Connective Tissue

 

• ​Connective tissue consists of cells dispersed in a matrix.

• The cells located in the tissue manufacture and secrete proteins into the spaces between the cells, that form the ground substance of the matrix; mainly consisting of proteins.

• This ground substance is usually a fluid, but it can also be mineralized and solid, as in bones.

• Connective tissues are highly vascularized (contain many blood vessels), unlike epithelial tissue.

• The main function of connective tissue is to provide support to the other tissues of the body.

• Connective tissue is classified according to the types of cells it contains and the type of ground substance found between them.

 

Types of connective tissue

• Areolar (loose)

• Adipose

• Dense fibrous 

• Cartilage

• Bone

• Blood

 

Areolar Tissue

This is the most abundant tissue found all over the human body and is also known as loose connective tissue. Its major function is to hold everything together. It supports and nourishes (via the blood vessels) other tissues in the body.

 

Structure

Cell Type

Mainly consists of fibroblasts that manufacture and secrete the proteins collagen and elastin

Also contains mast cells and macrophages that are important for the inflammatory process during healing. 

Matrix

Consists of the proteins collagen that is very strong hence provide strength to the tissue and elastin that provides elasticity to the tissue

 

Adipose Tissue

Adipose tissue is located under the skin, around the kidneys, eyeballs and heart, buttocks and breasts. It provides a reserve of food for energy, insulates the body against heat loss and provides support and protection to the organs it protects.

 

Structure

Cell Type

Consists of closely packed fat cells that contain a large fat filled vacuole

Matrix

Consists of a small amount of the protein collagen 

 

 

 

 

 

                                                                                                                           

 (Image by Zlir'a (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons)

 

 

Dense Fibrous Tissue

There are two main types of dense fibrous tissue; regular and irregular. They are classified by the direction of the collagen fibres

 

Structure

Cell Type

Fibroblasts

Dense Regular Matrix

• Collagen fibres run in the same direction making the tissue strong

• Located in ligaments (connect bones), tendons (connect muscles to bones), dura mater (surrounds and protects the brain and spinal cord) and fascia (encloses and protects muscles)

Dense Irregular Matrix

• Collagen fibres run in different directions making tissue more flexible

• Located in the dermis of the skin

 

Cartilage

Cartilage is an unusual connective tissue in that it doesn't have any blood vessels in it. Therefore if cartilage is damaged it doesn't heal very well.

 

There are three main types of cartilage:

• Hyaline (located in the rings that support the trachea)

• Elastic (located in the outer ear)

• Fibrocartilage (located in the discs of the spine)

 

Structure

Cell Type

Chondrocytes usually arranged in groupings of 2-4 cells surrounded by a pocket of fluid called a lacuna

Matrix

Protein Gel

 

Bone

Bone is a highly vascularized tissue and is only capable of growing in width, not length. Bones grow in length at the growth plate that is only present in children. The growth plate is made of hyaline cartilage which can grow both in width and length. This is found near the ends of the bone. Over time the hyaline cartilage becomes bone, and once all the hyaline cartilage is converted to bone growth stops.

 

There are two types of bone tissue; compact and spongy.

 

Compact bone tissue

• Consists of osteocytes arranged in concentric rings (Haversian systems) closely packed together, making it very strong.

• It forms the outer covering of bones

• If the whole bone was made of compact bone tissue it would be too heavy, making movement much more difficult

 

Spongy (cancellous) bone tissue

• Less dense than compact bone tissue

• Doesn't contain Haversian systems 

• Borders cavities that contain marrow

• Red marrow is filled with blood and functions to make new blood cells. In adults, the only bones that contain red marrow are found in the sternum, ribs, pelvis and spine

• Yellow marrow is filled with fat

 

Structure

Cell Type

Osteocytes

• Osteoblasts secrete calcium minerals that form the matrix of the bone tissue

• Osteoclasts break down calcium minerals to be reabsorbed back into the blood for other functions such as blood clotting, heart activity and the nervous system

Matrix (Hard)

• calcium salts

• Collagen Fibres

 

Blood

Blood makes up about 8% of body weight. It consists of a watery matrix (plasma) that makes up about 55% of the blood and cells that make up about 45% of the blood.

 

Cell Types

Red blood cells

• More abundant (4-6 million/㎣)

• Biconcave discs with no nucleus (increase surface area and space for haemoglobin)

• Formed in the bone marrow (sternum, spine, ribs - adult)

• Have a lifespan of 4 months because no genetic material and therefore unable to repair themselves

• Transport oxygen around the body by attaching to haemoglobin

 

White blood cells

• Less abundent (7000/㎣)

• There are five main types of white blood cell that are then further divided into other types

• White blood cells form part of the immune system 

 

Platelets

• Platelets are not cells but very small, irregulary shaped, non-nucleated fragments of bone marrow cells

• Play an important roll in blood clotting

 

Matrix

Plasma consisting of about 90% water and the remaining 10% proteins and other solutes.

The majority of proteins in the plasma are manufactured in the liver

 

The main functions of plasma are:

• To carry food (glucose and amino acids)

• Transport enzymes, hormones and antibodies around the body

• Contains fibrinogen which is required for blood clotting