Skeletal System

The skeletal system is one of the most important systems in the human body, providing structure, support, and protection to our organs and tissues. It consists of bones, cartilage, ligaments, and tendons, and is responsible for a range of functions, including movement, storage of minerals and lipids, and blood cell formation.

·         Support and protection for our internal organs: The skull, for example, protects the brain, while the ribcage protects the heart and lungs. In addition, the bones of the vertebral column provide support for the entire body, allowing us to stand upright and move around.

·         Movement: Bones are attached to each other and to muscles by strong, fibrous tissues called ligaments and tendons, respectively. When muscles contract, they pull on the bones, causing them to move. This allows us to walk, run, jump, and perform a wide range of other activities.

·         Storage of minerals: Minerals like calcium and phosphorus are stored in the bones and released into the bloodstream as needed. In addition, bone marrow, which is found in the spongy interior of bones, is responsible for the production of blood cells, including red blood cells, white blood cells, and platelets.

Bones are the main component of the skeletal system, and there are 206 named bones in the human body. They come in a range of shapes and sizes, from the long, cylindrical bones in our arms and legs to the flat bones in our skulls and pelvis. Each bone is made up of both organic and inorganic materials, including collagen fibers and calcium phosphate crystals, which give it its strength and flexibility.

The skeletal system can be divided into two main parts: the axial skeleton and the appendicular skeleton. The axial skeleton consists of the bones of the skull, vertebral column, and ribcage, while the appendicular skeleton consists of the bones of the arms, legs, pelvis, and shoulder girdle.

The skeletal system is involved in the regulation of lipids in the body. Adipose tissue, or fat, is stored in the yellow bone marrow of certain bones, such as the femur and humerus. This fat can be used as an energy source in times of need.

Skeletal Tissue

Skeletal tissue is a specialized connective tissue that forms the structural framework of the body. It provides support, protection, and enables movement. Bones are the primary components of the skeletal tissue. They are composed of various types of cells and extracellular matrix, which collectively determine their unique mechanical and biological properties. Compact bone is structured in Haversian systems.

The Haversian system, also known as the osteon, is a fundamental structural unit of compact bone tissue. This system is responsible for supporting and protecting the body, as well as facilitating movement and other essential bodily functions. The Haversian system is composed of several distinct parts, including the Haversian canal, the lamellae, the lacunae, and the canaliculi.

·         The Haversian canal is the central channel within the osteon that contains blood vessels, nerves, and lymphatic vessels.

·         The lamellae are concentric rings of calcified matrix that surround the Haversian canal and contain osteocytes, or bone cells, within the openings called lacunae.

·         The canaliculi are small, interconnecting channels that allow for communication between the osteocytes and the Haversian canal.

The Haversian system is responsible for several critical functions within the body. One of its primary functions is to provide structural support and protection to the body. The compact bone tissue that makes up the Haversian system is much denser and stronger than other types of bone tissue, making it ideal for supporting the weight of the body and protecting internal organs from injury.

It is involved in the regulation of calcium and phosphorus levels within the body. As bone tissue is broken down and rebuilt, calcium and phosphorus are released into the bloodstream, where they can be used by other tissues and organs. This process is essential for maintaining healthy bones, as well as for supporting various bodily functions, such as muscle contraction and nerve transmission. The Haversian system also plays a crucial role in bone remodeling, which is the process by which bone tissue is broken down and rebuilt over time. This process allows bones to adapt to changes in the body, such as growth or changes in activity levels. As bone tissue is broken down and rebuilt, the Haversian system is responsible for laying down new bone tissue in a way that maintains the strength and integrity of the bone.

The Haversian system is also involved in the repair of bone tissue after injury or trauma. When bone tissue is damaged, the Haversian system is activated to initiate the repair process. This involves the recruitment of specialized cells, such as osteoblasts and osteoclasts, which work together to rebuild damaged bone tissue and restore its strength and function.

