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10.1.1. The bones

The bones

Bones are living organs made up of collagen and calcium and phosphorus salts, which give it hardness.

Several parts of the bone are distinguished:

  • Epiphysis: are the ends of the long bones. They are very light because they are made up of spongy bone tissue. It is the area that engages in the joints.

In the spaces left by the spongy bone tissue is the red bone marrow, responsible for the production of blood cells.

  • Diaphysis or cane: it is the elongated part of the bone that is between the epiphyses. It is made up of compact bone tissue, which provides rigidity to the bone. It contains quite a few nerves and capillaries.

In the central part of the diaphysis is the medullary cavity, which contains adipose tissue that constitutes the yellow bone marrow.

  • Metaphysis: is the area of ​​union between the epiphysis and the diaphysis. In times of growth it contains cartilage, which will later be replaced by bone tissue.
  • Processes: they are the projections of the bone, where the muscles, ligaments and tendons are inserted.
  • Periosteum: it is a membrane that covers the bone, although it is not present in the joints (epiphysis), since it is replaced by cartilage, which protects from friction.
  • Endostium: membrane of connective tissue that lines the medullary cavity.

Partes de un hueso

By OpenStax Anatomy and PhysiologyOpenStax [CC BY 4.0], via Wikimedia Commons

Activity: Parts of a bone.

Activity: Crossword about bones.

Bones can be classified according to their shape:

  • Long: found in the upper limbs (arm and forearm) and lower limbs (thigh and leg), they are cylindrical in shape, and form levers. Its main function is to perform movements. For example, the femur.
  • Elongated: they are similar to long bones, but do not have a medullary cavity. For example, the ribs.
  • Flat: they are large bones with a protective function. For example, the bones of the skull, shoulder blade, or pelvis.
  • Short: cubic and small. They constitute structures with complex movements, where their shape allows them to cushion shocks. For example, the bones of the wrists of the hands.
  • Irregular: varied in shape, such as the vertebrae, the bones of the face or those of the ear.

Activity: Types of bones.

Activity: Classification of bones.

Woven bone

The bone tissue is a type of connective tissue that forms the bone.

Bone connective tissue is made up of cells surrounded by a bone matrix, a substance made up mainly of proteins, mineral salts of phosphate and calcium carbonate.

Two types of bone tissue can be distinguished:        

Compact bone tissue

It is located in the external part of the long bones forming the diaphysis, in the flat bones and in different areas of the short bones.   

Spongy bone tissue

It is found in the epiphysis  of long bones, in the inner area of long and flat bones, and in different areas of short bones.

Activity: Bone tissue.

Experiments with your body: Resistance of the bones.

Answer in your notebook

10.1.- How are the upper extremities similar and different from the lower ones?

Answer in your notebook

10.2.- What bones are the ribs attached to?

Bone growth and hormonal system

Due to the action of different hormones, bone can change in size throughout a person's life if calcium salts are deposited or released.

  • The somatotropin (hormone growth), the androgens and calcitonin, produced in the gland thyroid, stimulating the deposition of salts calcium in the bones, favoring their growth.
  • The parathyroid hormone produced in the glands parathyroid, and cortisol produce removal of salts calcium from bones.

Enlargement on bone formation and growth

Research activity on achondroplasia and acromegaly

Osteoporosis Research Activity

Activity: Growth of bones.

Activity: Crossword on bone growth.

Answer in your notebook

10.3.- Why are older people more likely to have a bone fracture than in the case of a young person, even if they make fewer sudden movements?


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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.