Name and describe three osmoregulatory- excretory structures seen in animals?

Answer 1

Functions

* Osmoregulation - Maintenance of the internal fluid composition of the cells (water and dissolved components, especially ions) relative to its environment.
o Evolutionarily, this was the primary function of the system and is still a major function in aquatic animals.
* Waste Removal - Of dissolved wastes, especially nitrogen containing (nitogenous) compounds.
o In more advanced animals, the waste removal function of the excretory system results in an interdependent relationship with the circulatory system.

Osmotic Balance

* Osmosis - In living organisms, refers to the diffusion of water across a semi-permeable membrane.
* The rate of osmosis is strongly affected by the concentration gradient of water inside and outside the cell.
* Relative concentrations of dissolved substances (hypertonic, higher - hypotonic, lower) affects gradient.
* For any aquatic animal it is important to maintain a balance between the dissolved substances ("salts") and water concentrations within the cell vs. outside.
* This does NOT necessarily mean equilibrium, ie. isotonic conditions where molecules move randomly across cell membrane in both directions.
* In order to maintain an osmotic balance, a system of pumping H2O and salts must be developed.
* Earliest development of excretory system.
* The earliest structure involved with osmoregulation is found in animal-like Protista and freshwater members of the P.Porifera. It is the contractile vacuole. Freshwater implies that the salt concentration is LOWER than the organisms that live there (ie the environment is HYPOTONIC to the organisms.
* Cytoplasmic "bubble" with muscle filaments that squeeze excess water out.
* Osmoconformers - aquatic animals whose body fluid composition is essentially isotonic with environment.
* Includes most oceanic invertebrate groups, and the hagfishes of the vertebrates.
* In the cases of the P.Cnidaria and Echinodermata, there is NO osmoregulatory/excretory system.
* Although osmoconformers, many invertebrates are able to regulate their ion balances to maintain isotonicity.
* Osmoconformers are very limited in the range of conditions that they can withstand and so typically exhibit narrower ranges of living conditions.
* Osmoregulator - an animal able to maintain an ideal salt to H2O balance in the cells regardless of environmental conditions.
* Includes most aquatic vertebrates and coastal invertebrates.
* Coastal invertebrates need to osmoregulate because of often rapid changing in water salinities.
* Osmoregulators expend energy to actively pump H2O and salts into and out of the body.
* Freshwater osmoregulators are typically hypertonic (hyperosmotic) to the environment and must pump large amounts of H2O out of the body.
* Salt water animals are usually hypotonic (hypoosmotic) to their surroundings and must drink water and eliminate excess salts.
* Terrestrial animals have developed various systems that conserve water and important salts. Their diet and metabolism also play important roles in H2O conservation.
* It is possible for some osmoregulators to shift from salt water to fresh and back.
* This must be done slowly to allow acclimation, shifts in physiology to accomodate different osmotic conditions.
* Many fishes exhibit diadromy, a migration from one osmotic environment to another in order to reproduce. Two types:
o Anadromy - Fishes that move from salt water to fresh to reproduce, e.g. salmon
o Catadromy - Fishes that move from fresh to salt water to reproduce, e.g. eels.

Liquid Waste Production

* During the breakdown of proteins, amino acids are further broken down by deamination, the removal of the amine (NH2) functional group.
* This combines with a hydrogen ion to form NH3+, ammonia, which is highly toxic to cells.
* There are 3 potential fates for ammonia produced by metabolism:
1. Transport in dilute solution form and excrete as liquid.
2. Conversion to urea, a larger, less toxic molecule which can be stored or transported and excreted as a liquid or paste.
3. Conversion to uric acid, a very large stable molecule. Excrete as a paste or crystal.
* The progression from #1 to 3 above involves more energy expenditure, but less H2O.
* Urine - A liquid composite of #1 to 3, PLUS dissolved proteins, ions and other metabolites.

Excretory Systems

* P.Porifera, Cnidaria, Echinodermata - no systems of any kind, nitrogenous wastes released as ammonia via diffusion.
* P. Platyhelminthes - Excretory system of protonephridia.
o AKA "flame cells", flagellated cells draw wastes/fluids across membrane and discharge to outside via nephridiopores.
o Primarily an osmoregulatory system.
o Wastes removed by diffusion.
* P.Nematoda - Special glandular cells, (renette cells/glands) release excretory wastes to outside.
o AKA "lateral lines"; the gland shape and location of excretory pore is of taxonomic significance.
* P. Mollusca - Metanephridium is the basic osmoregulatory/excretory structure.
o Ciliated funnel that drains coelom.
* P.Arthropoda - For aquatic forms, the system is glandular (antennal or green glands, coxal glands).
o The glands act as a filtering device, extracting wastes and fluids from blood.
o Needed salts are reabsorbed along the tubule leading to external opening.
o Terrestrial forms have a system of Malpighian tubules(MT).
o The MT consists of a series of tubes surrounding and opening into the intestine.
o Secretion of K+ ions into the tubule sets up a pressure gradient that drags H2O, uric acid, ions and other molecules into the tubules.
o Most H2O and K+ is reabsorbed by special glands near the rectum.
o Uric acid is excreted in crystalline form or a very thick paste (conservation of H2O).
* P. Annelida - System consists of many nephridia.
o Ciliated funnels draining the coelom as in molluscs (metanephridial structure), but tubules are intertwined with blood vessel and extract wastes from the blood as well.
* P.Chordata, S.p Vertebrata - Possess the nephric kidney.
o The basic unit of the kidney is the nephron, which is a filter through which substances are forced by blood pressure.
o About 2,000,000 nephrons in human kidneys!
o There are three stages to nephric function:
1. Filtration - Various substances in blood are forced into nephron from blood vessels.
+ About 180 liters of fluid per day enter nephrons, almost 99% is recovered!
2. Reabsorption and Secretion - Occurs in several parts of the nephron. Needed substances plus water that were forced into the nephron are pumped bak into blood vessels, and some other substances mainly salts, dialyse into the nephron in this region.
3. Excretion - Nephrons empty urine into collecting tubules, which eventually pass the urine to the muscular bladder, which forces urine outside the body by muscle contraction.

Excretion in Vertebrates

* Freshwater fishes - do not reabsorb water in kidneys. Produce large amounts of dilute urine. Absorb salts at the gills.
* Saltwater fishes - Drink water and pump out excess salts at gills or via special glands.
* Amphibians - Similar to freshwater fishes.
* Reptiles - Freshwater are like fishes and amphibians.
o Marine - possess special salt glands that excrete excess salt, usually duct to eyes.
o Terrestrial - Kidney reabsorbs large amounts of water to avoid dehydration. Excreta is usually almost dry.
* Birds and Mammals - Urine is highly concentrate.
o Like reptiles, marine birds may have special salt glands to excrete excess salts. However, the glands are usually associated with the nasal openings.

Answer 2

7abebty, Alby w Rou7e we can't describe our mothers in only three words, we can wirte a book and we won't finish the describing of our mothers. We never can't give the love, the care etc. to our mothers back.

Answer 3

the nephron, the ureter, the urethra, the sweat gland

;-)