Fluid and Electrolyte Balance Flashcards
Kidneys regulate:
- solute and water content, which also determines volume
- acid-base balance
Composition is also affected by…
exchange between different compartments of body
Name some of the components of body.
- cells
- connective tissue
- gastrointestinal tract
- sweating
- respiration
To maintain homeostasis, what comes in the body must eventually be:
used or excreted
Water intake + metabolically produced =
water output + water used
Name 2 ways to intake water.
- gastrointestinal tract
- metabolism
Name 4 ways of water output.
- insensible loss
- sweating
- gastrointestinal tract
- kidneys
What is normovolemia?
normal blood volume
What is hypervolemia?
high blood volume due to positive water balance
What is hypovolemia?
low blood volume due to negative water balance
balance:
input + production = utilization + output
In the proximal tubule, ___% of filtered water is reabsorbed.
70%
the primary solute in the proximal tubules is
sodium
What is actively transported across the basolateral membrane and establishes gradient in the proximal tubule?
Na+
What is reabsorbed in the distal tubules and collecting ducts?
most remaining water
Water reabsorption in the distal tubules and collecting ducts are regulated by:
- ADH (vasopressin)
- indirectly through aldosterone
Describe osmosis.
- Water diffuses down the concentration gradient
- Water moves from area of low solute concentration to area of high solute concentration
- Water reabsorption follows solute reabsorption
Osmolarity of body fluids =
300 mOsm (milliosmoles of solute per liter of plasma)
No osmotic force for:
water to move between fluid compartments
Kidneys compensate for changes in osmolarity of extracellular fluid by…
regulating water reabsorption
Water reabsorption is a ____ process, and is based on ____ _____.
- passive
- osmotic gradient
Principal cells deal with:
- water
- electrolytes
Intercalated cells deal with:
acid-base balance
Osmolarity of interstitial fluid of renal medulla varies with _____.
depth
Lower osmolarity near _____.
cortex
Greater osmolarity near _____.
renal pelvis
_____ is critical to water reabsorption.
gradient
Fluid in proximal tubule = ____ mOsm
300 mOsm
Describe fluid in descending limb.
- osmolarity increases as it descends
- osmolarity = interstitial fluid
- osmolarity > descending limb
Describe fluid in ascending limb.
- osmolarity decreases as it ascends
- osmolarity < interstitial fluid
- osmolarity < descending limb
Urea is generated by _____.
liver
Urea eliminates ______.
nitrogen
Urea is _____ water soluble.
extremely
Urea requires:
urea transporters
Describe facilitated diffusion of urea.
- collecting duct to capillaries
- makes up 40% of gradient
Transport of urea through UTA from filtrate to peritubular fluid approximately ___% of the osmolarity of the gradient.
40%
What is the vasa recta?
- straight vessels-capillaries
- prevents diffusion of water and solutes from dissipating the medullary osmotic gradient
Describe the descending limb of vasa recta.
- 300 mOsm
- as it descends, water leaves capillaries by osmosis and solutes enter by diffusion
Describe the ascending limb of vasa recta.
- 325 mOsm
- water moves into plasma and solutes move into interstitial fluid
- osmolarity is higher due to the lack of urea transporters
____% of water reabsorbed in PCT and is ____ regulated.
- 70%
- not regulated
____% of water reabsorbed in DCT and is regulated by ____.
- 20%
- ADH
___% of water is reabsorbed in collecting ducts and is regulated by ____.
- 10%
- ADH
Water reabsorption is dependent on:
- gradient
- permeability
- length of Loop of Henle
How is water reabsorption dependent on gradient?
dependent on osmotic gradient established by countercurrent multiplier
How is water reabsorption dependent on permeability?
- dependent on epithelium permeability to water
- water permeability dependent on water channels
Aquaporin-3 is present in:
basolateral membrane always
Aquaporin-2 is present in:
apical membrane only when ADH present in blood
What happens when the membrane of late distal tubule and collecting duct is impermeable to water?
- water cannot leave the tubules
- no water reabsorption
- more water is excreted in urine
ADH stimulates:
the insertion of water channels (aquaporin-2) into apical membrane
Water is reabsorbed by _____.
osmosis
Maximum urine concentration is _____ mOsm.
1400 mOsm
Maximum amount of water reabsorbed depends on:
length of loop of Henle
Describe the regulation of ADH secretion.
- Posterior pituitary (hypothalamus)
- Osmoreceptors in the brain
- Baroreceptors detecting BV/BP
- ↓ baroreceptor activity = ↑ ADH secretion
What is hypernatremia?
high plasma sodium
What is hyponatremia?
low plasma socium
What is the primary solute in ECF?
sodium
Sodium is critical for:
- normal osmotic pressure
- to function of excitable cells
Na+ is _____ filtered.
freely
Na+ is reabsorbed (___%) in:
- 70%
- PCT, DCT, and collecting ducts
There is ____ secretion of Na+.
no
What regulates Na+ absorption?
