Tissues and Cell Junctions Quiz

Tissue Level of Organization

• Tissues are groups of similar cells and their products, originating from the same region of the embryo, working together to perform a specific structural or physiological role in an organ.

Origin of Tissues

• Tissues originate from the three primary germ layers: endoderm, mesoderm, and ectoderm.
• Epithelium arises from all three germ layers.
• Connective tissue and muscle derive from the mesoderm.
• Nerve tissue originates from the ectoderm.

Tissues

• Tissues are groups of similar cells with a common embryonic origin and function.
• Histology is the study of tissues.
• Pathologists examine tissue changes to diagnose disease, including forensic pathology.

Biopsy

• Biopsy involves removing living tissue for microscopic examination, often via surgery or needle biopsy.
• It's frequently used for cancer diagnosis.
• Tissue is preserved, sectioned, and stained before observation (micrographs).

Cell Junctions

• Cell junctions are contact points between adjacent plasma membranes.
• Three primary functions:
  • Form fluid-tight seals between cells.
  • Anchor cells together or to extracellular material.
  • Act as channels allowing ions and molecules to pass between adjacent cells within a tissue.
• Types include tight junctions, adherens junctions, gap junctions, desmosomes, and hemidesmosomes.

Tight Junctions

• Adjacent plasma membranes fuse with proteins, creating a watertight seal between cells.
• Common in tissues lining the digestive tract and bladder.

Adherens Junctions

• Holds epithelial cells together.
• Structural components include dense protein plaques and microfilaments extending into cytoplasm.
• Integral membrane protein connects cells.

Gap Junctions

• Tiny space between adjacent plasma membranes with protein channels (connexons) forming fluid-filled tunnels.
• Facilitates cell communication via ions and small molecules.
• Important in muscle and nerve impulse transmission, especially in the heart and gut.

Desmosomes

• Resist cellular separation and disruption.
• Similar to adherens junctions but with intermediate filaments (e.g., keratin) crossing the cytoplasm.
• Provides structural support, particularly in cardiac muscle.

Hemidesmosomes

• Half a desmosome anchoring cells to the extracellular material, such as the basement membrane.
• Connects cells to the basement membrane.

4 Basic Types of Tissues

• Epithelial, connective, muscle, and nerve tissues differ by cell type, functions of cells, characteristics of the surrounding matrix, and the ratio of cells to matrix.

Epithelial Tissue

• Covers surfaces, lines organs' cavities, and forms glands.
• Specialized cells closely packed.

General Features of Epithelial Tissue

• Closely packed cells forming continuous sheets.
• Cells sit on a basement membrane.
• Avascular (no blood vessels); nutrients diffuse from underlying connective tissue.
• Good nerve supply.
• High degree of rapid cell division.
• Two main categories: covering/lining and glandular.

Basement Membrane

• Basal lamina from epithelial cells and reticular lamina from connective tissue cells.
• Holds epithelial cells to connective tissue.
• Cell migration guide during development.

Types of Epithelium

• Covering/lining (skin, lining of organs, ducts).
• Glandular (secreting portions of glands, like thyroid or sweat glands).

Classification of Epithelium

• Arrangement of layers (simple or stratified).
• Shape of cells (squamous, cuboidal, columnar, transitional).
• Pseudostratified cells appear multilayered but are single.

Simple Squamous Epithelium

• Single layer of flat cells (endothelium, mesothelium).
• Controls diffusion, osmosis, and filtration.
• Nuclei centrally located.

Simple Cuboidal Epithelium

• Single layer of cube-shaped cells.
• Nuclei round and centrally located.
• Found in kidney tubules, some glands.

Nonciliated Simple Columnar Epithelium

• Single layer of rectangular cells with finger-like cytoplasmic projections called microvilli.
• Unicellular glands (goblet cells) secrete mucus, lubricating the GI, respiratory, reproductive, and urinary systems.

Ciliated Simple Columnar Epithelium

• Single layer of rectangular cells with cilia.
• Mucus moved by cilia occurs in the respiratory system and uterine tubes.

Pseudostratified Columnar Epithelium

• Single layer of cells, but nuclei positioned at different depths gives a multilayered appearance.
• Found in respiratory system, male urethra, and epididymis.

Stratified Squamous Epithelium

• Several layers of flat cells.
• Keratinized (dead cells filled with keratin) — skin.
• Nonkeratinized (moist living cells) — mouth, vagina.

Papanicolaou Smear

• Collects sloughed uterine and vaginal cells.
• Detects precancerous cells.
• Recommended for sexually active women over 18.

Simple Columnar Ciliated and Non-Ciliated

• Single layer of cells with rectangular shape.
• Simple columnar epithelium with cilia—motile extensions—moves mucus.
• Found in respiratory and uterine tubes.

Stratified Cuboidal Epithelium

• Multilayered.
• Surface cells cuboidal.
• Rare (sweat glands' ducts, male urethra).

Stratified Columnar Epithelium

• Multilayered.
• Surface cells columnar.
• Rare (large ducts).

Transitional Epithelium

• Multilayered tissue.
• Surface cells vary from round to flat to accommodate stretching during expansion inside hollow organs.
• Lines the urinary bladder.

