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group of cells that are similar in structure and perform a common or related function






enhances contrast


minor distortions that altered tissues contain

Epithelial Tissue

a sheet of cells that covers a body surface or lines a body cavity. Functions: protection, absorption, filtration, excretion, secretion, and sensory reception

epithelium (plural: epithelia), (epithe = laid on, covering)

(2 main types: Covering and Lining and Glandular Epithelium

Covering and Lining Epithelium

forms the outer layer of the skin, dips into and lines the open cavities of the cardiovascular, digestive, and respiratory systems, and covers the walls and organs of the closed ventral body cavity

Glandular Epithelium

fashions the glands of the body

Apical-Basal Surface

cells regions near the apical surface differ from those near the basal surface in both structure and function


finger like extensions of the plasma membrane

Special Charactersistics of Epithelium

2. Specialized Contacts (cell close together/cell sheets)
3. Supported by connective tissue
4. Avascular but innervarted
5. Regeneration


supplied by nerve fibers


contains no blood vessels

Basal Lamina

adjacent to basal surface, noncellular adhesive sheet consisting of glycoprotiens secreted by epithelial cells.

Functions: acts as a selective filter that determines which molecules diffusing from the underlying connective tissue are allowed to enter epithelium

Reticular Lamina

deep to the basal lamina, layer of extracellular materials (collagen fibers)

Basement Membrane

formed together by Basal and Reticular laminae

Functions: reinforces the epithelial sheet, helping it to resist stretching, and tearing forces

Classification of Epithelia

each epithelium is given two names the first indicates (1) how many cell layers and the second (2)describes the shape of the cell

Simple Epithelia

consists of a single layer of cells

locations: typically found where absorption, secretion, and filtration occur

Stratified Epithelia

composed of 2 or more layers of cells (if stratified, name according to top layer of cells)

locations: common in high abrasion areas, such as the skin surface and the lining of the mouth

(2) Cell Types

1. Squamous
2. Cuboidal
3. Columner


flat, disclike, nucleus in center, slight bump


cubelike, 6 sides, nucleus near the center (could be oval), little dimension


like a column, long linear cell, nucleus near the basal, never at top

Simple Squamous Epithelium

simplest of epithelia

Function: allows passage of materials by diffusion and filtration, in sites where protections is not important; secretes lubricating substances in serosae

Location: Kidney glomeruli; air sacs of lungs; lining of heart, blood vessels, and lymphatic vessels; lining of ventral body cavity


simple squamous epithelia in body which reflects its location. Provides a slick, friction - reducing lining in lymphatic vessels and in hollow organs of the cardiovascular system


the epithelium found in serous membranes lining the ventral body cavity and covering its organs

Simple Cuboidal Epithelium

Function: secretion and absorption

Location: Kidney tubules; ducts and secretory portions of small glands; ovary surface

Tip: Associate with kidney and salvary glands

Simple Columner Epithelium

layer may contain mucous-secreting unicellular glands (goblet cells)

Function: absorption; secretion of mucus, enzymes and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action

Location: Nonciliated type lines most of the digestive tract (stomach to anal canal), gallbladder, etc

Pseudostratified Columner Epithelium

Description: single layer of cells of differing heights, some not reaching the free surface; nuclei seen at different levels; may contain mucous-secreting cells and bear cilia (gives appearance that their are many different layers of cells)

Function: secretion, particularly of mucus; propulsion of mucus by ciliary action; known for absorption

Location: Nonciliated type in makes sperm carrying ducts and ducts of large glands; ciliated variety lines the trachea, most of the upper respiratory tract. Also asscociate with lungs

Stratified Squamous Epithelium

Description: thick memabrane composed of several cell layers; basal cells are cuboidal or columner and metablically active; in the keratinized type the surface cells are full of keratin and dead; basal cells are active in the mitosis and produce the cells of the more superficial layers

