Chapter 6 – Bones & Skeletal Tissues

A comprehensive set of vocabulary flashcards covering key concepts related to bones and skeletal tissues, including definitions and processes.

Skeletal system

Made up of skeletal cartilages plus bone tissue (compact and spongy) with marrow, nerves, blood vessels, and periosteum/endosteum.

Functions of bone

Support, protection, movement (levers), mineral storage (Ca2+, PO4 3−), blood cell formation (hematopoiesis), triglyceride storage, and hormone production (osteocalcin).

Bone classifications by shape

Long (humerus), short (carpals), flat (sternum), irregular (vertebrae); sesamoid is a special type of short bone (patella).

Types of cartilage

Hyaline (articular, costal, respiratory, nasal), elastic (ear, epiglottis), fibrocartilage (intervertebral discs, menisci, pubic symphysis).

Avascular nature of cartilage

Cartilage heals poorly because chondrocytes receive nutrients through diffusion rather than direct blood supply.

Appositional growth

Adds matrix at the surface via perichondrial chondroblasts.

Interstitial growth

Expands from within as chondrocytes divide in lacunae.

Structure of long bone

Diaphysis (shaft) with medullary cavity; epiphyses at ends with articular cartilage; metaphyses/epiphyseal line; periosteum outside, endosteum inside.

Periosteum

A double-layered membrane with an outer fibrous layer (dense irregular CT) and an inner osteogenic layer with osteogenic cells.

Endosteum

A thin membrane lining internal bone surfaces (trabeculae and canals) containing osteogenic cells.

Red marrow location in infants

Located in the medullary cavities of long bones and spongy bone.

Red marrow location in adults

Found in the trabecular cavities of flat/irregular bones (sternum, hip) and proximal epiphyses of the humerus/femur.

Yellow marrow

Fat-rich marrow in medullary cavities that can revert to red marrow during severe anemia or blood loss.

Bone markings

Projections, depressions, and openings that serve as attachment sites, joint surfaces, and passages for nerves/vessels.

Osteon (Haversian system)

The structural unit of compact bone composed of concentric lamellae around a central canal with vessels and nerves.

Perforating (Volkmann’s) canals

Transverse canals that connect periosteum, central canals, and medullary cavity for vascular/nerve supply.

Lacunae

Small cavities that house osteocytes.

Canaliculi

Tiny channels that connect lacunae for nutrient and waste exchange.

Circumferential lamellae

Lamellae that encircle the entire bone just deep to periosteum/endosteum.

Interstitial lamellae

Remnants of old osteons found between currently existing osteons.

Spongy bone (trabecular bone)

Characterized by a lattice of trabeculae aligned along stress lines; contains lamellae and osteocytes but no osteons.

Osteogenic (osteoprogenitor) cells

Stem cells in the periosteum and endosteum that give rise to osteoblasts.

Osteoblasts

Bone-forming cells that secrete osteoid (collagen + ground substance) and initiate mineralization.

Osteocytes

Mature bone cells that monitor and maintain the bone matrix.

Bone lining cells

Flat cells on bone surfaces that help maintain the matrix.

Osteoclasts

Large multinucleate cells that resorb bone by secreting acids and proteases.

Organic component of bone

Osteoid (collagen type I + ground substance) provides tensile strength and resilience.

Inorganic component of bone

Hydroxyapatite crystals (calcium phosphates) provide hardness and resistance to compression.

Ossification (osteogenesis)

The process of bone tissue formation, including initial formation in the embryo and lifelong remodeling.

Intramembranous ossification

Process where flat bones of the skull and clavicles form.

Endochondral ossification

Process where most bones of the skeleton, including long bones, form using a hyaline cartilage model.

Steps of intramembranous ossification

(1) Ossification centers form; (2) Osteoid secreted and calcifies; (3) Woven bone and periosteum form; (4) Lamellar bone replaces woven bone.

Key steps of endochondral ossification

(1) Bone collar forms; (2) Cartilage calcifies; (3) Periosteal bud invades; (4) Diaphysis elongates; (5) Secondary ossification centers form.

Complete endochondral ossification remains

Articular cartilage and the epiphyseal plate.

Epiphyseal plate zones

Resting (reserve), proliferation, hypertrophic, calcification, ossification.

Proliferation zone activity

Chondrocytes divide, pushing the epiphysis away.

Hypertrophic zone activity

Older chondrocytes enlarge and lacunae erode.

Calcification zone activity

Matrix calcifies, chondrocytes die.

Ossification zone activity

Osteoclasts clear cartilage, osteoblasts lay down bone.

Hormones regulating bone growth

Growth hormone, thyroid hormone, and sex hormones.

Appositional growth of bone

Growth in thickness with osteoblasts adding bone under periosteum.

Epiphyseal plates closure age

About 18 years in females and 21 years in males.

Bone remodeling

Continuous process involving bone deposition by osteoblasts and resorption by osteoclasts.

Bone deposit markers

Osteoid seams and calcification front.

