Skeletal System: Function, Parts, and Main Organs

One of the most important—but underappreciated—systems in the body is the skeletal system.

Systems like the digestive system, cardiovascular system, and immune system tend to get the most attention because they’re active at all times. The skeletal system, on the other hand, seems largely passive except when you’re in motion.

However, the truth is that your skeletal system works around the clock, just in a different way than many of your other internal systems and functions.

In this blog article, we’re going to answer the question “What does the skeletal system do?”

We’ll examine what parts make up your musculoskeletal system and how it’s divided into different bones and joints. We’ll also dive into what the skeletal system does to keep you healthy. We’ll even look at what happens when your skeletal system health suffers due to common disorders or malnutrition.

But keep reading to the end and you’ll get some simple yet highly effective strategies that will help you keep your skeletal structure with all its many bones and joints in tip-top shape!

Introduction to the Skeletal System

The skeletal system—also called the “musculoskeletal system”—is the body’s structural support. It provides structure and facilitates an upright posture. It also protects your internal organs and critical systems from external damage and impact.

Your bones do most of their work when you move, but they also play a role in sitting or lying comfortably. Finally, they make blood cells and are needed for storing minerals for your body.

Primary Functions of the Skeletal System

The skeletal system provides the body with structure, support, and protection. It also enables movement, produces blood cells, and stores essential minerals.

Support

The main function of your skeletal system is to provide support. Think of your bones as a framework that the rest of your body—your skeletal muscles, soft tissues, organs, and network of nerves—is built around.

Without your bones, your body would collapse. You’d be nothing more than soft tissue and “meat” inside a “bag” of skin. Thanks to the support your bones provide, your body holds its shape and stands upright. 

Protection

Your bones protect vital organs from damage. For example, your brain is housed inside your skull, where thick bone plates reduce the risk of injury to your most crucial organ.

Your heart and lungs are protected by your rib cage, and many of your reproductive organs are protected by your pelvis.

Movement

Muscles do the work of actually moving you, but as soft tissue, they can’t work on their own. They need something to attach to, something to move—to rotate, bend, or extend.

Your bones provide the attachment points for your muscles to connect to. When your muscles contract, the bones respond and movement is enabled.

Mineral Storage

Your bones store most of the Vitamin D, calcium, and phosphorus in your body. These minerals are needed for the production of healthy bone tissue, but also for other internal functions.

By providing storage for these minerals, your bones ensure your body always has a ready supply when needed.

Blood Cell Production

Blood cells are produced in the marrow at the center of your bones in a process called “hematopoiesis”.

Bone marrow isn’t present in all bones. In the bones where it is present, it serves as the production center for red blood cells that transport oxygen and nutrients. It also produces white blood cells that are crucial for immune defense.

Energy Storage

Bone marrow isn’t only necessary for producing new blood cells. Yellow bone marrow also provides storage of energy in the form of lipids (fats).

Bone marrow adipocytes store fat so your body always has a ready energy source as needed.

Main Parts of the Skeletal System

The skeletal system is made up of several key parts that work together to support and protect the body. These parts include bones, joints, cartilage, ligaments, and tendons, each with a specific role in maintaining structure and enabling movement.

Bones

The bones are the primary component of your skeletal system.

The human body contains around 270 bones at birth, but as you age, bones fuse together until only around 206 bones remain in the adult human skeleton.

There are five different types of bones in the human body:

• Long bones, which have a long, thin shape. A long bone, such as those in your arms and legs, functions as a lever to facilitate movement.
• Short bones, which have a squat, cubed shape. These bones—which include your wrist and ankle bones—are typically surrounded by soft tissue and form your joints.
• Flat bones, which are flattened and have a broad bone surface. These bones—which include your shoulder blades, ribs, skull, and breast bone—serve as shields to protect a wider surface area from impact or damage.
• Irregular bones, which have a shape that doesn’t quite fit into any of the other bones categories. The bones of your spinal column are irregular bones.
• Sesamoid bones, which are very small ovular bones. These are found in the hands and feet and serve as a pulley to reduce stress on short, delicate bones as muscles and ligaments pull on them.

Put together, these five types of bones account for roughly 14% of your body weight. They form the rigid structure of your body and serve as attachment points for your muscles.

Bones are made up of specialized structures that give them strength and durability. The cortical bone, also known as compact bone, forms the dense outer layer of bones and provides structural support and protection. Inside the bone, the bone matrix—a combination of collagen fibers and mineral deposits—gives bones their strength and flexibility, allowing them to withstand pressure and stress.

