CH 44 NOTES
Osmoregulation and Excretion
Osmoregulation
Process by which animals control solute concentrations and balance water gain and loss Necessary for systems to function properly Ions must remain at levels to allow muscles, nerves
and body cells to work correctly Essential for Homeostasis
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Uptake vs Loss of Water
Water uptake and loss must balance If water uptake is excessive, animal cells can swell
and burst If water loss is substantial, cells can shrivel and die
(plasmolysis)
Osmosis – passive process by which water enters and leaves cells Occurs when two solutions differ in osmotic pressure
(osmolarity)
Osmolarity
Isoosmotic – two solutions with same osmolarity No net movement of water (still moves, but at equal
rates)
If two solutions differ in osmolarity: Hyperosmotic – solution with more solutes (less
water) Hypoosmotic – solution with less solutes (more water)
Water flows from a hypoosmotic solution to a hyperosmotic one
Osmoconformer
Animal that is isoosmotic with it’s surroundings
Marine AnimalsNo tendency to gain or lose waterLive in water that has a stable composition so
have a constant internal osmolarity
Osmoregulator
Controls internal osmolarity independent of its environment
Animals can live in non-marine environments (fresh water, land) or marine
If they live in a hypoosmotic environment – must be able to get rid of excess water
If they live in a hyperosmotic environment – must take in water
Environmental Changes
Stenohaline – animals that cannot tolerate changes in external osmolarity (most animals)
Euryhaline – animals that can survive large fluctuations in external osmolarity Animals in tidal areas, salmon
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Marine Animals
Most invert marine animals are osmoconformers
Must actively transport solutes to maintain homeostasis
Marine vertebrates and some inverts are osmoregulators Ocean dehydrates these animals (lose water) Balance water loss by drinking lots of seawater and
pump out salts through active transport (gills or kidneys)
Freshwater Animals
Body fluid of freshwater animals is hyperosmotic to the fresh water
Water diffuses IN to the cells and salt leavesThese animals drink almost NO waterUrine is very dilute (lots of water in urine)Salts are replenished by eating
Salmon - live in both environments and change their osmoregulation when they move
Temporary Water
Some animals live in small ponds that dry outEnter a dormant state called Anhydrobiosis
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Terrestrial animals
Animals on land always threatened with dehydration
Body covering reduces water loss Waxy exoskeleton Shells Dead, keratinized skin
Nocturnal – many animals (esp. desert) are active at night to reduce evaporative water loss
All must drink and eat moist foods
Energetics of Osmoregulation
Costs energy to maintain an osmolarity difference with environment
Use active transport to maintain correct solute concentrations needed for homeostasis
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Excretion
Process that gets rid of nitrogenous metabolites and other waste produces
Come from break down of nitrogen containing molecules (like proteins and nucleic acids) that release ammonia – very toxic to cells
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Forms of Nitrogenous Waste
Ammonia Very toxic to cells Can only be tolerated in very small amounts Animals that excrete ammonia must be surrounded by
lots of water Most common in aquatic species Aquatic inverts – release ammonia across body
surface Fish – ammonia lost across gills
Forms of Nitrogenous Waste
Urea Produced in the liver Made by converting ammonia with carbon dioxide Low toxicity Can be transported in circulatory system and stored
safely Animals must expend energy to produce urea Seen in mammals, most amphibs (adults), sharks,
some marine bony fish and turtles
Forms of Nitrogenous Waste
Uric Acid Relatively non toxic Does not dissolve in water Released as semi-solid paste Very little Water lost Needs even MORE energy to make than urea Seen in insects, land snails, many reptiles and birds
Excretory Processes
Urine – Fluid Waste made in four steps1. Filtration - Body fluid comes in contact
with selectively permeable membrane of a transport epithelium. Pressure drives a process where small solutes and water (filtrate) are driven across the epithelium (large molecules stay in body fluid)
2. Reabsorption – Filtrate becomes a waste product after useful molecules are recovered and returned to body fluid by active transport
Excretory Processes
3. Secretion – Non essential solids and wastes, toxins and excess ions are extracted from body fluids into the filtrate
4. Excretion – filtrate (urine) leaves the system and the body
Protonephridia
Network of dead-end tubules connected to the outside
Flame bulbs are at end of each protnephridium
Cilia project into tubules and draw water and solutes from fluid
Filtrate moves through tubules and empties into external environment
Seen in flatworms (no coelom), rotifers
Metanephridia
Open internally to the coelomEach segment has a pair of metanephridia
surrounded by capillariesCilia beat, draw fluid into collecting tubule
with bladderUrine moves through tube and solutes are
reabsorbedWaste is released to outsideSeen in Annelids (earthworms)
Malpighian Tubules
Extend from dead end tips immersed in hemolymph to openings in digestive tract
No filtrationTransport epithelium secretes solutes into
tubuleWater follows by osmosisFluid passes to rectumSolutes pumped back into hemolymphNitrogenous wastes eliminated as dry matter
along with fecesSeen in insects, terrestrial arthropods
Kidneys
Function in osmoregulation and excretionNumerous tubules are highly organized and
associated with capillariesAlso include ducts that carry urine from
tubules out of kidneySeen in vertebrates and some other
chordates
Mammal Excretory System
Kidney – pairedRenal artery – brings blood to kidneyRenal vein – drains blood from kidneyReceives nearly 25% of blood exiting the
heartUreter – urine exits kidney through this tubeUrinary Bladder – storage place for urineUrethra – carries urine to the outside
Kidney Structure
Nephron – functional unit with long tubule and ball of capillaries called a Glomerulus
Bowman’s capsule - surrounds the glomerulus
Filtration of Blood
Occurs as blood pressure forces fluid from blood in the glomerulus into Bowman’s capsule Capillaries are permeable to water and small solutes Impermeable to blood cells and large molecules Filtrate contains salts, glucose, amino acids, vitamins,
nitrogenous wastes, and other small molecules
Path of Filtrate
From Bowman’s capsule to Proximal tubules Recapture ions, water and valuable nutrients. Ammonia is
synthesized and added to filtrate To Descending Loop of Henle
Reabsorb water To Ascending Loop of Henle
Impermeable to water Contains ion channels NaCl is reabsorbed
To Distal Tubule Contributes to pH regulation by controlled secretion of H+ and
reabsorption of HCO3 To Collecting Duct
Reabsorption of water can occur if needed
To Bladder
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