Structure of Bone Tissue

Bone tissue is composed of both organic and inorganic components. The organic component includes collagen fibers, which provide flexibility and strength to the bone, and non-collagenous proteins that are involved in mineralization. The inorganic component includes hydroxyapatite crystals, which provide the bone with hardness and rigidity.

There are four types of bone cells: osteoblasts, osteocytes, osteoclasts, and bone lining cells. Each of these cells has a unique function in maintaining healthy bone tissue.

·         Osteoblasts are bone-forming cells that are responsible for synthesizing and depositing the organic matrix of bone tissue. They are derived from mesenchymal stem cells and are located on the surface of the bone. Osteoblasts secrete collagen fibers and other organic molecules that form the initial structure of bone tissue. They also promote the mineralization of the bone tissue by depositing calcium and other minerals onto the organic matrix. Once they have completed their function, some of the osteoblasts become trapped in the mineralized bone tissue and differentiate into osteocytes.

·         Osteocytes are the most abundant type of bone cell and are located within the bone tissue. They are derived from osteoblasts and are responsible for maintaining the bone tissue. Osteocytes are involved in the regulation of bone remodeling by sensing mechanical forces and chemical signals. They also play a role in the maintenance of bone density and the regulation of mineral homeostasis. Osteocytes communicate with each other and with other bone cells through a network of channels called canaliculi.

·         Osteoclasts are bone-resorbing cells that are responsible for breaking down and removing the mineralized bone tissue. They are derived from monocytes and are located on the surface of the bone. Osteoclasts are multinucleated cells that secrete acid and enzymes to dissolve the mineralized bone tissue. They play a critical role in bone remodeling by removing old bone tissue and making way for new bone formation.

·         Bone lining cells are flattened cells that cover the surface of the bone tissue. They are derived from osteoblasts and are involved in the regulation of bone remodeling. Bone lining cells are quiescent cells that become active in response to bone remodeling signals. They can differentiate into osteoblasts or osteoclasts depending on the needs of the bone tissue.

·         Osteoprogenitor cells are bone-forming cells that are derived from mesenchymal stem cells. They are found in the inner lining of the periosteum, the endosteum, and in the bone marrow. Osteoprogenitor cells have the ability to differentiate into osteoblasts and are involved in bone repair and regeneration. They are also essential for bone growth and development. Osteoprogenitor cells are activated in response to bone injury or damage. They proliferate and differentiate into osteoblasts, which synthesize new bone tissue to replace the damaged tissue. Osteoprogenitor cells are also involved in the process of bone remodeling, in which old bone tissue is removed and new bone tissue is formed.

Function of Bone Cells

The bone cells work together to maintain healthy bone tissue by regulating bone formation and resorption. Osteoblasts and osteocytes work together to synthesize and deposit new bone tissue. Osteoclasts, on the other hand, break down and remove old bone tissue. Bone lining cells regulate the activity of osteoblasts and osteoclasts and play a role in the maintenance of bone density.

Skeletal tissue is a complex and dynamic tissue that is essential for the proper functioning of the body. The bone cells work together to maintain healthy bone tissue by regulating bone formation and resorption. Understanding the structure and function of bone cells is critical for the diagnosis and treatment of bone diseases such as osteoporosis, osteoarthritis, and bone cancer.

Osteoblasts are bone-forming cells that synthesize and deposit the organic matrix of bone tissue. Osteocytes are the most abundant type of bone cell and are involved in the regulation of bone remodeling, maintaining bone density, and mineral homeostasis. Osteoclasts are bone-resorbing cells that break down and remove old bone tissue, while bone lining cells regulate the activity of osteoblasts and osteoclasts.

The five types of bone cells, including osteoblasts, osteocytes, osteoclasts, bone lining cells, and osteoprogenitor cells, play important roles in maintaining healthy bone tissue.

·         Osteoblasts are bone-forming cells that synthesize and deposit the organic matrix of bone tissue.

·         Osteocytes are involved in the regulation of bone remodeling, maintaining bone density, and mineral homeostasis.

