Epithelia NOT COMPLETED

Question 1

How many tissues type are there and can you name them?

Answer 1

There are 4: Epithelial, Nerve, Muscular and Connective.

Question 2

Where are epithelial cell located and on what?

Answer 2

Generally boundary controlled internal and external environments

1. Cover surface to form glands.
2. Present in every organ

Question 3

Epithelia cells perform which variety of functions?

Answer 3

Skin - Protection
Glands - Secretion
Small intestine - Absorption
Lungs - Diffusion

Question 4

What are the common properties of epithelial cells?

Answer 4

Dynamic barrier (to allow an import/export of substances).

                   This is facilitated by: 1. Connected via tight junctions so decrease in free diffusion. 2. Distinct apical, basolateral domains with differing membrane properties and functions (polarised).

                            Epithelial cells are: 1. Avascular 2. Lack extracellular fibres 3. Minimal extracellular space

                                  Polarity: 1. Apical membranes- external. Example: GI tract. 2. Basolateral - Extracellular compartment

Specialisation of both surfaces.

                                 Basement Epithelial cells connected to basement membrane, provides mechanical support, control access to nutrients, ions, proteins, oxygen. This membrane regulates cell growth + division, restricting metastatic cell migration in cancer progression, ensures the survival of epithelia without blood supply.

STRUCTURE:
The basement membrane consists of two components: basal lamina - provides support, secreted by epithelial cells, and reticular lamina, anchoring basal lamina to connective tissue, and limiting contact between epithelial cells and underneath.

Question 5

List the type of glands and note their secretions?

Answer 5

Two main types:
1. Endocrine - single/different cell types that secrete directly into bloodstream.
2. Exocrine - multicellular glands have complex ducts secrete directly into epithelial cells.

Example of glands:
Sebaceous glands - secrete sebum.
Serous glands - isotonic fluid containing enzymes.
Mucus glands - secrete mucus

Question 6

Why are junctional complexes involved in the polarisation of epithelial cells?

Answer 6

Epithelial cell polarization is when these cells develop distinct top and bottom parts. This happens for several important reasons:

Special Jobs: Epithelial cells have different jobs, like absorbing, blocking stuff, or secreting substances. Polarization helps them do their jobs effectively.

Blocking Barriers: In places like the digestive tract and skin, polarization creates a barrier that stops things from moving where they shouldn’t.

Controlled Movements: Polarisation helps control the movement of molecules in and out of cells by having separate top and bottom parts.

Talking with Neighbours: Epithelial cells connect with their neighbouring cells through specific structures (junctional complexes.)

            These junctional complexes include:

1. Tight Junctions: They act like a zipper, sealing the space between cells and controlling what can pass through.
2. Adherens Junctions: These help cells stick together and play a role in deciding the overall cell organization.
3. Desmosomes: These provide mechanical strength to tissues, like glue that holds cells together.
4. Gap Junctions: They allow direct communication between cells, like little tunnels for messages.
5. Hemidesmosomes: These anchor the bottom part of cells to their surroundings.

To achieve this polarization, cells use different protein complexes and signalling pathways to organise themselves correctly. The junctional complexes are like a team that ensures cells are in the right place and can do their jobs effectively.

Question 7

How the structure of the epithelium relates to its function

Answer 7

Cell Layers:
1. Simple Epithelium: single layer of cells. Found in tissues where absorption, secretion, or filtration is the primary function. allows for efficient exchange of molecules.
For example, the lining of the small intestine is simple columnar epithelium, which is adapted for absorption.

2. Stratified Epithelium: has multiple layers of cells provides protection against mechanical stress and abrasion. #
   For instance, the skin’s outer layer is stratified squamous epithelium, which serves as a protective barrier.

Cell Shape:
1. Squamous Epithelium: Flat and thin. Well-suited for efficient diffusion and filtration. The alveoli in the lungs are lined with simple squamous epithelium to facilitate gas exchange.

2. Cuboidal and Columnar Epithelium: More specialized for secretion and absorption. Have a larger volume for housing organelles involved in these processes.
   For example, the lining of the small intestine is made of simple columnar epithelium, which is adapted for absorption.
3. Transitional Epithelium: This can change its shape to allow for stretching. It lines structures like the urinary bladder, which need to expand to store urine.

Surface Specializations:
1. Cilia: Some epithelial cells have cilia on their apical surfaces. Ciliated epithelium is found in the respiratory tract, where the cilia move mucus and trapped particles out of the airways.

2. Microvilli: On the surface of some epithelial cells, increase the surface area for absorption and are found in the small intestine to enhance nutrient absorption.

Cell Junctions:
1. Epithelial cells are closely packed, form various junctions like tight junctions, adherens junctions, and desmosomes. These junctions help maintain the integrity of the tissue, control the passage of substances, provide structural support.

2. Basement Membrane:
   Epithelial cells sit a basement membrane, which acts as barrier and support structure. Helps anchor the epithelium to underlying connective tissue, regulates movement of molecules between epithelium and surrounding tissue.

Specialised Features:
Certain epithelia have unique adaptations. For example, the epithelium in the stomach contains specialized cells called gastric pits that secrete digestive enzymes, while the epithelium in the kidney tubules has specialized cells for reabsorbing water and ions.