Chapter 5 Tissues Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Histology Study of Tissues Epithelial Tissue Connective Tissue Nervous and Muscular Tissue Intercellular Junctions, Glands and Membranes Tissue Growth, Development, Death and Repair

The Study of Tissues 200 Different cell types Four primary tissue classes epithelial tissue connective tissue muscular tissue nervous tissue Histology (microscopic anatomy) study of tissues organ formation Organ = structure with discrete boundaries composed of 2 or more tissue types

Features of Tissue Classes Tissue = similar cells and cell products arose from same region of embryo Differences between tissue classes types and functions of cells characteristics of matrix (extracellular material) fibrous proteins ground substance clear gels (ECF, tissue fluid, interstitial fluid, tissue gel) rubbery or stony in cartilage or bone space occupied by cells versus matrix connective tissue cells are widely separated little matrix between epithelial and muscle cells

Embryonic Tissues Embryo begins as single cell 3 Primary germ layers divides into many cells and layers (strata) 3 Primary germ layers ectoderm (outer) forms epidermis and nervous system endoderm (inner) forms mucous membrane lining GI tract and respiratory system and digestive glands mesoderm (middle) becomes mesenchyme wispy collagen fibers and fibroblasts in gel matrix gives rise to muscle, bone, blood

Tissue Techniques and Sectioning Preparation of histological specimens fixative prevents decay (formalin) sliced into thin sections 1 or 2 cells thick mounted on slides and colored with histological stain stains bind to different cellular components Sectioning reduces 3-dimensional structure to 2-dimensional slice

Sectioning Solid Objects Sectioning a cell with a centrally located nucleus Some slices miss the cell nucleus In some the nucleus is smaller

Sectioning Hollow Structures Cross section of blood vessel, gut, or other tubular organ. Longitudinal section of a sweat gland. Notice what a single slice could look like.

Types of Tissue Sections Longitudinal section tissue cut along longest direction of organ Cross section tissue cut perpendicular to length of organ Oblique section tissue cut at angle between cross and longitudinal section

Intercellular Junctions All cells (except blood) anchored to each other or their matrix by intercellular junctions

Tight Junctions Encircle the cell joining it to surrounding cells zipperlike complementary grooves and ridges Prevents passage between cells GI and urinary tracts

Desmosomes Patch between cells holding them together cells spanned by filaments terminating on protein plaque cytoplasmic intermediate filaments also attach to plaque Uterus, heart and epidermis

Gap Junctions Ring of transmembrane proteins form a water-filled channel small solutes pass directly from cell to cell in embryos, cardiac and smooth muscle

Simple Versus Stratified Epithelia Stratified epithelium contains more than one layer named by shape of apical cells Simple epithelium contains one layer of cells named by shape of cells

Simple Squamous Epithelium Single row of flat cells Permits diffusion of substances Secretes serous fluid Alveoli, glomeruli, endothelium, and serosa

Simple Cuboidal Epithelium Single row cube-shaped cells with microvilli Absorption and secretion, mucus production Liver, thyroid, mammary and salivary glands, bronchioles, and kidney tubules

Simple Columnar Epithelium Single row tall, narrow cells oval nuclei in basal half of cell Absorption and secretion; mucus secretion Lining of GI tract, uterus, kidney and uterine tubes

Pseudostratified Epithelium Single row of cells some not reaching free surface nuclei give layer stratified look Secretes and propels respiratory mucus

Stratified Epithelia More than one layer of cells Named for shape of surface cells exception is transitional epithelium Deepest cells on basement membrane Variations keratinized epithelium has surface layer of dead cells nonkeratinized epithelium lacks the layer of dead cells

Keratinized Stratified Squamous Multilayered epithelium covered with dead squamous cells, packed with keratin epidermal layer of skin Retards water loss and barrier to organisms

Nonkeratinized Stratified Squamous Multilayered surface epithelium forming moist, slippery layer Tongue, oral mucosa, esophagus and vagina

Stratified Cuboidal Epithelium Two or more cell layers; surface cells square Secretes sweat; produces sperm and hormones Sweat gland ducts; ovarian follicles and seminiferous tubules

Transitional Epithelium Multilayered epithelium surface cells that change from round to flat when stretched allows for filling of urinary tract ureter and bladder

