Human Body Bones

The human skeleton of an adult consists of 206-208 bones, depending on the counting of the sternum (which may alternatively be included as the manubrium, body of sternum, and the xiphoid process) It is composed of 270 bones at birth, but later decreases to 80 bones in the axial skeleton and 126 bones in the appendicular skeleton. Many small accessory bones, such as some sesamoid bones, are not included in this count. As a human ages, some of its bones fuse, a process which typically lasts until sometime within the third decade of life. Therefore, the number of bones in an individual may be evaluated differently throughout their life. In addition, the bones of the skull and face are counted as separate bones, despite being fused naturally. Some reliable sesamoid bones such as the pisiform are counted, while others, such as the hallux sesamoids, are not. Individuals may have more or fewer bones than the average (even accounting for developmental stage) owing to anatomical variations. The most common variations include sutural (wormian) bones, which are located along the sutural lines on the back of the skull, and sesamoid bones which develop within some tendons, mainly in the hands and feet. Some individuals may also have additional (i.e., supernumerary) cervical ribs or lumbar vertebrae.

Stronget & Longest Bone = Femur.  Shortest Bone = Stapes.

Types of Bones:

There are five types of bones in the human body:
Long Bones: Long bones are some of the longest bones in the body, such as the Femur, Humerus, and Tibia but are also some of the smallest including the Metacarpals, Metatarsals, and Phalanges. The classification of a long bone includes having a body which is longer than it is wide, with growth plates (epiphysis) at either end, having a hard outer surface of a compact bone and a spongy inner known a cancellous bone containing bone marrow. Both ends of the bone are covered in hyaline cartilage to help protect the bone and aid shock absorption.

Short Bones: Short bones are defined as being approximately as wide as they are long and have a primary function of providing support and stability with little movement. Examples of short bones are the Carpals and Tarsals - the wrist and foot bones. They consist of only a thin layer of compact, hard bone with cancellous bone on the inside along with relatively large amounts of bone marrow.

Flat Bones: Flat bones are as they sound, strong, flat plates of bone with the main function of providing protection to the bodies vital organs and being a base for muscular attachment. The classic example of a flat bone is the Scapula (shoulder blade). The Sternum (breastbone), Cranium (skull), ilium (hip bone) Pelvis and Ribs are also classified as flat bones. Anterior and posterior surfaces are formed of compact bone to provide strength for protection with the centre consisting of cancellous (spongy) bone and varying amounts of bone marrow. In adults, the highest number of red blood cells are formed in flat bones.

Sesamoid Bones: Sesamoid bones are usually short or irregular bones, embedded in a tendon. The most obvious example of this is the Patella (knee cap) which sits within the Patella or Quadriceps tendon. Other sesamoid bones are the Pisiform (smallest of the Carpals) and the two small bones at the base of the 1st Metatarsal. Sesamoid bones are usually present in a tendon where it passes over a joint which serves to protect the tendon.

Irregular Bones: These are bones in the body which do not fall into any other category, due to their non-uniform shape. Good examples of these are the Vertebrae, Sacrum, and Mandible (lower jaw). They primarily consist of cancellous bone, with a thin outer layer of compact bone.

Bones of the skeleton are split into two groups:
Appendicular Skeleton: bones of the limbs, shoulders, and pelvic girdle.
Axial Skeleton: bones of the skull, vertebral column, thoracic cage.
Bone Marrow:
Bone marrow is found in almost all bones where cancellous bone is present. The marrow is responsible for making around 2 million red blood cells every second. It also produces lymphocytes or the white blood cells involved in the immune response.


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