Epithelial Tissue

Epithelial Tissue

1. Covers surfaces or line body cavities Or form glands e.g oil gland, hormone producing gland

   • Glands
     • • Glands make a product and secrete it. • There are TWO main types: – Firstly those that secrete onto surfaces via ducts are called Exocrine glands – Examples include sweat glands, sebaceous (oil secreting) glands, liver, pancreas etc.
     • Endocrine
       • And Endocrine glands that secrete hormones (chemical messengers) that travel around the body in the blood (help control homeostasis) – They secrete directly into the blood and do not have ducts (ductless glands) – Examples include pituitary gland, adrenal gland, Islets of the pancreas etc.

2. • Some surfaces, epithelia need to allow easy passage of materials across the layer • Some surfaces, epithelia need to protect what lies beneath • Some surfaces, epithelia need to be waterproof • Some surfaces, epithelia need to move materials over their surface

   • • To allow easy passage of materials right across the layer – epithelia need to be thin. Just a single layer of cells will do this. • To protect what lies beneath – epithelia need to be thick. Many layers of cells will do this. • To be waterproof – add a waterproofing agent. The chemical keratin will do this.

3. Classifying Epithelial Tissue

   • A single layer of cells is described as SIMPLE
   • Many layers of cells is described as STRATIFIED
   • – Flattened shape = squamous – Cube shape = cuboidal – Column shape = columnar
   • • A thin, flattened layer of cells (squamous) that is only one layer thick (simple) is described as: simple squamous • A thin, flattened layer of cells (squamous) that is many layers thick (stratified) is described as: stratified squamous • A single layer of cube shape cells (cuboidal) only one layer thick (simple) is described as: simple cuboidal etc.
   • Some epithelial cells have cilia on their surface. These epithelia are described as ciliated e.g. simple ciliated columnar epithelia
   • Simple ciliated columnar epithelia – a single layer (simple) of column shaped cells (columnar) with cilia on the surface (ciliated)
   • Microvilli Structure related to function: Why would you want to increase the surface area of a cell? To increase the rate of absorption!

4. Pseudostratified ciliated columnar epithelium Pseudo = false; So we have what appears to be layers of cells that are column shaped and each cell is covered in cilia

   • Cells that may appear to be both stratified squamous or stratified cuboidal depending on if they are stretched or not. • This epithelium is found in places that need to stretch a lot and is known as transitional epithelium • Typical of the bladder and ureters

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