzyme facilitates bicarbonate reabsorption in the proximal tubule?

Carbonic anhydrase

Where in the nephron is the Na⁺/H⁺ exchanger (NHE3) active?

Proximal tubule

What segment of the nephron reabsorbs Na⁺, K⁺, and Cl⁻ via NKCC2?

Thick ascending limb

What is the role of NKCC2 in the nephron?

Reabsorbs Na⁺, K⁺, and 2Cl⁻ in the thick ascending limb

Which hormone increases water reabsorption in the collecting duct?

ADH (antidiuretic hormone)

Which channel is inserted into the apical membrane by ADH?

Aquaporin-2

Which part of the nephron is impermeable to water?

Thick ascending limb

What is the function of epithelial sodium channel in the collecting duct?

Reabsorbs sodium

Where does aldosterone act in the nephron?

Principal cells of distal tubule and collecting duct

What is the effect of aldosterone on epithelium sodium channel?

Upregulates epithelium sodium channel to increase Na⁺ reabsorption

What transporter maintains the Na⁺ and K⁺ gradients in renal tubular cells?

Na⁺/K⁺ ATPase

What role does aldosterone play in sodium handling? 

Increases sodium reabsorption in the distal nephron

Which transporter is key in sodium reabsorption in the thick ascending limb? 

Na-K-2Cl 

Where is ammonium primarily excreted in the kidney

Proximal tubule

What stimulates potassium secretion in the distal nephron?

High tubular flow rate

Does acidosis or alkalosis decrease renal potassium secretion

Acidosis

What is the advantage of using inulin to measure GFR?

It is freely filtered and neither secreted nor reabsorbed

What does the term freely filtered mean?

Small molecules filtered without restriction at the glomerulus

What effect does angiotensin II have on the kidney?

Constriction of efferent arteriole 

What happens to oncotic pressure in glomerular capillaries as blood flows through?

It increases

What effect does increased plasma protein concentration have on GFR?

Decreases GFR

What effect does increased Bowman’s space pressure have on filtration?

It decreases net filtration pressure

What is the effect of efferent arteriole constriction on RPF?

It decreases RPF

What happens to net filtration pressure if πGC increases significantly?

It decreases

What condition can increase Bowman’s capsule hydrostatic pressure?

Obstruction (e.g., kidney stone, tumor)

What is the role of mesangial cells in glomerular filtration?

They can contract and reduce surface area for filtration

What is the main determinant of GFR in healthy physiology?

Glomerular capillary hydrostatic pressure (PGC)

How does high sympathetic tone affect afferent arterioles?

Causes vasoconstriction

What type of epithelium lines the proximal tubule?

Simple cuboidal epithelium with a brush border

What type of transport mechanism does SGLT2 use?

Secondary active transport

What is the effect of a high tubular flow rate on sodium reabsorption in the proximal tubule?

Reduces reabsorption due to limited contact time

Which transporter is found on the apical membrane of the thick ascending limb?

NKCC2

What segment of the nephron creates the corticomedullary osmotic gradient?

Loop of Henle (especially TAL)

Which segment is impermeable to water but reabsorbs solutes?

Thick ascending limb of Henle

Which ion’s reabsorption is enhanced by paracellular transport in TAL?

Calcium and magnesium