Podcast
Questions and Answers
What characteristic of the glomerular filtrate is most critical for the kidneys to regulate the volume and composition of bodily fluids?
What characteristic of the glomerular filtrate is most critical for the kidneys to regulate the volume and composition of bodily fluids?
- It contains a higher concentration of plasma proteins than blood.
- It is devoid of any cellular components.
- It has a significantly lower osmotic pressure than blood plasma.
- Its composition is nearly identical to plasma, excluding larger proteins and cells. (correct)
In tubular epithelial cells, what role do tight junctions play in the absorption and secretion processes?
In tubular epithelial cells, what role do tight junctions play in the absorption and secretion processes?
- They directly regulate the activity of ATPase pumps.
- They maintain functional polarity by restricting protein movement between apical and basolateral sides. (correct)
- They facilitate the transport of large proteins across the cellular membrane.
- They actively secrete ions against their electrochemical gradient.
Which factor most directly facilitates the movement of water across tubular epithelial cell membranes?
Which factor most directly facilitates the movement of water across tubular epithelial cell membranes?
- The presence of tight junctions preventing paracellular water movement
- Active transport of electrolytes creating an osmotic gradient (correct)
- Direct energy expenditure by aquaporins
- Hydrostatic pressure differences between the filtrate and the interstitium
A patient's urine sample shows a high glucose concentration despite normal blood glucose levels. Which transporter dysfunction is the LEAST likely cause?
A patient's urine sample shows a high glucose concentration despite normal blood glucose levels. Which transporter dysfunction is the LEAST likely cause?
How does the kidney ensure nearly all filtered protein is reabsorbed under normal physiological conditions?
How does the kidney ensure nearly all filtered protein is reabsorbed under normal physiological conditions?
A patient has increased protein in their urine due to tubular damage. What factor is LEAST likely to contribute to this condition?
A patient has increased protein in their urine due to tubular damage. What factor is LEAST likely to contribute to this condition?
What is the primary mechanism by which amino acids are reabsorbed in the proximal convoluted tubule?
What is the primary mechanism by which amino acids are reabsorbed in the proximal convoluted tubule?
Why is the reabsorption of bicarbonate in the proximal convoluted tubule essential for acid-base homeostasis?
Why is the reabsorption of bicarbonate in the proximal convoluted tubule essential for acid-base homeostasis?
A drug that inhibits carbonic anhydrase in the proximal convoluted tubule would MOST directly impair:
A drug that inhibits carbonic anhydrase in the proximal convoluted tubule would MOST directly impair:
What role do organic ion transporters in the proximal convoluted tubule play in maintaining homeostasis?
What role do organic ion transporters in the proximal convoluted tubule play in maintaining homeostasis?
What is the significance of the countercurrent mechanism in the Loop of Henle for urine concentration?
What is the significance of the countercurrent mechanism in the Loop of Henle for urine concentration?
Which segment of the nephron is LEAST permeable to water, contributing to the dilution of the filtrate?
Which segment of the nephron is LEAST permeable to water, contributing to the dilution of the filtrate?
How do loop diuretics like furosemide affect kidney function by disrupting salt reabsorption?
How do loop diuretics like furosemide affect kidney function by disrupting salt reabsorption?
What is the primary function of the early distal convoluted tubule in regulating fluid and electrolyte balance?
What is the primary function of the early distal convoluted tubule in regulating fluid and electrolyte balance?
How does aldosterone influence sodium reabsorption and potassium secretion in the late distal convoluted tubule and collecting duct?
How does aldosterone influence sodium reabsorption and potassium secretion in the late distal convoluted tubule and collecting duct?
What is the primary role of ADH (Vasopressin) in the late distal convoluted tubule and collecting duct regarding urine concentration?
What is the primary role of ADH (Vasopressin) in the late distal convoluted tubule and collecting duct regarding urine concentration?
How do intercalated cells in the late distal convoluted tubule and collecting duct contribute to acid-base balance?
How do intercalated cells in the late distal convoluted tubule and collecting duct contribute to acid-base balance?
Which combination of factors listed MOST directly results in hyperkalemia?
Which combination of factors listed MOST directly results in hyperkalemia?
