Down to the Bare Bones

Composition & Function

Bones toKnow

Functions of Bone

◊ Support: Gives us something to hang our muscles on

◊ Protection of internal organs◊ Movement: Bones form joints that act like

hinges◊ Storage: Calcium◊ Blood Cell Formation

Blood Cell Formation

Hematopoiesis = Generation of new blood cells

Occurs in the bone marrow (inside, center portion of bone)

Skull, sternum, long bones, and pelvis

2 Types of Osseous (Bone) Tissue

Bone is “Connective Tissue”• Spongy

– Porous, lighter but still strong

– Softer bone tissue– Interior of bones and at

ends (epiphysis)– More vascularized than

compact bone– NOT the same thing as

bone marrow

• Compact– Hard bone– Surface of bones– Shafts (diaphysis) of long

bones made mostly of compact tissue

Spongy Bone vs. Compact Bone

• Spongy bone

• Compact bone

Bone Anatomy

Bone Anatomy

• Outside covered with PERIOSTEUM– Contains blood vessels, nerves, and osteoblasts (bone-

building cells)– Made up of dense connective tissue that connects with

ligaments and tendons• Deep to periosteum is COMPACT BONE

– Holes in compact bone (Haversian canals) carry blood vessels and nerves from periosteum

• Deep to compact bone is SPONGY BONE• Deep to spongy bone is MEDULLARY CAVITY with

BONE MARROW

Bone Marrow

• Yellow Bone Marrow– Found in most bones

– Mainly adipose (fat) tissue storage

– Can be converted to red bone marrow if extreme blood loss

• Red Bone Marrow– Only within the spongy

bones of ribs, vertabrae, sternum, and pelvis

– Produces red blood cells and lymphocytes (white cells like B-cells and T-cells0

Types of Bones

• Long bones– Arms, legs, hands, feet (metacarpals and

metatarsals)– Mostly compact bone– Slightly curved to absorb shock

• Short bones– Carpals, tarsals, and phalanges– Irregular, cube-shaped bones

Types of Bones

• Flat bones– Skull, scapula, ribs, sterum, pelvis– Anchor muscles

• Irregular bones– Any bone that doesn’t fit into one of the other

groups!– Vertebrae and some facial bones

Bone Classification by Shape

Also, patella (kneecap) is a special type of “floating bone” called aSESAMOID BONE.

How do Bones Grow?

• Start as CARTILAGE (no blood vessels)• OSSIFICATION: Osteoblasts (bone building

cells) start to replace cartilage tissue with bone tissue by secreting calcium salts.

• Growth happens at epiphyseal plate (growth plates)

• By age 16-25 all the cartilage in the plate is replaced by bone.

Bone Fractures

&

Remodeling

Compound: Bone breaks through the skin

Transverse

Spiral

Comminuted

X-rays

How Fractures Heal

• Hematoma (huge bruise and blood clot) forms to protect area

• Fibrocartilage splint forms after dead cells are removed by phagocytes.

• Osteocytes move into area and gradually replace the fibrocartilage with bone callus.

• Bone remodeling occurs.

Steps in Fracture Healing

Bone Remodeling

Osteocytes (Bone Cells)•Osteoblasts

•“Make Deposits” – Bone Builders•These cells secrete new bone extracellular matrix•Take calcium out of blood

•Osteoclasts•Dissolve bone•Release calcium

Osteoclasts

Steps to Remodeling (wheel)

1. Pre-osteoclasts are attracted to remodeling site.

2. Pre-osteoclasts fuse to form “regular” osteoclasts.

3. Osteoclasts dig out a cavity or tunnel.

4. Calcium dug out is reabsorbed by the blood for use in the body.

5. Osteoclasts disappear.

6. Osteoblast-making cells (stem cells) appear in the cavity created.

7. Stem cells turn into pre-osteoblasts.

8. Pre-osteoblasts mature into “regular” osteoblasts.

9. Osteoblasts release osteoid (bone matrix without calcium).

10. Calcium and phosphorus are added to the osteoid.

11. Area waits for the next round to happen (dormant).

In a child:

Osteoblast activity > Osteoclast activity

In an adult:

Want a balance, Osteoblast activity = Osteoclast activity

What regulates this activity?

HORMONES!• Chemical messengers released into blood

stream

• Produced by the glands of the Endocrine System

Hormones Related to Bone Remodeling

• Calcitonin – Made by thyroid gland•Inhibits osteoclast activity•Increase rate of Ca2+ excretion

•Parathyroid (PTH) – Made by parathyroid

•Stimulates osteoclasts•Increases intestinal absorption of Ca2+

•Decreases the rate of Ca2+ excretion

Effects of Exercise

•When stressed, calcium salt crystals emit a minute electrical field.

•The electrical fields attract osteoblasts.

Summary

•PTH and Calcitonin determine when and if bone is broken down or

formed.

•Stresses of muscles pulling on bone determine where bone is made.