Water and Solute Balance Flashcards
properties of water
- dipole moment
- ability to form hydrogen bonds
- high specific heat (good for regulating body temp)
- high latent heat of evaporation(good for cooling body)
- high latent heat of fusion (water is hard to freeze)
- bodies of water expand when frozen
- good solvent
colligative properties
characteristics of a solution that depend on the number of molecules dissolved in a given volume
- all related to concentration of solute in water
- more solutes in water= higher boiling point, lower freezing point
osmosis
diffusion of solvent molecules into are of high solute concentration
- water will flow to more concentrated side of membrane
- higher osmotic pressure= more concentrated solution
flux
water movement, rate of flow of matter or energy across a unit area
permeability
rate at which a substance penetrates a membrane under a given set of conditions
diffusion rates depend on
- concentration gradient (greater concnetration gradient= greater diffusion)
- electrical (ionic gradient)
- temperature ( greater temp= greater diffusion)
- membrane area (greater area = greater diffusion rate)
- size of solute (smaller size = greater diffusion rate)
- polar substance has minimal diffusion
3 routes by which substances cross membranes
1) through aqueous channels/pores
2) dissolves into lipid bilayer and diffuses across
3) molecule combines with a carrier molecule dissolved in the membrane
lipid bilayer
- phospholipids arrange in a bilayer
- polar heads outward
- non-polar tails inward away from water
- membrane is impermeable to polar molecules
extrinsic
attached to surface
- more polar R groups
Intrinsic
more nonpolar R groups
liquid-crystalline state
- range of temp is dependent on type of fatty acid in phospholipid
- more unsaturated FA have greater tolerance of membrane to lower temps
passive diffusion
- down a concentration gradient
- no carrying or energy involved
- occurs through pores in membrane (polar molecules) or directly through lipid bilayer (nonpolar molecules)
active transport
involves a carrier molecule (probably a protein) which carries the molecule from one side to the other
- exhibits saturation kinetics
- can occur against a concentration gradient
- pumps maintain gradients
saturation kinetics
as concentration of solute increases, the protein carrier gets saturated and rates of diffusion level off
facilitative transport/facilitated diffusion
passive diffusion with a carrier molecule
- down an electrical/concentration gradient
- no direct energy is required
- exhibits saturation kinetics
exchange diffusion
involves a carrier
- no energy directly required
codiffusion
involves a carrier
- no direct energy, but indirectly there is
iso-osmotic cell
osmotic concentrations are the same inside and outside of the cell
hypo-osmotic cell
cell has lower osmotic concentration inside than out
- cell will shrink
hyperosmotic cell
osmotic concentration outside is less than inside (cell will swell)
isotonic cell
volume is constant
hypotonic cell
volume inside decreasing
- water flows in
hypertonic cell
volume inside increases
- water flows out
euryhaline
cells that tolerate high salt concentrations (extracellular and intracellular)
stenohaline
narrow tolerance to salt
- a lot of effort is put into maintaining gradients, if salt balance is thrown off the cell will have a hard time
osmoconformers
allow their osmolarity to vary with salt water
- includes most marine invertebrates
- their environment is relatively stable
- quite tolerant of high salinity (euryhaline)
osmoregulator
- will maintain a relatively constant osmolarity, in spite of external environment
- includes most freshwater invertebrates, most vertebrates and terrestrial invertebrates and vertebrates
concentrations for both Osmo conformers and regulators
(Na+ and K+ for blood vs inside cell)
- blood concentration normally high Na+, low K+
- inside cell normally high K+, low Na+
- also high organic molecules
- some insects have unusually high K+
adaptations in freshwater teleost fish
