TISSUES

TYPES OF TISSUE A tissue is a group of similar cells that function together to perform a specialized activity (differentiation). Histology is the study of tissues. The major types of tissues are: Epithelial, Connective, Muscular, and Nervous.

Epithelial Tissue Is the only tissue that is constantly regenerated in large amounts. The 2 types of epithelium are: Lining and Glandular. Epithelium contains very little intracellular material and is avascular (no blood supply)

General features of Epithelium Consist of closely packed cells. Contain a free surface open to body cavities, lining of organs, or exterior of body. Avascular Do not have a nerve supply. High regeneration rate.

Function of Epithelium Protection Secretion Absorption Excretion Sensory Reception Reproduction

Covering and Lining Epithelium Classified by Shape: squamous, cuboidal, columnar, or transitional. Classified by Arrangement of layer: simple, stratified, or pseudostratified. Some epithelium also contain cilia and/or secrete mucous.

Simple Squamous Simple squamous epithelium functions to diffuse gases and movement of fluid via osmosis. Location: lines heart, lymph nodes, abdominal cavity, and serous secretions. Main function is Filtration and absorption.

Simple Squamous Epithelium

Simple Squamous Epithelium

Simple Squamous

Simple Cuboidal Secretes tears and saliva and absorbs water in kidney tubules. Location: covers ovaries, lines kidney tubules, eye lens, and retina. Function: secretion and absorption.

Simple Cuboidal

Simple Cuboidal

Simple Cuboidal

Simple Columnar May have microvilli, which serve to increase surface area or goblet cells to secrete mucous. Location: lines GI tract, stomach excretory ducts or glands, gallbladder. Function: secretion and absorption.

Simple Columnar

Ciliated Columnar

Simple Ciliated Columnar Lines respiratory tract, uterine tubes, and uterus. Moves mucous by ciliary action

Stratified Squamous Contain protein called keratin and serves as a protective barrier against microbes and water. (keratinization) Lines the mouth, tongue, esophagus, vagina, and outer layers of skin. Function: Protection

Stratified Squamous

Stratified Cuboidal Rare type of epithelium, serves as a protective layer. Comprises ducts of sweat glands, conjunctiva of eye, pharynx, and male urethra. Function: Protection

Stratified Columnar Lines male urethra. Function: Protection and Secretion.

Goblet Cells

Transitional Epithelium Found in organs which have to expand. Acts to prevent organ rupture. Lines urinary bladder, urethra, and ureter tubes.

Pseudostratified Columnar Serves as functional structure for ducts and tubes throughout the body and provides for movement of materials. Lines large excretory ducts, epididymis,male urethra, eustachian tubes, male reproductive tract.

Glandular Epithelium Principal function is Secretion. A gland consist of one cell or a group of cells, highly specialized for secretions into ducts, onto surfaces, and into the blood. Exocrine glands secret products which empty onto external or internal surfaces. Ex: sweat glands, salivary glands, and digestive tract glands.

Glandular Endocrine glands: are ductless, release hormones, and secrete their products directly into the blood circulation. Examples: pituitary gland and adrenal glands.

Connective Tissue Most abundant tissue in the body. Highly vascular (blood supply) Contains a variety of cells with a large amount of intracellular matrix. Functions: protection, support, binding, and storage.

General Features of Connective Tissue Consists of 3 basic elements: cells, ground substance, and fibers. The 3 components together form the Matrix. Do not generally occur on free surfaces. Contains a nerve supply; except cartilage.

General Features Cont…. Highly vascular; except for cartilage. The matrix can be gelatinous, fibrous, or calcified.

Connective Tissue Cells Fibroblasts – generate the protein fibers. Macrophages – destroy foreign invaders, similar to a white blood cell Plasma cells – generate and form matrix for red blood cells. Mast cells – generate histamine in response to allergens or tissue injury

Connective Tissue Matrix Matrix gives unique characteristics to each tissue type. Contains protein fibers embedded into fluid, gel, or solid Ground Substance. Fibers include: Collagen, Elastic, and Reticular.

Fibers Cont….. Collagen – very tough and resist pulling. Arranged into bundles for strength. Most abundant fiber in body. Made up of protein. Elastic – smaller and thinner than collagen. Made up of the protein elastin which provides strength and elasticity. Reticular – comprised of collagen and glycoproteins, provides strength to support blood vessels.

Classification of Connective Tissue Embryonic Tissue – found in developing fetus. Includes Mesenchyme and Mucous connective. Adult Tissue – includes Loose, Adipose, Dense, Elastic, and Reticular. Osseous (bone) and Vascular (blood) are specialized connective tissues.

Embryonic Mesenchyme – stem cells which differentiate to form all connective tissues.

Mucous Connective

Areolar Location: around organs, dermis, subcutaneous layer. Function: strength, elesticity, and support.

Adipose Location: subcutaneous, heart, kidneys, bones, joints. Function: heat loss reduction, support, protection, store energy (fat).

Collagenous Location: tendons, ligaments, heart, bone, liver, lymph nodes. Function: support and attachment.

Elastic Location: lungs, arteries, trachea, bronchi, and vocal cords. Function: stretching.

Reticular Location: liver, spleen, lymph nodes. Function: forms stroma and basal laminae of organs.

Hyaline Cartilage Location: Ends of long bones, larynx, bronchi, and embryonic skeleton. Function: movement at joints, support, flexibility.

Fibrocartilage Location: joints between hips, intervertebral disc, and knees. Function: support and fusion.

Elastic Cartilage Location: epiglottis, external ear, and eustachian tubes. Function: Support and shape.

Osseous Tissue (bone) Forms structure and frame of body. Functional unit is called an osteon or haversian system.

Vascular Tissue (blood) Made up of erythrocytes (red), leukocytes (white), and thrombocytes (platlets).

Muscle Tissue Specialized tissue which contracts, provides movement, maintains posture, and produces heat. 3 Types: Skeletal (attached to bone), Cardiac (heart) and Smooth or Visceral found in organs. Skeletal and Cardiac are striated, while smooth is non-striated.

Muscle Tissue Cont… Smooth and Cardiac are involuntary controlled by the brain without thinking about it. Skeletal is voluntary. You think the movement then it happens.

Nervous Tissue Specializes in electrical conduction to send signals throughout the body. Neuron – nervous cell made up of 3 parts: Dendrites, Cell body, and axon. Neuroglia (glia) – support cells that help neurons function.

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