lymph capillaries

(noun)

Tiny thin-walled vessels, closed at one end and located in the spaces between cells throughout the body, collect fluid from the tissues.

Related Terms

Examples of lymph capillaries in the following topics:

  • Lymphatic Capillaries

    • Lymph capillaries are tiny, thin-walled vessels, closed at one end and located in the spaces between cells throughout the body.
    • Lymphatic circulation begins in the smallest type of lymph vessels, the lymph capillaries.
    • This opens the lymph capillaries more, increasing their volume and reducing their pressure to further facilitate fluid flow into the capillaries.
    • This also explains why lymph flows into the lymph capillaries easily, since fluid follows proteins that exert oncotic pressure.
    • The lymphatic capillaries bring lymph further into the lymphatic vessels.

  • Lymph Transport

    • 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.
    • The lymph capillaries feed into larger lymph vessels.
    • The lymph vessels that receive lymph fluid from many capillaries are called collecting vessels.

  • Distribution of Lymphatic Vessels

    • Afferent lymphatic vessels flow into a lymph node and carry unfiltered lymph fluid.
    • This fluid is mainly water from plasma that leaks into the intersitial space in the tissues due to pressure forces exerted by capillaries (hydrostatic pressure) or through osmotic forces from proteins (osmotic pressure).
    • 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.
    • Like cardiovascular capillaries, lymph capillaries are well distributed throughout most of the body's tissues, though they are mostly absent in bone or nervous system tissue.
    • In comparison to cardiovascular capillaries, lymphatic capillaries are larger, distributed throughout connective tissues, and have a dead end that completely prevents backflow of lymph.

  • Lymphatic Tissue Development

    • From the jugular lymph sacs, lymphatic capillary plexuses spread to the thorax, upper limbs, neck, and head.
    • The next lymph sac to appear is the unpaired retroperitoneal lymph sac at the root of the mesentery of the intestine.
    • Capillary plexuses and lymphatic vessels spread from the retroperitoneal lymph sac to the abdominal viscera and diaphragm.
    • The last of the lymph sacs, the paired posterior lymph sacs, develop from the iliac veins.
    • The posterior lymph sacs produce capillary plexuses and lymphatic vessels of the abdominal wall, pelvic region, and lower limbs.

  • Lymphatic Vessel Structure

    • 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.
    • The activity of smooth muscles allows lymph vessels to slowly pump lymph fluid through the body without a central pump or heart.
    • Larger lymph vessels have many more layers of adventitia than do smaller lymph vessels.
    • The smallest vessels, such as the lymphatic capillaries, may have no outer adventitia.
    • Valves are found in larger lymph vessels and collecting vessels and are absent in the lymphatic capillaries.

  • Lymphoid Tissue

    • The lymphatic endothelial cells proliferate into sacs that eventually become lymph nodes, with afferent and efferent vessels that flow out from the lymph nodes.
    • This process begins with he lymph nodes closest to the thoracic and right lymph ducts, which arises from immature subclavian-jugular vein junction.
    • The lymph nodes organized around other lymph trunks, such as those in the abdomen and intestine, develop afterwards from nearby veins.
    • Smaller lymph vessels and lymphatic capillaries develop after that until the lymphatic system is completed at the closed end of each lymphatic capillary.
    • The thymus and bone marrow are primary lymphoid tissue, while the lymph nodes, tonsils, and spleen are secondary lymphoid tissue.

  • Venules

    • Venules are small blood vessels in the microcirculation that connect capillary beds to veins.
    • Venules range from 8 to 100μm in diameter and are formed when capillaries come together.
    • In contrast to regular venules, high-endothelial venules (HEV) are specialized post-capillary venous swellings.
    • HEVs enable lymphocytes (white blood cells) circulating in the blood to directly enter a lymph node by crossing through the HEV.
    • Venules form when capillaries come together and converging venules form a vein.

  • Functions of the Lymphatic System

    • 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).
    • These conditions force fluid from the capillaries into the tissues.
    • The lymphatic system is a blunt-ended linear flow system, in which tissue fluids, cells, and large extracellular molecules, collectively called lymph, are drained into the initial lymphatic capillary vessels that begin at the interstitial spaces of tissues and organs.
    • Lymph nodes located at junctions between the lymph vessels also filter the lymph fluid to remove pathogens and other abnormalities.
    • Lymph drainage vessels that line the intestine, called lacteals, absorb the chylomicrons into lymph fluid.

  • Capillaries

    • Capillaries do not function independently.
    • The capillary bed is an interwoven network of capillaries that supplies an organ.
    • Sinusoidal - Sinusoidal capillaries are a special type of fenestrated capillaries that have larger openings (30-40 μm in diameter) in the endothelium.
    • Sinusoid blood vessels are primarily located in the bone marrow, lymph nodes, and adrenal gland.
    • Capillary beds may control blood flow via autoregulation.

  • Movement of Fluid Among Compartments

    • It pushes water out of small tight junctions in the capillaries.
    • The balance between the two forces differs at different points on the capillaries.
    • Tissue fluid can pass into the surrounding lymph vessels, and eventually ends up rejoining the blood.
    • If positive, fluid will tend to leave the capillary (filtration).
    • If negative, fluid will tend to enter the capillary (absorption).