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• 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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• 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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– 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.
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Stratified squamous epithelium
Areolar connective tissue
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• 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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• Nonliving extracellular material
– is abundant in connective tissues
– characteristics are responsible for the nature of the specific connective tissue.
• Consists of
• Ground substance
• Fibers
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Areolar
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Hyaline cartilage
Bone
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• Occupies the area around the cells and fibers
– Interstitial fluid
– Complex mixture of proteins (structural and organizational) .
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Areolar, wm Dense regular (tendon)
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– ( 1 ) collagen,
– ( 2 ) elastic,
– ( 3 ) reticular .
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• 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 .
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Areolar, wm
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Dense regular (tendon)
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– appear yellow in fresh preparations. Thus, they are often called “ yellow fibers .”
– allowing the tissue to stretch and recoil .
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Elastic cartilage
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Elastic fibers (artery)
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– are thinner and more branched
( 1 ) providing a structural framework
( 2 ) providing strength .
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Reticular fibers, lymph node
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– high vascularity , such as found in areolar, to no vascularity , such as found in cartilage tissues.
Areolar (wm)
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Hyaline cartilage
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Bone
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• 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” 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
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• Dense regular, dense irregular, elastic
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• 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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• Consists of large groups of fat cells ( adipocytes ) distributed in areolar 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 distributed in the body, especially subcutaneously and around internal organs .
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• 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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• Consists mostly of dense bundles of parallel (regular arrangement) collagenous fibers
– may have a wavy appearance.
– Fibrocytes are found among the collagenous fibers.
• Functions in providing great strength for attachments
– collagen fibers resist stretching when tension is applied end-to-end .
• Locations include
– ( 1 ) tendons and ( 2 )
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• 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 sheets surrounding muscles (fasciae) and some organs such as the liver and lymph nodes.
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• 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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• 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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• 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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• Consists of dense, compact, collagenous fiber bundles with little ground substance.
– The fiber bundles are wavy and nearly parallel with chondrocytes located along their surface.
• Functions include ( 1 ) providing strength and ( 2 ) resisting compression .
• Locations include ( 1 ) the fibrocartilage discs (intervertebral discs) that separate the vertebrae, ( 2 ) part of the knee joint and ( 3 ) the symphysis pubis (connects the two pubic bones).
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• Consists of abundant collagenous and 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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• 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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• Compact bone
– organized in units called Haversian systems ( 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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• 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).
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