Aim:
To study the structural characteristics of Epithelial and connective tissue and Microscopically identify the given slides.
Objectives:
- Be able to identify each tissue type.
- Be able to identify associated structures.
- Know the location of each tissue type.
- Know the function of each tissue type.
INTRODUCTION: Tissue
A tissue is a group of cells that usually have a common origin in an embryo and function together to carry out specialized activities. The structure and properties of a specific tissue are influenced by factors such as the nature of the extracellular material that surrounds the tissue cells and the connections between the cells that compose the tissue.
Body tissues can be classified into four basic types according to their structure and function:
- Epithelial tissue covers body surfaces and lines hollow organs, body cavities, and ducts; it also forms glands. This tissue allows the body to interact with both its internal and external environment.
- Connective tissue protects and supports the body and its organ. Various types of connective tissue bind organs together, store energy reserves as fat, and help provide the body with immunity to disease-causing organisms.
- Muscular tissue is composed of cells specialized for contraction and generation of force. In the process, Muscular tissue generates heat that warms the body.
- Nervous tissue detects changes in a variety of conditions inside and outside the body and responds by generating electrical signals called nerve action potentials( nerve impulses) that activate muscular contraction and glandular secretion.
EPITHELIAL TISSUE
An epithelial is a layer or sheet of cells that covers a surface or lines a cavity. Functions of epithelia include formation of a protective layer ( epidermis), absorption of water and solutes ( intestine), secretion ( intestine, various glands) and excretion(kidney tubules).
Classification of epithelia is generally based upon two criteria: number of cell layers and cell shape.
I. Number of cell layer
- Simple epithelia are one cell layer thick
- Stratified epithelia are two or more cell layers thick
- Pseudostratified epithelium is an intermediate type that appears stratified but really is one cell layer thick.
II. Cell shape
- Squamous
- Cuboidal
- Columnar
The shape of epithelial cells may be squamous, cuboidal or columnar; intermediate forms are often encountered. Stratified epithelia are classified according to the shape of the cells at the free surface and can be squamous, cuboidal, columnar, or transitional. Transitional epithelia line cavities in the urinary tract, which may be distended, and the thickness of the epithelium varies with the degree of distention.
Beneath the layer of epithelial cells is an underlying non-cellular structure known as the basal lamina, which is secreted by the epithelial cells. The basal lamina is often associated with an additional layer secreted by other cells. Together the basal lamina and the underlying layer make up the basement membrane, which can usually be seen with light microscopy. Higher magnification(e.g., electron microscopy) is usually required to resolve the basal lamina.
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