·         Osteoclasts are bone-resorbing cells that break down and remove old bone tissue.

·         Bone lining cells regulate the activity of osteoblasts and osteoclasts.

·         Osteoprogenitor cells are bone stem cells that have the ability to differentiate into osteoblasts and are involved in bone repair, regeneration, and growth.

Types of Bones

Bones are an essential component of the human skeletal system, providing support, protection, and mobility. They are classified into several types based on their shape, structure, and function. In this explanation, we will discuss the different types of bones in detail.

·         Long bones are the most common type of bones in the body and are responsible for the support and movement of the body. They have a long, cylindrical shape, with a shaft or diaphysis, and two ends or epiphyses. Examples of long bones include the femur, humerus, and phalanges.

·         Short bones have a cube-like shape and are found in the wrist and ankle. They are responsible for stability and support of these joints. Examples of short bones include the carpals and tarsals.

o    Sesamoid bones are small and round and are embedded in tendons, near joints. They protect the tendon from excessive wear and tear and improve the leverage of muscles. Examples of sesamoid bones include the patella, pisiform, and interphalangeal bones.

o    Wormian bones, also called intra sutural bones, are small bones that develop in the sutures of the skull. They are not present in all individuals, and their function is still unknown.

·         Flat bones are thin and flat and are found in areas of the body that require protection, such as the skull, ribs, and sternum. They also serve as a site for muscle attachment. Examples of flat bones include the scapula, ilium, and sternum.

·         Irregular bones have a unique shape that does not fit into any of the other categories. They are found in various parts of the body, including the vertebrae, facial bones, and pelvic bones. Irregular bones provide support and protection and serve as a site for muscle attachment.

Bone Fractures

Bone fractures are a common injury that can occur due to trauma or repetitive stress. The severity and classification of a fracture depend on several factors, including the type of fracture, the extent of the injury, and the location of the break.

Classification of Bone Breaks

Shapes of Bone Breaks

The other aspect of bone fractures is the various shapes of breaks. There are five main shapes of bone breaks that we will examine: transverse, compacted, spiral, commuted, and oblique. There are two more break that are more common in children, the greenstick, as well as epiphyseal breaks.

·         Transverse fractures occur when the bone breaks in a straight line perpendicular to the bone's axis. These fractures are typically caused by a direct blow to the bone or a fall.

·         Compacted fractures occur when the bone is compressed, causing the bone to buckle or bend. These fractures are typically caused by a direct blow to the bone or a fall.

·         Spiral fractures occur when the bone breaks in a spiral pattern around the bone's axis. These fractures are typically caused by a twisting force on the bone.

·         Commuted fractures occur when the bone is broken into three or more pieces. These fractures are typically caused by a high-energy impact, such as a car accident or a fall from a great height.

o Depression Fractures are a type of commuted fracture where a portion of the bone breaks away and moves inward.

·         Oblique fractures occur when the bone breaks at an angle to the bone's axis. These fractures are typically caused by a direct blow to the bone or a fall.

·         Greenstick fractures occur when the bone is bent but not completely broken. These fractures are typically seen in children because their bones are more flexible than adults' bones.

·         Epiphyseal fractures occur at the end of long bones and are common in children because their bones are still growing. These fractures can affect growth and require careful management to avoid future problems.

Bones of the Skeletal System

The human body has 206 named bones, each of which plays an essential role in maintaining the structure and function of the body. Here is a detailed explanation of all the bones of the human body and their functions.

Axial Skeleton

Bones in the axial skeleton include bones from the skull through the coccyx without the upper and lower limbs.

Cranial Bones

The skull bones include the cranial bones and facial bones. The cranial bones form the braincase, while the facial bones provide the framework for the face. The bones in the skull include:

·         The frontal forms the forehead and the upper part of the eye sockets. It contains the supraorbital foramen/notch, which is a small opening above each eye that allows blood vessels and nerves to pass through. The glabella is a smooth area between the eyebrows. It also houses the frontal sinuses.

o    The coronal suture joins the frontal bone with the parietal bones.

