Connective TissueBIO 351

Dr. Barbara T. Wizer

Characteristics of Connective Tissue

• Most abundant tissue in the body• Vascular• Cells scattered widely in extra-cellular

matrix• Does not occur on free surfaces

Connective Tissue Functions

• Binds one kind of tissue to another (loose connective tissue, tendons)

• Support (bone and cartilage)• Physical protection (bones, adipose tissue)• Immune protection (white blood cells)

Classification of Connective Tissue

• Connective tissue proper– Loose or areolar– Dense irregular

connective tissue (dermis of the skin)

– Dense regular connective tissue

a.) collagenous (tendons)

b.) elastic– Reticular– Adipose

• Specialized connective tissue– Hyaline cartilage– Elastic cartilage – Fibrocartilage – Bone– Blood

Basic Components of Connective Tissues

• Cells• Protein Fibers• Ground

Substance

Together, the protein fibers and ground substance are referred to as the “extracellular matrix”

Major Cell Types within Connective Tissue Proper

• Fibroblasts – the most common cell type within C.T. Synthesize fibers and ground substance

• Macrophages – Derived from monocytes which leave the bloodstream and enter tissue. Function as phagocytes that destroy bacteria

• Mast Cells – specialized WBCs that contain granules of heparin (anticoagulant) and histamine (vasodilator). Mediate inflammation.

• Plasma Cells – derived from B lymphocytes and are responsible for synthesis of antibodies

• Leukocytes – WBCs that migrate into C.T. by diapedesis, especially during inflammation

• Adipose (fat) cell – stores fat (triglycerides)

Connective Tissue Cells

Quiescent fibroblasts (“fibrocytes”) are elongated cells with thin cytoplasmic extensions

Mast cells are oval C.T. cells which are filled with granules which, when released, trigger inflammation

Connective Tissue Cells

The nucleus of plasma cells is spherical and eccentrically placed containing an arrangement of chromatin that resembles the face of a clock. The pale area of cytoplasm (arrows) is the location of the Golgi apparatus. The darker basophilic areas represent mostly rough endoplasmic reticulum involved in synthesis of antibodies.

Fibers - Collagenous: made of the protein collagen (most

abundant protein in the body); form the bulk of tendons and ligaments (called “white fibers” because they look white in living tissue)

– Elastic: made of the protein elastin; allow stretch and recoil (called “yellow fibers). Found in skin, blood vessel walls, and lungs.

– Reticular: made up of thinner collagen fibers coated with glycoprotein; form a scaffold-like framework in organs. Not visible in routine H&E stains. Abundant in reticular connective tissue which forms the “stroma” (a scaffold-like support framework) of soft organs such as spleen & lymph nodes.

Ground Substance

• Ground substance: component of C.T., an amorphous substance that fills the spaces between the cells and fibers.

• May be fluid, semifluid, gelatinous, or calcified.

• Supports cells, binds them together, stores water, and provides a medium through which substances are exchanged between blood and cells.

Ground Substance

• Contains water and and assortment of large organic molecules:– GAGs (glucosaminoglycans) – polysaccharides

which trap water, making the ground substance more jelly-like. Ex. hyaluronic acid (component of synovial fluid which lubricates joints

– Proteoglycans – core proteins to which GAGs are attached. Examples: chondroitin sulfate (gives cartilage its stiffness), and dermatan sulfate.

Extracellular Matrix

• See Figure 5-1, page 130

– Anatomy & Physiology, 7th ed., Patton and Thibodeau

Survey of Connective Tissues

Loose (Areolar) Connective Tissue

• Widely distributed, well-vascularized• Major function is to connect adjacent

structures of the body• Stretchable and easily pulled apart during

dissection• Locations include lamina propria of mucous

membranes, hypodermis, serosal linings of peritoneal and pleural cavities, and superficial fascia

Areolar tissue

Dense Irregular Connective Tissue

• Composed primarily of dense bundles of collagenous fibers interwoven in irregular, swirling arrangements that can withstand stresses applied from any direction

• Major cell type is the fibroblast• Locations include the dermis (inner layer of

the skin), fibrous capsule of organs and joints, and deep fascia surrounding muscles

Dense Irregular Connective Tissue

Dense Regular Connective Tissue

• Also called “collagenous dense regular fibrous tissue”

• Composed primarily of parallel collagen fibers which withstand a considerable amount of tensile stress when the pulling force is applied in one direction

• Major cell type is the fibroblast• Locations include ligaments, tendons, and

aponeuroses

Dense Regular Connective Tissue

Tendon

Elastic Connective Tissue

• Sometimes referred to as “elastic dense regular connective (fibrous) tissue”

• Composed of parallel arrangement of primarily elastic fibers. Space between fibers is filled with thin collagen fibers and fibroblasts

• Limited distribution - yellow ligaments of vertebral column, walls of some arteries

Elastic Connective Tissue

Reticular Connective Tissue• A three dimensional web (the word reticular means

“like a net”) composed of slender, branching reticular fibers forming the stroma of the bone marrow and lymphoid organs (spleen, lymph nodes)

• Associated with specialized fibroblasts called reticular cells which partially cover the reticular fibers with cytoplasmic processes – creating cell-lined spaces through which blood or lymph percolates

• Macrophages, lymphocytes, and plasma cells are abundant

Reticular C.T. .

Adipose Tissue

• Type of C.T. in which adipocytes (fat cells) predominate

• Stores energy in the form of triglycerides• Provides thermal insulation and supports and

protects organs• Locations include hypodermis (tissue), around

kidneys and eyeballs, abdomen, breasts, and other genetically determined areas (e.g. hips or thighs)

Adipose tissue

Cartilage• 3 types - Hyaline cartilage – most abundant type, found in

ribs (costal cartilage), the growth plates (epiphyseal plates) of bones, respiratory passages (tracheal rings, bronchi), nose

- Elastic cartilage – external ear (pinna), epiglottis, eustachian tube

- Fibrocartilage – intervertebral discs, menisci of knees, pubic symphysis

Characteristics of Cartilage

• Major cell type is the chondrocyte housed within spaces called lacunae (the young active form of the cell is the chondroblast)

• Avascular – note that this is an exception to the rule that C. T. is vascular, so cartilage heals slowly

• Extracellular matrix varies as to the type of fiber depending on the function of the cartilage. Fibrocartilage has collagen fibers which impart greater strength to provide for weight–bearing.