Which statement best describes the differences in solute handling between the proximal tubule and the collecting duct?
Which statement best describes the differences in solute handling between the proximal tubule and the collecting duct?
A patient with uncontrolled diabetes mellitus has persistently high blood glucose levels. How does this MOST directly affect urine production and composition?
A patient with uncontrolled diabetes mellitus has persistently high blood glucose levels. How does this MOST directly affect urine production and composition?
In which condition is the primary defect in the proximal tubule?
In which condition is the primary defect in the proximal tubule?
What is the primary location where tubular fluid osmolarity can increase to 1200 mOsm/L?
What is the primary location where tubular fluid osmolarity can increase to 1200 mOsm/L?
Which of the following best describes the physiological response to a severe drop in blood pressure concerning renal handling of salt and water?
Which of the following best describes the physiological response to a severe drop in blood pressure concerning renal handling of salt and water?
Why does altering the permeability of the distal tubules and collecting ducts affect the final urine volume and concentration?
Why does altering the permeability of the distal tubules and collecting ducts affect the final urine volume and concentration?
How does damage to the glomerulus affect urine composition?
How does damage to the glomerulus affect urine composition?
If the Na+/K+ ATPase pump is inhibited throughout the nephron, what result would likely occur?
If the Na+/K+ ATPase pump is inhibited throughout the nephron, what result would likely occur?
Which best characterizes glomerulotubular balance?
Which best characterizes glomerulotubular balance?
If a person ingested a drug that decreased the afferent arteriole radius of the glomerulus, how would that MOST directly affect filtrate volume with all else held constant?
If a person ingested a drug that decreased the afferent arteriole radius of the glomerulus, how would that MOST directly affect filtrate volume with all else held constant?
A mutation that causes over-expression of the Na+/K+/2Cl synporter symporter (NKCC2) in the loop of Henle would result in all of the following EXCEPT:
A mutation that causes over-expression of the Na+/K+/2Cl synporter symporter (NKCC2) in the loop of Henle would result in all of the following EXCEPT:
What is the most likely outcome in urine electrolyte composition when a patient takes a drug that has a similar function to vasopressin?
What is the most likely outcome in urine electrolyte composition when a patient takes a drug that has a similar function to vasopressin?
Which action related to kidney filtration is most likely to occur during a sympathetic 'fight-or-flight' response in the body?
Which action related to kidney filtration is most likely to occur during a sympathetic 'fight-or-flight' response in the body?
A competitive inhibitor medication is designed to block aldosterone receptors in the late distal tubule and collecting ducts. What is the anticipated effect on final urine composition?
A competitive inhibitor medication is designed to block aldosterone receptors in the late distal tubule and collecting ducts. What is the anticipated effect on final urine composition?
Which of the following characterizes the function of the thin ascending limb in the loop of Henle regarding urine concentration?
Which of the following characterizes the function of the thin ascending limb in the loop of Henle regarding urine concentration?
How do ACE inhibitors lead to lower blood pressure?
How do ACE inhibitors lead to lower blood pressure?
How are proteins reabsorbed for use within the body?
How are proteins reabsorbed for use within the body?
What direct effect occurs on the medullary concentration gradient when vasopressin secretion is chronically impaired?
What direct effect occurs on the medullary concentration gradient when vasopressin secretion is chronically impaired?
An investigator who discovers a new drug that blocks aquaporin channels in the late distal tubule and the collecting duct would expect to see which of the following?
An investigator who discovers a new drug that blocks aquaporin channels in the late distal tubule and the collecting duct would expect to see which of the following?
A patient showing edema is prescribed a loop diuretic which acts on the ascending loop of Henle. What changes can be recorded in urine analysis after the medication?
A patient showing edema is prescribed a loop diuretic which acts on the ascending loop of Henle. What changes can be recorded in urine analysis after the medication?
A newly developed drug blocks the reabsorption of urea in the medullary collecting duct. How will this medication impact a normal person's urine?
A newly developed drug blocks the reabsorption of urea in the medullary collecting duct. How will this medication impact a normal person's urine?
Blocking reabsorption of sodium chloride impacts reabsorption of water through which mechanism?
Blocking reabsorption of sodium chloride impacts reabsorption of water through which mechanism?
