Structure and function of the kidney II

Question 1

six subdivisions of kidney function

Answer 1

1. regulation of extracellular fluid volume and BP
2. Regulation of blood osmorality (300 mOsM)
3. Maintenance of ion balance eg Na+
4. Homeostatic regulation of plasma pH (7.38-7.42)- via secretion and/or reabsorption of H+ and HCO3-
5. Excretion of metabolic and other wastes eg urea, hormones,urobilinogen
6. Production of hormones eg synthesis of erythropoetin

Question 2

Law of mass balance

Answer 2

mass balance = existing body load + intake or metabolic production - excretion or metabolic removal

Question 3

Kidneys primary function

Answer 3

maintenance (homeostasis) of fluid and electrolyte balance

not removal of wastes

Question 4

Hypotonic solution

Answer 4

h20 in cell swells
200 mOsm/L outside
bursts
lower conc of solute outside than inside the cell, so water moves in causing cell to swell

Question 5

Hypertonic solution

Answer 5

h20 out, cell shrinks
400 mOsm/L outside
concentration of solute higher outside cell

Question 6

isotonic

Answer 6

solution that doesn’t cause a difference in cell size

Won’t change as concentration of water same on both sides

Question 7

What do kidneys regulate

Answer 7

salt concentration

Question 8

sodium excreted=

Answer 8

sodium filtered-sodium reabsorbed (sodium is not secreted)

Question 9

Why is Na+ important in regulating blood volume

Answer 9

Controls movement of water across PM- water will follow movement of sodium if that membrane is permeable to water

Question 10

How does body detect changes in Na+/salt concentration

Answer 10

detects indirectly as changes in blood volume, with baroreceptors and osmoreceptors in the hypothalamus

Question 11

low sodium =

Answer 11

low blood volume

Question 12

sodium deficiency

Answer 12

hyponatremia
kidney disease or over consumption of h20
brain damage, cancer

Question 13

sodium excess

Answer 13

hypernatremia
loss of water- high NA levels
fever, vomiting, diarrhea

Question 14

K+ deficiency

Answer 14

hypokalemia
causes abnormal transferal of electrical impulses
excessive urination, kidney failure

Question 15

K+ excess

Answer 15

Hyperkalemia
Intake of laxative/diuretics
vomiting, diarrhea

Question 16

Calcium deficiency

Answer 16

hypocalcemia
eating disorders etc
muscle cramps, weakness

Question 17

Calcium excess

Answer 17

Hypercalcemia
due to breast cancer, kidney failure
depression, kidney stones

Question 18

Mg deficiency

Answer 18

hypomagnesemia
over consumption of alcohol, malnutrition
results in inability of intestines to absorb

Question 19

Mg excess

Answer 19

Hypermagnesemia

adrenal insufficiency

Question 20

How do kidneys regulate urinary volume, osmorality and acidity

Answer 20

cortico-medullary osmotic gradient
regional differences in permeability of nephron and collecting duct
Regional differences in selective reabsorption (passive/active) and secretion in nephron and collecting duct
Arrangement and proximity of peritubular capillaries and vasa recta

Question 21

Basolateral membrane of tubule

Answer 21

adj to ISF

Question 22

Luminal membrane

Answer 22

adj to tubular fluid (useful diagram)

Question 23

tubular membrane transport

Answer 23

concentration gradient drives transport of tubular filtrate in the lumen into tubular cell
Requires facilitated or carrier systems to cross basolateral membrane

Question 24

2 types of cellular reabsorption for Na+ ions

Answer 24

paraxellular ie between epithelial tubule cells which is passive
Transcellular ie through tubule cells, active process because ATP required (Na+/K+ ATPase in basolateral membrane) to move Na+ ions uphill against electrochemical/concentration gradient from epithelial tubule cell into ISF- example of primary active transport

Question 25

What does the electrochemical Na+ gradient do

Answer 25

acts as a driving force for movement of water and other solutes: provides driving force to move K+ and H+ ions from ISF into tubule- secretion
Also drives transportation of nutrients into ISF by being transported with Na+ ions

Question 26

Which part of loop of henle is water permeable and which part not

Answer 26

Descending limb water permeable and ascending not

Question 27

What does the active transport of Na+ into ISF do to other Na+ ions

Answer 27

keeps intracellular conc of Na+ low compared to tubular lumen, so Na+ moves ‘downhill into tubular epithelial cells

Question 28

reabsorption of glucose in the PCT

Answer 28

Use secondary active transport with Na+ ions (Na+/glucose symporter) to move glucose from lumen into cell, then glucose diffuses facilitatively (using transporter) into blood/ISF

Question 29

How is water reabsorbed in the PCT

Answer 29

as ions are reabsorbed, water follows passively by osmosis. Removal of solutes from tubular lumen decreases local osmolarity of fluid adjacent to the cell, and the appearance of solute in the ISF just outside the cell increases the local osmolarity, and the difference in water conc causes net diffusion of H2O

Question 30

Movement of H2O in loop of henle

Answer 30

In the thin segment descending limb there is permeability to H2O and solutes, but to a lesser extent. water moves by osmosis from the tubule into ISF and solutes from vasa recta and ISF into the tubule.
Whereas in the thin segment of the ascending limb there is not permeability to H2O but there is to solutes, so they diffuse out of the tubule and into ISF and vasa recta.

Question 31

Reabsorption in the thick segment of the ascending loop

Answer 31

Not permeable to water

Na+ moves by active transport, and K+ and Cl- move by cotransport, put of the tubule

Question 32

Reabsorption in the DCT and collecting duct

Answer 32

Water moves by osmosis from DCT and collecting duct
Na+ moves by active transport and Cl- moves by cotransport out of the DCT and collecting duct
Reabsorbed water and solutes enter peritubular capilaries and vasa recta

Question 33

Overview proximal tubule

Answer 33

70% Na removed by active transport
chloride and water follow passively
Secretion of acid, absorption of bicarbonate

Question 34

Descending loop overview

Answer 34

water permeable, not salts as much

osmotic loss of water concentrates salts in lumen

Question 35

Ascending loops overview

Answer 35

Thin segment, salt permeable, not water
salts diffuse out of lumen
Thick segment: active Na+ and Cl- and K+ cotransport

Question 36

distal tubule overview

Answer 36

ACtive Na+ and Cl- co transport

permeable to water

Question 37

How is the gradient between filtrate in the lumen of the tubule and the cytosol of the tubule maintained

Answer 37

Primary active transport, using sodium-potassium ion pumps on basolateral mem

Question 38

nutrient reabsorption in the PCT

Answer 38

transported along with Na+ ions via secondary active transport into cytosol of tubule cells
Nutrients then move by facilitated diffusion into ISF

Question 39

Bicarobonate reabsorption in the PCT

Answer 39

Movement of H+ ions into tubule provides driving force to reabsorb HCO3- ions
In the tubule lumen, H+ ions bind with HCO3- ions to form carbonic acid, which dissociates into CO2 and H20.
CO2 diffuses into tubule cell, combining with H2O to form carbonic acid there. The carbonic acid dissociates into HCO3- and H+ ions. HCO3- ions move into ISF by facilitated diffusion

Question 40

Reabsorption of other ions and urea in PCT

Answer 40

Na+ movement drives movement of CL- ions by transcellular and paracellular pathways, whch draws other positively charged ions and nitrogenous wastes into the blood

Question 41

H+ secretion

Answer 41

in the pct via antiporter with Na+

secondary