Connective Tissues

Connective Tissue– Most abundant tissue

– Functions are variedConnective tissues bind, support, protect, serve as frameworks, fill spaces, store fat, produce blood cells, protect against infection, and repair tissue damage.

– Characteristics• Specialized cells, relatively few cells, widely scattered

• Highly vascular

• Much matrix

– Extracellular protein fibers

– Ground substance (fluid)

Classification of Connective Tissues– Embryonic connective tissues

• Mesenchymal cells: stem cells that can differentiate into other types of cells found in connective tissue

– Adult connective tissues• Fluid connective tissue: contains distinctive cells in

a watery matrix, includes blood and lymph

• Supporting connective tissue: contains specialized cells, matrix contains closely packed fibers, includes cartilage and bone

• Connective tissue proper: many differnet types of cells, thick ground substance, includes adipose tissue (fat) and tendons

Embryonic Connective Tissues

Cell Types Found in Connective Tissue– Fibroblasts

• Produce and maintain the protein fibers that are found in the matrix

• Fixed cells that are slender or stellate (star-shaped

– Macrophages (a type of white blood cell)• “Big eaters”-engulf damaged cells or pathogens that

enter the connective tissue

• Large ameoboid cells

• May be fixed or wandering

Additional Connective Tissue Cells– Adipocytes

• Fixed fat cells• Contain a large droplet of fat that pushes the cells

nucleus to one side, causing the cell to resemble a class ring

– Mesenchymal cells• Stem cells that can divide (mitosis) and differentiate

into other types of cells that can replace damaged connective tissue

– Melanocytes• Fixed cells that produce and store melanin, a brown

pigment that gives tissue a dark color

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– Lymphocytes (another type of white blood cell)• Move throughout the body• Numbers increase where there is tissue damage• May turn into plasma cells, which produce antibodies

that fight infection

– Microphages (another type of white blood cell)• Function life macrophages but are smaller

– Mast cells• Around blood vessels• Wandering cells that produce histamine & heparin,

which stimulate inflammation and the allergic response

Connective Tissue Fibers– Collagen fibers

• Most common type• Long, straight, unbranched• Protein fibers wound together like a rope• Flexible, but stronger than steel when pulled from either

end• Form ligaments, tendons

– Reticular fibers• Thin• Branched and woven into rough, flexible network• Form a framework that’s tough but flexible• Can resist forces from many different directions• Stabilizes cells and blood vessels

– Elastic fibers• Branched and wavy• Thin• Stretch and recoil• Contain elastin protein

Ground Substance– Extracellular fluid in connective tissue

– clear, colorless

– consistency similar to syrup, which slows the spread of bacteria and other pathogens

Types of Adult Connective Tissue

Classification of Adult Connective Tissues

Connective Tissue Proper: Loose Connective Tissue

– Also called areolar tissue– Fibers not abundant– Contains all 3 types of fibers and a wide variety

of cells– Serves as “packing material”- fills space

between organs, provides cushioning– Allows distortion without damage, is resilient– Examples of locations

• Between skin and muscles• Around digestive tract• Around blood vessels

Loose Connective Tissue

Connective Tissue Proper: Adipose Tissue:– Similar to loose connective tissue– Most of the volume is adipocytes– Provides padding, cushions, slows heat loss,

food reserve, packs and fills spaces– Locations

• Wherever there is loose connective tissue

Adipose Tissue

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Brown fat- Adipose tissue found in infants and the upper body of

young children

- Is highly vascularized, which causes it to appear brown

- Oxygen provided by the blood vessels allows for the rapid breakdown of the stored fat in this tissue

- This breakdown releases much energy that is used to heat circulating blood

- This helps to keeps infants and small children warm since their bodies are so small, they have less insulation, and their muscles do nor produce very much heat

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Interesting Fact• Adipocytes in adults do not divide

• The number of fat cells is pretty much established in the first few weeks of life

• It would seem that getting rid of some of these fat cells (ex. liposuction) would result in a permanent loss of fat and weight.

