The skeletal system is composed of bones and joints that protect soft tissues and support the body. Bones give the body structure and allow movement in many ways.
A baby has 300 bones at birth that fuse to form 206 bones by adulthood. Boys and girls have an equal number of bones. However, certain attributes, such as the shape of the pelvis and bone density, can differ in boys and girls.
Read this post to learn more about the various types and components of bones and ways to take care of children’s bones for healthy growth.
Types, Structure, And Layers Of The Bones
Although bones have a firm structure, they grow and change all the time as any other body part. Bones are mainly made of collagen, which is a growing tissue. Collagen provides the framework for the bone, while calcium phosphate adds hardness and strength to the frame. Most of the body’s calcium is deposited in the bones and teeth to strengthen them.
Although bones have different shapes and sizes, they are made of similar materials (1).
- The periosteum is the outermost layer of bone. It is a dense, thin membrane with blood vessels and nerves.
- The cortical bone (compact bone) is the outer dense and compact layer, which is hard and smooth. It is what you see when you look at a bone.
- The cancellous bone (trabecular bone) layer lies within the compact bone. It is the inner honeycomb-like spongy part. It is a firm layer but not as hard as the compact bone.
- Bone marrow is the innermost layer of the bone, and it is protected by the cancellous bone. It may look like jelly, and it is the place where the blood cells are made.
How Do Bones Grow And Fuse?
The 300 bones at birth become 206 bones by adulthood due to the fusion of bones caused by the replacement of cartilage with bone. Cartilage, a type of tissue felt at the tip of the nose, separates the ends of two bones.
The ends of the bones have cartilaginous growth plates. The osteoblasts (bone cells) are supplied with nutritious blood by capillaries (tiny blood vessels). These bone cells begin to cover the cartilage with bone tissue and eventually replace it.
The final shape and size of a bone depend on the growing tissue in the bone. Bones grow until age 25 in most people, and the growth plate closes by this age (2). Growth plates are a weaker part of the bone and are more vulnerable to fractures in children.
The Skeletal System
The following are the various key bones and joints in the body.
Skull is a bony structure that forms the head. The primary function of the skull is to protect the brain. Although it may seem like a single bone, the skull is made of many bones. The cranial bones form the upper part of the skull that encases the brain, while facial bones form the frontal part or face (3).
Babies have space (soft spot) between skull bones to allow brain development. Once the brain growth is complete, the skull bones fuse through special joints known as sutures.
Cranial bones consist of the following.
- A pair of parietal bones forms the top and sides of the skull.
- A temporal bone is located near each ear, forming the sides and base of the skull.
- The frontal bone is located in the forehead. It includes the orbit (the bony part of the eye socket) and the nose’s bony part.
- The occipital bone is a trapezoid-shaped bone that forms the back of the skull.
- The ethmoid bone is located in the roof of the nose and separates the nasal cavity from the brain.
- The sphenoid bone is situated in the middle of the skull and protects the brain.
Facial bones consist of the following.
- The maxilla is a prominent facial bone that forms the upper jaw.
- The mandible is the lower jaw that forms the mouth with the maxilla.
- A zygomatic bone is located on each side of the face. They are also called cheekbones.
- The nasal bones are a couple of small, oblong-shaped bones in the middle-upper part of the face.
- The vomer is a bone in the nasal cavity.
- A lacrimal bone is present on each side of the nose and forms a part of each eye socket.
- The palatine bones are a couple of bones that form the parts of the oral cavity, nasal cavity, and orbit.
- The inferior nasal concha is a scroll-shaped bone in the lateral wall of the nasal cavity.
Bones in the ear help in hearing by transmitting sound vibrations from the air to a fluid-filled cavity. The three tiny ear bones known as auditory ossicles are:
- Malleus is a hammer-shaped small bone in the middle ear.
- Incus is an anvil-shaped bone.
- Stapes is a stirrup-shaped bone.
Hyoid bone (lingual bone or tongue bone) is a horseshoe-shaped bone located between the chin and thyroid cartilage in the front of the neck. This bone is anchored to the other bones distantly through muscles and ligaments.
