Skeletal System and Joints Review

What are the main functions of the skeletal system?

Support, protection, movement, mineral and fat storage, blood cell production, acid-base balance, and hormone production.

What is hematopoiesis?

Production of blood cells in red bone marrow.

What does yellow bone marrow store?

Fat (triglycerides).

What is the axial skeleton?

The central skeleton: skull, vertebral column, ribs, and sternum; 80 bones.

What is the appendicular skeleton?

The limbs and pectoral and pelvic girdles; 126 bones.

How many bones are in the typical adult skeleton?

206.

What are examples of long bones?

Femur, humerus, tibia, metacarpals, and phalanges.

What are examples of short bones?

Carpals and tarsals.

What are examples of flat bones?

Skull bones, ribs, sternum, and scapula.

What are examples of irregular bones?

Vertebrae.

What is a sesamoid bone?

A bone that develops within a tendon, such as the patella.

What do osteogenic cells do?

Develop into osteoblasts.

What do osteoblasts do?

Build bone by secreting osteoid.

What do osteocytes do?

Maintain bone matrix and detect mechanical stress.

What do osteoclasts do?

Resorb (break down) bone.

How does an osteoblast become an osteocyte?

It becomes trapped in the matrix it secretes.

What is osteoid?

The organic bone matrix, rich in collagen.

What provides bone flexibility?

Collagen in the organic matrix.

What provides bone hardness?

Mineral salts, especially calcium phosphate as hydroxyapatite.

Why does the body store calcium in bone?

To support bone structure and maintain calcium for muscle contraction, nerve signaling, and clotting.

Why is phosphate important?

It mineralizes bone and is needed for ATP, DNA, RNA, and membranes.

Where is parathyroid hormone (PTH) produced?

Parathyroid glands.

What triggers PTH secretion?

Low blood calcium.

What does PTH do?

Raises blood calcium by promoting bone resorption indirectly, kidney calcium conservation, and calcitriol activation.

Where is calcitonin produced?

C cells of the thyroid gland.

What does calcitonin do?

Inhibits osteoclasts and tends to lower blood calcium; its role in adults is relatively minor.

Where is active vitamin D (calcitriol) produced?

Vitamin D from skin/diet is processed in liver and activated in kidneys.

What does calcitriol do?

Increases intestinal absorption of calcium and phosphate, supporting mineralization.

Which hormone raises blood calcium when it is low?

PTH.

Which hormone increases intestinal calcium absorption?

Calcitriol (active vitamin D).

What is the diaphysis?

The shaft of a long bone, mainly compact bone.

What are epiphyses?

The enlarged ends of a long bone, containing spongy bone.

What is the metaphysis?

The region between the diaphysis and epiphysis.

What is the medullary cavity?

The central cavity of the shaft containing marrow.

What is articular cartilage?

Hyaline cartilage covering joint surfaces to reduce friction.

What is the periosteum?

Outer connective tissue covering bone except at articular cartilage; involved in nourishment, attachment, and repair.

What is the endosteum?

Thin lining of internal bone surfaces, involved in remodeling.

What is compact bone?

Dense bone tissue organized into osteons.

What is spongy bone?

Lightweight internal bone tissue organized into trabeculae with marrow spaces.

What is an osteon?

A cylindrical structural unit of compact bone.

What is a central (Haversian) canal?

An osteon canal containing blood vessels and nerves.

What are concentric lamellae?

Rings of mineralized matrix surrounding a central canal.

What are lacunae?

Small spaces containing osteocytes.

What are canaliculi?

Tiny channels connecting osteocytes and nutrient sources.

What are perforating (Volkmann) canals?

Canals connecting vessels and nerves across osteons.

What are trabeculae?

Thin plates or beams of spongy bone arranged largely along stress lines.

Why do trabeculae align along stress lines?

To resist mechanical loading efficiently without excessive weight.

Does spongy bone contain typical osteons?

No; it is arranged into trabeculae.

What is the epiphyseal plate?

Hyaline cartilage growth plate allowing long bones to lengthen.

What is the resting zone of the growth plate?

Reserve cartilage anchoring the plate near the epiphysis.

What happens in the proliferative zone?

