Histology: epithelial tissue

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Epithelial Tissue

There are 10 types that are derived from ectoderm, mesoderm and endoderm embryonic germ layers. It consists of epithelial cells that make cohesive sheets (epithlia) and covers ALL body surfaces, cavities and tubes and can be for diffusion, absorbtion/secretion, physical protection or containment.

It is highly cellular, rapidly divides and always has a basement membrane. It depends on connective tissue as it has no blood vessels (avascular). The top surface (apical), sides (lateral) and bottom (basal).

Functions:

1. Tight junctions form impermeable barriers

2. Gap juntions that allow movement of molecules between cells

3. Desmosome junctions provide mechanical support

4. Hemidesmosomes: attach to the cytoskelton of basal cells to the basement membrane.

Histology is the "microscopic study of the structure, composition and function of tissues"

Tissue is a collection of specialised cells of similar morphology which together perform a specific function(s)

Differentiation is the specialization of cells.

organelle -> cell -> tissue ->organ -> organism

Histopathology is the microscopic study of diseased tissue samples to provide accurate diagnostic information.

1. Define the cause of the disease

2. Establish the mechanism of effect (how it has happened)

3. Examine structural changes to cells, tissues and organs

4. Assess changes to functional activity

Classification:

1. Number of cell layers

Simple: single layer of cells good for diffusion/absorbtion/secretion

Stratified: several layers of cells good for protection from friction and injury. Acts as a barrier to water, disease and some toxins.

2. Shape of constituent cells

Squamous: flattened cells where the height is less than the diameter.

Cuboidal: cube shaped cells where the height and diameter are similar.

Columnar: tall and thin cells where the height is 2/3x greater than the diameter.

3. Presence of surface specialisation

Cillia: hair like structures that move material from one place to another.

Microvilli: fine invaginations of the cell surface to increase SA.

Keratin: only found on the skin as a protective layer

Simple or straitified: Squamous, Cuboidal, Columnar

Simple: Ciliated columnar, Pseudostratified columnar

Stratified: Squamous keratinising or Transitional

Glands

Made from an in-growth from epithelial surface and has cell(s) that produce aqueous secretion.

Endocrine: secrete from the basement membrane to surrounding fluid

Exocrine: secrete through a duct or directly onto the apical.

Merocrine: secreted by exocytosis

Holocrine: secreted by the rupture of gland cells

Apocrine: accumulate on top of cells and then it breaks down