IndietroChapter 7: The Skeletal System – The Axial Skeleton (Principles of Anatomy and Physiology, 15th Edition)
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The Axial Skeleton and Homeostasis
Role of the Axial Skeleton in Homeostasis
The axial skeleton plays a crucial role in maintaining homeostasis by providing protection and support for vital organs and contributing to mineral storage.
Protection of Organs: The cranium surrounds the brain, the vertebrae protect the spinal cord, and the ribs encase the heart and lungs.
Calcium Storage: Bones act as reservoirs for calcium, an essential ion for physiological processes, and can release or store calcium as needed.
Divisions of the Skeleton
Axial vs. Appendicular Skeleton
The human skeleton is divided into two main divisions, each with distinct components and functions.
Axial Skeleton (80 bones): Includes the skull, auditory ossicles, hyoid bone, vertebral column, ribs, and sternum. It forms the central axis of the body and provides protection for the central nervous system and thoracic organs.
Appendicular Skeleton (126 bones): Comprises the bones of the upper and lower limbs and the girdles (pectoral and pelvic) that attach the limbs to the axial skeleton. It is primarily involved in movement.
Division of Skeleton | Structure | Number of Bones |
|---|---|---|
Axial Skeleton | Skull (Cranium, Face), Hyoid bone, Auditory ossicles, Vertebral column, Thorax (Sternum, Ribs) | 80 |
Appendicular Skeleton | Pectoral girdles (Clavicle, Scapula), Upper limbs (Humerus, Ulna, Radius, Carpals, Metacarpals, Phalanges), Pelvic girdle (Hip bones), Lower limbs (Femur, Patella, Tibia, Fibula, Tarsals, Metatarsals, Phalanges) | 126 |
Types of Bones
Classification by Shape
Bones are classified into five main types based on their shape, each adapted for specific functions.
Long Bones: Greater length than width (e.g., humerus, femur). Designed for leverage and movement.
Short Bones: Cube-shaped (e.g., wrist bones, tarsals). Provide stability and support with limited motion.
Flat Bones: Thin layers of parallel plates (e.g., sternum, cranial bones). Offer protection and broad surfaces for muscle attachment.
Irregular Bones: Complex shapes (e.g., vertebrae, some facial bones). Have varied functions including protection and support.
Sesamoid Bones: Shaped like a sesame seed (e.g., patella). Develop in tendons and protect them from stress and wear.
Additional info: Sutural bones are small, extra bone plates located within the sutures of cranial bones and are not included in the standard 206 bones count.
Summary Table: Types of Bones by Shape
Type | Description | Example |
|---|---|---|
Long | Greater length than width | Humerus, femur |
Short | Cube-shaped | Carpals (wrist bones) |
Flat | Thin, parallel plates | Sternum, cranial bones |
Irregular | Complex shapes | Vertebrae, facial bones |
Sesamoid | Shaped like a sesame seed, develop in tendons | Patella |
Key Terms and Definitions
Axial Skeleton: The part of the skeleton forming the central axis, including the skull, vertebral column, and thoracic cage.
Appendicular Skeleton: The part of the skeleton consisting of the limbs and girdles.
Homeostasis: The maintenance of a stable internal environment in the body.
Calcium: A mineral stored in bones, essential for muscle contraction, nerve function, and blood clotting.
Examples and Applications
Example: The ribs (part of the axial skeleton) protect the heart and lungs from physical trauma.
Application: Disorders of the axial skeleton, such as osteoporosis, can lead to decreased calcium storage and increased risk of fractures.
