Differentiation and tissue Formation Muscle Tissue Epithelial Tissue Connective Tissue Nervous Tissue

Cell Differentiation After undergoing cell division [mitosis] to increase in quantity, some cells change shape and structure to perform special functions in the body This is called cell differentiation

Coded in the genes of the chromosomes in every cell is the information needed to produce anyone of the specialised cells in the human body. During differentiation only those genes that control the information relevant to one particular cell type will operate.

During differentiation of Muscles cells for example, genes relevant to muscles development ‘switch on’ While genes that control irrelevant characteristics – such as those for nerve, stomach, bone and skin cells – will switch off. Cells with similar structure and function are usually grouped together, these groups are called ‘tissue’

Four main types of tissue Muscle tissue Cells that have the ability to contract and shorten in length on both a voluntary and involuntary basis E.g.. Moving a limb or the heart beating

Epithelial tissue Connective tissue cells packed very closely together in continuous layers as surfaces or linings and glands E.g. skin, lining of digestive tract, the walls of blood vessels and glands Connective tissue joins different types of tissue and provides support for the body and it’s organs E.g. bone, cartilage, blood and connective tissue proper [tendons and ligaments]

Nervous tissue forms a network throughout the body to rapidly conduct and coordinate messages between the brain, nerve cells and muscles

Bone Development The bones of people are often thought of as being like the ones seen in a museum, dry, brittle and composed of minerals Bones are actually living structures, with approximately only half of the material they are made up of consisting of minerals

The other half of the structure of bones is made up of cellular material such as blood vessels, nerve cells, and fat and protein fibres. The process in which bones form in the body is called ossification.

Ossification Begins during the prenatal period and continues into adulthood. Cartilage begins to form at the end of the first month after fertilisation and forms structures shaped like bones Gradually these structures are transformed into bones by osteoblasts

Osteoblasts are specialised cells on the surface of the bone that build up bone around themselves. Gradually the osteoblasts become trapped, and from this time on they can no longer build bone. These cells are now known as osteocytes and are responsible for maintaining the daily cellular activities of bone tissue

How bones increase in length The epiphyseal plate is the growing region located near the ends of the long bones, such as those found inside the arms and legs The plate allows bones to grow in length until early adulthood During growth periods cartilage cells are produced by mitosis along the epiphyseal plate, at the same time cartilage cells next to the bone shaft are being replaced by osteoblasts.

The osteoblasts secrete mineral salts, resulting in a build up of bone along the junction with the epiphyseal plate and the bone shaft – this causes the bone to increase in length

Remodelling of bones Remodelling refers to the process whereby old bone tissue is replaced with new bone tissue Even after bones have reached their full adult shape and size, old bone tissue is continually being replaced, this ensures that bones are always at their strongest

Osteoclasts within the bones break down bone by secreting enzymes Osteoclasts within the bones break down bone by secreting enzymes. These enzymes dissolve collagen and mineral salts [including calcium] that harden the bone These are then transported in the blood to other parts of the body, where the dissolved calcium can be used for functions such as nerve impulses, blood clotting and muscle contractions Bone therefore serves as one of the body’s storage areas for calcium

Many different stresses are placed on the bones Many different stresses are placed on the bones. These include changes in weight, size, muscle strength and activity patterns Bones respond to these stresses by remodelling

Bones response to aging One of the consequences of aging is the progressive loss of the body’s ability to react to it’s changing needs As we age the body becomes slower and less able to react to the stresses placed on the bones This can lead to the weakening of bones due to the loss of calcium and other minerals and can lead to a decrease in bone mass which can inturn lead to osteoporosis