Which cellular adaptation would most likely be observed for proximal convoluted tubule cells?
Which cellular adaptation would most likely be observed for proximal convoluted tubule cells?
Why can kidney damage cause anemia?
Why can kidney damage cause anemia?
A mutation disrupts the function of the Na+/K+ ATPase pump specifically in the basolateral membrane of the proximal convoluted tubule cells. What is the MOST likely direct consequence?
A mutation disrupts the function of the Na+/K+ ATPase pump specifically in the basolateral membrane of the proximal convoluted tubule cells. What is the MOST likely direct consequence?
A researcher is studying a novel drug that selectively targets aquaporins in the nephron. If the drug completely blocks aquaporin-1 channels, which of the following would be the MOST direct expected outcome?
A researcher is studying a novel drug that selectively targets aquaporins in the nephron. If the drug completely blocks aquaporin-1 channels, which of the following would be the MOST direct expected outcome?
A patient with a genetic disorder exhibits a significantly reduced number of functional Na+-H+ exchangers (NHEs) in the apical membrane of the proximal tubule cells. Which of the following compensatory mechanisms is LEAST likely to occur in response to this defect?
A patient with a genetic disorder exhibits a significantly reduced number of functional Na+-H+ exchangers (NHEs) in the apical membrane of the proximal tubule cells. Which of the following compensatory mechanisms is LEAST likely to occur in response to this defect?
In a clinical study, researchers are investigating the effects of a drug that inhibits carbonic anhydrase specifically within the tubular lumen. Which of the following changes in urine composition and electrolyte balance would MOST likely be observed?
In a clinical study, researchers are investigating the effects of a drug that inhibits carbonic anhydrase specifically within the tubular lumen. Which of the following changes in urine composition and electrolyte balance would MOST likely be observed?
A novel toxin selectively impairs the function of the Na+/K+/2Cl- cotransporter (NKCC2) in the thick ascending limb of the loop of Henle. Predict the MOST direct effect on urine concentration and volume.
A novel toxin selectively impairs the function of the Na+/K+/2Cl- cotransporter (NKCC2) in the thick ascending limb of the loop of Henle. Predict the MOST direct effect on urine concentration and volume.
What distinguishes tubular secretion from reabsorption in the nephron?
What distinguishes tubular secretion from reabsorption in the nephron?
How do tubular epithelial cells contribute to urine formation?
How do tubular epithelial cells contribute to urine formation?
How does the Na+/K+ ATPase pump in the basolateral membrane of tubular cells contribute to transepithelial solute transport?
How does the Na+/K+ ATPase pump in the basolateral membrane of tubular cells contribute to transepithelial solute transport?
A drug that inhibits the Na+/H+ exchanger (NHE) in the proximal tubule would directly affect the reabsorption of which substance?
A drug that inhibits the Na+/H+ exchanger (NHE) in the proximal tubule would directly affect the reabsorption of which substance?
A patient is diagnosed with Fanconi syndrome. Considering the functions of the proximal tubule, which set of abnormalities would be MOST expected in their urine?
A patient is diagnosed with Fanconi syndrome. Considering the functions of the proximal tubule, which set of abnormalities would be MOST expected in their urine?
Why does the osmolarity significantly increase as the filtrate flows down the descending limb of the Loop of Henle?
Why does the osmolarity significantly increase as the filtrate flows down the descending limb of the Loop of Henle?
What is the direct effect of the Na+/K+/2Cl- cotransporter (NKCC2) in the thick ascending limb of the loop of Henle on the medullary interstitium?
What is the direct effect of the Na+/K+/2Cl- cotransporter (NKCC2) in the thick ascending limb of the loop of Henle on the medullary interstitium?
In the distal convoluted tubule (DCT), what effect does parathyroid hormone (PTH) have on calcium reabsorption?
In the distal convoluted tubule (DCT), what effect does parathyroid hormone (PTH) have on calcium reabsorption?
A patient presents with a condition that causes decreased aldosterone secretion. What changes in electrolyte balance and blood pressure would you expect to observe?
A patient presents with a condition that causes decreased aldosterone secretion. What changes in electrolyte balance and blood pressure would you expect to observe?
