Blood Filtration by the Nephron

Question 1

Steps of Blood Filtration

Answer 1

1. Glomerular Filtration
2. Tubular Reabsorption
3. Loop of Henle Countercurrent Mechanism
4. DCT + Tubular Secretion
5. Collecting Duct + Urine Formation

Question 2

STEP 1: Glomerular Filtration

Answer 2

1. blood enters the nephron via the afferent arteriole + reaches the glomerulus (filtrate is collected in the renal tubules)
2. high blood pressure in the glomerulus forces almost all solutes through the glomerular capillary walls into the Bowman’s capsule
3. endothelial cells of the glomerular capillaries have leaky connections, allowing passive diffusion of solutes
4. filtration is nonspecific and requires NO ENERGY

Question 3

STEP 2: Tubular Reabsorption

Answer 3

• the proximal convoluted tubule reabsorbs most ions, nutrients, water
• nutrients and electrolytes are reabsorbed actively using ATP while water follow passive osmosis
• sodium reabsorption occurs via active transport, creating an osmotic gradient that pulls water into the peritubular capillaries

Question 4

STEP 3: Loop of Henle Countercurrent Mechanism

Answer 4

• the descending limb is permeable to water and impermeable to solutes, allowing water to leave due to high salt concentration in the renal medulla
• the ascending limb is impermeable to water and actively transports nutrients out, maintaining the osmotic gradient

Question 5

Countercurrent Mechanism

Answer 5

helps concentrate urine, while the vasa vesta acts as the countercurrent exchanger to maintain the medullary CG

Question 6

STEP FOUR: DCT + Tubular Secretion

Answer 6

• most nutrients and water have been reabsorbed at this point
• the DCT allows regulated absorption of nutrients influenced by hormones
• tubular secretion removes metabolic wastes and unwanted solutes in the DCT and early collecting duct
• reabsorption in the DCT includes passive and active transport

Question 7

STEP FIVE: Collecting Duct + Urine Secretion

Answer 7

• collecting duct collects remaining filtrate and delivers it to the renal pelvis
• water reabsorption continues, regulated by ADH (PASSIVE)
• final urine composition depends on body hydration and electrolyte balance
• waste is excreted

Question 8

Simplified Pathway

Answer 8

1. Glomerulus
2. Proximal Convolutes Tubule
3. Descending loop of Henle
4. Ascending loop of Henle
5. Distal Tubule
6. Collecting Duct