Connective Tissues · Connective Tissue Proper • Connective tissue “proper” include the...

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Connective TissuesFeaturesCharacteristicsClassification

Connective Tissues ProperCartilageBoneBlood

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General Features

• Widely distributed tissues of the body. • Locations include bones, tendons, ligaments,

cartilage, blood, and the abundant loose connective tissues (such as adipose) located in and around other tissues.

• Functions include providing (1) a framework, (2) support, (3) binding, (4) protection, (5) insulation, and (6) transportation (specifically for blood).

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Characteristics

• Identification and functions of connective tissues involves at least three characteristics:– Cellularity– Matrix– Vascularity

• Three fundamental elements of connective tissues– Cells– Ground substance– Fibers

• (Ground substance and fibers are components of matrix)

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Cellularity– Cells are dispersed in a substance called the

extracellular matrix– In addition to the structural cells of the connective tissue,

many other types of cells may be present.– Connective tissues are not organized into distinctive

cellular membranes (as seen in the organization of cells of epithelia). However, membranes or “sheets” of connective tissue are common in the body.

Stratified squamous epitheliumAreolar connective tissue

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Cellularity - Types of Cells• Structural cells

– May be named (by prefix) according to type of tissue• Chondro - cartilage• Osteo - bone• Fibro – structural cells of connective tissue proper• Hemo – blood

– Activity of cell may be indicated by suffix• Cyte – mature (or maintaining) cell of the tissue• Blast – cell actively dividing and producing tissue substance• Clast – cells that are active in “breakdown”

• Associated cells include– White blood cells (neutrophils, eosinophils, basophils),

mast cells, plasma cells, macrophages, fat cells

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Matrix• Nonliving extracellular material

– is abundant in connective tissues– characteristics are responsible for the nature of the

specific connective tissue.

• Consists of• Ground substance• Fibers

BoneHyaline cartilage

Areolar

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Ground Substance• Occupies the area around the cells and fibers

– Interstitial fluid– Complex mixture of proteins (structural and

organizational).

Areolar, wm Dense regular (tendon)

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Fibers• Fibers are distinctive protein threads

embedded in the ground substance. • Three common fibers

– (1) collagen, – (2) elastic, – (3) reticular.

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Collagen Fibers• Most abundant of the three fibers

– Their long collagen protein structure makes them appear as fine clear threads in fresh preparations. Thus, they are often called “white fibers.”

• Functions include– (1) providing structural framework– (2) providing strength.

Dense regular (tendon)Areolar, wm

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Elastic Fibers• Long fibers made of the protein elastin

– appear yellow in fresh preparations. Thus, they are often called “yellow fibers.”

• Functions include – allowing the tissue to stretch and recoil.

Elastic fibers (artery)Elastic cartilage

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Reticular Fibers• Similar to collagenous fibers

– are thinner and more branched• Functions include

(1) providing a structural framework(2) providing strength.

Reticular fibers, lymph node

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Vascularity• Varying degrees of vascularity.

– high vascularity, such as found in areolar, to no vascularity, such as found in cartilage tissues.

Bone

Areolar (wm)Hyaline cartilage

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CLASSIFICATION• Based upon three characteristics of matrix:

– (1) the types of fibers, – (2) the type of ground substance– (3) the structural arrangement.

• According to these characteristics classified into four types: – (1) connective tissue proper, – (2) cartilage, – (3) bone,– (4) blood.

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Connective Tissue Proper• Connective tissue “proper” include the “typical”

connective tissues which are all connective tissues except blood, bone, and cartilage

• The matrix is characterized by – (1) being flexible, – (2) having a viscous ground substance, and – (3) by having abundant fibers.

• The structural cells are either fibroblasts or fibrocytes. • The two subclasses of connective tissue proper are

– (1) Loose connective tissue• Areolar, adipose, reticular

– (2) Dense connective tissue• Dense regular, dense irregular, elastic

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LOOSE CONNECTIVE TISSUES

• Areolar• Adipose• Reticular

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Areolar• Structural cells are fibrocytes.

– Other cell types include mast cells(produce histamine) and macrophages (leukocytes which function in phagocytosis).

• Matrix contains– Abundant collagenous and elastic

fibers loosely dispersed in the ground substance.

• Functions include– (1) attaching, (2) packing (3)

supporting tissues and organs.• Locations:

– widely distributed throughout the body. It attaches the skin to underlying tissues, surrounds and supports many organs such as blood vessels, and glands.

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Adipose Tissue• Consists of large groups of fat

cells (adipocytes) distributed inareolar connective tissue.

• The matrix is compressed between the cells and is usually not observed.

