Connective Tissue

Connective Tissue

Chapter 5 & 6

Lecture Objectives

  • At the end of the lecture, the student should be able to:

    • List the different types of connective tissue.

    • Describe the cells of connective tissue.

    • Describe the structure of the different types of connective tissue.

    • Relate the structure to the function of the connective tissues.

    • Analyze why a particular type of connective tissue is found in the site that it is.

Overview of Connective Tissue

  • Definition: Connective tissue is the most abundant and widely distributed of primary tissues.

  • Major Functions:

    • Binding and support.

    • Protecting.

    • Insulating.

    • Storing reserve fuel.

    • Transporting substances such as blood.

  • Three Main Classes:

    • Connective tissue proper.

    • Embryonic connective tissues.

    • Specialized connective tissues.

Functions of Connective Tissue

  • A. Structural Support - Provides stroma of organs.

  • B. Defense - Involves phagocytosis and immune functions.

  • C. Protection - Acts as a physical barrier.

  • D. Exchange Medium - Facilitates nutrient and waste exchange.

  • E. Energy Storage - Stores energy reserves.

Classification of Connective Tissue

  • Common Origin: All types of connective tissues are derived from mesenchyme.

  • Fluid Connective Tissue: Includes lymph and blood.

  • Loose Connective Tissue: Characterized by fewer fibers and more ground substance.

  • Dense Connective Tissue: More fibers and less ground substance, can be categorized into:

    • Compact Bone

    • Spongy Bone

  • Embryonic Connective Tissues: Includes mesenchyme and mucoid connective tissue.

  • Specialized Connective Tissues: Include varieties such as:

    • Hyaline cartilage

    • Fibrocartilage

    • Elastic cartilage

  • Types of Dense Connective Tissue:

    • Regular

    • Irregular

    • Elastic

  • Loose Connective Tissues:

    • Areolar

    • Adipose

    • Reticular.

Components of Connective Tissue

  • Extracellular Matrix: Composed of fibers and ground substance.

  • Types of Fibers:

    • Elastic fibers.

    • Collagen fibers.

    • Reticular fibers.

  • Types of Cells:

    • Mesenchymal cells.

    • Fibroblasts.

    • Adipocytes.

    • Reticular cells.

    • Macrophages.

    • Mast cells.

    • Plasma cells.

    • Leukocytes.

Cell Types in Connective Tissue
Mesenchymal Cells

  • Found in embryonic or mesenchyme CT.

  • Pluripotent with cytoplasmic extensions.

  • Do not produce fibers; respond to matrix and surrounding signals to specialize.

Fibroblasts

  • Most common type of connective tissue cell.

  • Synthesizes type I collagen fibers and ground substance.

  • Types of Fibroblasts:

    • Active: Characterized by an abundant cytoplasm and pale nucleus, involved in wound repair.

    • Quiescent: Resting state, less active, spindle-shaped cell.

Medical Application of Fibroblasts

  • The capacity of connective tissue to regenerate is crucial in healing processes, particularly in tissue that does not undertake rapid cell division (like cardiac muscle).

  • Post-injury, connective tissue fills gaps, forming dense irregular scar tissue, primarily through fibroblast activity.

Adipocytes

  • Specialized cells for storing neutral fats and generating heat.

  • Characteristics:

    • Abundant throughout various connective tissues.

    • Signet ring appearance due to a large lipid droplet, with a flattened nucleus at the edge.

Reticular Cells

  • A type of fibroblast that synthesizes reticular fibers (type III collagen).

  • Contributes to the stroma of lymphoid tissues and bone marrow.

Macrophages

  • Derived from monocytes in the bone marrow.

  • Function within the mononuclear phagocytic system with roles in:

    1. Defense and Repair.

    2. Immune Function - Present antigens to T-cells.

  • Major Locations:

    • Blood, connective tissues, lymphoid organs, lungs, etc.

Mast Cells

  • Characterized by distinct cytoplasmic granules that show metachromasia (color change of certain dyes).

  • Granule Contents:

    • Heparin (anticoagulant).

    • Histamine (increases vascular permeability and contracts smooth muscles).

    • Chemotactic factors for eosinophils and neutrophils.

  • Surface receptors for IgE indicate involvement in allergic reactions.

Plasma Cells

  • Large, oval cells derived from B-lymphocytes.

  • Notably basophilic cytoplasm and eccentric nuclei with a "clock-face" appearance.

  • Function: Produce antibodies and are abundant in inflamed tissues.

Types of Connective Tissue Diversifications
Connective Tissue Proper

  • Loose (Areolar) Connective Tissue:

    • Most abundant and highly vascularized, contains various cell types, predominantly fibroblasts and macrophages.

    • Flexible, provides packing around organs.

  • Dense Irregular Connective Tissue:

    • Comprises fibroblasts and type I collagen arranged irregularly, found in dermis, periosteum.

  • Dense Regular Connective Tissue:

    • Fibroblasts with type I collagen arranged in parallel to provide high tensile strength, evident in tendons and ligaments.

  • Dense Elastic Connective Tissue:

    • Contains parallel arrays of elastic fibers and type I collagen. Found in specific ligaments and elastic arteries.

Embryonic Connective Tissues

  1. Mesenchyme:

    • Undifferentiated precursors (pluripotent cells) with an extracellular matrix lacking fibers.

  2. Mucoid (Mucous):

    • Found mainly in the umbilical cord (known as Wharton’s jelly) rich in hyaluronic acid and type I collagen.

Specialized Connective Tissues

  • Adipose Tissue: Composed of large aggregates of adipocytes; various roles include energy storage, thermal insulation, shock absorption, and packing.

    • Types:

    • White Adipose Tissue (unilocular).

    • Brown Adipose Tissue (multilocular), generates heat in newborns.

  • Reticular Connective Tissue: A mesh framework for bone marrow and lymphoid organs, rich in reticular fibers and macrophages.