ion & water balance Flashcards
what are the 3 homeostatic processes
osmotic regulation (osmotic pressure of body fluids)
ionic regulation (conc. of specific ions)
nitrogenous waste excretion (excretion of end-products of protein metabolism)
how do solutes move through water
by diffusion
what formula tells us the rate of diffusion
fick equation
fick equation
(dQ/dt)= DA(dC/dX)
D= diffusion coefficient
A= diffusion area
(dC/dX)= size of concentration gradient
water diffuses from a ___ solution to a ___ solution
hyposmotic solution to a hyperosmotic solution
what is tonicity
affect of a solution on cell volume
cells shrink in ____ solution
hypertonic (higher osmolarity outside than inside cell)
water leave the cell by osmosis
cells swell in___solution
hypotonic (lower osmolarity outside than inside cell)
water enters the cell by osmosis
cell neither shrinks nor swells in ___ solution
isotonic
no net osmosis
why is it important to regulate cell osmolarity?
increased intracellular osmolarity can interfere w/ cellular processes
can change cell volume
what does each cause?
moderate cell swelling
excessive cell swelling
excessive cell shrinkage
disruption of membrane
cell lysis (membrane ruptures)
macromolecular crowding
what do cells do to control cell volume
transport solutes in and out of extracellular fluid bc water follows solutes by osmosis
what does regulating the composition of extra cellular fluid by animals do for the cells
provides cells with external solution that allows them to maintain appropriate cell volume
what is Na+ regulated by
Na+/K+ ATPase and Na+/H+ exchanger
what is K+ regulated by
Na+/K+ ATPase
what is Cl- regulated by
generally distributed passively (Goldman equation)
what is Ca2+ regulated by
Na+/Ca+ antiporter
Ca2+ ATPase
cells usually increase their volume by actively importing which ions
NKCC
NA+, K+, Cl-, Cl-
cells usually decrease their volume by exporting which ions
opening K+ channels
Cl- channels also open, Cl- leaves cells in response to hyperpolarizing effects of K+ movement
what does water move through to get into the cell
aquaporins
ionic and osmotic challenges in marine environment
gaining salt and losing water
ionic and osmotic challenges in fresh water environment
lose salts and gain water
ionic and osmotic challenges in terrestrial environment
tend to lose water
2 strategies to meet ionic challenges
ionoconformer (in marine animals, little control over ion profile within the extracellular space)
ionoregulator (most vertebrates, control ion of extracellular space)
2 strategies to meet osmotic challenges
osmoconformer (internal and external osmolarity similar, marine invertebrates)
osmoregulator (osmolarity constant regardless of external environment, most vertebrates)
2 words describing ability to cope w/ external salinities
stenohaline (tolerate only narrow range)
euryhaline (tolerate wide range)
describe euryhaline osmoconformer
allows osmolarity to decrease in parallel with water until death
describe stenohaline osmoconformer
dies after very modest osmotic disruption
euryhaline osmoregulator
maintain a nearly constant internal state but eventually succumbs
stenohaline osmoregulator
can defend its internal osmolarity over a narrow range of external osmolarities
compatible solute
little affect on macromolecular function
glycerol, glucose, uncharged amino acids
perturbing solute
disrupt macromolecular function
Na+, K+, Cl-, SO4+, charged amino acids
counteracting solute
disrupt function on their own
counteract disruptive effects of other solutes when combined
how do animals compensate for passive ion and water movements?
by active transport of ions across osmoregulatory epithelia
(gills, kidney, digestive system)
only birds and mammals can produce ____ urine at the kidneys
concentrated (hyperosmotic relative to blood)
epithelial tissue properties for ion movement
asymmetrical distribution of membrane transporters
cells connected by tight junctions form a impermeable sheet of tissue
2 main routes of transport used by epithelial cells
transcellular transport (movement through the cell)
Paracellular transport (movement between cells, ‘leaky epithelia’)
osmoregulation in freshwater fish
passively gain water, loses ions across gill and gut
produces dilute urine to get rid of water
actively absorbs ions at gill
osmoregulation in marine fish
passively lose water, gain ions across gill and gut
cannot produce concentrated urine
drinks to obtain water
actively secretes ions at gill
what do fish gills possess to transport ions
ionocytes on filaments and lamellae
ionocytes generally have a lot of mitochondria + high levels of Na+/K+ ATPase activity to drive ion movement
mechanisms of salt secretion
Na+/K+ ATPase creates -60mV charge
sets up condition for NKCC to enter the cell
Na+ moves back into blood via Na+/K+ ATPase
K+ re-enters blood via diffusion/leaks
Cl- moves down electrical gradient through Cl- channel from epithelium into environment
for Na+ to leave the animal, travel through Na+ specific channel between epithelial cells
mechanisms of salt uptake
goal is to gain Na+ and Cl-
Na+/K+ ATPase creates -60mV charge
creates condition for Na+ uptake
Na+/K+ ATPase lets 3Na+ enter blood for 2K+
CO2 enters cell and produce H+ and HCO3-
ATP pumps out protons
HCO3- exits cell and drives Cl- uptake
Cl- doesn’t want to enter cell bc the cell is -60mV but lots of HCO3- exiting cell drives Cl- to enter
Cl- enters blood via Cl- channels
smoltification
process where a juvenile salmon becomes ready for entry into marine water
metabolic changes + morphological changes + osmoregulatory system changes
what do salt glands in birds and reptiles do?
