Water and Salt Physiology

how does ADH/AVP work

-AVP attaches to vasopressin receptor protein of collecting duct --> cAMP --> protein kinase A --> stimulates insertion of aquaporins in cells of collecting duct -collecting duct collects more water which goes into extracellular fluid

how do salt glands work

-active transport of salt from blood into secretory tubules -released through ducts to nostril, mouth, or orbital

loop of Henle gets water moving

-actively transport one solute into tubule so tubule now was higher osmotic pressure -water comes into tubule by osmosis, which dilutes concentration of other solute in tubule -other solute diffuses into tubule

ADH = AVP

-antidiuretic hormone (arginine vasopressin) conserves water -produced by hypothalamus -secreted from posterior pituitary gland -target tissue - nephron of kidney

single effect in loop of Henle

-ascending loop actively transports NaCl out (impermeable to water) -descending loop loses water to interstitial fluid and gains solutes passively

ANP

-atrial natriuretic peptide secreted in response to high blood pressure -inhibits vasopressin release, renin release, aldosterone release, Na+ reabsorption -enhances fluid and Na+ excretion to lower blood pressuere

freshwater teleost fish

-hyperosmotic (tend to gain water and lose ions); don't need to drink water -gills designed to uptake more Na+ and Cl-

marine shark

-hyperosmotic (unexpected) but hypoionic to sea water -high concentration of urea and TMAO instead of ions -water and ions want to go into shark

amphibians

-hyperosmotic to freshwater (tend to gain water)

reptiles

-hyperosmotic to freshwater; hyposmotic to saltwater

marine teleost fish

-hyposmotic and hypoionic (tendency to lose water and gain ions) -drink seawater

juxtaglomerular cells

-in arterioles leading up to glomerulus -have stretch receptors -if low stretch from low blood pressure, juxtaglomerular cells secrete renin -low blood pressure also inhibits macula densa of distal tubule (wrapped around), which usually inhibits renin -renin raises blood pressure

gill in teleost fish

-involved in gas exchange -involved in ion and waste transport (ions in for freshwater fish, ions out for marine) -special Rh channels to get rid of ammonia -relatively permeable (useful and costly)

antidiuresis

-kidney produces concentrated urine -ADH makes collecting duct permeable to water

diuresis

-kidney produces dilute urine -collecting duct is impermeable to water (no aquaporins)

basic process of kidneys

-makes urine from blood plasma, which contains water, urea (N), ions -urine drains into renal pelvis --> ureter --> urinary bladder --> urethra --> out of body

what is ultrafiltration

-pressure-driven bulk flow of fluid into nephron -creates primary urine

RAAS

-renin-angiotensin II-aldosterone system -renin converts angiotensinogen (produced by liver) to angiotensin I --> angiotensin II -angiotensin II stimulates secretion of vasopressin from pituitary gland (promotes thirst and stimulate constriction of arterioles); higher pressure -angiotensin II promotes aldosterone secretion from adrenal cortex -aldosterone --> reabsorption of Na+ & water and secretion of K+ -makes sure pressure is high enough for filtration system to work

what is primary urine

-water, glucose, salts, urea -no large molecules (filtered out) -blood plasma in glomerulus gets pushed through podocytes (filter) to become primary urine in Bowman's capsule (the crescent thing)

importance of ions (3)

1. affect 3D conformation of enzymes and proteins 2. maintain key electrical gradients across membranes 3. muscle contraction and nerve-impulse transmittion

importance of water (3)

1. affects volume of cells and tissues 2. hydrostatic pressure 3. medium to dissolve ions

parts of kidney (4)

1. cortex 2. medulla 3. renal papilla 4. renal pelvis/ureter

other ways of regulation (2)

1. ionic regulation (maintain constant concentration of inorganic ion) 2. volume regulation (regulation of total amount of water in a body fluid)

obligatory water losses (3)

1. respiratory 2. urinary 3. fecal

all kidneys (3)

1. tubular elements connected to outside 2. produce and eliminate aqu. solution derived from body fluids 3. regulate composition and volume of body fluid via excretion of solutes and water

glomerular filtration rate

GFR = Kf(PGC- PBS - πGC) Kf - filtration coefficient PGC - Glomerular capillary blood pressure PBS - Bowman's capsule hydrostatic pressure πGC - Colloid osmotic pressure

freshwater animals have U/P ration

U/P < 1 (dilute urine to get rid of excess water that it took on)

freshwater teleost fish U/P ratio

U/P < 1 (dilute urine to get rid of excess water that was gained by osmosis)

