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Chapter 44. Osmoregulation and Excretion. Overview: A Balancing Act. Physiological systems of animals operate in a fluid environment Relative concentrations of water and solutes must be maintained within fairly narrow limits Osmoregulation: Regulates solute concentrations, and

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Chapter 44

Chapter 44

Osmoregulation and Excretion


Overview a balancing act
Overview: A Balancing Act

  • Physiological systems of animals operate in a fluid environment

  • Relative concentrations of water and solutes must be maintained within fairly narrow limits

  • Osmoregulation:

    • Regulates solute concentrations, and

    • alances the gain and loss of water



Fig. 44-1 and conserve solutes


Concept 44 1 osmoregulation balances the uptake and loss of water and solutes
Concept 44.1: Osmoregulation balances the uptake and loss of water and solutes

  • Osmoregulation is based largely on:

    • Controlled movement of solutes between internal fluids and the external environment


Osmosis and osmolarity
Osmosis and Osmolarity water and solutes

  • Cells require a balance between osmotic gain and loss of water

  • Osmolarity:

    • The solute concentration of a solution

    • Determines the movement of water across a selectively permeable membrane

  • If two solutions are isoosmotic, the movement of water is equal in both directions

  • If two solutions differ in osmolarity, the net flow of water is from the hypoosmotic to the hyperosmotic solution


Fig. 44-2 water and solutes

Selectively permeable

membrane

Solutes

Net water flow

Water

Hypoosmotic side

Hyperosmotic side


Osmotic challenges
Osmotic Challenges water and solutes

  • Osmoconformers:

    • Consist only of some marine animals

    • Are isoosmotic with their surroundings

    • Do not regulate their osmolarity

  • Osmoregulators:

    • Expend energy to control water uptake &loss in a hyperosmotic or hypoosmotic environment


  • Stenohaline water and solutesanimals:

    • They cannot tolerate substantial changes in external osmolarity

    • Most animals are stenohaline

  • Euryhaline:

    • Animals can survive large fluctuations in external osmolarity


Fig. 44-3 water and solutes


Marine animals
Marine Animals water and solutes

  • Most marine invertebrates are osmoconformers

  • Most marine vertebrates & some invertebrates are osmoregulators

  • Marine bony fishes are hypoosmotic to sea water

  • They lose water by osmosis and gain salt by diffusion and from food

  • They balance water loss by drinking seawater and excreting salts


Fig. 44-4 water and solutes

Gain of water and

salt ions from food

Osmotic water

loss through gills

and other parts

of body surface

Uptake of water and

some ions in food

Excretion

of salt ions

from gills

Uptake

of salt ions

by gills

Osmotic water

gain through gills

and other parts

of body surface

Gain of water

and salt ions from

drinking seawater

Excretion of salt ions and

small amounts of water in

scanty urine from kidneys

Excretion of large

amounts of water in

dilute urine from kidneys

(a) Osmoregulation in a saltwater fish

(b) Osmoregulation in a freshwater fish


Fig. 44-4a water and solutes

Excretion

of salt ions

from gills

Osmotic water

loss through gills

and other parts

of body surface

Gain of water and

salt ions from food

Gain of water

and salt ions from

drinking seawater

Excretion of salt ions and

small amounts of water in

scanty urine from kidneys

(a) Osmoregulation in a saltwater fish


Freshwater animals
Freshwater Animals water and solutes

  • Freshwater animals constantly take in water by:

    • Osmosis (from their hypoosmotic environment)

  • They lose salts by:

    • Diffusion

  • They maintain water balance by:

    • Excreting large amounts of dilute urine

  • Salts lost by diffusion are replaced by:

    • Foods

    • Uptake across the gills


Fig. 44-4b water and solutes

Osmotic water

gain through gills

and other parts

of body surface

Uptake of water and

some ions in food

Uptake

of salt ions

by gills

Excretion of large

amounts of water in

dilute urine from kidneys

(b) Osmoregulation in a freshwater fish


Animals that live in temporary waters
Animals That Live in Temporary Waters water and solutes

  • Some aquatic invertebrates in temporary ponds:

    • Lose almost all their body water, and

    • Survive in a dormant state

  • This adaptation is called:

    • Anhydrobiosis


Fig. 44-5 water and solutes

100 µm

100 µm

(b) Dehydrated

tardigrade

(a) Hydrated tardigrade


Land animals
Land Animals water and solutes

  • Land animals manage water budgets by:

    • Drinking and eating moist foods, and

    • Using metabolic water

  • Desert animals get major water savings from:

    • Simple anatomical features, and

    • Behaviors such as a nocturnal life style


Fig. 44-6 water and solutes

Water

balance in a

kangaroo rat

(2 mL/day)

