67. Physiology - Distal Na+, K+ Handling

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which transporters are primarily responsible for sodium chloride reabsorption in the distal tubule cells?

Sodium/proton exchanger and K+/Na+ transporter

Sodium-glucose co-transporter and Na+/Ca2+ exchanger

Sodium-Potassium-ATPase and Na+/Cl- co-transporter (correct)

Na+/H+ antiporter and Na+/K+ pump

Which cell type is primarily responsible for hydrogen ion secretion in the distal nephron?

Intercalated cells (correct)

Principal cells

Podocytes

Mesangial cells

What is the primary distinction between titratable acids and ammonium excretion?

Titratable acid excretion requires the presence of fixed buffers, whereas ammonium excretion does not. (correct)

Titratable acids are related to renal metabolism, while ammonium is primarily a waste product.

Titratable acids involve bicarbonate, while ammonium does not.

Ammonium is produced in the proximal tubule, titratable acids are produced in the collecting duct.

How does total body potassium excess influence hydrogen ion handling by the nephron?

It reduces hydrogen ion secretion. Signup and view all the answers

Which factor is NOT involved in modulating distal nephron sodium reabsorption?

Urea concentration Signup and view all the answers

How does inhibition of carbonic anhydrase affect the formation of H+ ions?

It decreases the secretion of H+ ions. Signup and view all the answers

What is the lowest possible pH that can be established in the urine due to primary active transport in the distal tubule?

4.4 Signup and view all the answers

Which factor favors the secretion of H+ ions in the renal tubule?

Increased negativity of tubular fluid (TF) Signup and view all the answers

What is a significant error in understanding renal acid-base handling?

Confusing H+ excretion with H+ secretion Signup and view all the answers

During the secretion of H+ ions, which components in tubular fluid lead to the formation of titratable acid?

HPO42- and H2PO4- Signup and view all the answers

What is the primary function of distal convoluted tubule cells?

Reabsorption of Na+ and Cl- Signup and view all the answers

Which of the following best describes the basolateral membrane potential of distal convoluted tubule cells?

-80 mV Signup and view all the answers

The Na,Cl co-transporter in distal convoluted tubule cells is sensitive to which type of diuretic?

Thiazide diuretics Signup and view all the answers

What maintains the low intracellular Na+ concentration in distal convoluted tubule cells?

Na,K ATPase Signup and view all the answers

Which cell type in the distal nephron is responsible for secreting K+?

Principal cells Signup and view all the answers

Which ions are reabsorbed in the distal convoluted tubules through the Na,Cl co-transporter?

Na+ and Cl- Signup and view all the answers

What is the process through which water reabsorption is primarily regulated in the distal nephron?

Sodium absorption Signup and view all the answers

What role does Cl- play in the reabsorption process in distal convoluted tubules?

Cl- is reabsorbed passively down its transcellular electrical gradient Signup and view all the answers

What is the primary process by which the kidney excretes acid in the form of phosphates and ammonium?

Secretion of H+ that meets phosphates or ammonia Signup and view all the answers

How does the kidney replace the bicarbonate (HCO3-) consumed in buffering acids from protein metabolism?

Through excretion of acids and reabsorption of bicarbonate Signup and view all the answers

What role does carbonic anhydrase play inside renal intercalated cells?

It facilitates the formation of bicarbonate from CO2 and H2O Signup and view all the answers

What is the result of the bicarbonate that is formed in renal intercalated cells?

It enters the bloodstream as 'new' HCO3- Signup and view all the answers

Why is the replacement of bicarbonate important for maintaining acid-base balance?

To prevent the accumulation of acids produced by metabolism Signup and view all the answers

What happens to CO2 produced during acid buffering in the extracellular fluid (ECF)?

It is expelled through the lungs Signup and view all the answers

In the buffering process, what does H+ react with to produce either phosphates or ammonia in the renal tubular fluid?

Bicarbonate Signup and view all the answers

What is meant by 'new' HCO3- formed in the kidneys?

Bicarbonate not previously present in the kidney Signup and view all the answers

What happens to renin levels when there is an increased NaCl load to the macula densa?

Renin levels decrease Signup and view all the answers

How does a low glomerular filtration rate (GFR) affect Na+ reabsorption during hemorrhage?

Na+ reabsorption decreases Signup and view all the answers

What is the primary role of the kidney in relation to blood pressure and volume?

To regulate Na+ reabsorption Signup and view all the answers

What occurs when there is an increased Na+ load delivered to the principal cell?

Na+ reabsorption increases Signup and view all the answers

Which factor might override the effects of aldosterone on Na+ reabsorption?

Increased Na+ load Signup and view all the answers

What is the potential consequence of high Na+ reabsorption in the distal nephron?

Increased K+ secretion Signup and view all the answers

Why might the kidney struggle to predict the net result of simultaneous signals from Na+ load and aldosterone?

The stimuli can provide opposing messages Signup and view all the answers

What physiological phenomenon is compared to the kidney's processing of conflicting inputs?

Decision-making under pressure Signup and view all the answers

What is the primary role of aldosterone in the kidney regarding potassium and sodium?

