Skeletal System and Bone Anatomy Flashcards
Bone Structural Classifications
Long Bone: Named for its shape; longer than it is wide.
Short Bone: Cube-shaped bone structure; roughly equal in length and width.
Flat Bone: Characterized by a broad and thin structure.
Irregular Bones: Defined by having an irregular, complex shape that does not fit other structural categories.
Sesamoid Bone: Specialized, small, flat, and oval-shaped bones located directly within tendons. These bones provide a distinct mechanical advantage by improving muscle leverage.
Bone Histology and Internal Organization
Compact Bone:
Hard and dense osseous tissue forming the outer layer of a bone.
Specialized to resist linear compression forces applied straight down, as well as twisting forces.
Spongy Bone:
Internal bone structure located deep to compact bone.
Allows long bones to effectively resist compression applied from multiple directions.
Formed by a network that provides a central cavity for housing bone marrow.
Structural Anatomy of Bones
Long Bone Structure
Periosteum: A dense membrane covering long bones that is rich with blood vessels and nerves. It provides approximately of the overall blood supply to the bone.
Perforating Fibers: Structural fibers that anchor the periosteum firmly to the underlying bone matrix.
Diaphysis: The central shaft of a long bone.
Houses an inner hollow space known as the marrow cavity, which contains red or yellow bone marrow.
Epiphysis: The expanded region at each end of a long bone.
Covered externally by articular cartilage composed of hyaline cartilage.
Endosteum: A thin internal membrane lining spongy bone that plays an active role in maintaining bone homeostasis.
Epiphyseal Lines: Remnants of childhood growth plates (epiphyseal plates) that separate each epiphysis from the diaphysis.
Structure of Short, Flat, Irregular, and Sesamoid Bones
These bones lack a diaphysis, epiphyses, marrow cavity, epiphyseal lines, or epiphyseal plates.
Structural Composition: Consists of a periosteum covering two outer layers of compact bone with a single inner layer of spongy bone (termed diploe) situated between them.
Diploe contains bone marrow.
Certain flat and irregular bones contain hollow, air-filled internal spaces designated as sinuses.
Vascularization and Bone Marrow
Blood and Nerve Supply
Nutrient Arteries: Key blood vessels supplying approximately of the blood supply to the internal bone tissue. The epiphysis receives a portion of its blood from nutrient arteries as well.
Bone Marrow Types
Red Bone Marrow:
Formed of loose connective tissue supporting blood-forming hematopoietic stem cells.
The relative quantity of red bone marrow decreases progressively with age.
In adult skeletons, red bone marrow is restricted to specific sites: pelvis, femur, humerus, vertebrae, ribs, sternum, clavicle, scapula, and select skull bones.
Yellow Bone Marrow:
Composed mainly of triglycerides, adipocytes, and blood vessels.
Osteogenesis and Ossification Pathways
Ossification (Osteogenesis): The biological process of bone tissue formation.
Intramembranous Ossification
Converts embryonic mesenchymal tissue directly into osteoblasts.
Commences at a primary ossification center.
Key characteristics:
Spongy bone forms first.
Compact bone forms second.
Endochondral Ossification
Process of bone formation built upon a pre-existing hyaline cartilage model.
Initiates at a primary ossification center.
Gives rise to all bones of the body except for the skull and the clavicles.
Converts chondroblasts into functional osteoblasts.
Key Bone Cells
Osteoblasts: Cells responsible for secreting an organic matrix that subsequently calcifies to generate new bone tissue.
Osteocytes: Mature bone cells formed when osteoblasts become trapped inside small spaces called lacunae.
Bone Growth Mechanisms
Longitudinal Growth
Involves the continuous division of chondrocytes within the epiphyseal plate.
The epiphyseal plate is organized into 5 functional zones, ordered from top to bottom:
Zone of Reserve Cartilage: Contains inactive cells not involved directly in bone growth, which can be recruited if necessary.
Zone of Proliferation: Contains actively dividing chondrocytes.
Zone of Hypertrophy and Maturation: Houses mature, enlarged chondrocytes.
Zone of Calcification: Region where dead chondrocytes undergo matrix calcification.
Zone of Ossification: Contains calcified chondrocytes alongside active osteoblasts building matrix.
Appositional Growth
Growth resulting in an increase in both bone length and width.
Osteoblasts located between the bone surface and periosteum continually lay down new bone matrix.
Appositional growth in width can persist even after the epiphyseal plates have fully closed.
Hormonal Regulation of Bone
Hormones: Chemical messengers secreted by endocrine glands directly into the bloodstream to regulate physiology.
Growth Hormone:
Synthesized and released by the pituitary gland.
Present in highest concentrations during infancy and childhood, though secreted continuously throughout life.
Testosterone:
Primary male sex hormone secreted throughout life.
Promotes bone deposition and increases appositional growth.
Accelerates epiphyseal plate closure, causing growth plates to close completely by age 16 to 17.
Estrogen:
Primary female sex hormone, whose production ceases following menopause.
Induces complete epiphyseal plate closure by age 14 to 15.
Inhibits osteoclast activity to preserve bone mass.
Parathyroid Hormone (PTH): Functions directly to increase blood calcium concentrations.
