Tissues: The Living Fabric - Academic Computer Center

Tissues: The Living Fabric  To optimize functions, body cells are organized into tissues  Four basic tissue types exist in humans –

Epithelial tissue

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Connective tissue

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Muscle tissue

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Nervous tissue

 Epithelial tissue –

Lining and covering epithelium  Cover internal or external surfaces (all exposed body surfaces)  Located on the skin, GIT, respiratory tract

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Glandular epithelium  Specialized secretory structures

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Functions  Protection, absorption, filtration, excretion and secretion

 Special Characteristics of Epithelium  Specialized contacts –

Cells are held closely together forming continuous sheets

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Adjacent cells are tightly bound to each other via specialized contacts (desmosomes and tight junctions)

 Polarity –

An apical surface and a basal surface is present in all epithelia

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The apical surface is exposed to the body exterior or cavity of an internal organ  Bears cilia or microvilli

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The basal surface is attached to the underlying tissue

 Supported by connective tissue –

Epithelial tissue sheets rest on an underlying layer of connective tissue that also provides support

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The basal lamina of the epithelial tissue and the reticular lamina of the connective tissue join together to form a basement membrane

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The basement membrane is the interface between the epithelial tissue and the connective tissue

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Special Characteristics of Epithelium

 Avascularity  Epithelia do not contain blood vessels but is innervated  Nutrients are obtained from the exposed or underlying surface  Regeneration  Epithelial cells are exposed to damage  They have the ability to regenerate and replace the cells that slough off the surface

Classification of Epithelia  Shape –

Squamous

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Cuboidal

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Columnar

 Degree of layering –

Simple

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Stratified

 Simple epithelia –

Consist of a single cell layer

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Line surfaces used for exchange

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Located in the GIT, respiratory tract, inner surface of blood vessels and heart chambers

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Classification of Epithelia

 Stratified epithelia –

Several layer of cells (additional protection)

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Different cell layers may have different cell types

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Epithelia is named with respect to the cells of the apical layer

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Found on the surface of the skin and the lining of the mouth

Simple Squamous Epithelia  Description –

Flat thin cells with very little cytoplasm shaped like fried egg

 Location –

Found lining the alveoli and blood vessels (endothelium), lymph vessels, and ventral body cavity (mesothelium)

 Function –

Passage of materials by diffusion and filtration in areas where protection is not a priority

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Secretes lubricating substances in serosae

 Simple Cuboidal Epithelium  Description –

Single layer of cubelike cells with large spherical centrally placed nuclei

 Function –

Secretion and absorption

 Location –

Kidney tubules

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Surface of the ovary

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Ducts and secretory parts of small glands

Simple Columnar Epithelium  Description  Single layer of tall cells with round nuclei  Apical surfaces may contain microvilli  Tissue may contain goblet cells (mucus- secreting cells)  Function

 Absorption, secretion  Location  GIT (from stomach to anal canal)

 Pseudostratified Columnar Epithelium  Description  Single layer of cell with differing heights (false stratification)  May contain goblet cells and bear cilia  Function  Secretion (primarily mucus)  Mucus propulsion by ciliary action  Location  Nasal cavity, trachea and bronchi

 Stratified Squamous Epithelia  Description  Several call layers  Basal cells are cuboidal or columnar  Surface cells are squamous  Keratinized type has the protein keratin that helps in preventing water loss  Function  Provides protection to underlying areas subject to abrasion  Location Nonkeratinized type Esophageal lining, mouth, vagina Keratinized Epidermis of the skin

Transitional Epithelium  Description

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Basal cells are cuboidal or columnar

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Surface cells are dome-shaped or squamouslike depending on the degree of stretch of the organ

 Function –

Allows distention of urinary organs

 Location –

Ureters, bladder and parts of urethra

 Glandular Epithelia  Glands make and secrete watery substances referred to as secretions  Two types exist –

Endocrine (ductless) glands  Release secretions directly into the blood stream or lymph

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Exocrine glands (glands have ducts)  Release secretions onto body surface or into body cavities

 Classification of Exocrine Glands  Unicellular –

Goblet cell

 Multicellular –

Have a secretory portion (acinus) and duct  Structurally classified as simple (straight duct) or compound (branched duct)  Classified based on secretory units as tubular (tube-shaped acinus), alveolar (flasklike acinus), and tubuloalveolar if both are present.

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Figure 4.4b Goblet cell (unicellular exocrine gland).

