Vanders Renal Ch6 Flashcards
What are the approximate percentages of sodium reabsorbed in the major tubular segments?
65% in the proximal tubule, 25% in the thin and thick ascending limbs of Henle’s loop, 10% in the distal convoluted tubule and collecting-duct system
What are the approximate percentages of water reabsorbed in the major tubular segments?
Approximately 65% in the proximal tubule, varies in the loop of Henle, distal tubule, and collecting-duct system
Describe proximal tubule sodium reabsorption.
Involves apical membrane sodium entry mechanisms and basolateral Na-K-ATPase
Why is chloride reabsorption coupled with sodium reabsorption?
To maintain electroneutrality; the movement of sodium, a cation, must be accompanied by an equivalent movement of an anion
What are the maximum and minimum values of urine osmolality?
Maximum: 1400 mOsm/kg, Minimum: varies depending on hydration status
Define osmotic diuresis.
Increased urine output due to the presence of osmotically active substances in the renal tubules
Define water diuresis.
Increased urine output due to high water intake or low solute concentration
What is meant by obligatory water loss?
The minimum volume of water that must be excreted to eliminate waste products
Describe the handling of sodium by the descending and ascending limbs.
Sodium is not reabsorbed in the descending limb; reabsorbed in the ascending limb
What role do sodium-potassium-2 chloride symporters play?
They are involved in sodium transport in the thick ascending limb
How is water handled by the descending and ascending limbs?
Water is reabsorbed in the descending limb; not reabsorbed in the ascending limb
What does ‘separating salt from water’ refer to?
The ability to excrete either concentrated or dilute urine by independently controlling the reabsorption of solutes and water
How does antidiuretic hormone affect water and urea reabsorption?
Increases water reabsorption and promotes urea reabsorption in the collecting duct
What are the characteristics of the medullary osmotic gradient?
It allows for the concentration of urine and is generated by the thick ascending limb and urea recycling
What happens to the medullary osmotic gradient during water diuresis?
It is partially ‘washed out’ due to increased urine output and reduced solute concentration
What percentage of filtered sodium and chloride is reabsorbed in the proximal tubule?
About 65% of filtered sodium and more than 60% of filtered chloride
What is the main route of sodium excretion from the body?
Via the kidneys
What is the primary active transport mechanism for sodium reabsorption?
Na-K-ATPase pumps in the basolateral membrane
What is the primary source of body water?
Metabolically produced water and ingested water
What is insensible loss?
Continuous water loss through evaporation from the skin and respiratory passages
How does the kidney respond to a large water load?
Produces a large volume of very dilute urine
What is the role of aquaporins in water reabsorption?
Facilitate water movement across tubular cell membranes
What is the maximum urinary concentration the human kidney can produce?
1400 mOsm/kg
What is the significance of obligatory water loss?
It is necessary to excrete organic waste and varies with physiological states
What is the approximate minimum volume of water required to dissolve 600 mOsm of solute?
0.43 L/day
This is calculated as 600 mmol/1400 mOsm/L.
What is the term for the volume of urine that must be excreted to eliminate waste, regardless of hydration status?
Obligatory water loss
This volume can change with different physiological states.
How can increased tissue catabolism affect obligatory water loss?
It increases obligatory water loss
This occurs during conditions like fasting or trauma.
What unique adaptation allows the kangaroo rat to survive without drinking water?
It relies on the water content of its food and metabolic water
This allows it to meet its hydration needs without external water sources.
What is the primary mechanism for sodium reabsorption in the early proximal tubule?
Antiport with protons
This involves the exchange of sodium for hydrogen ions.
What happens to the protons that are secreted into the tubular lumen?
They combine with filtered bicarbonate to form carbon dioxide and water
This process involves bicarbonate reabsorption.
What major anion is reabsorbed along with sodium in the early proximal tubule?
Bicarbonate
The concentration of bicarbonate decreases markedly in the tubular fluid.
How is chloride reabsorbed in the proximal tubule?
