Bone Anatomy

Bone is a rigid tissue that is a part of the vertebrate skeleton in all animals. Bones are responsible for protecting the various organs of the body, it is also responsible for producing the Red blood cells and the white blood cells, it also provides shape and supports the body and helps in the movements, Bones also help in storing the minerals in the body. Bones have multiple functions and they are very lightweight but also strong. Bones have a complex external and internal structure and they come in a variety of shapes and sizes. 

Bone tissue or the osseous tissue is a specialized connective tissue that is also very hard. Internally the bone tissue resembles the honeycomb matrix which is responsible for giving the bone its rigidity or toughness. Bone tissue is not made of only one type of cells rather it is made of many different types of bone cells. Bone cells such as the Osteocytes and the osteoblasts are involved in the formation and the mineralization of the bones whereas osteoclasts are responsible for the resorption or the reabsorption of the bone tissue. The flattened osteoblasts modify themselves into lining cells that help in forming a protective layer on the bone surface. The mineralized matrix of the bone tissue consists of both the organic and inorganic components of the bone minerals made up of various salts. 

Bone tissue is a mineralized tissue and it has two types of bones which are the cancellous bone and the cortical bone. Bone marrow, blood vessels, cartilage, periosteum, and endosteum are the other types of tissue found in the bone. At the time of birth, a newly born baby has 270 bones in his or her body but as time passes by many of these bones fuse together, and later there are 206 separate bones in an adult body excluding the numerous sesamoid bones. The smallest bone in the human body is the stapes in the middle ear and the largest bone in the human body is the femur or the thigh bone. 

Types of Bone Cells 

Bone is considered to be a metabolically active tissue that is composed of many types of cells. When bones are viewed microscopically, they consist of hard, homogenous intercellular material within or upon, and based on that we consider there are four characteristics cell types which are osteoblasts, osteocytes, osteoclast, and bone mesenchymal stem cells. Osteoblasts are mainly responsible for the mineralization and the creation of bone tissue. They are also responsible for depositing and synthesizing the protein matrix of new intercellular materials on bone surfaces. Osteoclasts are the large multinucleated cells that usually work from the bone surface. and helps in the reabsorption of bones by a direct chemical and enzymatic attack. Osteocytes are trapped within the intercellular material and reside in the cavity by the name lacuna and communicate with other osteocytes as well as free bone surfaces with the help of extensive filamentous protoplasmic extensions. Both osteocytes and osteoclasts are involved in the reabsorption of the bone tissue. Osteoprogenitors are the cells from which both osteocytes and osteoclast cells are derived from. The mesenchymal stem cells of the bones which are undifferentiated are present in the loose connective tissue which is between the condensed fibrous tissue which covers the outside of the bone and in the trabeculae which are along the vascular channel. Mesenchymal stem cells are multipotent stem cells that are found in the bone marrow and are very important for making and repairing the skeletal tissues such as cartilages, fat sound in the bone marrow and the bones. 

Depending on how the osteocytes and the protein fibrils of the bones are arranged the bones are of two types are Woven bones and lamellar bones. In woven bones, the collagen bundles and the osteocytes are randomly arranged whereas in the lamellar bones both the fibrils and the osteocytes are aligned or arranged in a clear manner. 

Bones in the Human Body

Bones make up the entire skeletal system of the body and are majorly responsible for the storage of different macronutrients, providing rigidity and hosing the bone marrow. Bones are also responsible for producing the red blood cells and white blood cells and also helps in providing structural outline and movement. As discussed above bones are made up of three types of bone cells and out of those three, the osteocytes are the most common cells which are found in the mature bone and are responsible for maintaining bone growth and density.

The total bones in the human body are two hundred and six and several types of bones are grouped due to their features such as shape, placements, and other additional properties. A joint helps in connecting two or more bones. The skeleton acts as a lever that drives the force of the movement with the help of the attached tendons and musculature. The inner core of bones or the medulla is filled with either the red bone marrow or the yellow bone marrow with the adipose tissue. 

The bones which are developed are of endochondral and membranous forms. These two characteristics of the bones along with the shape of bones have been used to classify the skeletal system. There are five types of bones and they are long bones, short bones, flat bones, sesamoid bones, and irregular bones. 

Types of Bones 

1. Long Bones: 

The long bones are mainly characterized by having a shaft, the diaphysis which is much longer than its width. A shaft and a diaphysis connect two ends known as the epiphysis. The epiphysis is mostly made up of compact bones with a lesser amount of marrow and is located within the medullary cavity and the areas of spongy, cancellous bones at the end of the bones. Humerus, ulna, radius, fibula, tibia, femur, metacarpal bones, and phalanges are the group of bones included in the long bones. Except for the eight carpal bones of the wrist, the sesamoid bone of the kneecap, and the seven articulating tarsal bones of the ankle, most bones of the limbs including those of the finger and the toes are the long bones. 

2. Short Bones: 

The short bones are only a thin layer of compact bones surrounding a spongy interior that is considered to be more or less cuboid. The bones of the wrist and the ankles are the small bones in human body or the small bones.

3. Flat Bones: 

Flat bones are generally curved and thin. Two parallel layers of compact bones cover both the spongy bones and the bone marrow space. The group of bones that are included in the flat bones is skull bones, ribs, sternum, and scapulae.

4. Irregular Bones: 

Irregular bones consist of thin layers of compact bones covering a mass of mostly spongy bones. They have complicated and irregular-shaped bones. The irregular bones are not categorized by the shape but by the bone content. The bones that come under the category of irregular bones are the bones of the spine, pelvis, and a few bones of the skull.

