Skin

Question 1

Define Skin

Answer 1

An organ composed of different tissues:

• Epidermis (epithelial tissue)
• Dermis (connective tissue)
• Subcutaneous level (adipose tissue)
• Extra structures: glands, blood vessels and nerves, hairs

Question 2

Organ vs Tissue?

Answer 2

Tissues are groups of similar cells that have a common function. An organ is a structure that is composed of at least two or more tissue types and performs a specific set of functions for the body.

Question 3

Describe the different layers of the epidermis and their composition

Answer 3

1) Stratum corneum
- cutaneous barrier
- keratinised squamous stratified epithelium
- no nuclei
- no cell junctions
- layer varies thickness depending on region (thicker on feet, thinner on fingers)

2) Stratum granulosum
- mechanisms responsible for skin impermeability are found

3) Stratum spinosum
- increase in mechanical adhesions

4) Stratum basale
- regenerative capacity (unipotent stem cells of epithelial tissue)
- cuboidal cells kept together by junctions
- attached to basement membrane

Then basement membrane then dermis

Question 4

What is the function and importance of keratinocytes?

Answer 4

Keratinocytes are the predominant cells in the epidermis, which are constantly generated in the basal lamina and go through maturation, differentiation, and migration to the surface

Functions:
1) Produce keratin in granules and organise themselves into filaments responsible for structural integrity of cell

2) In spinous and granulosum Layers: keratinocytes produce lamellar bodies (vesicles) containing glycosphingolipids, phospholipids and ceramides > secreted between granulous and corneum layers
- these compounds create a cell envelope (lipid covering) on external side of stratum granulosum > key for impermeability

Hydro-repellent Barrier of Skin

• Cellular Covering: layer of insoluble proteins (very rich in PROLINE) mechanically strengthens plasma membrane
• Lipid Covering: lipids anchored to cell surface makes it water repellent

Also Impermeability is increased by tight junctions in deeper layers

Question 5

Which cell types are present in the epidermis?

Answer 5

1) Keratinocytes
2) Immigrant cells
- Melanocytes
- Langerhan Cells
- Merkel Cells

Question 6

What are the roles of the Immigrant Cells of the Epidermis?

Answer 6

MELANOCYTES:

• originate from neural crest
• located in basal and spinous layers
• produce melanosomes which contain melanin
• melanin protects against sunlight and melanocytes are activated by sun exposure
• don’t form junctions In Spinous and Granulosum Layers: keratinocytes, instead they interact through production of melanosomes which are endocytosed by keratinocytes > form MELANIN UNIT

LANGERHANS CELLS
- originate from monocytes
- located in spinous layer
- Immune cells of the skin: active in phagocytosis and expose parts of the antigen on the plasma membrane > antigen-presenting cells
> then they can migrate to basal membrane, pass into blood/lymphatic vessels and reach lymph nodes > stimulate immune system to produce immunological reaction

MERKEL CELLS

• mechanoreceptors: feel pressure and tension
• located in basal layer
• connected through desmosomes to the keratinocytes