• Groups of cells similar in structure and function

• Epithelial
• Connective

• Nerve

• Muscle

Epithelial Tissue

• Cellularity – composed almost entirely of cells
• Special contacts – form continuous sheets held together by tight junctions and desmosomes
• Polarity – apical and basal surfaces
• Supported by connective tissue – reticular and basal laminae
• Avascular but innervated – contains no blood vessels but supplied by nerve fibers
• Regenerative – rapidly replaces lost cells by cell division

form continuous sheets held together by tight junctions and desmosomes

Classification of Epithelia

simple or stratified

and

• Squamous, cuboidal, or columnar

Epithelia: Simple Squamous

• Single layer of flattened cells with disc-shaped nuclei and sparse cytoplasm
• Functions  

• Diffusion and filtration
• Provide a slick, friction-reducing lining in lymphatic and cardiovascular systems

• Present in the kidney glomeruli, lining of heart, blood vessels, lymphatic vessels, and serosae

Epithelia: Simple Cuboidal

• Single layer of cube-like cells with large, spherical central nuclei
• Function in secretion and absorption

• Present in kidney tubules, ducts and secretory portions of small glands, and ovary surface

Epithelia: Simple Columnar

• Single layer of tall cells with oval nuclei; many contain cilia
• Goblet cells are often found in this layer
• Function in absorption and secretion
• Non-ciliated type line digestive tract and gallbladder
• Ciliated type line small bronchi, uterine tubes, and some regions of the uterus
• Cilia help move substances through internal passageways

Epithelia: Pseudostratified Columnar

• Single layer of cells with different heights; some do not reach the free surface
• Nuclei are seen at different layers
• Function in secretion and propulsion of mucus

• Present in the:                                                        male sperm-carrying ducts (non-ciliated)              and trachea (ciliated)

Epithelia: Stratified Squamous

• Thick membrane composed of several layers of cells
• Function in protection of underlying areas subjected to abrasion 

• Forms the external part of the skin’s epidermis (keratinized cells), and linings of the esophagus, mouth, and vagina (non-keratinized cells)

Epithelia: Stratified Cuboidal and Columnar

• Stratified cuboidal

• Quite rare in the body
• Found in some sweat and mammary glands
• Typically two cell layers thick

• Stratified columnar 

• Limited distribution in the body
• Found in the pharynx, male urethra, and lining some glandular ducts
• Also occurs at transition areas between two other types of epithelia

Epithelia: Transitional – one location

• Several cell layers, basal cells are cuboidal, surface cells are dome shaped
• Stretches to permit the distension of the urinary bladder

• Lines the urinary bladder, ureters, and part of the urethra

Epithelia: Glandular

• A gland is one or more cells that makes and secretes an aqueous fluid, ie, sweat glands
• Classified by:

• Site of product release – endocrine or exocrine
• Relative number of cells forming the gland – unicellular or multicellular

Endocrine Glands

• Ductless glands that produce hormones
• Secretions include amino acids, proteins,           glyco-proteins, and steroids
• Secrete product outside the cells and let the blood, insterstitial fluid, etc. pick it up.

Exocrine Glands  (They have an exit so, exo-crine)

• More numerous than endocrine glands
• Secrete their products onto body surfaces (skin) or into body cavities
• Examples include mucous, sweat, oil, and salivary glands
• The only important unicellular gland is the goblet cell
• Multicellular exocrine glands are composed of a duct and secretory unit

• Merocrine

• products are secreted by exocytosis (e.g., pancreas, sweat, and salivary glands)

• Holocrine 

• products are secreted by the rupture of gland cells (e.g., sebaceous glands)  (holocrine = the hole thing breaks)

• Found throughout the body; most abundant and widely distributed of primary tissues
• Connective tissue proper
• Cartilage
• Bone (osseous)
• Blood  (yes, blood is a connective tissue and this makes a really cool test question ‘cause it’s not intuitive)

Functions of Connective Tissue

• Binding and support
• Protection
• Insulation

• Transportation (RBC’s)

