Chapter 44Osmoregulation and Excretion

Fig. 44-2Selectively permeablemembraneNet water flowHyperosmotic sideHypoosmotic sideWaterSolutes

Osmoregulation- the control of the concentration of body fluids.

Diffusion- movement of substance from an area of greater concentration to an area of lower concentration

Osmosis- diffusion of water through a semipermeable membrane

Adaptation to Marine EnvironmentReducing salt

Seabird and marine iguana- nasal salt secreting glandSea snake- sublingual glandCrocodile- lacrimal glandFish gills- chloride cellsShark- rectal gland

Salt Excretion in Birds

Nitrogenous Waste ExcretionAmmonia- toxicExcrete directly into water- jelliesDetoxifyureaUrea- need lots of water to get rid ofUric Acid- birds & reptilesmore costly to produce than urea, but needs less water to be removed

Strategies to remove Nitrogenous Waste

Osmoconformer: isoosmoticOsmoregulator: hyper-, hypo-, ureoosmotic Euryhaline: wide tolerance rangeStenohaline: narrow tolerance rangeBalancing NaCl in BloodOsmols- total solute concentration in moles of solute/liter of solution

Marine Fish: hypoosmoticH2O continually leaves bodycontinually drinks seawaterexcretes salt through gillsproduces small amts of dilute urineLess salt than external environment

Freshwater Fish: hyperosmoticH2O continually enters bodydoes not drinks waterproduces large amts of dilute urineMore salt than external environment

Shark and Coelacanth: ureoosmoticMaintains high levels of urea and TMAO in bloodexcretes salt through rectal glandcoelacanthRana cancrivora

Hagfish: ionosmoticnonregulatorSeawater concentration = internal concentration

Osmolarity- measure of total solutes(dissolved particles)

IonsFW m osmol/l SW m osmol/lNa+1470 Cl-1550Ca++ variable10 Total101000

Osmolarity in Freshwater and Saltwater

Adaptations to Dry Environment

Many desert animals dont drink waterKangaroo rats lose so little water that they can recover 90% of the loss from metabolic water and gain the remaining 10% in their diet of seeds.Also have long loop of Henle

Most excretory systems produce a filtrate by pressure-filtering body fluids into tubules.

Flatworms have an excretory system called protonephridia, consisting of a branching network of dead-end tubules.The flame bulb draws water and solutes from the interstitial fluid, through the flame bulb, and into the tubule system. Diverse excretory systems are variations on a tubular theme

Metanephridia consist of internal openings that collect body fluids from the coelom through a ciliated funnel, the nephrostome, and release the fluid through the nephridiopore.Found in most annelids, each segment of a worm has a pair of metanephridia.

Insects and other terrestrial arthropods have organs called Malpighian tubules that remove nitrogenous wastes and also function in osmoregulation.These open into the digestive system and dead-end at tips that are immersed in the hemolymph.

Nephron

Hormonal Control via Negative Feedback

Fig. 18.16Regulation of Aldosterone secretion by renin-angiotensin-aldosterone (RAA) pathway

Moment of Zen