Connective Tissue
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Tissues - collections of similar cells and the substances surrounding them
Tissue classification based on:
1. structure of cells,
2. composition of noncellular extracellular matrix,
3. and cell function
Embryonic Tissue
 3 major germ layers that form the embryonic disc (source of stem cells)
 Endoderm
 Inner layer
 Forms lining of digestive tract and derivatives
 Mesoderm
 Middle layer
 Forms tissues as such muscle, bone, blood vessels
 Ectoderm
 Outer layer
 Forms skin and neuroectoderm
Connective Tissue
• Most diverse and abundant tissue and widely distributed of the primary
tissues. Amounts vary in particular organs. Example:
Skin is primarily connective tissue
Brain has very little connective tissue
Common Characteristics of C.T.
– Mesenchyme as their common tissue of origin
(Mesenchyme (embryonic tissue) derived from mesoderm)
– Varying degrees of vascularity, Example:
C.T. ranges from avascular (cartilage) to poorly vascularized (dense connective tissue) to
highly vascularized
– Nonliving extracellular matrix, consisting of ground substance (separates the cells of the
tissue and enables connective tissue to withstand physical trauma) and fibers
– Cells are not as abundant nor as tightly packed together as in epithelium
Connective Tissue Origins
Lineage of CT cells from stem cells
Note: all CT cells can make all CT molecules
EMBRYONIC CONNECTIVE TISSUE
Functions of Connective Tissue
• Enclose organs as a capsule and separate organs into layers. Areolar
• Structural support and movement (capsules, bone, cartilage)
• Connect tissues to one another. Tendons and ligaments.
• Insulation and Storage. Fat.
• Nutrition and Transport. Blood.
• Defense and Protection. (non-specific and immune) Bone, cells of
the immune system.
Structural Elements of Connective Tissue
Three main elements:
• Cells – fibroblasts, chondroblasts, osteoblasts, hematopoietic stem cells, and
others
– secrete the proteins needed for fiber synthesis and components of the
extracellular matrix
• Ground substance – unstructured material that fills the space between cells
• Fibers – collagen, elastic, or reticular
Protein fibers
 Collagen fibers. Composed of the protein collagen most common, appear white
in the living state, composed of 28 types Collagen makes up approx. 25% of the
protein which is approx. 20-25% of human body weight. Strong, flexible,
inelastic; great tensile strength (i.e. resist stretch). Perfect for tendons,
ligaments
 Elastic fibers. (Yellow and refractive when alive) - larger than white. Contain
molecules of protein elastin that resemble coiled springs, no striations.;
stretches 1.5 x its resting length;
Only 1/10 as strong as white. Returns to its original shape after stretching or
compression. Perfect for lungs, large blood vessels.
 Reticular fibers. Formed from fine collagenous fibers (Collagen Type III), variant
of white fiber, but very thin 0.5 to 2 mm ; form branching networks (stroma).
Strongly argyrophilic. Resists stretching. Fill spaces between tissues and organs.
• Properties of the cells and the composition and arrangement of extracellular
matrix elements vary tremendously
– Resulting in an amazing diversity of connective tissues
– Matrix can be delicate and fragile (soft packing around an organ) to ropelike (tendons and ligaments)
• Even though there are diverse types they still have a common plan:
– Prototype (model) used is areolar connective tissue
• All other subclasses are simply variants of this common tissue type
AREOLAR CONNECTIVE TISSUE
Areolar Connective Tissue
• Everywhere in body (except brain)
• Function: 1- Exchange of nutrients to & from blood vessels.
2- Binds structures together.
3- Limits spread of infection
Reticular Connective Tissue
Adipose Tissue
• Poor blood supply, highly vascular insulator, shock absorber & energy store
• Cells account for 90% of tissue mass (little matrix present), 2 types white
&brown
Dense Regular Connective Tissue
White in fresh state, less flexible & more resistant. Withstand stretch& for
transparency
Tendons: connect muscle to bone. Ligaments: connect bone to bone. Cornea
Dense Irregular Connective Tissue
• Bundles and sheets of collagenous and elastic fibers oriented in multiple
directions
• In walls of elastic arteries (Aorta & large arteries), lungs (Bronchi, bronchioles &
around alveoli), vertebral C.T,Ligaments & Vocal cords.
• Strong, yet elastic; allows for recoil of tissue after being stretched
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