Evolving for Harsh Ocean Conditions Surviving extreme temperatures, pressures, and salinity

Water and Electrolyte Regulation How do organisms respond to changes between salt water, fresh water and terrestrial environments?

I. Background on Solutions Solution is a liquid (solvent) with a solid (solute) dissolved in it. Semipermeable membrane: allows certain molecules through (water, gas) while preventing the movement of others (solutes, salt, glucose) Osmosis is movement of water from high concentration to low concentration, across a semipermeable membrane

Active transport and facilitate diffusion are needed for solutes to pass across semipermeable membranes Organisms tend to maintain homeostasis. Semipermeable membranes keep body fluids of marine organisms separated from seawater and participates in vital exchange processes

Measurements –Measured as conductivity (µS/cm, microsiemens), often expressed as parts per thousand solute. –Osmotic pressure: force that must be applied to a side of a semipermeable membrane to prevent water flow to that side. –Osmolarity: # of osmoles in a solution. –Osmoles: Moles of solute in a solution that contribute to its tonicity. –Tonicity: a measure of the ability of a solution to exert pressure on a membrane

Categories of tonicity –Isotonic or isoosmotic Equal osmolarity on both sides a of a semipermeable membrane –Hypertonic or hyperosmotic High osmolarity, high salinity Water moves across semipermeable membrane into hypertonicity Results in cells loosing water and shrinking as they loose water (cells undergo crenation, or scalloping of membrane) –Hypotonic or hypoosmotic Low osmolarity, low salinity Water moves away from hypotonicity, toward hypertonicity Results in cells explanding as they fill with water, and possible lysis

II. Salinity Categories Brine is >50 0/00 S –(1L of sea water contains >50g salts) Sea water is /00 S Brackish water range /00 S Freshwater is <0.5 0/00 S

III. Water and Salt Effects and Balance Osmoconformers- These organisms are isotonic with the environment. H 2 O loss is equal to H 2 O gained. –These organisms are stenohaline: having limited tolerance to salinity changes. Greek: stenos = narrow, close. Halos = salt

Osmoregulators- despite external salinities, they maintain homeostasis by using osmoregluatory mechanisms –These organisms are euryhaline and can tolerate a wide range of salt concentrations –Many can move between sea and freshwater (esturine organisms) ex. Salmon Greek: Eurys = wide. Halos = salt

Osmoregulatory Mechanisms –Body fluids are 18 0/00 S –In seawater H 2 O loss by osmosis (scales help reduce this) Organism drinks seawater Salt is excreted by chloride cells in gills (active transport) Kidneys produce small quantities of salty urine –In freshwater H 2 O gain by osmosis (scales help reduce this) Salt absorbed by chloride cells in gills (active transport) Kidneys produce large volumes of dilute urine

IV. Kidney Basics The greatest water and electrolyte regulator Kidney has two layers –Outer cortex Contains proximal and distal convoluted tubules –Inner medulla Contains Henle’s loop and collecting ducts

Nephron is the basic functional unit of a kidney –Has two components Circulatory tubular –Carries out 3 processes (filtration, absorption, and secretion) 1. Filtration –Blood is filtered –Plasma proteins remain in blood 2. Absorption –From lumen of tubual –Reabsorbed by blood (not all)

–Tubular substance holds back large molecules that will not pass via gradient alone. They need factilitated diffusion, which is not available. –Driving force out of capillary into tubule is blood pressure~50mm Hg –Net filtration pressure~8mm Hg –Driving force into capillary »Plasmic osmotic pressure -non-filterable protein ~32mm Hg »Tubular pressure -tubular pressure ~10mm Hg

Glomerular filtrate is the stuff filtered which filtrate is formed is directly proportional to filtrate pressure The length, or presence, of Henle’s loop is dependent on a species water/salt retention needs.

3. Tubular secretion –Important in urine formation –Transport mechanism becomes saturated from too much of a particular solute and are secreted

–Excess H 2 O Increased urine production –Pale colored with high water content (dilute) Increases blood volume  stroke volume  cardiac output  mean arterial pressure  blood glomerulus  filtration pressure  urine production

–Lack of H 2 O Decreased production of normal urine (is concentrated) Decreases blood volume  stroke volume  cardiac output  mean arterial pressure  blood glomerulus  filtration pressure  filtrate formed  urine production Blood osmolarity increases (plasma osmolarity increases) –Detected by neurosecretory cells of hypothalamus »When stimulated, manufacture a chemical called vasopressin (ADH, Antidiuretic hormone, in most mammals) -Makes collecting ducts more permeable to H 2 O *More H 2 O moves from collecting ducts to inner medulla >small amounts of concentrated urine are produced

Excess salt –  Na +  plasma osmolarity  blood volume…. Lack of salt –  Na +  plasma osmolarity  blood volume Triggers secretion of aldosterone *increases absorption of Na + and H 2 tubule *increases secretion of K + into blood. None is filtered into tubule -  K +  alsosterone secretion  stimulates tubules to add K + to filtrate  K + Is removed in urine  aldosterone caused retention of salt and water while promoting potassium excretion. FYI: Aldosterone receptor blockers are used to treat low blood pressure

Osmoregulation summary

V. Summary Applications Freshwater problems –Water gain –Solute loss Seawater problems –Water loss –Solute gain

Birds and reptiles –Small glomerulus, less filtration, small amounts of concentrated urine Freshwater fish and amphibians –Large glomerulus, no loop of Henle, large amounts of dilute urine Marine mammals –Very small or absent glomerulus, no loop of Henle, very small amounts of urine Sharks –Countercurrent flow in loops to concentrate salts, which are excreted as a hypertonic solution via rectal gland Marine birds and reptiles –Nasal salt glands, hypertonic secretions (like tears) via counter-current multiplier mechanism

Marine fishes –Nephron formation –Urea retention increases osmolarity to decrease water problems –Osmoconformers have no regulatory mechanisms –Osmoregulators have active transport of Na + and Cl - Chloride cells in gills (active transport of salt)

Mollusks and crustaceans –Green glands are tubular structures and the base of antennae Filtration Absorption secretion