Human Body Systems: Bones, Joints, and Blood Fundamentals

The Human Locomotor System

The bones together form the skeleton, and the joints are the passive locomotor apparatus, which is mobilized by the muscular system.

Key Functions of Bones

• Protection: Bones form rigid walls that protect important organs, such as the skull.
• Rigidity: They provide structural rigidity to the body.
• Muscle Attachment: Bones provide sites for muscle insertions.
• Hematopoiesis: They are the place of origin for blood cells.
• Mineral Storage: Bones store minerals (e.g., chlorine, fluorine, magnesium).

Bone Classification, Structure, and Function

Bones are classified into different types based on their shape and structure:

1. Long Bones

   Long bones differ in their structure. The shaft (diaphysis) consists of a thick-walled hollow cylinder composed of compact bone (cortical bone), which surrounds a central cavity containing the bone marrow (medullary cavity). The two ends, or epiphyses, consist primarily of spongy bone tissue. A strong, fibrous membrane, the periosteum, lines the outside of the bone. Examples include the femur, humerus, and tibia.

2. Flat Bones

   Flat bones consist of two compact lamellae (layers) between which lies cancellous (spongy) bone material. Examples include the scapula and the bones of the skull.

3. Short Bones

   Short bones are made up of compact bone on the exterior and spongy bone in the interior. Examples include bones of the hand and foot.

Arthrology: The Study of Joints

Arthrology is the term applied to the study of joints, these being the union of two or more skeletal bones.

Types of Joints

1. Synarthrosis Joints

   Synarthrosis joints are fixed and allow no movement between the bones that form them. Examples include the flat bones of the skull.

2. Amphiarthrosis Joints

   Amphiarthrosis joints are slightly movable joints where the articular surfaces are separated by an intermediary structure (e.g., cartilage or ligament), allowing only slight movement. Examples include the vertebrae.

3. Synovial Joints

   Synovial joints allow a wide range of motion. Examples include the hip joint and the humeroscapular joint (shoulder).

Blood: Composition and Functions

Blood is a vital liquid formed by blood cells suspended in plasma. The human body contains approximately 5 liters of blood.

Components of Blood

1. Plasma

   Plasma is a liquid composed primarily of water, minerals, and proteins.

2. Blood Cells

   1. Red Blood Cells (Erythrocytes)

      Estimated at 4,500,000 per mm³, red blood cells contain hemoglobin for oxygen transport.

   2. White Blood Cells (Leukocytes)

      Estimated at 7,500 per mm³, their primary mission is to defend the body.

   3. Platelets (Thrombocytes)

      Numbering approximately 250,000 per mm³, platelets play an important role in blood clotting.