Epiphysis facts for kids

Quick facts for kids Epiphysis
Structure of a long bone, with epiphysis labeled at top and bottom.

An epiphysis is one of the rounded ends or tips of a long bone that ossify from a secondary center of ossification. Between the epiphysis and diaphysis (the long midsection of the long bone) lies the metaphysis, including the epiphyseal plate (growth plate). At the joint, the epiphysis is covered with articular cartilage; below that covering is a zone similar to the epiphyseal plate, known as subchondral bone. The epiphysis is found only in mammals which means it is a mammalian synapomorphy.

The epiphysis is filled with red bone marrow, which produces erythrocytes (red blood cells).

Structure

There are four types of epiphysis:

1. Pressure epiphysis: The region of the long bone that forms the joint is a pressure epiphysis (e.g. the head of the femur, part of the hip joint complex). Pressure epiphyses assist in transmitting the weight of the human body and are the regions of the bone that are under pressure during movement or locomotion. Another example of a pressure epiphysis is the head of the humerus which is part of the shoulder complex. Condyles of femur and tibia also come under the pressure epiphysis.
2. Traction epiphysis: The regions of the long bone which are non-articular, i.e. not involved in joint formation. Unlike pressure epiphyses, these regions do not assist in weight transmission. However, their proximity to the pressure epiphysis region means that the supporting ligaments and tendons attach to these areas of the bone. Traction epiphyses ossify later than pressure epiphyses. Examples of traction epiphyses are tubercles of the humerus (greater tubercle and lesser tubercle), and trochanters of the femur (greater and lesser).
3. Atavistic epiphysis: A bone that is independent phylogenetically but is fused with another bone in humans. These types of fused bones are called atavistic, e.g., the coracoid process of the scapula, which has been fused in humans, but is separate in four-legged animals. os trigonum (posterior tubercle of talus) is another example for atavistic epiphysis.
4. Aberrant epiphysis: These epiphyses are deviations from the norm and are not always present. For example, the epiphysis at the head of the first metacarpal bone and at the base of other metacarpal bones

Bones with an epiphysis

There are many bones that contain an epiphysis:

1. Humerus: Located between the shoulder and the elbow.
2. Radius: One of two bones located between the in the forelimb below the elbow. In anatomical position, the radius is lateral to the ulna.
3. Ulna: One of two bones located between the in the forelimb below the elbow. In anatomical position, the ulna is medial to the radius.
4. Metacarpal: Bones of the forelimb. They are distal to the wrist bones, proximal to the phalanges of the forelimb.
5. Phalanges: Bones that are nearest the end of the limbs.
6. Femur: Located between the hip and the knee. Forms the upper half of the knee joint. (The longes human bone.)
7. Fibula: One of two bones in the lower leg. Forms part of the lower half of the knee joint. Part oIt is lateral to the tibia and smaller.
8. Tibia: One of two bones in the lower leg. Forms part of the lower half of the knee joint. It is medial to the fibula and does most of the weight bearing.
9. Metatarsal: Bones near the distal end of the hindlimb, and proximal to the phalanges for the other four.

Additional images

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  Long bone

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  Longitudinal section of head of left humerus.

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