Calcitonin: Functions directly to decrease blood calcium concentrations.
Bone Remodeling Dynamics
Bone Remodeling Process: A dynamic cycle where new bone is synthesized via bone deposition, and existing bone is broken down via bone resorption.
Bone formation and loss take place simultaneously, but deposition proceeds at a substantially faster rate than resorption.
Physical responses to force:
Compression: Temporary mechanical force that stimulates bone deposition.
Tension: Stretching forces applied to bone trigger bone deposition.
Pressure: Continuous, sustained pressure induces bone resorption.
Key influencing factors: Hormonal regulation and age (as systemic protein synthesis declines over time).
Cellular mechanisms:
Osteoclasts: Secrete hydrogen ions () to chemically break down bone matrix.
Osteoblasts: Secrete specific enzymes to construct and deposit bone matrix.
Division of the Skeleton
Axial Skeleton
Primary function is to protect the body core and internal vital organs.
Skull: Composed of 22 bones that encase the brain and establish the facial framework.
Vertebral Column: Composed of 33 individual bones forming the spine, sacrum, and coccyx.
Thoracic Cage: Formed by 12 pairs of ribs, the sternum, and the thoracic vertebrae.
Appendicular Skeleton
Primary function is to enable body movement.
Pectoral Girdle: Consists of the scapulae and clavicles; serves to support and anchor the bones of the upper limb.
Four Regions of the Upper Limb:
Brachium: The humerus, which is the largest and strongest bone in the upper body.
Antebrachium (Forearm): Consists of two bones—the lateral radius and the medial ulna.
Carpus (Wrist): Composed of 8 carpal bones organized into 4 distinct rows.
Manus (Hand): Composed of 5 metacarpals and 14 phalanges.
Pelvic Girdle: Composed of the os coxae (coxal or hip bones), formed by the fusion of the ilium, ischium, and pubis.
Four Regions of the Lower Limb:
Femoral: Contains the femur—the longest and strongest bone in the human body—and the triangular patella (kneecap).
Crural: Consists of two bones—the lateral fibula and the medial tibia.
Tarsal: Composed of 7 short bones forming the ankle structure.
Pedal: Composed of 5 metatarsals and 14 phalanges.
Bone Surface Features
Depressions
Openings or spaces of varying depths located within a bone structure.
Facet: A shallow, flattened or near-flat surface where two adjacent bones articulate.
Fossa: An indentation or groove in a bone into which another anatomical structure fits.
Fovea: A shallow pit.
Groove (Sulcus): A elongated indentation through which a narrow vessel or structure travels.
Openings
Passageways or holes that permit blood vessels and nerves to traverse through a bone.
Canal (Meatus): A tunnel-like passage extending through a bone.
Fissure: A narrow slit-like opening in a bone.
Foramen: A shallow or flat hole through a bone.
Projections
Bony extensions that serve as joint connection sites or attachment points for muscles, tendons, and ligaments.
Condyle: A smooth, rounded articular surface at the end of a bone.
Crest: A prominent ridge along a bone.
Head: A distinct, rounded projection located on the epiphysis of a bone.
Tubercle: A small, rounded bony projection.
Tuberosity: A large, rough tubercle projection.
Epicondyle: A small projection situated adjacent or superior to a condyle.
Spine: A sharp, slender bony process.
Process: Any distinct bony projection (a broad anatomical term).
Protuberance: An outgrowth or swelling on a bone surface.
Trochanter: A massive, unique projection found exclusively on the femur.
Line: A long, narrow ridge that is less prominent than a crest.
Cranial, Facial, and Axial Anatomy
Skull Bones
Cranial Bones: 8 total bones that form the protective cranium.
4 Single Bones: Frontal bone, Occipital bone, Ethmoid bone, Sphenoid bone.
2 Paired Bones: 2 Temporal bones, 2 Parietal bones.
Facial Bones: 14 total bones that construct the facial framework.
6 Paired Bones: Maxillary bones, Zygomatic bones, Nasal bones, Lacrimal bones, Palatine bones, Inferior nasal conchal bones.
2 Single Bones: Mandible, Vomer.
Sutures: Fibrous joints that tightly fuse the individual bones of the skull together.
Sinuses: Air-filled, membrane-lined cavities situated within specific cranial and facial bones.
Hyoid Bone: A distinct bone that serves as an attachment point for various muscles vital to swallowing and speech.
Vertebral Column Structure
Composed of 33 individual bones (vertebrae).
Intervertebral Foramen: Openings between adjacent vertebrae that allow spinal nerves to exit the spinal cord.
Vertebral Classifications:
Cervical vertebrae: 7 bones.
Thoracic vertebrae: 12 bones.
Lumbar vertebrae: 5 bones.
Sacral vertebrae: 5 fused bones forming the sacrum.
Coccygeal bones: 3 to 5 fused bones forming the coccyx.
Intervertebral Discs: 23 fibrocartilaginous pads positioned between adjacent vertebral bodies that absorb mechanical shock and bind the column together.
Nucleus Pulposus: A central, jelly-like structure functioning as a shock absorber.
Annulus Fibrosus: An outer ring composed of fibrocartilage that encapsulates the nucleus pulposus and unites adjacent vertebrae.