• Functions – (1) as a reserve energy

source, – (2) as an insulator from heat

loss, and – (3) structurally (supports and

cushions organs).• Locations:

– Adipose is widely distributedin the body, especiallysubcutaneously and around internal organs.

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Reticular • Consists of a network of thin, delicate, highly branched reticular fibers and reticular cells.

• Functions include– forms supporting

framework • Locations:

– soft organs such as the lymph nodes and spleen.

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DENSE CONNECTIVE TISSUES

• Dense regular• Dense irregular• Elastic

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Dense Regular• Consists mostly of dense

bundles of parallel (regular arrangement) collagenousfibers– may have a wavy

appearance.– Fibrocytes are found

among the collagenousfibers.

• Functions in providing great strength for attachments– collagen fibers resist

stretching when tension is applied end-to-end.

• Locations include– (1) tendons and (2)

ligaments

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Dense Irregular • Consists mostly of irregularly arranged collagenous fiber bundles– bundles (groups of

collagenous fibers) are interwoven in many directions.

– Fibrocytes are dispersed among the fibers

• Function in providing great strength in many directions

• Locations include (1) the dermis (skin) and (2) connective tissue sheetssurrounding muscles (fasciae) and some organs such as the liver and lymph nodes.

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Elastic• Consists of irregularly

arranged elastic fibers with scattered fibroblasts

• Functions in providing (1) strength, (2) stretch, and (3) recoil.

• Locations include the (1)vocal cords, (2) walls of large arteries, and (3)respiratory airways such as trachea and bronchi.

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CARTILAGE• Characteristics

– a matrix which is semisolid and slightly flexible – consists mostly of collagen fibers embedded in a protein

ground substance– avascular– chondrocytes are the structural cells of mature cartilage– perichondrium, a membrane of dense irregular connective

tissue, forms the surface of most cartilage. • Functions as a (1) supportive and (2) structural connective

tissue• Three types of cartilage are presented for study:

– Hyaline cartilage– Fibrocartilage– Elastic cartilage

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Hyaline Cartilage

• Consists of abundant collagenous fibers that are embedded in ground substance. – This gives the matrix a firm structure

with an amorphous appearance (you cannot identify the detail of the fibers or ground substance).

• Functions in providing (1) support, (2) a structural framework, and (3) cushion.

• Locations– locations include (1) where the ribs

connect to the sternum (called costal cartilage), (2) the ends of long bones(called articular cartilage), (3) the tip of the nose, and (4) the framework of larger respiratory airways.

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Fibrocartilage• Consists of dense, compact,

collagenous fiber bundles with little ground substance. – The fiber bundles are wavy and

nearly parallel with chondrocyteslocated along their surface.

• Functions include (1) providing strength and (2) resisting compression.

• Locations include (1) the fibro-cartilage discs (intervertebral discs) that separate the vertebrae, (2) part of the knee joint and (3) the symphysispubis (connects the two pubic bones).

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Elastic Cartilage

• Consists of abundant collagenousand elastic fibers embedded in ground substance. – The ground substance blends

with the collagenous fibers making them invisible.

– The elastic fibers usually stain dark blue.

– Chondrocytes are distributed among the fibers.

• Functions include providing (1) support and (2) flexibility.

• Locations include the (1) external ear and the (2) epiglottis (cartilage structure that closes the opening to the airway when swallowing food).

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BONE• Contains collagenous fibers and calcium salts

– calcium salts make bone tissue hard,– collagenous fibers give it strength

• Functions include– (1) providing protection– (2) serving as attachment sites for muscles and connective

tissues– (3) providing reserves for minerals– (4) blood cell production (marrow)– (5) providing a site for fat deposit (yellow marrow).

• Two structural types of bone tissue, – (1) compact– (2) spongy

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Bone Tissue• Compact bone

– organized in units called Haversiansystems (osteons).

• Haversian system contains a – Haversian (central) canal which

contains blood vessels.– Matrix consists of mineral salts

(about 2/3 mostly tricalcium phosphate, or hydroxyapatite) and 1/3 collagen fibers

– Lamellae (concentric rings of matrix) surround each Haversian canal

– Osteocytes in circular-rows separate the lamellae

– Canaliculi (small canals ) interconnect the osteocytes.

• Spongy bone– organized into plates called trabeculae.

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Blood

• Consists of formed elements and plasma– Formed elements are the cells

(erythrocytes, or RBCs, and leukocytes,or WBCs) and platelets, the non-cellular elements (cell fragments)

• Matrix is fluid component called plasma.• Functions include transportation of

– (1) oxygen,– (2) carbon dioxide, – (3) nutrients, – (4) wastes, and – (5) hormones;– (6) and promotes immune and

inflammatory responses (leukocytes). • Location

– cardiovascular system (heart and the blood vessels).