Cartilage

Cartilage is a smooth, strong, and flexible type of connective tissue found throughout the body. It is often found between bones-the space we call, the joints.

It’s present in a number of places around the body, including:

• At the ends of your bones;
• In your nose;
• On your ears;
• Connecting your ribs to your sternum.

Cartilage is present to provide cushioning and reduce friction at the joints. It prevents the bones from rubbing or grinding against each other and facilitates smooth movement.

One important type of cartilage is articular cartilage, which covers the ends of long bones within joints. This smooth, slippery tissue helps absorb mechanical loads and reduces friction during movement.

Ligaments

Ligaments are strong, fibrous bands of connective tissue that stabilize and support joints. They connect living bones and prevent excessive movement to keep joints properly aligned during motion.

Ligaments work with muscles and tendons around the bone shaft to maintain balance and control. Due to their limited blood supply, ligaments heal more slowly than other tissues, which makes joint protection and stability even more important.

Tendons

Tendons are dense, fibrous bands of connective tissue that connects muscles to bones and allow the body to move with strength and precision. When muscles contract, tendons pull on the bones to create movement. This action enables joints to hinge, twist, lever, bend, or extend.

Tendons provide critical support where bones meet, especially in the shoulders, knees, and cervical spine, where stability and flexibility are both necessary. Their durable structure absorbs impact, prevents muscle injury and ensures smooth, controlled motion throughout the body.

Divisions of the Skeletal System

The skeletal system is divided into two main parts: the axial skeleton and the appendicular skeleton. These divisions work together to support the body, enable movement, and protect vital organs.

Axial Skeleton

The axial skeleton is the part of the skeletal structure responsible for maintaining your upright posture.

There are 80 bones included in the axial skeleton, including:

• The vertebral column (32 to 34 bones);
• The sternum and thoracic  cage (12 pair of ribs);
• The skull (22 bones plus 7 additional “associated” bones).

The axial skeleton supports the weight of your head and upper body, providing support for the upper extremities. It also provides support and protection for your vital organs and forms the central “framework” of your body.

Appendicular Skeleton

The appendicular skeleton is the part of your skeletal structure responsible for locomotion, aka movement. They are located in your hands, arms, legs, and feet.

There are 126 bones in the appendicular skeleton, including:

• The pectoral girdle;
• The upper limbs;
• The pelvic girdle;
• The lower limbs.

The bones of the appendicular skeleton twist, bend, flex, and extend to facilitate movement. They also provide protection for other organs, including the digestive, reproductive, and excretory organs.

Key Bones and Their Functions

Each bone in the body serves a distinct purpose beyond structural support. Below are the main things you need to know about the main bones in the human body.

Skull

The skull’s primary function is to protect your brain.

While it provides support for sensory structures—the eyes, nose, mouth, and ears that feed stimuli into your brain—it’s main job is to shield soft, delicate brain tissue from damage or injury.

Vertebral Column 

Your vertebral column, also called spine, is your body’s main central support system. It provides a solid, sturdy structure capable of weight bearing while still allowing for freedom of movement.

The spine is divided into sections, including the cervical vertebrae in the neck and the lumbar vertebrae in the lower back, each designed to balance mobility and support.

The spinal column also houses the spinal cord, the bundle of nerves that connect your brain to the rest of your body.

Rib Cage

The rib cage, thoracic cage, is a vital structure that protects the heart, lungs, and other organs in the chest. It consists of 12 pairs of ribs connected to the spine and sternum, forming a sturdy yet flexible shield.

The rib cage also expands and contracts to support breathing by allowing the lungs to fill with air. Like most bones in the body, the ribs contain bone marrow, which contributes to blood cell production.

In growing individuals, the ribs contain a growth plate that allows the bones to lengthen and develop properly during childhood and adolescence.

Pelvis

The pelvis connects to the base of the spinal column to serve as another piece of the support system. It also connects the upper body to the lower body to both provide support and enable movement.

The bones of the pelvis protect your reproductive and some of your excretory organs, too.

Limbs

Your arms and legs—what we call the limbs—are needed for movement and a host of other critical functions, including grabbing, lifting, gripping, and many more.

The upper limbs (your arms) are made up of many bones:

• The humerus in your upper arm;
• The radius and ulna in your forearm;
• The carpal, metacarpal, and phalanges bones in your hand and wrist.

These bones facilitate movement of your arms.

Mirroring your upper limb bones are your lower limb bones:

• The femur, your upper leg bone;
• The patella, your kneecap;
• The tibia and fibula, the two bones in your lower leg;
• The tarsal, metatarsal, and phalanges bones in your ankle and feet.