What is the primary mechanism by which ADH increases water reabsorption in the collecting duct?
What is the primary mechanism by which ADH increases water reabsorption in the collecting duct?
How do intercalated cells in the collecting duct respond to a decrease in blood pH?
How do intercalated cells in the collecting duct respond to a decrease in blood pH?
What is the effect of increased plasma protein concentration on glomerular filtration?
What is the effect of increased plasma protein concentration on glomerular filtration?
What is the effect on urine production if a drug blocks aquaporin channels in the collecting duct?
What is the effect on urine production if a drug blocks aquaporin channels in the collecting duct?
Damage to the glomerulus most directly affects urine composition how?
Damage to the glomerulus most directly affects urine composition how?
How is urea reabsorbed for use within the body?
How is urea reabsorbed for use within the body?
What is the main advantage of countercurrent multiplication?
What is the main advantage of countercurrent multiplication?
What transport mechanism is primarily responsible for glucose reabsorption in the proximal tubule?
What transport mechanism is primarily responsible for glucose reabsorption in the proximal tubule?
What effect will a drug that increases afferent arteriolar resistance and efferent arteriolar resistance have on glomerular filtration rate (GFR)?
What effect will a drug that increases afferent arteriolar resistance and efferent arteriolar resistance have on glomerular filtration rate (GFR)?
Which transport mechanism is primarily involved in the reabsorption of amino acids in the proximal tubule?
Which transport mechanism is primarily involved in the reabsorption of amino acids in the proximal tubule?
How does increased hydrostatic pressure affect the filtration rate?
How does increased hydrostatic pressure affect the filtration rate?
How does the kidney contribute to anemia?
How does the kidney contribute to anemia?
What would be a result of decreasing the radius of both the efferent and afferent arterioles?
What would be a result of decreasing the radius of both the efferent and afferent arterioles?
If the amount of Na/K ATPase pumps increase on the basolateral membrane, which event would occur?
If the amount of Na/K ATPase pumps increase on the basolateral membrane, which event would occur?
If the thick ascending limb is impermeable to water and permeable to ions, then:
If the thick ascending limb is impermeable to water and permeable to ions, then:
How osmolarity in filtrate change as it enter the loop of Henle and then enter the ascending loop of Henle?
How osmolarity in filtrate change as it enter the loop of Henle and then enter the ascending loop of Henle?
What describes best the role of Type A intercalated cells?
What describes best the role of Type A intercalated cells?
What describes how the kidney regulate blood pressure?
What describes how the kidney regulate blood pressure?
How would an ACE inhibitor medication work to lower hypertension?
How would an ACE inhibitor medication work to lower hypertension?
The reabsorption of water occurs where?
The reabsorption of water occurs where?
Damage to what area impacts ability to concentrate urine?
Damage to what area impacts ability to concentrate urine?
What will characterize the function of the thin ascending limb in the loop of Henle with regard to urine concentration?
What will characterize the function of the thin ascending limb in the loop of Henle with regard to urine concentration?
What is the main function of tight junctions?
What is the main function of tight junctions?
What is the main function of Aquaporin-1?
What is the main function of Aquaporin-1?
What is the primary result from inhibiting carbonic anhydrase?
What is the primary result from inhibiting carbonic anhydrase?
Overactivity of the Na+/K+/2Cl- cotransporter (NKCC2), will result in what effect?
Overactivity of the Na+/K+/2Cl- cotransporter (NKCC2), will result in what effect?
Why is it important to reabsorb bicarbonate?
Why is it important to reabsorb bicarbonate?
Which mechanism helps maintain low [Na+]i?
Which mechanism helps maintain low [Na+]i?
What section in the tubule has cuboidal epithelial cells?
What section in the tubule has cuboidal epithelial cells?
In the proximal convoluted tubule (PCT), a drug that inhibits the Na+/H+ exchangers (NHEs) on the apical membrane would MOST directly affect the reabsorption of which of the following substances?
In the proximal convoluted tubule (PCT), a drug that inhibits the Na+/H+ exchangers (NHEs) on the apical membrane would MOST directly affect the reabsorption of which of the following substances?
