SATHEE: Connective Tissue

Connective Tissue

A group of cells along with intercellular substances that perform a specific function is called a tissue.

There are mainly four different types of tissues present in our body:

Epithelial Tissue
Connective Tissue
Muscle Tissue
Nervous Tissue

Epithelial Cells - provide a covering or lining

2. Muscular - Helps in movement

3. Neural Networks Respond to Stimuli

Supports
Links
Cushions

What is Connective Tissue?

[Types of Connective Tissue](#Types of Connective Tissue)

[Loose Connective Tissue](#Loose Connective Tissue)

[Dense Connective Tissue](#Dense Connective Tissue)

Specialized Connective Tissue

Connective Tissue Disorder

Connective tissue is a type of tissue in the body that provides support and structure to other tissues and organs. It is made up of cells and fibers that are embedded in a matrix of proteins and other molecules.

Connective tissues, as the name implies, support and connect different tissues and organs of the body. They are widely distributed in every part of the body. They originate from the mesoderm (the middle germinal layer of the embryo).

The cells of connective tissue are embedded in an intercellular framework composed of protein fibers such as collagen and elastin, which are secreted by the cells. Additionally, the cells secrete a thin gel of polysaccharides, forming the matrix or ground substance along with the fibers.

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The elasticity, flexibility and strength of the connective tissues are due to fibres. The function and types of connective tissues depend on the nature of the intercellular substance present.

Connective tissues contain three types of fibres:

Collagen
Elastic
Reticular

Collagen Fibres are the most widespread type of fibrous protein, and are highly flexible with a tensile strength comparable to steel.

Elastic fibres form a network which can be stretched, similar to a rubber band. These fibres are composed of the protein elastin, and are capable of returning to their original shape and size once the force is removed.

Reticulate fibres consist of collagen and glycoproteins and are thin, forming a delicate network that connects connective tissues to neighbouring tissues.

Stationary cells: Fibroblasts or adipose cells

Migrating cells: Macrophages, mast cells, monocytes, lymphocytes

Fibroblasts are cells found in developing tissues that play an important role in wound healing. They are spindle-shaped and are located between collagen fibers. Additionally, these cells secrete tropocollagen and other substances that make up the extracellular matrix.

Macrophages, also referred to as scavenger cells, are responsible for wandering through connective tissues, cleaning up debris, and removing bacteria and other antigens through phagocytosis.

| Also see: Types of Epithelial Tissue|

Types of Connective Tissue

The classification of connective tissue is as follows:

Loose Connective Tissue

2. Dense Connective Tissue

3. Specialized Connective Tissue

Loose Connective Tissue

Loose connective tissues are found throughout the body, providing both support and elasticity. Blood vessels, nerves, and muscles are all surrounded by a layer of loose connective tissue. Additionally, these tissues, along with adipose tissues, form the subcutaneous layer that attaches muscles and other structures to the skin.

The fibres and cells are loosely arranged in the semi-fluid matrix. They are found between many organs as a filling and act as a shock absorber and reservoir for salt and fluid.

Areolar Tissue: It is a type of connective tissue present under the skin that supports epithelium. It is composed of randomly distributed collagen fibres, fibroblasts, mast cells, and macrophages. It provides support to the organs in the abdominal cavity, fills the space between muscle fibres, and wraps around blood and lymph vessels.

Adipose Tissue: They are present beneath the skin and store fat. It serves as a cushion and helps to regulate body temperature in colder climates.

White adipose tissues protect kidneys and are also found in the back of the eye, in the hump of camels, blubber of whales, etc.

Brown adipose tissue is found in infants, polar bears, penguins, and other animals found in cold regions. It contains more mitochondria and can generate 20 times more heat than other types of fat. This metabolic heat is released to help keep the animal warm.

Reticular Connective Tissue: It is composed of reticular fibers and provides structural support for organs such as the liver, lymph nodes, and spleen.

| Also see: Difference Between Areolar And Adipose Tissue |

Dense Connective Tissue

In dense connective tissue, fibroblasts and fibres are tightly packed. Their primary purpose is to provide support and transmit mechanical forces. Compared to loose connective tissue, they are less flexible. The arrangement of collagen fibres allows them to be divided into two types:

Dense Regular Tissue: This type of connective tissue is characterized by the regular orientation of its collagen fibers. The fibers are arranged in parallel bundles, providing enhanced tensile strength and resistance to stretching in the direction of the fiber orientation. Examples of dense regular tissue include tendons and ligaments.

