01-04 Anatomie und Physiologie I

Tissue Families / Basic Tissues

• Tissue diversity arises from cellular differentiation and specialization.
• Four basic tissue types share common properties but differ in function, cell shape, and extracellular matrix (EZM) composition.
• Organs typically contain at least two, usually all four, basic tissue types.

Basic Tissue Types and Functions

• Connective and Supportive Tissue
  • Functions: Structure, nutrient supply, storage, defense, forms stroma of fat, bone, and cartilage.
  • EZR content: Varies from low to high.
• Epithelial Tissue
  • Functions: Covers surfaces, forms glands, houses receptors; makes up the parenchyma of internal organs.
• Muscle Tissue
  • Functions: Contraction; constitutes parenchyma of muscles.
• Nervous Tissue
  • Functions: Information transmission, processing, and storage; forms parenchyma of the nervous system.

Connective and Supportive Tissues: Common Properties

• Fixed Cells
  • Originate locally from precursor cells, contribute to fiber types (collagen I, II, III).
  • Types:
    • Type I (collagenous tissue, over 90%): Bone includes Hydroxyapatite.
    • Type II (cartilage, vitreous body).
    • Type III (reticular fibers, reticular and fat tissue; basement membrane).
    • Type IV (non-fibrillar, part of the basal lamina).
    • Type VII (anchor fibers, connection between skin layers).

Connective Tissue Overview

• Cells
  • Fixed: Fibrocytes/Fibroblasts are tissue organizers; capable of regeneration.
  • Free: Varied numbers based on the type; increase during inflammation.
• Collagenous Tissue
  • Composed mainly of Type I collagen fibers, varies in elastic fiber quantity.
  • Loose Connective Tissue: Rich in cells, supports organs, forms lamina propria.
  • Dense Connective Tissue: Fewer cells, thicker fibers; functions mechanically (e.g., tendons, ligaments).

Specialized Connective Tissues

• Adipose Tissue
  • Composed of fixed adipocytes, non-dividing, minimal EZM.
  • White Adipose Tissue: Stores fat, structural functions located in subcutaneous layers and abdomen.
  • Brown Adipose Tissue: Multi-vacuolar adipocytes involved in non-shivering thermogenesis, important in infants.
  • Beige Adipose Tissue: Flexible function, related to thermogenesis and fat storage.

Cartilage Tissue

• Cells
  • Fixed chondrocytes located in ECM lacunae; do not regenerate post-growth.
• Types of Cartilage:
  • Hyaline Cartilage: Type II collagen, elastically allows for flexibility; found in the embryo skeleton and adult joints.
  • Elastic Cartilage: Contains unmasked elastic fibers; found in the outer ear and epiglottis.
  • Fibrocartilage: Contains both Type II and I collagen; provides tensile strength found in joints' discs and intervertebral discs.

Bone Tissue

• Cells
  • Fixed osteocytes form networks via extensions and gap junctions; undergo turnover and repairs via precursor cells.
• Mineralization:
  • Hydroxyapatite crystals form a strong composite with collagen.
• Bone Types:
  • Woven Bone: Unorganized matrix, found during growth and healing.
  • Lamellar Bone: Organized structure, represents healthy mature bone.

Development, Growth, and Replacement of Connective and Supportive Tissues

• Stem Cells
  • Mesenchymal stem cells give rise to fixed cells through asymmetric division maintaining self-renewal and differentiation.
• Precursor Cells
  • Undergo symmetric division, used up through differentiation into specialized cells like fibroblasts, adipocytes, chondrocytes, and osteocytes.
• Embryonic Mesenchyme:
  • Serves as the structureless connective tissue precursor, while adults contain fibroblasts that retain stem cell functions.

Tissue Families / Basic Tissues

• Diversity in tissues results from cell differentiation and specialization.
• Four basic tissues can be classified based on function, cell shape, and extracellular matrix (ECM) proportion.
• All basic tissue types can be further divided into subtypes.
• Organs contain at least two, often all four basic tissue types.

Proportions of Extracellular Matrix and Functions

• Connective and supporting tissues: High ECM proportion; provide structure, supply, storage, and defense.
• Epithelial tissue: Minimal ECM; forms surfaces, glands, and receptors, contributing to the parenchyma of the internal organs.
• Muscle tissue: Some ECM; facilitates contraction, integral to muscle parenchyma.
• Nervous tissue: Minimal ECM; responsible for information transmission, processing, and storage, making up the nervous system parenchyma.

Epithelial Tissue Overview

• Epithelia defined by organization: single-layered (simple), multi-layered (stratified), or pseudo-stratified.
• Cell shapes in superficial layers: flat (squamous), cube-shaped (cuboidal), tall (columnar).
• Specialized features include cell projections (e.g., microvilli, stereocilia, cilia) and junctional complexes (e.g., tight junctions).