- plasma is hyperosmotic to surrounding water
- water tends to flow in and ions flow out
must get rid of water and retain ions - low permeability of body surface to limit influx of water
- kidney is designed to get rid of water, produces a large volume of hypotonic and hypoosmotic urine
- active uptake of ions from water (use of chloride cells in epithelia of gills–> actively transport Cl- and Ma+ out of water, water still follows
vasotocin(freshwater)
vasoconstrictor of efferent arterioles
- increases GFR, inc urine volume
corticosteroids
increase urine volume by increasing GFR
- also inc Na+ uptake
prolactin
very important to FW fish to increase Na+ retention at gills
- helps promote active transport in gills
Salt water fish
- fish plasma is hypo-osmotic to SW
- water leaves fish and ions tend to diffuse in
fish need to retain water and get rid of ions
vasotocin (SW)
vasoconstricts afferent arterioles to decrease GFR–> limits urine production
adaptations in SW fish
body surface, srink, kidney, chloride cells
- low permeability in body surface
- drink SW–> inc in water, but also inc Na+, Cl-, and K+ concentrations
- Kidney has low volume output for water concentration (secrete isosmotic urine, divalent ions excreted by gut/kidney, monovalent via gills)
- chloride cells excrete salts through outward active transport against conc/electrical gradients without loss of water–> Cl pump is electrogenic (pumps Cl- out, creating charge for net ion fluc, Na+ follows)
cortisol (SW)
- very important to SW fish
- increases Na+ transport at gills
amphibians in aquatic environments
- kidney similar to fish
- use skin and bladder
- active transport of Na+ out of bladder, with water following
marine mammals
- drink salt water
- efficient kidney that can secrete inc ions in a small urine volume
reptiles and birds in an aquatic environment
drink, how do they get rid of salts
- drink salt water
- don’t have as efficient of a kidney as mammals
- rely on other organ to get rid of salt (SALT GLANDS/RECTAL GLANDS)
salt glands
active transport of NaCl into tubule lumen to be excreted down nasal canal
- strong electrogenic Cl- pump with Na+ passively following
rectal glands
in elasmobranchs produces hypertonic Na+ solution
- also electrogenic Cl- pump
water gain
- drink
- skin/body surfaces (amphibians)
- metabolic water, water in food
water losses
- urine
- feces
- evaporation over the body surface and across respiratory surfaces
kangaroo rat
- nocturnal
- doesn’t drink water or eat succulent plants (diet is only dry seeds)
- gets most of water metabolically
- long loop of Henle–> more efficient kidney so they can excrete a greater osmolarity urine with same volume
- low volume, highly concentrated urine
- has long, narrow trachea that cools air as it is exhaled (air holds less water)–> water condenses and is reabsorbed
intermittent countercurrent heat exchange
- separate in time, not space
- during inhalation, walls lose heat to inhaled air, become cooler
- exhalation, warm lung air passes over cool surface and water condenses
- decreases water loss
camel physiological adaptations
- hump of camel contains lipid which animal draws from ro metabolize for energy and water
- kidney will concentrate urine
- very tolerant to dehydration
- avoids explosive heat death
- stores heat (during day stores heat to dec heat flux and water loss), unloaded at night (when temp is lower)
- high insulation to avoid heat loss
- can stop urination and store urea in tissues
- countercurrent heat exchanger (temporally–> same as kangaroo rat)
steps to explosive heat death
- as water is lost, volume of blood decreases and viscosity increases–> makes heart work harder (inc pumping)–> still have dec circulation so heat won’t dissipate–> inc body heat leads to death
(less blood = heart has to work harder to pump blood around= dec circulation = elevated temp)
nephridia
most common type of excretory organ among invertebrates
- simple branching tube opening to outside via a pore
- 2 types: protonephridia and metanephridia