Endocrine and Exocrine Glands Secrete substances composed of epithelial tissue Exocrine glands connect to surface with a duct (epithelial tube) Endocrine glands secrete (hormones) directly into bloodstream Mixed organs do both liver, gonads, pancreas Unicellular glands – endo or exocrine goblet or intrinsic cells of stomach wall

Exocrine Gland Structure Stroma = capsule and septa divide gland into lobes and lobules Parenchyma = cells that secrete Acinus = cluster of cells surrounding the duct draining those cells

Types of Exocrine Glands Simple glands - unbranched duct Compound glands - branched duct Shape of gland acinar - secretory cells form dilated sac tubuloacinar - both tube and sacs

Types of Secretions Serous glands Mucous glands produce thin, watery secretions sweat, milk, tears and digestive juices Mucous glands produce mucin that absorbs water to form a sticky secretion called mucus Mixed glands contain both cell types Cytogenic glands release whole cells sperm and egg cells

Merocrine and Apocrine Secretion Merocrine glands release their product by exocytosis tears, gastric glands, pancreas, etc. Apocrine glands are merocrine glands with confusing appearance (apical cytoplasm not lost) mammary and armpit sweat glands

Holocrine Gland Secretory cells disintegrate to deliver their accumulated product oil-producing glands of the scalp

Connective Tissue Widely spaced cells separated by fibers and ground substance Most abundant and variable tissue type Functions connects organs gives support and protection (physical and immune) stores energy and produces heat movement and transport of materials

Cells of Connective Tissue Fibroblasts produce fibers and ground substance Macrophages phagocytize foreign material and activate immune system arise from monocytes (WBCs) Neutrophils wander in search of bacteria Plasma cells synthesize antibodies arise from WBCs Mast cells secrete heparin inhibits clotting histamine that dilates blood vessels Adipocytes store triglycerides

Fibers of Connective Tissue Collagen fibers (white fibers) tough, stretch resistant, yet flexible tendons, ligaments and deep layer of the skin Reticular fibers thin, collagen fibers coated with glycoprotein framework in spleen and lymph nodes Elastic fibers (yellow fibers) thin branching fibers of elastin protein stretch and recoil like rubberband (elasticity) skin, lungs and arteries stretch and recoil

Connective Tissue Ground Substance Gelatinous material between cells absorbs compressive forces Consists of 3 classes of large molecules glycosaminoglycans – chondroitin sulfate disaccharides that attract sodium and hold water role in regulating water and electrolyte balance Proteoglycan (bottlebrush-shaped molecule) create bonds with cells or extracellular macromolecules adhesive glycoproteins protein-carbohydrate complexes bind cell membrane to collagen outside the cells

Fibrous Connective Tissue Types Loose connective tissue gel-like ground substance between cells types areolar reticular adipose Dense connective tissue fibers fill spaces between cells types vary in fiber orientation dense regular connective tissue dense irregular connective tissue

Areolar Tissue Loose arrangement of fibers and cells in abundant ground substance Underlies all epithelia, between muscles, passageways for nerves and blood vessels

Reticular Tissue Loose network of reticular fibers and cells Forms supportive stroma (framework) for lymphatic organs Found in lymph nodes, spleen, thymus and bone marrow

Adipose Tissue Empty-looking cells with thin margins; nucleus pressed against cell membrane Energy storage, insulation, cushioning subcutaneous fat and organ packing brown fat (hibernating animals) produces heat

Dense Regular Connective Tissue Densely, packed, parallel collagen fibers compressed fibroblast nuclei Tendons and ligaments hold bones together and attach muscles to bones

Dense Irregular Connective Tissue Densely packed, randomly arranged, collagen fibers and few visible cells withstands stresses applied in different directions deeper layer of skin; capsules around organs

Cartilage Supportive connective tissue with rubbery matrix Chondroblasts produce matrix called chondrocytes once surrounded No blood vessels diffusion brings nutrients and removes wastes heals slowly Types of cartilage vary with fiber types hyaline, fibrocartilage and elastic cartilage

