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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 (store nutrients), white blood cells (tissue response to injury), mast cells (Detect foreign microorganisms) and macrophages (eat foreign material)

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)

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