Hyoid bone plays a role in breathing, swallowing, and speaking. It may also allow the movement of the tongue and pharyngeal structures and keeps them in place.
The spine (vertebral column or backbone) is the bone located at the center of the back. One can feel the bone as bumps with fingers. This bone helps you hold the body in an upright position and lets you bend and twist. The spine’s primary function is to protect the spinal cord, a nerve bundle that connects the brain with the body.
The spine has a soft S-shape due to spinal curves. It is not a single bone and consists of 33 bones, each known as a vertebra, which is shaped like a ring. The vertebrae interlock with each other to form the spine. Each vertebra has three main components to serve functions.
- Vertebral body for load-bearing
- Transverse processes for ligament attachment
- Vertebral arch for protection of the spinal cord
There are various types of vertebrae in the human body that do different functions (4).
- Cervical vertebrae are the first seven vertebrae of the vertebral column located from the head, through the neck, and up to the top of the upper back. These provide mobility and stability to the head and neck.
- Thoracic vertebrae are the next 12 vertebrae that help hold the ribs in place in the thoracic cavity. Although the thoracic vertebrae have limited mobility, they protect vital organs, such as the heart and lungs.
- Lumbar vertebrae are five vertebrae that bear the weight of the body. They are larger in size and support physical functions, such as lifting and carrying heavy objects.
- The sacrum is a triangular bone formed by the fusion of five vertebrae. It is located in the back part of the pelvic cavity. The bone helps stabilize and strengthen the pelvis.
- The coccyx or tailbone is a triangular bone formed by three to five coccygeal vertebrae. This is the lowest part of the vertebral column, located at the bottom of the pelvis. Coccyx acts as an insertion point for pelvic floor muscles.
A cartilage called an intervertebral disc is present between the vertebrae to prevent friction and absorb shock. Discs also cushion the vertebrae when we jump, twist, or make any movement.
Ribs and Sternum
The cage of bones around the chest is called ribs. It protects the tissues and organs located in the thoracic region, including the heart, lungs, liver, and major blood vessels. You can feel your ribs on the sides of your torso.
You can find similar ribs on the right and left sides of the body. Most people have 12 pairs of ribs, but rarely some may have extra or fewer ribs. All 12 pairs of ribs are anchored to the spinal column on the thoracic vertebrae (5).
Sternum (breastbone) is a bone in the central part of the chest. The first seven pairs of ribs are directly attached to the sternum. The next three pairs of ribs are attached to the sternum through cartilage. The last two ribs are not attached to the sternum, so they are called floating ribs. These two pairs of ribs are securely attached to the thoracic vertebrae, so they cannot move away from their place.
Arms and Hands
The scapula (shoulder blade) is a triangular bone in the shoulder and provides attachment to the arm. The clavicle (collarbone) is present between the shoulder blade and breastbone (sternum).
Humerus is the arm bone located above the elbow joint. The bones of the forearm, located between the elbow and wrist, are the radius and ulna. These bones are wider at the ends than in the middle to provide strength (6).
Each thumb has two bones and the fingers have three bones each. The middle part of the hand has five bones allowing its movement. The hand bones enable functions such as writing, holding, and grasping.
Pelvis and Legs
The pelvis is a bowl-shaped bony structure supporting the spine. It includes two large hip bones in the front and sacrum and coccyx in the back. The pelvis protects the lower parts of the digestive system, urinary system, and reproductive system.
Large and strong bones of the legs support the body weight. The femur, the longest bone in the body, goes from the pelvis to the knee. Patella (knee cap), a triangular-shaped bone, protects the knee joint. The other two leg bones, the tibia and fibula, are located below the knee joint. All these bones are wider at their ends than the middle to provide strength (7).
Bones of feet help in standing and walking. Leg bones are connected to the talus, a bone in the foot. Below it is the calcaneus (heel bone). The midfoot has a pyramid-like group of bones that help to arch the feet. The forefoot has five toes (phalanges) and five pairs of metatarsals. The big toe has two tiny bones, and the other toes have six bones each.
The joint is the place where two bones meet. Joints can be of the following types.