protonephridia
- inner portion of tubule is closed off
metanephridia
- inner portion is open
- with nephrostome: open, funnel like, ciliated end
3 mechanisms of kidney
- ultrafiltration
- reabsorption
- secretion
glomerulus
capillary bed in Bowman’s capsule
- responsible for first step in urine filtration
ultrafiltration
- blood pumped into glomerulus
- walls are premeable and blood is filtered
- filtrate accumulates in lumen of Bowman’s capsule
- salts, sugars filter through
- large proteins, RBC won’t
at proximal tubule
- lumen contains urinary filtrate, composition of fluid in tubule is isosmotic to blood plasma
- contains glucose, amino acids, salts, but no RBC or proteins
- needs to be a way to reabsorb these things
- requires active transport systems
net movement of water from plasma to tubule
what is it caused by
results from: hydrostatic blood pressure, back pressure in tubule, pressure due to excess of proteins –> net filtration pressure
vasoconstriction of afferent arteriole
less urine
vasoconstriction of efferent arteriole
more urine
reabsorption
where does it occur
99% of water and most salts, sugars are reabsorbed
- occurs through length of tubule
- involves active transport and diffusion
- distal tubule: most electrolytes reabsorbed here
- proximal tubule: most of glucose
secretion
-involves active transport
- secretion of ammonia ion, H+, K+
- important in regulation of blood H= and pH buffers (bicarb)
freshwater fish kidneys
- designed to lose lots of water
- have high number of glomeruli for filtration –> so urine is of high volume but low osmolarity
- # of electrolytes are being reabsorbed
- urine is hypotonic to blood
salt water fish kidneys
include structure of kidney
- must remove slats and retain water
- less glomeruli–> lose less water
- no distal tubule to prevent uptake of salts
- SW fish excrete isosmotic urine (divalent ions excreted out by kidney, monovalent at gills)
- some SW fish are aglomerular–> kidney doesn’t use filtration (uses diffusion and active transport_
- not a lot of reabsorption
kidney of amphibians and reptiles
- essentially like a FW teleost kidney
- 3 processes
- glomeruli and tubules
- importance of bladder, salt glands, and skin
kidney of aves and mammals
problem with water loss–> have to reabsorb most of it
- able to secrete a concentrated urine
cortex
outer layer of kidney
- contains malpighian bodies and proximal and distal tubules
medulla
- inner portion of kidney
- contains Loop of Henle and collecting duct
loop of Henle
connects proximal and distal tubule
- contains thin descending limb, thin ascending limb, and thick ascending limb
thin descending limb
- No NaCl active transport
- low permeability to NaCl; urine is concentrated–> hypertonic fluid
- permeable to water
- entirely passive
- urine vol dec
- urea and NaCl conc inc
- as it turns loop at bottom = isosmotic to “inner medulla” fluid
thin ascending limb
- Permeable to NaCl and urea, not to water
- NaCl diffuses out, urea diffuses in (passive)
- inc urea conc inside
- lower osmolarity inside
thick ascending limb
- impermeable to water, not to urea
- active transport of Cl- (Na+ passively follows)
- Use of Na-K-2Cl cotransporter
- lowers osmolarity
- hyposmotic/iosmotic to interstitial fluid
2 types of kidney nephrons
Juxtamedullary (penetrates inner medulla) and Cortical (does not penetrate)
proximal convoluted tubule
- concentrates glomerular filtrate
- 75% of Na+ is removed (act transport)–> 75% water and Cl- follows passively
- water permeable membrane, presence of aquaporins
- glucose and organics reabsorbed (AA, glucose: carrier mediated)
- reabsorbed HCO3-, increases H+ secretion (dec pH)
- leads to fluid of reduced volume which is isosmotic with plasma
distal convoluted tubule
- volume dec further
- impermeable to urea–> urea conc inc more
- secretion of K+, H+, and NH3 (active transport)
- some reabsorption of Na+ and Cl-, HCO3-
- water permeable (influenced by vasopressin)
collecting duct
