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TISSUES TISSUES Groups of cells similar in structure and function 2 or more different tissue types must be present to be classified as an organ. Histology is the study of tissues 4 types total TISSUES Types of tissues Epithelial tissue Connective tissue Muscle tissue Nerve tissue EPITHELIAL TISSUES FUNCTIONS: PROTECTION ABSORPTION FILTRATION SECRETION They also: -line and cover every external and internal surface of the body -provide lubrication -contains all three junctions(gap, tight, and desmosome) EPITHELIAL TISSUES Characteristics Avascular: does not contain a blood supply Die and replace themselves quickly Make thin layers • • • Innervated: has a nerve supply Always supported by connective tissue Always has 2 surfaces • • Apical: open or free side Basal: attached to connective tissue Shape Classification Squamous: flattened, scale-like cells irregular borders many tight junctions Cuboidal: square or rounded in shape Commonly line lumens(space or a duct) Columnar: rectangular or column shape cells Usually simple Produce lots of fluid (goblet cells) Line the digestive tract Layers Simple= one layer of cells Stratified= 2 or more layers of cells Pseudostratified= false layers- only one layer present **stratified squamous= most common epithelial tissue Function: Allows passage of materials by diffusion and filtration in sites where protection is not important; secretes lubricating substances in serosae. Location: Kidney glomeruli; air sacs of lungs; lining of heart, blood vessels, and lymphatic vessels; lining of ventral body cavity (serosae). Function: Secretion and absorption. Location: Kidney tubules; ducts and secretory portions of small glands; ovary surface. (c) Simple columnar epithelium Description: Single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucussecreting unicellular glands (goblet cells). Simple columnar epithelial cell Function: Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action. Location: Nonciliated type lines most of the digestive tract (stomach to anal canal), gallbladder, and excretory ducts of some glands; ciliated variety lines small bronchi, uterine tubes, and some regions of the uterus. Basement membrane Photomicrograph: Simple columnar epithelium of the stomach mucosa (860X). Figure 4.3c (d) Pseudostratified columnar epithelium Description: Single layer of cells of differing heights, some not reaching the free surface; nuclei seen at different levels; may contain mucussecreting cells and bear cilia. Cilia Mucus of mucous cell Pseudostratified epithelial layer Function: Secretion, particularly of mucus; propulsion of mucus by ciliary action. Location: Nonciliated type in male’s sperm-carrying ducts and ducts of large glands; ciliated variety lines the trachea, most of the upper respiratory tract. Trachea Photomicrograph: Pseudostratified ciliated columnar epithelium lining the human trachea (570x). Basement membrane Figure 4.3d (e) Stratified squamous epithelium Description: Thick membrane composed of several cell layers; basal cells are cuboidal or columnar and metabolically active; surface cells are flattened (squamous); in the keratinized type, the surface cells are full of keratin and dead; basal cells are active in mitosis and produce the cells of the more superficial layers. Stratified squamous epithelium Function: Protects underlying tissues in areas subjected to abrasion. Nuclei Location: Nonkeratinized type forms the moist linings of the esophagus, mouth, and vagina; keratinized variety forms the epidermis of the skin, a dry membrane. Basement membrane Connective tissue Photomicrograph: Stratified squamous epithelium lining the esophagus (285x). Figure 4.3e (f) Transitional epithelium Description: Resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells dome shaped or squamouslike, depending on degree of organ stretch. Transitional epithelium Function: Stretches readily and permits distension of urinary organ by contained urine. Location: Lines the ureters, urinary bladder, and part of the urethra. Basement membrane Connective tissue Photomicrograph: Transitional epithelium lining the urinary bladder, relaxed state (360X); note the bulbous, or rounded, appearance of the cells at the surface; these cells flatten and become elongated when the bladder is filled with urine. Figure 4.3f Glandular and Epithelial Tissue Duct glandular: glands that have ducts Exocrine glands Very numerous Sweat glands, salivary glands, oil glands, tear glands Merocrine glands: glands that make secretions, dump them into a lumen, and muscles squeeze the product out- sweat glands. Have a low cellular death Holocrine glands: cells lyse to secrete their products- oil glands High cellular death 2. Ductless glandular: glands that do not have ducts. Endocrine gland Pituitary, thymus, thyroid, adrenal Uses the blood stream to deliver its products Very few glands and their effects will last longer Connective Tissue Most abundant and widely distributed tissue Functions: 1. bind and support 2. Protection 3. insulation 4. transportation Connective tissue Classes Connective tissue proper Cartilage Bone Blood In order to be classified as connective tissue, you must have the following: -common origin(arise from mesenchyme) -vary in vascularity -extracellular matrix: non-living area surrounding each cell Table 4.1 Connective Tissue: Structural Requirements Ground substance: extra cellular matrix Fibers: strands of protein that provide support Cells: living portion of connective tissue -fibroblast: makes fibers -chondroblast: makes cartilage -ostoeblast: makes bone cells -hemocytoblast: makes blood cells Hemotopoietic stem cell A. Connective Tissue Proper 1. Loose areolar tissue: most common Supports and binds tissues Retains/holds body fluids Defends against infection Helps store nutrients 2. Loose Adipose tissue: fat (Connective cont.) Nutrient storage Insulation A. Brown fat: warms body, thermoregulates, insulates, nutrient, metabolism B. white fat: stores excess material and causes body to appear heavy 3. Dense Regular Tissue (Connective cont.) Ligaments: hold /attach bones to bones Tendon: hold/attach muscles to bones B. Cartilage Connective Tissue Avascular and not innervated and gets its nutrients through diffusion of other tissues. 