HISTO WEEK 1

Introduction to Histology

  • Histology: study of the tissues of the body and how these tissues arrange to form organs.

    • Greek origins: "histos" = tissues, "logos" = study of.

    • Focus: cells, extracellular components, organization into tissues, organs, organ systems, and the human individual.

The Cellular Structure

The Cell

  • Basic Unit: Cells are the structural and functional units of all tissues.

  • Cell Differentiation: Cells become organized in tissues with specialized functions, often changing shape.

Differentiated Cells Specialize In One Activity

  • Muscle Cells: Movement.

  • Epithelial Cells: Form adhesions and tight junctions.

  • Fibroblasts, Bone Cells, Cartilage: Synthesize and secrete extracellular matrix components.

  • Neurons: Convert stimuli into action potentials.

  • Cells of Digestive Glands: Synthesize and secrete digestive enzymes.

  • Cells of Mucous Glands: Synthesize and secrete glycoproteins.

More Specialized Cells

  • Adrenal Gland, Testes, Ovary Cells: Synthesize and secrete steroids.

  • Kidney and Salivary Gland Duct Cells: Ion transport.

  • Macrophages and Neutrophils: Intracellular digestion.

  • Adipocytes: Store fats.

  • Intestinal Cells: Metabolic absorption.

Cell Membrane (Plasmalemma)

  • Function: Selectively regulates passage of materials into and out of the cell.

  • Components:

    • Glycoproteins: Proteins with carbohydrate attached.

    • Glycolipids: Lipids with carbohydrate attached.

    • Phospholipid Bilayer: Basic structural framework.

    • Proteins: Integral and peripheral membrane proteins.

    • Cholesterol: Modulates membrane fluidity.

Membrane Proteins

  • Functions: Specific recognition and signaling; key in cell-environment interactions.

  • Phospholipids: Amphipathic; hydrophobic tails and hydrophilic heads.

Membrane Components

  • Glycocalyx: Cell surface coating.

    • Glycolipids and Glycoproteins: Important for cell recognition and adhesion.

Organelles

Ribosomes

  • Assemble polypeptides from amino acids; involved in protein synthesis.

Endoplasmic Reticulum (ER)

Rough ER

  • Site of synthesis for membrane-bound proteins, enzymes for lysosomes.

Smooth ER

  • Involved in lipid synthesis, carbohydrate metabolism, detoxification, and calcium release.

Golgi Apparatus

  • Completes modifications of proteins from the rough ER.

  • Functions in packaging proteins and directing them to proper destinations:

    • Cis Face: Receiving region.

    • Trans Face: Shipping region.

Lysosomes

  • Intracellular digestion sites containing hydrolytic enzymes; essential in cells with phagocytic activity (macrophages, neutrophils).

Proteasome

  • Degrades non-functional proteins; recognizes ubiquitin, marking proteins for breakdown.

Mitochondria

  • Known as the cell's powerhouse; site for ATP synthesis.

  • In stressed cells, releases cytochrome C to trigger apoptosis (cell death).

Peroxisome

  • Enclosed by a single membrane; produces and degrades hydrogen peroxide through oxidase and catalase.

Cytoskeleton

  • Role: Determines cell shape, organelle movement, and cell motility.

  • Composed of microtubules, microfilaments (actin filaments), and intermediate filaments.

Inclusions

  • Accumulated metabolites with no metabolic activity; examples include:

    • Lipid droplets (adipocytes).

    • Glycogen granules (storage of glucose).

    • Melanin (pigmentation).

    • Lipofuscin (derived from lysosomal digestion).

    • Hemosiderin (derived from erythrocyte phagocytosis).

Nucleus

  • Function: Contains machinery for DNA replication and RNA synthesis.

  • Components:

    • Nuclear Envelope: Largest cellular structure.

    • Chromatin: DNA and protein mass.

    • Nucleoli: Specialized chromatin regions.

The Cell Cycle

Distinct Phases

  • Interphase: G1 (growth), S (DNA synthesis), G2 (preparation for mitosis).

  • Mitosis: Division of the cell to produce daughter cells.

  • G0 Phase: Temporary or permanent halt in cell cycle.

Mitosis and Meiosis

Mitosis

  • Cell division producing two identical diploid cells.

Meiosis

  • Specialized division for sperm and egg formation, yielding four unique haploid cells.

  • Involves two rounds of division and genetic recombination.

Comparison of Mitosis and Meiosis

  • Mitosis: Produces two diploid cells, genetically identical.

  • Meiosis: Produces four haploid cells, genetically unique.

References

  • Mescher, Anthony L. (2024). Junqueira's Basic Histology: Text & Atlas, 17th International ed. McGraw Hill.

  • Esteban and Gonzales' Textbook of Histology 6th edition. Eduardo G. Gonzales. C & E Publishing, Inc. 2022.