These bones are thicker than the upper limb bones because they are weight-bearing and need to support the upper body. They’re also crucial for locomotion.

Bone Structure and Composition

Bone structure and composition are designed to provide strength, support, and flexibility. Understanding how bones are built reveals how they withstand pressure, produce blood cells, and store essential minerals.

Bone Tissue

The osseous system, what we call “bones”, are made up of two types of tissue:

• Compact bone tissue, the dense outer layer that provides strength and support in osseous structures. Bones contain around 80% compact bone tissue.

• Cancellous bone tissue, a spongy bone tissue that contains trabeculae, rod-like structures that run through the tissue. It’s lighter, more flexible, and less dense. It makes up around 20% of your bone tissue.

Bones are also covered by the periosteum, an outer layer that serves as a protective “sheath” but also contains a lot of blood vessels and nerve endings.

Bone Marrow

In the cancellous bone tissue, two types of bone marrow are present:

• Red marrow, which produces red and white blood cells. It’s typically found in the center of flat bones, long bones, your hips, and vertebrae.
• Yellow marrow, which stores lipids and stem cells that can become cartilage, fat, or bone cells. It’s typically found in the center of long bones only.

Together, red and yellow bone marrow play roles in blood cell production and energy storage to support overall bone health and body function.

Bone Cells

There are three types of bone cells that comprise bone tissue:

• Osteoclasts, which use acids to break down old, used bone tissue (a process called “bone resorption”). This is done to remodel injured bones, and also creates the pathways through which blood vessels and nerves can travel.
• Osteoblasts, which produce osteoid, a protein mixture that mineralizes and turns into new bone tissue. Their primary job is to repair damage and facilitate bone formation as needed.
• Osteocytes, which are inactive mineralized osteoblasts. Their job is to support metabolic functions inside your bones and facilitate communication between the bone cells.

While bones may seem like a more “passive” internal system, the truth is that they are always repairing and recycling. These three bone cell types enable the constant restoration and refreshment of bone tissue.

Types of Joints in the Skeletal System

There are three types of joints in the skeletal system:

• Fibrous joints, also called “immovable joints”. They’re made up of thick bands of tightly woven connective tissue. The sutures in the skull bones are an example of fibrous joints.
• Cartilaginous joints, also called “partially movable joints”. They’re formed of fibrous cartilage or hyaline, and facilitate some movement while still maintaining a strong structure. The intervertebral discs and the joints between the ribs and sternum are examples of cartilaginous joints.
• Synovial joints, or “highly movable joints”. These joints are freely mobile inside a cavity, formed from bones connected but surrounded by fluid-filled capsules (filled with synovial fluid) that provide cushioning and smooth motion. The shoulder and hip joints are examples of synovial joints.

These three types of joints work together to provide the body with a balance of stability, flexibility, and movement.

Joint Types by Movement

Hinge joints are joints that “open” and “close” in a single direction. Both the elbow and knee joint are hinge joints.

Ball-and-socket joints are joints that feature the rounded end of one bone inserted into a “socket” (or indentation) in another bone. The shoulder and hip joints are both ball-and-socket joints.

Pivot joints are joints that rotate in place, but never leave their original position. The joints in your neck are pivot joints.

Gliding joints (also called plane joints) are joints that facilitate sliding or gliding movement between joints. Facet joints in your spine and the carpal joints in your wrist are gliding joints.

Common Skeletal System Disorders

Disruptions in the skeletal system can interfere with mineral homeostasis, affecting the balance of essential minerals like calcium and phosphorus. Many disorders result from weakened bones or improper deposition of calcium salts, leading to reduced strength and structural instability.

Below are the most common skeletal systems diseases you should know about and recognize.

Osteoporosis

Osteoporosis is a disease that reduces bone density and causes weakness, making the bones more prone to breaking (fracturing).

Osteoporosis is a common side effect of aging. Around the age of 30 or 35, your bones start to become less effective at repairing and restoring, and break down more than can be replaced. Over time, this can lead to reduction of bone density and strength.

People over 50 tend to be more at risk of osteoporosis, as are those who have gone through menopause, those who smoke, and those who have thinner, “smaller” bone structures.

Arthritis

Arthritis is a disease that causes inflammation and damage in your joints. It can be caused by excessive wear and tear (osteoarthritis) or by the body attacking joint tissue (rheumatoid arthritis, an autoimmune disorder).

Typically, arthritis will set into the joints that are most used: your hands, wrists, shoulders, lower back, hips, knees, feet, and ankles. However, in cases of rheumatoid arthritis, the damage can occur in any joint.

Arthritis is extremely common. It’s estimated to affect more than 1 in 3 Americans to some extent.