U/P ratio of amphibians

U/P < 1 (dilute urine); has glomerulus and distal tubule (generalized vertebrate nephron w/ intermediate segment); excretes urea;

U/P ratio for reptiles

U/P < 1 or =1; classic aquatic vertebrate kidney w/o intermediate segment; excrete semisolid uric acid into cloaca

marine teleost fish has U/P ratio

U/P = 1 (get rid of excess salts from gills)

marine shark U/P ratio

U/P ratio < 1 (secrete excess salts that diffuse in bc hypoionic and rectal gland secretes salty feces)

how can marine teleost fish drink seawater and not get dehydrated

active transport of Cl- and Na+ out of gills

types of urine

ammonia, urea, uric acid

countercurrent multiplication

bc fluid flows from descending limb to ascending limb, bottom of loop is more concentrated than top (vertical osmotic gradient)

animals in dryer environment are ______ at concentrating urine

better

osmotic conformity

blood osmotic pressure = osmotic pressure of the environmental water (on the isosmotic line)

types of fluids

blood plasma --> endothelium of blood capillary --> interstitial fluid --> cell membrane --> intracellular fluid

humidity is

content of water in the air

if you have glomerulus, you have

distal tubule (impermeable to water)

tonicity vs. osmoticity

focus on movement vs. focus on pressure

hyperosmotic regulators tend to

gain water by osmosis and lose ions by diffusion; actively gain ions through gills

where does filtration occur

glomerulus

path through kidney

glomerulus/Bowman's capsule --> proximal tubule --> loop of Henle --> distal convoluted tubule --> collecting duct

if you are more effective at water conservation, you will have a

higher relative rate of metabolic water production

all freshwater animals are

hyperosmotic regulators (fish has higher osmotic pressure, likely to take on water)

where are nephrons

in the renal medulla (under renal cortex)

what regulates blood plasma composition

kidneys (remove water, salts, and other solutes)

osmoregulation

maintenance of a near constant osmotic pressure in blood plasma

importance of body fluids in blue crabs

make crab bigger so it creates a larger shell to grow into

how to survive in arid environment

make hyperosmotic urine (U/P > 1) to retain water and secrete solutes (very concentrated urine!!)

salinity is the

measure of total concentration of all salts (<0.5 g/kg in freshwater; 0.5-15 mOsm)

thickness of _______ determines ability to concentrate urine

medulla (thicker medulla --> more concentrated; related to length of loop of Henle)

osmotic pressure is

minimum pressure applied to a solution to prevent the inward flow of water across a semipermeable membrane (tendency of a solution to take in water by osmosis; think: hyposmotic; hypo = low; low tendency to take on water)

osmotic U/P ratio

osmotic pressure of urine/osmotic pressure of plasma (represents relative osmoticity of URINE: isosmotic=1; hyperosmotic>1; hyposmotic<1)

preformed water vs. metabolic water

preformed is taken in from diet; metabolic is produced from metabolism

U/P ratio

ratio of urine to blood plasma composition

what if you can't concentrate salt in urine?

salt glands

turnover rate and body size

smaller animals have higher turnover %

colloid osmotic pressure

solutes in blood plasma that can't get into Bowman's capsule --> osmotic pressure for water to flow out Bowman's

do marine fish have glomerulus

some do, some don't (don't really need to filter blood to make dilute urine bc U/P = 1) -even w/ distal tubule, no intermediate segment

podocytes

specialized cells in cell wall of Bowman's capsule

osmosis is the

spontaneous net movement of solvent through a membrane into a region of higher solute concentration

bigger animals (body weight) have _______ medulla

thinner (related by max U/P ratio)

U/P >1

urine has higher osmotic pressure than blood plasma (didn't kick out water; kicked out solutes)

U/P <1

urine has lower osmotic pressure that blood plasma (kicked out water; didn't kick out solutes)

bigger animal (body weight) is ______ at concentrating urine

worse (lower max U/P ratio)

do freshwater fish have glomerulus in nephron of kidney

yes; used to filter blood --> produce more dilute urine (U/P < 1); intermediate segment

evaporation rate

𝐽=𝐾 (𝑊𝑉𝑃𝑠−𝑊𝑉𝑃𝑎)/𝑋 J = evaporation rate K = permeability of integument to water X = distance btw water vapor pressure of solution & atmosphere -proportional to difference in water vapor pressure