Skeletal System LectureLesson3:Bones and Bone

Growth

Function of the Skeletal System

– Provides shape and form– Support– Protection– Allows bodily motion– Produces blood – Stores minerals

Bones

• Over 300 when you are born

• 206 in the adult skeleton

• Half are in the feel and hands– 52 in the feet – 54 in the hands

Basic structure of a Long Bone

Epiphysis: ends of bone containing compact bone enclosing spongy bone.

Epiphyseal Growth Plate

Diaphysis: shaft containing compact bone surrounding a medullar cavity.

In addition, long bones possess:

Periosteum: connective tissue membrane on diaphysis.

Articular cartilage: glassy, hyaline cartilage allows smooth movement of joints at epiphyses.

periosteum

articular cartilage

Bone is like a labyrinth with passageways that contain vessels and nerves (known as bone matrix).

Bone is living, growing tissue. It is continually being changed and replaced (known as bone remodeling).

Bone is mostly made of collagen (protein) and calcium phosphate. Calcium phosphate is a mineral compound that adds strength and hardens the framework.

Bone is Living Tissue!

Bone Growth and Remodeling

Bone formation begins in embryo. It starts as hyaline cartilage which serves as the “model” or basis for bone structure.

• In the fetus, hyaline cartilage is covered with bone matrix by osteoblasts (temporarily giving bones a flexible interior with hard

outer shell).

•Next, ossification occurs. This involves the hyaline cartilage being digested away leaving a medullary cavity within the newly formed bone.

•By birth, most (but not all) cartilage has been converted to bone except in two areas:

1)articular cartilage at ends of long bones

2)epiphyseal plates (place where diaphysis and epiphysis meet).

ossification

Epiphyseal plate: site of bone growth, to allow us to grow taller.(this area has not ossified until late puberty thus on an x-ray of a femur, the epiphyseal plate appears black.)

Epiphyseal line: appears when growth has stopped.(this line occurs due to ossification when growth no longer occurring. On an x-ray, one can see a faint white line between diaphysis and epiphysis).

epiphyseal lineepiphyseal plate

o When we grow, our bones also increase in diameter (known asappositional growth).

o Osteoblasts in periosteum add bone tissue to the outside of the diaphysis. This allows our bones to grow larger and stronger to support more muscle mass.

Appositional Growth

Bone Remodeling is occurring continuously & is affected by:1) Pull of gravity & pull of muscles on skeleton (due to physical activity).Bone remodelingMartial arts bone remodeling training

2) Calcium levels in blood (remember osteoblasts and osteoclastswill constantly paste calcium on bones and eat away at calcium on bones to maintain homeostasis).

Classification of Bones

• Long Bones

• Short Bones

• Flat Bones

• Irregular Bones

Long Bone

• longer than wide

• bones of limbs & digits

Short Bones

• cube-like• bones of wrist and

ankle

Sesamoid Bone

• Small irregularly shaped bone embedded in tendon

• Patella, plantar side of the big toe

Flat Bones

• thin, flattened slightly curved

• Sternum and cranial bones

Irregular Bones

• odd-shaped

• vertebral, hip bones