21A/B: The Urinary System/Fluid and Electrolyte Balance

Question 1

hilium

Answer 1

medial indentation of the kidney where blood vessels and nerves enter/exit

Question 2

ureters

Answer 2

muscular tubes connecting from kidneys to urinary bladder

Question 3

detrusor muscles

Answer 3

surround the bladder and contract for urine elimination

Question 4

The outer surface covering the kidney is called the ___

Answer 4

fibrous capsule

Question 5

cortical nephrons vs. juxtamedullary nephrons

Answer 5

• cortical nephrons make up most of kidney’s nephrons (85%); regulatory functions
• juxtamedullary nephrons make up approx 15% of all nephrons; water conservation, forming concentrated urine

Question 6

movement of filtrate through the nephron (6 steps)

Answer 6

1. renal/glomerular corpuscle
2. proximal convoluted tubule (PCT)
3. nephron loop
4. distal convoluted tubule (DCT)
5. collecting duct
6. papillary duct

Question 7

renal corpuscle function

Answer 7

• filtration of blood

- H2O and plasma solutes enter glomerular capsule

Question 8

proximal convoluted tubule function

Answer 8

reabsorbs H2O, ions and organic nutrients from filtrate

Question 9

nephron loop function

Answer 9

• descending thin limb: reabsorbs H2O

- ascending thick limb: reabsorbs Na+, Cl-

Question 10

distal convoluted tubule function

Answer 10

• secretion of ions, acids, drugs, toxins

- variable reabsorption of H2O/Na+/Ca2+

Question 11

collecting duct function

Answer 11

• reabsorbs or secretes ions Na+/K+/H+/HCO3-

- variable reabsorption of H2O

Question 12

papillary duct function

Answer 12

• delivery of urine

Question 13

In the PCT, ___ is predominant.

Answer 13

reabsorption

Question 14

The DTL of the nephron loop is only permeable to ___ while the TAL is only permeable to ___.

Answer 14

water; solutes

Question 15

The flow of blood (in vasa recta) and filtrate are ___.

Answer 15

countercurrent

Question 16

antidiuretic hormone (ADH)

Answer 16

• increases permeability of DCT and collecting duct to H2O

- increases H2O reabsorption

Question 17

Explain the urinary reflex of continence.

Answer 17

• urine storage
• afferent impulses from stretch receptors in the bladder relax detrusor muscles and contract internal and external sphincters

Question 18

Explain the urinary reflex of micturition.

Answer 18

• urine voiding reflex (urination)
• afferent signals from bladder stretch receptors stimulate relaxation of internal and external sphincters and contraction of detrusor

Question 19

Difference between intracellular fluid (ICF) and extracellular fluid (ECF)

Answer 19

• ICF: cytosol inside the cells

- ECF: fluid components outside the cells (interstitial fluid, plasma, other bodily fluids)

Question 20

Adult males are made of _% water and _% solids while adult females are made of _% water and _% solids. In both sexes, __ > __.

Answer 20

• adult males: 60% water, 40% solids
• adult females: 50% water, 50% solids
• ICF > ECF in both sexes

Question 21

What does fluid balance refer to?

Answer 21

• when water gain (from sources) equals water elimination (from sinks)

Question 22

If you are dehydrated, how does your body compensate for dehydration?

Answer 22

• dehydration = decrease in ECF water while keeping concentration of ions the same
• decrease in ECF volume creates hypertonic solution compared to ICF
• osmotic shift occurs and water from ICF shifts to ECF, decreasing its volume
• both ICF and ECF become more concentrated

Question 23

Describe where the following ions are primarily found and how they are eliminated: Na+, K+, Ca2+ and Cl-

Answer 23

• Na+: bodily fluids; excreted through urine, sweat, feces
• K+: cytosol; excreted through urine
• Ca2+: bone; excreted through urine, feces
• Cl-: bodily fluids (HCl); excreted through urine, sweat

Question 24

Explain what happens during increasing sodium levels.

Answer 24

• high Na+ in ECF stimulates osmoreceptors
• increased ADH secretion (increases water reabsorption in kidneys, increased thirst to promote water consumption)
• high Na+ in ECF means increased ECF osmolarity = water shifts out of ICF
• ECF volume increases

Question 25

Explain what happens during decreasing sodium levels.

Answer 25

- low Na+ in ECF inhibits osmoreceptors - decreased ADH secretion promotes water loss by kidneys and thirst suppression - water loss decreases ECF volume to increase osmolarity back to homeostatic levels

Question 26

Explain what happens during significant ECF volume increases (by fluid gain/fluid and Na+ gain).

Answer 26

- cardiac muscle cells release natriuretic peptides that promote Na+ excretion - increased Na+ and water loss in urine - reduced thirst - inhibition of ADH/epinephrine/norepinephrine/aldosterone - peripheral vasodilation - decreases ECF volume

Question 27

Explain what happens during significant ECF volume decreases (by fluid loss/fluid and Na+ loss).

Answer 27

- baroreceptors increase release of ADH = increased thirst and water reabsorption - kidneys release renin, which activates angiotensin II = release of aldosterone = increased Na+ reabsorption - peripheral vasoconstriction - increases ECF volume

Question 28

What is the primary mechanism of K+ secretion?

Answer 28

- Na+/K+ exchange pump that ejects potassium ions while reabsorbing sodium ions - pumps regulated by aldosterone (stimulates Na+ reabsorption and K+ secretion)

Question 29

How is K+ reabsorbed?

Answer 29

- when pH in ECF is low, Na+/K+ pumps bind with H+ instead of K+ to excrete H+ ions to stabilize pH - causes K+ in ECF to rise