There are six levels of structural organisation that are relevant to understanding the form and function of the human body:
- The chemical level (eg. DNA)
The building blocks of the body.
- The cellular level (eg. a smooth muscle cell)
The basic structural and functional units of the body.
- The tissue level (eg. smooth muscle tissue)
Groups of cells (usually with a common embryonic origin) that work together to perform a certain function.
- The organ level (eg. the stomach)
Structures composed of multiple types of tissue that work together to perform a specific function.
- The system level (eg. the digestive system)
Related organs with a common function.
- The organismal level (eg. a human)
All the parts of the body functioning together to constitute a living creature.
The Body Systems
The human body is organised into eleven systems that are composed of related organs with a common function. However, some organs may belong to more than one of these systems. For example, the pancreas belongs to both the endocrine and digestive systems.
- The integumentary system
The principal functions are protection, detecting sensation, vitamin D synthesis (UVB activates a precuresor to calcitrol) and thermoregulation. The major components are skin, hair, nails, and sweat and oil glands.
- The muscular system
The principal functions are movement, posture, and heat. The major components are skeletal or striated muscle (usually attached to bones).
- The skeletal system
The principal functions are support and protection, storage of minerals, formation of blood cells, and storage of lipids. The major components are bones, joints, and cartilage. Red blood cells are created in red bone marrow, while lipids are stored in yellow blood marrow. Common staining techniques used for microscopy will remove fat from the sample, meaning that lipid storage cells often appear empty on the slide. Megakaryocytes are present in red marrow and are giant cells with numerous nuclei that produce platelets. Haemapoietic cells, which produce blood cells, are also found in…