The Lymphatic System and Immunity

Functions of Lymphatic System

• drains excess interstitial fluid

• transports dietary lipids

• immune responses

System consists of…

lymph, lymphatic vessels, structures + organs that contain lymphatic tissue (tissue that contains lymphocytes, red marrow

Lymphatic vessels

• look like small veins

• flow through lymph nodes

• differ from capillaries

  • greater permeability (large molecules like proteins and lipids)

  • larger diameter

  • one way flow (flows in but not out)

  • endothelial cells overlap

Movement of lymph

• skeletal muscle pump

  • compresses lymphatic vessels and veins

• respiratory pump

  • pressure changes during breathing helps move blood and lymph

• large vessels have smooth muscle

• valves help keep fluid from back flow

Organs and Tissues

• Primary

  • where stem cells divide to become immunocompetent (can mount a immune response)

  • red bone marrow and thymus

    • B (stay) and T (mature in thymus) cells are made in the red marrow

• Secondary

  • site were immune response occur

  • lymph nodes, spleen, lymphatic nodules

Thymus

• bi-lobed

• sternum and aorta

• outer cortex

  • immature T cells

• central medulla

  • mature T cells

Lymph Nodes

• along lymphatic vessels

• ~600 total

• superficial and deep

• grouped

  • mammary glands, axillae, groin

• cortex

  • B cells (also memory B cells), T cells, dendritic cells and macrophages

• medulla

  • B cells, plasma cells (B cells that secrete antibodies), T cells, macrophages

Spleen

• largest mass of lymphatic tissue

• consists of white pulp and red pulp

  • white

  • red

    • RBCs

    • macrophages

      • remove old RBCs and platelets

    • less immune cells than white

    • store platelets

    • produces RBCs in fetal development

Lymphatic Nodules

• lymphatic tissue not surrounded by connective tissue (capsule)

• not along vessels

• mucus membranes of GI tract, urinary tract, reproductive tract, and respiratory tract

Antimicrobial substances of innate immunity

• interferons

  • interfere with viral replication

  • activate neutrophils and macrophages

• complement

  • in plasma and plasma membranes

  • causes lysis of microbes, promotes phagocytosis, inflammation

• iron-binding proteins

  • inhibits growth of certain bacteria by reducing iron

• antimicrobial proteins

  • short peptides

  • microbes don’t develop resistance to these