Bone and the Skeletal System – Week 5

Vocabulary flashcards covering key terms and definitions from Week 5 lecture on bone and the skeletal system.

Skeletal System

The collective framework of bones, joints, cartilages, tendons, and ligaments that supports and moves the body.

Tendon

Dense connective tissue that connects muscle to bone.

Ligament

Dense connective tissue that connects bone to bone.

Bone Remodeling

Ongoing process of bone deposition by osteoblasts and bone resorption by osteoclasts, recycling ~5–7 % of bone mass each week.

Calcium Storage (in Bone)

Bones hold ~99 % of the body’s calcium, releasing or absorbing it to maintain blood levels of 9–11 mg/100 mL.

Haematopoiesis

Formation of red and white blood cells and platelets in red bone marrow cavities.

Long Bone

Bone whose length exceeds its width; has a shaft and two ends (e.g., humerus).

Short Bone

Roughly cube-shaped bone found in wrist and ankle; includes sesamoid bones like the patella.

Flat Bone

Thin, flattened, often curved bone such as the sternum, ribs, and skull bones.

Irregular Bone

Bone with complex shape not fitting other categories, e.g., vertebrae and pelvic bones.

Yellow Bone Marrow

Adipose-rich marrow in long-bone cavities that stores energy.

Red Bone Marrow

Marrow in flat bones that is the primary site of blood cell production.

Compact Bone

Dense outer layer of bone providing strength; visible to the naked eye.

Spongy Bone (Cancellous)

Light, porous bone inside; consists of trabeculae and houses marrow.

Osteoblast

Bone-forming cell that secretes osteoid and initiates mineralisation.

Osteocyte

Mature bone cell residing in a lacuna; maintains bone tissue.

Osteoclast

Large, multinucleated cell that resorbs bone matrix, releasing calcium.

Osteoid

Organic component of bone matrix made of collagen fibers and glycoproteins.

Hydroxyapatite

Inorganic mineral salts (mainly calcium phosphate) giving bone its hardness.

Diaphysis

Tubular shaft of a long bone composed of thick compact bone surrounding a marrow cavity.

Epiphysis

End of a long bone with outer compact bone and inner spongy bone.

Metaphysis

Region where diaphysis meets epiphysis; contains growth plate in children.

Epiphyseal Plate

Hyaline cartilage growth plate enabling lengthwise bone growth in children.

Epiphyseal Line

Remnant of the growth plate; marks end of longitudinal growth in adults.

Osteon (Haversian System)

Structural unit of compact bone consisting of concentric lamellae surrounding a central canal.

Lamellae

Concentric rings of bone matrix within an osteon.

Central Canal (Haversian Canal)

Channel in an osteon that houses blood vessels and nerves.

Lacuna

Small cavity within bone matrix that contains an osteocyte.

Canaliculi

Microscopic channels connecting lacunae, allowing osteocyte communication and nutrient flow.

Trabeculae

Needle-like struts forming the internal framework of spongy bone.

Intramembranous Ossification

Bone development from fibrous membranes, forming flat bones like the skull and clavicle.

Endochondral Ossification

Bone development by replacing hyaline cartilage; forms most bones.

Interstitial Growth

Lengthwise growth of long bones via cartilage division at the epiphyseal plate.

Appositional Growth

Increase in bone diameter as osteoblasts add new bone externally while osteoclasts resorb internally.

Growth Hormone (GH)

Pituitary hormone stimulating overall bone growth; modulated by thyroid hormones.

Steroid Hormones

Pubertal sex hormones that trigger growth spurts and later induce epiphyseal plate closure.

Calcitonin

Thyroid hormone that lowers blood calcium by stimulating osteoblast activity and bone deposition.

Parathyroid Hormone (PTH)

Hormone that raises blood calcium by stimulating osteoclast-mediated bone resorption.

Mechanical Stress

Physical forces on bone that stimulate remodeling and strengthening (e.g., weightlifting).

Bone Matrix

Combined organic (osteoid) and inorganic (hydroxyapatite) components forming hard yet flexible bone.

Organic Components of Bone

Cells plus osteoid; comprise ~35 % of bone mass and provide flexibility.

Inorganic Components of Bone

Mineral salts making up ~65 % of bone mass, providing hardness.

Haematoma

Blood clot that forms first step of bone fracture repair.

Soft Callus

Cartilaginous tissue that bridges a fracture during early healing.

Hard (Bony) Callus

New bone formed by osteoblasts replacing cartilage in fracture repair.

Osteoporosis

Disease where bone resorption exceeds deposition, causing brittle, porous bones.

Osteomalacia

Inadequate bone mineralisation in adults leading to soft, painful bones.

Rickets

Childhood condition of weakened bones due to vitamin D or calcium deficiency.