A patient is prescribed a medication that inhibits the Na+/K+/2Cl- cotransporter (NKCC2) in the thick ascending limb of the loop of Henle. What is the MOST likely effect on the osmolality of the medullary interstitium?
A patient is prescribed a medication that inhibits the Na+/K+/2Cl- cotransporter (NKCC2) in the thick ascending limb of the loop of Henle. What is the MOST likely effect on the osmolality of the medullary interstitium?
If a person's body is undergoing an acidotic state, how would the intercalated cells in the collecting duct respond to help restore blood pH?
If a person's body is undergoing an acidotic state, how would the intercalated cells in the collecting duct respond to help restore blood pH?
A researcher discovers a mutation that selectively impairs the function of aquaporin-1 channels in the proximal tubule. Predict the MOST direct effect on the nephron's handling of water and overall urine output.
A researcher discovers a mutation that selectively impairs the function of aquaporin-1 channels in the proximal tubule. Predict the MOST direct effect on the nephron's handling of water and overall urine output.
A previously healthy individual begins taking a new medication that inhibits aldosterone release from the adrenal cortex. How would their kidneys MOST likely respond to maintain electrolyte balance and blood pressure?
A previously healthy individual begins taking a new medication that inhibits aldosterone release from the adrenal cortex. How would their kidneys MOST likely respond to maintain electrolyte balance and blood pressure?
Flashcards
What is glomerular filtrate?
What is glomerular filtrate?
Fluid in the Bowman's capsule of the renal corpuscle.
What are tubular reabsorption and secretion?
What are tubular reabsorption and secretion?
Reabsorption removes substances from the tubular fluid; secretion adds substances.
What is tubular reabsorption?
What is tubular reabsorption?
The process by which solutes and water are removed from the tubular fluid and transported into the blood.
What is tubular secretion?
What is tubular secretion?
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What is passive secretion?
What is passive secretion?
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What is active secretion?
What is active secretion?
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What is functional polarity?
What is functional polarity?
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What are epithelial transport proteins?
What are epithelial transport proteins?
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What is the primary function of Na+/K+ ATPase pump?
What is the primary function of Na+/K+ ATPase pump?
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What are ion channels?
What are ion channels?
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How does transport occur with ion channels?
How does transport occur with ion channels?
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What are carriers?
What are carriers?
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What is the function of aquaporins?
What is the function of aquaporins?
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How is urine formed?
How is urine formed?
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What does the proximal convoluted tubule reabsorb?
What does the proximal convoluted tubule reabsorb?
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How does uptake occur in the PCT?
How does uptake occur in the PCT?
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What happens in early proximal tubule?
What happens in early proximal tubule?
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What is SGLT-2?
What is SGLT-2?
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What is glycosuria?
What is glycosuria?
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What is filtered in Glomerulus?
What is filtered in Glomerulus?
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What is filtered in the glomerulus?
What is filtered in the glomerulus?
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What is proteinuria?
What is proteinuria?
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What occurs in Fanconi Syndrome?
What occurs in Fanconi Syndrome?
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What are the permeability characteristics of the thin descending limb of the Loop of Henle?
What are the permeability characteristics of the thin descending limb of the Loop of Henle?
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What are the permeability characteristics of the thin ascending limb of the Loop of Henle?
What are the permeability characteristics of the thin ascending limb of the Loop of Henle?
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Loop of Henle actively reabsorbs?
Loop of Henle actively reabsorbs?
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How do loop diuretics work?
How do loop diuretics work?
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What is the DCT important for?
What is the DCT important for?
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What happens in DCT?
What happens in DCT?
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What occurs late Distal Convoluted Tubule/Collecting Ducts?
What occurs late Distal Convoluted Tubule/Collecting Ducts?
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What does aldosterone do?
What does aldosterone do?
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What do K-sparing diuretics do?
What do K-sparing diuretics do?
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High potassium intake result in ?
High potassium intake result in ?
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What do late DCT/CD do?
What do late DCT/CD do?
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What occurs in intercalated cells in the late DCT and CD?
What occurs in intercalated cells in the late DCT and CD?
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Kidney's primary function?
Kidney's primary function?
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What plasma components are filtered?
What plasma components are filtered?
