Connective Tissue - Histology (L1) Flashcards
Connective tissue
Most widespread and abundant tissue in the body. Surrounds other tissues, encases internal organs, sheathes muscles, wraps bones, encloses joints, composes the blood, forms the supportive framework for all organs.
Fibroblasts
The most common cells in connective tissues. Responsible for the maintenance of the integrity of many connective tissues by repairing damage over time, slowly replacing extracellular fibers and the matrix between them.
Extracellular matrix
Composed of the intercellular substances secreted by the connective tissue cells. This matrix allows for the diffusion of metabolites and is an important barrier to the spread of microorganisms. Matrices are composed of ground substances, such as hyaluronic acid, structural glycoproteins and interstitial fluid. Together with the embedded extracellular fibers the extracellular matrix of a connective tissue may be liquid, semisolid, or solid.
Connective tissue fibers
Most common: collagen and elastin
Collagen
Principal fiber type found in the matrix of most connective tissues and is the most abundant protein in the body. It is found in loose fibrous connective tissue, skin, tendons, ligaments and bone, in various arrangements from loose to dense. Parallel collagen fibers are often arranged into strong bundles which confer great tensile strength to the tissue those bundles are sometimes visible under the light microscope, but sometimes they are packed so close together they are not individually distinguishable. Collagen is secreted into the matrix in its precursor form of tropocollagen; in the matrix, the tropocollagen molecules polymerize to form collagen.
Elastin
A rubber-like material which is arranged as fibers and discontinuous sheets in the matrix particularly of skin, lung, and blood vessels. Elastin fibers impart elasticity (or stretchiness sand springiness) to connective tissues. Like collagen, elastin is synthesized by fibroblasts in a precursor form known as tropoelastin which undergoes polymerization after secretion.
Human blood smear
Blood and lymph are good examples of connective tissues with liquid matrices.
Erythrocytes/leukocytes
AKA red and white blood cells. In blood, floating in the plasma, which is the liquid matrix.
Fibrinogen/thrombin/fibrin
The fibers in blood are not collagen and elastin, but the soluble protein fibrinogen. When clotting occurs, a part of each fibrinogen molecule is cleaved off by the protease thrombin. The cleaved protein the polymerizes, subunits joining together into long, insoluble fibrin protein fibers, which contribute to the structure of the blood clot.
Platelets
Small platelets can be seen, which appear as tiny purple dots between cells, platelets are also involved in blood clot formation.
Loose fibrous connective tissue
AKA areolar tissue (spread). Widespread throughout the body, functioning to bind together the individual cells of muscles and nerves, to bind organs together and hold them in place, etc. In other words, it acts as a biological packing material between other tissues of more specific function.
In loose connective tissue, the fibers are not packed tightly together and they are oriented in many different directions.
Collagen and elastin
Contained in the matrix of loose fibrous connective tissue. Collagen fibers are pink stained, elastin fibers are blue stained. Both types of fibers are produced by the purple stained fibroblasts.
Tendon, long section, thin section
connect muscles to bones and ligaments, which connects bones to other bones, are composed of dense fibrous connective tissue. This tissue differs from loose fibrous connective tissue in that its elastin and collagen fibers are tightly packed together and are all oriented in the same direction, thus increasing strength and elasticity in that direction. These fibers are wavy in shape, and are closely packed in bundles, giving the tissue a characteristic wavy appearance.
May see flattened fibroblasts between the rows.
Adipose
AKA fat tissue. unique type of connective tissue. Unlike all the other connective tissues in this lab, adipose tissue is almost all cellular, with very little extracellular collagen in its tiny amount of extracellular matrix. Connects dissimilar tissue types. Often encases parts of organs where it acts as a protective, cushioning sheath, helping to prevent the ureter from being crushed.
Adipocytes appear to have a ring-like shape.
The triglycerides in adipocytes are an important energy reservoir for the organism.
Hyaline cartilage
This type of cartilage is the most abundant form in the body. It has a firm rubbery texture and is composed mostly of extracellular materials: many tightly packed collagen fibers, some elastin fibers, and a matrix high in the polymerized glycosaminoglycan hyaluronic acid.