Paracellularly and via channels
A significant amount of chloride reabsorption occurs paracellularly.
What is the primary transporter in the thick ascending limb of the loop of Henle?
Na-K-2Cl symporter (NKCC)
This transporter is targeted by loop diuretics.
What phenomenon allows for the independent control of water and salt excretion in the nephron?
Separation of salt and water reabsorption in the thick ascending limb
This is due to the low water permeability in this segment.
What is the osmolarity of the fluid leaving the loop of Henle?
Hypo-osmotic relative to plasma
This is a result of more sodium chloride being reabsorbed than water.
What term describes the cells in the distal tubule that are regulated by aldosterone?
Aldosterone-sensitive distal nephron
These include the distal convoluted tubule, connecting tubule, and cortical collecting duct.
What is the primary mechanism for sodium reabsorption in the early distal convoluted tubule?
Na-Cl symporter
This transporter is sensitive to thiazide diuretics.
What is one effect of the Na-K-2Cl symporter in the thick ascending limb?
It moves twice as much chloride as sodium into the cell
This creates a need for another pathway for sodium to maintain electroneutrality.
Which diuretics target the Na-Cl symporter in the distal convoluted tubule?
Thiazide diuretics
Examples include hydrochlorothiazide and chlorthalidone.
What is the primary pathway for chloride reabsorption in the distal convoluted tubule?
Transcellular via channels and K-Cl symporters
Sodium exits the cell through the Na-K-ATPase.
True or False: The descending limb of Henle’s loop reabsorbs sodium chloride.
False
The descending limb primarily reabsorbs water.
Fill in the blank: The primary cells in the cortical collecting duct are called _______.
Principal cells
These cells are responsible for sodium reabsorption via ENaCs.
What is the main function of the Na-K-ATPase in principal cells?
It drives sodium reabsorption while chloride leaves via channels and a K-Cl symporter.
What are the major transport pathways for sodium, chloride, and water in principal cells of the cortical collecting duct?
Sodium reabsorption via apical sodium channels (ENaC), chloride reabsorption mainly transcellular via intercalated cells, and water reabsorption via aquaporins controlled by antidiuretic hormone (ADH).
What characterizes the tubular epithelium in the connecting tubule and collecting duct system?
It is characterized by principal cells (approximately 70% of cells) and at least three types of intercalated cells.
What happens to water reabsorption in the connecting tubule?
It reabsorbs water in highly variable amounts depending on body conditions.
How does ADH influence water reabsorption in the collecting duct?
ADH increases the water permeability of principal cells by facilitating the presence of aquaporin 2 in the luminal membrane.
Fill in the blank: The activity of aquaporins in the collecting duct is controlled by _______.
[antidiuretic hormone (ADH)]
What is the osmolality of tubular fluid as it enters the collecting-duct system?
Typically a little above 100 mOsm/kg.
During antidiuresis, what happens to the final fluid in the collecting duct?
It becomes very hyperosmotic (1200 mOsm) due to the reabsorption of most remaining water.
What occurs during diuresis in the collecting duct?
No water reabsorption occurs in the cortical collecting tubule, resulting in very dilute final urine (70 mOsm).
True or False: The inner medullary collecting duct has no water permeability in the absence of ADH.
False. It has some water permeability even without ADH.
What is the role of vasopressin type 2 receptors in renal function?
They mediate the effects of ADH in the collecting ducts, particularly in water reabsorption.
What are the main components that develop the medullary osmotic gradient?
- Active NaCl transport by the thick ascending limb
- Very low water permeability of thick ascending limb cells
- Parallel arrangement of blood vessels and tubular segments
- Recycling of urea between collecting ducts and loops of Henle.
What happens if transport in the thick ascending limb is inhibited?
The osmotic gradient is not developed, leading to iso-osmotic urine.
How does the medullary osmotic gradient contribute to urine concentration?
It allows the tubules to pass through a region of hyperosmotic interstitium, drawing water out of the tubular fluid.