Fractures

Fractures are breaks in bones. Also called “broken bones”, they can be caused by impact, trauma (such as a sports injury), repetitive impact (running), or even occur as a side effect of osteoporosis or some other bone disorder.

A simple fracture (or closed fracture) is damage to the bone that doesn’t pierce the skin. A compound fracture (or open fracture) is damage to the bone that has punctured the skin and creates an open wound.

Fractures will typically be treated differently based on their location, type, pattern (the shape of the bone break), cause, and severity.

Scoliosis

Scoliosis is an abnormal curvature of your spine. Typically, the curvature is sideways, but may be accompanied by spinal twisting or rotation.

You may notice scoliosis in the form of uneven shoulders, an uneven waist, one hip higher than the other, or a prominence on either side of your back when you bend forward.

It’s not known what causes the main type of scoliosis, idiopathic scoliosis, though it’s believed genetics play the biggest role (it can be inherited through generations). However, congenital scoliosis is caused by birth defects that affect the spine’s formation in the womb. Other factors including, neuromuscular conditions (like muscular dystrophy or cerebral palsy), spinal infections, spinal injuries, and irregularities of the spinal cord can also cause scoliosis

Rickets and Osteomalacia

Rickets is a disease in childrens bones due to deficiencies in vitamin D, calcium, or both. It is created by defective mineralization of the growth plate.

Osteomalacia can be found in either adults or children due to defective mineralization of already formed osteoid.

Both conditions cause the bones to become soft and weak. Most likely a child that has Rickets will also have Osteomalacia.

These diseases can cause bone pain and muscle weakness.

Rickets can delay growth, motor skills development, and create skeletal deformities (like knock knees or bowed legs).

Maintaining Skeletal System Health

The adult skeleton is capable of repairing and restoring itself, but you can give it a helping hand by:

• Eating a balanced diet. Consume lots of protein, calcium, phosphorus, magnesium, and Vitamin D to keep your skeletal structure strong. 

• Exercise regularly. High-impact and weight-bearing exercise causes microscopic damage to the bones and joints that accelerate your internal repair processes. The result is a stronger, denser, more resilient skeletal structure and better bone health.

• Avoid smoking and excessive alcohol consumption. Both can accelerate bone density loss and weaken your bones.

• Improve your posture. Sitting, standing, sleeping, running, lifting, bending, and training in the proper erect posture will reduce the strain on your spinal column and your joints, and reduce the risk of injuries that could compromise mobility.

• Get screened regularly. Especially as you age and for menopausal women, consider regular bone density tests to detect osteoporosis in its earliest stages.

Supporting skeletal health also involves maintaining proper hormone balance, as the growth hormone plays a key role in bone development and repair. Additionally, since bones function as an endocrine organ by releasing hormones that regulate mineral balance, keeping them healthy is essential for overall body function.

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Conclusion

Your skeletal system is SO important!

It doesn’t just support your entire body, but it protects your organs, produces new blood cells, stores energy, and facilitates movement.

Keeping your bones and connective tissue in good health is the key to more efficient movement as you age. Adopt the simple habits we shared above to give your bones the nutrients, exercise, and protection they need to stay healthy and strong.

FAQs

What is the largest bone in the human body?

At around 18 inches long in a full-growth adult, the femur (thigh bone) is the largest bone in the human body. It’s also the strongest bone—capable of supporting up to 30 times your body weight.

Which bone is most often broken?

The most commonly broken bone is the clavicle, or collar bone. It’s frequently broken due to falls, car accidents, or contact sports.

What is the most painful bone to break?

As the largest bone in the human body, the femur is the most painful bone to break. In addition to extreme pain, it can damage arteries in your leg and cause severe—even fatal—bleeding.

How do bones heal after a fracture?

When a bone fractures, the body begins the healing process by forming a blood clot around the break. Mesenchymal stem cells then migrate to the injury site and differentiate into bone-forming cells and cartilage cells. These cells help create new bone tissue and fibrous connective tissue, which stabilizes the fracture and supports bone regeneration until full healing occurs.

What minerals strengthen the axial and appendicular skeletons?

The axial and appendicular skeletons are strengthened by minerals like calcium hydroxyapatite and calcium phosphate. These minerals form the hard, dense structure of bones, providing durability and supporting the body’s framework for movement and protection.

Resources

Skeletal System

Skeletal System (Musculoskeletal System)

Introduction to the Skeletal System

14.2: Introduction to the Skeletal System

Bones: All you need to know

Osteoporosis

Arthritis

Bone Fractures

Scoliosis

Osteomalacia

Rickets