Tissues and a Introduction to the Epithelium

Levels of Organization

atoms→molecules→organelles→cells

→tissues

In the body, tissues can be classified into the following functions:Epithelial – cover 1

Connective – support 2 Movement – muscle 3

Control – nervous 4

Epithelial Tissues

• Epithelial cells can be classified into 2 types, those that cover surfaces and cavities and those that form a glandular function.

Epithelial tissues have the following functions:

• Protection

• Absorption

• Filtration

• Excretion

• Secretion

• Sensory Reception

Characteristics of epithelial tissues:

• Epithelial cells have an upper or free surface.

Characteristics of epithelial tissues:

• Epithelial cells have an upper or free surface.

• This is known as the Apical Surface

Polarity

• The apical surface can be modified by microvilli or cilia.

• Microvilli are seen with cells associated with absorption.

Polarity

• The microvilli can be so thick that it can be described as a brush boarder.

Polarity

• The bottom side of the epithelial cell is called the basal surface.

• It is supported by a non cellular, adhesive sheet called the basal lamina.

Specialized Contacts

• Epithelial cells have contact with each other.

• These lateral contacts are the desmosomes and tight junctions.

Specialized Contacts

• The tight junction forms an impermeable junction between each cell and thus prevents diffusion between the cells.

Specialized Contacts

• The desmosomes help hold the cell’s shape with anchoring junctions scattered between each cell.

Connective Tissue Support

• The basilar surface attached to a connective tissue net work.

• There are two parts. The first is the basal lamina secreted from the epithelial cell.

• The second is the reticular lamina that is made of collagen which is produced by fibroblasts.

Connective Tissue Support

• Together the basal lamina and reticular lamina form the basement membrane.

• This forms the foundations which anchor the epithelial cells.

Avascular but Innervated

• Epithelial cells do not have a blood supply

• They depend on diffusion for the delivery of nutrients and removal of wastes.

• They do have a nerve supply, innervated, for sensory function.

Regeneration

• Do to their protective function; epithelial cells need to be continually replaced.

• Mitotic figures are not uncommon.

Cancer

• Many cancers are of epithelial origin.

• The greater the mitotic index, the greater the chance of cancer.

Cancer Types

Cancer Types

• Lung cancer caused by smoking typically starts in the bronchial epithelium

1 Picture & 1000 words