Human body structural levels 

The human body may be examined at four structural levels as:

  • cell
  • tissue
  • organ
  • system

Cells:
The human body consists of cells, The smallest structural and functional units.

figure 1. different type of cells

Tissues:

Groups of cells and extracellular matrix which are similar in morphology and function make up the body tissues.

There are four main types of tissues:

  • Epithelial tissue
  • Connective tissue
  • Muscular tissue
  • Nervous tissue

figure 2. one type of epithelial tissue (Simple columnar epithelium)

figure 3. connective tissues

figure 4. muscle tissues

figure 5. composition of nerve tissue

Organs:
Several different kinds of tissues are further organized in particular ways to form organs.
But they have different names.

For examples:

Stomach

Macrostructure just like a J- shaped sac.

Epithelium: covers the inner and outer surfaces

Connective tissue: submucosa

Smooth muscle: between them

Nervous tissue : neurons and nerve fibers are distributed inside the wall of stomach.

figure 6. stomach

Systems:

Several organs with related functions together form systems.

There are eight major systems in the body:

  • Nervous system
  • Circulatory system
  • Respiratory system
  • Digestive system
  • Urinary system
  • Reproductive system
  • Endocrine system
  • Motor system (skeletal and muscular system)
  • Integumentary system or Exocrine systemic

figure 7. human body systems

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