Tuesday, May 29, 2012



Learning Objective: To identify the components of connective tissue and describe their                                                    structure, composition & function.

        Connective tissue is made up of specialized cells and extracellular matrix composed of extracellular protein fibers and a ground substance
        Underlies epithelium, supports capillaries, small nerves

  • Functions of connective tissue
1.      Establishing a structural framework
2.      Transporting fluids and dissolved materials
3.      Protecting delicate organs
4.      Supporting, surrounding and interconnecting tissues
5.      Storing energy reserves e.g. fat
6.      Defending the body from microorganisms
7.      Cell growth and differentiation

Structural Elements of Connective Tissue
-        Extracellular matrix (ECM) is  composed of three structural elements:
A.     Protein fibers
B.     Ground substance
C.     Cells/Fluid

A.     Ground Substance
        Is an interstitial (tissue) fluid within which are one or more of the molecules listed below:
a)      Hyaluronic acid: a very slippery polysaccharide which serves as a good lubricant for joints.
– Gelatinous, separates cells, traps extracellular fluid; lubricates joints; gives shape to eyeballs; fills body spaces

b)      Proteoglycans: Large polysaccharide molecules bound to a protein core.Polysaccharides called glyocosaminoglycans (chondroitin sulfate,keratin sulfate).Protein part attaches to hyaluronic acid. Able to trap large amounts of water.
§         Glycosaminoglycans (GAGs) are attached to proteoglycans
ü      They trap water. As GAGs increase, so does viscosity
chondroitin sulfate – capable of being mineralized; found in cartilage, bones, skin, blood vessels
dermatin sulfate – harder; found in skin, tendons, blood vessels, heart valves
   keratin sulfate - still harder; bone, cartilage, cornea of the eyes

c. Adhesive molecules: hold proteoglycan aggregates together.
                                                                                 i.            Chondronectin in cartilage,
                                                                               ii.            osteonectin in bone,
                                                                              iii.            fibronectin in fibrous connective tissue (Binds cells, collagen and GAG)
                                                                             iv.            Laminin  mediates attachment of epithelial cells to basal laminae
        Cells have membrane receptors, integrins, that bind collagen, fibrinectin, laminin and other extracellular structural components
        Functions as a molecular sieve through which nutrients diffuse between blood capillaries and cells
B. Fiber
-        Long, rope-like protein extracellular polymers embedded in the ground substance
-        Present in variable proportions in the different types of connective tissues
-        Fiber provide structural support, adhesion, connect cells
-        Three types: collagen, reticular and elastic fibers.
-        Collagen and reticular fibers are composed of various types of collagen, elastic fibers are composed mainly of elastin
1.      Collagen fibers (white fibers)
-        Large fibers made of the protein collagen
-        The most abundant  fibers  (collagen type I)
-        Un-branched
-        Promote tissue flexibility.
-        Localized in tendons, ligaments, cartilages
-        Identified in histological sections by staining with various acidic dyes.
2.      Elastic fibers (yellow fibres)
-        Intermediate fibers made of the protein elastin.
-        Branching fibers that allow for  stretch and recoil
-        can be stretched to 150% of its original length
-        Localized in lung, urinary bladder, skin, large blood vessels (aorta)
-  Stained using elastin-specific dyes, such as resorcin-fuchsin, aldehyde-fuchsin, or orcein.

3.      Reticular fibers
-    Small delicate, branched fibers that have same chemical composition of collagen (predominantly collagen type III)
-        Branched
-        Fill spaces between tissues and organs.
-        Localized in  liver, spleen, lymph nodes, haematopoietic organs
-        Stained using silver salt impregnation
C. Cells
-        Fewer, rarely touching, surrounded by a matrix
-        Immature forms (-blasts) secrete the matrix and can still divide
-        Once the matrix is secreted, the cells mature into -cytes which have decreased cell divisions and secrete less matrix material- chondro- cartilage, osteo- bone, fibro – connective, etc. Fibroblasts – connective tissue proper
  1. Fibroblasts - secrete the proteins needed for fiber synthesis and components of the extracellular matrix
  2. Adipose (adipocytes) - Common in some tissues (dermis of skin); rare in some (cartilage)
  3. Mast cells - Common beneath membranes; along small blood vessels. Can release                                 heparin, histamine, and proteolytic enzymes in response to injury.
  4. Leukocytes (WBC’s) - Respond to injury or infection
  5. Macrophages - Derived from monocytes (a WBC).  Phagocytic; provide protection
  6. Chondroblasts - form cartilage
  7. Osteoblasts - form bone
  8. Hematopoietic stem cells - form blood cells
  9. Undifferentiated mesenchyme (stem cells) - Have potential to differentiate into adult cell types

