Osmoregulation - Part 1 (11/12)

What is Osmoregulation?

The process by which an animal controls the concentrations of both water and dissolved molecules in its body

What are electrolytes?

Substances that separate into ions when dissolved in water

What is Osmotic Stress?

When water or electrolyte imbalances disrupt the metabolic processes of the cell

Why can disturbances in water and electrolyte concentrations cause osmotic stress, cell damage, and death?

Hypotonic Environment

• If the cell swells too much due to the intake of water, the cell will explode and die

Hypertonic Environment

• If the cell shrivels up too much, it disrupts the metabolic processes of the cells and the cell dies

How does diffusion work?

What’s needed for Diffusion

1. A concentration gradient of an atom or molecule across a membrane

2. The membrane is permeable to that stom or molecule

THEN it will diffuse across the membrane until the concentration of the atom or molecule is equal on both sides

How does osmosis work?

Wherever there is a concentration gradient, osmosis will occur

• Water flows from the side with high concentration to that of low concentration

• “water follows salt”

What does ‘osmolarity’ mean?

The concentration of all dissolved solutes that can cause osmosis

What does ‘hypertonic’ mean?

The concentration of solutes (stuff dissolved in water) is higher on the outside of the cell

What does ‘hypotonic’ mean?

The concentration of solutes (stuff dissolved in water) is lower on the outside of the cell

What does ‘isotonic’ mean?

The concentration of solutes (stuff dissolved in water) is the same on both sides

How does cell water and electrolyte concentrations change in hypertonic and hypotonic environments?

Hypertonic

• Lose water by Osmosis

• Gain excess electrolytes by diffusion

Hypotonic

• Gain excess water by osmosis

• Lose electrolytes by diffusion

What are osmoregulators?

Animals whose body cells have a different osmolarity than their environment

What are osmoconformers?

Animals whose body cells have the same osmolarity as their surroundings

Which animals fall into osmoregulators or osmoconformers?

Osmoregulators

• All other marine fish that live in seawater aside from osmoconformers

• Freshwater fish

Osmoconformers

• Marine invertebrates and marine fish with cartilage-based skeletons

What are the different osmotic stresses and imbalances that happen in marine and freshwater fish?

Marine

• Live in a high osmolarity (hypertonic) environment

  • Lose water by osmosis

  • Gain excess electrolytes by diffusion

Freshwater

• Live in a low osmolarity (hypotonic) environment

  • Gain excess water by osmosis

  • Lose electrolytes by diffusion

How do marine fish osmoregulate?

Marine - High osmolarity (hypertonic) environment

• Replace water by drinking seawater, produce little urine

  • Drinking adds extra excess electrolytes

    • Excess electrolytes go back to environment through gills

      • Gills have a protein that move salt by active transport

How do freshwater fish osmoregulate?

Freshwater - Low osmolarity (hypotonic) environment

• Get rid of excess water by producing lots of urine, drink very little

  • Lost electrolytes from diffusion are absorbed back into the body through the gills

    • Gills have a protein that moves electrolytes by active transport

How are fish that are able to live in both marine and freshwater environments are able to osmoregulate in both types?

They are able to swap the location of their active transporter (what moves the electrolytes)

• Marine is located on the inside of the gill cells

  • Electrolytes pushed out into water

• Freshwater is located on the outside of the gill cells

  • Electrolytes pulled in from water

What are the different osmotic stresses and imbalances (water and electrolyte losses/gains) in terrestrial animals?

Water Loss

1. Evaporation from respiratory surfaces (ex. lungs) during breathing

2. Evaporation from body surface exposure to air

Electrolyte Loss

• Freshwater sources are hypotonic, so electrolytes are lost in the gut by drinking

• Electrolytes lost in urine

What is retention?

The act of absorbing a substance back into the body before it’s excreted

What is filtration?

Separating the water-based fluid of the body from cells and other large molecules

What is reabsorbtion?

Selectively absorbing the parts of the filtered material that we want to retain

How do insects prevent water loss?

Minimize loss of water:

1. Insects have a thick exoskeleton that is coated in hydrophobic wax

• Chitin minimizes diffusion

• Wax layer blocks evaporation of water from the body

2. Respiratory system can be closed

• Respiratory openings (spiracles) can be closed by small muscles

  • Minimizes water loss from the respiratory system

How do insects perform osmoregulation using the Malpighian tubules?

Malpighian tubules

• “primitive kidneys”

  • Retention

• In direct contact with the insects hemolymph (blood)

• Removes only electrolytes, water, and waste products from the hemolymph by acting as a filter

How do insects perform osmoregulation using the Hindgut?

Hindgut

• Reabsorbs the amount of electrolytes and water that the insect must retain

Malpighian tubule is the filter, hindgut is the reabsorber

• All waste products and any excess water or electrolytes are removed from the body in the feces