Osteoclast bone resorption mechanism

Acidify the resorption bay and release enzymes; dissolved products are transcytosed into blood.

Calcium homeostasis importance

Critical for nerve impulses, muscle contraction, blood coagulation, and cell division.

Role of parathyroid hormone (PTH) in calcium control

Triggers osteoclast activity to release calcium into the blood.

Role of calcitonin in calcium control

Inhibits osteoclasts and lowers blood calcium at high doses.

Wolff’s law

Bone grows or remodells in response to mechanical stress.

Examples supporting Wolff’s law

Handedness, thickened curved bone where loaded, trabecular arches.

Fracture classification by position and completeness

Position: nondisplaced vs displaced; completeness: complete vs incomplete.

Fracture classification by orientation and skin involvement

Orientation: linear vs transverse/spiral/oblique; skin: open (compound) vs closed (simple).

Common fracture types and key features

Comminuted (many pieces), compression (crushed), spiral (twist), epiphyseal (plate separates), depressed (skull), greenstick (incomplete).

Stages of fracture repair

(1) Hematoma; (2) Fibrocartilaginous callus; (3) Bony callus; (4) Remodeling.

Osteomalacia

Poor mineralization in adults due to vitamin D or calcium deficiency.

Rickets

Childhood osteomalacia with bowed legs due to unmineralized epiphyseal plates.

Osteoporosis

Condition where resorption exceeds deposit leading to porous bones.

Osteoporosis risk factors

Postmenopausal women, low estrogen, inactivity, smoking, drugs, and genetics.

Osteoporosis prevention/treatment

Weight-bearing exercise, calcium/vitamin D, avoid smoking/alcohol, and certain medications.

Paget’s disease

Excessive bone turnover leading to weak bones.

Prenatal origins of the skeleton

Develops from hyaline cartilage and fibrous membranes.

Long bone status at birth

Diaphyses mostly ossified; epiphyses largely cartilaginous.

Peak bone mass and changes

Peaks by early 20s; gradual bone loss after 30-40 years.

Definitions: Tuberosity, crest, trochanter

Tuberosity: large rounded projection; crest: narrow ridge; trochanter: large blunt projection.

Definitions: Line, tubercle, epicondyle, spine, process

Line: narrow ridge; tubercle: small rounded projection; epicondyle: raised area; spine: sharp projection.

Definitions: Head, facet, condyle, ramus

Head: expansion on a neck; facet: smooth joint surface; condyle: rounded surface.

Definitions: Groove, fissure, foramen, notch

Groove: furrow; fissure: narrow slit; foramen: hole; notch: indentation.

Definitions: Meatus, sinus, fossa

Meatus: canal-like passage; sinus: cavity; fossa: shallow basin.

Nourishment of compact bone

Periosteal vessels via perforating and central canals.

Metaphysis

Region where the diaphysis meets the epiphysis containing the epiphyseal plate.

Articular surface coverage

Hyaline cartilage reduces friction and absorbs shock at synovial joints.

Red vs yellow marrow distribution factors

Age, bone type, physiological needs determine marrow type distribution.

Trabecular alignment along stress lines

Optimizes strength with minimal mass based on mechanical loading.

Triggers for bone deposit

Mechanical stress, microdamage, and sufficient calcium/phosphate levels.

Regulators of bone beyond PTH/calcitonin

Calcitriol (vitamin D), glucocorticoids, thyroid hormone, sex hormones.

Fracture-prone bones in osteoporosis

Vertebral bodies (compression), femoral neck (hip fractures).

Distinguishing greenstick from comminuted fractures

Greenstick is an incomplete bend/break; comminuted is shattered.

Higher risk of open fractures

Increased risk of infection due to exposure through skin.

Slow healing of menisci and discs

Fibrocartilage has poor blood supply which limits nutrient delivery.

Effects of aging and disuse on cartilage and bone

Cartilage calcifies, and bone atrophies with reduced loading.

Role of periosteum in healing

Osteogenic layer provides progenitors for forming callus and new bone.

Osteocyte signaling in remodeling

Detect strain via canaliculi and coordinate activity of osteoblasts/osteoclasts.

Lab indicating bone formation increase

Elevated alkaline phosphatase suggests bone formation, like healing or Paget’s.

Vitamins critical for bone quality

Vitamin D, vitamin C, and vitamin K support different bone qualities.

Importance of epiphyseal plate fractures

Can impair future growth if damaged (Salter-Harris injuries).

Osteogenesis imperfecta (OI)

Genetic collagen defect leading to brittle, fracture-prone bones.

Impact of bed rest on bones

Weakens bones due to reduced mechanical stress affecting osteoblast activity.

Strength and lightness of flat bones

Compact bone sheets sandwich spongy diploë for strength with low mass.

Woven vs lamellar bone

Woven has random collagen, while lamellar has organized structure, making it stronger.

Enthesophyte

Bony outgrowth at a tendon or ligament attachment site due to repetitive traction.