Chapter 4, Problem 1RQ

List the general characteristics of epithelium, and then describe the basic types of epithelial tissues in terms of specific characteristics and functions.

Summary Introduction

To list and describe: The general characteristics of epithelium and describe the basic types of epithelial tissues in terms of specific characteristics and functions.

Introduction: Tissue organization is a level of organization formed structurally and functionally by similar group of cells and intercellular materials that are observed in multicellular organisms. The organization of specialized tissues varies and depends on the complexity of the organism, structure and function of the cells, and environment of the organism.

Explanation of Solution

The general characteristics of epithelium (epithelial tissue) are as follows:

1. 1. Cellularity: Epithelial tissues consist of densely packed cells with least or no extracellular matrix between the cells.
2. 2. Polarity: Epithelial tissues consist of an apical surface (made up of either microvilli or cilia) and basal surfaces (made up of basal lamina).
3. 3. Attachment to the basement membrane: The basal surface of the epithelial tissues is bounded to thin basement membrane to form a selective molecular barrier between the epithelial tissue and the underlying connective tissue.
4. 4. Avascularity: Epithelial cells lack blood vessels for receiving nutrients instead the nutrients are obtained directly from the apical surface or across the basal surface through diffusion.
5. 5. Extensive innervation: It can detect slight changes that occurred in the region at which it is present because epithelial cells are richly supplied by the nerve tissue.
6. 6. High regeneration capacity: Epithelial cells possess high regeneration capacity and can undergo frequent cell divisions.

The basic types of epithelial tissues in terms of specific characteristics and functions are as follows:

Types of epithelium	Characteristics	Function
Simple Squamous epithelium	Single layer of epithelial cells that are flat, wide, and irregular in shape with a flattened nucleus.	It allows diffusion of substances through this layer.
Simple cuboidal epithelium	Single layer of epithelial cells that are thick and cube shaped with a spherical nucleus.	It helps in absorption and secretion.
Simple columnar epithelium	Single layer of epithelial cells that are slender and taller in shape with an oval cell nucleus.	This tissue can absorb or secrete substances and may contain cilia to move substances.
Pseudo-stratified epithelium	It lines the nasal passage, throat, reproductive tract, and other parts where cilia are present.	This layer sweeps mucus or some other fluid across the surface of a tissue.
Stratified squamous epithelium	Two or more layers of epithelial cells which are flat, wide, and irregular in shape with a flattened nucleus.	It deals with protective function.
Stratified cuboidal epithelium	Two or more layers of epithelial cells that are cube shaped with a spherical nucleus.	It deals with protective function.
Stratified columnar epithelium	Two or more layers of epithelial cells those are slender and taller in shape with an oval cell nucleus.	It deals with protective function.