Connective Tissue(CT)

Diversity of Connective Tissue

Types and Functions:• Loose Connective Tissue: Areolar and fat

– insulation, protection (padding), loosely connecting structures

• Dense Connective Tissue: Ligaments and tendons– binding and support

• Cartilage – protection, support

• Bone– support

• Blood– transportation

Common Characteristics of all CT

1. Embryonic origin: (mesenchyme)3. Composed of different types of cells within the tissue.

2. Has an extracellular matrix of fibers and ground substance.

Ground substance

4. Variation in amount of blood supply (vascularization)

5. All support epithelium

Loose Connective Tissue

Ex. 1: Areolar – most widely distributed type.– Gelatinous– Loosely packed; lots of liquid held in ground

substance– “packing material” cushioning organs,

subcutaneous, attaches skin to muscle.– Has all three fibers– Cells: fibroblasts, macrophages, mast cells,

and white blood cells– Swells during inflammation (edema)

collagen

Ground substance

Mast cell

Fibroblast

Elastin

Areolar (Prototype)

• Ex. 2: Adipose = Fat!– Loosely packed with sparse matrix– 90% of tissue is mature adipocyte cell– Most of each cell is a fat droplet, so nuclei

is displaced to the side– Richly vascularized– Nutrient storage, cushioning in areas like

abs, hips, around kidneys– High concentrations subcutaneous (under

skin) – shock absorber, insulation– Fat deposits act as local nutrient sources

around active organs (heart, muscles)

Loose Connective Tissue

Adipose

Adipose

• Ex. 3 Reticular– Only contains reticular fibers.– VERY DELICATE – a fine net of fibers

that act as a “soft” skeleton– Supports lympho nodes, bone

marrow, spleen, free blood cells.

Loose Connective Tissue

Dense Connective Tissue• Ex. 1: Dense Regular – Tendons and

Ligaments– Fibers predominate. – Abundant and crowded fibroblasts

make fibers– Little ground substance– Regular, parallel bundles of collagen

fibers– Resist tension: pull and stretching.– Ligaments connect bone to bone– Tendons connect muscle to bone.– Poorly vascularized

Regularly aligned collagen

Fibroblast nuclei

• Ex. 2: Dense Irregular– Thicker, irregularly arranged collagen.– Found where tension is applied in

different directions– Example: Dermis of skin, organs,

joints

Dense Connective Tissue

Dense Regular

Dense Irregular

Cartilage

Characteristics– Resists tension AND compression– Lots of collagen (strong) AND elastic

fibers (flexible)– No nerves or blood vessels– High content of proteoglycans 80%

water– Chondroblasts make matrix until end

of human adolescence– Mature Chondrocytes found in

cavities called lacunae (pit)

Hyaline Cartilage

• Looks glassy (hyalin = glass)• Few chondrocytes, all found in

lacunae• Mostly matrix – lots of collagen• Reduces friction, absorbs pressure• Covers ends of long bones, connects

ribs to sternum, forms rings in trachea and bronchi

Elastic Cartilage

• Looks almost identical to hyaline BUT more elastic fibers more flexible!

• Matrix appears more fibrous• More lacunae, closely spaced.• Found in ear and epiglottis

Hyaline Cartilage

Elastic Cartilage

Fibrocartilage

• Intermediate between dense regular CT and hyaline

• Consists of rows of chondrocytes and collagen fibers

• Compressible AND resists tension• Found in intervertebral discs.

Bone (Osseous Tissue)

• Most supportive tissue in body. • Matrix is similar to cartilage, but with

morer collagen (strong) surrounded by calcium salts

• Osteoblasts make collagen fibers and calcium salts deposited between fibers.

• Well vascularized• Osteocytes stored in lacunae• Bone marrow stores fat and makes blood

cells.

Blood

• Atypical connective tissue• Only classified as such because it

arises from same embryonic tissue• Blood cells are within a matrix of

blood plasma.• Fibers apparent only when blood

clots.

How do damaged tissues repair?

Injured cells release hormones and proteins to signal need for healthy cells to divide and migrate.

Steps to Tissue Repair1) Inflammation• Inflammatory

chemicals released by injured cells, macrophages, mast cells

• Vessels dilate, allowing clotting and plasma proteins and wbc to invade injured site.

• Clotting proteins begin clotting.

2) Restore Blood Supply

• Granulation tissue replaces clot, digested by macrophages

• New capillaries form.• Fibroblast in

granulation tissue make collagen and growth factors.

3) Regeneration or Fibrosis below scab

a) Regeneration: replacement w/ same tissue type

b) Fibrosis: replacement w/ fibrous connective tissue (scar)

Regeneration Capacity

Varies by tissues

High capacity No capacity

•Epithelial

•Bone

•Areolar CT

•Dense I. CT

•Blood forming tissue

•Dense R. CT •Cartilage •Cardiac Muscle

•Nervous Tissue

Fibrosis replaces tissue in non-regenerative tissues

• Mostly collagen• STRONG but lacks flexibility/elasticity• Cannot perform function of tissue that was replaced

Extracellular Matrix• Embeds cells of connective tissue• Medium for nutrients and other dissolved

substances that nourish cells• Made up of ground substance and fibers.• Ground substance

– Texture varies•Can be liquid, gel-like, semi-solid or hard.•depends on amount of cell adhesion proteins

that trap water called proteoglycans –More proteins, more solid ground

substance.

• Fibers provide strength and/or flexibility– Allows for weight bearing, withstanding of

mechanical abuse, tension – protects!!

Dense connective tissue, lots of fibers, little open space.

Loose connective tissue:

Lots of ground substance – fewer fibers

Fibers

• Embedded in ground substance• Adds strength/flexibility.• Created by undifferentiated “blast”

cells of extracellular matrix• 3 Kinds

1. Collagen: Strong2. Elastic: Flexible3. Reticular: Delicate

Collagen (white fibers)

• Rope-like bundles

• Tough, stronger then steel!

• Tension resistant

Return to fibers

Elastic (yellow fibers)

• Long, thin

• Branching networks

• Stretch and recoil ability for elasticity

• Highly concentrated in areas like skin, lungs, vessels where elasticity is needed

Back to common characteristics of CT

Reticular “network” fibers• Short, fine, delicate

• Collagenous, but with more give due to branching network

• Support soft tissue organs, blood vessels

• abundant in boundaries where connective tissue lines other tissues (ex. basement membrane)

Reticular fibers

Collagen

Blood vessel

Cells in Matrix• Cells of CT make and maintain the ground

substance and fibers of extracellular matrix (ECM).

• Each type of CT have immature and mature forms of these cells.

• Immature cells have suffix “-blast” – are actively mitotic and produce ECM.– Fibroblasts – make loose and dense CT proper– Chondroblasts – make cartilage– Osteoblasts – make bone– Hematopoeitic stem cells – make blood

• Mature cells have suffix “-cyte” – maintain health of matrix– Ex. Fibrocyte

• Mature “cyte” cells can reverting to “blasts” to regenerate matrix after injury.

What other cells are in CT?

• Accessory Cells:– White blood cells (macrophages,

plasma cells)– responsible for immune response

– Mast cells – responsible for inflammation following injury or infection.

– Fat cells – store nutrients

Back to common characteristics of CT