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Category: Medical

Topic: Fluid Dynamics

Level: Paramedic

Next Unit: Tonicity

7 minute read

Water Compartments

The liquid components of body fluid are classified in two main divisions known as the

  1. intracellular fluid (ICF): the fluid found inside the cells of the body
  2. extracellular fluid (ECF): the fluid found outside the cells of the body.


Extracellular Fluid

Extracellular fluid can even be further divided into:

PLASMA: the straw-colored liquid in the blood that suspends blood cells and makes up 55% of the body's total blood volume.

(Whole blood = plasma + red blood cells + other cells and circulated immunoglobulins, enzymes, proteins, etc.)

LYMPH: found in the lymphatic system and suspends and transports white blood cells away from tissues back into the circulatory system, aiding in the immune response.

Lymph also recirculates interstitial fluids extruded from capillaries due to hydrostatic and osmotic pressures:

  • INTERSTITIAL FLUID: solution that surrounds the tissue cells of humans and makes up the majority of the extracellular fluid. It exists in equilibrium with the exchange between both sides of the capillary beds.
  • SPECIALIZED FLUIDS: fluids in specific locations with specific tasks within those locations.
    • synovial fluid,
    • cerebrospinal fluid, and
    • aqueous and vitreous humor


Specialized Fluids

SYNOVIAL FLUID: the extracellular fluid found in the cavities of moveable joints and is tasked with reducing friction between the articular cartilage.

CEREBROSPINAL FLUID (CSF): the extracellular, crystal-clear fluid that fills the space between the arachnoid membrane and the pia mater in the brain (the INTRATHECAL space), and is found in the spinal cord as a cushioning buffer and providing mechanical and immunological protection.

Any other visual consistency other than crystal-clear indicates infection or bleeding.

AQUEOUS HUMOR: the extracellular fluid found filling the space in the front of the eyeball between the lens and the cornea serving to nourish the cornea and the lens and remove waste in parts of the eye that lack blood supply.

IN THE FIELD: Hyphema is bleeding in the anterior chamber of the eye (aqueous humor). It is always due to blunt force and is seen often associated with other-- life-threatening --trauma. In children as a stand-alone finding, it is an indication of abuse and reportable as your duty. Of course, any ER personnel will know this, so your responsibility is to transport any child with a fresh (red) hyphena or an older one (discoloration seen in the eye). Hyphema is a naked-eye (no pun intended) observation on your part; no specialized equipment is needed--it will be obvious 

VITREOUS HUMOR: more gelatinous in nature than the aqueous humor, the vitreous humor gives the eye its shape, helps absorb shocks, and keeps the retina pushed back and connected to the back wall of the eye.