HRE TBL 5 - Renal Physiology Part 1

What effect does aldosterone have on H⁺ secretion?

Increases H⁺ secretion by stimulating H⁺-ATPase in intercalated cells

What type of cells in the collecting duct secrete H⁺?

Type A intercalated cells

What is the role of type B intercalated cells?

Secrete HCO₃⁻ and reabsorb H⁺

Which nephron segment plays a role in acid-base balance via bicarbonate reabsorption?

Proximal tubule

What happens to potassium levels during loop diuretic use?

Hypokalemia due to increased distal K⁺ secretion

How does aldosterone promote potassium excretion?

Enhances ENaC-mediated Na⁺ reabsorption → lumen-negative → ↑ K⁺ secretion

What role does the basolateral Na⁺/K⁺ ATPase play in sodium reabsorption?

Creates low intracellular Na⁺ to drive luminal Na⁺ entry

Which segment of the nephron lacks aquaporin channels?

Thick ascending limb of the Loop of Henle

What is the importance of the medullary osmotic gradient?

Allows production of concentrated urine under ADH influence

How does urea recycling help concentrate urine?

Increases osmolality in the inner medulla, enhancing water reabsorption

What is the effect of ADH on urea transporters?

Increases urea permeability in inner medullary collecting duct

Which part of the nephron is responsible for glucose reabsorption?

Proximal tubule via SGLT2 and SGLT1

What transporter reabsorbs glucose in the early proximal tubule?

SGLT2

What transporter reabsorbs glucose in the late proximal tubule?

SGLT1

What happens to glucose in urine if transport maximum is exceeded?

Glycosuria occurs (e.g., in diabetes mellitus)

What is tubuloglomerular feedback?

Macula densa sensing NaCl → afferent arteriole constriction or dilation

How does the kidney respond to increased NaCl at the macula densa?

Constriction of afferent arteriole → ↓ GFR

What happens when NaCl is low at the macula densa?

Renin is released → RAAS activation

What is the effect of efferent arteriole constriction on GFR?

Increases glomerular hydrostatic pressure → ↑ GFR

How does severe constriction of the afferent arteriole affect GFR?

Decreases GFR due to reduced renal perfusion

How do prostaglandins affect renal arterioles?

Vasodilation of afferent arteriole → maintain GFR

How do NSAIDs affect renal perfusion?

Constrict afferent arteriole by blocking prostaglandins → ↓ GFR

What stimulates ANP release?

Atrial stretch due to increased ECF volume

What is the effect of ANP on collecting duct?

Reduces Na⁺ reabsorption by inhibiting ENaC

What happens to Na⁺ excretion with high effective circulating volume?

Increased sodium excretion (pressure natriuresis)

What does pressure natriuresis refer to?

Excretion of Na⁺ in response to increased arterial pressure

How does hypovolemia affect urea reabsorption?

Increased passive reabsorption in proximal tubule

Which part of the nephron contributes to dilute urine formation?

Thick ascending limb of Henle’s loop (NaCl reabsorption without water)

Which hormone increases thirst and sodium appetite?

Angiotensin II

What hormone reduces sodium appetite?

Atrial natriuretic peptide (ANP)

What type of water loss leads to hypernatremia?

Pure water loss (e.g., in diabetes insipidus)

What type of fluid loss can cause isonatremic dehydration?

Proportional loss of Na⁺ and water (e.g., diarrhea)

What is free water clearance?

Volume of water excreted in excess of solutes

What does negative free water clearance indicate?

Water retention (concentrated urine)

What is the function of principal cells in the collecting duct?

Reabsorb Na⁺ and water, secrete K⁺

What is the primary stimulus for ADH release?

Increased plasma osmolality

How does decreased blood volume influence ADH release?

Stimulates ADH release even at normal osmolality

What is osmotic threshold for ADH release?

~280–285 mOsm/kg

What is maximal urine osmolality in humans?

~1200 mOsm/kg

What is minimal urine osmolality in humans?

~50 mOsm/kg

What causes dilute urine in diabetes insipidus?

Lack of ADH effect on collecting duct

What is the major determinant of ECF volume?

Total body sodium content

What causes orthostatic hypotension in volume depletion?

Decreased preload → reduced cardiac output

Which condition involves water gain without sodium gain?

SIADH

Which receptor mediates ADH-induced aquaporin-2 insertion?

V2 receptor

Where is the thirst center located?

Hypothalamus

What happens to ECF volume in hyperaldosteronism?

Expansion due to sodium retention

What is the effect of cortisol on mineralocorticoid receptors?

