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Questions and Answers
Which of the following describes flat bones?
Which of the following describes flat bones?
What is the primary composition of short bones?
What is the primary composition of short bones?
Which bone is classified as irregular?
Which bone is classified as irregular?
What comprises the diaphysis of a long bone?
What comprises the diaphysis of a long bone?
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Which structure secures the periosteum to the underlying bone?
Which structure secures the periosteum to the underlying bone?
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Which of the following is an example of a sesamoid bone?
Which of the following is an example of a sesamoid bone?
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How do flat bones differ from irregular bones?
How do flat bones differ from irregular bones?
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What primarily composes the epiphysis of a long bone?
What primarily composes the epiphysis of a long bone?
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What is the primary function of the articular cartilage in long bones?
What is the primary function of the articular cartilage in long bones?
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What does the epiphyseal plate do in a young, growing bone?
What does the epiphyseal plate do in a young, growing bone?
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Which description characterizes the endosteum of a long bone?
Which description characterizes the endosteum of a long bone?
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What fills the open spaces within spongy bone?
What fills the open spaces within spongy bone?
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What are osteocytes?
What are osteocytes?
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What forms the concentric circles of lacunae in compact bone?
What forms the concentric circles of lacunae in compact bone?
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What distinguishes the medullary cavity in adult long bones?
What distinguishes the medullary cavity in adult long bones?
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What does the epiphyseal line indicate in adult bones?
What does the epiphyseal line indicate in adult bones?
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What is the main function of the central (Haversian) canal in compact bone?
What is the main function of the central (Haversian) canal in compact bone?
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Which of the following accurately describes an osteon?
Which of the following accurately describes an osteon?
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What role do canaliculi play in the structure of compact bone?
What role do canaliculi play in the structure of compact bone?
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What is the significance of perforating (Volkmann's) canals in bone structure?
What is the significance of perforating (Volkmann's) canals in bone structure?
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How do organic parts of bone, such as collagen fibers, contribute to its properties?
How do organic parts of bone, such as collagen fibers, contribute to its properties?
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During ossification in long bones, what occurs first in the embryonic stage?
During ossification in long bones, what occurs first in the embryonic stage?
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What happens to the cartilage during the ossification process in a fetus?
What happens to the cartilage during the ossification process in a fetus?
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What are the two major phases of ossification in long bones?
What are the two major phases of ossification in long bones?
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Which property of bone allows it to resist tension and other forces effectively?
Which property of bone allows it to resist tension and other forces effectively?
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Which statement about calcium salts in bone is true?
Which statement about calcium salts in bone is true?
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Which of the following bones is NOT part of the cranial bones?
Which of the following bones is NOT part of the cranial bones?
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Which bone in the skull is attached by a freely movable joint?
Which bone in the skull is attached by a freely movable joint?
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Which region of the vertebral column has the most vertebrae?
Which region of the vertebral column has the most vertebrae?
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Which component is formed by the fusion of five vertebrae?
Which component is formed by the fusion of five vertebrae?
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What type of joint connects the bones of the skull?
What type of joint connects the bones of the skull?
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Which part of the vertebral column is associated with the lower back?
Which part of the vertebral column is associated with the lower back?
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Which of the following bones is part of the facial bones?
Which of the following bones is part of the facial bones?
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What type of joint is found where the teeth meet the facial bones?
What type of joint is found where the teeth meet the facial bones?
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Which type of joint allows for slight movement and is found in the pubic symphysis or intervertebral joints?
Which type of joint allows for slight movement and is found in the pubic symphysis or intervertebral joints?
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Which of the following is NOT a distinguishing feature of synovial joints?
Which of the following is NOT a distinguishing feature of synovial joints?
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What is the role of bursae in relation to synovial joints?
What is the role of bursae in relation to synovial joints?
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What primarily connects the bones in cartilaginous joints?
What primarily connects the bones in cartilaginous joints?
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Study Notes
Essentials of Human Anatomy & Physiology, Chapter 5: The Skeletal System
- The skeletal system comprises bones, joints, cartilages, and ligaments
- The skeleton is divided into two parts: axial and appendicular.
- The human adult skeleton consists of 206 bones.
- Two primary types of bone tissue are compact and spongy bone, characterized by their density and internal structure.
- Flat bones consist of a layer of spongy bone between two thin layers of compact bone.
- Other classifications of bones include long, short, and irregular bones.
- Long bones are typically longer than they are wide, with a shaft and enlarged ends. The majority of limb bones (excluding wrist, ankle, and kneecap bones) fall into this category. Examples include the femur and humerus.
- Flat bones are thin, flattened, and usually curved, with two layers of compact bone sandwiching a layer of spongy bone. Examples are ribs, sternum, and most skull bones.
