Human Anatomy and Physiology I - Cells and Tissues

Human Anatomy and Physiology I

Topic 2: Cells and Tissues

  • Tissue culture is a key aspect of studying cells and tissues.

  • The topic is described as exquisite and marvelous.

Updates and Reminders

  • General updates and reminders regarding the course.

Topic 1 Review Questions

  1. What is the difference between anatomy and physiology?

  2. Gross anatomy is the study of structures visible to the naked eye.

  3. The study of tissues is called histology.

  4. To analyze the metabolic activity of tissues in the body, you would use a radiographic technique such as PET (Positron Emission Tomography).

  5. One structure located in the thoracic cavity is the heart.

  6. A serous membrane has two layers.

  7. The pleural membrane surrounds the lungs.

  8. One structure located in the right hypochondriac region of the abdomen is the liver.

Microscopic Anatomy: Cytology vs Histology

  • Cytology: Study of individual cells.

  • Histology: Study of tissues and their structure.

  • An example includes cardiac muscle cells and cardiac muscle tissue.

Objective 1: Extracellular/Intracellular Materials

  • Multicellular organisms comprise cells located in varying chemical environments.

Definitions

  • Intracellular Materials: Materials found within cells, including cytoplasm, organelles, and inclusions (e.g., fat, hemoglobin, glycogen, keratin).

  • Extracellular Materials: Materials found between cells; may also be called intercellular material and can lie between cells in a tissue or in body cavities.

Components of Extracellular Material

  • Fluid: Includes water, inorganic materials (e.g., electrolytes, dissolved O₂, and CO₂), and small organic molecules (e.g., glucose, amino acids).

  • Interstitial Fluid: Fluid found between cells of a tissue.

  • Plasma: Extracellular fluid of blood.

  • Synovial Fluid: Fluid found in synovial joints.

  • Cerebrospinal Fluid: Fluid surrounding the brain and spinal cord.

Matrix

  • The matrix consists of proteins and polysaccharides secreted by cells of a tissue.

  • Functions of the Matrix:

    • Determine the physical properties of a tissue.

    • Stabilize the physical structure of the tissue.

    • Regulate cell division, migration, proliferation, shape, and function.

  • Proteoglycans: Examples include hyaluronic acid and glycosaminoglycans (GAGs).

Fibers and Attachment Proteins

  • Fibers: Collagen fibers, elastic fibers, and reticular fibers are components of the extracellular matrix.

  • Attachment Proteins: Non-collagen proteins that organize the matrix and help cells attach to it.

Objective 2: Cell Adhesion

  • Cells in a multicellular organism can adhere to one another or to their environment through cell adhesion molecules (CAMs).

Cell Adhesion Molecules (CAMs)

  • Help guide cell movement during:

    • Embryonic development

    • Wound repair

  • Functions:

    • Attach cells to each other and to the matrix.

    • Control cell shape.

Types of Cell Adhesion

  • Cell-Cell Adhesion: Interaction between cells.

  • Cell-Matrix Adhesion: Interaction between cells and the extracellular matrix.

Major Types of Cell Junctions

  • Tight Junctions: Membranes of adjacent cells fuse, forming impermeable barriers. Examples include the intestine and kidney, where diffusion is not wanted.

  • Desmosomes: Cells are separated by a small space but are held together by interlinker proteins, allowing stability under tension. Found in skin, muscle, and cervix cells.

  • Gap Junctions: Allow ions and small molecules to pass directly between cells, enabling communication. Found in embryonic cells, muscle, and some nerve cells for rapid signaling.

Objective 3: Cell Signaling

  • Some cell surface molecules act as receptors binding to extracellular signaling molecules (ligands).

Key Terms

  • Receptor: A membrane-bound protein that binds to a ligand.

  • Ligand: A molecule that specifically binds to receptors.

  • Signaling Cell: The cell that produces and secretes the ligand.

  • Target Cell: The cell that bears the receptors for a ligand.

Types of Signaling

  • Contact-Dependent Signaling: Via cell surface receptors, important in development and immune responses.

  • Extracellular Signaling Molecules: Include three types:

    1. Paracrine Factors: Act locally (e.g., histamine).

    2. Neurotransmitters: Released by neurons (e.g., acetylcholine).

    3. Endocrine Hormones: Released into the bloodstream affecting distant targets (e.g., epinephrine).

Classes of Receptors

  1. Catalytic Protein Receptors (Tyrosine Kinase)

  2. Chemically Gated Ion Channels

  3. G Protein-Coupled Receptors (GPCR)

Objective 4: Tissue Categories

  • Tissue: A group of cells that are similar in structure, function, and embryologic origin.

  • Histology: The study of the microscopic structure of tissues.