Chondrocytes divide and form columns.

What happens in the hypertrophic zone?

Chondrocytes mature and enlarge.

What happens in the calcified matrix zone?

Cartilage calcifies, chondrocytes die, and osteoblasts deposit bone.

What is the epiphyseal line?

Bony remnant after the growth plate closes.

What is appositional growth?

Increase in bone diameter through outer bone deposition and inner resorption.

Which cells add bone beneath the periosteum?

Osteoblasts.

Which cells resorb bone along the medullary cavity?

Osteoclasts.

What is intramembranous ossification?

Bone forms directly from mesenchymal connective tissue; common in flat skull bones.

What are the basic steps of intramembranous ossification?

Mesenchymal cells become osteoblasts → osteoid forms and calcifies → woven bone develops → mature bone remodels.

What is endochondral ossification?

Bone forms by replacing a hyaline cartilage model; forms most long bones.

What are the basic steps of endochondral ossification?

Cartilage model → bone collar and cartilage calcification → primary center in shaft → secondary centers in ends → residual articular cartilage and growth plates.

Where is the primary ossification center?

Diaphysis (shaft).

Where are secondary ossification centers?

Epiphyses (ends).

What is bone remodeling?

Resorption of old/damaged bone followed by new bone formation.

How does exercise affect bone?

Weight-bearing and resistance loading stimulate adaptation and help maintain or increase bone strength.

What is Wolff's law?

Bone adapts its structure to the mechanical loads placed on it.

What is a fracture?

A crack or break in bone.

What is a closed fracture?

A fracture with intact skin.

What is an open fracture?

A fracture communicating with the outside through a wound.

What is a comminuted fracture?

Bone broken into several fragments.

What is a greenstick fracture?

An incomplete fracture, especially common in children.

What is a spiral fracture?

A fracture line twisting around the bone.

What is a transverse fracture?

A break across the shaft.

What is an oblique fracture?

A diagonal break.

What are the four stages of fracture healing?

Hematoma → fibrocartilaginous (soft) callus → bony (hard) callus → remodeling.

What happens during hematoma formation?

Broken blood vessels bleed; a clot forms and inflammation begins.

What is a soft callus?

Temporary collagen-and-cartilage bridge across the fracture.

What is a hard callus?

Spongy bone replacing the soft callus.

What happens during fracture remodeling?

Excess bone is removed and bone shape and strength are gradually restored.

What is hyaline cartilage used for in the skeleton?

Articular surfaces, growth plates, endochondral bone templates, and flexible support.

Why does cartilage heal slowly?

It lacks blood vessels (is avascular).

What is an articulation?

A joint where bones, or bone and cartilage, meet.

What is structural joint classification based on?

Material connecting bones and presence or absence of a joint cavity.

What is functional joint classification based on?

Amount of movement permitted.

What are the three structural joint classes?

Fibrous, cartilaginous, and synovial.

What is a fibrous joint?

Bones connected by dense fibrous connective tissue, without a joint cavity.

What is a cartilaginous joint?

Bones joined by hyaline cartilage or fibrocartilage, without a joint cavity.

What is a synovial joint?

A freely movable joint with a fluid-filled joint cavity.

What are the three functional joint classes?

Synarthrosis (immobile), amphiarthrosis (slightly mobile), diarthrosis (freely mobile).

What is a synarthrosis?

An immobile or nearly immobile joint, such as skull sutures.

What is an amphiarthrosis?

A slightly mobile joint, such as the pubic symphysis.

What is a diarthrosis?

A freely movable joint; all synovial joints are diarthroses.

What is a suture?

Fibrous joint between skull bones.

What is a syndesmosis?

Fibrous joint joined by ligament or interosseous membrane.

What is a gomphosis?

Fibrous joint anchoring a tooth in its socket.

What is a synchondrosis?

Cartilaginous joint joined by hyaline cartilage.

What is a symphysis?

Cartilaginous joint joined by fibrocartilage.

What is the articular capsule?

Outer fibrous capsule and inner synovial membrane enclosing a synovial joint.

What does the synovial membrane do?

Produces synovial fluid.

What does synovial fluid do?

Lubricates the joint and nourishes articular cartilage.