Structure and function of skin Flashcards
What is the integument system?
The skin, hair, and nails
- skin is largest and heaviest organ (15%)
What are the main functions of skin?
- barriers against dehydration infection injury solar radiation
- thermoregulation
- sensation
- repair
- vitamin D production
What are the 3 layers of the skin?
1) epidermis
outer epithelial layer
2) dermis
middle connective tissue
3) hypodermis
inner fatty later
What is the basal layer of the epidermis?
First single layer, containing stem cells and attached to the dermis.
Stem cells constantly proliferate, and are dynamic.
Daughter cells constantly move ‘up’ (distally) through the epidermis, differentiating as they go, until they are shed from the outer surface. This takes 20-50 days.
What is the stratum spinosum of the epidermis?
The spiny layer. Cells have many desmosomes here, visible as ‘spines’ between the cells. Strong bonds hold the epidermis together
What is the stratum granulosum of the epidermis?
1-4 layers of cells containing prominent granules of ‘keratohyalin’ - precursor of the protein keratin.
Also contain lamellar bodies containing lipids (seen by TEM).
Cells are differentiating to form the outermost layer.
What is the stratum corneum of the epidermis?
The outer protective layer of the epidermis. Many cells thick.
Squamous cells which have lost their nuclei and are cornified, full of ‘horny’ keratin (from keratohyalin granules), thus tough and resistant to injury.
Nonpolar lipids (waterproof) are between the cells from lamellar bodies.
What are melanocytes?
- cells responsible for pigment
Have a dendritic form. They synthesise melanosomes (pigment granules) and transfer them to basal keratinocytes through long dendrites.
Keratinocytes arrange melanin pigment in a cap distal to the nucleus. Especially found in the basal layer. Black-skinned people only have about 10% as many skin cancers as white people with the same lifestyle. It is hard to identify melanocytes using just a histological section, as they look similar to the pale Merkel cells.
What are Langerhans cells?
- cells involved in defence
Have an immune system function. They are antigen-presenting cells, like macrophages. They are dendritic cells, forming a network through the whole epidermis. They are small, pale cells in the non-basal layers of the epidermis.
What are Merkel cells?
- cells involved in sensation
Where is vitamin D3 produced?
- in the epidermis
- mostly in basal cells but also stratum spinosum
- requires uv light to be produced (and moreso in dark skin as there is a melanin barrier)
What is the dermis?
- dense, irregular connective tissue filled with collagen fibres which run in all directions
- collagen provides tensile strength, so protection against abrasion and impact
- also contains elastin, a protein complex which provides elasticitiy
- also carries blood and nerve supply for the epidermis. rich in blood vessels
Why is the dermal-epidermal border wavy?
To resist shear forces
What does the hypodermis contain?
- fat droplets
- quite richly supplied with blood which can take nutrition from the fat if it needs it, or lay down new fat
- hypodermic syringes touch this layer
- has glands, hair follicles, nerves, blood vessels
- thickest layer of skin
What are eccrine sweat glands?
normal sweat glands which secrete sweat onto skin surface, which cools the body by evaporation
