Fluid compartments and fluid balance

Question 1

Body fluid

Answer 1

Refers to the water in the body and its dissolved substances

Question 2

2/3rds of fluid

Answer 2

Within cells (Intracellular fluid (ICF))

Question 3

1/3rd of fluid

Answer 3

Includes all other body fluids (not within cells) (Extracellular fluid (ECF))

Question 4

80% of ECF

Answer 4

Interstitial fluid (between cells)

Question 5

20% of ECF

Answer 5

Blood plasma

Question 6

What separates the ICF from the interstitial fluid

Answer 6

Selectively permeable cell membrane

Question 7

What separates the interstitial fluid from the blood plasma

Answer 7

Blood vessel capillary walls
- Although fluids are in constant movement from one compartment to the other, the volume and concentration of fluid in each compartment is kept relatively stable

Question 8

Main component of all body fluids

Answer 8

Water

Question 9

Fluid balance

Answer 9

The required amount of water is present and correctly proportionated between the fluid compartments. It also means that the correct amounts of dissolved substances are present in the fluid compartments

Question 10

Osmosis

Answer 10

Primary mechanism that causes water to move into and out of the body fluid compartments. The concentration of solutes in body fluids is therefore a major determinant of fluid balance

Question 11

Electrolytes

Answer 11

Most of the solutes in body fluids. They are compounds that dissociate into ions

Question 12

Aldosterone

Answer 12

Dehydration includes a reduction of blood volume - This lowers blood pressure and reduces the GFR.
Reduced BP stimulates the release of the adrenal cortex hormone ‘Aldosterone’. This hormone increases the reabsorption of sodium ions from the kidney filtrate which also draws out water from the filtrate, further decreasing urine output. Urine will be more concentrated

Question 13

4 general functions of electrolytes

Answer 13

1. Many are essential minerals
2. Their concentration in body fluids controls the movement of water between the fluid compartment
3. They help maintain the correct pH (Blood pH = 7.2 - 7.4) balance required for cellular activities
4. Allow the production of ‘Action Potentials’ required for the transmission of nervous impulses

Question 14

Action potentials

Answer 14

The basic events the nerve cells use to transmit information from one place to another.
They are a brief electrical signal that travels along the membrane of a nerve cell (neuron) or muscle cell. It is generated when there is a sudden change in the cell’s membrane potential, causing a rapid depolarization followed by repolarization. This electrochemical impulse allows for the transmission of signals within the nervous system and is essential for various physiological processes, including communication between nerve cells and muscle contraction.

Question 15

What controls the solute concentration of the ICF

Answer 15

Cell membrane

Question 16

What controls the solute of the ECF/Blood plasma

Answer 16

The kidneys

Question 17

Sodium (Na+)

Answer 17

• Most abundant extracellular ion
• Necessary for the conduction of action potentials in nervous and muscle tissues (nervous impulses)
• Abundant role to play in maintaining the correct electrolyte balance to the ECF

Question 18

Potassium (K+)

Answer 18

• Most abundant electrolyte in the ICF
• Acts along with sodium to establish action membrane potentials in nervous and muscle tissues
• Helps to maintain fluid volume in cells
• Abnormal K+ levels adversely affect neuromuscular and in particular cardiac muscle funtion

Question 19

Main mechanism that controls potassium concentration

Answer 19

• The exchange of sodium for potassium in the DCT and collecting ducts.
  When ECF potassium levels are high, more aldosterone is secreted.
  This increases sodium absorption but in exchange, potassium gets excreted.
  When ECF potassium levels are low, aldosterone secretion decreases so less potassium is excreted.

Question 20

Calcium

Answer 20

98-99% stored in bone - The remainder is principally found as an ECF electrolyte.
ECF calcium plays an important role in blood coagulation, neurotransmitter release, maintenance of muscle tone, and normal nervous and muscle functioning

Question 21

Hormones that regulate calcium in the blood

Answer 21

• Parathyroid hormone - parathormone 9
  (PTH)
• Calcitonin (CT) from the thyroid gland