Lecture 25

Question 2

What is glomerular filtration rate (GFR)?

Answer 2

Volume of filtrate formed per minute; ~125 mL/min in men, ~105 mL/min in women.

Question 3

Daily filtrate volume?

Answer 3

~180 L/day (men) and ~150 L/day (women).

Question 4

How much filtrate becomes urine?

Answer 4

~1–2 L/day because >95% is reabsorbed.

Question 5

Pressures determining filtration?

Answer 5

Hydrostatic pressure vs colloid osmotic pressure.

Question 6

Hydrostatic pressure definition?

Answer 6

Fluid pressure pushing water toward lower pressure.

Question 7

Osmotic pressure definition?

Answer 7

Pulling force created by solutes attracting water.

Question 8

Why is osmotic pressure in Bowman’s capsule ~0?

Answer 8

Proteins cannot cross filtration membrane.

Question 9

Net filtration pressure (NFP)?

Answer 9

GBHP – CHP – BCOP ≈ 10 mmHg.

Question 10

Why small changes affect GFR?

Answer 10

Because NFP is small, slight pressure changes alter filtration.

Question 11

Myogenic autoregulation?

Answer 11

Afferent arteriole constricts when stretched to keep GFR constant.

Question 12

Autoregulation MAP threshold?

Answer 12

Works above ~60 mmHg; below this, renal failure risk increases.

Question 13

Sympathetic effect on kidneys?

Answer 13

Vasoconstriction → ↓GFR; renin release if BP too low.

Question 14

Renin response?

Answer 14

Renin → angiotensin II → vasoconstriction + aldosterone.

Question 15

Main nephron reabsorbing structures?

Answer 15

PCT, loop of Henle, DCT, collecting duct.

Question 16

Water reaching collecting duct?

Answer 16

~10% of filtrate water (~18 L).

Question 17

Where are most solutes reabsorbed?

Answer 17

Proximal convoluted tubule (PCT).

Question 18

ADH function?

Answer 18

Inserts aquaporins → increases water reabsorption.

Question 19

Aldosterone function?

Answer 19

Reabsorbs Na+; water follows → increases blood volume.

Question 20

ANP function?

Answer 20

Promotes Na+ and water excretion → lowers BP.

Question 21

Obligatory vs facultative water reabsorption?

Answer 21

Obligatory: PCT water follows Na+. Facultative: ADH‑regulated.

Question 22

Apical membrane?

Answer 22

Faces nephron lumen.

Question 23

Basal membrane?

Answer 23

Faces interstitial fluid/blood.

Question 24

Examples of Na+ symport substances?

Answer 24

Cl–, Ca2+, amino acids, glucose, phosphate.

Question 25

Na+/H+ antiporter role?

Answer 25

Regulates H+ excretion and bicarbonate recovery.

Question 26

How is bicarbonate recovered?

Answer 26

HCO3– + H+ → H2CO3 → CO2 + H2O; reassembled inside cell.

Question 27

Descending limb permeability?

Answer 27

Permeable to water; filtrate becomes hypertonic.

Question 28

Ascending limb permeability?

Answer 28

Impermeable to water; pumps Na+ out → filtrate becomes hypotonic.

Question 29

Countercurrent multiplier?

Answer 29

Opposing flows + ion pumping create medullary gradient.

Question 30

Why slow flow in vasa recta?

Answer 30

Preserves gradient; prevents solute washout.

Question 31

Urine movement in ureters?

Answer 31

Peristalsis, not gravity.

Question 32

Detrusor muscle?

Answer 32

Smooth muscle of bladder wall.

Question 33

Internal vs external urethral sphincter?

Answer 33

Internal: involuntary; External: voluntary.

Question 34

Urge to void?

Answer 34

Begins at ~150 mL bladder volume.

Question 35

Incontinence threshold?

Answer 35

~300–400 mL bladder volume.

Question 36

Micturition reflex?

Answer 36

Stretch → sacral spinal cord → detrusor contracts, internal sphincter relaxes.

Question 37

Why UTIs more common in females?

Answer 37

Short urethra allows bacterial entry more easily.