Urinary System: Urine

Question 1

Kidneys maintain the body’s

Answer 1

Fluid osmotic concentration (amount of solute in body fluids)

Question 2

Dehydration (elevated blood osmolarity) results in

Answer 2

A small volume of concentrated urine
◦ conserves water to lower blood osmolarity

Question 3

Overhydration (lower blood osmolarity) results in

Answer 3

A large volume of dilute urine
◦ gets rid of water to bring blood osmolarity up

Question 4

In the juxtamedullary nephrons & associated vasa recta counter current is created by

Answer 4

◦ fluid flowing in opposite directions in two adjacent segments of same tube with hairpin turn
◦ establishes & maintains a medullary osmotic gradient from cortex to depths of medulla – allows kidneys to vary urine concentration

Question 5

The juxtamedullary nephron loop is a

Answer 5

Countercurrent multiplier

Question 6

The vasa recta is a

Answer 6

Countercurrent exchanger

Question 7

Regarding the countercurrent mechanism: the descending limb is permeable to

Answer 7

H2O (NaCl cannot leave)

Question 8

Regarding the countercurrent mechanism: the ascending limb is permeable to

Answer 8

NaCl (H2O cannot leave)

Question 9

NaCl reabsorption in the ascending limb creates a positive feedback loop through establishing

Answer 9

An osmotic gradient in the surrounding interstitial fluid to favour H2O reabsorption from adjacent descending
◦ As filtrate moves through loop, H2O leaves in descending = concentrated filtrate = increased osmolarity
◦ Concentrated filtrate moves into ascending removes NaCl = decreased osmolarity

Question 10

Compared to the ascending and descending limbs, blood within the vasa recta
remains

Answer 10

Isosmotic to surrounding fluid

Question 11

The vasa recta maintains the countercurrent multiplier’s osmotic gradient due to

Answer 11

H2O & solutes being able to move freely in & out of it

Question 12

To concentrate urine:

Answer 12

◦ Juxtamedullary nephron loop creates the medullary osmotic gradient
◦ Vasa recta maintains the medullary osmotic gradient

Question 13

Hormone that increases the number of aquaporins in collecting tubule (duct) cells

Answer 13

Antidiuretic hormone (ADH)
◦ more aquaporins = more water reabsorption into bloodstream
◦ results in more concentrated urine

Question 14

To conserve water during dehydration urine concentration is controlled by

Answer 14

The medullary osmotic gradient
◦ allows for regulation of urine osmolarity to exceed 300 mOsm
◦ w/o you could only produce urine that is the same concentration as your body fluids

Question 15

Dehydration results in

Answer 15

↑ ADH (adds aquaporins) → ↑ H2O reabsorption → small volume of concentrated urine

Question 16

Overhydration results in

Answer 16

↓ ADH (removes aquaporins) → ↓H2O reabsorption → large volume of dilute urine

Question 17

Diuretics increase urine output by

Answer 17

◦ Inhibiting ADH release to ↓ H2O reabsorption (ex: alcohol)
◦ Inhibiting Na+ & obligatory water reabsorption in PCT (ex: caffeine, hypertension drugs)

Question 18

An osmotic diuretic is

Answer 18

A substance that is not reabsorbed & carries H2O with it (↓ H2O reabsorption)
◦ Diabetes mellitus – unusually high glucose concentration pulls H2O from the body

Question 19

Urine is composed of

Answer 19

◦ 95% H2O
◦ 5% solutes (nitrogenous wastes urea, uric acid
& creatinine)

Question 20

pH of urine is

Answer 20

6 (slightly acidic); varies from about 4.5–8.0 based on metabolism or diet

Question 21

Pigment from hemoglobin breakdown that gives urine yellow colour

Answer 21

Urobilin (urochrome)

Question 22

Ammonia scent of urine results from

Answer 22

Bacterial metabolism of urea

Question 23

Tubes that actively convey urine from the kidneys to the bladder are

Answer 23

Ureters
◦ inner mucosa is continuous with the kidney pelvis & the bladder
◦ urine propelled via peristalsis from double-layered muscularis

Question 24

Urinary bladder is

Answer 24

A muscular sac that expands to store urine until voiding
◦ Capacity of ~ 500-800 ml
◦ expansion permitted by layer of detrusor muscle & highly folded inner mucosa of transitional epithelium (rugae)

Question 25

Urethra is

Answer 25

A muscular tube that drains urine from the body
◦ 3–4 cm long in females
◦ ~ 20 cm in males

Question 26

Involuntary urethral sphincter
◦ detrusor smooth muscle

Answer 26

Internal urethral sphincter

Question 27

Voluntary urethral sphincter
◦ skeletal muscle

Answer 27

External urethral sphincter

Question 28

Micturition (urination) requires simultaneous:

Answer 28

◦ Contraction of detrusor muscle
◦ Relaxation of internal & external urethral sphincters

Question 29

Afferent impulses from bladder’s stretch receptors relayed to pons & cerebral cortex provide

Answer 29

Conscious awareness of bladder fullness
◦ induces conscious urination via relaxing external urethral
sphincter

Question 30

Micturition (urination) is stimulated by

Answer 30

Parasympathetic pathways

Question 31

Micturition (urination) is inhibited by

Answer 31

Sympathetic pathways