Tissues

Tissues

• Groups of that have similar structure and function. Tissues are classified on how cells are arranged and by what kind and how much interstitial material is found between the cells

• Histology- the study of tissues• Tissues combine to form organs• Various organs make up body

systems

Four Types of Tissue

• Epithelial• Connective• Muscle• Nervous

Epithelial Tissue

• Skin which covers and protects the underlying tissues from UV exposure, toxic chemicals, and bacterial pathogens.

• Lining of the digestive tract-absorbs nutrients

• Secretory glandular tissue-hormones, enzymes

• Excretory function-sweat and urea

Basement Membrane

• Specialized membrane that anchors the epithelial cells to underlying tissue; also serves as a protection for connective tissue

Epithelium

• Classified based on cell shapeSquamous epithelial cellsCuboidal epithelial cells Columnar epithelial cells

• Classfied by arrangement– Simple- one layer– Stratified- more than one layer

Epithelium

• Simple squamous epithelium- simple layer of flat cells; useful for filtration and exchange; found in alveolar sacs of lungs, lines blood vessels

• Simple cuboidal epithelium- found in glands and in kidney tubules; active in secretion and absorption

• Simple columnar epithelium- lines the digestive tract; tall columnar cells that are specialized for secretion and absorption; often have microvilli

Epithelium

• Pseudostratified columnar epithelium- simple columnar epithelium that appears stratified; lines the upper respiratory tract; ciliated goblet cells

• Stratified squamous epithelium- multilayered; resistant to abrasion; lines the esophagus; keratinized skin epidermis

Epithelium

• Stratified cuboidal epithelium- ducts of the large glands

• Stratified columnar epithelium- forms junctions between other epithelial types

• Transitional epithelium- modified stratified squamous epithelium; lines the bladder; responds to repetitive stretching

Endothelium

• Layer of squamous epithelium that forms the lining of blood vessels, lymphatic vessels. Endocardium-endothelium that lines the heart.

• Epithelial membranes- are bound to an underlying connective tissue layer. Mucous membranes line all body cavities that open to the exteral environment; usually ciliated; secretes enzymes, absorbs nutrients, secretes mucus.

Mesothelium

• Serous tissue that lines the cavities of the body. Consists of a squamous cell layer overlying a sheet of connective tissue. Examples: pleura, pericardium, peritoneum.

Glandular Epithelium

– Glands are involutions of epithelial cells specialized for synthesizing and secreting a particular products.

– Exocrine glands-associated with secretory ducts; sweat glands, sebaceous glands, mammary glands, and salivary glands

– Endocrine glands- ductless glands that secrete directly into the bloodstream; thyroid gland, pituitary gland

– Goblet Cell- unicellular glands that secrete mucus; interspersed among the epithelial cells within mucous membranes

Connective Tissue

– Provides for movement and support for other types of tissue. Most abundant and widely distributed tissue of the body. Functions: support, protection, binding insulation, and transportation.

– Originate from embryonic mesenchyme– Matrix-Intercellular material; fibrous substance that

may be fluid, gel-like, or firm. Fibers of collagen and elastin are also embedded in this matrix.

– Connective tissue can be categorized into three subgroups: loose connective tissue, dense connective tissue, and specialized connective tissue.

Loose Connective Tissue

• Areolar connective tissue: Most widely distributed type; very elastic and resistant to tearing; basic support tissue organs, muscles, blood vessels and nerves; fascia which attaches skin to the muscle tissue underneath.

• Cell types: Fibroblasts-form fibrils; active in injury repair

Cell Types in Areolar Connective Tissue

• Fibroblasts- have the ability to form fibrils; active in the repair of injury

• Histiocytes- phagocytic cells that consume debris and microorganisms outside the circulatory system. Motile histiocytes are called macrophages

• Mast cells- function in the production of histamine (an inflammatory substance produced in response to allergies) and heparin (a natural anticoagulant)

Adipose Tissue

• Contains a large amount of fat cells; acts as a firm protective packing around and between organs, muscle fibers, nerves and it supports the blood vessels; acts as an insulator and provides energy reserves; found in the subcutaneous layer

• Adipocytes- cell type found in adipose tissue

Reticular Tissue

• Fine network of fibers that forms the stroma (framework) of the liver, bone marrow, and lymphoid organs such as the spleen and lymph nodes

Dense Connective Tissue

• Composed of densely packed protein fibers

• Subdivided into subgroups based on how the fibers are arranged and the proportions of collagen and elastin fibers present in the tissue.

Dense Regular Tissue

• Dense parallel bundles of collagen fibers in a regular arrangement; few cells present ; high tensile strength; forms tendons, ligaments, and aponeuroses

• Tendons- have a majority of tough collagen fibers

• Ligaments- have a combination of tough collagen and elastin fibers.

