Home to connective tissues!
In contrast to loose connective tissue types where protein fibers are small and less abundant, dense connective tissues possess large, robust fibers that impart to these tissues considerable strength. Fibers are so numerous the extracellular matrix contains few if any open spaces where ground substance is visible. The absence of open spaces between cells or fibers is subsequently a key identifying trait of dense connective tissues. Also, in dense connective tissues, there are fewer types of cells, the vast majority being fibroblasts or fibrocytes.
Since the protein fibers are the dominant component of these tissues the types of fibers and their orientation within these tissues is the basis for the naming scheme. Dense connective tissues contain either collagen or elastic protein fibers. Therefore, there are dense collagenous connective tissues and dense elastic types. The collagenous types, far more abundant, are also called fibrous or "white" connective tissues. Collagen appears white in tissues that are unstained, hence the name. Elastic fibers, on the other hand appear yellow in unstained tissues and are commonly referred to as "yellow" connective tissue.
In any body locale where strength of interconnection is a requirement, dense connective tissues are found. Forces transmitted across tissues determine how the protein fibers are placed within each tissue type. For example, tendons and ligaments are "cords" of the body that must resist linear forces along their lengths. If you were to cut a rope and examine its core of fibers, you would see these as interwoven strands running in a common direction, parallel to the length of the rope for maximum strength. In similar design, fibers in tendons, ligaments, and aponeuroses(flat, tendon sheaths) run in a common direction. This arrangement of fibers is called dense regular. Your body has both fibrous and elastic tendons. Most tendons and ligaments require strength and inelasticity so the fibrous type is prevalent. In the neck and back where flexibility and stretch are important functional requirements of tissues, some tendons and ligaments are elastic.
Now, contrast tendons with the connective tissues that attach skin to underlying muscles of the hand or foot. As you grasp objects in your hand or pivot your foot, forces are placed across the skin from any of a number of directions. The protein fibers anchoring skin in these locales counter variable forces by being arranged randomly. These fiber configurations are called dense irregular. Dense irregular connective tissues are always fibrous types with a preponderance of collagen fibers. Here is a comparison of dense regular and dense irregular connective tissues.
Dense regular and irregular connective tissues serve as key interconnective components that hold supportive cartilage and bone to other body structures. For example, most muscles of the body require tendons for attachment to bone. Also, many bones attach to one another via ligaments. The forces generated along tendons and ligaments dictate supportive connective tissue wrappings of muscles, bones, and cartilage also must be strong as these are the sites where the tendons or ligaments attach. The connective tissue wrappings around muscle, cartilage, nerves, and bone are named perimysium, perichondreum, perineurium and periosteum respectively. Note that the prefix "peri" means "around". Remember, these connective tissue wrappings are named on the basis of specific anatomical location but all are dense regular or dense irregular connective tissues. Let's look at examples of dense connective tissues now. See if you can determine whether these are dense regular or dense irregular types!
Connective tissue of a tendon or ligament!
Dermis anchoring the skin to the palm of the hand!
A second example of perichondreum!
Skeletal muscle fibers attaching to periosteum!
If you noticed that perichondreum can appear as dense regular and dense irregular, you are right! This is also true for periosteum. Both of these connective tissues are dense regular in many locales. However, where tendons, ligaments, and muscles attach, fibers from the connective tissues associated with these structures interweave with those of the periosteum or perichondreum for strength. The result is a dense irregular arrangements of fibers.
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