Lymphatic System Overview

Lymphatic Organs

• Lymph nodes, spleen, tonsils, and thymus are all lymphatic organs.

Lymph Vessels

• Lymph vessels transport lymph fluid, which is composed of blood plasma, lymphocytes, and antibodies.

Spleen

• The spleen is the largest lymphoid organ in the body.
• It filters blood, stores erythrocytes, and phagocytoses damaged or aged red blood cells.
• The spleen is the site of proliferation for B and T lymphocytes and the manufacturing of antibodies.
• The spleen is divided into two regions:
  • Red pulp: Contains splenic cords and blood sinusoids (Billroth cords).
  • White pulp: Includes the central artery and lymphatic nodules.
• The spleen lacks cortex and medulla.
• It is located in the abdomen.
• The spleen has a capsule composed of dense irregular collagenous connective tissue, elastic fibers, and smooth muscle cells. This capsule is thicker at the hilum.
  • Sepra (trabecula) are a network of reticular fibers and collagenous connective tissue that form the frame work of the spleen.
• Nerves, blood, and lymph vessels enter and leave the spleen at its hilum.
• It is an intraperitoneal organ covered by simple squamous epithelium (peritoneum).

White Pulp

• Contains a central artery, lymphatic nodules, and antigen-presenting cells.
• Lymphatic nodules primarily consist of B lymphocytes.

Marginal Zone

• The marginal zone is located between the red and white pulps.
• It receives capillary loops from the central artery, which drain into small sinusoids at the periphery of the lymphatic nodules.
• The marginal zone is the initial site where blood contacts the splenic parenchyma.
• It is richly supplied by phagocytic macrophages and antigen-presenting cells.
• The marginal zone is where T and B lymphocytes enter the spleen before being segregated to their specific locations.

Histology of the Spleen

• Splenic Nodules (White Pulp):
  • Central zone contains B lymphocytes.
  • Red pulp contains RBCs and plasma cells.
  • Cords of Billroth
• Capsule:
  • Trabeculae
• Central Artery:
  • Periarterial Lymphoid Sheath (PALS): Contains T lymphocytes.
• Splenic Marginal Artery:
  • Arterial loops
  • Receive B lymphocytes
  • Macrophages

Reproduction in Protozoa

• Protozoa reproduce both asexually and sexually.
• Asexual reproduction is the primary mode of reproduction.
• Asexual reproduction involves fission, which is the division of a parent cell into daughter cells.
• The cell body divides after the nucleus divides.

Asexual Reproduction

• Binary fission:

  • This is the most common type of asexual reproduction in protozoa.
  • The nucleus elongates and divides into two parts.
  • The cell then constricts in the middle to form two daughter cells.
  • This can be transverse or longitudinal depending on the type of protozoa.
  • Flagella and cilia are distributed among the daughter cells, and new ones are formed.
  • Contractile vacuoles are either shared or formed anew.

• Multiple fission:

  • The nucleus divides repeatedly before the cytoplasm divides.
  • The cytoplasm separates into as many parts as there are nuclei, forming spores.
  • Spores can be enclosed in a spore case or naked.
  • Spores can be amoeboid, flagellated or ciliated.

• Cyst formation:

  • Protozoa can form cysts for protection or reproduction.
  • Cysts are formed by a process called encystment.
  • During encystment, the protozoan becomes rounded, loses its organelles of locomotion, ejects food vacuoles, and contractile vacuoles disappear.
  • The protozoan secretes a gelatinous covering that hardens into a chitinous epicyst.
  • Cysts help in the dispersal of species.

• Plasmotomy:

  • Asexual division of a multinucleate protozoan, where the cytoplasm divides but the nuclei do not.
  • Each daughter cell later regains the number of nuclei by nuclear division.

• Budding:

  • This is an unequal division of the parent body, producing one or more buds.
  • The nucleus of the buds is a part of the parent nucleus.
  • The bud is smaller than the parent and may grow into an adult.
  • Budding can be exogenous (buds form on the surface of the parent) or endogenous (buds form inside the cytoplasm).

• Parthenogenesis:

  • Development of a gamete into an adult without fertilization.
  • Mostly occurs in female gametes.

• Regeneration:

  • The ability to form new tissue to replace a lost part.
  • Any nucleated portion of a protozoan is capable of regeneration.

Sub-types of Cysts

• Resting cysts:
  • Enable the protozoan to proceed undisturbed in its normal activities.
• Resistance cysts:
  • Formed against unfavorable environmental conditions.
• Gametocysts:
  • Where gametes unite for reproduction.
• Oocysts:
  • Contain a zygote.
• Sporocysts:
  • Where multiple fissions occur to form sporozoites.

Explore the key components of the lymphatic system, including lymphatic organs like the spleen, lymph nodes, tonsils, and thymus. Dive into the function of lymph vessels and the specialized structure of the spleen, focusing on its unique regions and roles in the immune response.