• However, this is not the case. Even though these adipocytes don’t divide, mesenchymal cells can become adipocytes.

• Therefore, when adipocytes are removed, mesenchymal cells produce more to take their place!!!

Human Anatomy, 3rd editionPrentice Hall, © 2001

Liposuction?!?

Connective Tissue Proper: Reticular Tissue– Reticular fibers form a strong, 3-D network– Provides strength and support– Forms the framework (stroma) of many organs– Supports the cells in many organs such as the

liver and spleen

Reticular Tissue

Dense Connective Tissue– Most of its volume is made of collagen fibers– Types

• Dense Regular Connective Tissue

• Dense Irregular Connective Tissue

• Elastic Connective Tissue

Dense Regular Connective Tissue– Lots of collagen fibers that are parallel to one

another and are packed tightly– Cells – fibroblasts in rows between bundles– Examples

• Tendons- connect muscle to bone

• Ligaments- connect bone to bone, can tolerate moderate stretching

• Aponeuroses- attach muscle to muscle

Dense Regular Connective Tissue

Dense Irregular Connective Tissue– Dense woven mesh of collagen fibers– Provides strength and support in various

directions– Occurs in sheets– Locations

• Periosteum (around bone)

• Perichondrium (around cartilage)

• Fibrous capsules of some organs (liver, kidney, spleen)

• Fasciae

• Dermis (skin)

Dense Irregular Connective Tissue

Dense Connective Tissue: Elastic Tissue– Lots of elastic fibers– Fibroblasts in spaces between fibers– Provides stretch and strength– Found in respiratory passages and walls of

blood vessels– Elastic ligaments are like rubber bands and help

to stabilize vertebrae in the spinal column

Elastic Connective Tissue

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Fluid Connective Tissue: BloodBlood • Half of the volume of blood is red blood

cells (RBC’s or erythrocytes), which transport oxygen and some carbon dioxide

• Watery ground substance is called plasma, which contains small number of white blood cells (WBC’s or leukocytes) and large numbers of proteins(antibodies)

• White blood cells are part of the immune system, protect the body from pathogens, and include neutrophils, eosinophils, basophils, lymphocytes, and monocytes

• Platelets are tiny packets of cytoplasm that contain enzymes and proteins responsible for clotting

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Human Anatomy, 3rd editionPrentice Hall, © 2001

Blood

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White Blood Cells

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Human Anatomy, 3rd editionPrentice Hall, © 2001

Fluid Connective Tissue: Lymph• In the tissues, filtration (diffusion) moves water and

solutes out of the blood vessels and into interstitial fluids.

• Interstitial fluids surround body cells.

• When interstitial fluids enter small passages called lymphatics, it is called lymph.

• Lymph contains no antiobodies, and is made almost entirely of lymphocytes.

Supporting Connective Tissues: Cartilage– Dense network of collagenous fibers & elastic

fibers – Gel-like matrix contains chondroitin sulfates– Cells – chondrocytes (cartilage cells) in

pockets called lacunae• Chondroblasts (immature chondrocytes)

– Perichondrium – surrounds surface of cartilage, contains two layers:

1. Dense irregular: outer layer, provides support, protection, attachment,

2. Cellular layer: inner layer, contributes to growth and maintenance of cartilage

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Cartilage– Growth

• Interstitial: chondrocytes divide, daughter cells produce more matrix, inflates cartilage like a balloon, occurs only during fetal development

• Appositional: inner cellular layer of perichondrium cells divide and differentiate into chondrocytes, occurs from fetal development all the way into adolescence

Growth of Cartilage

Types of Cartilage– Hyaline cartilage– Fibrocartilage– Elastic cartilage

Hyaline Cartilage– Most common– Contains collagen fibers that make it tough but

flexible– Provides flexibility and support, reduces

friction between bones– Locations

• Ends of bones (joints)

