Hello again, everyone! This is Matt from Kenhub, and in this tutorial, we will explore the different types of bones found in the human skeleton.
There are five types that are generally recognized, and they’re identified by their forms, either endochondral or membranous, and by their general shape. They are the following: long, short, flat, sesamoid, and irregular.
We’ll start with the long bones. They have a more complex anatomy, so this will be the most challenging group to learn. Long bones develop via endochondral ossification, a process in which the hyaline cartilage plate is slowly replaced.
A shaft or diaphysis connects the two ends known each as the epiphysis. The marrow cavity is enclosed by the diaphysis which is thick, compact bone. The epiphysis is mainly spongy bone and is covered by a thin layer of compact bone. The articular ends participate in the joints. The metaphysis connects the diaphysis and epiphysis at the neck of the bone and is the place of growth during development.
This group of bones includes the humerus, ulna, radius, fibula, tibia, femur, metacarpals, and phalanges.
Next are the short bones which consist of a thin external layer of compact bone, covering a vast spongy bone and marrow, making a shape that is more or less cuboid. The carpal and tarsal bones fall into this category.
In flat bones, two layers of compact bone cover both spongy bone and bone marrow space. They grow by replacing connective tissue, and fibrocartilage covers their articular surfaces. This group is compiled of the skull bones, ribs, sternum, and the scapulae.
A thin layer of compact bone covers a mass of mostly spongy bone in our next group: the irregular bones. This group is not categorized by shape but by bone content and includes bones of the skull, vertebrae, and hip.
Sesamoid bones are found at the end of long bones in the limbs where the tendons cross. For example, the patella bone in the knee. They protect the tendons from excess wear by developing within the tendon and reducing friction.