·         There are two parietal bones that are located on the sides and superior of the skull, forming the majority of the cranial vault.

o    The sagittal suture runs along the midline of the skull, separating the two parietal bones.

·         There are two temporal bones that are situated on the sides of the skull. They have several important features, including the zygomatic process, which extends forward to articulate with the zygomatic bone (cheekbone). The external acoustic meatus/canal is the passage leading to the middle ear. The styloid process is a slender projection, and the mastoid process is a bony prominence behind the ear.

o    The squamous suture connects the temporal bone with the parietal bone on the side of the skull.

·         The occipital bone is found at the back of the skull. It contains the large foramen magnum, through which the spinal cord passes.

o    The lambdoid suture joins the occipital bone with the parietal bones.

o    Sutural bones, also known as Wormian bones, are small extra bones that occasionally appear within the sutures of the skull. They are considered variations of normal bone development.

·         The sphenoid bone is located at the base of the skull. It includes the sella turcica, which houses the pituitary gland. It also houses the sphenoid sinuses.

·         The ethmoid bone is situated between the eyes. It has a crista galli, a triangular process that projects upward and supports the cribriform. It also houses the ethmoid sinuses.

o    There are superior, intermediate, and inferior nasal conchae that form the walls of the nasal cavity that arise from the ethmoid and maxillary bones.

Facial Bones

The facial bones provide the framework for the face and include:

·         There are two maxillae bones that form the upper jaw that house the maxillary sinuses. They have infraorbital foramen, which are openings below the eye socket, and the incisive foramen/fossa, which is located on the roof of the mouth.

·         There are two zygomatic bones that form the cheekbones and have the temporal process that completes the zygomatic arch from the temporal bone.

·         The mandible or lower jawbone, is the only movable bone of the skull. It consists of the body, which forms the chin, or mental protuberance, and the ramus, which connects to the skull. The mental foramen are small openings on the front of the mandible that allows blood vessels and nerves to pass through.

·         There are two nasal bones that form the bridge of the nose.

·         There are two lacrimal bones that form the medial wall of the orbit and include the lacrimal fossa.

·         There are two palatine bones that form the posterior part of the hard palate.

·         The vomer is a thin, flat bone located in the nasal cavity, dividing it into two sides.

·         The hyoid bone is a U-shaped bone located in the neck, just above the larynx. It supports the tongue and provides attachment points for certain muscles.  *Not technically a facial bone.

Thoracic Cage

The thoracic cage includes the ribs, sternum, and thoracic vertebrae. The thoracic cage protects the organs in the thoracic cavity and includes:

·         There are seven pairs of true ribs (Ribs 1-7). The first seven pairs of ribs are called true ribs because they directly attach to the sternum via their own costal cartilage.

·         There are three pairs of false ribs (Ribs 8-12). Ribs 8-10 are known as false ribs because their costal cartilage indirectly connects to the sternum, attaching to the cartilage of the rib above.

o    There are two pairs of floating ribs (Ribs 11-12). Ribs 11 and 12 are called floating ribs because they do not have any attachment to the sternum, only connecting to the vertebrae at the back.

·         The sternum, or breastbone, is a flat bone located in the center of the chest. It consists of three parts: the manubrium, the sternal body, and the xiphoid process. The jugular notch is a concave indentation at the superior edge of the manubrium, between the clavicular articulations.

Appendicular Skeleton

These bones include bones of the upper and lower limbs including the pectoral and pelvic girdles.

Pectoral Girdle

The pectoral girdle consists of the scapula and clavicle. It holds the arms to the thoracic trunk.

·         The scapula, or shoulder blade, is a flat, triangular bone located on the upper back. It has several important features, including the acromion process, which forms the tip of the shoulder; the coracoid process, which serves as an attachment point for muscles and ligaments; the glenoid cavity, which articulates with the humerus to form the shoulder joint; and the spine of the scapula, a bony ridge on the posterior side.

