Urine 2L

Flashcards covering the renal corpuscle location and structure, urine formation processes, filtration pressures and NFP, filtration membrane components, mesangial cells, and water/sodium reabsorption (obligatory vs. facultative).

Where is the renal corpuscle located?

In the renal cortex.

What two structures make up the renal corpuscle?

The glomerulus and the glomerular (Bowman’s) capsule.

What is the function of the glomerulus?

It filters blood; blood enters via the afferent arteriole and exits via the efferent arteriole.

What are the layers of the glomerular capsule?

Visceral layer: touches glomerulus; permeable. Parietal layer: outer; impermeable. Capsular space: collects filtrate.

What are the three main processes in urine formation?

Filtration, Reabsorption, and Secretion.

Where does glomerular filtration occur and what is filtered?

In the glomerulus; water and small solutes are filtered into the capsular space.

What is reabsorption in the nephron?

Movement of water, ions, and nutrients from the tubule back into the blood.

What is secretion in the nephron?

Movement of substances (like waste, excess ions) from blood into the tubule.

How are reabsorption and secretion opposite?

Reabsorption moves substances from tubule to blood; Secretion moves substances from blood to tubule.

What is hydrostatic pressure in the glomerulus?

Blood pressure that pushes fluid out of capillaries into the capsular space (~55 mmHg).

What is colloid osmotic pressure?

Pressure from proteins (e.g., albumin) pulling water back into the blood (~30 mmHg); opposes filtration.

What is capsular hydrostatic pressure?

Pressure from filtrate in the capsule pushing back against filtration (~15 mmHg).

How is net filtration pressure (NFP) calculated?

NFP = Glomerular Hydrostatic Pressure – Colloid Osmotic Pressure – Capsular Hydrostatic Pressure.

What does a positive NFP mean?

Filtration occurs; filtrate is formed.

How does NFP affect GFR?

↑NFP → ↑GFR; ↓NFP → ↓GFR.

Why is GFR important?

It controls how fast filtrate moves and how much is reabsorbed vs lost in urine.

What are the three layers of the filtration membrane (from inside → out)?

1. Endothelium of glomerulus;

2. Basement membrane;

3. Visceral layer of the glomerular capsule (podocytes).

What is the function of the glomerular endothelium?

Has pores that allow small solutes through but block blood cells.

What does the basement membrane block?

Large proteins like albumin.

What are podocytes and pedicels?

Podocytes = filtration cells; pedicels = their “feet” that form filtration slits.

What are mesangial cells and where are they found?

Modified smooth muscle cells in the glomerulus between capillaries.

What are the functions of mesangial cells?

Structural support (mesangial matrix); release growth factors; immune/inflammation control; phagocytosis (clean debris).

What is obligatory water reabsorption?

Water follows Na+ passively via osmosis; occurs in the PCT; not hormone-regulated.

Where does obligatory water reabsorption happen?

Mainly in the proximal convoluted tubule (PCT).

What is facultative water reabsorption?

Adjustable water reabsorption depending on hydration status; hormone-regulated (by ADH).

Where does facultative water reabsorption occur?

Collecting tubules and collecting ducts.

How does ADH affect water reabsorption?

ADH increases aquaporins in collecting ducts to allow more water reabsorption.

How much sodium is reabsorbed in the PCT?

About 65%.

Why is sodium reabsorption important in the PCT?

1. Helps retain Na so less is lost in urine;

2. Drives reabsorption of water, glucose, and nutrients;

3. Supports fluid balance and blood pressure;

4. Uses Na+ pumps to keep sodium moving correctly.