Histology and Cell Biology Test 1 Review

Histology and Etymology

  • Histology: This is the study of the microscopic structure and function of tissues, specifically looking at how cells and associated tissues are organized.
  • Tissues: A structure formed by the grouping of cells with similar characteristics in both form and function.
  • Cell Etymology and Terminology:
    • Cyt-: Cell.
    • Endo-: Within.
    • Inter-: Between.
    • Lys-: To break up.
    • Phag-: To eat.
    • Pino-: To drink.
    • Glyc-: Sweet.
    • Lip-: Fat.
    • Nucle-: Kernel or core.
    • Mono-: One.
    • Poly-: Many.
    • Syn-: Together.

The Human Cell

  • Nature of the Cell: The cell is the smallest unit capable of independent existence and represents the smallest unit of organization in the human body.
  • Core Functions:
    • Absorption: Taking in materials.
    • Assimilation: The use of digested and absorbed materials to manufacture new cell parts.
    • Respiration: Cellular energy production.
    • Irritability: Reaction to a specific stimulus.
    • Conductivity: Transmission of impulses.
    • Growth: Increase in size or complexity.
    • Reproduction: Division and multiplication.
    • Excretion: Expulsion of waste products.
  • Extracellular Interaction: Cells interact with the environment through active processes requiring energy (active transport):
    • Exocytosis: The expulsion of materials out of the cell by fusing a vesicle membrane with the plasma membrane.
    • Endocytosis: The uptake of materials into the cell.
      • Pinocytosis: Often referred to as "cell drinking."
      • Phagocytosis: Often referred to as "cell eating."

Cellular Organelles and Structures

  • Cell Membrane (Plasma Membrane): A semipermeable phospholipid bilayer that surrounds the cell, acting as a selective barrier and diffusion regulator. It contains proteins that provide structural reinforcement and act as receptors for hormones, neurotransmitters, and immunoglobulins.
  • Cytoplasm (Cytosol): A clear liquid medium enclosed by the cell membrane that contains organelles, inclusions, and vacuoles (spaces or cavities).
  • Nucleus: The largest and densest organelle, present in all cells except mature red blood cells and blood platelets. It serves as the site for production of DNA (genetic information) and RNA (information carrier for protein synthesis).
    • Nucleolus: Contained within the nucleus; produces rRNA and nucleotides.
    • Chromatin: The form of DNA within the nucleus; it contains chromosomes and appears as diffuse stippling under a low-power microscope.
    • Nucleoplasm: The fluid portion of the nucleus containing essential proteins.
    • Nuclear Envelope: A double-layered membrane surrounding the nucleus.
    • Nuclear Pores: Openings in the nuclear envelope.
  • Mitochondria: Known as the "powerhouse" of the cell, these are the most numerous organelles. They convert energy from food molecules into adenosine triphosphate (ATPATP). They possess two membranes, the inner of which is folded into cristae to increase surface area.
  • Ribosomes: Termed "protein factories," they are comprised of protein and RNA and are responsible for synthesizing proteins.
  • Endoplasmic Reticulum (ER): The cell's "highway system," consisting of parallel, interconnected membrane-bound channels.
    • Rough ER: Studded with ribosomes; involved in protein modification and transport to the Golgi Apparatus.
    • Smooth ER: Lacks ribosomes; contains enzymes for manufacturing lipid molecules and steroid hormones.
  • Golgi Apparatus: The "chemical processing and packaging center." It is the second-largest organelle, consisting of a stack of 3 to 20 flattened sacs. It sorts, condenses, and packages proteins for exocytosis.
  • Lysosome: The "sewer system," containing hydrolytic and digestive enzymes like hyaluronidase to destroy worn cell parts or foreign substances. These are produced by the Golgi Apparatus.
  • Cytoskeleton: Provides basic stability and compartmentalizes the cytoplasm.
    • Microfilaments: Delicate, threadlike proteins arranged in a meshwork; responsible for cell motility and various cellular movements.
    • Microtubules: Thick, stiff tubes that form the internal skeleton, maintaining cell shape. They are structural components of cilia, flagella, centrioles, and the mitotic spindle.
    • Intermediate Filaments: Thicker threadlike structures involved in intercellular junctions and mitosis. An example is the tonofilament.
  • Inclusions: Metabolically inert, transient substances like stored nutrients (glycogen, lipids) or pigments (melanin).

