Homeostasis - General Zoology - Lecture Slides, Slides for Zoology. Alagappa University

Zoology

Description: Homeostasis, Osmoregulation, Excretion, Osmosis, Osmoconformers, Osmotic Challenges, Osmoregulators, Hyperosmotic, Osmotic Regulation, Stenohaline, Hypoosmotic Regulators. Above mentioned terms and points represent this lecture of general zoology course. A full series of lectures can be found in my documents.
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Homeostasis

Homeostasis

Homeostasis refers to maintaining internal stability within an organism and returning to a particular stable state after a fluctuation.

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Homeostasis

 Changes to the internal environment come from:  Metabolic activities require a supply of

materials (oxygen, nutrients, salts, etc) that must be replenished.

 Waste products are produced that must be expelled.

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Homeostasis

 Systems within an organism function in an integrated way to maintain a constant internal environment around a setpoint.  Small deviations in pH, temperature,

osmotic pressure, glucose levels, & oxygen levels activate physiological mechanisms to return that variable to its setpoint.  Negative feedback

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Osmoregulation & Excretion

Osmoregulation regulates solute concentrations and balances the gain and loss of water.

Excretion gets rid of metabolic wastes.

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Osmosis

 Cells require a balance between osmotic gain and loss of water.

Water uptake and loss are balanced by various mechanisms of osmoregulation in different environments.

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Osmosis

Osmosis is the movement of water across a selectively permeable membrane.  If two solutions that are separated by a

membrane differ in their osmolarity, water will cross the membrane to bring the osmolarity into balance (equal solute concentrations on both sides).

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Osmotic Challenges

Osmoconformers, which are only marine animals, are isoosmotic with their surroundings and do not regulate their osmolarity.

Osmoregulators expend energy to control water uptake and loss in a hyperosmotic or hypoosmotic environment.

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Osmotic Regulation

Most marine invertebrates are osmotic conformers – their bodies have the same salt concentration as the seawater.  The sea is highly stable, so most marine

invertebrates are not exposed to osmotic fluctuations.

 These organisms are restricted to a narrow range of salinity – stenohaline.  Marine spider crab

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Osmotic Regulation

 Conditions along the coasts and in estuaries are often more variable than the open ocean.  Animals must be able to

handle large, often abrupt changes in salinity.

Euryhaline animals can survive a wide range of salinity changes by using osmotic regulation.  Hyperosmotic regulator

(body fluids saltier than water)

 Shore crab.

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Osmotic Regulation

 The problem of dilution is solved by pumping out the excess water as dilute urine.

 The problem of salt loss is compensated for by salt secreting cells in the gills the actively remove ions from the water and move them into the blood.  Requires energy.

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Osmotic Regulation - Freshwater

 Freshwater animals face an even more extreme osmotic difference than those that inhabit estuaries.

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Osmotic Regulation - Freshwater

 Freshwater fishes have skin covered with scales and mucous to keep excess water out.

 Water that enters the body is pumped out by the kidney as very dilute urine.

 Salt absorbing cells in the gills transport salt ions into the blood.

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Osmotic Regulation - Freshwater

 Invertebrates and amphibians also solve these problems in a similar way.

 Amphibians actively absorb salt from the water through their skin.

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Osmotic Regulation – Marine

 Marine bony fishes are hypoosmotic regulators.  Maintain salt concentration at 1/3 that of seawater.  Marine fishes drink seawater to replace water lost by

diffusion.  Excess salt is carried to the gills where salt-secreting cells

transport it out to the sea.  More ions voided in feces or urine.

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Osmotic Regulation – Marine

 Sharks and rays retain urea (a metabolic waste usually excreted in the urine) in their tissues and blood.

 This makes osmolarity of the shark’s blood equal to that of seawater, so water balance is not a problem.

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Osmotic Regulation – Terrestrial

 Terrestrial animals lose water by evaporation from respiratory and body surfaces, excretion (urine), and elimination (feces).

 Water is replaced by drinking water, water in food, and retaining metabolic water.

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Osmotic Regulation – Terrestrial

 The end-product of protein metabolism is ammonia, which is highly toxic.  Fishes can excrete ammonia directly

because there is plenty of water to wash it away.

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Osmotic Regulation – Terrestrial

 Terrestrial animals must convert ammonia to uric acid.  Semi-solid urine – little water loss.  In birds & reptiles, the wastes of developing

embryos are stored as harmless solid crystals.

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Osmotic Regulation – Terrestrial

 Marine birds and turtles have a salt gland capable of excreting highly concentrated salt solution.

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