cartilage unit 1

Bone

Compact Spongy

Function

support the body provide a framework provide attachment sites for muscles protect underlying tissues helps provide flexibility form structural models for growing bones

Rigid Connective Tissue Cartilage

Hyaline Elastic Fibrous

matrix

It is actually the composition of this matrix which gives each type of connective tissue its individual characteristics. Matrix itself is actually composed of two different things. These are protein fibres and ground substance.

Fibrous connective tissue

Tendons Ligaments

protein fibres

The fibres consist of long protein molecules that are embedded in the ground substance. They are produced by the tissue cells which are themselves contained within the matrix. There are two types of fibres contained in the connective tissue we will study - collagen fibers made from collagen or "tropocollagen" molecules and elastic fibers made from elastin molecules.

Elastic

This is the least common type of cartilage found in the body. It has a yellowish appearance due to elastic fibres of elastin molecules in the intercellular matrix. Elastic cartilage is not very "strong" by comparison to hyaline cartilage, but it is much more flexible and it also has some elasticity. It is found in areas where its primary property, elasticity - the ability of a substance to return to an initial form after deformation - is of importance. The most obvious places where elastic cartilage can be found is in the external part of the ear and the epiglottis.

Hyaline

This is the most common type of cartilage in the body. It has a milky white, yet glassy appearance. This is due to the composition of its matrix. It consists of fine collagenous fibres embedded in a firm gel ground substance. This structure gives hyaline cartilage good strength with some flexibility. It is the "main structural" cartilage of the body and is used to replace bone wherever greater flexibility is needed. It is located throughout the body in places such as the ends of bones at many joints, the "soft" part of the nose, and the rings of the trachea and bronchial tubes. It is also the type of cartilage that makes up a great deal of the thoracic cage and the entire fetal skeleton.

Fibrous

This type of cartilage has a duller, white appearance. It consists of thick collagenous fibres contained in a firm gel ground substance. It is very tough and has great tensile strength. The difference between it and hyaline is that fibrous cartilage has a much denser matrix which contains far fewer chondrocytes and thicker collagen fibres. The main function of fibrocartilage is to serve as a shock absorber for structures where excessive pressures are generated. It is therefore located in areas where great stresses are common. The intervertebral discs of the spinal column, the meniscus cartilage of the knee, and the cartilage of the symphysis pubis joint are all fibrous cartilage.

Tissue cells

are then contained in this intercellular matrix but are "far" apart, relatively speaking.

connective tissue

composed mostly of an intercellular material called "matrix."

cartilage

connective tissue viewpoint would be that it consists of cells called chondrocytes contained in small chambers called lacunae. These lacunae are completely surrounded by intercellular matrix. The consistency of the ground substance is "gel-like." The composition of the fibres varies with the type of cartilage.

Ground Substance

described as an amorphous (shapeless or formless), extracellular material which serves as a diffusion medium in the spaces around the cells and fibers, and it plays a major role in determining the physical nature of a connective tissue.

three different types of cartilage

fibre type (collagen or elastic) and the fibre density (fine or thick) Hyaline Cartilage Elastic Cartilage Fibrous Cartilage or "Fibrocartilage"

Collagen molecules

protein fibers which have a white color to the unaided eye, so we call them "white fibers." They are the major structural protein in the human body. In tissue the collagen fibers come together to form large bundles. Collagen fibers are only slightly flexible; they have great tensile strength, and are not very elastic. The collagen molecule is a triple helix formed by three extended protein chains that wrap around one another. Many rod-like collagen molecules are cross-linked together in the extracellular space to form collagen fibrils (top) that have the tensile strength of steel.

Elastin molecules

protein fibers which have a yellowish or ivory color to the unaided eye, so we call them "yellow fibers." In tissue the elastin molecules often form large "web-like" structures. Elastic fibers are highly elastic and more flexible than collagen. However, they have much less tensile strength.Elastin polypeptide chains are cross-linked together to form rubberlike, elastic fibers. Each elastin molecule uncoils into a more extended conformation when the fiber is stretched and will recoil spontaneously as soon as the stretching force is relaxed.