The Tissue Level of Organization

Transcription

1 The Tissue Level of Organization Tissues A groups of similar cells, usually having similar embryonic origin and specialized function Histology: the study of tissues Four general types Epithelial Muscle Connective Nervous Tissues develop from separation of germinal layers in early development Germinal Layers Three layers Ectoderm Mesoderm Endoderm Epithelia develop from all three layers Connective and muscle tissue from mesoderm Nervous tissue from ectoderm Cell Junctions Most cells are stationary - anchored to other cells, basement membranes, and connective tissue With some exceptions: phagocytes and some embryonic cells Three primary types Tight junctions Fluid-tight seals between cells Epithelial cells that line stomach, intestines and urinary bladder More Cell Junctions Anchoring junctions Fasten cells to each other or extracellular material Tissues subjected to friction and stretching (outer layer of skin, heart muscle, uterus, and lining of gastrointestinal tract Adherens junctions - microfilament attachment on interior of plaques (e.g. epithelia cells) Plaques composed of proteins just inside cell membrane Transmembrane glycoproteins Frequently with adhesion belt Even More Cell Junctions Desmosomes - Similar to adherens but also have intermediate filaments that connect plaques within cells (e.g. in epidermis and heart muscle) Hemidesmosomes - connects cells to extracellular material with transmembrane glycoprotein (e.g. basement membrane) Gap junctions Allow spread of excitability in some nerve cells, and muscle of heart and 4-1

2 gastrointestinal tract Connexons - protein tubes that allow movement of small cytosol molecules between cells Epithelial Tissue Forms superficial layer of skin & some internal organs, inner lining of blood vessels, duct, & body cavities, and interiors of respiratory, digestive, urinary and reproductive organs Characteristics: Closely packed together Arranged in continuous sheets of one or more layers Many cell junctions More Epithelial Tissue Organized with apical and basal surfaces apical exposed to interior of body cavity or organ basal attached to basement membrane which is composed of basal lamina secreted by epithelial cells and reticular lamina secreted by underlying connective tissue Avascular (exchange dependent on diffusion) Innervated Capacity for regeneration Even More Epithelial Tissue Epithelial functions include: protection, filtration, lubrication, secretion, digestion, absorption, transportation, excretion, sensory reception, reproduction Two general types Covering and lining epithelium Glandular epithelium Covering and Lining Epithelium Classified based on arrangement of layers and shape Layers: simple, stratified, pseudostratified Shapes: squamous, cuboidal, columnar, transitional Glandular Epithelium Mass of cells adapted for secretion into ducts, onto a surface or into blood Two types Endocrine (ductless) - secretory products released to extracellular space (unicellular and multicellular) Exocrine: - secrete products directly into ducts Holocrine: product released when cell dies (e.g. oil glands) Merocrine: exocytosis (e.g. salivary glands, pancreas, and mammary glands (previously thought to be apocrine) Epithelial Tissue Types Study Exhibit 4.1 Connective Tissue 4-2

3 Most widespread tissue in body Binds together, supports and strengthens other tissues, protects & insulates internal organs and compartmentalizes structures (e.g. skeletal muscles) Blood & lymph responsible for transport Adipose tissue stores energy and insulates More Connective Tissue Characteristics: Made up of three parts cells, ground substance, and fibers, the last two filling substantial extracellular space Do not occur on free surfaces Highly vascular (except cartilage and tendons) Innervated (except cartilage) Extracellular matrix determines tissue type (fluid, gelatinous, fibrous, calcified) Ground substance varies Different fiber types Connective Tissue Cells Fibroblasts - most abundant type and found in all connective tissues Important contributors to ground substance and fibers Macrophages - fixed or wandering, phagocytic Plasma cells - mature B-lymphocytes producing antibodies Mast cells - histamine producing cells near blood vessels Adipocytes - lipid storage WBC s Ground Substance Hyaluronic - viscous substance that binds cells and lubricates joints Chondroitin sulfate - jelly-like substance that supports and adheres in cartilage, bone, skin, and blood vessels Dermatan sulfate - skin, tendons, blood vessels, and heart valves Keratan sulfate - bone, cartilage, and cornea Adhesion proteins - stabilizes cells Fibers Three types Collagen - thick bundles of protein (25% of all protein), resistant to stretching yet flexible, found in bone, cartilage, tendons, & ligaments Elastic - thin branching network of elastin & fibrillin, stretches up to 150%, found in skin, blood vessels, and lungs Reticular - thin, branched collagen coated with glycoprotein, support for blood vessels, fat deposits, nerves, muscle fibers, basement membranes and organ structure - stroma Connective Tissue Types 4-3

4 Study Exhibit 4.2 Mesenchyme - semifluid ground substance and reticular fibers Precursor to other types of connective tissue Loose connective tissue Areolar - semifluid ground substance and all three types of fibers Adipose Reticular More Connective Tissue Types Dense connective tissue Dense regular Dense irregular Elastic Cartilage Hyaline - most abundant, usually surrounded by perichondrium (ex. articular cartilage) Fibrocartilage - lacks perichondrium (e.g. intervertebral discs) Elastic Bone, blood & lymph Epithelial Membranes Combination of epithelia and connective tissue Include: Mucous: line cavities that open to exterior (gastrointestinal, respiratory, urinary, & reproductive), mucous produced by goblet cells lubricate surfaces in tracts Serous: line body cavities (parietal) and cover organs (visceral), serous fluid reduces friction Cutaneous: later Synovial Membranes Only connective tissue - areolar Line joint cavities, bursae and tendon sheaths Synovial fluid reduces friction Muscle Tissue Provides motion, maintenance of posture, and heat production Three types Skeletal: attached to bones, striated, numerous nuclei, voluntary Cardiac: heart wall, striated, branched, one nucleus, involuntary Smooth: walls of hollow structures, not striated, one nucleus, involuntary Study Exhibit 4.3 Nervous Tissue Quickly communicate between parts of the body, sensitive to stimuli, interpret 4-4

5 information, coordinate action Two types Neurons: generate and conduct electrical impulses Neuroglia: provide protection and support for neurons Tissue Repair Replacement of damaged or dead cells (not possible for nervous, skeletal and cardiac muscle tissues and slow for smooth muscle) Mitosis of undifferentiated stem cells frequently source of new cells Parenchymal (functional) vs. stromal (support - fibroblast) repair fibrosis More Tissue Repair Importance of Vitamins A, B, C, D, E, & K and adequate protein Blood supply Effect of aging (metabolic and cell division rates) 4-5