Kidney Function: Ultrafiltration and Reabsorption

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Questions and Answers

What percentage of filtrate is typically reabsorbed in the proximal convoluted tubule?

90%

95%

70%

85% (correct)

What characterizes the ascending limb of the loop of Henlé?

Wide and impermeable to water (correct)

Narrow and permeable to water

Thick walls and highly permeable to sodium

Thin walls and impermeable to ions

The counter-current multiplier refers to which process in the loop of Henlé?

Water potential gradient established by opposing flows (correct)

Filtration of liquid in opposite directions

Enhanced absorption through parallel flow of liquids

Exchange of oxygen and carbon dioxide

What is primarily responsible for the increased hydrostatic pressure within the glomerulus?

The presence of the efferent arteriole Signup and view all the answers

Which structure is specifically adapted to increase reabsorption surface area in the proximal convoluted tubule?

Microvilli Signup and view all the answers

Which of the following is NOT a component that resists the movement of filtrate out of the glomerulus?

Peritubular capillaries Signup and view all the answers

What type of cells line the walls of the glomerular capillaries?

Endothelial cells Signup and view all the answers

What is the main function of the distal convoluted tubule?

Final adjustments to water and salts reabsorption Signup and view all the answers

What role do mitochondria play in cells of the proximal convoluted tubule?

Produce ATP for active transport Signup and view all the answers

What substance is NOT typically filtered out during ultrafiltration in the nephron?

Proteins Signup and view all the answers

What is the primary function of the renal (Bowman's) capsule in the nephron?

To collect glomerular filtrate Signup and view all the answers

How much water is estimated to leave the body as urine from the daily intake?

1 dm³ Signup and view all the answers

In the loop of Henlé, what is the significance of the hairpin shape?

Enhances the counter-current exchange mechanism Signup and view all the answers

How do the kidneys maintain the body's calcium level?

By regulating mineral ions in urine Signup and view all the answers

Which statement is correct about the glomerulus in mammals?

It is unique in having both afferent and efferent arterioles. Signup and view all the answers

Which process describes the selective reabsorption in the nephron?

The movement of substances from filtrate back into the blood Signup and view all the answers

What is the primary role of podocytes in the kidney?

To facilitate ultrafiltration in the glomerulus Signup and view all the answers

Which structure increases the surface area for reabsorption in the proximal convoluted tubule?

Microvilli Signup and view all the answers

What is the function of the descending limb of the loop of Henlé?

To passively reabsorb water Signup and view all the answers

Where does most reabsorption occur within the nephron?

Proximal convoluted tubule Signup and view all the answers

During ultrafiltration, what path does the filtrate take from the glomerulus?

Through the endothelial cells and into the renal capsule Signup and view all the answers

What substance is primarily active in endocytosis within tubule cells?

Pinocytic vesicles Signup and view all the answers

How does the concentration of sodium ions change as filtrate moves along the nephron?

It decreases in the proximal convoluted tubule and increases in the collecting duct Signup and view all the answers

What feature differentiates the ascending limb from the descending limb of the loop of Henlé?

Active transport of sodium ions Signup and view all the answers

Study Notes

Kidney Function - Ultrafiltration and Selective Reabsorption

Kidneys regulate blood composition, maintaining a constant water potential, removing wastes (e.g., urea), regulating minerals, and blood pressure. Red blood cell production is also regulated.
Blood enters the kidney through the renal artery, branching into millions of arterioles. Each arteriole leads to a renal (Bowman's) capsule, forming a glomerulus (capillary network).
The glomerulus's afferent arteriole (incoming) is wider than the efferent arteriole (outgoing), creating hydrostatic pressure. This forces water, glucose, mineral ions, and other small molecules (up to 68000 relative molecular mass) into the renal capsule. This filtration under pressure is ultrafiltration.
Filtrate is prevented from fully leaving by capillary endothelium, basement membrane, epithelial cells of renal capsule, intracapsular pressure, and glomerulus' low water potential.
Specialized podocytes in the renal capsule have "feet" (podocyte) allowing fluid to pass between, not through them. The glomerular capillaries have large spaces (100 nm) between their cells.
Filtrate is similar to blood plasma except for plasma proteins.

The Glomerulus - a Unique Capillary Bed

The glomerulus is unique. This is an arteriole supplying blood, and another draining it (efferent arteriole), unlike other capillary beds.
This structure is important for creating the hydrostatic pressure necessary for ultrafiltration to occur.
The efferent arteriole further divides into peritubular capillaries, draining into a venule, away from the glomerulus.
The efferent arteriole merging into further capillaries increases hydrostatic pressure within the glomerulus.

Selective Reabsorption

Nearly 85% of filtrate is reabsorbed into the blood in the proximal convoluted tubule, because molecules smaller or below 68000 relative molecular mass are filtered out and many are essential to the body's functions.
About 180 dm³ of water enter the nephrons daily, with only 1 dm³ exiting as urine.
Reabsorption of water in the proximal convoluted tubule is 85%.

The Loop of Henle

The loop of Henle, a hairpin-shaped structure in the medulla, is crucial for concentrating urine. It creates conditions (i.e high ion concentration, low water potential) for water reabsorption in the distal convoluted tubule.
The descending limb is thin-walled, highly permeable to water.
The ascending limb is thick-walled, impermeable to water.
Sodium ions are actively pumped out of the ascending limb into the interstitial region. This creates a concentration gradient.
Water passively moves out of the descending limb, lowering filtrate water potential.
The loop acts as a counter-current multiplier, establishing a gradient in the interstitial fluid of the kidney, necessary for the further reabsorption of water in the collecting duct.

Distal Convoluted Tubule

The distal convoluted tubule, controls water and salt balance, and adjusts pH by selectively reabsorbing ions.
This reabsorption is hormone-regulated.
Microvilli and mitochondria allow rapid reabsorption in the distal tubule.

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Description

This quiz explores the critical processes of ultrafiltration and selective reabsorption in kidney function. Learn how kidneys regulate blood composition and maintain water potential while removing waste products. Discover the role of the glomerulus, afferent and efferent arterioles, and specialized structures involved in kidney filtration.