Skeletal System Overview

Overview

This lecture introduces the skeletal system, focusing on bone tissue, bone structure, bone development, and key functions of the skeletal system.

Four main bone cells: osteogenic cells (stem cells), osteoblasts (build bone matrix), osteocytes (maintain bone tissue), and osteoclasts (break down bone matrix).
Bone matrix consists of minerals (mainly calcium) for hardness and collagen for strength.
Lacunae are small cavities in the matrix that protect bone cells.

Compact bone: dense outer layer, made of osteons/haversian systems with central canals for blood vessels and nerves.
Spongy bone: inner tissue with trabeculae (bars) and large spaces; houses red bone marrow that produces blood cells.

Bones have markings: openings (foramina), depressions, and projections.
Bone shapes: flat (e.g., sternum), long (e.g., humerus), short (e.g., carpals), round/sesamoid (e.g., patella), and irregular (e.g., vertebrae).

Key parts: epiphysis (ends), diaphysis (shaft), compact bone (outer layer), spongy bone (inner), medullary cavity (contains yellow marrow), periosteum (outer membrane), endosteum (inner lining), and articular cartilage (joint padding).
Red marrow in spongy bone produces blood cells; yellow marrow (adipose) in the medullary cavity stores fat and can convert to red marrow if needed.

Endochondral ossification: most bones form from a cartilage model (hyaline), with bone replacing cartilage during fetal development through growth plates (epiphyseal plates).
Intramembranous ossification: flat bones form directly from fibrous membranes.
Growth hormone stimulates cartilage growth for bone lengthening during childhood.

Osteoblasts build bone; osteoclasts sculpt and reshape it.
Bone fractures heal first with a hematoma (blood clot), followed by osteoblast and osteoclast activity to repair and reshape bone.

Hypercalcemia (high blood calcium): thyroid releases calcitonin, activating osteoblasts to store excess calcium in bone.
Hypocalcemia (low blood calcium): parathyroid glands release PTH, activating osteoclasts to release calcium from bone.

Provides support and body shape.
Stores minerals (mainly calcium) and lipids (in yellow marrow).
Produces blood cells (hematopoiesis) in red marrow.
Protects organs (e.g., skull for brain, thoracic cage for heart/lungs).
Facilitates movement by providing attachment points for muscles and forming joints for motion.
Enables body growth by lengthening long bones during development.

Osteogenic cell — stem cell that produces all other bone cell types.
Osteoblast — cell that builds bone matrix.
Osteocyte — mature bone cell that maintains bone tissue.
Osteoclast — cell that breaks down bone matrix.
Compact bone — dense outer bone tissue with osteons.
Spongy bone — inner bone tissue with trabeculae and marrow spaces.
Lacunae — small spaces in bone matrix holding bone cells.
Epiphysis — end of a long bone.
Diaphysis — shaft of a long bone.
Periosteum — outer membrane covering bone.
Medullary cavity — central cavity in long bones containing marrow.
Red marrow — tissue that forms blood cells.
Yellow marrow — fat-storing tissue in bones.
Endochondral ossification — bone formation from cartilage.
Intramembranous ossification — bone formation from membranes.
Epiphyseal plate — growth plate of cartilage where bone lengthens.
Hematopoiesis — blood cell production in marrow.
Calcitonin — hormone promoting bone formation to lower blood calcium.
Parathyroid hormone (PTH) — hormone promoting bone breakdown to raise blood calcium.

Review textbook chapters on bone tissue, bone structure, and bone development.
Study diagrams showing bone anatomy and bone cell types.
Prepare to learn the names and features of individual bones in the next chapter.