1. hyaline: gristle Most abundant Found at the ends of all long bones Keeps bones from crushing 2. Elastic: -similar to hyaline, but more elastic fibers -maintains shape with flexibility -external ear 3. Fibrocartilage -absorbs compression shock -interval disks (g) Cartilage: hyaline Description: Amorphous but firm matrix; collagen fibers form an imperceptible network; chondroblasts produce the matrix and when mature (chondrocytes) lie in lacunae. Function: Supports and reinforces; has resilient cushioning properties; resists compressive stress. Location: Forms most of the embryonic skeleton; covers the ends of long bones in joint cavities; forms costal cartilages of the ribs; cartilages of the nose, trachea, and larynx. Chondrocyte in lacuna Matrix Costal cartilages Photomicrograph: Hyaline cartilage from the trachea (750x). Figure 4.8g (h) Cartilage: elastic Description: Similar to hyaline cartilage, but more elastic fibers in matrix. Function: Maintains the shape of a structure while allowing great flexibility. Chondrocyte in lacuna Location: Supports the external ear (pinna); epiglottis. Matrix Photomicrograph: Elastic cartilage from the human ear pinna; forms the flexible skeleton of the ear (800x). Figure 4.8h (i) Cartilage: fibrocartilage Description: Matrix similar to but less firm than that in hyaline cartilage; thick collagen fibers predominate. Function: Tensile strength with the ability to absorb compressive shock. Location: Intervertebral discs; pubic symphysis; discs of knee joint. Chondrocytes in lacunae Intervertebral discs Collagen fiber Photomicrograph: Fibrocartilage of an intervertebral disc (125x). Special staining produced the blue color seen. Figure 4.8i C. Bone (Connective Tissue) Provides the skeletal system 1. compact bone-dense bone that forms the exterior margins of the bone 2. Spongy bone- honeycomb webbing of bone at the ends of long bone that give strength without weight. D. Blood ( Connective tissue) Blood: most fluid of all connective tissues Formed elements: RBC, WBC, platelets Plasma: extracellular matrix: water and dissolved compounds Muscle Tissue Functions: 1. support 2. protection 3. shapes body 4. produces movement Characteristics: 1. Highly cellular 2. highly vascular 3. innervated 4. contain myofilaments Muscle Tissue: Three Types 1. Skeletal: muscles attached to bones Cells: long, cylindrical, and multinucleated Visible striations Voluntarily controlled (a) Skeletal muscle Description: Long, cylindrical, multinucleate cells; obvious striations. Striations Function: Voluntary movement; locomotion; manipulation of the environment; facial expression; voluntary control. Location: In skeletal muscles attached to bones or occasionally to skin. Nuclei Part of muscle fiber (cell) Photomicrograph: Skeletal muscle (approx. 460x). Notice the obvious banding pattern and the fact that these large cells are multinucleate. Figure 4.10a Muscle Tissue : Types 2. Cardiac: muscle of the heart only Cells: short, branching cells, and uninucleated Visible striations Intercalated discs: areas where cardiac cells merge. Involuntarily controlled (b) Cardiac muscle Description: Branching, striated, generally uninucleate cells that interdigitate at specialized junctions (intercalated discs). Striations Intercalated discs Function: As it contracts, it propels blood into the circulation; involuntary control. Location: The walls of the heart. Nucleus Photomicrograph: Cardiac muscle (500X); notice the striations, branching of cells, and the intercalated discs. Figure 4.10b Muscle Tissue: Types Smooth: muscles of hollow organs and vessels Cells, long, spindle shaped, and uninucleated (central) No visible striations Involuntarily controlled (c) Smooth muscle Description: Spindle-shaped cells with central nuclei; no striations; cells arranged closely to form sheets. Function: Propels substances or objects (foodstuffs, urine, a baby) along internal passageways; involuntary control. Location: Mostly in the walls of hollow organs. Smooth muscle cell Nuclei Photomicrograph: Sheet of smooth muscle (200x). Figure 4.10c Nervous Tissue Functions: produces/sends electrical impluses Control over all body systems/functions 2Types: 1. neuron: highly specialized cell tht can propagate an impluse by moving ions across its membrane Longevity Long in length characteristics: dendrites, axons, neurotransmitters, cell body, axon terminals 2. supporting cells: specialized cells desighned to carry out functions for the nervous system/neurons specifically Nervous tissue Description: Neurons are branching cells; cell processes that may be quite long extend from the nucleus-containing cell body; also contributing to nervous tissue are nonirritable supporting cells (not illustrated). Nuclei of supporting cells Neuron processes Cell body Axon Dendrites Cell body of a neuron Function: Transmit electrical signals from sensory receptors and to effectors (muscles and glands) which control their activity. Location: Brain, spinal cord, and nerves. Neuron processes Photomicrograph: Neurons (350x) Figure 4.9