CONNECTIVE TISSUES• Most abundant type of tissue

• Fills internal spaces, provides structural support for other tissues, and stores energy reserves

• Includes tissues such as fat, bone, and blood

• Most types are well vascularized

• All types have a common origin (mesenchyme)

• Includes 3 components:

– specialized cells

– extracellular protein fibers

– ground substance

• fluid or semi-solid which surrounds cells

3 Major Cell Types

1. Fibroblast– Most common fixed

cell

– Large, star shaped

– Produces fibers by secreting protein into matrix

2. Macrophages• Wandering Cells that

originate as WBC’s

• Function as scavengers that clear foreign particles Phagocytosis

• Also, play a role in immunity by allerting other WBC’s of foreign particles

3. Mast Cells• Large, widely

distributed cells• Associated with

inflammation• Releases heparin

and histamine

• 3 CATEGORIES:• Connective tissue proper

• tissue with many types of cells and extracellular fibers in a syrupy ground substance ex. Adipose tissue

• Fluid connective tissue• cells suspended in a watery matrix that contains dissolved

proteins ex. Blood

• Supporting connective tissue• low diverse cell population and a matrix of closely packed

fibers ex. Bone and cartilage

CLASSIFICATION

CONNECTIVE TISSUE PROPER• Composed of many kinds of cells

– Fibroblasts, Macrophages, Adipocytes

• 3 types of fibers– Collagen - long, straight unbranched; flexible but strong

ex: tendons, ligaments

– Reticular – cells suspended in a watery matrix that contains dissolved proteins Bone & Cartilage: stabilizes cells & vessels

– Elastic - contains the protein “elastin”. Branched, wavy, will contract after stretching ex: elastic ligaments

• Ground Tissue - – high viscosity; slows the spread of pathogens to make them

easier for phagocytes to catch

Real life apps

Connective Tissue Proper

• Loose connective tissue (areolar)– characterized by white and

yellow fibers between fibroblasts

– packing material of the body, cushions, attaches skin to the body, supports blood vessels

• Adipose tissue– dominated by

adipocytes

– energy storage, brown fat in infants (highly vascularized)

– each cell consists of large vacuole filled with triglycerides

• Reticular Connective Tissue– complex open

framework of reticular fibers

• supports walls of organs such as liver and spleen

• Dense Connective Tissue– consists of many closely packed

collagen fibers, elastin fibers, and few fibroblasts

• regular - collagen fibers are parallel to each other

– tendons, ligaments

• irregular - collagen fibers are randomly arranged and interwoven : provides strength to resist forces applied from many directions; interwoven meshwork

– dermis

Elastic Connective Tissue

• - consists of mainly yellow elastic fibers

– parallel or branching

– walls of hollow organs, large arteries, heart etc.

FLUID CONNECTIVE TISSUES

• Ground substance – plasma

• Blood contains formed elements: Erythrocytes, leukocytes, Platelets

• Arteries carry blood from heart to capillaries, water and solutes move into interstitial fluid, Veins return blood to heart

• Erythrocytes: carry oxygen (confined to vessels)

• Leukocytes: fight infection (wander)

• Platelets: blood clotting

Supportive Connective Tissue Bone & Cartilage

• I. Cartilage– Cells: Chondrocytes

– Matrix: Firm gel of proteoglycans

– Avascular: heals slowly

– Covering: Perichondrium: Composed of 2 layers• Outer layer: dense irregular tissue

• Inner layer: cells

– Growth: Interstitial & Appositional• Appositional: undergoes extensive remodeling on a regular basis

• Interstitial:

– 3 main types

Hyaline - Tightly packed collagen fibers– Most Common Type– Looks like white glass– Functions: Reduces friction, important in growth and

repair of bones– Locations: Between bone surfaces, nose, trachea,

intercostal cartilage

• Elastic - Numerous elastic fibers– flexible– Functions: Provides support but

distorts without damage– Locations: Ears, nose, epiglottis

• Fibrocartilage - matrix dominated by collagen fibers– Extremely durable– Functions: Resists compression,

limits movement– Locations: Between vertebrae,

pads within knee joints

• II. Bone - Most rigid connective tissue– Cells - Osteocytes

– Matrix - 1/3 collagen fibers & mixture of calcium salts

– Vascularized - caniculi - extensive blood vessels in matrix for exchange of materials

– Covering - Periosteum (2 layers)• fibrous outer layer

• cellular inner layer

– Growth - Appositional• undergoes extensive remodeling on a regular

basis

• responds to stresses: grow thicker & stronger = exercise