BIOL 348 Chapter 6 - Bones

Functions of the Skeletal System

Support, Storage, Blood Cell Production, Protection, and Leverage

Skeletal System

Organ system for protection and support, it is composed of Bones, Cartilages, and Ligaments

Bone (Osseus) Tissue

Dense, supportive connective tissue that produces a solid matrix of calcium and salt around collagen fibers

Bone Matrix

A mixture of organic compounds such as collagen and inorganic compounds such as hydroxyapatite that allows for bone to have compressional strength and flexibility (Reinforced concrete)

Hydroxyapatite

A mixture of calcium phosphate and calcium hydroxide that makes up the hard bone

Osteoprogenitor cells

Mesenchymal stem cells within the endosteum and priosteum

Osteoblasts

Bone forming cells that secretes Osteoids

Osteocytes

Mature Osteoblasts

Osteoclasts

Bone breaking cells (Secretes HCl and other enzymes)

Compact bone

Solid, dense, and forms the external surface of long and flat bones

Spongy Bone

Also known as Trabeculae (beans) and forms the internal surface of bones

Osteon

Basic structural unit of compact bone and are arranged in concentric lamellae around a central canal that has blood vessels.

Circumferential Lamellae

Fills the outer region of compact bone and binds osteons together

Periosteum

Collagen that surrounds the bone and ties everything together

Perforating fibers

Fibers that anchor the periosteum to the lamellae

Endosteum

Incomplete cellular layer that lines the medullary cavity (cavity inside the bone)

How many bones does a typical adult have?

~206 bones

Bone Classifications

Shape, Internal tissue organization, bone markings

Bone Shapes (6)

Sutural, Irregular, Short, Long, Flat, Sesamoid

Diaphysis

Shaft of a long bone, composed of compact bone and the medullary cavity

Epiphysis

Ends of a long bone, mostly spongy bone surrounded by compact bone

Metaphysis

Where Diaphysis and Epiphysis meet

Red Bone Marrow

Produces blood cells in spongy bone

Yellow Bone Marrow

Adipose tissue storage in the medullary cavity

Distribution of force on bones

Compression on the medial side results in tension on the lateral side of long bones (Vice versa)

How long do bones grow for?

~25 years

Osteogenesis

Process of bone formation

Calcification

The process of depositing calcium salts

Occurs during bone ossification and in other tissues

Ossification

Process of replacing other tissues with bone, it can be Endochondral or Intramembranous ossification

Endochondral Ossification

Ossifies bones that originate as hyaline cartilage and occurs in 6 steps for most bones

Endochondral Ossification Step 1

Cartilage model forms

Endochondral Ossification Step 2

Bone collar forms

Endochondral Ossification Step 3

1st ossification center

Endochondral Ossification Step 4

Medullary cavity

Endochondral Ossification Step 5

2nd ossification center

Endochondral Ossification Step 6

Growth continues

Appositional Growth

Thickens and strengthens long bones by addition of layers in the circumferential lamellae

What happens to Epiphyseal cartilage after puberty?

It ossifies and appears as an epiphyseal line on Xrays

Intermembranous Ossification

Also known as dermal ossification, this is the process where mesenchyme turn into bone tissue without cartilage model, it occurs in three steps

Intermembranous Ossification Step 1

Mesenchymal cells aggregate and differentiate into osteoblasts to begin ossification process as a series of spicules

Intermembranous Ossification Step 2

As spicules interconnect, they trap blood vessels within the bone

Intermembranous Ossification Step 3

Over time, the bone structure takes the shape of spongy bone, and then areas of the spongy bone may be removed later to create the medullary cavities.

What is the function of the nutrient artery?

It supplies epiphyseal cartilage.

What is the function of the nutrient vein?

It drains blood from the bone.

What do the nutrient artery and vein enter through?

The nutrient foramen.

What type of blood vessels are the nutrient artery and vein?

A single pair of large blood vessels.

Metaphyseal Vessels

supply the epiphyseal cartilage

where bone growth occurs

Periosteal Vessels

blood to superficial osteons

secondary ossification centers during development

Process of Remodeling

Replacement of mineral reserves, recycles and renews bone matrix, involves osteocytes, osteoblasts, and osteoclasts.

Vitamin C

Stimulates osteoblast differentiation and collagen synthesis

Vitamin A

Stimulates osteoblast activity

Vitamin K and B12

Synthesizes bone proteins

Calcium ions are vital to

Membranes, Neurons, and Muscle Cells

Fracture Repair Step 1

Clot forms and bone cells die

Fracture Repair Step 2

Formation of Fibrocartilage to stabilize fracture

Fracture Repair Step 3

Ossification of Cartilage

Fracture Repair Step 4

Remodeled to original look

Osteopenia

Occurs when 30-40 years old and results in thinner/weaker bones

Osteoporosis

Occurs when 45 and results in severe bone loss

Effects of menopause

Loss of estrogen and loss of signaling for osteoblasts