- Short bones are generally cube-shaped, containing mostly spongy bone with an outer layer of compact bone. Examples include carpals (wrist bones) and tarsals (ankle bones).
- Irregular bones have irregular shapes and do not fit into the other bone classification categories. Examples include vertebrae and hip bones.
Functions of Bones
- Support the body
- Protect soft organs (e.g., skull protects brain, rib cage protects thoracic organs)
- Allow movement via attached muscles
- Store minerals and fats (e.g., calcium, phosphorus
- Support hematopoiesis (blood cell formation) which happens within internal marrow cavities
Structure of Bone
- Diaphysis (shaft): Composed mostly of compact bone, forms the central part of a long bone.
- Periosteum: Fibrous connective tissue membrane covering the outer surface of the diaphysis, secured to underlying bone by perforating fibers.
- Endosteum: Connective tissue membrane lining the inner surface of the diaphysis.
- Medullary cavity: Cavity within the shaft that contains yellow marrow (mostly fat) in adults, and red marrow for blood cell production until about age 6 or 7.
- Epiphyses (ends): Contain spongy bone enclosed by a thin layer of compact bone, covered externally by articular cartilage to reduce friction at joint surfaces.
- Epiphyseal line: Remnant of the epiphyseal plate (flat plate of hyaline cartilage) in adult bones. The epiphyseal plate is responsible for lengthwise bone growth during development.
Microscopic Anatomy of Bone
- Osteocytes: Mature bone cells located in the bone matrix.
- Lacunae: Cavities in the bone matrix that house osteocytes.
- Lamellae: Concentric circles of lacunae arranged around the central (Haversian) canal.
- Central (Haversian) canal: Opening in the center of an osteon (Haversian system), running lengthwise through bone and carrying blood vessels and nerves.
- Osteon (Haversian system): A unit of compact bone containing central canal and matrix rings, serving as the structural and functional unit.
- Canaliculi: Tiny canals that connect the central canal to lacunae, forming a transport system connecting all bone cells to a nutrient supply.
- Perforating (Volkmann's) canal: Canal perpendicular to the central canal, carrying blood vessels and nerves.
Bone Properties
- Bone is relatively lightweight but resists tension and other forces.
- Organic parts (collagen fibers) make bone flexible and resilient.
- Calcium salts make bone hard and resistant to compressive forces.
Bone Formation, Growth, and Remodeling
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Ossification is the process of bone formation.
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It begins on hyaline cartilage models or fibrous membranes.
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Long bone growth involves two major phases:
- Osteoblasts form bone matrix on a cartilage model or fibrous membrane.
- Encased cartilage is replaced by bone and the cartilage is digested, creating a medullary cavity.
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Bones continue to grow in width (appositional growth) by osteoblasts adding new bone matrix on the outside and osteoclasts removing bone from the inside.
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Hormones, especially growth hormone and sex hormones, control bone growth.
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Throughout life, bones are remodeled, responding to calcium ion levels in the blood and the pull of gravity and muscles on the skeleton.
Bone Fractures
- A fracture is a break in a bone.
- Types: closed (simple) fracture vs. open (compound) fracture.
- Repair involves four major stages: hematoma formation, fibrocartilage callus formation, bony callus formation, and bone remodeling.
Axial Skeleton
- Forms the central axis of the body and consists of:
- Skull: Cranium and facial bones.
- Vertebral column: 26 vertebrae separated by intervertebral discs (cervical, thoracic, lumbar, sacrum and coccyx vertebrae).
- Bony thorax: Sternum and ribs (true ribs, false ribs, and floating ribs).
Appendicular Skeleton
- Includes 126 bones of the limbs (appendages).
- Pectoral girdle (clavicle and scapula)
- Pelvic girdle (hips)
Joints
- Joints are articulations where bones meet. Functionally joints either hold bones together securely or allow for mobility.
- Two classifications (functional and structural).
- Functional: Synarthroses (immovable), Amphiarthroses (slightly movable), and Diarthroses (freely movable).
- Structural: Fibrous (e.g. sutures, syndesmoses, gomphoses, generally immovable or slightly movable), cartilaginous (e.g. synchondroses, symphyses, immovable or slightly movable), synovial (freely movable). Synovial joints have articular cartilage, a joint cavity, an articular capsule, and reinforcing ligaments.
- Common synovial joint types include plane, hinge, pivot, condylar, saddle, and ball-and-socket.
- Bursae and tendon sheathes are flattened fibrous sacs lined with synovial membrane that reduce friction in synovial joints.
Developmental Aspects of the Skeleton
- Skeletal development occurs from birth to adulthood and involves the transformation of initial cartilage and fibrous membrane models into adult bone.
- Fetal skulls have fontanels (soft spots) which allow for brain growth during pregnancy and infancy; they eventually ossify.
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