Definition of tissue

Group of similar cells that usually have a similar embryological origin an are specialized for a particular function

Definition of histology

The science that deals with the study of tissues

Pathologists

Physicians who specialize in laboratory studies of cells and tissues, aid other physicians in making diagnoses; and perform autopsies

Autopsies

Post-mortem examination

Biopsies

Sample of living tissue removed for microscopic examination

Four principal types of various tissues of the body

Epithelial, connective, muscular, and nervous tissue

Epithelial tissue

Covers body surfaces, lines hollow organs, body cavities, and ducts; and forms glands

Connective tissue

Protects and supports the body and its organs, binds organs together, stores energy reserves as fat, and provides immunity

Muscle tissue

Responsible for movement and generation of force

Nervous tissue

Initiates and transmits action potentials (nerve impulses) that help coordinate body activities

All tissues and organs of the body develop from one or more of the three primary germ layers

Ectoderm, endoderm, and semederm

Extracellular fluid (ECF)

External to all body cells, providing a medium for dissolving and mixing solutes, transporting substances, and carrying out chemical reactions

Interstitial (intercellular) fluid

Subdivision of the ECF fills the microscopic spaces (interstitial spaces) between cells in tissues

Plasma

The other subdivision of the ECF, is the liquid portion of blood, found in blood vessels

The extracellular substance of connective tissue consists

Matrix

Matrix

Contains protein fibers embedded in a fluid, gel, or solid ground substance

Ground substance contains

Number of large molecules, including adhesion proteins

Most cells within a tissue remain

In place, anchored to other cells, basement membranes, and connective tissues. Exceptions include phagocytes and embryonic cells involved in differential and growth

Cell junctions

Points of contact between adjacent plasma membranes

Three types of cell junctions serve distinct functions

Tight junctions, anchoring junctions, and communicating junctions

Tight junctions

Form fluid-tight seals between cells and are common among epithelial cells

Tight junctions can be seen

Lining the stomach,intestines, and urinary bladder

Anchoring junctions

Fasten cells to one another or to the extracellular material, common in tissues subjected to friction and stretching, and include desmosomes, hemidesmosomes, and adherens juctions

Anchoring junctions can be seen

Outer layer of skin, muscle of heart, neck of uterus, and lining of gastrointestinal tract

Communicating junctions

Allow the rapid spread of action potentials from one cell to the next in some parts of the nervous system and in muscle of the heart and gastrointestinal tract

Communicating junctions can be seen

In a developing embryo, chemical and electrical signals that regulate growth

Gap juction

The microscopic structure that function as a communicating juction

The subtypes of epithelium (epithelial tissues) include

Covering and lining epithelium and glandular epithelium

General features of epithelial tissues

• Consist mostly of closely packed cells with little extracellular material
• Arranged in sheets, in either single or multiple layers
• Apical and basal surface attached to a basement membrane
• Many cell junctions are present, providing secure attachments among the cells
• Avascular; exchange of materials between epithelium and adjacent connective tissue by diffusion
• Adhere firmly to nearby connective tissue via a thin extracellular layer, the basement membrane
• Have a nerve supply
• Have a high capacity for a renewal (high mitotic rate)
• Derived from all three primary germ layers

Epithelia function includes

Protection, filtration, lubrication, secretion, digestion, absorption, transportation, excretion, sensory reception, and reproduction

The arrangement of covering and lining epithelium reflects

Its location and function

Layers are arranged as

Simple (one layer), stratified (several layers), and pseudostratified (one layer that appears as several)

Cell shapes include

Squamous (flat), cuboidal (cube-like), columnar (rectangular), and transitional (variable)

Simple squamous epithelium

Consist of a single layer or flat, scale-like cells adapted for diffusion and filtration

Simple squamous epithelium is found

In lungs and kidneys; in serous membranes, it functions in osmosis and secretion

Endothelium

Lines the heart and blood vessels

Mesothelium

Lines the thoracic and abdominopelvic cavities and covers the organs within them

Simple cuboidal epithelim

Consist of a single layer of cube-shaped cells, adapted for secretion (mucus, perspiration, and enzymes) and absorption (the intake of fluids or other substances by cells)

Simple cuboidal epithelium is found

Covering ovaries, in kidneys and eyes, and lining some glandular ducts

Simple columnar noncilliated epithelium

Consist of a single layer of non-cilliated rectangular cells, functions in secretion of mucus and in absorption

Simple columnar non-cilliated epithelium is found

Lining most of the gastrointestinal tract, where specialized cells containing microvilli perform absorption and goblet cells secrete mucus

Simple columnar ciliated epithelium

Consist of a single layer of ciliated rectangular cells, moves fluids or particles along a passageway bu ciliary action

Simple columnar ciliated epithelium is found

In a few portions of the upper respiratory tract, uterine tubes, uterus, some paranasal sinuses, and the central canal of the spinal cord

Stratified squamous epithelium

Consist of several layers of cells win which the top layer is flat and performs a protective function; keratinized and nonkeratinized

Keratin

Protein that is waterproof, resistant to friction, and helps repel bacteria

Stratified squamous epithelium keratinized variety forms are found

On the outer layer of the skin

Stratified squamous epithelium nonkeritinized variety forms are found

Lining the the mouth, esophagus, part of the epiglottis, vagina, and covers the tongue

Stratified cuboidal epithelium

Consist of several layers of cells in which the top layer is cube-shaped; functions in protection

Stratified cuboidal epithelium is found

In ducts of adult sweat glands and parts of the male urethra

Stratified columnar epithelium

Consist of several layers of cells in which the top layer is rectangular

Stratified columnar epithelium is found

in portions of the male urethra and large excretory ducts of some glands

Transitional epithelium

Consist of several layers of cells whose appearance is variable, is capable of stretching and this permits distention of an organ

Transitional epithelium is found

Lining the urinary bladder and portions of ureters and the urethra

Pseudostratified columnar epithelium

Consist of only one layer but gives the appearance of many; it functions in secretion and movement of mucus by ciliary action

Pseudostratified columnar epithelium is found

Lining larger excretory ducts of many large glands, part of the make urethra, and the auditory (Eustachian) tubes. The ciliated variety with goblet cells lines most of the upper respiratory tract

Gland

Single cell or a mass of epithelial cells adapted for secretion

Endocrine glands

Sweat, oil, and digestive glands secretes their products into ducts that empty at the surface of covering and lining epithelium or directly onto a free surface

Exocrine glands are classified into two structural types:

Unicellular and multicellular

The functional classification of exocrine glands is based on