Connective tissue consists of three main components: cells , protein fibers , and an amorphous ground substance. Together the fibers and ground substance make up the extracellular matrix. Whereas the other tissue types epithelium, muscle, and nervous tissue are largely made up of cells, the extracellular matrix is the major component of most connective tissue.
This chapter will focus on the basic types of connective tissue, while subsequent chapters examine the specialized connective tissues cartilage , bone , and blood. Connective tissue is classified based on the characteristics of its cellular and extracellular components.
The main criteria are the type of cells, arrangement and type of fibers, and composition of the extracellular matrix.
Loose areolar connective tissue has a sparse, irregular network of collagen and elastic fibers suspended within a relatively large amount of ground substance. Dense regular connective tissue is composed of type I collagen fibers oriented in the same direction. It provides tensile strength in one direction. Dense irregular connective tissue contains type I collagen fibers woven in multiple directions. It provides tensile strength in multiple directions.
Embryonic connective tissue is formed during the development of the embryo. 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. The surface of hyaline cartilage is smooth. Both strong and flexible, it is found in the rib cage and nose and covers bones where they meet to form moveable joints.
It makes up a template of the embryonic skeleton before bone formation. A plate of hyaline cartilage at the ends of bone allows continued growth until adulthood. Adipose tissue is a connective tissue with a predominance of adipocytes. Slide 2 Peripheral Nerve, Osmium Tetroxide. Lipid is preserved and stained black when the tissue is prepared using osmium tetroxide as a fixative.
Slide 49 Esophagus. Leukocytes are white blood cells that are readily found in connective tissue. Lymphocytes similar in size to red blood cells are the most common connective tissue leukocyte. Aggregates of lymphocytes are often found associated with the mucosal epithelium of the GI tract, such as this slide of the esophagus.
They have a small amount of slightly basophilic cytoplasm and a large, darkly stained nucleus because of condensed chromatin. Use Slide 51 pyloric stomach to compare lymphocytes no visible cytoplasm to plasma cells which contain abundant cytoplasm. Slide 80 Pancreas. Observe the eosinophils surrounding the large duct in the center of this slide.
These cells are another type of leukocyte that are identified by their bilobed nucleus and refractile specific granules that are stained by eosin. Connective tissue can be classified as either connective tissue proper or specialized connective tissue.
Connective tissue proper includes: loose connective tissue also called areolar and dense irregular connective tissue.
Specialized connective tissue types include: dense regular connective tissue, cartilage, bone, adipose tissue, blood, and hematopoietic tissue. The majority of specialized connective tissues will be studied in future laboratories. Slide 13 Trachea. Loose connective tissue areolar is located under the thick eosinophilic basement membrane of the respiratory epithelium in the trachea.
Cartilage contains chondrocytes and chondroblasts chondro - cartilage which secrete the type of ECM found in cartilage, respectively. Blood vessels contain Endothelial cells, the simple squamous endothelium that lines the circulatory system, which are covered in the section on epithelia.
Also present, just underneath the epithelium of blood capillaries, are cells called Pericytes - perivascular cells - peri is greek for 'around , which can divide and provide a source of new fibroblasts, especially following tissue injury.
Finally, smooth muscle is commonly found in connective tissue.
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