Chapter 5 Histology - Lecture notes 5 PDF

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HISTOLOGY...

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Chapter 5 Histology Basis of Histology 200 different cell types Organs

- Composed of two or more tissue types Tissue

- Similar cells and cell products - Shared embryonic origin Major categories of tissues

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Epithelial tissue Connective tissue Muscle tissue Nervous tissue

Embryonic Formation of Tissues Human development begins as fertilized egg

- Divides into identical, smaller cells - Cell organize themselves into layers Three primary germ layers

- Ectoderm (outer layer) Gives rise to epidermis which folds in to become nervous system - Endoderm (inner layer) Becomes lining of digestive and respiratory tracts - Mesoderm (everything in between) Transformed into mesenchyme Gives rise to muscle, connective tissue, bone, blood

Interpreting Tissue Sections  Cross section of tubular organ  Longitudinal section of coiled tube

Epithelial Tissue  

Simple epithelium One layer of cells Named by shape of cells Sits on basement membrane Stratified epithelium - More than one layer - Named by shape of apical cells - Upper layers do not reach basement membrane

Simple squamous epithelium  Single row of flat cells  Rapid diffusion across membrane, secretes serous fluid  Air sacs, lining of blood vessels, surface membrane over organs

Simple cuboidal epithelium  Single layer of square/round cells with central nucleus  Absorption and secretion  Kidney, Liver, thyroid, mammary and salivary glands

Simple columnar epithelium Single row of tall, narrow cells with basal nucleus - Microbial goblet cells

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Absorption and secretion Lining of GI tract, reproductive tract and kidney tubules

Ciliated Pseudostratified Epithelium Looks multilayered but all cells sit on basement membrane - Nuclei at several levels within tissue - With cilia and goblet cells Secretes and propels mucus Respiratory tract and portions of male urethra

Stratified Epithelia Two to twenty or more layers of cells - Deepest cells undergo mitosis - Daughter cells push towards surface - Exfoliation or desquamation Two kinds of stratified squamous epithelium - Keratinized - Nonkeratinized

Keratinized Stratified Squamous Epithelium    

Multiple cell layers Surface cells flat, scaly and dead Epidermis Resists abrasion; prevents water loss & infection

Nonkeratinized Stratified Squamous

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 Surface cells not dead  Resists abrasion and penetration of pathogens  Tongue, oral mucosa, esophagus, vagina and anal canal

Stratificeer Cuboidal Epithelium  Two or more cell layers surface cells square or Round  Uncommon  Ducts of sweat glands sperm producent tubeless, hormone producent cells in ovary

Transitional Epithelium  Multilayered; surface cells change shape when stretched  Allows for filling of urinary tract

Connective Tissue: Overview Abundant and widely distributed Cells widely separated Variable vascularity Function        

Binding of organs Structural framework of body Physical protection immune protection Movement Energy and mineral storage Heat production Transport of nutrients, wastes and hormones

Derived from mesenchyme (mesodermal layer)

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Components of Connective Tissue Cells - Fibroblasts - Macrophages - Neutrophils and lymphocytes - Plasma cells - Mast cells - Adipocytes Fibers - Collagen fibers - Reticular fibers - Elastic fibers Ground substance

Ground Substance Gelatinous to rubbery consistency Absorbs compressive forces Contains three classes of large molecules  Glycosaminoglycans (GAG) Chondroitin sulfate Heparin Hyaluronic acid  Proteoglycan  Adhesive glycoproteins

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Types of Fibrous Connective Tissue Loose connective tissue - Much gel-like ground substance between cells - Types Areolar Reticular Dense connective tissue  Fibers all spaces between cells  Types vary in fiber orientation Dense regular connective tissue Dense irregular connective tissue

Areolar (Loose) Connective Tissue Ground substance, elastic and collagen fibers, scattered cells Beneath all epithelia, filler between other organs and tissues Passageway for nerves and blood vessels

Reticular Connective Tissue Network of reticular fibers; filled with cells Forms storm (framework) for organs Lymph nodes, spleen, thymus and bone marrow

Dense Regular Connective Tissue Densely packed, parallel or wavy, collagen fibers; fibroblast cells Holds things together  Tendons attach muscles to bones; ligaments hold bones together

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Dense Irregular Connective Tissue Densely packed, randomly arranged collagen fibers; Scattered fibroblasts Withstands stresses from different directions Deep layer of skin, capsules around organs