·         The clavicle, or collarbone, is a long bone that connects the scapula to the sternum. It helps stabilize the shoulder and provides attachment points for various muscles.

Upper Limb Bones

The upper limb bones include the humerus, radius, ulna, carpals, metacarpals, and phalanges. The upper limb bones are involved in movement of the arms.

·         The humerus is the long bone of the upper arm. It has several key structures, including the head, which articulates with the glenoid cavity of the scapula; the greater tubercle and lesser tubercle, which serve as attachment points for muscles; the deltoid tuberosity, where the deltoid muscle attaches; the trochlea and capitulum, which are both involved in the articulation of the elbow joint.

·         The radius is one of the two bones of the forearm. It extends from the elbow to the wrist on the thumb side. Key features include the head of the radius, which articulates with the capitulum of the humerus; the radial tuberosity, where the biceps muscle attaches; and the radial styloid process, a bony projection at the wrist.

·         The ulna is the other bone of the forearm, running parallel to the radius. It has important structures such as the olecranon process, which forms the bony prominence of the elbow; and the ulnar styloid process, a projection at the wrist.

·         There are eight carpal bones that form the wrist joint.  These bones are arranged in two rows, with four bones in each row.

o    Proximal row

§  The scaphoid bone is the largest bone in the proximal row and is located on the lateral side of the wrist. It articulates with the radius bone.

§  The lunate bone is crescent-shaped and sits just medial to the scaphoid bone. It is one of the most important bones in the wrist and is a key player in wrist movements.

§  The triquetral bone is pyramid-shaped and located on the medial side of the wrist. It is involved in wrist extension and flexion.

§  The pisiform bone is the smallest bone in the proximal row and is situated on the palmar side of the wrist. It plays a crucial role in transmitting force from the wrist to the hand.

o    Distal row

§  The trapezium bone is located on the lateral side of the distal row and articulates with the thumb.

§  The trapezoid bone is located medial to the trapezium bone and is involved in hand movements.

§  The capitate bone is the largest bone in the wrist and is situated at the center of the distal row. It forms the base of the third metacarpal bone and is an important link between the wrist and the hand.

§  The hamate bone is located on the medial side of the wrist and has a hook-like process called the hamulus. It serves as an attachment site for ligaments and muscles and helps support the hand during gripping.

·         The metacarpal bones are long bones that form the framework of the hand and are numbered 1-5 from the thumb to the little finger.

·         There are 14 phalanges that form the fingers and are divided into three sections per finger, the proximal phalanx, the middle (intermediate) phalanx, and the distal phalanx, except the thumb which only has two.

Pelvic Girdle

 The pelvic girdle includes the coxal bones and the sacrum.

·         Each hip bone, also known as a coxal bone, is formed by the fusion of three bones: the ilium, ischium, and pubis. They together form the pelvic girdle, providing support for the lower limbs and protection for the pelvic organs.

o The acetabulum is a cup-shaped socket on the lateral surface of the hip bone, which articulates with the head of the femur to form the hip joint.

o The obturator foramen is a large opening between the ischium and pubis, covered by a fibrous membrane.

·         The ilium is the largest and uppermost part of the hip bone. It includes the iliac crest, a curved ridge along the top of the hip, and the anterior superior iliac spine, a bony prominence at the front of the hip.

·         The ischium is the posterior and lower part of the hip bone. It contains the ischial tuberosity, a bony prominence that supports the body weight when sitting.

·         The pubis is the anterior and lower part of the hip bone. The two pubic bones meet at the pubic symphysis, a cartilaginous joint in the midline.

Lower Limb Bones

The lower limb bones include the coxal, femur, tibia, fibula, tarsals, metatarsals, and phalanges. The lower limb bones support the weight of the body.

·         The femur is the thigh bone and is the longest and strongest bone in the human body. Key features include the femoral head, which articulates with the acetabulum to form the hip joint; the fovea capitis, a small pit on the head of the femur; the greater trochanter and lesser trochanter, which are attachment sites for muscles; and the medial condyle and lateral condyle, which articulate with the tibia.

