Connective Tissue (CT)

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Connective Tissue (CT)
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Connective Tissue

• A really diverse group of tissues
• Connective tissue (CT) is the most diverse of the
  four tissue types with a wide variety of
  functions. CT forms an extensive compartment in
  the body and can be considered as the "glue" that
  holds the body together.

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Composition of Connective Tissue

• Cells
• Extracellular matrix
• Ground substance
• fibres

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Cells of CT

• Fibroblasts
• the principal cells of connective tissue.
• Matrix secreting cells
• responsible for the secretion of all types of
  fibres (collagen, reticular, elastin) and the
  complex carbohydrates of ground substance.

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Cells of CT

• Chondroblasts chondrocytes
• the matrix-secreting cells of cartilage.
• Osteoblasts osteocytes
• the matrix-secreting cells of bone.
• Macrophages
• are phagocytic cells derived from monocytes.

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Cells of CT

• Adipose cells
• also called adipocytes, these cells are
  specialized to store lipids.
• Mast cells
• have granules containing histamine, heparin and
  anaphylactic factors.
• when released in response to an antigen, they
  cause hypersensitivity reactions, allergy and
  anaphylaxis.
• Lymphocytes
• cells responsible for immune responses that
  circulate in the blood.
• normally present in small numbers but their
  number increases dramatically at certain sites of
  tissue inflammation.
• Plasma cells
• are derived from B-lymphocytes and produce
  antibodies against a specific antigen.

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Cells of CT

• Neutrophils
• are white blood cells that act as phagocytes in
  the early stages of acute inflammation.
• Eosinophils
• are white blood cells that are found at sites of
  allergic reaction and parasitic infection.
• Basophils
• are white blood cells that are similar to mast
  cells in having vasoactive agents released in
  response to an allergen.
• Monocytes
• are white blood cells that will give rise to all
  the phagocytes namely macrophages

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Ground substance

• occupies the space between the cells and fibres
  of connective tissues.
• high water content
• consists largely of proteoglycans and hyaluronic
  acid.

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Fibres

• There are three types of fibres secreted by
  connective tissue cells collagen
  fibres, reticular fibres, and elastic fibres. The
  abundance and preponderance of different types of
  fibres varies in different CTs.

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Collagen fibres

• the most common fibre type
• flexible fibres with a high tensile strength.
• Type I collagen is the most prevalent type of
  collagen (90) - found in the dermis of the skin,
  bone, tendon, organ capsules and many other
  areas.
• Type II collagen found in cartilage are finer
• Type IV collagen is found in the basement
  membrane of epithelia.

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Reticular fibres

• closely related to collagen fibres.
• They are made of type III collagen fibers
• given their name because they are arranged in a
  mesh-like pattern.
• provide a supporting framework for the cellular
  constituents of various tissues and organs
• most are produced by fibroblasts.

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Elastic fibres

• thinner than collagen fibres
• they give tissue the ability to cope with stretch
  and distension.
• they are interwoven with collagen fibres in order
  to limit excessive stretching and tearing.
• found in certain ligaments (elastic ligaments),
  some cartilage (elastic cartilage) and in large
  arteries (elastic arteries).
• most are produced by fibroblasts.

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Classification of connective tissues

• Connective tissues are classified on the basis of
  types and relative abundance of cells, fibres and
  ground substance, and on the organization of
  fibres. The images below will introduce you to
  the diversity of connective tissues.

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Loose (or areolar) connective tissue

• abundant ground substance and thin and relatively
  sparse fibres.
• located beneath epithelia that line the internal
  surfaces of the body, glands and small vessels.

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Loose (or areolar) connective tissue
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Dense irregular connective tissue

• collagenous fibres make up the bulk of the tissue
  (give it strength)
• fibroblasts are scarce and usually the only cell
  type present.
• little ground substance is present.
• the fibres are typically arranged in bundles in
  various directions (hence irregular), which
  enables the tissue to withstand various stresses.
  
• found on the outside of many organs and in the
  dermis of the skin, meninges surrounding the
  spinal cord

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Dense irregular connective tissue
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Dense regular connective tissue

• collagenous fibres are packed in dense regular
  arrays, between which lie rows of cells
  (fibroblasts).
• found in tendons (which connect muscles to bones)
  and ligaments (which connect bones to bones,

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Dense regular connective tissue
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Adipose tissue

• adipocytes, which are specialized to store fat,
  are found throughout loose connective tissue.
• Fat cells appear as empty circles in which a
  peripheral nucleus can often be identified

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Adipose tissue
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Cartilage

• tissue whose cells, called chondrocytes, secrete
  a very specialized matrix. specifically
  hyaluronic acid, chondroitin sulfate and keratan
  sulfate.
• Collagen (type II) fibrils are also present in
  the matrix
• the chondrocytes sit in spaces called lacunae,
  which they fill during life.

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Hyaline Cartilage
Mostly collagen fibres found at the ends of ribs
in the larynx, trachea, and bronchi and on the
articular surface of bones.
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Elastic Cartilage

• found in the external ear, epiglottis, eustachean
  tube and larynx.

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Fibrocartilage

• consists of chondrocytes in combination with
  dense connective tissue
• found are the intervertebral disks, the symphysis
  pubis, and certain
• places where tendons attach to bone.

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Bone

• characterized by a mineralized extracellular
  matrix.
• the matrix is secreted by cells called
  osteocytes.
• consists of mostly of mineralized collagen fibres
  arranged in lamellae.

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Compact Bone

• Also known as dense or cortical bone
• consists of numerous units called osteons or
  Haversian systems which consists of a central
  Haversian canal which contains its vascular and
  nerve supply around which lamellae of collagen
  fibres are concentrically arrayed. Osteocytes lie
  in lacunae between the lamellae and make contact
  with other osteocytes, and ultimately the
  Haversian canal, via cell processes which they
  extend in little channels or canaliculi.
• Found in the long axis and diaphysis of the long
  bones

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Anatomy of a Bone
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Compact Bone
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Compact Bone
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Spongy Bone

• Also known as trabecular and cancellous bone
• the collagen is contained within the irregularly
  shaped trabeculae. The spaces between the
  trabeculae are filled with bone marrow which is
  actively involved in red blood cell formation.
• Found in the margins of the bone marrow cavity,
  ends of bones (epiphyses)

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Spongy Bone
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Hemopoietic tissue

• The only hemopoietic tissue in the adult is red
  bone marrow. Red bone marrow gives rise to red
  blood cells, granulocytes (neutrophils,
  eosinophils and basophils), monocytes and
  platelets. Lymphocytes are formed both in the red
  bone marrow and in lymphatic tissue.

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Blood

• fluid connective tissue that circulates throught
  the body.
• functions in bringing nutrients and oxygen to
  tissues, removing waste products, transporting
  hormones and with the immune response.

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Figure 12 illustrates a blood smear (RBC,
neutrophil and basophil)
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Figure 13 illustrates a blood smear (eosinophil,
RBC, platelets)
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Figure 14 illustrates a blood smear (lymphocyte,
eosinophil, RBC)
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Figure 15 illustrates a blood smear (monocyte,
neutrophil and lymphocyte, platelets)