Categories of Tissues

  1. Epithelial Tissue: Covers surfaces, lines cavities, and forms glands.

  2. Connective Tissue: Supports and protects the body; binds organs, stores fat, provides immunity.

  3. Muscle Tissue: Responsible for movement and generation of force.

  4. Nerve Tissue: Initiates and transmits electrical signals.

Development Origin of Tissues

  • Tissues are derived from primary germ layers:

    • Ectoderm: Forms epidermis and nervous system.

    • Mesoderm: Forms connective tissue and muscles.

    • Endoderm: Lines digestive and respiratory systems.

Objective 5: Epithelial Tissue – General Characteristics

  • Location: Covers body surfaces; lines cavities; forms glands.

  • Structure: Cell-rich, matrix-poor with cell junctions.

Specializations of Epithelial Cells

  • Basement Membrane: Thin membrane made of ECM; attaches epithelial to connective tissue, allowing diffusion of nutrient and wastes.

  • Polarity: Epithelial cells are polarized; they have an apical surface facing the lumen and a basal surface facing the basement membrane.

Membrane Structures

  • Cilia: Hair-like projections moving fluids, contain microtubules.

  • Microvilli: Surface projections increasing surface area, important for absorption, containing actin filaments.

  • Keratin: Cytoskeletal protein forming structures like hair and nails.

Classification of Epithelial Tissues

  • According to cell shape and number of layers:

    • Cell Shapes: Flattened (squamous), cube-shaped (cuboidal), tall and narrow (columnar).

    • Layers: Simple epithelium (one layer), stratified epithelium (multiple layers).

Specific Examples

  • Simple Squamous: Function in diffusion/filtration; found in blood capillaries.

  • Simple Cuboidal: Function in secretion/absorption; found in kidney tubules.

  • Simple Columnar: Function in secretion/absorption; found in the lining of the stomach and intestines.

  • Pseudostratified Columnar: Secretory function; found in trachea.

  • Stratified Squamous: Protection; found in skin, mouth, and throat.

  • Transitional Epithelium: Function in holding fluctuating volumes of liquid; found in the bladder).

Objective 6: Glandular Epithelium

  • Glands: Single cells or masses grouped for secretion.

    • Classes of Glands:

      • Exocrine: Secrete onto a body surface (e.g., sweat, saliva).

      • Endocrine: Secrete into the bloodstream (e.g., hormones).

Gland Classifications

  • Number of cells: unicellular or multicellular.

  • Duct arrangement: simple or compound.

  • Shape of secretory units: tubular or acinar (alveolar).

  • Secretory mechanisms: merocrine, holocrine, apocrine.

Objective 9: Connective Tissues – General Characteristics

  • Location: Most abundant tissue type, found virtually everywhere, not on body surfaces.

  • Functions:

    • Binding and support (e.g., bone, cartilage).

    • Protection (e.g., bone, cartilage, blood).

    • Insulation (e.g., adipose).

    • Transportation (e.g., blood).

Objective 10: Classes of Connective Tissues

  1. Mesenchyme: Embryonic connective tissue.

  2. Connective Tissue Proper: Includes loose connective tissue (areolar, adipose, reticular) and dense connective tissue (dense regular, dense irregular, elastic).

  3. Cartilage: Hyaline, elastic, fibrocartilage.

  4. Bone.

  5. Blood.

Cellular Components of Connective Tissue

  • Connective tissue cells start as blasts that produce and secrete matrix components and can undergo mitosis.

  • Mature cells are referred to as cytes and primarily maintain the matrix.

Common Connective Tissue Cells

  • Fibroblasts: Secrete the ground substance.

  • Chondroblasts/Cytes: In cartilage.

  • Osteoblasts/Cytes: In bone.

  • Adipocytes: Store fat and secrete leptin.

  • Mast Cells: Release histamine.

  • Macrophages: Ingest debris.

Objective 11: Epithelial Membranes

  • Types include:

    • Serous Membrane: Simple squamous epithelium and areolar connective tissue that reduces friction.

    • Mucous Membrane: Variable epithelium and areolar connective tissue that secretes mucus.

    • Cutaneous Membrane: Skin; stratified squamous epithelium and connective tissue.

Membrane Functions

  • Functions: Protect and lubricate surfaces.

  • Locations: Respiratory, digestive, and urogenital tracts.

Objective 12: Tissue Repair

  • Repair involves the release of growth factors, leading to cell division and migration. There are two methods:

    1. Regeneration: Replacement with identical tissue.

    2. Fibrosis: Replacement with scar tissue.

  • Repair depends on various factors including tissue type, blood supply adequacy, and health/nutritional status.

Inflammation and Repair Process

  • Initial inflammation leads to increased permeability of blood vessels, allowing white blood cells and plasma proteins to aid in repair.

  • Stages of repair include:

    1. Clot formation.

    2. Granulation tissue formation.

    3. Regeneration of epithelium over scar tissue.