- water reabsorbed (influenced by ADH)–> passive diffusion into hypertonic interstitial fluid, urine volume dec further
- NaCl is reabsorbed (influenced by ADH
- initially impermeable to urea, but in lower regions the epithelium becomes permeable to urea–> urea then passively diffuses out
- Medulla region inc in osmolarity (from urea and NaCl)
interstitial hyperosmolarity due to…
- active salt transport in thick ascending limb (cl- with Na+ passively following)
- Urea leaving lower collecting duct, increasing osmolarity
- high salt in thin ascending loop and diffuses out
electrogenic pump
1 ion gives rise to electric current and another passively follows
electrotonic pump
with counterion and no net charge
important points about kidney
- water is being reabsorbed (because if high osmolarity in interstitial fluid, vasopressin)
- urine volume decreases and urea is being concentrated (leads to hypertonic urine, high urea in collecting duct will diffuse into interstitial fluid and maintain high osmolarity)
vasa recta
countercurrent mechanism
- water is removed from the area by entering the vasa recta which removes it to the general circulation
- water is drawn out as blood descends–> concentrates proteins–> draws a lot of water into vessels upon ascent and removes it
- passive diffusion of Na+, urea–> draws water in–> Na+, urea recirculated to maintain high osmolarity (rids area of excess salt and water)
Glomerular Filtration Rate (GFR)
dependent on blood pressure (greater BP= greater GFR)
reabsorption
- mostly by active transport
- ex: glucose codiffusion with Na+ (requires carrier which can become saturated)
tubular maximum
max rate which tubules can transport and reabsorb a solute
renal thresholds
blood concentration when active transport systems are saturated]8
insect excretory system
- Malpighian Tubules
- how they secrete hypertonic urine
- mechanism based on transport of K+ and Cl- –> creates an osmotic gradient to bring H2O into lumen, generates concentration gradient between blood and fluid inside MT–> water drains into gut
- reabsorption of solutes in rectum
- circulatory system is not very important, so BP is low
- filtration isn’t very important
Malpighian Tubules
- vary in number
- blind ended tubules attached behind the midgut and before the hindgut
control of excretory system for vertebrates
hormonal systems
- variation in rates of urine production
- control from 2 hormonal systems–> Posterior Pituitary (ADH) and adrenal glands (aldosterone and corticosteroids)
Antidiuretic Hormone
- secreted by Posterior pituitary gland
- produced in hypothalamus, stored in posterior pituitary until release
- 2 types of ADH found in vertebrates: AVP and AVT
AVP (arginine vasopressin)
- found in mammals
AVT (arginine vasotocin)
- all lower vertebrates
effects of ADH
- main effect on collecting duct epithelium and distal tubules
- inc water permeability
- may also inc Na+ uptake
- net effect to inc water uptake–> decrease urine volume
- increase in water uptke, and decrease in urine volume–> inc ECF (extracellular fluids)–> inc blood pressure, dec blood osmolarity, dec blood viscosity
- except for FW fish, ADH dec urine volume by dec GFR or inc water reabsorption
AVT, vasotocin (In reptiles, amphibians, and SW teleost)
- dec GFR (constricts glomerili afferent arterioles, dec blood flow through glomerilus)–> dec urine volume
AVT (anurans)
- also affects skin–> to inc Na+ transport across skin into animal and inc water permeability
- also influences epithelium of urinary bladder to make it more permeable to water–> reabsorbs more water and excretes less
AVT (teleost)
FW vs SW
- Freshwater: AVT inc urine production by inc GFR–> vasoconstricts efferent arterioles; inc Na+ uptake across gills (also role for cortisol and prolactin)
- Saltwater: AVT dec urine volume–> dec GFR–> vasoconstricts afferent arteriole
control of ADH
osmolarity, BP, Angiotensin II, Baroreceptors
- cells in hypothalamus which are sensitive to changes in osmolarity
- inc in osmolarity->inc in ADH secretion-> water conservation-> dec urine production, inc ECF-> dec osmolarity of ECF