- Fixed joints that are not movable. The joint between skull bones, also called sutures, are fixed joints.
- Partially movable joints allow limited movement. The joints between the vertebrae are examples of partially movable joints.
- Movable joints allow the most movements. Most joints in the body are movable. The bone surfaces in the movable joints are covered with cartilages to reduce friction while moving. The synovial fluid in the joints also helps in smooth movement. Bones in movable joints are held together by ligaments.
There are several types of movable joints (8).
- Ball and socket joint: A ball-shaped structure fits into the cup-shaped (socket) structure of another bone. Shoulder and hip joints are examples of ball and socket joints.
- Hinge joint: The bone ends allow movements in two directions. Hinge joints are seen in the knees and elbows.
- Pivot joint: This type of joint allows rotational movements. The joint between the radius and ulna is a pivot joint that allows the palm to turn up and down.
- Gliding joint (plane joint or arthrodial joint): One bone slides over another in gliding joints. Ankle and wrist joints are examples of it.
- Saddle joint: These joints have opposing surfaces in concave and convex shapes that fit into one another. Thumb, thorax, middle ear, and heels have saddle joints.
- Condyloid joint (ellipsoid joint or condylar joint): The joint has an ovoid surface allowing movement in two planes. The wrist joint, atlanto-occipital joint (between occiput and spine), and joints in fingers and toes are examples of it.
Joints allow the movements of the bones. Children with arthritis and other joint issues can have limited joint movement or other mobility difficulties.
How To Take Care Of The Bones?
The following tips may help you to promote bone health (9).
- Wear helmets and other protective equipment during sports activities and bike rides to protect the skull. Always choose the right helmet and other sports equipment to reduce the risk of injuries.
- Physical activity could make the bones strong and reduce bone loss.
- Consume calcium- and vitamin D-rich foods in the diet. Bones require calcium, while vitamin D is necessary for the absorption of calcium. Dairy products, broccoli, kale, sardines, and tofu are some good sources of calcium. Oily fishes, such as tuna and salmon, eggs, fortified foods, such as milk and cereals, and mushrooms are good sources of vitamin D. If there is a deficiency, consult a doctor for calcium and vitamin D supplements.
- Treat eating disorders and hormone disorders, such as thyroid issues, on time to prevent bone loss.
- Follow the prescribed supplement dosage or recommended diet if taking long-term medications that may increase the risk of bone loss, such as corticosteroids or antiepileptics.
Facts About Bones
Bones are complex structures that fit together like a puzzle. They rely on muscles to make various movements at joints. Here are some interesting facts about human bones.
- Bones are strong and hard but are still lightweight.
- The longest bone in the human body is the femur located in the thigh.
- The smallest bone in the human body is the stapes (stirrup-shaped bone) located in the inner ear.
- The hand contains 27 bones, making it the body part with most bones.
- Red blood cells and white blood cells are made in the bone marrow.
- Bones store 99% of the body’s calcium reserves.
- Bones could be composed of up to 25% of water.
- Bones continuously undergo remodeling— constant breakdown of old bone tissue and formation of new bone tissue.
- Healthy children have more bone formation than breakdown.
- You cannot fracture a funny bone because it is not a bone. It is a part of the nerve running inside the elbow.
Bones are living tissues with their supply of blood vessels. They require minerals, protein, and vitamins for healthy growth and maintenance throughout life. Nutritional deficiencies could affect bone growth. Maintain a healthy diet, including calcium- and vitamin D-rich foods, to have good bone health.
2. Pediatric Skeletal Growth; Fairview
3. Bones of the Skull; Teach Me Anatomy
4. Spine Basics; The American Academy of Orthopedic Surgeons
5. The Thoracic Cage-the ribs and sternum; Human Anatomy and Physiology; Lumen learning
6. Upper Extremity; Handcare; The American Society for Surgery of the Hand
7. Atlas of Lower Extremity Anatomy; IMAIOS Anatomy
8. Anatomy of a Joint; University of Rochester Medical Center
9. Kids and Their Bones: A Guide for Parents; The NIH Osteoporosis and Related Bone Diseases
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