The Lymphatic System - CC

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1

Describe the structure and explain the main functions of the vessels and organs of the lymphatic system

The lymphatic system is composed of the lymphatic vessels [which returns up to 3L of leaked fluid and plasma proteins to the circulatory system] and the lymphatic tissues/organs [which is essential in body defense and resistance to disease].

Lymphatic vessels are present almost everywhere in the body [exceptions: bones, teeth, bone marrow, limited areas in the central nervous system [present in meninges]] and are very permeable. They begin with lacteals [microscopic blind-ended lymph capillaries]. Filaments attached to the flap-like mini valves anchor the endothelial cells to surrounding structures which, when more water is present, may open up the valves further to allow for more fluid intake.

The lymph nodes are clustered along the lymphatic vessels where they may converge to filter lymphatic fluid [macrophages remove and destroy microorganisms] and activate the immune system if needed.

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LYMPHATIC DUCT DRAINING LOCATIONS

...

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LYMPHOID CELLS

Immune system cells that fight infectious microorganisms that hae penetrated the epithelial layer and are beginning to proliferate into underlying connecive tissue. Lymphoid cells include lymphocytes [T-cell [manages immune response initiating cell to cell attacks] and B-cell [differentiate to make plasma cells that make antibodies that attach and destroy bacterium]], macrophages [phagocytize foreign substances and can be antigen presenters which may activate T-cells], and dendritic cells [antigen presenters that bring antigens to lymph nodes to notify action must be taken].

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LYMPHOID TISSUES

All lymphoid organs are composed of reticular connective tissue except for the thymus

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LYMPH NODES

Are discrete, encapsulated collections of diffused lymphoid tissue and follicles. They are approximately 2.3 cm long, divided into two compartments, the cortex and medulla, by trabeculae. The cortex are lymphoid follicles with germinal centers where peripheralization of B cells becoming up regulated begins. The medulla are medullary cord and large lymph sinuses.

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EFFERENT vs AFFERENT lymphatic vessels

Efferent vessels send the filtered fluid through, closer to the final destination. Afferent vessels brings the fluid to the lymph node. It is important to have more afferent vessels as 'stuff' is being filtered out to then reach the efferent vessels. This also serves as a way to slow the fluids so everything can be fully filtered.

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OTHER LYMPHOID ORGANS: SPLEEN

Composed of reticular CT like lymph nodes, although lymph nodes can filter the lymph [other organs only have efferent lymphatics]. The spleen is the largest lymphoid organ and is located beneath the diaphragm.

  1. site for lymphocyte proliferation; immune surveillance & response
  2. blood cleansing/recycling (old red blood cells, old platelets, debris)
  3. stores RBC products (iron) for recycling
  4. may be a site of RBC production in fetus
  5. stores blood platelets and monocytes

Produces white (immunities) and red (red blood cells) pulp

They have thin capsules and no protection from the rib cage which presents the consequence of being easily damaged and, having such a rich blood supply, may cause internal bleeding.

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OTHER LYMPHOID ORGANS: THYMUS

Composed of reticular CT like lymph nodes, although lymph nodes can filter the lymph [other organs only have efferent lymphatics]. T-lymphocytes acquire immunocompetence here, being prominent in newborns and starts to slowly atrophy after puberty [children have immature immune systems so the thymus gland tests T-cells to assure they are useful to keep safe whilst memory cells are being formed with each sickness they are exposed to - these take up the purpose of T-cells]. It is the only lymphoid organ that doesn’t directly fight antigens (lymphocyte maturation). The stroma consists of epithelial cells.

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MALT (Mucosa-associated lymphoid tissues)

These consist of the 4 tonsils that form a ring of lymphatic tissue at the entrance to the pharynx.

  • palatine tonsils: oral cavity
  • lingual tonsil: base of tongue
  • pharyngeal tonsil (adenoids): posterior wall of nasopharynx (back of nasal cavity)
  • tubal tonsils: entry of auditory tubes into pharynx (communicating pathway between back of the throat and the ears)
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AGGREGATES OF LYMPHOID NODULES

Peyer’s patches: lymph nodule clusters (wall of ileum)

Appendix: lymph nodules forming offshoot of cecum. This destroys bacteria and generate memory lymphocytes to better fight next time.

MALT: Peyer’s patches + appendix + tonsils + nodules in walls of bronchi, areas of GI tract & genitourinary system – in strategic locations to protect against microorganisms trying to enter the body

11

Explain the origin of lymph as well as it's transport.

Lymph is the excess fluid from the capillaries of the blood once they done filtering. This may cause swelling in the area. When this fluid is being brought back to the heart to be put back in the blood, it detours through lymph nodes that check and assure there are no abnormalities. The lymphatic collecting vessels have same 3 tunics as veins, but are thinner-walled with more valves and more anastomoses.

Lymphatic trunks: paired lumbar, bronchomediastinal, subclavian & jugular trunks; single intestinal trunk (from lower pelvic cavity and lower limbs, therefore thick)

  • Right lymphatic duct: drains lymph from right upper arm, head, thorax
  • Thoracic duct: drains lymph from both lower limbs, intestinal trunk, left thorax, left upper limb/head
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LYMPH TRANSPORT

There is no pump and thus uses the same return aids as for veins (muscles [rhythmic contractions of smooth muscle in walls of lymphatic trunks & ducts and contractions of muscles as the body moves], respiratory pressure changes, valves). Because of this, the system is slow, returning ~3 L/day to the blood, but this can be sped up with lcal movement. The blockage/removal of lymphatics during surgery can result in severe local edema. The drainage can be restored by regrowth from remaining vessels.