Intercellular Junctions

  • Tight Junctions: Fuses cell membranes together to create a "water-tight" seal, closing intercellular space. Found in the lining of the small intestine.
  • Gap Junctions: Tubular channels between cells that allow for the exchange of substances. Found in heart muscle cells and the digestive tube.
  • Desmosomes: Bonds that create "spot welds" to attach adjacent cells to each other. Prevalent in the outer skin and oral mucosa.
  • Hemidesmosomes: Attachments between a cell and an adjacent non-cellular surface (such as the basement membrane). These allow gingival tissue to adhere to tooth surfaces via epithelial attachment.

The Life Cycle of a Cell

  • Interphase: The stage of growth and DNA replication.
    • G1 Phase: The initial resting phase of cell growth.
    • S Phase: DNA replication involving chromatin and centrosome replication.
    • G2 Phase: The second resting phase of cell growth.
  • Mitosis (Cell Division): A continuous process dividing nuclear parts into two equal daughter cells.
    • Prophase: Chromatin condenses into chromosomes; centrioles move to opposite poles; the nuclear membrane and nucleolus disappear.
    • Metaphase: Chromosomes arrange midway between centrioles; spindle fibers attach to centromeres.
    • Anaphase: Centromeres split; chromatids are pulled by shortening spindle fibers toward opposite poles.
    • Telophase: Nuclear membranes and nucleoli reappear; chromosomes elongate into chromatin; microtubules disappear.
  • Cytoplasmic Division (Cytokinesis): The division of all cytoplasmic components into two identical daughter cells.
  • Differentiation: The process by which less specialized cells become more specialized (e.g., an ovum and sperm becoming a fetus).
  • Meiosis: The process occurring during the maturation of sex cells.

Classification of Basic Tissues

  • Embryological Origins:
    • Ectoderm: Develops into skin and oral mucosa.
    • Endoderm: Develops into the respiratory and digestive tract linings.
    • Mesoderm: Develops into the urinary tract, connective tissues, and muscles.
  • The Four Basic Tissues:
    1. Epithelial Tissue: Protective coverings; involved in secretion, sensory, and absorption.
    2. Connective Tissue: Support for soft parts; binds structures together.
    3. Muscular Tissue: Responsible for body movement.
    4. Nerve Tissue: Conducts impulses to control and coordinate activities.

Epithelial Tissue

  • General Characteristics: Covers and lines internal and external surfaces (vessels, cavities). It is highly regenerative through mitosis of deeper cells. It is avascular, relying on diffusion for nutrition from the underlying vascularized connective tissue.
  • Turnover Time: The time required for newly divided cells to be completely replaced.
    • Skin: Approximately 27 days27\,\text{days}.
    • Oral Cavity: Approximately 14 days14\,\text{days}.
  • Basement Membrane: A thin, acellular structure between epithelium and connective tissue.
    • Basal Lamina: Consists of the Lamina Lucida (clear layer) and Lamina Densa (dense layer).
    • Reticular Lamina: Contains collagen and reticular fibers.
  • Epithelium Classification:
    • Simple Squamous: Single layer of flat cells; filtering function. Locations: pulmonary alveoli, inner/middle ear, blood/lymphatic vessels (Endothelium), and serous cavities.
    • Simple Cuboidal: Cube-like cells; protection and secretion. Location: salivary gland ducts.
    • Simple Columnar: Rectangular cells. Contains goblet cells for mucin secretion. Can be ciliated (uterus, fallopian tubes) or non-ciliated (stomach, intestines).
    • Pseudostratified Columnar: Crowded cells with nuclei at different levels; appears layered but is a single layer. Lines the upper respiratory tract, nasal cavity, and paranasal sinuses.
    • Stratified Squamous (Non-Keratinized): Many layers; no keratin; kept moist by secretions. Locations: buccal/alveolar mucosa, soft palate, floor of mouth, esophagus, and cornea.
    • Stratified Squamous (Keratinized): Protective layer of keratin (tough, waterproof protein). Composed of five layers: Stratum basale, Stratum spinosum, Stratum granulosum, Stratum lucidum (only in palms/soles), and Stratum corneum (dead cells). Locations: skin, hard palate, attached gingiva, dorsal of tongue.
    • Transitional: Cells change shape (polyhedral to flat) based on stretch. Location: urinary bladder.