5. Sesamoid Bones: 

The sesamoid bones are implanted within the tendons. They are found at the end of the long bones, the place where the tendons cross. Sesamoid bones protect the tendons from excess wear and stress by reducing friction. The patella and the pisiform are examples of the sesamoid bones. 

Structure and the Chemical Composition of the Bone

There are two morphological types of bones that a long bone contains, and those are a cortical or a compact bone and Cancellous or trabecular or spongy bone. 

The cortical bone helps in forming a dense cylinder down the shaft of the bone which surrounds the central marrow cavity. Due to the low porosity, the cortical bone has a lower surface area than the cancellous bones but they account for eighty percent of the mass of the bones in the human body. At the end of the long bone, the cancellous or the trabecular bones are located which accounts for twenty percent of the total mass of the skeleton. The cancellous bones also have an open honeycomb structure. 

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Composition of the Bone: The collagen fibers and inorganic bone minerals in the form of small crystals are the main components that the bone consists of. The living bone of the human body is made up of 20% of water and its dry mass consists of approximately 60-70% of bone numerals. The bone also contains a very little amount of other substances such as inorganic salts and proteins but mostly it contains collagen. College is considered to be the main fibrous protein in the body and it also has a triple helical structure.

The composition of the mineral components can be approximated as hydroxyapatite (HA) which has a Ca :P the ratio of 5:3 whereas the bone minerals themselves have a Ca:P ratio which ranges between 1.37-1.87. This is due to the composition of the bone minerals which are more complex and contain ions such as carbonate, silicon, and zinc.

The cartilage is a collagen-based tissue that contains and very large protein-polysaccharide molecules that helps in forming a gel in which the collagen fibers are entangled. The bearing surfaces of the movable joints of the body are formed by the Articular or the hyaline cartilages. 

List of Bones in the Human Body

There are 206 bones in the human body excluding the teeth and the sesamoid bones. 

The axial skeleton consists of the spine, chest, head and contains 80 axial bones whereas the appendicular skeleton which includes the arms, shoulders, pelvic girdle, and legs consists of 126 bones in total. Let us study the skeletal system diagram which is given below and also let us list out all the 206 bones of the human body. 

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Spine or the Vertebral Column

There are 26 bones in the spine of a fully grown-up adult whereas there are 36 bones in a child. The 26 bones of the spine are listed below 

1. 7 bones in the cervical vertebrae

2. 12 ones in the Thoracic vertebrae 

3. 5 bones in the lumbar vertebrae 

4. One Sacrum bone. There are usually five bones at the time of birth but as the child grows the bones fuse to form a single bone. 

Chest or the Thorax 

There are 25 bones in the chest but sometimes there are additional cervical ribs in humans. 

1. In a pair of 12, we have 24 bones in the ribs 

2. One or 3 bones in the Sternum 

Skull

There are 23 bones in the skull. When we include the middle ear, the head will contain 29 bones in total. The names of the bone and their numbers are listed below. 

• 8 cranial bones 

• One occipital bone 

• 2 parietal bones 

• 2 temporal bones 

• one frontal bone 

• One sphenoid bone 

• one ethmoid bone 

• There are 15 facial bones 

• 2 Nasal bones 

• 2 Maxillae or the upper jaw bones 

• 2 lacrimal bone 

• 2 palatine bones 

• 2 cheekbones 

• 2 inferior nasal concha 

• 1 vomer

• 1 Hyoid bone 

• one Mandible 

• There are 6 bones in the middle ear, 3 on each side 

• 2 malleus 

• 2 incus and 

• 2 stapes  

Arm and the Hand Bone Anatomy

There are a total of 64 bones in the arms. The upper arm bone consists of 6 bones in total, 3 on each side. 2 Humerus, one pelvic girdle, 2 bones of the scapula, and 2 bones of clavicles. The lower arm consists of 4 bones in total, 2 on each side they are 2 Ulna,2 Radius.

There are 54 bones in the hand, 27 on each side, and the names of the bones are listed below

• One carpel 

• 2 Scaphoid bones 

• 2 lunate bone 

• 2 Triquetral bone

• 2 Pisiform bone

• 2 Capitate bone

• 2 Trapezium

• 2 Trapezoid bone

• 2 Hamate bone

• 10 Metacarpals bones in total with 5 on each side.

• Phalanges of the hand

• 10 Proximal phalanges in total with 5 on each side.

• 8 Intermediate phalanges in total with 4 on each side 

• 10 Distal phalanges in total with 5 on each side.

Bones of Pelvis

The pelvis or the hip bone is made up of three regions that are fused to form 2 coxal bones. The 2 bones are  ilium, ischium, and pubis.The two hip bones are attached to form the pelvis by the sacrum and the coccyx. 

Legs and the Foot Bone Anatomy

There are 60 bones in the legs. We have 2 Femur,2 bones in the patella or the knee caps,2 bones in the Tibia, 2 bones in the Fibula.

In the foot, we have 52 bones in total with 26 bones per foot. The tarsus or the tarsals consist of 

• 2 Calcaneus or heel bone

• 2 bones in the Talus

• 2 Navicular bones

• 2 Medial cuneiform bones

• 2 Intermediate cuneiform bones

• 2 Lateral cuneiform bones

• 2 Cuboid bones

The Metatarsals of the foot consist of 10 bones in total. The Phalanges of the foot consist of 10 Proximal phalanges bones, 8 Intermediate phalanges bones, and 10 Distal phalanges bones.