Dense Irregular Tissue

• Fibers are arranged different planes; resists tension exerted from different directions; dermis layer of the skin; fascia (muscle sheaths); joint capsules; outer coverings of the arteries.

Elastic Connective Tissue

• Elastin fibers; found in elastic ligaments and blood vessels; has both regular and irregular forms

Specialized Connective Tissues

• Connective tissues having specialized functions

• Cartilage• Bone• Blood

Cartilage

• Consists of chondrocytes- large round cells with spherical nuclei that are found in cavities called lacunae located in a firm matrix composed of protein and polysaccharides. Depending on the type of cartilage, various amounts of collagen and elastin fibers are embedded in the matrix enabling the cartilage to be flexible or very strong and resistant to motion.

Types of Cartilage

• Hyaline- has no collagen fibers in the matrix; most abundant type; found in the fetal skeleton which will later be ossified into bone; high resistance to wear. Also located at articulating surfaces of bones and in the trachea; septum of the nose

Fibrocartilage

• Has a majority of tough collagenous fibers embedded in the matrix; very dense and resistant to stretching. Located in the intervertebral disks and pubic symphysis

Elastic Cartilage

• Predominance of elastin fibers embedded in the matrix. Easily stretched and very flexible, found in the external ear, ear canals, and in the epiglottis

Bone

• Specialized connective tissue• of a firm, collagen-containing

matrix embedded with calcium salts; deposits of calcium cause rigidity

• Cells are called osteocytes• Forms the body’s skeleton

Types of Bone

• Compact Bone-forms the dense outer layer of bone

• Cancellous Bone- forms the inner spongy-looking tissue underneath the compact bone

Dentin

• Specialized connective tissue that is closely related to bone in structure but is harder and denser

• Enamel is secreted on to the dentin by special epithelial cells. This secretion occurs just before the teeth break through the gums.

Blood and Hematopoietic Tissue

• Composed of a fluid matrix (plasma)• Formed elements- red blood cells

(erythrocytes) and white blood cells (leukocytes)

• RBC’s and some WBC’s are formed in the bone marrow. Lymphocytes are formed in lymphatic tissue

• Circulating blood transports nutrients, O2, CO2, hormones, and waste products.

Lymphoid Tissue

• Found in the lymph nodes, thymus gland, spleen, tonsils, and adenoids

• Manufactures lymphocytes• Lymphocytes function in antibody

production; component of the human immune system.

Synovial Membranes

• Line the cavities of freely moving joints

• Line the bursae• Prevention of friction

Connective Tissue Functions

• Support• Nourishment- blood carries nutrients to

the cells of our body• Transportation of gases, enzymes and

hormones to cells• Connection• Movement• Protection• Attachment and separation

Muscle Tissue

• Consists of elongated cells (muscle fibers) that have the ability to contract

• Three types of muscle tissue:– Smooth muscle- involuntary muscle; uninucleate

cells; controlled by the autonomic nervous system– Striated (skeletal) muscle- voluntary muscle;

controlled by the central nervous system; multinucleate cells

– Cardiac muscle- found in the heart; striated and uninucleate cells; branching cells are connected by intercalated disks; controlled by the autonomic nervous system

Nervous Tissue

• Cellular Unit is the neuron• Brain, spinal cord, and nerves • Cell body, dendrites, and axon• Neurons have the ability to react to stimuli

– Irritability- ability of nerve tissue to respond to environmental changes

– Conductivity- Ability to carry a nerve impulse

• Neuroglial cells- nonconducting cells that support, insulate, and protect the neurons

Tissue Repair

Regeneration- replacement of destroyed tissue by the proliferation of the same kind of cells

Fibrosis- proliferation of fibrous connective tissue (scar tissue formation)

Type of tissue damaged and the severity of the wound will dictate the extent of either of these processes.

Read pg. 125-127. Note Figure 4.11

Development of Tissues

• Formation of three primary germ layers that specialize to form the four types of tissues– Ectoderm– Mesoderm– Endoderm

Tissue Development

• Epithelial Tissues are formed from all three germ layers– Endoderm forms the mucosae– Mesoderm forms the mesothelium

and endothelium– Ectoderm forms the epidermis– Mesoderm forms connective tissue

and muscle tissue– Ectoderm forms nervous tissue

Tissue Development

• Tissue cells except for neurons undergo mitosis until adult body size is reached; epithelial and connective tissue cells maintain mitotic activity after adult size is reached.

Tissue Aging

• Epithelial tissue becomes thinner• Tissue collagen level declines• Bone, muscle, and nervous tissue

begins to atrophy• Decreased efficiency of the

circulatory system contributes to the aging process.