Aplicaciones de la Norma

Module 3 Tissue Level of the Body’s Organisational Structure

Epithelial tissue is the tissue designed for the specific function of providing cover for all the surfaces of the body. All body surfaces whether internal or external are covered by epithelial tissue. Epithelial tissue that lines the body cavities that opens to the outside is mucous membranes or mucosae. The membranes that line the entire gastro intestinal tract, respiratory tract, excretory tract and the reproductive tract are mucous membranes. On the other hand, epithelial tissue that lines the body cavities which do not open directly to the outside, are called serous membranes. Serous membranes also cover the organs that are located in those cavities that do not open directly to the outside. A thin layer of serous fluid covers the serous membranes for lubrication purposes. Movement of organs within the thorax and abdominopelvic cavity is frictionless and without abrasion by the action of the serous fluid.

Cells in epithelial tissue are closely packed with little or no intercellular spaces. The cells are arranged in one or more layers. A thin sheet of connective tissue called the basement membrane separates the epithelial tissues from its underlying structures. The basement membrane provides structural support for the epithelium and binds it to the underlying tissues.

Figure 3.1.1: Cells of Epithelial Tissue. Source: OpenStax College (2013, Page 139).

An epithelial tissue is described as simple epithelial tissue if it is organized as a single layer of cells and stratified epithelial tissue if it is formed by several layers of cells. The shapes of the cells that form an epithelial tissue is used to name it. Thus, an epithelial tissue that is made up one layer of cells that appear squeezed is called a squamous epithelial tissue, the one made from a single layer of cells that are cubical in shape are called simple cuboidal

epithelial tissue. The simple columnar epithelial tissue is made up of cells that appears as columns. When an epithelial tissue is made up of more than one layer of cells, it is called a stratified epithelial tissue. For this reason, we have stratified squamous, stratified cuboidal and stratified columnar epithelial tissues.

Figure 3.1.2: Specific Epithelial Tissues, their Location and Functions. Source: OpenStax College (2013, Page 142).

An epithelial tissue that is made up one or more cells which are specialized for synthesizing and secreting chemical substances is known as a glandular epithelial tissue or glandular epithelium. A gland is classified either as an endocrine gland which is a ductless gland that releases secretions directly into surrounding tissues and fluids or an exocrine gland that contains ducts through which its secretions leave into the external environment.

4.0 Conclusion

You learnt the structure and function of epithelial tissue and how to distinguish between simple, stratified, squamous, cuboidal and columnar epithelia tissues. You also learnt how the different types of epithelial tissues can be modified with or without ducts to function as glands or glandular tissues.

5.0 Summary

Now that you have learned how cells are organised into epithelial tissues at the cellular level of the body‘s general structure and function, you are now ready to go a little bit further by studying this third level of organisation deeper at the connective tissue level.

Self Assessment Exercise

24. Discuss the different types of epithelial tissues in relation to their location on the body and functions.

25. Stratified squamous epithelial tissue consists of

a. many layers of flat surface cells that changed from rounded to flat at the surface such as found in lining of urinary bladder

b. One layer of columnar cells with cilia on their free surfaces found in the Linings of trachea—and fallopian tube.

c. many layers of flat surface and rounded lower cells as found in the epidermis and linings of the esophagus and vagina

d. one layer of flat cells as found in the alveoli of the lungs and capillaries.

26. Transitional epithelial tissue consists of __________

a. many layers of flat surface cells that change from rounded to flat at the surface such as found in lining of urinary bladder

b. one layer of columnar cells with cilia on their free surfaces found in the Linings of trachea—and fallopian tube.

c. many layers of flat surface and rounded lower cells as found in the epidermis and linings of the esophagus and vagina

d. one layer of flat cells as found in the alveoli of the lungs and capillaries.

27. An group of epithelial tissue cells, when seen under a microscope, appear arranged in a single layer and look tall and narrow, with their nuclei located close to the base of the cells is identified as _______________

a. Columnar b. Stratified c. Squamous d. transitional

28. Which of the following is the epithelial tissue that lines the interior of blood vessels?

a. Columnar b. Pseudostratified c. simple squamous d. transitional

29. Which type of epithelial tissue specializes in moving particles across its surface and is

found in airways and lining of the oviduct?

a. Transitional b. stratified columnar

c. pseudostratified ciliated columnar d. stratified squamous