Nail courses – Skeletal System
The bony skeleton of the body is made up of 206 bones. Bones constitute 10% of the body’s mass. The physical quality of bones is that they are hard (due to inorganic matters such as calcium, phosphor, magnesium) and flexible at the same time (due to organic constituents e.g. collagen fibers and the lamellar structure). Bones are joined together with connective tissue, ligaments, cartilage or joint. Bones, joints and ligaments together constitute the passive muscular system organs.
2. spine (is made up of vertebraes),
3. bones of the trunk,
- breastbone (sternum)
4. bones of the limb,
- bones of the upper limb,
– pectoral (shoulder) girdle,
– humerus (the top of the arm)
– forearm (ulna and radius),
– bones of the hand (carpals, metacarpals, phalanges).
- bones of the lower limb
– lower pelvic (hip) girdle,
– sacrum (belongs to the spine),
– femur (thigh)
– leg (tibia, fibula, patella),
– bones of foot (tarsal, metatarsal, phalanges).
According to their shape bones can be:
1. Long bones (including most limb bones), their characteristics:
- both their ends are covered with articular cartilage,
- the compact bone is thick and strong at the central part,
- inside its central part there is the so-called medullary cavity where yellow bone marrow (adipose marrow) is stored,
- their structure is spongy at both ends containing red bone marrow at a young age.
2. Short bones (including e.g. vertebrae, carpal and tarsal bones), their characteristics:
- they have varied shapes that are irregular and similar to cubes,
- they are closely attached together so there is little movement between them,
- their cortical bone is very thin,
- they have an almost completely spongy structure,
- the short bones of limbs are made up of adipose marrow, the vertebrates consisting of red marrow.
3. Flat bones (including the bones of cranium, hip bone, scapulas, sternum and ribs), their characteristics:
- they are shovel-or shell-shaped,
- they are closely attached and surround a cavity so they protect important soft parts,
- between layers of strong cortical bones a little spongy interior can be found including red bone marrow that is left throughout life.
4.Irregular bones (including some bones of the skull), their characteristics:
- their shape is varied,
- they contain an aeriferous cavity system.
Additional parts of bones:
1. Periousteum: fibrous layer that covers the outer surface of bones (except for the parts covered with articular cartilage). Its role:
- providing nutritives, it contains a lot of blood vessels (their removal results in bone necrosis),
- bone formation (increase in the width of bone)
– its inner layer contains progenitor cells that create bone tissue
– it produces new lines of bones layer by layer just like the annual rings of trees
- mechanical protection
– its outer fibrous layer absorbs external effects,
– due to its fullness of nerves it indicates early with strong pain the harmful or threatening effects made on the bone.
2. Bone marrow: it fills the inside of bones, it has two types:
- red marrow,
– creates red blood cells and partly white blood cells,
– can be found in e.g. flat or short bones,
- yellow marrow or adipose marrow,
– is developed from red marrow,
– can be found in the central part of adults’ long bones.
3.Cartilage: is situated at the ends or on the surface of bones, it forms the articular surfaces and connects the bones. Its types:
- hyaline cartilage (e.g. on articular surfaces),
- elastic cartilage (like outer ear),
- fibrocartilage (e.g. invertebral discs), straightens the unevenness of articular surfaces.
Most bones first develop as a cartilaginous substance which is gradually rebuilt as bone (this process continues until the growth is finished). The longitudinal growth of bones occurs in the cartilage lamina that is some mm thick and found on the border of the central part and at the ends of long bones.
Skeletal system functions:
- constitutes the passive muscular system organs, together with joints and ligaments,
- protects the vital organs of body (brain, spinal marrow, heart, lungs, etc.),
- provides a massive framework to the body,
- acts as levers and anchors for the muscles that induce movement,
- red marrow, which is found within the spongy structure of flat bones, vertebrates, as well as in thigh and humerus that are closer to the body, is an important blood- forming organ,
- it takes part in the metabolism of calcium and phosphor,
- it defines the height and proportions of the body.
Bones of hand (27 pieces) are moved in different directions by more than 30 muscles.
- Upper pectoral (shoulder) girdle:
- Upper arm:
– Carpus: 8 little short bones arranged in two rows.
– Metacarpus: contains 5 shortened long bones, the two ends of which have different shapes.
– are made up of 14 shortened long bones.
Bones of hand can be divided into three parts:
1. Carpal bones:
(8 little short bones arranged in two rows in the wrist. They form an arch which is convex on the dorsal surface and concave on the palmar side.They differ from the bones of the leg in the way that we can set one of our fingers against our other four ones and use them as an instrument).
2. Metacarpal bones:
(5 shorter bones in the palm, strong muscles and ligaments stretch between them forming the arch of the dorsal part of the hand. Each muscle and ligament attaches to a carpal bone and phalanx).
(14 pieces of shortened long bones. Thumb is made up of 2 phalanges others contain 3 phalanges.The third phalanx is called the distal phalanx).
Bones of the human foot can be divided into three parts:
- Tarsal bones,
- Metatarsal bones,
In contrast to the versatile mobility of the framework of the hand, the framework of the foot is an integrated static structure. Its fingers are short, much less movable than those of the hand, a body part which is greatly adapted for walking with a straight posture, running, etc. Nothing can be found even with a slightly similar structure to the human foot in the animal world. The foot is joined to the leg in the ankle joint, however, in contrast to the hand’s framework only through one tarsal bone, the talus. Tarsal bones are the most developed, the phalanges are vestigial (because of static conditions).
1.Tarsal bones (cuboid bones):
- talus (constitutes the upper arch-stone of tarsal and metatarsal that creates the arches of the foot, it bears the whole weight of the body. The weight is conveyed to the heel bone below and to the navicular bone in front),
- heel bone (Achilles tendon is attached here),
- navicular bone,
- 3 cuneiforms.
2. Metatarsal bones (long bones), (the second is the longest one out of the 5 metatarsal bones).
3. Bones of toes or phalanges (long bones) (are equivalent to the bones of digits, their number is 14.)