Introduction to the Tissue Level of Organization

Learning Objectives

  • Identify the main tissue types and discuss their roles in the human body
  • Identify the four types of tissue membranes and the characteristics of each that make them functional
  • Explain the functions of various epithelial tissues and how their forms enable their functions
  • Distinguish between tight junctions, anchoring junctions, and gap junctions
  • Distinguish between simple epithelia and stratified epithelia, as well as between squamous, cuboidal, and columnar epithelia
  • Describe the structure and function of endocrine and exocrine glands and their respective secretions
  • Explain the functions of various connective tissues and how their forms enable their functions
  • Identify and distinguish between the types of connective tissue: proper, supportive, and fluid
  • Describe the characteristics of muscle tissue and how these enable function
  • Identify the three types of muscle tissue
  • Compare and contrast the functions of each muscle tissue type
  • Explain how muscle tissue can enable motion
  • Discuss the characteristics of nervous tissue and how these enable information processing and control of muscular and glandular activities
  • Identify the classes of cells that make up nervous tissue
  • Discuss how nervous tissue mediates perception and response
  • Identify the main types of tissue membranes
  • Identify the cardinal signs of inflammation
  • List the body’s response to tissue injury
  • Explain the process of tissue repair
  • Discuss the progressive impact of aging on tissue
  • Describe cancerous mutations’ effect on tissue
This micrograph shows tissue surrounding several empty spaces. The epithelial tissue occurs at the border between the rest of the tissue and the empty spaces. The normal epithelium is composed of rectangular-shaped cells neatly organized side by side. Dark purple nuclei are clear at the bottom of the epithelial cells, where they attach to the rest of the tissue. The abnormal epithelium appears as a tangled area of purple nuclei, much thicker than the normal epithelium although no distinct cells are discernible.

Figure 1. Micrograph of Cervical Tissue. This figure is a view of the regular architecture of normal tissue contrasted with the irregular arrangement of cancerous cells. (credit: “Haymanj”/Wikimedia Commons)

The body contains at least 200 distinct cell types. These cells contain essentially the same internal structures yet they vary enormously in shape and function. The different types of cells are not randomly distributed throughout the body; rather they occur in organized layers, a level of organization referred to as tissue. The micrograph that opens this chapter shows the high degree of organization among different types of cells in the tissue of the cervix. You can also see how that organization breaks down when cancer takes over the regular mitotic functioning of a cell.

The variety in shape reflects the many different roles that cells fulfill in your body. The human body starts as a single cell at fertilization. As this fertilized egg divides, it gives rise to trillions of cells, each built from the same blueprint, but organizing into tissues and becoming irreversibly committed to a developmental pathway.