• Connects ribs and sternum

• Trachea

• Larynx

• Embryonic skeleton

Hyaline Cartilage

Fibrocartilage– Visible densely interwoven collagenous fibers

with scattered chondrocytes– Provides strength and rigidity– Resists compression, absorbs shock, prevents

damage from bone to bone contact– Locations

• Vertebral discs

• Symphysis pubis

• Forms pads at the joint(ex.knee)

Fibrocartilage

Elastic Cartilage– Threadlike network of elastic fibers with

chondrocytes– Provides strength and maintains shape, resilient

and flexible– Locations

• Pinna (flap) of ear

• Tip of nose

• Eustachian tube

Elastic Cartilage

Supporting Connective Tissue: Bone– Also called osseous tissue– Solid matrix : one-third consists of collagen fibers,

rest is calcium salts (calcium phosphate and calcium carbonate

– Collagen fibers make the bone flexible– Calcium salts make the bone hard and strong– Cells –

• Osteocytes (bone cells) in lacunae(pockets)• Osteoblasts (secrete bone)• Osteoclasts (break down bone)

– Lacunae are connected by cannaliculi- passages that allow lacunae to communicate with each other and to receive oxygen and nutrients

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Bone• Surrounded by a periosteum, which contains two layers.

(see perichondrium layers)

• Undergoes only appositional growth when the cells of the inner layer of the periosteum divide.

• Unlike cartilage, bones undergo extensive repair and replacement on a regular basis due to the action of osteoblasts and osteoclasts.

• Bones also respond to stresses placed upon them: A lot of stress- thick and hard, Inactivity- thin and brittle

Bone

Membranes– Epithelial layer + underlying connective tissue

= epithelial membrane– Types

• Mucous membrane: line cavities that communicate with the outside of the body, are kept moist at all times

• Serous membrane: line sealed internal body cavities (pleura, pericardium, peritoneum), secrete a fluid called transudate that helps to reduce friction

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Membranes

• Cutaneous membrane: the skin, covers the surface of the body, thick, waterproof, and dry

• Synovial membrane: exist at joints, secrete synovial fluid that lubricates the joints

Membranes

Fascia– Fascia is the collective term for sheets of

connective tissue– Functions

• Provide strength and stability

• Maintain positions of internal organs

• Provide a route for the distribution of blood vessels, lymphatics, and nerves

– 3 major components• Superficial fascia

• Deep fascia

• Subserous fascia

Superficial Fascia– Immediately deep to the skin

• Separates skin from underlying tissues and organs

– Composed of adipose tissue and loose connective tissue

– 2 layers• Outer usually contains fat• Inner layer is thin and elastic

– Functions• Storehouse for water and fat• Layer of insulation• Protection from blows• Pathway for nerves and vessels

Deep Fascia– Consists of dense connective tissue– Contains 2 layers

• Superficial and deep

– The dense connective tissue components are continuous with each other

• Eg. Connective tissue sheaths of muscles, tendons, periosteum

– Functions• Allows free movement of muscles• Carries nerves and blood vessels• Fills spaces between muscles• Sometimes provides the origin for muscles

Subserous Fascia– Composed of loose connective tissue– Lies between the deep fascia and the serous

membranes that line body cavities– Functions

• Forms the fibrous layer of serous membranes

• Covers and supports the viscera

• Attaches the parietal layer of serous membranes to the internal surface of the body wall.

• Allows movements of muscles without distortion of delicate linings.

The Fasciae

Muscular Tissue– Specialized cells– Function - contraction– 3 types

• Skeletal muscle

• Cardiac muscle

• Smooth muscle

Skeletal Muscle Tissue– Connected to bones– Striated– Multinucleated– Voluntary

Skeletal Muscle Tissue

Cardiac Muscle Tissue– Found in the heart– Striations– Intercalated discs– Involuntary

Cardiac Muscle Tissue

Smooth Muscle Tissue– Found in walls of internal organs– Nonstriated– Involuntary

Smooth Muscle Tissue

Nervous Tissue– Specialized cells– Function – conduction of electrical impulses– Cells

• Neurons

• Neuroglia

Nervous Tissue

The Development of Cancer