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This is a Biology Article
Growth and Development in Bones
Subject	Biology
Section	The Organism
Note

Contents 1 Skeleton 2 Functions of the Skeleton 3 Axial Skeleton 4 Appendicular Skeleton 5 Bones 5.1 Compact Bone 5.2 Spongy Bone 6 Cartilage 6.1 Hyaline 6.2 Yellow Elastic 6.3 White Fibrocartilage 7 Joints 7.1 Synovial Joint 7.2 Osteoporosis 8 Tendons 9 Ligaments 10 Skeletal Muscles 10.1 Antagonistic Muscles

Skeleton

The human skeleton is a hard framework of 206 bones that supports and protects the muscles and organs of the body. It is an endoskeleton consisting of bones and cartilage. It is divided into 2 parts;

1. The Axial Skeleton - supports head, neck, torso. It consists of the;

• Skull

• Vertebral column

• Ribs

• Sternum

1. The Appendicular Skeleton - Supports the limbs and attaches them to the rest of the body. It consists of the;

• Shoulder girdle

• Upper limbs

• Pelvic girdle

• Lower limbs

Functions of the Skeleton

• Allows and enables movement

• Forms red blood cells (in the red bone marrow)

• Forms joints - essential for the movement of the body

• Provides - a store of calcium salts and phosphorus

• Provides - attachment for muscles which move the joints

• Protection - of delicate body organs e.g. the skull (covers brain), thoracic cage (covers heart and lungs)

• Support - All body tissues (apart from cartilage and bone) are soft so without the skeleton, the body would be jelly -like and could not stand up. The bones and their arrangement give the body it's shape.

Axial Skeleton

• Skull - composed of 8 cranial bones, 14 facial bones. All bones are fused except the Mandible (lower jaw)

• Sternum - a flat thin bone at the centre of the chest

• Vertebral Column - 33 Vertebrae
  • 7 Cervical
  • 12 Thoracic
  • 5 Lumbar
  • 5 Sacrum
  • 4 Coccyx

• • The Sacral & Coccygeal vertebrae are fused
  • The remaining vertebrae articulate together to provide movements in the spine such as flexibility
  • Small discs of cartilage between each vertebrae act as shock absorbers against trauma to the spine
  • Pairs of spinal nerves emerge between the vertebrae from the spinal cord
  • Both muscles and ligaments hold the vertebrae in place

• Ribs - 12 pairs attached to the spine
  • First 7 ribs are known as "true ribs" joining to the sternum.
  • Next 3 are the false ribs, which also join to the 7th rib.
  • Last 2 are the floating ribs, only joined at one end to the spine.

Appendicular Skeleton

• Shoulder Girdle -
  • 2 Scapulae (shoulder blades) and 2 Clavicles (collar bone).
  • The 4 bones form an incomplete ring, articulating with the Sternum at the front.
  • 1 of the body's ball and socket joints is found here which is the articulation between the arm and the shoulder

• Pelvic Girdle - Appears to be one large cylindrical bone but are actually six fused bones ( it is 2 innominate bones, each 1 including an Ilium, Ischium & Pubis).
  • Is firmly attached to the spine.
  • The other ball and socket joint of the body is found here, it is the articulation between the femur of the leg and the pelvis.
  • The female pelvis is wider than the male.

• Limbs -
  • Arm - 1 Humerus, 1 Ulna, 1 Radius (each arm)
  • Wrist - 8 Carpal bones (each wrist)
  • Hand - 5 Metacarpal Bones (each palm)
  • Fingers - 14 Phalanges, 2 in each thumb & 3 in each other finger
  • Leg - 1 Femur, 1 Tibia, 1 Fibula, 1 Patella (each leg)
  • Ankle & Foot - 7 Tarsals, 5 Metatarsals (each foot)
  • Toes - 14 Phalanges in each foot, 2 in a big toe, 3 in each other toe

Bones

Bones are living tissue made from special cells called Osteoblasts. The tissue varies considerably in density and compactness: the closer to the surface of the bone, the more compact it is. Many bones have a central cavity containing marrow, a tissue which is the source of most of the cells of the blood and is also a site for the storage of fats.There are 2 main types of bone;