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How do the tubules alter the glomerular filtrate?
How do the tubules alter the glomerular filtrate?
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What may tubular epithelial cell do?
What may tubular epithelial cell do?
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How does filtrate osmolarity change?
How does filtrate osmolarity change?
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What is the PCT epithelium?
What is the PCT epithelium?
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What is passive diffusion?
What is passive diffusion?
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What is active transport?
What is active transport?
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How does water cross tubular epithelial cells?
How does water cross tubular epithelial cells?
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What are tight juctions?
What are tight juctions?
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How is water transported in kidneys?
How is water transported in kidneys?
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Name other segments of nephron?
Name other segments of nephron?
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What happens if filtered AA levels are elevated?
What happens if filtered AA levels are elevated?
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What transporters are for organic ions?
What transporters are for organic ions?
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What is bulk reabsorption?
What is bulk reabsorption?
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What is the main job of angiotensin II?
What is the main job of angiotensin II?
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What does ANP do?
What does ANP do?
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What does ADH do?
What does ADH do?
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What is Loop of Henle Function?
What is Loop of Henle Function?
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What is the thick ascending limbs Role
What is the thick ascending limbs Role
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Study Notes
- The lecture discusses the renal handling of salt and water in the formation of urine - part 1.
- The learning objectives include understanding glomerular filtrate composition, fluid and electrolyte transport, and urine composition.
- Also covered are the roles of different renal tubule segments and the mechanisms of reabsorption and secretion.
- Course: Renal System Module
- Code: MED 204
- Lecturer: Dr. Stephen Keely & Dr. Patrick Walsh
- Date: February 2025
Primary Kidney Function
- Kidneys regulate the volume and composition of bodily fluids.
- This is achieved through the formation of urine.
Glomerular Filtration
- Glomerular filtrate is the fluid in the Bowman's capsule lumen within the renal corpuscle.
- The formation rate is 115-125 ml/min, approximately 180L per day.
- Filtration occurs from blood through the glomerulus capillaries and Bowman's capsule podocytes.
- Filtration is driven by blood pressure, and all plasma components are filtered except large proteins and cells.
Renal Tubule Structure and Function
- The primary function of renal tubules in urine formation transforms glomerular filtrate.
- Tubular epithelial cells facilitate reabsorption which removes substances from the filtrate.
- Tubular epithelial cells also secrete, adding substances to the filtrate.
- Changes in filtrate osmolarity along the tubules drive water movement and urine formation.
Tubular Reabsorption
- Reabsorption is the process where solutes and water are moved from the tubular fluid back into the blood.
- Reabsorbed substances include electrolytes, glucose, proteins, amino acids, and urea.
- This process maintains homeostasis of blood volume, pressure, pH, and osmolarity.
- Solute absorption uses specific transport proteins arranged into pathways.
- Passive diffusion absorbs solutes through epithelial cells along concentration gradients.
- Active transport establishes concentration gradients using energy from Na+/K+ ATPase pumps.
- Filtrate osmolarity changes along the nephron:
- PCT: 300 mOsm/L which is the same as plasma
- Descending LoH: increases to 1200 mOsm/L as water is reabsorbed
- DCT & CD: osmolarity varies with permeability
Tubular Secretion
- Tubular secretion moves solutes from peritubular capillaries or interstitium into the tubular lumen.
- Secretion clears substances from the blood, unlike reabsorption which retains them.
- Secreted substances include waste/unwanted products like K+, H+, NH4+, creatinine, urea, hormones and drugs.
- Urea secretion into the tubular fluid contributes to urine formation.
- Secretion of H+ and NH4 is important for maintaining blood pH.
- Secretion uses similar processes to reabsorption, but in reverse.
- Passive secretion is the diffusion of molecules along osmotic or chemical gradients.
- Active secretion moves molecules against gradients using energy-dependent ATPase pumps.
Tubular Epithelial Cells
- Tubular epithelial cells differ along the nephron's length, depending on function.
- PCT cells are cuboidal epithelium which increase surface area for reabsorption which is supported by their rich mitochondria, which are needed for efficient reabsorption via active transport.
- In Loop of Henle "thick" and "thin" refer to cell size.