Baroreceptors: sensory organs located in large veins, measure changes in ECF volume, sensitive to changes in BPP - Inc BP-> dec ADH-> inc urine vol-> dec ECF vol-> dec BP
- low BP-> sensed by Baroreceptors-> inc ADH release-> inc water reabsorption in kidney-> inc ECF volume-> inc BP
- Angiotensin II-> inc in vasopressin release
effect of alcohol on urine production
- inc alcohol-> inc urine production
- inc volume of ECF-> dec ADH
- dec osmolarity of ECF-> dec ADH
- alcohol acts on brain to dec ADH
Water toxicity death
Inc ECF volume-> inc BP
- dec osmolarity-> gradient challenges (cells swell and lyse)
arid species
ADH
- greater need to retain water
- tend to maintain larger pituitary stores of ADH per unit body fat
- can synthesize ADH faster
Diabetes insipidus
- inc urine production due to hyposecretion of ADH
protein hormone
- binds to surface receptor on target cell (receptor is hormone and target cell specific)
- Receptor is G-protein linked receptor
- activated G-protein activates the enzyme adenyl cyclase–> converts ATP to cAMP
- cAMP becomes send messenger (activates specific protein kinase: cytosolic))
2nd messenger
- ex: cAMP
- provides amplification of signal and brings about a specific action on the part of the target cell
- ex: stimulates or inhibits enzymes or processes that are specific for a type of target cell
ADH at collecting duct
- binds membrane receptor, activates cAMP–> cell inserts AQP2 water pores into apical membrane–> water permeability and uptake occurs
- in absence of ADH, pores are withdrawn and stored in cytosolic vesicles
cAMP levels
- depends on rates at which it is synthesized and rates in which it is inactivated by phosphodiesterase
- enzyme converts cAMP to 5’ AMP
- inhibitors of phosphodiesterase inc cAMP levels
cortex tissue
synthesizes and secretes steroid hormones
medullary tissue
of neural origin, and secretes epinephrine and norepinephrine
3 levels of adrenal cortex
Zona Glomerulosa, Zone fasiculata, and Zona Reticularis
Zona Glomerulosa
produces the mineralocorticoid: aldosterone
Zona fasciculata
produces glucocorticoids
Zona Reticularis
produces estrogens and androgens
glucocorticoids
effect on carbohydrate metabolism
- glucose affecting steroids
- hyperglycemia: produces an inc in blood glucose, by breakdown of liver glycogen and conversion of AA and fats to glucose
ACTH
adrenal corticotropic hormone
- glucocorticoid
- regulated by CRH (corticotropin releasing hormone from the hypothalamus)
Mineralcorticoids
- effect osmoregulation and water balance
- primary effect: Na+
- impacts water retention and K+ secretion
Aldosterone
- inc Na+ reabsorption (active transport) indistal tubules of kidney nephron–> inc water reabsorption–> dec urine volume
- also inc K+ secretion into urine (active transport indistal tubules–> Na+ uptake favors K+ secretion
aldosterone effect in birds
inc salt gland efficiency (Na+ secretion)A
aldosterone in Amphibians
- inc Na+ reabsorption from bladder
- inc Na+ transport in skin
cortisol
- mineralocorticoid in teleost
- acts in osmoregulation
- FW fish: inc Na+ uptake across gills–> inc water uptake–> inc urine volume
- SW fish: inc Na+ transport out of gills
Renin-angiotensin System
renin is a proteolytic enzyme which is release by the juxtaglomerular apparatus (JGA)
- cells composed of macula densa cells at beginning of distal tubule and special renin secreting afferent arteriole cells in smooth muscle layer- renin released-> cleaves angiotensin-> angiotensin I-> converted in lungs by ACE-> angiotensin II
Angiotensin II
- hormone that affects the adrenal cortex to release aldosterone
- potent vasoconstrictor
- constricts arterioles, dec GFR–> inc water retention and BP
- also inc vasopressin release
aldosterone
released in response to Angiotensin II
- Inc Na+ uptake (active transport)
- Inc water uptake passively
triggers for Renin-Angiotensin, Aldosterone
- change in BP (dec distenstion of arteriole because of dec BP-> inc renin release-> aldosterone release-> Na+ uptake, water uptake, inc ECF vol-> higher BP)