What is the peak osmolality of the medullary interstitium during water deprivation?
Greater than 1000 mOsm/kg.
What is the primary solute composition of the medullary osmotic gradient?
- NaCl in the outer medulla
- Urea in the inner medulla.
Fill in the blank: The process of moving sodium from ascending to descending vessels is called _______.
[countercurrent exchange]
What is the significance of the arrangement of vasa recta in the medulla?
It allows for countercurrent exchange, maintaining the medullary osmotic gradient.
What happens to sodium transported out of the thick ascending limb in the outer medulla?
It accumulates due to lower blood flow, contributing to the osmotic gradient.
What is the peak concentration of sodium in the medulla?
300 mEq/L
This concentration is more than double its value in the general circulation.
How does sodium contribute to medullary osmolality?
About 600 mOsm/kg
Sodium is accompanied by chloride, which contributes to the overall osmolality.
What are the key processes that generate the medullary osmotic gradient?
- Active transport of sodium from the loop of Henle into the interstitium
- Countercurrent movement of water from descending to ascending vasa recta
- Recycling of urea from the inner medullary collecting ducts to the loop of Henle
What principle must be kept in mind regarding water in the medullary interstitium?
The amount of water in the medullary interstitium must remain nearly constant.
What role do endothelial cells of descending vasa recta play?
Contain aquaporins that facilitate water movement.
What is the effect of high oncotic pressure in blood entering the medulla?
Water is drawn from the outer medullary interstitium into the descending vasa recta.
What occurs in descending vessels versus ascending vessels in terms of solute and water exchange?
In descending vessels, water leaves and solute enters; in ascending vessels, water enters and solute leaves.
How does blood flow in the vasa recta affect medullary osmolality?
High blood flow can dilute the hyperosmotic interstitium.
What is the significance of urea in the medullary osmotic gradient?
Urea contributes significantly to the osmolality, accounting for 500-600 mOsm/kg.
What happens to urea in the proximal tubule?
About half is reabsorbed.
How does ADH influence urea permeability in the inner medullary collecting ducts?
ADH raises urea permeability by stimulating specific urea uniporters.
What is the effect of dehydration on glomerular filtration rate (GFR) and ADH levels?
GFR is low and levels of ADH are high.
What occurs during overhydration in terms of ADH levels and medullary solute?
ADH levels are low, leading to a washing out of medullary solute.
What is the relationship between sodium and chloride reabsorption?
Chloride reabsorption parallels sodium reabsorption mainly because most chloride transport is via a symporter with sodium.
What is the obligatory water loss in the kidney?
Occurs because there is always at least some excretion of waste solutes.
Which region of the tubule secretes water?
No region secretes water.
What happens if the thick ascending limb stops reabsorbing sodium?
The final urine would be dilute.
What is unlikely to happen if a healthy young person drinks a large amount of water?
An increase in water permeability in the medullary collecting ducts.
If the thick ascending limb stopped reabsorbing sodium, then the final urine would be:
dilute or concentrated, depending on ADH
If a healthy young person drinks a large amount of water, which of the following is unlikely to happen?
A decrease in osmolality of the cortical interstitium
After drinking a large amount of water, most of the water filtered by the glomerulus is:
excreted
The sodium in the body fluids includes sodium that is:
not osmotically active in bone and connective tissue
The obligatory solute excretion explains why a thirsty sailor cannot drink sea water, because:
the volume of urine would have to be much greater than 1 L
The medullary osmotic gradient is described without terms like ‘countercurrent multiplier’ for:
simplicity and clarity
Fill in the blank: Sodium in the mineral component of bone is not _____ active.
osmotically
True or False: Drinking sea water will lead to a net gain of salt for a thirsty sailor.
True
When a healthy young person drinks a large amount of water, one possible outcome is an increase in:
water permeability in the medullary collecting ducts
Fill in the blank: The events in local microenvironments in the renal medulla may be supplanted by more recent _____ findings.
anatomic