Connective Tissue (CT)

  • Structure: Cells are spaced apart with a large amount of matrix (fibers and intercellular substance).
  • Major Cell Types:
    • Fibroblasts: Most common; synthesize protein fibers and intercellular substance; fixed in tissue.
    • Macrophages (Monocytes): Phagocytes that ingest bacteria and dead cells.
    • Mast Cells (Basophils): Involved in allergic responses; release heparin (anticoagulant) and histamine.
  • Fibers:
    • Collagenous: Composed of collagen; high tensile strength.
    • Elastic: Composed of elastin; provides elasticity (e.g., soft palate, vocal cords).
    • Reticular: Composed of reticulin; fine, branching network (e.g., lymph nodes, spleen).
  • Connective Tissue Types:
    • Loose CT: Thin membranes; binds organs; protective padding. Found in the dermis.
    • Fibrous (Dense) CT: Strong collagenous fibers. Found in tendons, ligaments, and the eyes.
    • Adipose CT: Stores fat; heat insulator and cushion. Found in the hypodermis.
    • Reticular CT: Delicate network supporting blood vessels and internal organs (liver, spleen).

Specialized Connective Tissues

  • Cartilage: Firm, non-calcified, avascular tissue. Surrounded by a fibrous sheath called the perichondrium.
    • Chondroblasts: Produce cartilage matrix.
    • Chondrocytes: Mature cells that maintain the matrix, residing in spaces called lacunae.
    • Hyaline Cartilage: Contains fine collagen fibers; the precursor to most cartilage. Found in embryonic skeletons and the mandibular condyle.
    • Elastic Cartilage: Contains many elastic fibers. Found in the external ear and epiglottis.
    • Fibrocartilage: Transitional tissue with great tensile strength; lacks a perichondrium. Found in intervertebral discs and the TMJ.
  • Bone: Rigid, mineralized tissue. Highly vascularized for rapid healing.
    • Bone Cells: Osteogenic cells (stem cells), Osteoblasts (bone-building), Osteocytes (mature builders in lacunae), and Osteoclasts (bone-resorbing in Howship's lacunae).
    • Architecture: Osteon (unit structure), Haversian canal (longitudinal vascular canal), Volkmann’s canal (oblique vascular canal), Lamellae (concentric sheets), Canaliculi (tubular canals for cytoplasmic processes), and Sharpey’s fibers (anchor periosteum to bone).
    • Ossification:
      • Intramembranous: Bone formation within two CT sheets using appositional growth (e.g., maxilla, mandible, fontanelles).
      • Endochondral: Bone formation within a hyaline cartilage model using interstitial then appositional growth (e.g., long bones, head of mandible).
  • Hemopoietic Tissue (Blood): Fluid tissue without fibers.
    • Red Blood Cells (RBCs): Biconcave discs; transport oxygen via hemoglobin.
    • Platelets (Thrombocytes): Clotting function.
    • White Blood Cells (Leukocytes):
      • Neutrophils (PMNs): First to arrive at injury; phagocytosis.
      • Eosinophils/Basophils: Control inflammation and allergic reactions.
      • Monocytes: Become macrophages.
      • Lymphocytes: B, T, and NK cells involved in chronic immunity.

Muscle and Nerve Tissues

  • Muscle Tissue:
    • Skeletal: Voluntary, striated, threadlike cells. Organized into muscle fascicles, myofibers, myofibrils, and myofilaments.
    • Smooth: Involuntary, non-striated. Found in hollow organs and blood vessels.
    • Cardiac: Involuntary, striated. Features branched networks and intercalated discs.
  • Nerve Tissue:
    • Neuron: The functional cell. Comprised of dendrites (carry impulses to cell body), axon (carries impulses away), and the cell body (metabolic center).
    • Afferent (Sensory) Nerve: Carries information from the PNS to the CNS (e.g., pain, taste).
    • Efferent (Motor) Nerve: Carries information from the CNS to the PNS.
    • Nerve: A bundle of neural processes in the Peripheral Nervous System (PNS).
    • Synapse: The junction between two neurons or a neuron and an effector organ.
    • Ganglion: A grouping of neuron cell bodies outside the Central Nervous System (CNS).", "title": "Comprehensive Study Guide: Histology, The Cell, and Basic Tissues"}