Skeletal System Lecture Day 3: Bones and Bone Growth

Basic structure of a Long Bone ( see pg. 133 ): Epiphysis: ends of bone containing compact bone enclosing spongy bone. Diaphysis: shaft containing compact bone surrounding a medullar cavity. Cavity is red in children & yellow in adults (fat storage).

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 (see pg. 136): 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 line epiphyseal plate

o When we grow, our bones also increase in diameter (known as appositional 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). 2) Calcium levels in blood (remember osteoblasts and osteoclasts will constantly paste calcium on bones and eat away at calcium on bones to maintain homeostasis).

Ouch! Are we done yet?