Question

MCAT Tutorial: Urinary System

Answer 1

\({\bf{Overview:}}\)
- primary function is excretion/waste removal & maintaining homeostasis
- kidneys are the principal organ of the urinary system
> attached to the bladder via tubes (ureters)
- bladder is connected to the urethra which excretes urine outside the body
- controlled by sphincters in urethra

\({\bf{Structure~of~the~Kidney:}}\)



- two regions: cortex on the outside, medulla on the inside
> medulla is further composed of renal pyramids. medulla functions in ultrafiltration & osmoregulation
> pyramids are made of nephrons, the basic filtering unit

Answer 2

\({\bf{Nephron:}}\)
> renal corpuscle: the filtering unit
- contains glomerulus (capillary network, high pressure)
- Bowman's capsule: intakes glomerular filtrate from blood and outputs into the renal tubule

> renal tubule: contains the convuluted tubules and the loop of Henle

Answer 3

The Renal Tubule



> proximal tubule: site of resorption for water and glomerular filtrate
- glucose, amino acids, ionis, water
- passive/facilitated diffusion via sodium conc. gradient
- pH regulated through hydrogen/bicarbonate buffer system

> loop of Henle: contains descending limb and ascending limb
- descending: permeable to water
- ascending: permeable to sodium. sodium actively pumpted out, making the interstitial fliuid to be more hypertonic
- movement of fluid powered by conc. gradient

> distal tubule: site of active transport for water
- controlled by aldosterone (which increases sodium reabsorption and potassium secretion)

Answer 4

\({\bf{Other~Functions~of~the~Urinary~System:}}\)

Urine Collection:

- the tubules empty out into a duct
- controlled by ADH (antidiuretic hormone) which makes the duct more permeable to water, increasing conc. of urine.
- urine travels from kidney to ureter to bladder. has internal and eternal sphincter to control movement out of the body.

Blood Pressure Regulation:

- kidneys contain juxtaglomerular apparatus which detects changes in BP
- produces renin under low pressure conditions --> angiotensin I --> converted to angiotensin II --> increases blood pressure and aldosterone release

Answer 5

Anyway, that's the end of my tutorial, I hope it was a helpful resource. Source material is the 2nd Edition Barron's Prep book for the new MCAT