Function: protects underlying tissues in areas subjected to abrasion

Location: Nonkeratinized type forms the moist linings of the esophagus, mouth, and vagina; keratinized variety forms the epidermis of the skin, a dry membrane

Stratified Cuboidal Epithelium

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

Stratified Columner Epithelium

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

Transitional Epithelium

Description: resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columner; surface cells dome shaped or squamous like, depending on degree of organ stretch

Function: stretches readily and permits distension of urinary organ by contained urine

Location: lines the ureters, urinary bladder, and part of the urethra


consists of one or more cells that make and secrete (export) a particular product. This product, called secretion, is an aqueous (water based) fluid that usually contains proteins

ex: some glands release a lipid or steroid rich secretion

Gland Classification

endocrine( internally secreting) or exocrine (externally screting) depending on where they release their product, and as unicellular (one celled) or multicellular (many celled) based on relative cell number making up the gland

Endocrine Glands

ductless glands that secrete hormones that travel through lymph or blood to target organs directly into blood and lymphatic system

Exocrine Glands

More numerous than endocrine glands, secrete products into ducts and secretion released onto the body surfaces (skin) or into body cavities to reduce friction

ex: mucous, sweat, oil, and salivary glands

Unicellular Exocrine Gland

The only important unicellular gland is the goblet cell. Unicellular glands are sprinkled into the epithelial linings of the intestinal and respiratory tracts amid columner cells with other functions


a complex glycoprotien that dissolves in water when secreted


comes to be after Mucin is dissolved; a slimy coating that both protects and lubricates surfaces

Multicellular Exocrine Glands

structually more complex, and have two basic parts: an epitheliumderived duct and a sensory unit (acinus) consisting of secretory cells

Classification: Duct Type (Simple : unbranched duct; Compound: branched ducts) and structure of their secretory units (tubular: secretory cells form tubes) (alveolar: secretory cells form small flasklike sacs) (tubuloalveolar: if they have both types of secretory units)

Modes of Secretion: Merocrine (products are secreted by exocytosis)[ex: pancreas, sweat, and salivary galnds] and Holocrine (Products are secreted by rupture of gland cells)[ex: sebaceous glands]

Connective Tissue

found everywhere in the body, it is the most abundant and widely distributed tissue type. 3 main elements: ground substance, fibers, and cells. (ground fibers and cells make up the extracellular matrix

4 main types/classes (Connective Tissue Proper, Cartilage, Bone Tissue, Blood)

Major Functions: binding and support, protection, insulation, and as blood transportation

Characteristics of Connective Tissue

1. Common Origin ( all connective tissue arise from mesenchyme [an embryonic tissue] and hence have a kinship)
2. Varying Degrees of vascularity (all vascular except for cartilage)
3. Extracellular matrix (cells seperated by nonliving extracellular matrix [ground substances and fiber])

Ground Substance

the unstructured material that fills the space between the cells and contains the fibers. Medium through which solutes diffuse between blood capillaries and cells.

Composed of interstitial (tissue) fluid, cell adhesion protiens, and proteoglycans.

Cell Adhesion Protiens

fibronectin, laminim, and others. Serve mainly as a connective tissue glue that allows connective tissue cells to attach themselves to matrix elements


protein core and large polyssacharides (chrondroitin sulfate and hyaluronic acid). Trap water in varying amounts, affecting the viscosity of the ground substance


provide support of connective tissue. 3 types: Collagen (white fibers), Elastic, Reticular

Collagen Fibers

white fibers; are by far the strongest and most abundant. Provides high tensile strength

Elastic Fibers

long, thin fibers that form branching networks in the extracellular matrix. Contain rubber like protien, elastin, that allows them to stretch and recoil like rubberbands.

ex: skin, lungs, blood vessels

Reticular Fibers

short, fine, collagenous fibers with a slightly different chemistry and form. They are continous with collagen fibers and are higly branched forming delicate vessles. Abundant where connective tissue abuts other tissue types. Has ability to catch water.

