Anatomy Concept 1: Skeletal System

4 tissue types in bone

Connective, nervous, epithelial, and muscle tissue.

Total bones in human body

206 bones, making up about 1/5th of body weight.

Skeleton replacement rate

The skeleton completely rebuilds itself every 7-10 years.

Support function of skeletal system

Provides a rigid framework holding up the entire body.

Protection function of skeletal system

Guards vital organs like the brain (skull) and heart (rib cage).

Movement function of skeletal system

Skeletal muscles use bones as levers at joints via tendons.

Storage function of skeletal system

Stores minerals (calcium, phosphate) and energy as fat in yellow bone marrow.

Hematopoiesis

Blood cell formation that occurs in red bone marrow.

Hormone production by bones

Produces osteocalcin to regulate insulin, glucose, and blood calcium levels.

4 main bone shapes

Long, short, flat, and irregular bones.

Long bones characteristics

Longer than wide, mostly in limbs, act as levers (e.g., femur, humerus).

Short bones characteristics

Cube-shaped for support and stability (e.g., carpals, tarsals).

Sesamoid bones

Short bones embedded within tendons, like the patella (kneecap).

Flat bones characteristics

Thin, flat, and curved with large surface areas for muscle attachment (e.g., sternum, ribs).

Irregular bones characteristics

Highly specialized shapes like vertebrae and hip bones.

General internal bone structure

Dense compact bone on the outside surrounding porous spongy bone on the inside.

Osteon

The basic structural unit of compact bone; long cylinders acting as weight-bearing pillars.

Haversian (central) canal

Runs through the middle of each osteon, containing blood vessels and nerve fibers.

Trabeculae

Tiny bone struts in spongy bone that resist stress and house bone marrow.

3 types of bone markings

Projections (attachment), surfaces (joints), and depressions/openings (vessels/nerves).

Osteocytes

Cells that maintain bone structure, housed in gaps called lacunae.

Osteoblasts

Bone cells that build and construct bone by calcifying it.

Osteoclasts

Bone cells that break down and absorb bone tissue during remodeling.

Ossification (osteogenesis)

The process of bone tissue formation.

Intramembranous ossification

Bone develops from a fibrous membrane (e.g., skull bones, clavicle).

Endochondral ossification

Bone develops by replacing cartilage (e.g., all other bones).

Epiphyseal plates

Areas where cartilage remains to allow bone elongation during growth.

Purpose of bone remodeling

Prevents calcium in bones from crystallizing and becoming brittle.

Bone resorption

Osteoclasts digest calcium phosphate, returning calcium and phosphate to the blood.

Fracture treatment steps

Reduction (realignment) and immobilization (keeping stable to heal).

4 steps of bone repair

Hematoma forms, fibrocartilaginous callus forms, spongy bone replaces callus, remodeling.