Tendons and Ligaments:

Tendons attach skeletal muscles to bones. Ligaments attach two bones together.

Dense Irregular Tissue: This type of tissue is characterized by its mesh-like network of collagen fibers that are oriented randomly or irregularly. This arrangement gives the tissue uniform strength in all directions and is found in the dermis of the skin.

Specialized Connective Tissue

In addition to these, there are supportive connective tissues, such as cartilage and bone, which help to maintain correct posture and support internal organs.

Blood and lymph are fluid connective tissues that circulate in the body, aiding in interaction and communication among all the organs.

Cartilage: Cartilage is primarily found in the developmental stages of humans and serves as a supportive skeletal structure. As adults, most of the cartilage is replaced by bones, but it still provides support to certain structures. In humans, cartilage can be found between the bones of the spine, in the external ears, nose, and hands.

Cartilage is composed of chondrocytes which are encased in a tough, rubbery matrix, secreted by them. These cells also secrete collagen fibers that offer extra strength. Chondrocytes are found in cavities called lacunae, either in groups of two to four cells or individually. Cartilage has elasticity and is also firm, however, it does not have nerves, blood vessels, or lymph vessels.

Bones: Bones are the hardest connective tissues and are essential for maintaining the shape and posture of the body, as well as protecting internal organs. They are rich in collagen fibres and calcium, which give them strength and durability.

Osteocytes are the cells of the bone, present in lacunae and secreting the matrix. There is a substantial blood supply in bony tissues, and the cytoplasmic extension of osteocytes creates tiny channels known as canaliculi. These channels facilitate communication between osteocytes and capillaries.

Spongy bone is present in the core surrounded by the compact bone, which contains Osteons - spindle-shaped units. Each Osteon is composed of concentric layers of matrix called Lamellae, and within each Osteon are Osteocytes. Haversian Canals, which are surrounded by Lamellae, are central channels through which Capillaries and Nerves pass.

The yellow marrow contains fat, whereas red marrow produces blood cells. Both are found in the central marrow cavity, which is made up of spongy tissues (marrow).

Blood: Blood is composed of several cells found in the plasma. It consists of red blood cells (RBCs), white blood cells (WBCs) and platelets.

RBCs have haemoglobin and transport oxygen.

White Blood Cells (WBCs) act as a defense mechanism and help protect the body from foreign antigens.

Platelets are essential for blood clotting.

Plasma contains proteins, water, hormones, salts, etc., allowing it to transport these substances to different parts of the body.

Lymph: Lymph is a fluid that drains into the blood and transports absorbed fats that cannot enter the bloodstream directly. The fluid contains white blood cells (WBCs) which help fight infection and get rid of toxins and waste materials.

| Also see: MCQs On Connective Tissue |

Connective Tissue Disorder

Connective tissue disorders may be caused by mutations in genes, or by inherited faulty genes. Two genetic disorders of connective tissue are Epidermolysis Bullosa (EB) and Marfan Syndrome.

Marfan syndrome is caused by a mutation in the gene that produces the protein fibrillin-1. This disorder is characterized by a tall, thin body type, as well as spider-like fingers and toes.

EB is characterized by skin oversensitivity.

Autoimmune disorders occur when the body’s immune system starts attacking healthy tissues. This is the other type of connective tissue disorder.

Some of the autoimmune diseases of connective tissue are the following:

The systemic lupus erythematosus (SLE) is an inflammatory disorder of the skin and internal organs in which the body’s immune system starts attacking its own tissues. Symptoms of SLE include fever, swollen and painful joints, mouth ulcers, hair loss, and a butterfly rash.

Rheumatoid Arthritis (RA) is an autoimmune disorder that leads to damage in joints and deformities. It is caused by the immune system attacking the synovium - the membrane between joints.

Scleroderma: It is a condition characterized by thickening and hardening of the connective tissue. It can be localized, only affecting a certain area of the skin, or systemic, impacting vital organs.

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