·         The patella, or kneecap, is a small, triangular bone located in front of the knee joint. It protects the knee joint and assists in the movement of the leg.

·         The tibia, or shinbone, is the larger and stronger bone of the lower leg. It bears most of the body's weight. Key features include the intercondylar eminence, which separates the medial and lateral condyles; the tibial tuberosity, where the patellar ligament attaches; and the medial malleolus, a bony prominence on the inner side of the ankle.

·         The fibula is the thinner of the two bones in the lower leg. It runs parallel to the tibia and provides support for muscles and ligaments. The lateral malleolus is a bony prominence on the outer side of the ankle, formed by the fibula.

·         There are seven tarsal bones that form the ankle joint.

o    The talus is a large bone that sits at the top of the hindfoot, where it connects to the lower leg bones. It has a unique shape that allows it to articulate with both the tibia and fibula bones of the lower leg, as well as the calcaneus bone of the foot.

o    The calcaneus is the largest bone in the foot and sits at the bottom of the hindfoot, forming the heel. It provides attachment sites for the achilles tendon and other muscles and ligaments.

o    The navicular bone is located in the middle of the foot and articulates with the talus bone of the hindfoot and the cuneiform and cuboid bones of the forefoot.

o    The cuboid bone is located on the lateral (outer) side of the foot and connects to the calcaneus bone of the hindfoot and the fourth and fifth metatarsals of the forefoot.

o    There are three cuneiform bones, which are located on the medial (inner) side of the foot. They are named the medial, intermediate, and lateral cuneiforms, and they articulate with the navicular bone and the first, second, and third metatarsals.

·         There are five metatarsal bones that form the sole of the foot, 1-5 starting with the big toe going to the little toe.

·         The phalanges are the bones of the toes. Each toe has three phalanges, except for the big toe, which has two. The phalanges are named proximal, middle (intermediate), and distal, based on their location.

Overview

The skeletal system is a vital component of the human body, providing structure, support, and protection to organs and tissues. It consists of bones, cartilage, ligaments, and tendons, and performs various functions such as movement, mineral storage, and blood cell production.

There are 206 named bones in the human body, varying in shape and size. The skeletal system can be divided into the axial skeleton (skull, vertebral column, and ribcage) and the appendicular skeleton (arms, legs, pelvis, and shoulder girdle). It supports and protects internal organs and enables movement through the attachment of muscles to bones.

Mineral storage is another crucial function of the skeletal system, with bones storing minerals like calcium and phosphorus, releasing them into the bloodstream as needed. Bone marrow, found within bones, produces blood cells.

The skeletal tissue, composed primarily of bone, forms the structural framework of the body. It consists of various types of cells and extracellular matrix. The Haversian system, or osteon, is the basic unit of compact bone tissue, providing support, protection, and facilitating movement. It comprises the Haversian canal, lamellae, lacunae, and canaliculi.

The Haversian system plays essential roles in structural support and protection, regulation of calcium and phosphorus levels, bone remodeling, and repair. It involves bone-forming cells called osteoblasts, bone-maintaining cells called osteocytes, bone-resorbing cells called osteoclasts, and bone lining cells. Osteoprogenitor cells are bone stem cells involved in repair, regeneration, and growth.

Understanding the structure and function of bone cells is crucial for diagnosing and treating bone diseases and disorders like osteoporosis and bone cancer. Different types of bones, including long, short, flat, and irregular bones, serve various functions in the body.

Bone fractures are common injuries that can occur due to trauma or repetitive stress. They are classified based on factors such as open or closed fractures, displaced or nondisplaced fractures, and complete or incomplete fractures. Additionally, fractures can have different shapes, such as transverse, compacted, spiral, commuted, oblique, greenstick, and epiphyseal breaks.

The skeletal system is a complex and dynamic system that plays a crucial role in the human body. Understanding its structure, function, and various types of bones and fractures is essential for healthcare professionals in diagnosing and treating skeletal-related conditions and injuries.