Chapter 44

Osmoregulation and Excretion

Fig. 44-2

Selectively permeablemembrane

Net water flow

Hyperosmotic side Hypoosmotic side

Water

Solutes

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 gland

• Sea snake- sublingual gland• Crocodile- lacrimal gland• Fish gills- chloride cells• Shark- rectal gland

Salt Excretion in Birds

Nitrogenous Waste Excretion

• Ammonia- toxic- Excrete directly into water- jellies- Detoxifyurea

• Urea- need lots of water to get rid of• Uric Acid- birds & reptiles

- more costly to produce than urea, but needs less water to be removed

Strategies to remove Nitrogenous Waste

• Osmoconformer: isoosmotic

• Osmoregulator: hyper-, hypo-,

ureoosmotic

• Euryhaline: wide tolerance range

• Stenohaline: narrow tolerance range

Balancing NaCl in Blood

Osmols- total solute concentration in moles of solute/liter of solution

Osmols- total solute concentration in moles of solute/liter of solution

Marine Fish: hypoosmotic

H2O continually leaves body

continually drinks seawater

excretes salt through gills produces small

amts of dilute urine

Less salt than external

environment

Freshwater Fish: hyperosmotic

H2O continually enters body

does not drinks water

produces large amts of dilute urine

More salt than external

environment

Shark and Coelacanth: ureoosmotic

Maintains high levels of urea and TMAO in blood

excretes salt through rectal gland

coelacanth Rana cancrivora

Hagfish: ionosmotic

nonregulator

Seawater concentration = internal concentration

Osmolarity- measure of total solutes(dissolved particles)

Ions FW m osmol/l SW m osmol/lNa+ 1 470 Cl- 1 550Ca++ variable 10 Total 10 1000

Osmolarity in Freshwater and Saltwater

  Habitat Na+ Cl- Urea

seawater sw 478 558  

hagfish (Myxine) sw 537 542  

lamprey fw 120 96  

Goldfish (Carassius) fw 115 107  

Toadfish (Opsanus) sw 160    

Crab-eating frog (Rana) sw 252 227 350

Dogfish sw 287 240 354

freshwater ray fw 150 149 <1

coelacanth sw 197 199 350

Adaptations to Dry Environment

• Many desert animals don’t drink water

• Kangaroo 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