human bio week 12 levture 1 part 2

Lymphoid Cell Lineage

• Lymphocytes:

  • Small cells with a large nucleus filling most of the cell.

  • Tiny bit of cytoplasm around the rim.

  • Three main types, indistinguishable in standard blood smears without special stains.

  • Attack pathogens differently compared to innate immune cells.

  • Capacity to remember previous encounters with pathogens, showing specificity and memory.

B Cells (B Lymphocytes)

• Function: Produce and secrete antibodies.

  • Antibodies are specific to a particular pathogen (e.g., COVID, influenza A).

    • Example: B cells encountering COVID secrete antibodies that specifically recognize and affect COVID.

    • Influenza A infection triggers production of antibodies specific to influenza A.

• Classified as antigen-presenting cells.

  • Capable of finding an antigen and presenting it to other immune cells to generate a response.

Helper T Cells

• Function: Activate other leukocytes.

Cytotoxic T Cells

• Function: Recognize and kill infected cells (cytotoxic).

Summary Table

• Provides anatomical features and functions of cells covered.

Lymphoid Tissues

• Divided into two main types:

  • Central Lymphoid Tissue: Thymus gland and bone marrow.

  • Peripheral Lymphoid Tissue: Lymph nodes and spleen.

• Connected by lymphatic vessels.

  • Green branching structures in the image.

• Lymph:

  • Fluid within lymph vessels, similar to blood plasma.

  • High proportion of lymphocytes.

  • Originates from tissues and organs across the body.

  • Formed by fluid seeping out of blood vessels and draining into the lymphatic circulation.

  • Allows the immune system to monitor pathogens in tissues.

Central Lymphoid Tissue

• Bone Marrow:

  • Origin of all blood cells.

  • Contains hematopoietic stem cells that divide into myeloid and lymphoid lineages.

  • Site where B cells and most leukocytes reach maturity.

• Thymus Gland:

  • T cells migrate from the bone marrow to the thymus gland to mature.

• Maturation:

  • B cells mature in the bone marrow.

  • T cells mature in the thymus gland.

• After maturation, cells go to the periphery to monitor for pathogens.

• Mnemonic: B cells mature in Bone marrow, T cells mature in Thymus.

• Lymphocyte Maturation Process:

  • B and T cells arise from hematopoietic stem cells in the bone marrow.

  • T cells go to the thymus, B cells stay in the bone marrow to mature.

  • Mature cells enter circulation (blood and lymph) and go to peripheral lymphoid organs to monitor for pathogens.

Peripheral Lymphoid Tissue

• Aggregates of B cells, T cells, and other immune cells scattered throughout the body.

  • Include lymph nodes, spleen, tonsils, adenoids, appendix, and lymphatic nodules in the intestines.

• Strategically located to capture pathogens soon after they enter the body.

Spleen

• Highly vascularized structure in the abdomen (usually left side, above the stomach).

• Filters blood to detect pathogens.

• Blood flows through sinusoids, contacting immune cells.

• Antigen-presenting cells (macrophages and dendritic cells) mount immune responses.

• Phagocytes digest encountered pathogens.

Lymph Nodes

• About 800 scattered throughout the body.

• Concentrated areas in the neck, armpits, thorax, abdomen, and groin.

• Filter lymph instead of blood.

• Lymph enters through afferent lymphatic vessels and passes through the node, contacting immune cells.

• Antigen-presenting cells present antigens and mount a response if needed.

Tissue Resident Immune Cells

• Immune cells scattered throughout the body monitoring for pathogens.

• Resident in specific locations, not circulating in the blood.

• Example: Langerhans cells in the epidermis of the skin.

• Dermis contains macrophages, T cells, B cells, and dendritic cells.

• The immune system is present in every part of the body.