Connective Tissues – an Overview

What Is a Connective Tissue ?

Connective tissues are specialized for supporting, connecting and protecting other tissues. They include tendons and ligaments, which are components of the skeletal system. They also include adipose tissue that stores energy as fat, cartilage that forms joints, and blood with its white blood cells (WBCs), red blood cells (RBCs) and platelets.

Connective tissue is composed of a matrix containing fibrous proteins embedded in a ground substance. Connective tissues are generally less specialized than epithelial or neural tissues, but they perform crucial functions in the body.

Types of Connective Tissue

Connective Tissues may also be classified in terms of their function and composition.

  • Mesenchyme: Embryonic connective tissue, consisting of loose mesenchymal cells with few fibers or fixed cell types. This tissue has the potential to give rise to all other types of connective tissue.
  • Loose Connective Tissue: Loosely organized fibers suspended in ground substance, forming a matrix that allows the passage of fluids; found between muscles and organs and beneath the epithelial linings of structures such as the skin; includes areolar, reticular, and adipose tissues.
  • Adipose Tissue: Specialized loose connective tissue in which fibroblasts have been replaced by cells containing large amounts of fat; functions as a storage for energy (fat) reserves and as insulation for heat conservation.
  • Dense Connective Tissue (DCT): Dense bundles or sheets of collagen fibers surrounded by fibroblasts; found where tensile strength is required; includes dense regular, dense irregular, elastic, and reticular tissues.
  • Reticular Connective Tissue: Type of dense irregular connective tissue that forms branching networks serving as supporting framework for some organs (e.g., lymph nodes).

Histology of Cartilage

Cartilage is the most widespread type of connective tissue in the body. This tissue is made up of cartilage cells (chondrocytes) and extracellular matrix, which include collagen fibers, proteoglycans, and ground substance. Cartilage tissues mainly serve for supporting connections between bones. These tissues provide support to the skeletal system by serving as pads at joints and by ensuring a smooth motion of bones over one another as well as providing protection for some internal organs like trachea, bronchi etc. There are three types of cartilage:

  • Hyaline cartilage
  • Fibrocartilage
  • Elastic cartilage

Histology of Bone

Compact Bone: Compact bone is found in the outer layers of bones, and makes up the bulk of the skeleton. The reason compact bone is considered compact is because it is made up of tightly packed osteons, which are long cylindrical structures that look similar to slices of Swiss cheese. Each osteon consists of a central canal (haversian canal) that contains nerves, blood vessels and lymphatic vessels.

Within these canals are smaller channels called perforating (Volkmann’s) canals that connect with neighboring haversian canals. Wrapped around each haversian canal are rings of matrix called lamellae. Within each lamella there are extracellular fluid filled spaces that contain osteocytes, which are mature bone cells. These cells live within lacunae, small spaces present in the matrix formed by collagen fibers and proteins such as calcium phosphate and chloride salts.

Cancellous Bone: Cancellous bone has a spongy appearance due to its meshwork-like structure. It accounts for 25 percent of total bone mass and provides support with minimal weight penalty. The meshwork allows for red marrow to be present in adult bones. Cancellous bone exists at regions where strong support is not needed, such as at joints or where bones meet. Since cancellous bone contains red marrow it will be replaced by yellow marrow if exposed to low oxygen tensions.

Histology of Blood

Blood is a connective tissue in the sense that it has a liquid matrix. In fact, it is the most abundant liquid connective tissue in your body. Although the solid components of blood are suspended in a liquid matrix, it must be stressed that blood is not as simple as a mixture of cell and fluid components.

Rather, blood cells are suspended within a fluid matrix called plasma; this plasma contains proteins (such as albumin and globulin), lipids (such as cholesterol and triglycerides) and ions (such as calcium). Collectively, they form an intricate network that maintains the shape of red and white blood cells while simultaneously providing them with nutrients and oxygen.

Collagen and Its Function

Collagen is the most abundant protein in the body, and it’s one of the major building blocks of bones, skin, muscles, tendons and ligaments. Collagen forms a scaffold to provide strength and structure. Without collagen, our skin would be just a pile of cells on the floor. In this way, it plays an essential role in keeping us looking youthful.

As we age, however, collagen production begins to slow down and even stop completely. This means fine lines start to appear as that skin no longer has a strong foundation from below. The result is sagging skin with wrinkles everywhere – not exactly fit for the cover of Vogue!

Types of Collagen Fibers and Their Functions

Collagen fibers are classified into three types on the basis of their structure and function; they are type I, type II, and type III collagen. Most tissues and organs in the body contain all these three types of collagen but with variable proportions.

Type I Collagen is the most abundant and also the strongest type of collagen. The tissues in your body that are made up of this protein include tendons, bones, teeth, skin, ligaments, connective tissues surrounding muscles (fascia), etc. Basically, all those structures that need to be very strong in order to hold your body together contain a large proportion of this protein. In fact, around 90% of the total connective tissue content is made up of this specific protein.

Collagen Structure and Function

Collagen is the most abundant protein in the human body. It makes up 30% of all protein in the human body and is found in skin, bones, ligaments, tendons, cartilage, muscles and blood vessels. Collagen is a tough material that gives structure to these organs and tissues.

There are more than 20 different types of collagen. The three most common types are: type 1 collagen which is found in skin, tendon and muscle; type 2 collagen which is found in cartilage; and type 3 collagen that creates reticular fibers which give structure to liver cells, spleen cells and bone marrow cells. Type 4 collagen lines the basement membrane of your skin while type 5 collagen acts as a precursor to hair follicles and teeth enamel.

Vitamin C & Collagen Production in Body !

Vitamin C is an essential nutrient required for the biosynthesis of collagen in the body. Collagen is one of the main components of connective tissues that make up several body parts, including tendons, ligaments, skin, cornea and cartilage. Vitamin C is essential in healing wounds and repairing and maintaining bones and teeth. Vitamin C also helps to maintain capillaries, muscles, blood vessels and contributes to healthy gums.

Vitamin C plays an important part in regulating our immune system which guards against infections by bacteria and viruses from invading your body.

The human body does not produce vitamin C on its own; hence it has to be obtained from food or supplements. It is a water soluble vitamin and it is found in citrus fruits like oranges, green vegetables such as broccoli, Brussel sprouts and cabbage.