1. Compact Bone
2. Spongy Bone

Compact Bone

To the naked eye it looks like a solid structure but under a microscope it looks like a honeycomb (full of holes. Haversian Canals are passageways containing blood vessels, lymph capillaries and nerves which run through the tissue. The concentric rings of tightly packed mineral bars which surround the blood vessels are called Lamellae. Bone cells called Lacunae are responsible for laying down Lamellae and producing new bone if required. The blood cells that supply bone cells with nutrients, these blood cells are known as

1. Osteoblasts - Actively Dividing, lay down new Lamelle
2. Osteocytes - Non - dividing inactive bone cells
3. Osteoclasts - reduce the size of bone by removing Lamellae

Compact bone is found on the outside of most bones and in the shaft of long bones. Most of the compact bones are formed by Ossification. When we are first developed in the womb as the foetus, our skeleton is made of cartilage and filled with inorganic salts by the Osteoblasts which then form the hard bone structure. Bone is never the same, it is constantly changing. Compact bones of the skeleton surround a central core of yellow bone marrow, this contains fatty tissue and contains some white blood cells.

Spongy Bone

This type of bone looks like a sponge. It is found at the ends of the long bones. Spongy bone consists of a network of hardened bars surrounded by red one marrow. Red bone marrow is a soft tissue that is made up of cells that produce red blood cells and some white blood cells.

Cartilage

A firm and solid yet flexible tissue made up of cells (Chondrocytes) and some protein fibres. There are 3 types;

1. Hyaline
2. Yellow Elastic
3. White Fibrocartilage

Hyaline

• Structure - bluish- white, smooth cells grouped together in nests in a solid matrix
• Function
  • Reduce friction in movable joints
  • Act as a shock absorber

Yellow Elastic

• Structure - Yellow elastic fibres running though a solid matrix.
• Function
  • Flexibilty
  • Provides shape in outer ear

White Fibrocartilage

• Structure - white permeated fibres
• Function
  • Strong
  • Forms discs between the vertebrae
  • Allows for movement
  • Acts as shock absorber

Joints

Joints are the body's hinges. It is any point where 2 bones meet. There are 3 main types of joint;

1. Fixed
2. Slightly Moveable
3. Synovial

Synovial Joint

• 4 different types
  • Ball & Socket Joint (hip, shoulder)- permits movement in three planes, i.e., in all directions
  • Hinge Joint (knee, elbow, fingers)- movement in one plane during flexion and extension
  • Gliding Joint (wrist, ankle)- the bones move across each other, back-and-forth and side-to-side
  • Pivot Joint (neck)- allows a turning movement

Synovial Joints are freely movable. The parts of the 2 bones involved in the joint are covered with a layer of smooth cartilage. The synovial membrane produces synovial fluid which lubricates the joint allowing for easier movement.

Osteoporosis

Known as brittle bone disease. Bone is lighter and weaker.

• Cause:Calcium deficiency, accelerated bone loss especially in post - menopausal women
• Effect:Porosity and brittleness of bones
• Treatment:Oestrogen for menopausal females, vitamin D and calcium rich diet.
• Prevention:Continuous physical activity from a young age, calcium rich diet in youth.

Tendons

Structure:White fibrous cords, with no elasticity. They are different lengths and thicknesses and are very strong

Function:Attach muscle to bone

Ligaments

Structure:Fibrous tissue

Function: Attach bone to bone

Skeletal Muscles

Muscle is a group of specialised, elastic tissues. More of the human body is made up of muscle than any other tissue: 23% of a womans body weight and about 40% of a mans. Skeletal muscle is strong, it is always under our conscious control and it can tire easily.

Structure: Muscle tissue is bound together in bundles and contained in a sheath, the end of which extends to form a tendon. Muscle is

• 75% water
• 20% proteins
• 5% fats,mineral salts & glycogen

Functions:

• Movement
• Support for the joints
• Production of heat
• Maintain posture

Antagonistic Muscles

Are pairs of muscles, the action of one muscle is opposite to that of the other muscle, e.g. the biceps and triceps in the upper arm. These are voluntary muscle attached to the skeleton.

To bend the arm from a straight position,the Biceps contract and the Triceps relax to raise the lower arm.The arm then moves towards the shoulder. To do the opposite movement with the arm moving away from the shoulder to straighten out,the Triceps contract and the Biceps relax.