Chapter5 Histology

Histology Overview

  • Histology: The study of microscopic anatomy of tissues.

  • Tissue: A group of cells performing similar functions.

  • Organ: A collection of two or more tissues working together.

  • The human body consists of four main types of tissues:

    • Epithelial tissue

    • Muscular tissue

    • Connective tissue

    • Nervous tissue

Cell Junctions

  • Function:

    • Bind cells together and to extracellular materials.

    • Support cell growth and development.

    • Prevent tissues from disintegrating.

    • Facilitate communication between cells.

  • Types of Cell Junctions:

    • Tight Junctions: Prevent leakage of materials between cells (found in skin and stomach lining).

    • Desmosomes: Provide mechanical stability by anchoring cells.

    • Gap Junctions: Allow intercellular communication through connexons connecting adjacent cells.

Glands

  • Function: Secretion of substances for use or excretion from the body.

  • Composed mainly of epithelial tissue (secretory cells and ducts) and supportive connective tissue.

  • Types of Glands:

    • Exocrine Glands:

      • Have ducts.

      • Secrete onto epithelial surfaces (e.g., salivary, sweat glands).

    • Endocrine Glands:

      • No ducts.

      • Release hormones directly into bloodstream (e.g., adrenal, thyroid glands).

Exocrine Gland Structure

  • Stroma: The connective tissue framework, including capsule and septa.

  • Parenchyma: Secretory cells and ducts that produce gland products.

  • General features include lobes, lobules, acini, and ducts.

Types of Secretion Methods

  • Serous: Thin and watery secretion.

  • Mucous: Sticky and viscous secretion.

  • Modes of Secretion:

    • Merocrine: Secretion via exocytosis.

    • Apocrine: Budding from the apical surface.

    • Holocrine: Entire cells disintegrate to release their contents.

Membranes

  • Types of Membranes:

    • Serous Membrane: Lining of body cavities and organs (e.g., mesentery).

    • Mucous Membrane: Lining of various tracts including digestive, respiratory, and reproductive.

Membrane Structure

  • Mucous Membranes: Composed of epithelium, lamina propria (areolar connective tissue), and muscularis mucosae.

  • Serous Membranes: Include peritoneum, pleura, pericardium, and more.

Tissue Growth and Changes

  • Types of Growth:

    • Hyperplasia: Increase in cell number (common in skin and bone).

    • Hypertrophy: Increase in cell size (common in fat and muscle).

    • Neoplasia: Abnormal growth (tumor).

  • Differentiation: Process where unspecialized cells become specialized.

  • Metaplasia: Change from one mature tissue type to another.

  • Stem Cells:

    • Totipotent: Can become any cell type (embryonic).

    • Pluripotent: Can become any embryonic or adult cell but not extraembryonic.

    • Multipotent: Can develop into two or more cell types.

    • Unipotent: Limited to one cell type.

Tissue Degeneration and Repair

  • Types of Tissue Degeneration:

    • Atrophy: Reduction in size or deteriorating condition (e.g., from disuse).

    • Necrosis: Death of tissue due to injury or disease.

    • Apoptosis: Programmed cell death.

  • Repair Mechanism:

    • Regeneration: Replacement of damaged cells with the same type to restore function.

    • Fibrosis: Replacement with scar tissue which does not restore function.

Tissue Repair Phases

  1. Hemostasis: Clotting and scabbing to prevent further bleeding.

  2. Inflammatory Phase: Cleaning of the wound by immune cells.

  3. Fibroblastic Phase: Growth of new capillaries and granulation tissue.

  4. Remodeling Phase: Final stages, with restoration of epidermis and organization of scar tissue.