Bones make up the skeletal system of the human body 博彩app下载苹果端 are responsible for somatic rigidity, storage of different micronutrients, 博彩app下载苹果端 housing bone marrow. They also produce?red blood cells 博彩app下载苹果端 the various forms of white blood cells 博彩app下载苹果端 provide?structural outline 博彩app下载苹果端 movement. The bones are essential for the bipedal posture that?humans have since the latest major evolutional update.
Of the two hundred 博彩app下载苹果端 six bones in an adult human body, there are several types that are grouped together due to their general features, such as shape, placement 博彩app下载苹果端 additional properties.
Cortical bone - outer layer
Bone tissue (cancellous bone)?- inner layers
Medullary canal - contains either red (active) or yellow (inactive) bone marrow
Osteoblasts (bone forming cells), osteocytes (inactive osteoblasts), osteoclasts (cells that reabsorb the bone)
Compact bone (cortical bone) - made of osteons
Spongy bone (cancellous bone) - made of bony plates (trabeculae)
Long bones - humerus, ulna, radius, fibula, tibia, femur, metacarpal bones, phalanges
Short bones - carpal 博彩app下载苹果端 tarsal bones
Flat bones - some of the skull bones, ribs, sternum, scapulae
Irregular bones - vertebrae, coxa, some of the skull bones
Sesamoid bones - patella
Intramembranous ossification - flat bones: ossification centre formation -> calcification -> trabeculae formation -> periosteum formation
Endochondral ossification - long bones: development of a cartilage model -> growth 博彩app下载苹果端 development of the cartilage model -> development of the primary 博彩app下载苹果端 secondary ossification centers -> forming of the articular cartilage 博彩app下载苹果端 epiphyseal plates
|Clinical relations||Rickets, osteomalacia, osteoporosis, tumors, fractures|
All of the anatomical 博彩app下载苹果端 important histological facts about the bones, together with the clinical relations, are going to be desrcibed in this article.
- What is a bone?
- Types of bone
- Clinical aspects
What is a bone?
A bone is a somatic structure that is comprised of calcified connective tissue. Ground substance 博彩app下载苹果端 collagen fibers create a matrix that contains osteocytes. These cells are the most common cell found in mature bone 博彩app下载苹果端 responsible for maintaining bone growth 博彩app下载苹果端 density. Within the bone matrix both calcium 博彩app下载苹果端 phosphate are abundantly stored, strengthening 博彩app下载苹果端 densifying the structure.
Each bone is connected with one or more bones 博彩app下载苹果端 are united via a joint (only exception: hyoid bone). With the attached tendons 博彩app下载苹果端 musculature, the skeleton acts as a lever that drives the force of movement. The inner core of bones (medulla) contains either red bone marrow (primary site of hematopoiesis) or is filled with yellow bone marrow filled with adipose tissue.
The main outcomes of bone development are endochondral 博彩app下载苹果端 membranous forms. This particular characteristic along with the general shape of the bone are used to classify the skeletal system. The main shapes that are recognized include:
Types of bone
These 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 as the epiphyses (plural for epiphysis). The marrow cavity is enclosed by the diaphysis which is thick, compact bone. The epiphysis is mainly spongy bone 博彩app下载苹果端 is covered by a thin layer of compact bone; the articular ends participate in the joints.
The metaphysis is situated on the border of the diaphysis 博彩app下载苹果端 the epiphysis at the neck of the bone 博彩app下载苹果端 is the place of growth during development. This group of bones includes the:?
A thin external layer of compact bone covers vast spongy bone 博彩app下载苹果端 marrow, making a shape that is more or less cuboid. The carpal bones 博彩app下载苹果端 tarsal bones fall into this category.
Two layers of compact bone cover both spongy bone 博彩app下载苹果端 bone marrow space. They grow by replacing connective tissue. Fibrocartilage covers their articular surfaces. This group is compiled of the:
A thin layer of compact bone covers a mass of mostly spongy bone. This group is not categorized by shape, but by bone content 博彩app下载苹果端 includes the
- bones of the skull
Sesamoid bones are embedded within tendons. They are found at the end of long bones in the 博彩app下载安卓端s, where the tendons cross, for example the patella bone in the knee. Sesamoid bones protect the tendons from excess wear by?reducing friction.
Common bone diseases often affect the bone density, e.g. in young children due to malnutrition. For example, rickets is a bone deformity seen in young children who lack vitamin D. Their legs are disfigured 博彩app下载苹果端 they have trouble walking. The damage is irreversible though surgery may help. Osteomalacia 博彩app下载苹果端 osteoporosis are diseases seen mainly in adulthood.
Osteomalacia is the improper mineralisation of bone due to a lack of available calcium 博彩app下载苹果端 phosphate. The bone density decreases 博彩app下载苹果端 the bones become soft. Osteoporosis has been noted in all ages but mostly in postmenopausal 博彩app下载苹果端 elderly women. A progressive decrease in bone density increases the risk of fracture. Patients who are on long-term steroid medication are in particular risk.