The Human Body: Skeletal, Muscular, and Endocrine Systems
The Skeletal System
The skeletal system is made up of bones and joints. Bones are hard, light, and strong structures that form the framework of the body and provide protection for some organs. In locomotion, bones act as rigid levers moved by muscles.
Divisions of the Skeleton
The skeleton is divided into two zones:
- Axial skeleton: Consisting of the skull, vertebral column, and thoracic cage.
- Appendicular skeleton: Consisting of the thoracic and pelvic girdles and limbs.
- Shoulder girdle: Includes two clavicles and two scapulae.
- Pelvic girdle: Composed of two innominate bones, the sacrum, and the coccyx.
Joints
Joints serve as a union between bones. Some joints are fixed (e.g., skull bones), others are semi-mobile (e.g., vertebrae), and some are mobile (e.g., hip or wrist), acting as levers.
Bones of the Chest
The chest is formed by the ribs and sternum. The ribs articulate with the dorsal vertebrae and are joined by cartilage to the sternum. There are 12 pairs of ribs: seven true ribs, three false ribs, and two floating ribs.
The sternum is a flat bone located in front of the chest.
The Locomotor System
- Metabolic role: Bones act as reservoirs of mineral salts.
- Hematopoietic function: Bone marrow is involved in the formation of blood cells.
Classification of Bones
There are 206 bones in the human body.
- Long bones: Predominant length (e.g., femur, tibia). They have three parts: central, proximal and distal extremities.
- Short bones: Similar dimensions in three directions.
- Flat bones: Two dimensions excel.
- Irregular bones: Cannot be included in the above categories.
The Muscular System
Movement results from the combined action of the muscular system (muscles) and skeletal system (bones and joints). Together, they form the musculoskeletal system.
Muscles
Muscle parts:
- Belly: The center, capable of contraction.
- Tendons: The two extremes, attached to bones. One end is the head, the other the tail.
Simple muscles have a single belly. Compound muscles contain several bellies.
Muscle Contraction
Muscle contraction is controlled by the nervous system.
- Striated muscles: Involved in voluntary movement.
- Smooth muscles: Control involuntary movements of organs.
Endocrine Diseases
Endocrine disorders have widespread effects on the body and its vital functions.
Diabetes mellitus: Due to a defect in insulin production or function.
Main Musculoskeletal Diseases
- Bone diseases: Fractures, scoliosis (curvature of the spine), osteoporosis (weakening of bones).
- Joint diseases: Arthritis (inflammation), arthrosis (degeneration), dislocations, gout (uric acid accumulation).
- Soft tissue diseases: Bruises (caused by blows), sprains (ligament injuries), strains (muscle or tendon injuries).
Health
Health is physical, mental, and social well-being.
Illness
Non-infectious diseases are due to organ malfunction, accidents, aging, or genetics, and are not contagious.
Infectious diseases are caused by pathogens (viruses, bacteria). An epidemic affects many individuals in a zone; a pandemic spreads across the land.
Defenses: The Immune System
Immunity is resistance to and ability to combat pathogens.
- Innate immunity: Physical and chemical barriers (inflammation, phagocytosis, complement system).
- Adaptive immunity: Defenses developed over time (lymphocytes, antibodies, humoral and cell-mediated responses, primary response).