Tissue II

I. Connective Tissue

A. Functions

1. Binding and support

2. Protection

3. Insulation

4. Transportation

B. Common Characteristics

1. Origin—all connective arise from mesenchyme

            a. Mesenchyme is an embryological tissue derived from mesoderm germ layer

2. Vascularity varies based on type

3. Extracellular matrix

            a. Nonliving

                        i. Ground substance

                        ii. Fibers

            b. Separates the living components

            c. Allows tolerance of force, abuse and trauma

C. Structural Elements

1. Ground substance

            a. Fills space between cells

            b. Contains fibers

            c. Composition

                        i. Interstitial fluid

                        ii. Cell adhesion proteins—glues component together

                        iii. Proteoglycans—trap water; determine how stiff the ground substance is

2. Fibers—provide support

            a. Types

                        i. Collagen fibers—made from collagen; strong, high tensile strength

ii. Elastic fibers—made from elastin; stretches and recoils to bring tissue back to normal shape

iii. Reticular fibers—collagenous; branched and form networks; surround small blood vessels and support tissue of organs

3. Cells—blasts and cytes

1. Undifferentiated Cell Types—mitotically active; secrete ground substance and fibers

            a. Fibroblasts—connective tissue proper

            b. Condroblast—cartilage

            c. Osteoblast—bone

            d. Hematopoietic stem cells—blood

2. “Cytes”—mature; support existing matrix

3. Other cells associated with connective tissue

            a. Fat cells

            b. WBC’s—mast cells, macrophages, etc.

                        i. Mast cells participate in inflammation; histamine; perforin

                        ii. Macrophages—phagocytize foreign materials


II. Types of Connective Tissue—based on cell type, fiber type, and matrix composition

A. Embryonic connective tissue—Mesenchyme


1. Present in embryological life

2. Derived from mesoderm germ layer

3. Differentiates into other connective tissue type

B. Connective tissue proper

1. Subclasses:

            a. Loose connective tissue

                        i. Areolar

                        ii. Adipose

                        iii. Reticular

            b. Dense connective tissue

                        i. Dense regular

                        ii. Dense irregular

                        iii. Elastic

2. Areolar (loose) connective tissue


            a. Ground substance

                        i. Semi-fluid; viscous

                        ii. Hyaluronic acid

            b. Fibers—all three types

                        i. Arranged loosely

            c. Cells

                        i. Fibroblasts

                        ii. Macrophages

                        iii. Mast cells

            d. Widely distributed throughout body

            c. Binds body parts together

3. Adipose tissue—fat; modified areolar tissue used to store nutrients


            a. Small amount of matrix

            b. Adipose cells are densely packed together

                        i. Cell volume mostly oil droplet

            c. Abundant (Male 15%; Female 22%)

            d. Accumulates in subcutaneous tissue but can be anywhere

4. Reticular connective tissue


            a. Resembles areolar but only contains reticular fibers

            b. Fibroblasts and reticular cells

c. Forms internal framework in lymph nodes, spleen and bone marrow to support lymphocytes and other blood cells

5. Dense regular (fibrous) connective tissue—mostly fibers; force in one direction


a. Bundles of collagen running in the same direction

            i. Parallels direction of pull

b. Bundles are slightly wavy

            i. Permits stretching

c. Fibroblast, few other cells

d. Tendons

            i. Aponeuroses—flat sheet that connect muscles to bone or other muscles

e. Ligaments—bone to bone; have higher amount of elastin

6. Dense Irregular connective tissue—fibers run in multiple planes; oppose force in multiple direction


7. Cartilage—intermediate properties between connective tissue and bone; tough but flexible

            a. Avascular; no nervous tissue

            b. Ground substance

                        i. Chrondroitin sulfate

                        ii. Hyaluronic acid

                        iii. Chondronectin—adhesive protein

                        iv. Bound collagen fibers

                        v. Contains up to 80% water

            c. Association with dense irregular connective tissue (perichondrium)

                        i. Surrounds cartilage surface

            d. Chondroblasts

                        i. Found in groups (lacunae)

            e. Types of growth

                        i. Interstitial growth—within cartilage; early in development

                        ii. Appositional growth—onto superficial surfaces of cartilage

            f. Growth stops at adolescence when skeleton matures

8. Varieties of cartilage

            a. Hyaline


                        i. Most abundant

                        ii. Support with pliability

                        iii. Ends of long bones—articular cartilage; absorbs force of compression

                        iv. Embryonic skeleton prior to bone formation

                        v. Epiphyseal plates—actively growing regions of long bones

            b. Elastic—similar to hyaline with more elastin fibers


                        i. Very flexible

                        ii. Outer ear; epiglottis

            c. Fibrocartilage—connection between hyaline and ligament or tendon


                        i. Intermediate between cartilage and dense regular connective tissue

                        ii. Alternating rows of chondrocytes with collagen fibers

                        iii. Strong support, resistant to heavy pressure

                        iv. Intervertebral discs

9. Bone—matrix similar to cartilage but more rigid


            a. High collagen content with inorganic salts

            b. Osteoblasts—produce organic matrix

                        i. Lacunae

            c. Vascular

10. Blood—cells surrounded by nonliving plasma (therefore connective tissue)


            a. Matrix—soluble proteins

            b. Transportation


*Bone, muscle and blood will be considered in depth in subsequent lectures


III. Epithelial Membrane—continuous multicellular sheet composed of at least two tissue types (epithelia bound to underlying connective tissue); “simple organ”


A. Cutaneous membrane—skin

1. Keratanized stratified squamous attached to a thick layer of dense irregular connective tissue

2. Exposed to air

*To be discussed in detail during integument lecture

B. Mucous membrane—line cavities open to exterior; moist membranes

1. Stratified squamous or simple columnar epithelia

2. Function in absorption and secretion

3. Most secrete mucous, but not all (urinary tract)

4. Epithelia sheet attached to layer of loose connective tissue (lamina propria)

C. Serous membranes—moist membranes found in closed ventral cavities

1. Parietal and visceral layers

2. Simple squamous resting on a layer of loose connective tissue