Differentiation and Differentiation and tissue Formationtissue FormationMuscle TissueMuscle TissueEpithelial TissueEpithelial TissueConnective TissueConnective TissueNervous TissueNervous Tissue

Cell DifferentiationCell Differentiation

After undergoing cell After undergoing cell division [mitosis] to division [mitosis] to increase in quantity, increase in quantity, some cells change some cells change shape and structure shape and structure to perform special to perform special functions in the bodyfunctions in the body

This is called This is called cell cell differentiationdifferentiation

Coded in the genes Coded in the genes of the chromosomes of the chromosomes in every cell is the in every cell is the information needed information needed to produce anyone of to produce anyone of the specialised cells the specialised cells in the human body.in the human body.

During differentiation During differentiation only those genes that only those genes that control the control the information relevant information relevant to one particular cell to one particular cell type will operate.type will operate.

During differentiation of Muscles cells for During differentiation of Muscles cells for example, genes relevant to muscles example, genes relevant to muscles development ‘switch on’development ‘switch on’

While genes that control irrelevant While genes that control irrelevant characteristics – such as those for nerve, characteristics – such as those for nerve, stomach, bone and skin cells – will switch stomach, bone and skin cells – will switch off.off.

Cells with similar structure and function Cells with similar structure and function are usually grouped together, these are usually grouped together, these groups are called ‘tissue’groups are called ‘tissue’

Four main types of tissueFour main types of tissue Muscle tissue Muscle tissue

Cells that have the ability to contract and Cells that have the ability to contract and shorten in length on both a voluntary and shorten in length on both a voluntary and involuntary basisinvoluntary basis E.g.. Moving a limb or the heart beatingE.g.. Moving a limb or the heart beating

Epithelial tissueEpithelial tissue cells packed very closely together in continuous cells packed very closely together in continuous

layers as surfaces or linings and glandslayers as surfaces or linings and glands E.g. skin, lining of digestive tract, the walls of E.g. skin, lining of digestive tract, the walls of

blood vessels and glandsblood vessels and glands

Connective tissueConnective tissue joins different types of tissue and provides joins different types of tissue and provides

support for the body and it’s organssupport for the body and it’s organs E.g. bone, cartilage, blood and connective E.g. bone, cartilage, blood and connective

tissue proper [tendons and ligaments]tissue proper [tendons and ligaments]

Nervous tissueNervous tissue forms a network throughout the body to forms a network throughout the body to

rapidly conduct and coordinate messages rapidly conduct and coordinate messages between the brain, nerve cells and musclesbetween the brain, nerve cells and muscles

Bone DevelopmentBone Development

The bones of people are The bones of people are often thought of as being often thought of as being like the ones seen in a like the ones seen in a museum, dry, brittle and museum, dry, brittle and composed of mineralscomposed of minerals

Bones are actually living Bones are actually living structures, with structures, with approximately only half approximately only half of the material they are of the material they are made up of consisting of made up of consisting of mineralsminerals

The other half of the structure of bones is The other half of the structure of bones is made up of cellular material such as blood made up of cellular material such as blood vessels, nerve cells, and fat and protein fibres.vessels, nerve cells, and fat and protein fibres.

The process in which bones form in the body is The process in which bones form in the body is called ossification.called ossification.

OssificationOssification

Begins during the prenatal period and Begins during the prenatal period and continues into adulthood.continues into adulthood.

Cartilage Cartilage begins to form at the end of the begins to form at the end of the first month after fertilisation and forms first month after fertilisation and forms structures shaped like bonesstructures shaped like bones

Gradually these structures are Gradually these structures are transformed into bones by transformed into bones by osteoblastsosteoblasts

Osteoblasts are specialised cells on the Osteoblasts are specialised cells on the surface of the bone that build up bone surface of the bone that build up bone around themselves.around themselves.

Gradually the osteoblasts become Gradually the osteoblasts become trapped, and from this time on they can trapped, and from this time on they can no longer build bone.no longer build bone.

These cells are now known as These cells are now known as osteocytes and are responsible for osteocytes and are responsible for maintaining the daily cellular activities of maintaining the daily cellular activities of bone tissuebone tissue

How bones increase in How bones increase in lengthlength

The The epiphyseal plateepiphyseal plate is the growing region is the growing region located near the ends of the long bones, such located near the ends of the long bones, such as those found inside the arms and legsas those found inside the arms and legs

The plate allows bones to grow in length until The plate allows bones to grow in length until early adulthoodearly adulthood

During growth periods cartilage cells are During growth periods cartilage cells are produced by mitosis along the epiphyseal produced by mitosis along the epiphyseal plate, at the same time cartilage cells next to plate, at the same time cartilage cells next to the bone shaft are being replaced by the bone shaft are being replaced by osteoblasts.osteoblasts.

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

Remodelling of bonesRemodelling of bones

Remodelling Remodelling refers to the process refers to the process whereby old bone tissue is replaced with whereby old bone tissue is replaced with new bone tissuenew bone tissue

Even after bones have reached their full Even after bones have reached their full adult shape and size, old bone tissue is adult shape and size, old bone tissue is continually being replaced, this ensures continually being replaced, this ensures that bones are always at their strongestthat bones are always at their strongest

OsteoclastsOsteoclasts within the bones break down bone within the bones break down bone by secreting enzymes. These enzymes by secreting enzymes. These enzymes dissolve collagen and mineral salts [including dissolve collagen and mineral salts [including calcium] that harden the bonecalcium] that harden the bone

These are then transported in the blood to These are then transported in the blood to other parts of the body, where the dissolved other parts of the body, where the dissolved calcium can be used for functions such as calcium can be used for functions such as nerve impulses, blood clotting and muscle nerve impulses, blood clotting and muscle contractionscontractions

Bone therefore serves as one of the body’s Bone therefore serves as one of the body’s storage areas for calciumstorage areas for calcium

Many different stresses are placed on the Many different stresses are placed on the bones. These include changes in weight, bones. These include changes in weight, size, muscle strength and activity size, muscle strength and activity patternspatterns

Bones respond to these stresses by Bones respond to these stresses by remodellingremodelling

Bones response to aging Bones response to aging

One of the consequences of aging is the One of the consequences of aging is the progressive loss of the body’s ability to react to progressive loss of the body’s ability to react to it’s changing needsit’s changing needs

As we age the body becomes slower and less As we age the body becomes slower and less able to react to the stresses placed on the able to react to the stresses placed on the bonesbones

This can lead to the weakening of bones due to This can lead to the weakening of bones due to the loss of calcium and other minerals and can the loss of calcium and other minerals and can lead to a decrease in bone mass which can lead to a decrease in bone mass which can inturn lead to inturn lead to osteoporosisosteoporosis