Embryology of Bones

Embryology of BonesSalihu Moyosore AjaoMBBS(Zaria), M.Sc (Lagos), Ph.D. (Johannesburg)Department of AnatomyFaculty of Basic Medical SciencesCollege of Health SciencesUniversity of Ilorin

What is the total number of bones in the human body?Bones developed from which of the embryonic layers?Which bone was the first and the last to ossify in human being?Name two common metabolic diseases of the boneName the two types of bone ossificationRefresh your knowledgeBone is a type of vascularized dense connective tissue with cells embedded in a matrix composed of organic materials, mainly collagens fibres, and inorganic salts rich in calcium and phosphate.

Definition of boneThere are a total of about 206 bones in the entire human bodyBones forms the skeletal systemBones contains nerves and blood vesselsBones are attached to each other at joints

Facts about bones Gives the body shape and Structure Protects internal organs Provides for support for movementServe as storage tanks for some elements in the bodyUse as a means of defenseHaemopoietic activities

Functions of bones Osteoblasts: Bones forming cells

Osteocytes: Mature bones cells

OsteoclastsBone-destroying cellsBreak down bone matrix for remodeling and release of calciumBone remodeling is a process by both osteoblasts and osteoclasts is taking place

TYPES OF BONE CELLSMorphological classificationHistologicalEmbryological

Anatomical classifications of bones

Varieties of Bones

Copyright 2003 Pearson Education, Inc. publishing as Benjamin CummingsLong bones

Short bones

Flat bones

Irregular bones

Sesamoid bones

Pneumatic bonesAxial and appendicularAxial skeleton supports and protects organs of head, neck and trunk, they are the: skull, hyoid bone, vertebral column ,thoracic cage (80 bones)

Appendicular skeleton includes bones of limbs and bones that anchor them to the axial skeleton, they are the shoulder girdle, pelvic girdle and limb bones (126 bones)

DIVISION OF THE SKELETON

AXIAL SKELETONAPPENDICULAR SKELETONLong-long bones mostly bones of the limbs eg humerus, femurLong-short bones are present in the hand and feet (phalanges)Short bones cube or square shaped as seen in carpal bones of the wrist, tarsal of the ankle

Types of long bonesFlat bones: They are thin flat and curved bones eg Skull bones, Ribs, SternumIrregular bones: They have different shapes examples are vertebrae, hip bones Pneumatic bones: These are bones with air cells in them, examples are the ethimoid, frontal, maxilla, and sphenoidal bones

Types of bones continues.Basically, there are two types of bonesCompact bone-this is hard and dense bone, forms the outer layer of bones , s seen in the shaft of long bones. Spongy bone- this has more spaces than compact bones (honeycomb). Made up of a meshwork of bony plates filled with red marrow and is found at the end of long bones and the center of other bones

Histological types

SPONGY BONEEPIPHYSISARTICULAR CARTILAGECOMPACT BONEMEDULLARY CAVITYCOMPACT BONEDIAPHYSISYELLOW BONE MARROWPERIOSTEUMSHARPEYS FIBRESSTRUCTURE OF A LONG BONEDiaphysis-this is the shaft of the bone and contains the marrow cavity

Epiphysis- the irregular ends of the long bone

Epiphyseal line- this is present between the diaphysis and epiphysis of an adult long bone

Epiphyseal plate- this is a plate of hyaline cartilage present in children between the epiphysis and diaphysis ( allows growth of the bone)Anatomy of the long boneArticular cartilage- it covers the ends of the long bones (epiphysis)Periosteum-this is outside covering of bones except at the joint region where it is by membrane.Medullary cavity- it is found in the diaphysis of long bones, devoid of bone tissues and filled with red or yellow bone marrowEndosteum- this is the membrane that lines the inner surface of the bone medullary cavity. Has osteoblasts ( form new bone), osteoclasts (useful in bone resumption), and provide nourishment for the bonesAnatomy of bones.Look similar to each other histologicallyPresence of periosteum externally and endosteum internallyDo not have diaphysisHave no marrow cavity but have bone marrow in the spaces inside the boneThese spaces in the bones are called diploe and they often contains the red bone marrow

Anatomy of short /irregular/flat bonesEmbryologically, bones developed from the mesenchymal layer of the germ disc either by the direct transformation of condensed mesenchyme or be preceded by a cartilaginous model which is later replaced by bone How does bones developed?OSSIFICATIONThere are 2 major types of ossifications

Intramembranous ossification

Endochondral ossificationTypes of ossificationOsteoblasts simply lay down bone in fibrous tissue; there is no cartilage precursor. Examples are bones of the skull vault, face and clavicle.

Note: Growth in the thickness of other bones (subperiosteal ossification) is also by intramembranous ossificationIntramembranous ossificationThe pre-existing hyaline cartilage model of bone is gradually destroyed and replaced by bones. Most bones are formed in this way.

Note: It is essential to appreciate that the cartilage is not converted into bone Endochondral ossificationThere are basically two ossification centre in any bone, namely:

1. Primary ossification centre

2. Secondary ossification centreOssification centreThese are the first centre of ossification to appear in any bone during the developmental processes of the bone. The numbers from varies from one to two or even three depending on the bones. The site of primary ossification also varies from bones to bones.Primary ossification centreThese are centre that appear after the appearance of the primary centre of ossification. The indicate the future site of further development the bone(s). The numbers and sites varies from bones to bones and their coalition occurred after the initial fusion of the primary centre, however, they complete there activities ahead of the primary centre. Secondary ossification centreCongenital abnormalities of bone development

Infections affecting the bones

Traumatic injuries

Metabolic diseases of the bones

Bone MalignanciesRelevant clinical anatomyWhat is the total number of bones in the human body? (206)Bones developed from which of the embryonic layers? (Mesodermal layer)Which bone was the first and the last to ossify in human being? (Clavicle)Name two common metabolic diseases of the bone (Rickets and Osteomalacia)Name the two types of bone ossification (Endochondral and Intramembranous)Answers to the quiz Closing remarks from SD Rats

Remember, not all those that wear white coats save lives

28What else to say? Siyanbonga