- Thin limbs are squamous.
- Thick limbs are cuboidal.
- Two common properties of these cells facilitate absorption and secretion:
- tight junctions
- functional polarity
Tight Junctions
- Tight junctions are a point of contact between neighbouring cells.
- They consists of transmembrane proteins that form homotypic bonds with neighboring cells.
- Tight junctions are permeable to water, ions, and small molecules, forming a paracellular pathway.
- Structural components of tight junctions include occludins, claudins, and junctional adhesion molecules (JAM).
- They are closely associated with intracellular signalling and cytoskeletal proteins, controling permeability.
Functional Polarity
- Functional polarity in epithelial cells refers to their ability to express different transport proteins on apical and basolateral sides.
- This configuration enables vectorial transport of solutes.
Epithelial Transport Proteins
- Specialized proteins in epithelial cell membranes form pathways that enable water-soluble molecules to cross hydrophobic cell membranes.
- The 3 main types are:
- ATPase pumps
- Channels
- Carriers: co-transporters and exchangers
Na/K ATPase Pump
- The Na/K ATPase pump helps to drive the transport of tubular fluid and electrolytes.
- Its primary function is to maintain a low intracellular sodium concentration.
- This drives transepithelial solute transport.
Ion Channels
- Ion channels act as selective pores for certain ions.
- Their opening is gated and stimuli-responsive.
- Transport occurs passively along electrochemical gradients established by ATPase pumps.
Carriers
- Two types of carriers are present on renal tubules:
- Co-transporters (symporters)
- Exchangers (antiporters)
- Transport proteins arrange into specific pathways that facilitate the movement of solutes to and from filtrate across membranes.
- Water follows by osmosis.
Water Movement
- Water crosses cell membranes through tight junctions and paracellular space or via water channels called aquaporins.
- Aquaporins are expressed along tubules and is bidirectional
- Aquaporins transport solute-free water across membranes along prevailing gradients from active solute transport.
- Different Aquaporins occur in different regions regulated by antidiuretic hormone (ADH):
- Aquaporin-1 is abundant in proximal tubule and descending thin limb, mediating H₂O reabsorption.
- Aquaporins 3 and 4 occur in DCT and collecting ducts, and water reabsorption.
Summary
- The kidneys form urine by processing glomerular filtrate.
- Tubular absorption and secretion are controlled by epithelial cells.
- Water transport is passive and follows osmotic gradients.
- Osmotic gradients use transepithelial solute transport.
- Solute transport occurs using specific transport proteins on apical and basolateral cell surfaces, and include:
- ATPase pumps
- Ion Channels
- Carriers: cotransporters (symporters), and exchangers (antiporters)
Volume and Osmolarity
- In corpuscle filtration volume is 180L and osmolarity is 300 mOsm/L with a pH of 7.4.
- Tubule reabsorption and secretion yields a volume of 1.5L and osmolarity of 500-850 mOsm/L with a pH of 6.5
Proximal Convoluted Tubule (PCT) Function
- Early in the PCT many filtered solutes are reabsorbed as well as NaCl, ions, glucose, amino acids, phosphate, lactate, citrate, and urea.
- Uptake uses Na+/Nutrient Cotransporters (CT) with types for glucose, Pi, amino acids, and lactate.
- By the time filtrate exits the PCT, 100% of both glucose and amino acids are reabsorbed.
- Also reabsorbed are 70% sodium, 70% potassium, 90% bicarbonate, 85% phosphate, 50% urea, lactate, and citrate.
- The PCT also reabsorbed 70% passively of filtered water (about 130 L).
PCT - NaCl Reabsorption Mechanics
- The PCT is important in net sodium reabsorption
- The glomerular filtration rate is 26,000 mM Na daily, only 150 mM is excreted.
- Around 95.5% of filtered Na is reabsorbed, about 70% of this occurs in the PCT
- The basolateral Na+/K+ ATPase pump drives sodium reabsorption.
- Sodium absorption also works to maintains an electrochemical gradient across membrane
- Sodium enters the early PCT enters via apical Na+/solute co-transporters and Na+/H+ exchangers (NHEs).
- The early PCT is relatively Cl- impermeable.