ex: basement membrane of epithelial tissues, and ground capillaries, high degree in plasma


mitotically active and secretory cells = blast (imature) [create more cells for that particular tissue]. Mature cells = cytes ( In all 4 types of connective tissue)

Fibroblasts in connective tissue proper
Chondroblasts and Chondrocytes in cartilage
Osteoblasts and Osteocytes in bone (osteo means bone)
Hematopoietic stem cells in bone marrow
Fat cells, white blood cells, mast cells and macrophages

Cells Types

Classes of Connective Tissue

Connective Tissue Proper

Types: Loose Connective tissue and Dense Connective tissue

Loose: Aerolar, Adipose, Reticular
Dense: Dense regular, Dense irregular, Elastic

Connective Tissue Proper: loose connective tissue, aerolar

Description: Gel-like matrix with all three fiber types; cells: fibroblasts, macrophages, mast cells, and some white blood cells

Function: Wraps and cushions organs; its macrophages phagocytize bacteria; plays important role in inflammation; holds and conveys tissue fluid

Location: Widely distributed under epithelia of body, ex: forms lamina propria of mucous membranes; packages organs; surrounds capillaries

Areolar Connective Tissue

functions: supporting and binding other tissues (the job of the fibers), holding body fluids (ground substances role), defending against infection (via the activity of white blood cells and macrophages), and storing nutrients as fat (in fat cells)

Adipose (fat) Tissue

similar to Areolar Connective Tissue in structure and function, but nutrient storing ability is much greater. 90% of fat cells accounts for tissues mass.

Connective Tissue Proper: loose connective tisse, adipose

Description: Matrix as in Aerolar, but very sparse; closely packed adipocytes, or fat cells, have nucleus pushed to the side by large fat droplet

Function: Provides reserve a food fuel; insulates against heat lose; supports and protects organs

Location: Under skin in the hypodermis; around kidneys and eyeballs; within abdomen; in breasts

Connective Tissue Proper: loose connective tissue, reticular

Network of reticular fibers in a typical loose ground substance, reticular cells lie on the network

Function: Fibers form a soft internal skeleton (stroma) that supports other cell types including white blood cells, mast cells, and macrophages

Location: Lymphoid organs (lymph nodes, bone marrow, and spleen)

Connective Tissue Proper: dense connective tissue. dense regular

Description: primarily parallel collagen fibers; a few elastic fibers; major cells type is the fibroblast

Function: attaches muscles to bones or to muscles; attaches bones to bones; withstands great tensile stress when pulling force is applied in one direction

Location: Tendons, most ligaments, aponeuroses

Connective Tissue Proper: dense connective tissue: dense irregular

Description: Primarily irregularly arranged collagen fibers; some elastic fibers; major cell type is the fibroblast

Function: able to withstand tension exerted in many directions; provides structural strenght

Location: fibrous capsules of organs and of joints; dermis of the skin; submucosa of digestive tract. Can also be found in dermis layer of skin

Connective Tissue Proper: dense connective tissue, elastic

Description: dense regular connective tissue containing a high proportion of elastic fibers

Function: allows recoil of tissue following stretching; maintains pulsatile flow of blood through arteries; aids passive recoil of lungs following inspiration


Cartilage: hyaline

Description: Amorphous but firm matrix; collagen fibers form an imperceptible network; chonodroblasts produce the matrix and when mature (chondrocytes) lie in lacunae

Functions: Supports and reinforces; has resilient cushioning properties; resists compressive stress

Location: Forms most of the ends of the embryonic skeleton; covers the ends of long bones in joint cavities; forms costal cartilage of the ribs; cartilages of the nose, trachea, and larnyx

Cartilage: elastic

Description: Similar to hyaline cartilage, but more elastic fibers in matrix

Function: Maintains the shapes of a structure while allowing great flexibility.

