Human Anatomy and Physiology : I. Skeletal and Muscle System

The stapes is the lightest stirrup-shaped bone and the smallest bone in the human body found in the middle of humans ears. While femur is the largest bone in the human body. It is located in the upper leg which connects the knee at one end and fits into the hip socket at the other.

The human skull (excluding hyoid bone of the neck) consists of 28 bones. It consists of two parts, neurocranium and the facial skeleton (also called the viscerocranium). Neurocranium has 8 bones and there are 14 in the viscerocranium (facial bones) and remaining 6 bones occurs in the middle ear, which is helpful in listening.

Calcium phosphate is the principal form of calcium found in bovine milk and blood. About 70% of bone consists of hydroxyapatite, a calcium phosphate mineral (known as bone mineral). Up to 50% by volume and about 70% by weight of human bones is a modified form of hydroxyapatite.

The human rib cage is made up of 12 paired (total 24) rib bones. Each are symmetrically paired in right and left side. The ribs are flat, thin bones that together with the sternum make up the rib cage. The ribs provide protection for vital organs in the upper body, including the heart and lungs.

Each human long bone (including leg bone) is composed of a shaft (diaphysis) with two flared ends (epiphysis). The diaphysis resembles a hollow cylinder. It is made of hard compact bone that is resistant to bending. The inner cavity of the diaphysis contains yellow bone marrow that stores fat. The epiphysis is a thin shell of compact bone filled with a lattice or sponge-like structure that is surrounded by red bone marrow (which makes red blood cells).

An osteoclast is a type of bone cell that breaks down bone tissue. This function is critical in the maintenance, repair, and remodeling of bones of the vertebral skeleton. Osteoclasts are the cells that degrade bone to initiate normal bone remodeling and mediate bone loss in pathologic conditions by increasing their resorptive activity. They are derived from precursors in the myeloid/monocyte lineage that circulate in the blood after their formation in the bone marrow. These osteoclast precursors (OCPs) are attracted to sites on bone surfaces destined for resorption and fuse with one another to form the multinucleated cells that resorb calcified matrices under the influence of osteoblastic cells in bone marrow. Hence, both options (a) and (c) are correct.

Hip replacement surgery is typically recommended when hip pain significantly impacts daily activities or when other treatments have failed to provide relief. Common reasons for needing a hip replacement include:

• Arthritis: Including osteoarthritis and rheumatoid arthritis, which cause cartilage breakdown in the hip joint.
• Osteonecrosis: A condition where parts of the bone die due to decreased blood supply.
• Fractures: Broken bones resulting from falls or accidents.
• Persistent hip pain: Pain that doesn't respond to other treatments.

Cartilage is a strong, flexible connective tissue that protects our joints and bones. Cartilage is an important structural component of the body. It is a firm tissue but is softer and much more flexible than bone and can be bent. Outer ear and tip of the nose are examples of cartilage. On the other hand, the carpal bones are the eight small bones that make up the wrist (or carpus) that connects the hand to the forearm. These bones are hard and will break if bent. Hence, option (c) is the correct answer.

The atlantoaxial joint is a type of synovial joint that is classified as a biaxial, pivot joint. This joint resides in the upper part of the neck between the first and second cervical vertebrae, also known as the Atlas and Axis, respectively. It allows for turning of the head from side to side. The pivot joint classification means that it allows for rotation only and is formed by a central pivoting, bony structure that rotates around craniovertebral ligaments.