how?
excrete hyperosmotic solutions of Na+ and Cl-, large amount of salt excreted in small amount of water
hyperosmotic solutions produced by ion pumps and a countercurrent multiplier
what do rectal glands in elasmobranchs do?
empties into digestive tract (excreted as feces)
Na+ and Cl- actively transported from blood to lumen of gland
rate of salt excretion regulated by hormones
ion and water balance in terrestrial habitats
water loss across skin, respiratory surface, and urine
water gain by metabolic water, drinking, food
rate of water loss related to surface area to volume ratio
how does the nasal countercurrent heat exchanger work
incoming air is warmed and humidified
outgoing air is cooled and loses water
how is ammonia produced and why must it be excreted
produced during amino acid breakdown
bc it is toxic
3 forms ammonia nitrogen is excreted as
ammonia
uric acid
urea
advantages of ammonia excretion
released by deamination of amino acids
requires little energy to produce
disadvantage of ammonia excretion
highly toxic
requires large volumes of water to store and excrete
why is high pH a problem for ammonia excretion?
how is the problem solved?
NH3 + H+ <-> NH4+
high pH-> more NH3
less NH3 will be able to enter the urine and be excreted-> less NH3 excreted
NH4+ is the more toxic form and can substitute for K+ in nervous tissue, resulting in convulsions at high levels
solution:
as NH3 moves across epithelium into (gill) water, H+ATPase also releases H+ into the water-> create NH4+ in the water
keeps NH3 levels low so NH3 can continue to move into environment
advantage of uric acid excretion
few toxic effects
can be excreted in small volume of water
disadvantage of uric acid excretion
expensive to produce
advantage of urea excretion
only slightly toxic
relatively inexpensive to produce
disadvantage of urea excretion
urea is a perturbing solute
where is urea synthesized and where is it transported to?
synthesized in liver
transported by blood to kidney
how is urea used as an osmolyte?
why does the animal need it?
how is the urea’s perturbing effect counteracted?
used by elasmobranchs
increases plasma osmolarity
helps prevent water loss in marine environment
perturbing effects counteracted by methylamines
6 roles in homeostasis of vertebrate kidneys
ion balance
osmotic balance
blood pressure
pH balance
excretion of metabolic waste/toxins
hormone production
2 layers of mammalian kidney
how does urine leave the kidney
outer cortex + inner medula
urine leaves kidney via ureter
ureter empty into bladder
what is the nephron composed of
renal tubule
vasculature containing glomerulus and capillary beds
role of glomerulus in nephron
ball of capillaries that provides blood to kidney to be purified
surrounded by Bowman’s capsule
4 processes of urine production
FILTRATION (filtrate of blood formed at glomerulus)
REABSORPTION (specific molecules in the filtrate removed from lumen back into blood)
SECRETION (specific molecules added to the filtrate from blood)
EXCRETION (urine is excreted from the body)
where does filtration take place
blood from glomerulus moves into Bowman’s capsule/ proximal tubule
where does reabsorption take place
proximal tubule, loop of Henle, distal tubule
where does secretion take place
proximal tubule, distal tubule
what do foot processes provide for the glomerular capillaries
structural support for capillary
why are glomerular capillaries leaky?
bc want water + small solutes to filter through
blood cells and large macromolecules not filtered
what is glomerular filtration rate affected by
glomerular capillary hydrostatic pressure
Bowman’s capsule hydrostatic pressure
oncotic pressure (osmotic pressure dur to protein concentration)
net hydrostatic pressure drives blood filtration
osmotic pressure drives reabsorption from interstitium
how are most water and salt in primary urine reabsorbed?
by transport proteins and energy
rate of reabsorption limited by number of transporters and renal threshold
each zone of the nephron has transporters for specific solutes
what is renal threshold
concentration of a specific solute that will overwhelm reabsorptive capacity (no more can be reabsorbed)
eg. point at which glucose start to appear in urine
how is glucose reabsorbed
by secondary transport
how does diabetes relate to renal threshold
too much glucose in blood and urine
glucose too high in blood could cause metabolic issues
what molecules are reabsorbed passively
Na+ and other solutes
extracellular fluid is more concentrated than fluid in the lumen-> water move out of lumen
urea become more concentrated in lumen-> urea move out of lumen into blood by passive diffusion to be transported into bladder
urea leaves later than other solutes bc want to keep urea for creation of gradient for water filtration
what and how are molecules transported for secretion
removed from blood and transported into filtrate by transport proteins + energy
K+, NH4+, H+, pharmaceuticals, water-soluble vitamins
proximal tubule function
most solute and water reabsorption
solutes reabsorbed by Na+ cotransport
water follows by osmosis
also carries out secretion
loop of Henle function
descending limb: H2O reabsorption
ascending limb: impermeable to water, ion reabsorption
distal tubule function
reabsorption completed for most solutes
collecting duct function
drains multiple nephrons, carries urine to renal pelvis
how is the osmotic gradient in the medulla created and maintained
loop of Henle and collecting duct act as countercurrent multipliers to create osmotic gradients that facilitate transport processes
gradients maintained by vasa recta capillaries
what does the osmotic concentration of the final urine depend on?