- aldosterone
- ANP
What type of reabsorption does Na+ use?
- active
- Na+/K+ pump drives reabsortpion
Describe how aldosterone increases sodium reabsorption.
- Steroid hormone secreted from adrenal cortex
- Acts on principal cells of distal tubules and collecting ducts
- Increases number of Na+/K+ pumps on basolateral membrane
- Increases number of open Na+ and K+ channels on apical membrane
What secretes renin?
granular cells of juxtaglomerular apparatus
Capillary walls contain:
- angiotensin-converting enzyme (ACE)
- especially in lungs
Liver secretes:
angiotensinogen
Angiotensinogen is converted by renin into ______.
angiotensin I
Angiotensin I is converted by ACE into ______.
angiotensin II
Angiotensin II stimulates:
aldosterone production
The above system is called:
renin-angiotensin-aldosterone system (RAAS)
What acts as stimuli for renin release?
- Decreased pressure in afferent arteriole
- Renal sympathetic nerve activity
- Decreases in Na+ and Cl– in distal tubule filtrate
Relationship between hormones have a ______ outcome.
similar
What does ANP stand for?
atrial natriuretic peptide
ANP opposes _____.
aldosterone
ANP is secreted by:
atrial cells in response to distension of atrial wall
ANP increases ____.
GFR
An increase of GFR results in:
- dilation of afferent arteriole
- constriction of efferent arteriole
- relaxes mesangial cells
- decreases Na+ reabsorption by closing Na+ channels in apical membrane (increased Na+ excretion)
- decreases sympathetic activity to the kidney inhibits renin secretion
- washes out the medullary osmotic gradient (increased BF through vasa recta)
What is hyperkalemia?
high plasma potassium
What is hypokalemia?
low plasma potassium
Potassium is crucial for:
function of excitable cells
Glomerulus is _____ filtered.
freely
Potassium in PCT is:
reabsorbed
Potassium in DCT & collecting ducts are:
reabsorbed and secreted (regulated)
What regulates secretion of potassium?
- aldosterone
- K+ in plasma directly stimulates aldosterone release
- as K+ increases, more aldosterone is released
___% of filtered calcium is reabsorbed.
99%
70% of filtered calcium is reabsorbed in _____.
PCT
19-20% of filtered calcium is reabsorbed in _______.
the loop of Henle (ascending limb)
9-10% is reabsorbed in _____.
DCT
Reabsorption in _____ and _____ is regulated (hormones).
- loop of Henle
- DCT
Blood calcium is bound to:
carrier proteins
Ca2+ + protein =
Ca-protein
Blood calcium is ____ in plasma.
free
Free calcium:
freely filtered at glomerulus
What is hypercalcemia?
high plasma calcium
What is hypocalcemia?
low plasma calcium
Why is calcium balance critical?
- triggers exocytosis
- triggers secretion
- triggers muscle contraction
- increases contractility of cardiac and smooth muscle
Parathyroid hormone (PTH) is released from:
parathyroid glands
What is the stimulus to release PTH?
decreased Ca2+ in plasma
What does PTH do?
- Increases Ca2+ reabsorption by kidneys
- Stimulates activation of 1,25-dihydroxycholecalciferol in kidneys
- Stimulates resorption of bone
- Stimulates small increase in calcium absorption
- Overall effect: increased blood calcium
What is 1,25-(OH2)D3) or Cacitriol?
activated vitamin D3
What produces vitamin D3?
skin/sunlight
What converts vitamin D3 to inactive form?
liver
Low plasma Ca2+ detected by PTH in ______.
kidneys
PTH activates:
1,25-(OH2)D3) or Cacitriol
1,25-(OH2)D3) or Cacitriol does what?
- increased Ca2+ absorption in digestive tract
- Ca2+ reabsorption in kidneys
What is the opposing hormone to PTH?
calcitonin
Calcitonin is secreted by:
thyroid gland
Calcitonin is triggered by:
high plasma [Ca2+]
What actions does calcitonin have at target cells?
- increases bone formation
- decreases Ca2+ reabsorption by kidneys
Describe the physiological response to hemorrhage.
- decrease in blood volume = decrease in MAP
- neural control of heart and vasculature (baroreceptor reflex)
- hormonal control of blood volume (ADH, RAAS)
Why is exercise in the heat problematic?
- excessive sweating (loss of fluid and electrolytes)
- hypohydration or dehydration leads to reduction in aerobic performance by 7-60% (>2% of body mass)
- renal tubule damage (excess metabolites/acids)
Describe acclimatization.
- better ability to reabsorb electrolytes
- enhanced norepinephrine (NE) spillover increases erythropoiesis (replaces lost RBCs in urine and through hemolysis (muscle contraction/impact damage))