Can activate receptors unless inactivated by 11β-HSD2

What is the syndrome of apparent mineralocorticoid excess?

Deficiency of 11β-HSD2 → cortisol activates mineralocorticoid receptors

What is Liddle syndrome?

ENaC mutation causing increased sodium reabsorption → hypertension

How does spironolactone work?

Blocks aldosterone receptors in collecting duct

What is an example of an osmotic diuretic?

Mannitol

What is the effect of mannitol on ECF volume?

Expands ECF volume initially

Which hormone causes vasoconstriction and stimulates aldosterone?

Angiotensin II

What is the function of angiotensinogen?

Precursor to angiotensin I

Where is angiotensinogen produced?

Liver

What type of receptor is the angiotensin II receptor (AT1)?

G protein-coupled receptor

What is the effect of angiotensin II on proximal tubule?

Enhances Na⁺/H⁺ exchange → ↑ Na⁺ reabsorption

What is Bartter syndrome?

Defect in NKCC2 → mimics chronic loop diuretic use

What is Gitelman syndrome?

Defect in NCC → mimics thiazide use

What lab finding is shared by Bartter and Gitelman syndrome?

Hypokalemia and metabolic alkalosis

How does effective arterial blood volume differ from total blood volume?

Reflects perfusion rather than total fluid amount

What happens to RAAS in cirrhosis despite fluid overload?

Activated due to low effective arterial blood volume

What is one diagnostic clue to differentiate SIADH from hypovolemia?

High urine sodium in SIADH (>40 mmol/L)

What is the treatment of nephrogenic DI?

Thiazides, low salt/protein diet, NSAIDs

What is desmopressin?

ADH analog used to treat central DI

What effect does low Na⁺ delivery have on K⁺ secretion?

Reduces K⁺ secretion

What stimulates potassium secretion in the distal nephron?

High luminal sodium and flow rate

What can cause pseudohyponatremia?

Hyperlipidemia or hyperproteinemia (lab artifact)

What is osmolal gap?

Difference between measured and calculated plasma osmolality

What does an increased osmolal gap suggest?

Presence of unmeasured osmoles (e.g., ethanol, methanol)

What is the major determinant of ICF volume?

Intracellular osmoles (mainly K⁺)

What hormone is stimulated by hyperkalemia?

Aldosterone

What is the mechanism of action of amiloride?

Blocks ENaC in collecting duct

What is the effect of thiazides on calcium?

Increase calcium reabsorption → ↓ urine calcium

What condition is associated with impaired thirst mechanism?

Hypothalamic lesions or aging

What electrolyte abnormality is worsened by thiazide use?

Hyponatremia

What is the mechanism behind thiazide-induced hyponatremia?

Volume contraction + impaired dilution of urine

What is the main role of aldosterone in acid-base balance?

Promotes H⁺ secretion → helps alkalosis

What is the plasma osmolarity formula?

2[Na⁺] + glucose/18 + BUN/2.8

What is the role of aquaporins in the kidney?

Facilitate water reabsorption in response to ADH

What stimulates the thirst response more: volume depletion or hyperosmolality?

Hyperosmolality

What is the term for high urine output (>3 L/day)?

Polyuria

What is one way to distinguish psychogenic polydipsia from DI?

Low plasma osmolality with low ADH

What is one feature of water intoxication?

Hyponatremia with low serum osmolality

What is the expected urine osmolality in psychogenic polydipsia?

Very low (<100 mOsm/kg)

What is the expected plasma osmolality in SIADH?

Low (<275 mOsm/kg)

Which hormone suppresses ADH and promotes natriuresis?

ANP

What happens to plasma ADH during hemorrhage?

Increases

What determines whether urine is concentrated or dilute?

ADH activity and medullary gradient

What is one renal adaptation to chronic acidosis?

Ammonium (NH₄⁺) excretion increases

What are the three main physiological functions of the kidney?

Excretory, regulatory (homeostasis), and endocrine functions

Name one hormone produced by the kidney involved in blood pressure regulation.

Renin

Which kidney hormone stimulates red blood cell production?

Erythropoietin

Which vitamin is activated by the kidney?

Vitamin D (calcitriol)

What percentage of filtered sodium is reabsorbed in the proximal tubule?

Approximately 65%

Which transporter is primarily responsible for sodium reabsorption in the proximal tubule?

NHE3

Is the descending limb of the Loop of Henle permeable to water?

Yes

What transporter is found in the thick ascending limb of the Loop of Henle?

NKCC2 (Na⁺-K⁺-2Cl⁻ cotransporter)

What effect does aldosterone have on ENaC channels?

It increases their expression and activity