What is the Human Skeletal System?

The skeletal System is a rigid framework and support structure for the whole body. This system includes not only bones but also related tissues such as cartilage and ligaments.

Functions of Skeletal System-

1. Support
2. Protection
3. Movement
4. Storage
5. Hemopoiesis

Support- The Skeletal System supports our body and makes a suitable structure because all the softer tissues of the body laterally hang from the Skeletal framework and create our posture.

Protection- Hard bony boxes protect delicate structures enclosed within them. For example- the Skull protects the Brain, Ribs protect the Heart and Lungs.

Movement- Muscles are anchored firmly to bones, when the muscles contract and shorten they pull the bone thereby moving them.

Storage- It plays a vital role in maintaining blood calcium homeostasis. They serve as a safety deposit box for calcium. When the blood calcium increases above normal, calcium moves out of the blood into the bones for storage. Conversely when blood calcium decreases below normal calcium moves in an opposite direction.

Hemopoiesis- This term is used to describe the process of blood cell formation. It is a combination of two Greek Words: Hemo- Blood, and Poiesis- to make. Blood cell formation is a vital process carried on in red bone marrow. It is a soft connective tissue inside the hard walls of some bones.

Types of Bones-

1. Long Bones
2. Short Bones
3. Flat Bones
4. Irregular Bones

Structure of Long Bone-

Diaphysis or Shaft- This is a description of a hollow tube that is constructed from hard, compact bone. It is a sturdy and inflexible structure that is also lightweight, allowing for effortless mobility.

Medullary Cavity- The medullary cavity is a hollow area found inside the diaphysis of a bone. It contains soft yellow bone marrow, which is an inactive and fatty form of marrow that is typically found in the adult skeletal system.

Epiphysis- The ends of bones are composed of spongy bone tissue called epiphysis, which is filled with red bone marrow in small spaces.

Articular Cavity- The articular cavity is a thin layer of cartilage that covers each epiphysis. Its function is similar to that of a small rubber cushion placed over the ends of bones where they meet.

Periosteum- Remove the joint. The periosteum is a sturdy fibrous membrane that covers long bones, except for the joint surfaces where it is located.

Endosteum- The endosteum is a fibrous membrane that lines the medullary cavity.

Division of Skeletal-

The human skeleton has two divisions: The axial skeleton and the appendicular skeleton. Bones of the center axis of the body make up the axial skeleton. The bones of the skull, spine, chest, and hyoid bone in the neck are all in the axial skeleton. The bones of the upper and lower extremities of appendages make up the appendicular skeleton. The appendicular skeleton consists of the bones of the upper extremities and lower extremities.

1. Axial Skeleton 2. Appendicular Skeleton

Axial Skeleton- Eighty (80) bones are present in the axial skeleton.

1. Skull – It contains 28 bones.
   • Cranial Bones- Parietal (2), Temporal (2), Frontal (1), Occipital (1), Ethmoid (1), Sphenoid ) (1)
   • Facial Bones – Maxilla (2), Zygomatic (2), Mandible (1), Nasal (2), Platine (2), Inferior Nasal Inferior nasal concha (2), Lacrimal (2), Vomer (1)
   • Ear Bones (Auditory Ocicles) – Malleus (2), Incus (2), Stapes (2)
2. Spine (Vertebral Column) – Cervical vertebrae (7), Thoracic vertebrae (12), Lumbar vertebrae (5), Sacrum ( 1), Coccyx (1)
3. Thorax or Chest cage-
   • Ribs (24)
   • Sternum (1)
4. Hyoid Bone (1)

Appendicular Skeleton- There are one hundred and twenty-six (126) bones in the appendicular or appendicular skeleton.

1. Pectoral Girdle- clavicle or collar bone or clavicle (2), shoulder blade or scapula (2)
2. Upper Extremities–
   • Arms- Humerus (2), Radius (2), and Ulna (2)
   • Wrists- Carpals (16)
   • Hands- metacarpals (10), finger bones or phalanges (28)
3. Pelvic Girdle – Hip Bones (2)
4. Lower Extremities-
   • Legs – Femur (2), Patella (2), Tibia (2), Fibula (2)
   • Ankles – Ankle bone or Tarsals (14)
   • Feet – Metatarsals (10), Finger bones or Phalanges (28)