Water and salt physiology

What is osmotic pressure

The minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane

Where does water flow

Into areas with higher solute concentration

In two solutions, one with osmolarity of 200 and the other of 500, which direction will water flow for osmosis

Towards the 500

What three types of regulation of the composition of body fluids are possible

1. Osmotic regulation

2. Ionic regulation

3. Volume regulation

What is osmotic regulation

The maintenance of a constant or near constant osmotic pressure in body fluids

What is ionic regulation

The maintenance of constant or near constant concentration of an inorganic ion in a body fluid

What is volume regulation

Regulation of the total amount of water in a body fluid

How do freshwater animals blood osmotic pressures relate to water around them

Their blood osmotic pressures are hyperosmotic to freshwater

A freshwater fish takes on water from the environment. How does htis challenge regulation

• Challenges osmotic regulation as it lowers the osmotic pressure of the blood plasma

• Challenges ionic regulation as it dilutes ions in the blood plasma

• Challenges volume regulation as it increases water volume of body fluids

What do kidneys do

Important role in most animals. Regulate composition of blood plasma by removing water, salts and other solutes in controlled ways

How do gills work for keeping blood stable

Blood regulation for aquatic aniamls

Why are salt glands organs for blood regulation

Important for certain birds, lizards, turtles and othe rreptiles

How can the effect of kidney function in blood composition be analyzed

U/P ratios. Start with blood and produce urine. The output is compared with the input so you compare urine composition to plasma composition

U/P ratio reflects whether urine is isosmotic, hyposmotic, or hyperosmotic to the plasma. How do you know which one?

If the U/P is less than one, the urine is hyposmotic. If they are equal, it is isoosmotic

What does it mean when U/P ratio is less than one

Water is preferentially excreted and solutes are preferentially held back from excretion so plasma osmotic pressure increases

What does it mean when U/P ratio is greater than 1

Water is preferentially held back from excretion and solutes are preferentially excreted so plasma osmotic pressure goes down

How do ionic U/P ratios reflect ion concentrations

They reflect the effect of kidneys on individual ion concentrations. There is an ionic U/P ratio for each ion. Some ions can be preferentially excreted while others are retained

How are kidneys involved in volume regulation

By removing greater or lesser amounts of water. A large volume of urine is produced in response to taking on a large volume of water and vice versa. Volume regulation occurs even when osmotic regulation (Osmotic U/P ratio remains the same)

What are osmolytes

Solutes that can alter the osmotic pressure of a solution

If regulation of cell volume is essential in response to changes in extracellular osmotic pressure, what do cells do

Alter their total content of osmolytes in order to maintain a constant cell volume. If water flows in, they lower content of dissolved solutes to restore to original volume.

Which osmolytes do cells use?

Organic solutes as osmotic effectors

Why do animals tend to use organic molecules as osmotic effectors

Because they use osmotic effectors that do not disrupt enzyme function

• Compatible solutes: osmolytes that have little to no effect on the structure and function of macromolecules in the body fluid

• Counteracting solutes: osmolytes that individually have strong effects on macromolecules, but when used in teams of two or more cancel out each others effects

What is an example of counteracting solutesq

Elasmobranchs use urea and TMAO as counteracting solutes. If concentration of both of these increase at the same time, it remains constant

Why cant humans gain water fro mdrinking salt water

We would have to produce urine hyperosmotic in salt than the salty water. Our kidneys cannot do that