 Multicellular –

Classified based on secretory mode as:  Merocrine – secretes by exocytosis  Holocrine - secretory cells rupture to release secretion  Apocrine – apical portion of secretory cell ruptures to release secretion

 Connective Tissue  Most abundant and widely distributed tissue type. –

Four classes exist.

 Common characteristics –

Common origin  Develop from embryonic tissue called mesenchyme

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Degree of vascularity  May be avascular, mildly vascularized or richly vascularized

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Extracellular matrix  Non-living material surrounding cells  Composed of ground substance (IF, cell adhesion molecules, and proteoglycans) and fibers

 Connective Tissue Cells  Adipocytes – Store fat  Macrophages – Phagocytes  Fibroblasts - Produce fiber –

“-blast” = actively mitotic immature cell

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“-cyte” = mature cell

 WBCs – Immune cells –

Plasma cells – Produce antibodies

 Mast cells – Produce histamine and heparin

 Connective Tissue Fibers  Three types of fibers exist –

Collagen fibers (white fibers)  Most abundant and provides high tensile strength –

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Found in tendons and ligaments

Reticular fibers  Network of short, highly branched, collagenous fibers

 Used to support organs –

Elastic fibers  Long, thin, elastin fibers that stretch

 Types of Connective Tissue 

Connective tissue proper (excludes bone, cartilage and blood)

 Two subclasses exist

 Lose connective tissue –

(Areolar tissue) 

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Found throughout the body acting as packing material between tissues

Adipose tissue  Stores fat

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Reticular tissue  Found in the lymphatic system where it provides support to the cells of the immune system

 Dense connective tissue –

Dense regular  Includes tendons and ligaments

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Dense irregular  Found in skin, joint capsule and surrounding various organs

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Cartilage –

Properties are intermediate between dense connective tissue and bone

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Primary cells are chondrocytes

 Hyaline cartilage –

Most common

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Matrix has closely packed collagen fibers for strength and flexibility

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Found between ribs and the sternum, trachea and articular surfaces of most joints

 Elastic cartilage –

Contains lots of elastic fibers

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Found in the outer ear, epiglottis and larynx

 Fibrocartilage –

Densely packed with collagen

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Very tough

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Found between the vertebrae (intervertebral discs) and between the pubic bones (pubic symphysis)

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Covering and Lining Membranes

 Membranes are formed by epithelial and connective tissues –

Cutaneous membranes  Skin

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Mucous membranes (mucosae)  GIT, respiratory, reproductive, urinary tracts

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Serous membranes  Pleura, peritoneum and pericardium

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Synovial membranes  Joints –

Note that synovial membranes are NOT epithelial membranes and are solely made up of connective tissue

 Tissue Repair  Tissue injury results in body damage and increased susceptibility to pathogenic invasion  Tissue injury stimulates two major body responses –

Inflammatory response

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Immune response

 Tissue Response  Inflammatory response

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Remove harmful agents

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Prevent further injury

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Restore tissue health

 Immune response –

Specific and deadly attacks against invading pathogens

 Steps of tissue repair –

Inflammation  Chemicals (histamines) are released from damaged tissue and they cause capillaries to dilate and leak  Fluid enters injury site with more chemicals (clotting factors and antibodies)  WBCs enter site of injury

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Organization  New capillaries proliferate and restore proper blood flow to injured tissue  Clot is replaced by granulation tissue  Debris is phagocytized  Fibroblasts produce collagen fibers to help strengthen injured tissue  Epithelia regenerate

 Regeneration and fibrosis –

Scab detaches

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Regeneration is replacement of damaged tissue with new tissue

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Fibrosis is the proliferation of connective tissue to form scar  Fibrosis may occur depending on the type and severity of the injury  Epithelial tissue and bone tissue are good at regenerating without fibrosis  Dense regular connective tissue and cartilage have considerably less regenerative properties  Cardiac tissue and nervous tissue have essentially no functional regenerative capacity

Name the tissue –

Amorphous matrix that appears glassy

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Multiple layers of cells stacked in layers with the topmost layer consisting of flat cell

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Allow stretching of the organ in which it is found

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Can resist tensile strain or stress from multiple directions

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Posses cilia and goblet cells

 How does the structure of each tissue relate to its function? –

Simple squamous epithelium

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Dense regular connective tissue

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Stratified squamous epithelium (keratinized type)

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Simple columnar epithelium

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Fibrocartilage

 What is the level of structural organization? –

Collagen

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Elastin

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Lymphocytes

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Adipocytes

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Chondroblast

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Fibrocyte