Osmoregulation and Excretion

Osmoregulation and Excretion - Osmoregulation and Excretion...

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Osmoregulation and Excretion Osmoregulation balances the uptake and loss of water and solutes o Osmosis and Osmolarity Regardless of animal’s habitat or N waste product, its water gain must balance water loss. Osmosis is the diffusion of water across a slectively permeable membrane that separates 2 solutions differing in osmolarity (moles of solute per liter) Isoosmotic solutions are equal in osmolarity, and there is no net osmosis in between them. There is a net flow of h20 from a hypoosmotic (more dilute) to a hyperosmotic (more concentrated) solution o Osmotic Challenges Osmoconformers are isoosmotic w/ their surroundings Osmoregulators regulate their internal osmolarity. Must get rid of excess water if they live in a hypoosmotic medium or take in water to offset osmotic loss if they inhabit a hyperosmotic environment. Most animals are stenohaline, able to toleratoe only small changes in external osmolarity. Animals that are euryhaline can survive large differences in the osmotic environment. Most marine invertebrates are osmoconformers, whereas marine vertebrates are osmoregulators. Marine bony fishes are hypoosmotic to seawater Some animals are capable of anhydrobiosis, surviving desiccation, in a dormant state. o Energetics of Osmoregulation Osmoregulation is energetically costly b/c animals must actively transport solutes in order to maintain osmotic gradients needed to gain or lose water. The energy cost is related to the difference in osmolarity between animal and environment. Structure of Mammalian Excretory System o Blood enters each of the pair of bean-shaped kidneys through a renal artery and leaves by way of renal vein. o Urine exits the kidney through a ureter and is temporarily stored in the urinary bladder. Urine exits the body through the urethra o The outer renal cortex and inner renal medulla of the kidney are packed with excretory tubules and blood vessles. o A nephron consists of a long tubule with a cuplike Bowman’s capsule at the blind end that encloses a ball of capillaries called the glomerulus.
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o Filtration of the blood occurs as blood ressure forces water, urea, salts, glucose, amino acids, and other small molecules through the porous capillary walls and specialized capsule cells into Bowman’s capsule, forming the filtrate. o The filtrate passes through the proximal tubule, the loop of Henle (descending limb and ascending limb), and the distal tubule. Collecting ducts receive processed filtrate from many nephrons and
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This note was uploaded on 03/18/2011 for the course BIO 1A taught by Professor Schlissel during the Fall '08 term at University of California, Berkeley.

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Osmoregulation and Excretion - Osmoregulation and Excretion...

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