Back to Human Histology
Onward to the Collection of Connective Tissues
Connective tissues (abbreviated CT) are one of the four tissues of the human body (the others being muscular, epithelial, and nervous). Connective tissues can fill open spaces, create supportive structures, add elasticity, and form tendons and ligaments.
Connective tissues contain three components:
- specialized cellsThe basic structural and functional units of life.
- protein fibers
- ground substance (kinda like a background gel)
The protein fibers and the ground substance together are referred to as the matrix. These two components form a background into which the specialized cells are suspended. Most ground substances are made mostly of waterThe universal solvent essential for life. or have water as a component, with few exceptions. Bone tissue, for example, has a matrix made of hardened calcium salts.
It is useful to think of a connective tissue like a gelatin mold with suspended fruit that a distant relative brings to a summer BBQ, only to bake in the sun and become an unpleasing texture. The suspended fruits are the specialized cells while the gelatin is the matrix. In a gelatin mold, the gelatin powder is a mixture of proteinsLarge molecules made of amino acids with various functions in the body. capable of trapping the hot water you mix in to make the gelatin.
Most connective tissues contain fibroblasts, the cells responsible for secreting the protein fibers. However, many connective tissues contain cells specialized for their intended purpose. Below are just a few examples.
Protein fibers, along with the ground substance, comprise the matrix of a connective tissue. There are only three types of protein fibers that can be found in connective tissue:
- Collagen
- Elastin (not elastiC, elastiN)
- Reticular
Connective tissues such as areolar connective tissue contain all three protein fibers. Other connective tissues can contain two of these protein fibers, one of them, or even none. Below are some examples.
Dense Regular Connective Tissue
Dense regular connective tissue contains bundles of pink-stained collagenA structural protein in the dermis that provides strength and elasticity. fibers. These fibers are arranged in the same direction and are so tightly packed that they appear an intense red color.
*The white spaces in the picture are an artifact of the process of drying this tissue to make a slide (it contracts and cracks, just like dry skinThe body’s largest organ, providing protection and regulation.).
Elastic Cartilage Connective Tissue
The darkly stained elastin fibers look like scratches between the big chondrocytes of this tissue.
Reticular Connective Tissue
The darkly-stained reticular fibers create a mesh or network that traps these B cells in a lymph node.
Ground substance, along with protein fibers, comprise the matrix of any connective tissue. Ground substance is a gel-like material that fills open spaces between the protein fibers and the specialized cells. It is part of the ECM or extracellular matrix. It contains mostly water, depending on the tissue, and proteins such as GAGs (glycosaminoglycans), proteoglycans, and glycoproteinsProteins with carbohydrate groups attached, involved in cell signaling.. The ability of the ground substance to absorb stain is variable. The proteins can sometimes take up the stain, but the water will always evaporate as part of the drying process of making a histological slide. Therefore, when students look at certain tissues and ask where the ground substance is, it is hard to explain that it may not even be present or that it is the ‘background.”
Hyaline Cartilage Connective Tissue
Hyaline cartilageA flexible connective tissue found in joints, the ear, nose, and rib cage. Cartilage can be of three comes to be one of the most recognizable connective tissues with its glassy background. The specific combination of proteins present in the ground substance creates the purples and pinks of an H&E stain.
Compact Bone Connective Tissue
The straw-colored ground substance of bone tissue represents the solidified calcium salts that make up solid bones in your body. This solid matrix is created in sheets called lamellae (singular lamella) that can be seen in circular patterns around the large open spaces. Little holes called lacunae (singular lacunaSmall spaces in bone tissue where osteocytes reside.) are dotted around the lamellae and contain osteocytes.
Dense Irregular Connective Tissue
The white spaces in the picture are an artifact of the process of drying this tissue to make a slide (it contracts and cracks, just like dry skin). These rips and tears represent the water-rich ground substance of the dermisThe thick inner layer of the skin that contains blood vessels, nerves, and connective tissue. of your skin.
List of terms
- cells
- water
- proteins
- collagen
- skin
- glycoproteins
- cartilage
- lacuna
- dermis