Characteristics of Connective Tissue

• Connective tissues have:

• Mesenchyme as their common tissue of origin
• Varying degrees of vascularity
• Nonliving extracellular matrix, consisting of ground substance and fibers 

• No common tissue of origin

• Avascular

• All cellular

• Ground substance

• unstructured material that fills the space between cells

• Fibers

• collagen, elastic, or reticular

• fibroblasts, chondroblasts, osteoblasts, and hematopoietic stem cells

• contain “elastin” long, thin fibers that allow for stretch.  Found in lungs, skin, blood vessels

• branched collagenous fibers that form delicate networks, support and wrap

hematopoietic stem cells are “-blasts” until ..

they finish reproducing and secreting the matrix.  Then they mature and become “-cytes”, a more mature, resting state.  But, they can become –blasts again if the matrix is damaged and needs repair.

Hematopoietic stem cells are..

“-blasts” pretty much all the time

• blood

White blood cells, plasma cells, macrophages, and mast cells, (not plasma)

• Areolar connective tissue

• Gel-like matrix with all three connective tissue fibers 

• Collagen, Elastic, Reticular

• Fibroblasts, macrophages, mast cells, and some white blood cells
• Wraps and cushions organs
• Widely distributed throughout the body

• Adipose connective tissue

• Matrix similar to areolar connective tissue with closely packed adipocytes (fat cells)
• Reserves food stores, insulates against heat loss, and supports and protects
• Found under skin, around kidneys, within abdomen, and in breasts 
• Local fat deposits serve nutrient needs of highly active organs 

• Reticular connective tissue

• Loose ground substance with reticular fibers
• Reticular cells lie in a fiber network
• Forms a soft internal skeleton, or stroma, that supports other cell types
• Found in lymph nodes, bone marrow, and the spleen

Connective Tissue Proper: Dense Regular

• Parallel collagen fibers with a few elastic fibers
• Major cell type is fibroblasts
• Attaches muscles to bone or to other muscles, and bone to bone 
• Found in tendons, ligaments, and aponeuroses

Connective Tissue Proper: Dense Irregular

• Irregularly arranged collagen fibers with some elastic fibers
• Major cell type is fibroblasts
• Withstands tension in many directions providing structural strength
• Found in the dermis, submucosa of the digestive tract, and fibrous organ and joint capsules

Connective Tissue: Cartilage

• Hyaline cartilage

• Amorphous, firm matrix with imperceptible network of collagen fibers
• Chondrocytes lie in lacunae
• Supports, reinforces, cushions, and resists compression
• Forms the costal cartilage
• Found in embryonic skeleton, the end of long bones, nose, trachea, and larynx

Connective Tissue: Fibrocartilage

• Matrix similar to hyaline cartilage but less firm with thick collagen fibers
• Provides tensile strength and absorbs compression shock
• Found in intervertebral discs, the pubic symphysis, and in discs of the knee joint

Connective Tissue: Elastic Cartilage

• Similar to hyaline cartilage but with more elastic fibers
• Maintains shape and structure while allowing flexibility
• Supports external ear (pinna) and the epiglottis

Connective Tissue: Blood

• Red and white cells in a fluid matrix (plasma)
• Contained within blood vessels
• Functions in the transport of respiratory gases, nutrients, and wastes

• Branched neurons with long cellular processes and support cells
• Transmits electrical signals from sensory receptors to effectors
• Found in the brain, spinal cord, and peripheral nerves

Muscle Tissue: Skeletal

• Long, cylindrical, multinucleate cells with obvious striations
• Initiates and controls voluntary movement
• Found in skeletal muscles that attach to bones or skin

Muscle Tissue: Cardiac

• Branching, striated, uninucleate cells interlocking at intercalated discs
• Propels blood into the circulation
• Found in the walls of the heart

Muscle Tissue: Smooth

• Sheets of spindle-shaped cells with central nuclei that have no striations
• Propels substances along internal passageways (i.e., peristalsis)
• Found in the walls of hollow organs