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Questions and Answers
What type of bone is the ulna classified as?
Which of the following is NOT a function of the skeletal system?
What characterizes compact bone?
How many bones are there in the adult human skeleton?
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Which division of the skeletal system includes bones around the longitudinal axis?
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What is the primary function of the periosteum?
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Which type of ossification involves the development of bone from cartilage?
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At what stage of life does yellow bone marrow begin to replace red bone marrow in the distal long bones?
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Which statement about the structure of a long bone is true?
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Which is NOT a function of bone marrow?
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What makes up the appendicular skeleton?
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Which of the following regions is NOT part of the vertebral column?
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How many cervical vertebrae are in the cervical region?
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Which bone is part of the pelvic girdle?
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Which bones are classified as short bones?
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What are pneumatic bones characterized by?
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How many phalanges are there in each thumb?
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Which bone is NOT considered a long bone?
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Study Notes
Learning Outcomes
- Students should be able to describe the divisions of the skeletal system.
- Students should be able to identify different types of bones.
- Students should be able to describe the structure of a long bone and the periosteum.
Case Scenario
- A 22-year-old woman fractured her left ulna following a car accident.
- The ulna is a long bone.
Functions of the Skeleton
- The skeleton provides support for the body.
- It gives shape to the body.
- The skeleton protects soft organs.
- Movement is possible due to skeletal muscles attached to the bones.
- The skeleton stores minerals and fats.
- Blood cell formation occurs within the bones.
Bone Composition
- Bone consists of bone cells, an intercellular matrix made of collagen fibers, inorganic salts, and minerals.
Classification of Bones
- Compact (Hard) Bone: Dense and ivory-like, forming the surface of bones.
- Cancellous (Spongy) Bone: Found inside bones, consisting of trabeculae (tiny beams of bone) with spaces like a sponge.
Divisions of the Skeletal System
- Axial Skeleton: Contains bones along the longitudinal axis of the body. Includes the skull, sternum, ribs, vertebral column, and hyoid bone.
- Appendicular Skeleton: Consists of bones of the upper and lower limbs (extremities) and the girdles connecting the limbs to the axial skeleton.
Vertebral Column Regions
- Cervical Region: Contains the cervical vertebrae (C1-C7).
- Thoracic Region: Contains the thoracic vertebrae (T1-T12).
- Lumbar Region: Contains the lumbar vertebrae (L1-L5).
- Sacrum: A triangular bone formed by the union of five sacral vertebrae (S1-S5).
- Coccyx: Formed by the fusion of four coccygeal vertebrae.
Bones of the Upper Limb
- Shoulder Girdle: Consists of the scapula and clavicle. Connects the upper limb to the trunk at the sternoclavicular joint.
- Arm: Contains the humerus.
- Forearm: Contains the radius and ulna.
- Hand: Composed of the carpal (8), metacarpals (5), and phalanges (3 in each finger except thumb, which has 2).
Bones of the Lower Limb
- Pelvic Girdle: Consists of the hip bone and connects the lower limb to the axial skeleton at the sacroiliac joint.
- Thigh: Contains the femur.
- Leg: Contains the tibia and fibula.
- Foot: Composed of the tarsal bones (7), metatarsals (5), and phalanges (3 in each toe except the big toe, which has 2).
Divisions of Bones Based on Shape
- Long Bones: Examples include the humerus, femur, metacarpals, and phalanges.
- Short Bones: Examples include the carpal and tarsal bones.
- Flat Bones: Examples include the vault of the skull, ribs, sternum, and scapula.
- Irregular Bones: Various shapes, e.g., vertebrae, hip bone.
- Pneumatic Bones: Contain air spaces, e.g., maxilla, frontal bones.
- Sesamoid Bones: Small bones embedded in tendons, e.g., patella (kneecap).
Structure of a Long Bone
- Diaphysis: Shaft of the bone, formed of outer compact bone covered by periosteum and an inner medullary cavity.
- Epiphysis: Two ends of the bone, composed of cancellous bone covered by compact bone. The articular surface is covered by hyaline cartilage.
- Metaphysis: Part of the diaphysis close to the epiphysis.
- Epiphyseal Plates: Cartilaginous discs between the epiphysis and diaphysis that allow for the growth of bone in length.
Periosteum
- A fibrous connective tissue covering the surrounding bone, except at the site of articular cartilage.
- Highly sensitive due to its rich nerve supply.
- Functions:
- Provides attachment for muscles, tendons, and ligaments.
- Provides a source of blood supply to the bone.
- Contributes to bone growth in width.
- Helps in the healing of fractured bones.
Bone Marrow
- It is a fatty, vascular tissue found in the medullary cavity of long bones and the spaces of cancellous bone.
- Involved in the formation of blood cells.
- The type of bone marrow changes with age:
- At birth: All marrow cavities are filled with red bone marrow.
- During childhood: Yellow bone marrow replaces red bone marrow in the distal long bones.
- In adults: Red bone marrow is only present in the spaces of spongy bones (in the skull, vertebrae, sternum, ribs, hip, upper end of the femur, and humerus). The medullary cavities of all long bones contain only yellow bone marrow.
Classification of Bones Based on Ossification
- Membranous Ossification: Bone develops from a membrane of connective tissue called mesenchymal ossification. Examples include the skull bones, shaft of the clavicle, and facial bones.
- Cartilaginous Ossification: Bone develops from cartilage. Examples include all other bones of the body.
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