Section 3 - Water

Water comprises what % of body weight?

60%

Very lean animals have a higher or lower water % of body weight?

Higher

• In contrast, obese animals have less water weight

Water is a universal ___?

SOLVENT!

Solute

Material dissolved in water

What all does water do? (3 things)

• Universal solvent

• Acts as a lubricant for joints, fibers, materials, etc

• Acts as a heat sink—can store heat

Diffusion

The movement of molecules from areas of high concentration to areas of low concentration due to the natural vibration of the molecule

Brownian motion

Results in erractic, random movement of molecues due to the circling of electrons around the nucleus

What happens during diffusion?

Molecules/ions will spread out as far apart from each other as possible and attempt to create equal distribution among that space.

• Think of perfume being sprayed from the corner of the room. Initially, the odor is congested in that corner. However, over time, the odor spreads throughout the room until its evenly distributed

Water can move in and out of the cell membrane

True. The cell membrane is semi-permeable.

Protein Pore (and in the case of water?)

A protein forming a hydrophilic canal through the lipid bilayer

• In the case of water, an aqua pore

Smaller particles move freely across the membrane in response to what?

Their own concentration on either side of the membrane; osmosis

Osmosis

The passive movement of water across the membrane

Osmotic Pressure

The attraction or pressure of the particles that draw water to either side of the membrane

• Measurement of the tendecy of water to osmose

How does water itself specifically balance itself?

Water goes to higher concentrations of solvent.

Isotonic

When water-ased solution is in balance with the body and its cells

• Under normal conditons, the blood plasma is isotonic with body cells

If a solution is lower in dissolved particles (solvent) vs the cell it surrounds… what happens? what is the solution called?

• Water will move toward the higher particle concentration (i.e., the cell). This will cause the cell to swell and burst

• Hypotonic

  • Think “Hippo”

If a solution is higher in dissolved particles (solvent) vs the cell it surrounds… what happens? what is the solution called?

• Water will move toward the higher particle concentration (i.e., the solution). This will cause the cell to shrink

  • Hypertonic

Hydrophobic vs Hydrophilic parts of the cell membrane

• Hydrophobic - cell membrane

• Hydrophilic - pores in the membrane

The lipid bilayer is ____ charged

Highly

If a particle is the same charge as the lipid bilayer, the particle will be ___? If its the opposite?

• Same = repelled

• Opposite = attracted

Simple Diffusion/Transport

• Same as in air with no barrier (CO2, O2, Steroids)

• Passive transport — no energy required, response to gradient

Facilitated Diffusion/Transport

• Molecules move through a protein that forms a canal or pore across the membrane (can be gated)

  • When gate is open, molecules can stream through the pore

• Configurational change in the binding protein of pore

  • Binds molecules to the membrane → protein changes configuration → flips the molecule to the other side

• Both are passive forms — no energy required

Active Diffusion/Transport

• Requires ATP (Na/K pump)

• Often against concentration gradient

80% of water in the body is __cellular while 20% is __cellular

1. Intra

2. Extra

Lessthan 1% of total water across the body is where?

Across the body in specific locations (cerebrospinal fluid, digestive tract, intraocular fluid)

The pool of water within the body remains constant

False. It changes constantly

How can one gain more water in the body?

1. Drinking

2. Metabolizing

   1. 10-15% of daily water gain in most species; 100% in some desert animals and reptiles

Sensible Water Loss

Water loss from the body that can be sensed and regulated

• Urine and feces

  • 99% of the water that enters the lumen of organs (kidney, stomach, intestines) is reabsorbed.

    • Remember that the lumen is considered outside of the body

• Usually under very tight control

Insensible Water Loss

Water loss from the body that cannot be sensed or regulated

• Sweating and breathing

  • Breathing also warms the air

How is water maintained in the body?

Involves nervous pathways, blood supply, hormones, and conscious thought

Why do larger animals have it easier in balancing water?

Larger mass with a smaller surface area; less water is lost per unit of surface area.

• This means that smaller animals typically suffer dehydration faster

Electrolytes

Body salts that help regulate osmosis—deposited on the surface alongside water when sweating

Why do cells actively pump electrolytes into the extracellular space?

Prevent issues due to formation of a hypotonic condition in the extracellular fluids

Dehydration

• Immediate loss of extracellular water

• Eventual loss of intercellular fluid and electrolytes

• Rehydration requires electrolyte replacement

Stimulus for thirst

• Thirst is a conscious desire for water

• Hypothalamus causes dehydration of thirst cells that line blood vessels through the hypothalamus

  • Thirst cells trigger:

    • Antidiuretic hormone to trigger the kidney to retain water

    • The thought of thirst

Relief of thirst

• Wetens the pharynx

• Distends the stomach to slow the rate of drinking

  • From there, water crosses into the bloodstream and rehydrates thirst cells