depends on the permeability of distal tubule and collecting duct
impermeable-> dilute urine (water not reabsorbed)
permeable-> concentrated urine (water reabsorbed from collecting duct)
mechanism for concentrating urine
ascending limb of loop of Henle actively pumps Na+ out of tubule lumen, Cl- and K+ follow
causes increased ion concentration in interstitial fluid of medulla
causes water to move passively out of descending limb
how does vasa recta maintain osmotic gradient
ions pumped out from ascending loop
water flows out of descending tubule by osmosis
point where vasa recta enters medulla, blood is isoosmotic w/ cortex
as blood moves deeper into medulla, loses water and picks up ions from interstitial fluid (ions from ascending loop)
when blood flows back towards cortex, high plasma osmolarity causes water from descending tubule to be reabsorbed
how does vasopressin affect the kidney
peptide hormone
antidiuretic hormone (reduce excretion of water)
increases water reabsorption from collecting duct
alcohol and caffeine inhibits release of vasopressin
increases cell permeability by increasing number of aquaporins
what does aldosterone do?
what does this do to blood pressure and volume?
increases Na+ (and water) retention
raises blood pressure by increasing blood volume
steroid hormone
stimulates Na+ reabsorption from urine by activating transcription factor for transcription of genes for transporters
enhances K+ excretion (bc Na+/K+ exchange)
to lower osmolarity in the kidney, it is better to…
get rid of Na+ than reabsorbing water
what are the pathways that compensate for dehydration
dehydration= plasma osmolarity up
angiotensin II up-> vasopressin up-> H2O reabsorption by kidney
angiotensin II up-> aldosterone down-> Na+ reabsorption by kidney down-> osmolarity down
describe the excretory control of homeostasis after water intake
problem-> plasma volume up, plasma osmolarity down
solution-> urine volume up-> plasma volume down-< homeostasis
describe the excretory control of homeostasis after salt intake
problem->plasma osmolarity up-> salt excretion up-> plasma osmolarity down-> homeostasis
difference between protonephridia in worms and metanephridia in molluscs + annelids
protonephridia: fluids taken from interstitial space into lumen w/ reabsorption, similar to vertebrate kidney tubule, mostly freshwater
metanephridia: fluid taken from blood or coelom into lumen w/ some reabsorption
describe the malpighian tubule in insects
blind ending sac, empties into hind gut
primary urine formed by secretion, not filtration
reabsorption and secretion in hindgut further modifies primary urine
no ultrafiltrate is created and secretion is driven by H+ATPase
characteristic of chondrichthian (shark) kidneys
extracellular fluid is slightly hyperosmotic to seawater due to high urea concentrations
countercurrent arrangement recovers up to 90% of the urea from primary urine
final urine is slightly hypoosmotic relative to shark plasma (bc urea recovered by plasma) and isotonic to sea water
Lack loop of Henle
characteristic of fish kidneys
freshwater: ions reabsorbed from primary urine, excrete diluted urine, most ion + water + N+ excretion requirement met by gills and skin
Marine: small amounts of urine, some marine fish lack glomeruli, most ion + water + N+ excretion requirement met by gills and skin
ALL LACK loop of Henle
how are amphibian kidneys different in larval and adult forms
larval: pronephros, empties into coelom, excrete of dilute urine (in aquatic environment)
adult: mammal-like nephron, reduce glomerular filtration rate, reabsorb water from bladder (conserve water)
what is the biggest advantage of having a loop of Henle?
what do birds + reptiles without loop of Henle do?
can produce concentrated urine
longer loop of Henle and thicker medulla-> more concentrated urine
birds + reptiles without loop of Henle conserve water by excreting uric acid
what is conservation physiology
scientific discipline applying physiological concepts + tools + knowledge to characterize biological diversity and ecological implications
understanding how organisms, populations, and ecosystems respond to environmental change and stressors
what do fishes living in the high salinity lake need to worry about
passive ion gain and water loss
how can one assess the salinity tolerance of a fish and what are assumptions?
higher salinity tolerance-> recovery of osmoregulatory status within 5 days exposure to that salinity
assumption: osmoregulatory status following 5 days is predictive of 30 days
