Connective Tissues

Connective Tissue

– Most abundant tissue

– Functions are varied

Connective 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!!!

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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 oxygenand some carbon dioxide

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

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

• Platelets are tiny packets of cytoplasm thatcontain enzymes and proteins responsible forclotting

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Human Anatomy, 3rd edition

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Blood

Human Anatomy, 3rd edition

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White Blood Cells

B

L

Human Anatomy, 3rd edition

Prentice 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

Human Anatomy, 3rd edition

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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