Water

balance in

a human

(2,500 mL/day)

Ingested

in food (0.2)

Ingested

in food (750)

Ingested

in liquid (1,500)

Water

gain

(mL)

Derived from

metabolism (250)

Derived from

metabolism (1.8)

Feces (0.09)

Feces (100)

Water

loss

(mL)

Urine

(1,500)

Urine

(0.45)

Evaporation (1.46)

Evaporation (900)


Fig. 44-6a water and solutes

Water

balance in a

kangaroo rat

(2 mL/day)

Water

balance in

a human

(2,500 mL/day)

Ingested

in food (0.2)

Ingested

in food (750)

Ingested

in liquid (1,500)

Water

gain

(mL)

Derived from

metabolism (250)

Derived from

metabolism (1.8)


Fig. 44-6b water and solutes

Water

balance in a

kangaroo rat

(2 mL/day)

Water

balance in

a human

(2,500 mL/day)

Feces (0.09)

Feces (100)

Water

loss

(mL)

Urine

(1,500)

Urine

(0.45)

Evaporation (900)

Evaporation (1.46)


Energetics of osmoregulation
Energetics of Osmoregulation water and solutes

  • Osmoregulators must expend energy to maintain osmotic gradients


Transport epithelia in osmoregulation
Transport Epithelia in Osmoregulation water and solutes

  • Animals regulate the composition of body fluid that bathes their cells

  • Transport epithelia:

    • Are specialized epithelial cells that regulate solute movement

    • Are essential components of:

      • Osmotic regulation, and

      • Metabolic waste disposal

    • Are arranged in complex tubular networks

  • An example is in:

    • Salt glands of marine birds, which

    • Remove excess NaCl from the blood


Fig. 44-7 water and solutes

EXPERIMENT

Nasal salt

gland

Ducts

Nostril

with salt

secretions


Fig. 44-8 water and solutes

Vein

Artery

Secretory

tubule

Secretory

cell

Salt gland

Capillary

Secretory tubule

Transport

epithelium

NaCl

NaCl

Direction of

salt movement

Central duct

Blood

flow

Salt secretion

(b)

(a)


An animal s nitrogenous wastes reflect its phylogeny and habitat
An animal’s nitrogenous wastes reflect its phylogeny and habitat

  • The type and quantity of an animal’s waste products may greatly affect its water balance

  • Among the most important wastes:

    • Proteins & nucleic acids breakdown nitrogenous products

  • Toxic ammonia (NH3):

    • Some animals convert toxic ammonia to less toxic compounds prior to excretion


Forms of nitrogenous wastes
Forms of Nitrogenous Wastes habitat

  • Different animals excrete nitrogenous wastes in different forms:

    • Ammonia

    • Urea

    • Uric acid


Fig. 44-9 habitat

Proteins

Nucleic acids

Amino

acids

Nitrogenous

bases

Amino groups

Most aquatic

animals, including

most bony fishes

Mammals, most

amphibians, sharks,

some bony fishes

Many reptiles

(including birds),

insects, land snails

Ammonia

Uric acid

Urea


Fig. 44-9a habitat

Most aquatic

animals, including

most bony fishes

Many reptiles

(including birds),

insects, land snails

Mammals, most

amphibians, sharks,

some bony fishes

Ammonia

Urea

Uric acid


Ammonia
Ammonia habitat

  • Animals that excrete nitrogenous wastes as ammonia:

    • Need lots of water

    • They release ammonia:

      • Across the whole body surface, or

      • Through gills


Urea habitat

  • The liver of mammals & most adult amphibians:

    • Converts ammonia to less toxic urea

  • The circulatory system carries:

    • Urea to the kidneys

    • The kidneys excrete it

  • Conversion of ammonia to urea:

    • Is energetically expensive

    • Excretion of urea requires less water than ammonia


Uric acid
Uric Acid habitat

  • Uric acid:

    • Mainly excreted by insects, land snails, and many reptiles, including birds

    • Is largely insoluble in water and can be secreted as a paste with little water loss

    • Is more energetically expensive to produce than urea


Concept 44 3 diverse excretory systems are variations on a tubular theme
Concept 44.3: Diverse excretory systems are variations on a tubular theme

  • Excretory systems:

    • Regulate solute movement between internal fluids and the external environment


Excretory processes
Excretory Processes tubular theme

  • Most excretory systems produce urine by refining a filtrate derived from body fluids

  • Key functions of most excretory systems:

    • Filtration: pressure-filtering of body fluids

    • Reabsorption: reclaiming valuable solutes

    • Secretion: adding toxins and other solutes from the body fluids to the filtrate

    • Excretion: removing the filtrate from the system


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