Excretion - Salt & Water Balance Organs involved in...

Info iconThis preview shows pages 1–7. Sign up to view the full content.

View Full Document Right Arrow Icon
Organs involved in maintaining water and salt balance also include excretion of nitrogenous wastes as part of their normal function
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Gains and losses of water and salts must be balanced by animals; that is, the volume and concentration of gains must equal that of losses (homeostasis, remember?) The environment in which an animal lives determines the types of challenges that must be met to maintain water & salt balance (a fish living in a lake has quite a different problem compared to a lizard living in the desert, for example). Excretory organs (kidneys and other organs) function to maintain constant water and salt content in the body, as well as serving as a route for excreting nitrogenous wastes.
Background image of page 2
Fish face different challenges in fresh and salt water Gain of water and salt ions from food and by drinking seawater Osmotic water loss through gills and other parts of body surface Excretion of salt ions from gills Excretion of salt ions and small amounts of water in scanty urine from kidneys Uptake of water and some ions in food Osmotic water gain through gills and other parts of body surface Uptake of salt ions by gills Excretion of large amounts of water in dilute urine from kidneys Freshwater fish Marine Fish No salt! Dilute medium Lots of salt! Concentrated medium
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Terrestrial Animals Water balance in a human (2,500 mL/day = 100%) Water balance in a kangaroo rat (2 mL/day = 100%) Ingested in food (0.2) Ingested in food (750) Ingested in liquid (1,500) Derived from metabolism (250) Derived from metabolism (1.8) Water gain Feces (0.9) Urine (0.45) Evaporation (1.46) Feces (100) Urine (1,500) Evaporation (900) Water loss Kangaroo rats live in a water poor environment, their water ration is in food (some individuals may never even drink water throughout their lifetime!) In contrast, humans must live in environments where fresh water is abundant.
Background image of page 4
Transport of solutes Water cannot be transported, rather water movement follows osmotic gradients (from low to high solute concentration). The fluid generated by excretory organs is urine. Urine is formed by a two- step process: 1) Filtration-bulk flow of interstitial fluids into a tubule; this fluid is very similar in composition to body fluids except for large molecules 2) Secretion/resorption-the filtrate is modified by active transport of solutes into/from the filtrate as it travels through the excretory tubule so that a highly modified urine is ultimately released. This two-step system is quite flexible, for example allowing desert animals to conserve water while excreting salts, and fresh water animals to eliminate excess water while retaining salts.
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Most animals live in water Most animal life on this planet lives in the ocean. To simplify their water and salt balance issues, their body fluids are the same concentration ( iso-osmotic ) as the surrounding seawater (hence, no net water movement!). This is not possible for freshwater critters, who are saltier than the surrounding
Background image of page 6
Image of page 7
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 05/23/2011 for the course BIOLOGY 1520 taught by Professor Davidgarton during the Fall '09 term at Georgia Tech.

Page1 / 36

Excretion - Salt & Water Balance Organs involved in...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online