Fluid compartments and fluid balance Flashcards
Body fluid
Refers to the water in the body and its dissolved substances
2/3rds of fluid
Within cells (Intracellular fluid (ICF))
1/3rd of fluid
Includes all other body fluids (not within cells) (Extracellular fluid (ECF))
80% of ECF
Interstitial fluid (between cells)
20% of ECF
Blood plasma
What separates the ICF from the interstitial fluid
Selectively permeable cell membrane
What separates the interstitial fluid from the blood plasma
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
Main component of all body fluids
Water
Fluid balance
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
Osmosis
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
Electrolytes
Most of the solutes in body fluids. They are compounds that dissociate into ions
Aldosterone
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
4 general functions of electrolytes
- Many are essential minerals
- Their concentration in body fluids controls the movement of water between the fluid compartment
- They help maintain the correct pH (Blood pH = 7.2 - 7.4) balance required for cellular activities
- Allow the production of ‘Action Potentials’ required for the transmission of nervous impulses
Action potentials
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.
What controls the solute concentration of the ICF
Cell membrane
What controls the solute of the ECF/Blood plasma
The kidneys
Sodium (Na+)
- 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
Potassium (K+)
- 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
Main mechanism that controls potassium concentration
- 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.
Calcium
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
Hormones that regulate calcium in the blood
- Parathyroid hormone - parathormone 9
(PTH) - Calcitonin (CT) from the thyroid gland