Hyaline Cartilage Rubbery matrix; dispersed collagen fibers; clustered chondrocytes in lacunae supports airway, eases joint movements Ends of bones at movable joints; sternal ends of ribs; supportive material in larynx, trachea, bronchi and fetal skeleton

Elastic Cartilage Hyaline cartilage with elastic fibers Provides flexible, elastic support external ear and epiglottis

Fibrocartilage Hyaline cartilage with extensive collagen fibers (never has perichondrium) Resists compression and absorbs shock pubic symphysis, meniscus and intervertebral discs

Bone Spongy bone - spongy in appearance delicate struts of bone covered by compact bone found in heads of long bones Compact bone - solid in appearance more complex arrangement cells and matrix surround vertically oriented blood vessels in long bones

Bone Tissue (compact bone) Calcified matrix in lamellae around central canal Osteocytes in lacunae between lamellae Skeletal support; leverage for muscles; mineral storage

Other Tissues

Muscle Tissue Elongated cells stimulated to contract Exert physical force on other tissues move limbs push blood through a vessel expel urine Source of body heat 3 histological types of muscle skeletal, cardiac and smooth

Changes in Tissue Types Tissues can change types Differentiation unspecialized tissues of embryo become specialized mature types mesenchyme to muscle Metaplasia changing from one type of mature tissue to another simple cuboidal tissue before puberty changes to stratified squamous after puberty

Tissue Growth Hyperplasia = tissue growth through cell multiplication Hypertrophy = enlargement of preexisting cells muscle grow through exercise Neoplasia = growth of a tumor (benign or malignant) through growth of abnormal tissue

Tissue Shrinkage and Death Atrophy = loss of cell size or number disuse atrophy from lack of use (leg in a cast) Necrosis = pathological death of tissue gangrene - insufficient blood supply gas gangrene - anaerobic bacterial infection infarction - death of tissue from lack of blood decubitus ulcer - bed sore or pressure sore Apoptosis = programmed cell death cells shrink and are phagocytized (no inflammation)

Tissue Repair Regeneration Fibrosis replacement of damaged cells with original cells skin injuries and liver regenerate Fibrosis replacement of damaged cells with scar tissue function is not restored healing muscle injuries, scarring of lung tissue in TB or healing of severe cuts and burns of the skin keloid is healing with excessive fibrosis (raised shiny scars)

Tissue Engineering Production of tissues and organs in the lab framework of collagen or biodegradable polyester fibers seeded with human cells grown in “bioreactor” (inside of mouse) supplies nutrients and oxygen to growing tissue Skin grafts already available research in progress on heart valves, coronary arteries, bone, liver, tendons

Wound Healing of a Laceration Damaged vessels leak blood Damaged cells and mast cells leak histamine dilates blood vessels increases blood flow increases capillary permeability Plasma carries antibodies, clotting factors and WBCs into wound

Wound Healing of a Laceration Clot forms Scab forms on surface Macrophages start to clean up debris

Wound Healing of a Laceration New capillaries grow into wound Fibroblasts deposit new collagen to replace old material Fibroblastic phase begins in 3-4 days and lasts up to 2 weeks

Wound Healing of a Laceration Epithelial cells multiply and spread beneath scab Scab falls off Epithelium thickens Connective tissue forms only scar tissue (fibrosis) Remodeling phase may last 2 years

Membranes

Membrane Types Cutaneous membrane = skin stratified squamous epithelium over connective tissue relatively dry layer serves protective function Synovial membrane lines joint cavities connective tissue layer only, secretes synovial fluid Serous membrane (serosa) –internal membrane simple squamous epithelium over areolar tissue, produces serous fluid covers organs and lines walls of body cavities

Mucous Membranes Epithelium, lamina propria and muscularis mucosae Lines passageways that open to the exterior: reproductive, respiratory, urinary and digestive Mucous (movement of cilia) trap and remove foreign particles and bacteria from internal body surfaces

Stem Cells

Stem Cells Undifferentiated cells with developmental plasticity Embryonic stem cells totipotent (any cell type possible) source = cells of very early embryo Pluripotent (tissue types only possible) source = cells of inner cell mass of embryo Adult stem cells (undifferentiated cells in tissues of adults) multipotent (bone marrow producing several blood cell types) unipotent (only epidermal cells produced)

END of Tissues