It stimulates both sodium reabsorption and potassium secretion. Signup and view all the answers

Which buffers are primarily utilized in the distal nephron for H+ secretion?

Ammonia, phosphate, and bicarbonate Signup and view all the answers

How is bicarbonate (HCO3-) reabsorbed in the distal nephron?

In exchange for chloride ions at the basolateral membrane. Signup and view all the answers

What is the role of the H+-ATPase in the distal nephron?

It allows the reclamation of bicarbonate and excretion of H+. Signup and view all the answers

What happens when H+ is secreted into the tubular fluid?

It binds to bicarbonate, forming carbon dioxide and water. Signup and view all the answers

Which statement about the handling of HCO3- in the distal nephron is true?

The last HCO3- is reclaimed through ATPase activity without traversing the apical membrane. Signup and view all the answers

What is the lowest urine pH that can be achieved due to urinary acidification?

4.4 Signup and view all the answers

Which of the following components is not involved in the buffering process within the distal nephron?

Urea Signup and view all the answers

Study Notes

Learning Objectives

Distal tubule and collecting duct function in sodium chloride reabsorption
Distal tubule cell transporters for sodium and potassium
Principal cell channels for sodium and potassium transport
Inhibition of transporters affecting diuresis
Mechanisms modulating distal nephron sodium reabsorption/potassium secretion/reabsorption

Acid Handling

Cell types involved in hydrogen ion secretion/reabsorption in distal tubule and collecting duct
Differentiation between titratable acid and ammonium excretion
Distinction between acid excretion and secretion
Calculation of net acid excretion
Source of renal ammonium and its processing by nephron segments
Factors affecting hydrogen ion secretion and excretion (pCO2, pH, carbonic anhydrase, filtered buffers, electrical potential)

Relationship Between Potassium and Hydrogen

Effect of potassium secretion/reabsorption on hydrogen ion secretion
Concept of total body potassium deficit/excess and its effects on hydrogen ion handling
Impact of body pH on total body potassium content and plasma potassium concentration

Overview of Tubular Solute Handling

Sodium (Na+) reabsorption and potassium (K+) secretion/reabsorption in early and distal nephron segments
Quantitative and regulatory aspects of water reabsorption/secretion in early and distal nephron segments
Role of H+ in regulating urinary pH in distal nephron
Proximal tubule's role in handling the bulk of solute/water

Distal Convoluted Tubule

Main function: Na+ and Cl- reabsorption
Impermeable to water
Membrane potential: basolateral -80 mV (K+ potential), apical -55 mV (net, Na+ and K+ potentials)
Sodium chloride co-transporter (NCC)
Na,K ATPase and chloride channels on basolateral membrane

Na,Cl Co-transporter

Inhibition by thiazide diuretics for hypertension treatment

Principal Cell

Reabsorption of Na+, Cl-, and H₂O
Secretion of K+
Basolateral Na,K-ATPase and K+ channels
Apical Na+ channels (ENaC)
Low intracellular Na+ and negative PD facilitate Na+ entry
High intracellular K+ facilitates K+ secretion

Paracellular Pathway

Chloride driven by lumen negative transcellular voltage

Factors Affecting Distal Na+ Reabsorption and K+ Secretion

Aldosterone: synthesized in adrenal cortex, increases in response to angiotensin II, ↑Na+ reabsorption, ↑K+ secretion, regulated by blood pressure and volume alterations
Na+ load (delivery): ↑Na+ load ↑ Na+ reabsorption and ↑K+ secretion, ↓Na+ load ↓Na+ reabsorption and ↓K+ secretion.
Non-reabsorbable anions (e.g., phosphate, ketones, penicillins): more negative tubular fluid, inhibit Na+ reabsorption and promote K+ secretion.
Distal tubular fluid flow rate: ↑flow rate ↑bending of luminal cilia, ↑secretion of K+, independent of other factors.

Effect of Na+ Load

Independent of renin-Ang II-aldosterone system
Increased Na+ load leads to increased Na+ reabsorption and K+ secretion.
Influence of GFR changes.
Effect of disturbances in body volume status

Cellular Dilemma (Principal Cell)

Conflicting inputs affecting principal cell function
Role of opposing messages in regulatory mechanisms of the kidney

Non-Reabsorbable Anions

Phosphate, ketones, penicillins, bicarbonate
Impact on transtubular potential difference (PD) and Na+ & K+ handling.

Distal Tubular Flow Rate

Increased flow bends cilium, leading to opening of Ca2+-sensitive K+ channels
Higher plasma [K+], ↑K+ secretion
Increased flow rate promotes K+ secretion

Two More Roles for Kidney

Reclamation of all filtered HCO₃
Excretion of H⁺ generated by metabolism
Luminal active transport, electrical gradient, and H+/K+ exchange.

Five Factors Affecting H+ Secretion

Partial pressure of CO₂
Cell pH
Carbonic anhydrase activity
Amounts of filtered/secreted buffers
Electrical potential difference

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz explores the critical functions of the distal tubule and collecting duct in sodium chloride reabsorption and acid-base balance. It covers mechanisms of potassium and hydrogen ion transport, including the role of various transporters and factors influencing their activity. Assess your understanding of renal processes essential for maintaining electrolyte and acid-base homeostasis.