What are the functions of irregular bones

Structure and function of bones and joints

bone

Bone building and bone formation. As the child grows, the bone ends (epiphyses) still consist of cartilage tissue (blue in the picture). Starting from a bone core, the cartilage becomes increasingly ossified until only a cartilaginous coating and a cartilage zone remain in the border area between the end of the bone and the shaft. From this cartilage zone, called the growth plate, the further longitudinal growth starts. It is complete when the growth plate is completely ossified towards the end of puberty. Only one layer of the original cartilage mass remains on the articular surfaces of the end of the bone, the articular cartilage. Within the shaft of the long bones in children there is red, blood-forming bone marrow, which turns into yellow, fatty bone marrow with age.
Gerda Raichle, Ulm

The human skeleton consists of 208 to 214 Bone. The number varies between individuals, as the hand, foot and spine, in particular, can contain different amounts of bones. The long ones form the supporting structure of the limbs Long bonesto which z. B. Counting humerus, ulna and radius, femur, tibia and fibula. They each consist of the two Bone ends (Epiphyses) and the one in between Bone shaft (Diaphysis). In addition to the long bones, various other types of bones are involved in the structure of the skeleton: the flat bones, the z. B. skull, pelvis and ribs form the short bonesthat v. a. located in the wrist, as well irregular bones, e.g. B. vertebrae or mandible. As Sesame bones small round bones are called, the number and size of which are individually different; its largest and most famous representative is the kneecap.

Bone augmentation.Parts of the bone that lie within a joint are covered by a layer of cartilage, which reduces the frictional forces that occur. Outside of joints covers a well-perfused one Periosteum (Periosteum) the surface. It protects and nourishes the outer layer of bone and is used to insert ligaments and tendons. Their extreme sensitivity to pain is familiar to anyone who has ever bumped their shin.

Below the periosteum lies a layer of dense bone tissue of varying thicknesses. This layer is called in the area of ​​the bone shaft Compact, at the ends of the bones Cortex. The latter is detached from the inside of the bone Cancellous bone, a sponge-like structure made of fine Trabeculae. This construction ensures great stability of the bone with a relatively low weight. In adults there is v. a. Adipose tissue, also red, blood-forming in the flat bones Bone marrow. The bone substance consists of various types Bone cells (Osteocytes) that are in a Bone matrix from calcium-containing Hydroxyapatite, Proteins (e.g. collagen), water and other substances are embedded.

The growth plate is at risk in the case of bone fractures. If she is injured, as here with a 5-year-old girl with a fracture on her inner ankle, there is a risk of bone growth being disrupted. The arrow (left picture) points to the fracture line that cuts through the lower growth plate of the tibia. As a result, a leg length difference or an axis deviation can arise (right picture). The growth plate injuries are divided into degrees of severity. While conservative therapy is successful in severity grade 1, injuries from severity grade 2 must be treated surgically.
Georg Thieme Verlag, Stuttgart

Bone formation. The process of Bone formation, Called osteogenesis or ossification, is essentially the same for child bone growth and for ossification of bone fractures. A distinction is made between two forms: Producing with direct ossification Osteoblasts, bone-forming cells, the bone matrix right in place. In contrast, with chondral ossification, cartilage tissue initially develops, which is gradually replaced by bone tissue. During the child's bone growth, the still cartilaginous bones form in the womb Bone nuclei. These ossified areas become larger and finally fuse, so that only narrow areas of cartilage remain between the end of the bone and the bone shaft Growth plates or epiphyseal plates. The bone continues to grow in length from them until they finally ossify towards the end of the second decade and thus complete the pubertal growth phase.

The trabeculae perform the same function as steel supports and load-bearing walls of a building. They take the load from "above", distribute it and give the bone strength. Thinning out the trabeculae - this is e.g. This is the case, for example, with osteoporosis - even minor incorrect loads lead to fracture of the bone. The femoral neck is very susceptible to this because it has to bear a considerable static load due to the axis that the femoral neck forms with the femoral head.
Georg Thieme Verlag, Stuttgart

Even after this growth phase, the bone is not ready, but is constantly building, breaking down and changing. Various hormones are involved in this process in complicated control circuits, in particular the sex hormones estrogen and testosterone, the bone-building calcitonin from the thyroid gland and the bone-breaking parathyroid hormone from the parathyroid gland. Vitamin D is also required to process calcium, an important component of the bone matrix. Up to the age of 35, the building processes predominate and the bone mass increases constantly. Thereafter, the bone mass usually decreases by about a year
1,5 %.

Joints

When bones become one joint join together, determined v. a. the shape of the bone surfaces involved, what movements are possible in this area. Both Ball joints A spherical joint head lies in a joint socket in the hip and shoulder and allows movements in all directions. A Hinge jointAs it is located in the ankle joint, on the other hand, only allows movements around one axis, since its joint surfaces are designed as a roller and groove. At Saddle joints like the thumb saddle joint, two Y-shaped joint surfaces interlock and allow movements in two mutually perpendicular directions. There are other shape variants Egg joints (between the skull and the uppermost vertebra), flat joints (e.g. between vertebral processes) and Tenon jointsthat allow pure rotary movements, e.g. B. between the two upper cervical vertebrae or between ulna and radius.

Every joint is taut Joint capsule which it guides and protects against contortions. As Synovial membrane (Synovialis) formed, inner layer of the capsule secretes into the Joint cavity a viscous liquid that Synovial fluid or synovia. This fulfills two important tasks: It nourishes the avascular Articular cartilagethat coats the articular surfaces and increases its gliding ability at the same time.

Authors

Dr. med. Arne Schäffler in: Gesundheit heute, edited by Dr. med. Arne Schäffler. Trias, Stuttgart, 3rd edition (2014). Revision and update: Dr. med. Sonja Kempinski | last changed on at 15:47