Bones

Bones are your body’s main form of structural support. They’re made of hard, strong tissue that gives your body its shape and helps you move.

Your bones are like the frame under the walls of your home. If you’ve ever watched a home improvement show and seen the internal structure of a house, that’s what your bones are. They’re the supports and beams that keep your body strong and stable.

Your bones are living tissue like any other part of your body. It might not seem like it. But they’re constantly growing, changing and reshaping themselves.

Visit a healthcare provider if you feel bone pain. Go to the emergency room if you experience trauma or think you might have a broken bone.

What do they do?

Your bones support your body. They keep your body stable when you’re not moving. And they help you move when you’re active.

Bones secure and support lots of important tissue throughout your body. Think about the walls of your home again. Instead of holding drywall, plumbing and wiring in place, your bones are connected to a lot of tissue. Examples include:

• Muscles
• Nerves
• Tendons
• Ligaments

Some bones protect your internal organs. For example, your skull guards your brain. And your ribcage shields your heart, lungs and other organs near your chest.

Bones contain and protect your bone marrow. Bone marrow is a soft, fatty tissue that produces important cells, like:

• Red blood cells
• White blood cells
• Platelets

How many bones are in the human body?

Adults have between 206 and 213 bones. Babies are usually born with 270 bones that grow together and fuse into their adult skeletons.

It might be surprising to learn that some people have more bones than others. The range comes from differences in people’s skeletons. Some people have a different number of ribs. Or you may have fewer bones in your spine than usual.

Healthcare providers divide your bones into two main groups:

• Your axial skeleton: This refers to the 80 bones in your head, neck, back, chest and pelvis.
• Your appendicular skeleton: These are all the other bones that attach to your axial skeleton. The bones in your shoulders, arms and legs are part of it.

Types of bones

Healthcare providers classify bones based on shape and size.

Long bones

Long bones are exactly what they sound like. They’re the longest bones in your body. They’re mostly in your arms and legs. Examples of long bones include your:

• Thigh bones
• Upper arm bones
• Shin and calf bones

Short bones

Short bones are thinner and weaker than long bones. They include:

• Some bones in your hands
• Some bones in your wrists
• The bones in your ankles and feet

Flat bones

Flat bones are wider and less round than other bones. Some examples are:

• The plates that make up your skull
• Your shoulder blades
• Your breastbone

Sesamoid bones

Sesamoids are small bones embedded in tendons or muscles. They’re usually near joints. Some examples include:

• Your kneecaps
• Sesamoid bones in your hands
• The tiny bones in your middle ear

Irregular bones

These are bones that don’t fit well into any other category. They can have a shape or structure that doesn’t match any other type of bone. Some irregular bones include your:

• Spine bones
• Bones in your pelvis
• The hyoid bone in your neck
• Your tailbone

What are they made of?

Bones are made of cells and proteins. They have two main layers:

• The cortex (compact bone) is the tough, hard outer layer. It’s the thick shell you see in most illustrations or photos of bones.
• Cancellous bone (spongy bone) is inside the cortex. It’s much less dense and is more flexible. This is where bone marrow is made and stored.

Your bones replace their own cells throughout your life. Special cells called osteoblasts and osteoclasts automatically grow and replace your bone tissue. Osteoblasts form new bone tissue. Osteoclasts break down old bone tissue to make room for new, healthier tissue to replace it.

The periosteum covers most of your bones. It’s a network of blood vessels and nerves that wraps around them. It gives them fresh blood and their ability to feel.

What are the common conditions and disorders that affect bones?

Broken bones and osteoporosis are the most common bone issues.

A fracture is the medical name for a broken bone. Any bone can break. It’s more common in smaller, weaker bones. Breaking stronger bones can happen during a serious trauma like a car accident. Go to the emergency room if you think you have any kind of fracture, no matter which bone is broken.

Osteoporosis weakens your bones. This makes them more likely to break suddenly. Many people don’t know they have osteoporosis until it causes a fracture. There usually aren’t obvious symptoms. Talk to a healthcare provider about a bone density test. Especially if you’re over 65 or know osteoporosis runs in your family.

Longest and strongest bone in the body?

Your thigh bone is the longest, biggest bone in your body. Its medical name is the femur. Most adults’ femurs are around 18 inches long. That’s around 46 centimeters.

The femur is also the strongest bone. It can support up to 30 times your body weight.

Smallest bone

The three ossicle bones in your ear are the smallest bones in the body. These tiny bones are important to your hearing. They carry sound vibrations to your inner ear. The hammer (malleus), anvil (incus) and stapes (stirrup) are all less than an inch (2.54 cm) long. The stapes is the smallest. It’s usually one-tenth of an inch long (3.5 mm).