- Macula densa cells are senstive to amt of Na+ transport across tubules (renin secretion is inversely proportional to rate of Cl- or Na+ transport across distal tubule: inc renin release because of dec Na+ in plasma OR inc Na+ in distal tubule)
- cells in adrenal ccortex (zona glomerulosa) are directly sensitive to changes in Na+ in plasma (dec in Na+ plasma-> inc aldosterone secretion-> inc Na+ uptake
Low BP
inc ADH and increase aldosterone release–> inc BP
High osmolarity
effect on ADH and aldosterone
inc ADH (which inc water uptake), dec aldosterone
low osmolarity
ADH, renin, aldosterone
ADH decrease (dec in water uptake)–> dec in blood volume–> renin inc–> aldosterone release–> inc Na+ uptake–> inc blood volume
Atrial Natriuretic Peptide
- opposite effects of aldosterone
- produced by heart muscle
- targets distal tubules to dec Na+ reabsorption, and inc Na+ excretion
- inc GFR
- inhibits ADH, renin, and aldosterone release
- inc Na+ ecretion from gills
steroid mode of action
- pass through cell membrane
- bind to intracellular receptor
- hormone/receptor complex moves into nucleus
- interacts with specific DNA sequences
- steroid hormones are slower acting than protein hormones
aldosterone mode of action
inc rates of synthesis of mRNAs which are used for certain transport enzymes participating in Na+ uptake
de-amination
when AA is metabolized
- the amino group (NH2) is removed and forms ammonia (NH3)–> NH4+ (ammonium ion= toxic)
transamination
when an amino group is transferred to another AA
- usually transferred to glutamate which is then converted to glutamine (which is deaminated in kidney or gills and ammonia is liberated)
forms of nitrogen excretion
1) ammonia
2) urea
3) uric acid
ammoniotelic
- animals use ammonia
- NH3 (NH4+)
- NH4+ is very toxic, and extremely soluble in water
- formed by deamination of proteins and AA
- used by animals with access to lots of water
Ureotelic
- urea
- less toxic
- quite soluble
- readily diffuses across membranes
- synthesis via urea cycle
- animals with more of problem with water balance will use this and get by with less water loss
uricotelic
- uric acid
- only slightly soluble in water
- pathway for purine synthesis
- metabolized by some to allantoin and allantoic acid
- used by animals in very dry habitats
ammoniotelic disadvantages
-NH4+ is very toxic
- only lose 1 Na
ammoniotelic advantages
- very soluble in water
- no eleborate pathways requires
- no energy is required to produce NH4+
uriotelic disadvantages
- needs extra pathways and enzymes for its synthesis
- takes 3 ATPs per 1 molecule synthesized
- lose 1 carbon atom
ureotelic advantage
- less toxic
- removal of 2N–> for same inc in osmolarity, you get rid of twice as much
uricotelic disadvantages
- lots of pathways involved
- high amount of energy expenditure
- 4-5 ATPs/uric acid molecules
- loss of 5 carbons
Uricotelic advantages
- insoluble–> aniimals can get rid of N2 excretion products without losing much water
- less toxic than even urea
- removal of 4 N groups
- won’t contribute to osmolarity concentration
determining factors of excretion method
- water availability
- embryonic factors: animals that excrete uric acid produce a cleidoic egg; embryos are isolated and build up of uric acid can be tolerates, can be metabolized by some organisms into allantoin and allantoic acid
- diet
- life stage
ammoniotelic animals
- FW and SW invertebrate
- FW and SW teleosts
Ureotelic animals
- mammals
- elasmobranch fishes
- some lungfish release both NH4+ and urea
- amphibians switch from NH4 to urea in developmental process
uricotelic organisms
- terrestrial gastropods
- insects
- squamates (reptile) lizards
- birds
- all with water balance problems
mixed animals
- chelonids (turtles)–> urea and uric acid (some een NH4)
- crocodiles–> ammonia (mostly in water), uric acid
guanotelic animals
- arachnids, scorpions, some ticks
- excrete mainly guanine material
- similar to uric acid (purine), extremely insoluble, very dry