Simple Epithelium

• Consists of a single layer of cells from the basement membrane to the free surface.
• Types include:
  • Simple squamous epithelium: Found in endothelium, mesothelium, and alveoli.
  • Simple cuboidal epithelium: Characteristic of kidney tubules; may possess microvilli.
  • Simple columnar epithelium: Present in gastric mucosa, renal collecting ducts, intestinal mucosa, with microvilli or cilia in specific areas.

Stratified Epithelium

• Composed of multiple cell layers; superficial cells do not touch the basement membrane.
• Stratification leads to a continuous cell turnover with basal cell regeneration.
• Types include:
  • Stratified columnar epithelium: Found in conjunctiva and pancreatic ducts.
  • Non-keratinized stratified squamous epithelium: Located in the oral cavity, pharynx, larynx, esophagus, anal canal, vagina, and cornea; potential precursor to carcinoma through keratinization (e.g., leukoplakia).
  • Keratinized stratified squamous epithelium: The epidermis of the skin and dorsal surface of the tongue.

Transitional Epithelium (Urothelium)

• Multi-layered with variable cell shapes; especially prominent in the urinary system.
• Composed of large surface cells (umbrella cells) that vary with stretching.
• Features specialized vesicular structures (crusta) aiding in membrane material reserve.

Pseudostratified Epithelium

• Unique form of simple epithelium displaying multiple rows of nuclei; all cells contact the basement membrane but not all reach the surface.
• Commonly found in respiratory epithelium with cilia and stereocilia in the epididymis and vas deferens.

Polar Organization of Epithelial Cells

• Epithelial cells exhibit polarized structure with distinct functional domains.
• Tight junctions separate the apical and basal membranes, leading to specialized functions in secretion and absorption.
• Goblet cells and endocrine cells within the epithelial tissues are capable of producing mucus or hormones.

Glandular Epithelium

• Exocrine glands: Typically have a duct, often located in epithelial layers; can be tubuloalveolar (e.g., salivary glands, pancreas).
• Types of secretion include:
  • Tubular: straight or coiled, producing a protein-poor secretion on demand.
  • Tubuloacinar: with storage features, producing protein-rich secretions that require more time to synthesize.
  • Alveolar: larger storage capacity, producing fat-rich secretions through apocrine mechanisms.

Muscle Tissue Characteristics

• Muscle tissue generates and transmits force through the interaction of actin and myosin, triggered by calcium ions.
• Force is transferred directly through actin to the cell membrane and indirectly via the cytoskeleton.
• Muscle tissues are categorized into smooth, striated, and cardiac types, characterized by distinct structural and functional features.

Tissue Families / Basic Tissues

• Tissue diversity arises from cell differentiation and specialization.
• Four basic tissue types share common properties and can be distinguished by function, cell shape, and extracellular matrix proportion.
• Organs typically consist of at least two and usually all four basic tissue types.

Basic Tissue Types and Their Functions

• Connective and Supportive Tissue: Provides structure, nutrition, storage, and defense; includes stroma and parenchyma of fat, bone, and cartilage.
• Epithelial Tissue: Forms surfaces, glands, and receptors; constitutes the parenchyma of internal organs.
• Muscle Tissue: Responsible for contraction; forms the parenchyma of muscles.
• Nervous Tissue: Facilitates transmission, processing, and storage of information; forms the parenchyma of the nervous system.

Nervous Tissue Overview

• Comprises the parenchyma of both the central nervous system (CNS) and peripheral nervous system (PNS).
• Includes components of the brain, spinal cord, cranial nerves, spinal nerves, plexuses, and the enteric nervous system located in the gastrointestinal tract.
• Neurons encode information through changes in membrane potential, with resting potential at -70mV, depolarization indicating excitation, and hyperpolarization indicating inhibition.

Neurons

• Communication occurs over long distances via axons, crossing the CNS-PNS boundary.
• Information processing and storage happen in cell bodies, dendrites, and synapses.

Glial Cells

• Non-neuronal supporting cells essential for nervous tissue function.
• Various types of glial cells exist, each with specific roles in the CNS and PNS.

Regeneration in Nervous Tissue

• PNS offers a favorable environment for nerve fiber regeneration and may assist in wound healing.
• CNS exhibits minimal to no regeneration of long nerve fibers, leading to severe diseases like multiple sclerosis due to glial cell dysfunction.

Types of Glial Cells

• Astrocytes: Star-shaped cells providing waste disposal, energy supply, activity regulation, and forming barriers against blood vessels; regulate neurite growth.
• Oligodendrocytes: Form myelin sheaths in the CNS and restrict growth and regeneration.
• Microglia: Resident macrophages acting in immune defense; assist in pruning neurons and synapses during development.
• Ependymal and Plexus Cells: Ependymal cells line the ventricle system with cilia; plexus cells are involved in cerebrospinal fluid production.
• Schwann Cells: Cover axons in the PNS, play a role in pain sensation, and support fiber regeneration.
• Satellite Cells (Mantel Cells): Surround nerve cell bodies in the PNS, providing structural support.