Specialized cells in connective tissue defend the body from microorganisms that enter the body. Transport of fluid, nutrients, waste, and chemical messengers is ensured by specialized fluid connective tissues, such as blood and lymph. Adipose cells store surplus energy in the form of fat and contribute to the thermal insulation of the body.
Loose connective tissue is found between many organs where it acts both to absorb shock and bind tissues together. It allows water, salts, and various nutrients to diffuse through to adjacent or imbedded cells and tissues. Adipose tissue consists mostly of fat storage cells called a dipocytes that store lipids as droplets that fill most of the cytoplasm figure 4.
A large number of capillaries allow rapid storage and mobilization of lipid molecules. Fat contributes mostly to lipid storage, can serve as insulation from cold temperatures and mechanical injuries, and can be found protecting internal organs such as the kidneys and eye. Areolar tissue shows little specialization. It contains all the cell types and fibers previously described and is distributed in a random, web-like fashion.
It fills the spaces between muscle fibers, surrounds blood and lymph vessels, and supports organs in the abdominal cavity.
Areolar tissue underlies most epithelia and represents the connective tissue component of epithelial membranes, which are described further in a later section. Figure 4. Areolar Tissue. This is a loose connective tissue widely spread throughout the body.
It contains all three types of fibers collagen, elastin, and reticular with much ground substance and fibroblasts. Reticular tissue is a mesh-like, supportive framework for soft organs such as lymphatic tissue, the spleen, and the liver Figure 4.
Reticular cells produce the reticular fibers that form the network onto which other cells attach. Dense connective tissue contains more collagen fibers than does loose connective tissue. As a consequence, it displays greater resistance to stretching. There are three major categories of dense connective tissue: regular, irregular, and elastic. Dense regular connective tissue fibers are parallel to each other, enhancing tensile strength and resistance to stretching in the direction of the fiber orientations.
Ligaments and tendons are made of dense regular connective tissue. In dense irregular connective tissue, the direction of fibers is random. This arrangement gives the tissue greater strength in all directions and less strength in one particular direction. In some tissues, fibers crisscross and form a mesh.
In other tissues, stretching in several directions is achieved by alternating layers where fibers run in the same orientation in each layer, and it is the layers themselves that are stacked at an angle. The dermis of the skin is an example of dense irregular connective tissue rich in collagen fibers. Dense irregular elastic tissues give arterial walls the strength and the ability to regain original shape after stretching Figure 4.
The distinctive appearance of cartilage is due to the presence of polysaccharides called chondroitin sulfates, which bind with ground substance proteins to form proteoglycans. A layer of dense irregular connective tissue, the perichondrium, encapsulates the cartilage. Cartilaginous tissue is avascular, thus all nutrients need to diffuse through the matrix to reach the chondrocytes.
This is a factor contributing to the very slow healing of cartilaginous tissues. The three main types of cartilage tissue are hyaline cartilage, fibrocartilage, and elastic cartilage Figure 4.
Hyaline cartilage , the most common type of cartilage in the body, consists of short and dispersed collagen fibers and contains large amounts of proteoglycans. Under the microscope, tissue samples appear clear. It is found in joint capsules, in the connective tissue that envelops muscles muscle fascia , and it forms dermis of skin.
It is impact resistant. Look at this image and make sure you can recognise loose and dense connective tissue. This is an example of dense regular connective tissue. Can you identify the cells fibroblasts and collagen fibres? Notice how the fibres are all aligned. In this type of tissue, the collagen fibres are densely packed, and arranged in parallel. This type of tissue is found in ligaments which link bone to bone at joints and tendons connections between bones or cartilage and muscle.
These are powerfully resistant to axially loaded tension forces, but allow some stretch. Classification of Connective Tissue What is connective Tissue? The ICOI updates it membership records periodically on the web and annually by membership renewals.
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