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Module: BIOM - 1010

Lecturer: Dr Zhu

Date: 14/11/16

Connective Tissue Part 1
o

Connective tissue is one of the four main types of tissue in the body, the other three are:
 Epithelial
 Muscle
 Nervous

o

Connective tissue Is the most widely abundant and distributed of the four main tissues in the body, it
serves some major functions such as:
 Binding and support
 Protection
 Insulation
 Storage of reserve fuel
 Transporting substances

o

We can further classify connective tissue into four main classes:
 Connective tissue proper
 Cartilage
 Bone
 Blood (will be done by another lecturer)

o

All connective tissue has common characteristics:
 They all have a common origin stemming from the embryo
 They all arise from mesenchymal tissue
 They all have varying degrees of vascularity
 Cartilage is avascular
 Bone is highly vascularised
 The cells are suspended in an extracellular matrix
 This is a protein-sugar mesh
 The matrix supports cells so they can bear weight, withstand tension and endure abuse

o

The exact composition of connective tissue varies considerably, however, there are 3 components to the
structure of connective tissue:
 Ground substance
 This is an unstructured gel-like material that fills the space between cells
 This is a medium by which solutes diffuse between the capillaries
and cells
 There are a number of components to the ground substance:
 Interstitial fluid
 Cell adhesion proteins
 Proteoglycans
 Water, in varying amounts, affecting viscosity
Extracellular
 Fibres
matrix
 Collagen
 These are the strongest and most abundant fibres
 They provide toughness and tensile strength
 The main types are 1, 2, 3, 4, 5
 Elastic fibres
 These are networks of long, thin elastin fibres that allow for
stretch and recoil
 Reticular fibres
 These are short, branched, collagenous (not collagen) fibres

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Cells
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o

The branches form ‘fuzziness’

Blast cells
 They are an immature form of cell that actively secrete group substance and
extracellular matrix fibres
 There are a number of types of blast cells:
o Fibroblasts
 In connective tissue proper
o Chondroblasts
 In cartilage
o Osteoblasts
 In bone
o Hematopoietic stem cells
 In bone marrow
Cyte cells
 These are mature, less active cells and help maintain the health of the matrix
There are a number of other cells too:
 Adipose cells
 White blood cells
 Mast cells
 Macrophages

Connective tissue proper
 All mature connective tissues except bone, cartilage and blood belong to connective tissue proper
 There are two subclasses of connective tissue proper:
 Loose connective tissue
 Areolar
o Wildly located under epithelia
o Forms lamina propria
o They package, wrap and cushion organs
o They hold organs in place and convey tissue fluid
o They surround capillaries
o Their macrophages phagocytose bacteria
o They play a role in inflammation
 Adipose
o White adipose
 Similar to areolar tissue but store more nutrients
 Cells are called adipocytes and also contains other cells:
 Preadipocytes
 Fibroblasts
 Macrophages
 They have a sparse matrix
 It is richly vascularised
 It is found in a number of locations:
 Subcutaneous
 Breasts
 Around the kidneys
 In the abdomen
 It makes up ~25% of the weight of a woman and ~20% of a man
 It has a number of specific functions:
 Store energy
o Lipogenesis/lysis
 Insulation
 Support and protection

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o Perirenal fat
o Behind eyeballs
 Hormones, such as:
o Leptin
o Adiponectin
o Oestradiol
o Brown adipose
 This uses lipid fuels to heat the blood stream rather than to produce
ATP like white adipose
 They have a round nucleus
 They have many small vacuoles of fat
 They contain many mitochondria
 They have even more capillaries than white adipose tissue
 They are located in a few areas:
 New-born babies (5% of body mass) on their backs
 Not found as much in adults, around collar bones and the
neck
 They also have a number of functions:
 In babies, they generate body heat as they cannot shiver
 In adults, they burn calories to release heat
o There is ongoing research for this
Reticular
o Resembles areolar tissue but the fibres are thinner
o The fibroblast cells are called reticular cells
 They secrete reticular fibres that are made of thin collagen
o The fibres form a mesh-like stroma that act as a support for blood cells in
lymph nodes, spleen and bone marrow
o They have a number of locations and functions related to them:
 Around the kidney and liver
 Provide support (by formation of the stroma) around the
lymphoid organs
 In the spleen
 In the lymph nodes
 They also aid other cells such as white blood cells, mast cells
and macrophages
 In the bone marrow
Below are 4 images of areolar (top left), white adipose (top right), brown adipose
(bottom left) and reticular tissue (bottom tight)

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Dense connective tissue
 Dense regular
o This has a high tensile strength and can withstand high stretching and
tension
o It consists of bundles packed with thick collagen fibres
 These run parallel to the direction of stretch and are slightly wavy
so can stretch a little
o The fibroblasts produce collagen fibres and ground substance
 However, they have little ground substance and cells and are
mostly fibres
o They are poorly vascularised
o They are located in:
 Tendons
 Most ligaments
 Aponeuroses
o They also have a number of specific functions:
 Attach muscle to bone, muscle to muscle or bone to bone
 To withstand great tensile stress
 Dense irregular
o These have the same elements as regular tissue but the bundles of
collagen are thicker and arranged more irregularly
 They tend to form sheets rather than bundles
o They are located in:
 The fibrous capsule of organs and joints
 In the dermis of the skin
 The submucosa of the digestive tract
o Their function is to:
 Provide structural strength
 Withstand tension exerted in more than one direction
 Elastic
o Some ligaments are very elastic
 For example, ligaments connecting adjacent vertebrae
o They are also found in the wall of many large arteries
 This is because they need to stretch when blood enters and constrict
to push it forwards
o They allow the recoil of the lungs
o They contain a high proportion of elastic fibres
o They are found in:
 The wall of large arteries
 The walls of bronchial tubes
 Some ligaments
 The following are some images of dense regular (left), irregular (middle) and elastic
tissue (right):



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