Glandular Epithelium

• Derived from surface epithelial cells.
• Exocrine glands secrete products onto a free surface via ducts (e.g., sweat, saliva).
• Endocrine glands secrete hormones into the bloodstream.
• Unicellular or multicellular glands.

Structural Classification of Exocrine Glands

• Unicellular glands (e.g., goblet cells).
• Multicellular glands — branched (compound) or unbranched (simple).
• Tubular or acinar (flask-like) shape.

Examples of Simple Glands

• Unbranched ducts.

Examples of Compound Glands

• Branched ducts distinguished as acinar or tubular.

Duct of Multicellular Glands

• Stratified cuboidal epithelium.

Simple Cuboidal Epithelium (Example of Endocrine Gland)

• Forms thyroid follicles.
• Contains hormone-producing epithelial cells.
• Stores hormone precursors.

Connective Tissue

• Found between cells.
• Supports and binds structures.
• Stores energy as fat.
• Provides disease immunity.

Connective Tissue (types)

• Fibrous (loose and dense).
• Supportive (bone and cartilage).
• Fluid (blood and lymph).

Connective Tissue (cell types)

• Blast cells (fibroblasts, chondroblasts, osteoblasts) retain division capacity.
• Cyte cells (fibrocytes, chondrocytes, osteocytes) are mature, non-dividing cells.
• Macrophages (engulf), plasma cells (produce antibodies), mast cells (release histamine), and adipocytes (fat storage).

Connective Tissue (types - Fibrous - Loose)

• Areolar: -Fibroblasts, plasma cells, macrophages, mast cells and white blood cells. -Contains all three fiber types. -Gelatinous ground substance.

• Adipose: -Fat-storage area of adipocytes is surrounded by a layer of connective tissue. -Reduces heat loss.

• Reticular: -Forms a network of fibers. -Framework for organs such as liver, spleen, lymph nodes, and bone marrow.

Connective Tissue (types - Fibrous - Dense)

• Dense regular:
  • Parallel collagen fibers with fibroblasts between bundles. -Forms tendons.
• Dense irregular: -Irregularly arranged, interwoven collagen fibers. -Forms the dermis of skin.
• Elastic: -Branching elastic fibers with fibroblasts.
  • Found in vocal cords, lung tissue, and ligaments.

Connective Tissue (types - Supportive)

• Cartilage (hyaline, fibro, elastic): -Tough and rubbery, with collagen fibers embedded in ground substance. -Hyaline: reduces friction, mostly in joints. -Elastic: maintains shape after deformation, ear, nose. -Fibro: withstands tension and stress, intervertebral discs.

• Bone: -Compact and spongy bone. -Compact: osteons and lamellae with calcium and phosphate. -Spongy: no osteons, lattice-like trabeculae with red bone marrow.

Connective Tissue (types - Fluid)

• Blood: -Cells (red and white blood cells and platelets) in a liquid matrix (plasma).

• Lymph: -Interstitial fluid in lymphatic vessels, lower protein content than plasma.

  • Transports cells and substances.

Membranes

• Epithelial layer on supporting connective tissue (lamina propria). -Mucous: line cavities (open to outside). -Serous: line closed cavities. -Synovial: line joint cavities.

• Types: mucous, serous, synovial, cutaneous.

Muscle Tissue

• Cells shorten, producing movement.
• Types: skeletal, cardiac, smooth.

Skeletal Muscle

• Long, cylindrical cells with multiple peripheral nuclei.
• Striated (striped appearance).
• Voluntary (conscious control).

Cardiac Muscle

• Branched cells with a single central nucleus.
• Striated.
• Involuntary (automatic control).
• Specialized intercellular connections (intercalated discs).

Smooth Muscle

• Spindle-shaped cells with a single central nucleus.
• Nonstriated.
• Involuntary (automatic control).

Nerve Tissue

• Conducts electrical signals.
• Detects changes inside and outside the body.
• Responds with nerve impulses.
• Composed of nerve cells and neuroglia.
• Nerve cell structure includes a cell body with dendrites receiving signals and axons transmitting signals.

Tissue Engineering

• Growing new tissues in the lab.
• Scaffolding as a substrate for cell growth.
• Research in progress targets various tissues (insulin-producing and dopamine-producing cells, bone, tendons, heart valves, intestines, bone marrow).

Tissue Repair (Restoring Homeostasis)

• Replacing worn-out or damaged tissue.
• Fibrosis: replacement with connective tissue (scar formation).
• Regeneration: restoration using original cell types (parenchymal cells).

Important Clinical Terminology

• Regeneration vs. fibrosis.
• Granulation tissue—actively growing connective tissue.
• Adhesions: abnormal joining of tissue due to surgery or inflammation.

Conditions Affecting Tissue Repair

• Adequate nutrition (protein, vitamin C).
• Proper blood circulation is needed for O₂ and nutrient delivery.
• Aging process causes changes in collagen and elastin quality, slowing cell division and protein synthesis.
• Other factors such as autoimmune disorders (Sjögren's Syndrome) or chronic inflammatory diseases (SLE) also affect tissue repair.