        Have a common mesenchymic origin

Types of Connective Tissues
  1. True (Proper) CT
a)      Loose CT
                                                         i.            Areolar (loose fibrous) connective tissue
                                                       ii.            Adipose tissue
                                                      iii.            Reticular connective tissue
a)      Dense CT
                                                         i.            Dense (fibrous) regular connective tissue
                                                       ii.            Dense (fibrous) irregular connective tissue
  1. Support CT
a)      Cartilage
                                                         i.            Hyaline cartilage
                                                       ii.            Elastic cartilage
                                                      iii.            Fibrocartilage
  1. Liquid CT
                                                         i.            Blood
                                                       ii.            Lymph

1.      True or Proper Connective Tissue
a)      Loose Connective Tissue:
                                                               i.      Areolar tissue-Widely distributed under epithelia
                                                             ii.      Adipose tissue-Hypodermis, within abdomen, breasts
                                                            iii.      Reticular connective tissue-Lymphoid organs such as lymph nodes
  1. Areolar  (loose fibrous) connective tissue
Description: Gel-like matrix with all three fiber types: Cells: fibroblast,                                     macrophages, mast cells, and some white blood cells.
Function:    Wraps and cushions organs: its macrophages phagocytize bacteria:                      plays important role in inflammation: holds and conveys tissue fluid.
Location:   Widely distributed under epithelia of body, e.g forms lamina propria                                of mucous membrane; packages organs: surrounds capillaries, nerves

ii.                        Adipose loose connective tissue
Description: Consists of adipocytes; "signet ring" appearing fat cells. They store energy in the form of triglycerides (lipids). have nucleus pushed to the side by large fat droplet

Function:     Provides reserve fuel; insulates against heat loss; supports and protects organs

Location:     Found in subcutaneous layer, around organs and in the yellow marrow of long bones

iii.                        Reticular CT
     Description: Consists of fine interlacing reticular fibers and reticular cells
     Function:   Forms the framework (stroma) of organs and binds together smooth muscle tissue cells
     Location:     Liver, spleen and lymph nodes
b. Dense Connective Tissue:
                                 i.            Dense regular connective tissue:           
                               ii.            Dense irregular connective tissue:

i.                        Dense regular Connective Tissue
-        Consists of bundles of collagen fibers and fibroblasts
-        Forms tendons, ligaments and aponeuroses
-        Function = provide strong attachment between various structures
ii.                        Dense Irregular CT
-        Consists of randomly-arranged collagen fibers and a few fibroblasts
-        Found in fasciae, dermis of skin, joint capsules, and heart valves
-        Function = provide strength

2.      Supportive Connective Tissue:

         Cartilage and bone support the rest of the body
        Grows via interstitial and appositional growth
        Matrix is a firm gel containing chondroitin sulfate
        Cells called chondrocytes
        Cells found in lacunae
        Perichondrium separates cartilage from surrounding tissues
        Three types: hyaline, elastic and fibrocartilage

a)      Cartilage
                                 i.            Hyaline
Description: Amorphous but firm matrix; collagen fibers form an imperceptible               network; chondroblasts produce the matrix and then mature (chondrocytes) lie in lacunae
Function: Supports and reinforces: has resilient cushioning properties; resists                             compressive stress
               Location:  Forms most of the embryonic skeleton; covers the ends of long bones                                 in joints cavities; forms costal cartilages of the ribs; cartilages of the  nose, trachea,  and larynx.

                              ii.            Fibrocartilage
-        Matrix similar to but less firm that that in hyaline cartilage
-        Thick collagen fibre oredominate
-        Found in the pubic symphysis, intervertebral discs, discs in synovial joints (menisci of the knee) & Bone-tendon junction
-        Function = support and fusion, and absorbs shocks.
-        Deceptively similar to dense CT- Lacunae
iii. Elastic Cartilage
-        Threadlike network of elastic fibers within the matrix.
-        Similar to hyaline cartilage
-        Found in external ear, auditory tubes, and epiglottis.
-        Function = gives support, maintains shape, allows flexibility
Fluid connective tissues
         Distinctive collections of cells in a fluid matrix
        Formed elements and plasma
         Red blood cells, white blood cells and platelets
        Arteries carry blood away, veins carry to the heart
        Capillaries allow diffusion into the interstitial fluid
        Interstitial fluid entering the lymphatic vessels

Membranes are simple organs
-        Form a barrier
-        Composed of epithelium and connective tissue
-        Four types
1.      Cutaneous - Covers the body surface
2.      Synovial- Incomplete lining within joint cavities
3.      Serous-Line sealed internal cavities
                 -Form transudate

4.      Mucous - Line cavities that communicate with the exterior
                                -Contain lamina propria


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