Location: Supports the external ear (pinna); epiglottis

Cartilage: fibrocartilage

Description: Matrix similar to but less firm than that in hyaline cartilage; thick collagen fibers predominate

Function: Tensile strength with the ability to absorb compressive shock

Location: Intervertebral discs; pubic symphysis; discs of knee joint

Others: bone (osseous tissue)

Description: hard, calcified matrix containing many collagen fibers; osteocytes lie in lacunae. Very well vascularized

Function: bone supports and protects (by enclosing); provides levers for the muscles to act on; stores calcium and other minerals and fat; marrow inside bones is the site for blood cell formation (hematopoiesis)

Location: (bones)

Others: blood

Description: red and white blood cells in a fluid matrix (plasma)

Function: Transport of respiratory gases, nutrients, wastes, and other substances

Location: contained within blood vessels

Nervous Tissue

the main component of the nervous system - the brain, spinal cord, and nerves - which regulates and controls body functions

Description: Neurons are branching cells; cell processes that may be quite long extend from the nucleus-containing cell body; also contributing to nervous tissue are nonirritable supporting cells (not illustrated)

Function: transmit electrical signals from sensory receptors and to effectors (muscled and glands) which control their activity

Location: brain, spinal cord, and nerves

Muscle Tissue

highly cellular, well vascularized tissues that are responsible for most types of body movement. Muscle cells contain mayofilaments, elaborate versions of actin and myosin filaments that bring about movement or contraction in all cell types.

Skeletal Muscle

Description: long, cylindrical, multinucleate cells; obvious stritations

Function: Voluntary movement; locomotion; manipulation of the environment; facial expression; voluntary control

Location: in skeletal muscles attached to bones or occasionally to skin

Cardiac Muscle

Description: Branching striated, generally uninucleate cells that interdigitate at specialized junctions (intercalated discs)

Function: as it contracts it propels blood into the circulation, involuntary control

Location: the walls of the heart

Smooth Muscle

Description: Spindle-shaped cells with central nuclei; no striations; cells arranged closely to form sheets

Function: propels substances or objects (foodstuffs, urine, a baby) along internal passageways; involuntary control

Location: mostly in the walls of hollow organs

Covering and Lining Membranes

A body membrane that incorpotates more then one type of tissue. 3 types: Cutaneous, Mucous, and Serous

Cutaneous Membrane

is your skin. Organ system consisting of keratinized stratified squamous epithelium (epidermis) firmly attached to a thick layer of dense irregular connective tissue (dermis). Dry membrane

Mucous Membranes

line body cavities that open to the exterior, such as those of the hollw organs of the digestive, respiratory and urogenital tracts. Wet or moist membranes.

Serous Membranes

are the moist membranes found in closed ventral body cavities. Consisits of simple squamous epithelium resting on a thin layer of loose connective (aerolar) tissue.

Serosae—membranes (mesothelium + areolar tissue) in a closed ventral body cavity.
Parietal serosae line internal body walls
Visceral serosae cover internal organs

Tissue Repair

Steps of tissue repair: Inflammation sets the stage, Organization restores the blood supply, Regeneration


Release of inflammatory chemicals, Dilation of blood vessels, Increase in vessel permeability, Clotting occurs

Organization and Restored Blood Supply

The blood clot is replaced with granulation tissue
Epithelium begins to regenerate, Fibroblasts produce collagen fibers to bridge the gap, Debris is phagocytized

Regeneration and Fibrosis

The scab detaches, Fibrous tissue matures; epithelium thickens and begins to resemble adjacent tissue, Results in a fully regenerated epithelium with underlying scar tissue

Developmental Aspects of Tissue

first event of embryonic develpoment is the formation of three primary germ layers. (Superficial to deep) ectoderm, mesoderm, and endoderm. These germ layers specialize to form the four primary tissues (epithelium, connective, nervous, and muscle)

Germ Layers

Nerve tissue arises from ectoderm, Muscle and connective tissues arise from mesoderm, Epithelial tissues arise from all three germ layers

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