Bone Cells, Energy Systems, and Muscle Contraction: Key Concepts for Biology and Physiology

Osteoblasts

Cells that build bone and increase bone density.

Osteoclasts

Cells that break down bone and release calcium into the bloodstream.

Difference between osteoblasts and osteoclasts

Osteoblasts build bone; osteoclasts break bone.

Bone density

A measure of how strong or thick bone tissue is; increases with osteoblast activity and decreases with osteoclast activity.

Osteoporosis

A condition where bone density is low due to more osteoclast activity than osteoblast activity.

Parathyroid hormone (PTH)

A hormone that increases blood calcium levels by stimulating osteoclasts.

Hyperparathyroidism

Excess PTH that causes too much bone breakdown and high blood calcium.

Homeostasis

Maintaining stable internal conditions such as blood calcium levels.

Fracture healing process

Osteoclasts clean damaged bone; osteoblasts rebuild new bone.

Calcium (Ca2+) role in bone

Stored in bones; released when osteoclasts break bone down.

ATP

The main energy molecule of the cell that stores energy in phosphate bonds.

Where energy is stored in ATP

Energy is stored in the high-energy bonds between phosphate groups.

ADP + Pi

The products of ATP breakdown after energy is released.

Myosin

The thick filament in muscle that forms cross bridges with actin.

Actin

The thin filament pulled by myosin during contraction.

Cross bridge

Temporary connection between myosin and actin during contraction.

Sliding Filament Theory

Myosin pulls actin inward to shorten the muscle using ATP.

Glycolysis

Anaerobic energy system that produces ATP quickly.

Lactic Acid System

Anaerobic pathway that produces lactic acid when oxygen is low.

Oxidative system

Aerobic energy system that produces ATP slowly but efficiently using oxygen.

Cellular respiration

Process in mitochondria that produces ATP from glucose and oxygen.