sys phys exam 3

kidneys and blood

kidneys cleanse blood and adjust its composition, so it has a rich blood supply

nephrons

structural and functional units that form urine; two main parts are renal corpuscle and renal tubule

parts of the renal tubule

proximal convoluted tubules, nephron loop (aka Loop of Henle), distal convoluted tubule

empties into collecting duct

parts of the renal corpuscle

glomerulus and Glomerular (Bowman’s) capsule; regulate rate of filtration formation and blood pressure

glomerulus

part of renal corpuscle that allows efficient filtrate (plasma-derived) formation

Glomerular (Bowman’s) capsule

part of renal corpuscle that contains podocytes and filtration slits in between that allows filtration to pass into capsular space

kidney physiology

180 L of fluid are processed daily, but only 1.5 L becomes urine. they filter the body’s entire plasma volume 60x a day. urine is produced from filtrate and contains <1% original filtrate.

3 processes involved in urine formation and blood composition adjustment

1. Glomerular filtration: cell- and protein-

free filtrate

2. Tubular reabsorption: returns 99% of

substances from filtrate to blood

3. Tubular secretion: moves substances

from blood to filtrate

filtration membrane

porous membrane between blood and interior of glomerular capsule. allows water and solutes smaller than plasma proteins to pass through. no cells can pass.

3 layers of filtration membrane

1. fenestrated endothelium of glomerular capillaries

2. basement membrane

3. foot processes (the extensions) of podocytes with filtration slits in b/w that repel macromolecules, allow molecules smaller than 3 nm (water, glucose, amino acids, nitrogenous wastes)

why do plasma proteins not filter out (remain in blood)

they maintain colloid osmotic pressure, preventing loss of all water to capsular space

** proteins in filtrate= membrane issue

outward vs inward pressures

outward= forces that promote filtrate formation

inward= forces inhibiting filtrate formation

HP_gc (glomerular blood pressure)

an outward pressure. chief force pushing out water and solutes from the blood. pressure is relatively higher here due to small diameter of vessel. (55 mmHg)

HP_cs (capsular space pressure)

inward pressure. filtrate pressure in capsule abt 15 mmHg

OP_gc (colloid osmotic pressure in capillaries)

inward pressure.“pull” of proteins in blood; 30 mmHg

net filtration pressure (NFP)

sum of forces; responsible for filtrate formation. the main controllable factor controlling glomerular filtration rate (GFR)

glomerular filtration rate (GFR)

volume of filtrate formed per minute by both kidneys (normal is 120-125 mL/min)

directly proportional to net filtration pressure, total SA available for filtration, filtration membrane permeability

filtration pressure=

Glomerular hydrostatic pressure - (capsular hydrostatic pressure + glomerular capillary osmotic pressure)

intrinsic controls (renal autoregulation)

maintain GFR in kidneys

GFR and blood pressure correlation

Increased GFR causes increased urine output, which lowers blood pressure, and vice versa

tubular reabsorption

quickly reclaims most tubular