interstitial fluid

Examples of interstitial fluid in the following topics:

• Fluid Compartments

  • The major body fluid compartments include: intracellular fluid and extracellular fluid (plasma, interstitial fluid, and trancellular fluid).
  • The extracellular fluid can be divided into two major subcompartments, interstitial fluid and blood plasma.
  • Interstitial fluid (or tissue fluid) is a solution that bathes and surrounds the cells of multicellular animals.
  • The interstitial fluid is found in the interstitial spaces, also known as the tissue spaces.
  • It is the smallest component of extracellular fluid, which also includes interstitial fluid and plasma.

• Lymphatic Capillaries

  • These regulate the pressure of interstitial fluid by draining lymph from the tissues.
  • Lymphatic capillaries collect lymph fluid from the tissues, which allows them to regulate the pressure of interstitial fluid.
  • When pressure is greater in the interstitial fluid than in lymph due to accumulation of interstitial fluid, the minivalves separate slightly like the opening of a one-way swinging door so that fluid can enter the lymphatic capillary.
  • Diagram showing the formation of lymph from interstitial fluid (labeled here as "tissue fluid").
  • Describe the location, structure, and role of lymphatic capillaries in maintaining the pressure of the interstitial fluid

• Capillary Dynamics

  • Oncotic or colloid osmotic pressure is a form of osmotic pressure exerted by proteins in the blood plasma or interstitial fluid.
  • Hydrostatic pressure is the force generated by the pressure of fluid within or outside of capillary on the capillary wall.
  • Movement from the bloodstream into the interstitium is favored by blood hydrostatic pressure and interstitial fluid oncotic pressure.
  • Alternatively, movement from the interstitium into the bloodstream is favored by blood oncotic pressure and interstitial fluid hydrostatic pressure.
  • Due to the pressure of the blood in the capillaries, blood hydrostatic pressure is greater than interstitial fluid hydrostatic pressure, promoting a net flow of fluid from the blood vessels into the interstitium.

• Functions of the Lymphatic System

  • The lymphatic system plays a prominent role in immune function, fatty acid absorption, and removal of interstitial fluid from tissues.
  • It is responsible for the removal and filtration of interstitial fluid from tissues, absorbs and transports fatty acids and fats as chyle from the digestive system, and transports many of the cells involved in immune system function via lymph.
  • Interstitial fluid accumulates in the tissues, generally as a result of the pressure exerted from capillaries (hydrostatic and osmotic pressure) or from protein leakage into the tissues (which occurs during inflammation).
  • One of the main functions of the lymphatic system is to drain the excess interstitial fluid that accumulates.
  • Edema is any type of tissue swelling from increased flow of interstitial fluid into tissues relative to fluid drainage.

• Bulk Flow: Filtration and Reabsorption

  • Capillary fluid movement occurs as a result of diffusion (colloid osmotic pressure), transcytosis, and filtration.
  • When moving from the bloodstream into the interstitium, bulk flow is termed filtration, which is favored by blood hydrostatic pressure and interstitial fluid oncotic pressure.
  • When moving from the interstitium into the bloodstream, the process is termed reabsorption and is favored by blood oncotic pressure and interstitial fluid hydrostatic pressure.
  • Proteins and other large molecules are filtered out of the oxygenated blood in the glomerulus and pass into Bowman's capsule and the tubular fluid contained within.
  • Tubular reabsorption is the process by which solutes and water are removed from the tubular fluid and transported into the blood.

• Open and Closed Circulatory Systems

  • The blood is called hemolymph because it mixes with the interstitial fluid.
  • (a) In closed circulatory systems, the heart pumps blood through vessels that are separate from the interstitial fluid of the body.
  • (b) In open circulatory systems, a fluid called hemolymph is pumped through a blood vessel that empties into the body cavity.

• Movement of Fluid Among Compartments

  • Extracellular fluid is separated among the various compartments of the body by membranes.
  • To prevent a build up of tissue fluid surrounding the cells in the tissue, the lymphatic system plays a part in the transport of tissue fluid.
  • If positive, fluid will tend to leave the capillary (filtration).
  • If negative, fluid will tend to enter the capillary (absorption).
  • Note the concentration of interstitial solutes (orange) increases proportionally to the distance from the arteriole.

• Distribution of Lymphatic Vessels

  • The lymphatic system is a circulatory system for lymphatic fluid, comprising a network of conduits called lymphatic vessels that carry the fluid in one direction toward the heart.
  • Afferent lymphatic vessels flow into a lymph node and carry unfiltered lymph fluid.
  • The lymphatic vessels start with the collection of lymph fluid from the interstitial fluid.
  • When the pressure for interstitial fluid in the interstitial space becomes large enough it leaks into lymph capillaries, which are the site for lymph fluid collection.
  • As the lymph vessels become larger, their function changes from collecting fluid from the tissues to propelling fluid forward.

• Lymphatic Vessel Structure

  • While blood and lymph fluid are two separate substances, both are composed of the same water (plasma or fluid) found elsewhere in the body.
  • This layer mechanically transports fluid.
  • The endothelium is designed with junctions between cells that allow interstitial fluid to flow into the lumen when pressure becomes high enough (such as from blood capillary hydrostatic pressure), but does not normally allow lymph fluid to leak back out into the interstitial space.
  • When the pressure of lymph fluid increase to a certain point due to filling with more lymph fluid or from smooth muscle contraction, the fluid will be pushed through the valve (opening it) into the next chamber of the vessel (called a lymphangion).
  • Lymph fluid can only flow forward through lymphangions due to the closing of valves after fluid is pushed through by fluid accumulation, smooth muscle contraction, or skeletal muscle contraction.

• Lymph Transport

  • Lymph transport refers to the transport of lymph fluid from the interstitial space inside the tissues of the body, through the lymph nodes, and into lymph ducts that return the fluid to venous circulation.
  • Lymphatic capillaries are the site of lymph fluid collection from the tissues.
  • The fluid accumulates in the interstitial space inside tissues after leaking out through the cardiovascular capillaries.
  • In addition to interstitial fluid, pathogens, proteins, and tumor cells may also leak into the lymph capillaries and be transported through lymph.
  • This is where lymph fluid reaches the end of its journey from the interstitial space of tissues back into blood circulation.