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