- Cl - concentrations increase in the filtrate
- The late PCT's Cl- is reabsorbed passively through the paracellular pathway.
PCT - Glucose Reabsorption
- Glucose is reabsorbed in the early portion of the PCT.
- The amount reabsorbed is proportionate to filtered amount but this is limited by transporter maximum rate (TmG = 2 mmol/min).
- Glucose undergoes secondary active transport using gradient derived from basal Na/K ATPase activity for reabsorption.
- Uptake occurs through Na+/Nutrient cotransporter which primarily sodium/glucose co-transporter, SGLT-2 and SGLT-1.
- Basolateral Na/K ATPase pumps Na+ out in exchange for K+ which crosses the apical membrane through SGLT2.
- The transport drags in cotransport of Na+ along a Glucose carrier (GLUT 2).
- Sodium exits into interstitium through the original pump together with glucose.
- Since the same action moves glucose in same direction its a symporter - and this is the traget Gliflozins.
Glycosuria
- Almost all the glucose in the PCT is reabsorbed.
- Tmg is only 3 times higher than the normal filtered lead, increases in filtered load may lead to glucose being excrted = glycosuria.
- Glycosuria is detectable by a simple dipstick test
- Elevated plamsa glucose causes a high glucose called hyperglycaemia which is indicative of Diabetes mellitus (Type 1 or 2). Both Type 1 or 2 are characterized by persistently high blood glucose levels - and causes diuersis.
- Normal plamsa glucose can be present in hypoglycaemia die to redcued tubular reapsorptive acpaity, or renal blood flow.
PCT Protein
- Protein reabsorption is dpeendent on molecular size, smaller size makes it easier to get filtered.
- Lower sized proteins are eaier to be reabsorbed.
- Elevated plasma levels fo a protein lead to inrased filtation.
Protein repasobtion by PCT
- Filtered proteins bind to recports.
- bound proteins undergo endocytosis and fuse to form lysosomes.
- lysosome proteases degrade proteins with resultant exit of amino acids.
Proteinuria
- An increased amount of protien in the uring and is diagnosed as foam and/or by a dipstick test .
- Can be from damage or a high protien load or dysfunction.
Amino Acids
- Amino acids (AA) can derive from 3 sources
- glomerular filtration
- enzymatic degradation eg hormoens
- diffusion
- 80% of AAs are reabsorbed in the first PCT
- the are absorbed by N+ in the first third.
Loop of Henle's Role
- The three functions are Thin Descending Limb, and Thin Ascending Limb, and Thick Ascending Limb
- The function is maintaneac highly concentrated in the medulla while driving water absoprtion from the tuble
- Osmolart is affected with most found iin the coretx
Salt Reapsorption
Loop Of Hinle
Loop Diuretics
- Act by inhibiting NKCC2 in the thick ascending limb of the loop of Henle
- Inhibit salt reabsorption more potently than most other diuretics
- can be increased several times over - referred to as “high ceiling diuretics”.
Distal Convoluted tubule
- Approximately 80% of the filtered water has been recovered by end of the loop, with 36L entering the DCT and with with another 10-15% being recovered here
- This segment 5 mm long and has two types:
- Early - no water
- Late - water, aduretric formol
Late Distal Convoluted tubule + Collecting Duct
- 2 epethilal with primciapll cell with transports
- K secretion increases significantly in the late
- DCT/CD in parallel with ENaC expression
Distal CONVULATED TUBULE + CLOOECTING DUCTS
- *80% of the bdyt's k is traceullular, lofe threatening!
- high potassium
- low potssioum!
- potassium secretion
Distal Convoluted Collecting:
Combines to fine tune depending on water
Summary
- Most of the golemrular filtrati is Reabsorbed in the pct!
- 20% of h20 and 25% of ions
Summary
- The kidneys form urine by processing glomerular filtrate.
- Tubular absorption and secretion are controlled by epithelial cells.
- Water transport is passive and follows osmotic gradients.
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- Osmotic gradients uses transepithelial solute transport. .
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Description
Explore the renal handling of salt and water in urine formation. Understand glomerular filtrate composition and the functions of renal tubules. Learn about fluid and electrolyte transport, reabsorption, and secretion mechanisms.