Adipose Tissue Large fat globule, thin rim cytoplasm; nucleus pressed against cell membrane Energy storage with constant turnover, insulation, Cushioning White fat in adults; Brown fat in children

Cartilage  Stiff, rubbery matrix external ear and tip of nose  Chondroblasts produce matrix around themselves - Called chondrocytes when trapped in lacunae  Minimal blood vessels so healing is slow  Types of cartilage - Hyaline cartilage - Elastic cartilage - Fibrocartilage  Perichondrium

Hyaline Cartilage Clear, glassy matrix due to fineness of collagen fibers Joint movements, holds airway open, provides structure for vocal cords

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Joint surfaces, airway, vocal cords

Elastic Cartilage Similar to hyaline with added elastic fibers Provides flexible, elastic support - External ear and epiglottis

Fibrocartilage Cartilage full of large, coarse bundles of collages fibers Resists compression and absorbs shock Never has perichondrium - Pubic symphysis and intervertebral discs

Bone Tissue Two forms of osseous tissue  Compact bone Dense, calcified tissue Cells and matrix form concentric lamellae (layers) around central canal Blood vessels and nerves in central canal  Spongy bone Spongy in appearance filled with spaces Delicate struts of bone: trabecular Covered by compact bone Found in ends of long bones and middle of flat bones

Compact Bone Tissue

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 Osteocytes separated by mineralized matrix  Canaliculi connect all lacunae containing Osteocytes to haversian or central canal  Osteon  Bones of skeleton = organs built from compact and spongy bone tissue, bone marrow, hyaline cartilage and dense irregular connective tissue

Blood Plasma-liquid ground substance Cells and cell fragments - Erythrocytes (RBCs) - Leukocytes (WBCs) - Platelets Functions - Transport gases, nutrients, wastes, heat, clotting agents, chemical signals, defensive cells

Nervous Tissue Neurons – scattered Large cells - Neurosoma - Axons and dendrites Glial cells - Smaller supportive cells Function - Internal communication Brain, spinal cord, nerves and ganglia

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Muscular Tissue Cells specialized to contract in response to stimulation Function  Exert physical force  Source of body heat Three types of muscle - Skeletal muscle - Cardiac muscle - Smooth muscle

Tight Junctions Binds epithelial cells tightly together along edges of apical surface Cells linked by transmembrane cell-adhesion proteins Prevents passage of materials between cells

Desmosomes    

Single spot of attachment formed by two cells Resists cells pulling apart (epidermis, uterine cervix, heart) Cytoskeleton linked to plaque beneath cell membrane Transmembrane proteins reach out from plaque to neighboring cell

Gap Junctions  Connexon = six transmembrane proteins in a ring  Connects two cells with water-filled pore  Ions, glucose, amino acids pass to next cell in embryo

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 Electrical excitation passes from cell to cell - Cardiac and smooth muscle

Glands Cell or organ that secretes substances for use elsewhere in the body Originate as invagination of surface epithelium Classification - Exocrine Duct releases secretion at surface or lumen - Endocrine No ducts Secretes products into bloodstream Unicellular glands Organs with endocrine and exocrine functions

Exocrine Gland Structure Connective tissue capsule and storma - Septa or trabecular - Lobes and lobules Parenchyma - Synthesizes and secretes product

Ducts of Exocrine Glands Simple or compound duct system Shape of gland

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- Tubular - Acinar (acinus or alveolus) - Tubuloacinar

Types of Secretions Serous glands - Thin, watery secretions Perspiration, milk, tears, digestive juices Mucous glands - Glycoprotein mucin absorbs water to form mucus Salivary glands, goblet cells Mixed glands - Contain both serous and mucous cells Salivary glands Cytogenic glands - Release whole cells (sperm and egg cells)

Merocrine Gland Secretion   -

Exocytosis of vesicles Tear glands, pancreas, gastric glands, and others Apocrine glands Axillary sweat glands, mammary glands Exocytosis

Holocrine Gland Secretion  Whole cell disintegrates  Secretion = cell fragments and product synthesized  Oil glands of scalp and glands of eyelids

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Membranes Cutaneous membrane (skin) - Stratified squamous epithelium on dense irregular connective tissue Mucous membrane (mucosa) - Epithelium over lamina propria and muscularis mucosae - Lines passageways that open to the outside Serous membrane (serosa) - Simple squamous epithelium on areolar connective tissue - Lines body cavities and viscera (mesothelium) Peritoneum, pericardium, pleurae Synovial membrane - Composed of connective tissue only - Lines synovial cavities and secretes synovial fluid

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