Structure and function of the kidney II Flashcards
six subdivisions of kidney function
- regulation of extracellular fluid volume and BP
- Regulation of blood osmorality (300 mOsM)
- Maintenance of ion balance eg Na+
- Homeostatic regulation of plasma pH (7.38-7.42)- via secretion and/or reabsorption of H+ and HCO3-
- Excretion of metabolic and other wastes eg urea, hormones,urobilinogen
- Production of hormones eg synthesis of erythropoetin
Law of mass balance
mass balance = existing body load + intake or metabolic production - excretion or metabolic removal
Kidneys primary function
maintenance (homeostasis) of fluid and electrolyte balance
not removal of wastes
Hypotonic solution
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
Hypertonic solution
h20 out, cell shrinks
400 mOsm/L outside
concentration of solute higher outside cell
isotonic
solution that doesn’t cause a difference in cell size
Won’t change as concentration of water same on both sides
What do kidneys regulate
salt concentration
sodium excreted=
sodium filtered-sodium reabsorbed (sodium is not secreted)
Why is Na+ important in regulating blood volume
Controls movement of water across PM- water will follow movement of sodium if that membrane is permeable to water
How does body detect changes in Na+/salt concentration
detects indirectly as changes in blood volume, with baroreceptors and osmoreceptors in the hypothalamus
low sodium =
low blood volume
sodium deficiency
hyponatremia
kidney disease or over consumption of h20
brain damage, cancer
sodium excess
hypernatremia
loss of water- high NA levels
fever, vomiting, diarrhea
K+ deficiency
hypokalemia
causes abnormal transferal of electrical impulses
excessive urination, kidney failure
K+ excess
Hyperkalemia
Intake of laxative/diuretics
vomiting, diarrhea
Calcium deficiency
hypocalcemia
eating disorders etc
muscle cramps, weakness
Calcium excess
Hypercalcemia
due to breast cancer, kidney failure
depression, kidney stones
Mg deficiency
hypomagnesemia
over consumption of alcohol, malnutrition
results in inability of intestines to absorb
Mg excess
Hypermagnesemia
adrenal insufficiency
How do kidneys regulate urinary volume, osmorality and acidity
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
Basolateral membrane of tubule
adj to ISF
Luminal membrane
adj to tubular fluid (useful diagram)
tubular membrane transport
concentration gradient drives transport of tubular filtrate in the lumen into tubular cell
Requires facilitated or carrier systems to cross basolateral membrane
2 types of cellular reabsorption for Na+ ions
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
What does the electrochemical Na+ gradient do
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
Which part of loop of henle is water permeable and which part not
Descending limb water permeable and ascending not
What does the active transport of Na+ into ISF do to other Na+ ions
keeps intracellular conc of Na+ low compared to tubular lumen, so Na+ moves ‘downhill into tubular epithelial cells
reabsorption of glucose in the PCT
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
How is water reabsorbed in the PCT
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
Movement of H2O in loop of henle
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.
Reabsorption in the thick segment of the ascending loop
Not permeable to water
Na+ moves by active transport, and K+ and Cl- move by cotransport, put of the tubule
Reabsorption in the DCT and collecting duct
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
Overview proximal tubule
70% Na removed by active transport
chloride and water follow passively
Secretion of acid, absorption of bicarbonate
Descending loop overview
water permeable, not salts as much
osmotic loss of water concentrates salts in lumen
Ascending loops overview
Thin segment, salt permeable, not water
salts diffuse out of lumen
Thick segment: active Na+ and Cl- and K+ cotransport
distal tubule overview
ACtive Na+ and Cl- co transport
permeable to water
How is the gradient between filtrate in the lumen of the tubule and the cytosol of the tubule maintained
Primary active transport, using sodium-potassium ion pumps on basolateral mem
nutrient reabsorption in the PCT
transported along with Na+ ions via secondary active transport into cytosol of tubule cells
Nutrients then move by facilitated diffusion into ISF
Bicarobonate reabsorption in the PCT
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
Reabsorption of other ions and urea in PCT
Na+ movement drives movement of CL- ions by transcellular and paracellular pathways, whch draws other positively charged ions and nitrogenous wastes into the blood
H+ secretion
in the pct via antiporter with Na+
secondary
