Water Balance

Question 1

Explain how body temperature is controlled.

Answer 1

Water is important in the body as it has a high ability to absorb and retain heat. This allows it too stabilise body temperature. The process of sweating also carries heat away from the body.

Body temperature is regulated by negative feedback as well as this.

Question 2

Recognise the importance of water in the body and list its functions.

Answer 2

Universal solvent.
Chemical reactions occur in water.
Found as a major component of plasma and cells.
Lubricant of joints and organs.
High ability to absorb and retain heat.

Question 3

Describe how water balance in the body is maintained.

Answer 3

Osmoreceptors and baroreceptors detect if the body water levels decrease. They send messages to the thirst centre in the hypothalamus which then send signals which cause the release of ADH and the sensation of thirst and a dry mouth.

Question 4

Define body fluid compartments and state their relative proportions.

Answer 4

(In a 70kg male)
Intracellular fluid - 66% (25L)
Extracellular fluid - 24% (12L)
Plasma - 6% (3L)
Joints, CSF etc - 3% (0.7L)

Question 5

Describe how water moves through fluid compartments in the body.

Answer 5

Osmotic pressure

Exerted by solutes drawing water into area of low water.

Question 6

SOLUTE

Answer 6

The minor component in a solution dissolved in the solvent

Question 7

SOLUTION

Answer 7

A homogeneous mixture of one or more dissimilar substances (usually liquid + solute)

Question 8

OSMOLALITY

Answer 8

The concentration of a solution expressed as the total number of solute particles/KG

Question 9

OSMOLARITY

Answer 9

The concentration of a solution expressed as the total number of solute particles

Question 10

TONICITY

Answer 10

Ability of a solution to affect the cell

Question 11

ELECTROLYTES

Answer 11

Soluble inorganic molecules whose ions conduct electricity in a solution e.g Na+ K+

Question 12

List common electrolytes and state their function.

Answer 12

SODIUM (Na) - most dominant extracellular ion. Creates osmotic pressure. Needed for nerve conduction and propagation of action potentials. Controlled by ANP/Aldosterone.
POTASSIUM (K) - Needed for nerve conduction (returning cell to its resting state after excitation). In muscles and excitable cells.
CALCIUM (Ca) - Too much causes excess PT hormone, fatigue and weakness. Too little causes muscle cramps due to increased muscle excitability. Needed for bone formation.

Question 13

Explain how substances move in and out of the cell.

Answer 13

Via membrane proteins
Membrane channels that are always open which allow water and hydrophilic solutes to diffuse in and out of the cell (Aquaporins).
Channel proteins that have to be opened by either voltage changers or the binding of neurotransmitters etc.
Carriers which bind to solutes and transfer them across the membrane such as pumps (facilitated diffusion and active transport).
Exocytosis