Connective tissue is the most widespread and diverse of all the tissues, and they have three main components, cells, protein
fibers and ground substance. Ground substance is produced by connective tissue cells, it is a non cellular material and it can be
solid, semisolid, or viscous, meaning thick and sticky. The cells and protein fibers reside within this ground substance, and the ground substance and protein
fibers together are often referred to as the extracellular matrix. There are many functions that the different types of connective tissues perform,
such as in many cases it provides protection for internal organs, for instance the skull protects the brain. It can also provide structural support as bones
provide the framework for the body. Connective tissues connect and bind certain structures, for instance ligaments bind bone to bone, and tendons bind muscles to bones.
It also provides for storage of some nutrients as bones store calcium and phosphorus. It is important in transportation, as blood, which is a connective tissue,
transports nutrients, gases and wastes throughout the body. And connective tissue helps with immune function, as many connective tissues contain
white blood cells that protect the body from invaders. Now we are going to go through the various types of connective
tissues, and the basic structure of each of these types. On the screen is a board with the different classifications of connective tissues.
As you can see, there are three main classifications, connective tissue proper, supporting connective tissue and fluid connective tissue.
Connective tissue proper, which is sometimes referred to as fibrous because it has many fibers in its extracellular matrix, is divided into 2 subgroups
based on the proportions of cells, fibers and ground substance. Subgroup one is loose connective tissue and it has fewer cells and fibers
and more ground substance than subgroup two, dense connective tissue. There are 3 main types of loose connective tissue.
Areolar connective tissue has a viscous ground substance with both collagen and elastic protein fibers. It is highly vascularized, meaning it has a good blood supply,
and it contains a large number of fibroblast cells, which produce many components of the extracellular matrix. It surrounds
certain organs and blood vessels and binds skin. Adipose connective tissue is also highly vascularized and is comprised primarily of adipocytes,
which are fat cells, and have very little extracellular matrix. Adipocytes are filled with fat droplets, which push the nucleus toward the plasma membrane.
There are two types of adipose connective tissue, white and brown. Brown adipose tissue is found more in infants and newborns,
and white adipose tissue stores energy, insulates some organs, and provides a cushion against shocks to the body. Adipose connective tissue
is located throughout the body, as it can be found under the skin, and surrounding various organs.
Reticular connective tissue has a viscous ground substance with a branching network of reticulin fibers within it. Reticular cells and the fibers provide a
supportive framework in the spleen, lymph nodes and bone marrow. Now for dense connective tissue, which also has three main types.
Dense regular connective tissue consists of tightly packed parallel collagen fibers with a limited amount of ground substance and fibroblast cells
squeezed between the fiber layers. This tissue does not have a good blood supply, so when injured it takes a long time to heal.
This tissue is found in tendons and ligaments as it can withstand a lot of stress. Dense irregular connective tissue consists of collagen fibers
that are clumped together forming an irregular pattern. It also contains fibroblast cells, and has more ground substance and a much richer blood supply
than dense regular connective tissue. This tissue can handle stress in multiple directions, and is found in the dermis of the
skin and in the periosteum which covers bone. Elastic connective tissue consists of densely packed elastic fibers, with fibroblasts scattered throughout.
It is found in the trachea, vocal chords and walls of some arteries.
Next, let’s look at the second classification of connective tissues, supporting connective tissue,
which also has two subgroups, cartilage and bone, with cartilage having a semisolid matrix and bone having a solid matrix.
There are 3 main types of cartilage. Hyaline cartilage consists of chondrocyte cells, which support and repair the cartilage matrix, and these cells occupy
small spaces called lacunae and are scattered throughout the matrix. It has a poor blood supply causing injuries to heal slowly, and sometimes not at all.
Hyaline cartilage is the most common type of cartilage and it caps the bones of synovial joints, is found in the nose and in the respiratory passage.
Fibrocartilage consist of dense, wavy looking collagen fibers and it too has chondrocyte cells in lacunae. Fibrocartilage acts a great shock absorber
and is resistant to compression. It is the toughest form of cartilage and it is what makes up the discs of the spine and the meniscus in the knee joint.
The third type of cartilage is elastic cartilage. Elastic cartilage contains some collagen fibers, and a high number of elastic fibers,
and it also has chondrocyte cells in lacunae. This cartilage has a high degree of flexibility and can be found in the external ear and in the epiglottis,
which prevents swallowed food from entering the trachea. Bone is the second type of supporting connective tissue, it is more solid than cartilage
but less flexible and it has a rich blood supply. The extracellular matrix of bone consists of collagen fibers and mineral salt crystals
and bone cells called osteocytes that occupy small spaces called lacunae and are scattered throughout the matrix. Bones provide support
and protection and also provide a point of attachment for muscles. There are two main bone tissue types, compact and spongy.
Compact bone form cylindrical structures called osteons, which look like rings, and they surround a central canal that houses nerves and blood vessels.
Spongy bone has a lattice like look to it, and it is located in the interior of a bone and it is strong but lightweight. Next up is the third classification of
connective tissues, fluid connective tissue, which also has two subgroups, blood and lymph. Blood tissue is comprised of formed elements and has a
liquid ground substance called plasma. The formed elements include red and white blood cells, and platelets. The plasma contains proteins as well.
The red blood cells transport oxygen and carbon dioxide, the white blood cells protect the body from foreign invaders,
platelets help with clotting the blood and the plasma transports nutrients, wastes and hormones throughout the body.
Lymph originates from the interstitial fluid that surrounds tissue cells. And it transports fats and white blood cells throughout the body.
And that be the basics on connective tissue.