S3: The Structure and Function of Skin Flashcards
What does integuent/integuementary system refer to?
It refers to the skin, hair and nails.
It is the largest and heaviest organ of the body.
How does the skin act as a barrier?
It prevents:
- Dehydratation. This is achieved by the epidermis and lipids stop it from evaporating.
- Infection where the epidermis is a impervious barrier and also an immune system (langerhan cells)
- Injury/Abrasion - all layer contribute. The epidermis is strong and rapid healing, thick where friction occurs. The dermis has collagen so is tough and the hypodermis acts as a shock cushion.
- Solar radiation where the stratum corneum in the epidermis contains melanin pigment.
How does the skin thermoregulate and insulate?
The hypodermis acts as an insulator and it regulates temperature via thermoreceptors.
It is also a homeostatic organ, regulating body temperature via sweat production and blood flow, e.g. gym and snow. It is not a fluid homeostatic mechanism, as we do not adjust our fluid volume by controlling sweat production, but we do lose water through skin.
Functions of the skin
- Barrier
-Thermoregulation - Insulator
- Sensation via nerves and receptors
- Repair - Epidermis normally proliferates and dermis-fibroblasts fills gaps in skin with new collagen that
epidermis can attach to. - Vitamin D production - the skin is also a secretory organ and the epidermis is the site of production
What are the three layers of the skin?
- Epidermis
- Dermis
- Hypodermis
What does the skin contain?
- Glands
- Hairs
- Sense Organs
Briefly describe the three layers of the skin
Skin is composed of the thin epidermis on the top which is the part continuously growing and being shed.
The dermis is much looser connective on which the epidermis sits.
The subcutic/hypodermis is the inner fatty layer
Describe the histology of the layers of the skin
The cells in the epidermis are very close together giving a very intense whereas the tissue in the dermis is much looser with cells further apart so it stains less intensely. The dermis layer is thicker than epidermis in the tissue section.
Fat doesn’t stain at all so it appears as the white round bits.
Give examples of epidermis being thin and thick in different parts of the body
Thick epidermis e.g. heel
Thin epidermis e.g. abdomen
Name the four main layers of the epidermis
- Stratum basale
- Stratum spinosum
- Stratum granulosum
- Stratum corenum
Describe the stratum basale
It is the layer that is on the bottom, at the base of the epidermis and top of dermis.
Stratum basale is a single layer containing stem cells that divide and push upwards. As they move up, they differentiate and they get more glattened until they are shed from the outer surface.
Describe the stratum spinosum
This is the layer above the stratum basale.
The layer looks spiny because it contains lots of desmosomes. These are connections between cells that hold the cytoskeletons of cells together.
They are strong cellular adhesions holding the epidermis together making the skin into a good barrier.
Describe the stratum granulosum
There are two things in these granular cells:
- Keratohyalin granules (precursor to keratin).
- Lamellar bodies that are full of lipids.
Both these things differentiate to form the top layer (stratum corneum).
Describe stratum corneum
This is the top layer. They are squamous cells that have lost their nuclei and are cornified (full of ‘horny’ keratin from keratohyalin granules) so they are touch and resistant to injury.
Non polar lipids (waterproof) are between the cells and they come from lamellar bodies.
Why is the skin oily and soft but nails and hair hard?
Most skin is oily and soft, this is because the cells contain soft keratin. However other parts such as nails and hair contain hard keratin.
Does the epidermis have blood supply?
No
What is the stratum lucideum?
It is the clear layer containing immature keratin that is halfway between stratum granulosum and stratum corneum.
What are the 3 other epidermal cell types in the skin (that aren’t part of the skin)?
- Melanocytes (pigment)
- Langerhans cells (defence)
- Merkel cells (sensation)
Describe role and mechanism of melanocytes in the skin
Melanocytes allow pigmentation in the skin. Melanocytes release melanin which is taken up by surrounding cells - the rate at which it is processed determines colour of skin.
They do this by synthesisng melanosomes (pigment granules) and transfers them to basal keratinocytes though long dendrites.
- Melanin pigment is mostly in basal epidermis
- Colour of skin depends on presence of eumelanin
What is vitiligo?
It is the loss of melanocytes, causing change in pigmentation.
Describe role and mechanism of Langerhans cells
Langerhans cells are immune cells that act as antigen presenting cells. They are also dendritic cells forming a network.
What are Merkel cells?
They are sensory cells in the skin associated with nerve endings.
Describe vitamin D production
- Vitamin D3 is made in the epidermis
- It occurs mostly in stratum basale but also in stratum spinosum
- It requires UV light and more UV in darker skin due to melanin barrier
- It is converted to active form in liver and kidney : 1,25 dihydroxyvitamin D3
What is vitamin D deficiency called?
Vitamin D is commonly deficient in the UK. In adults it is called osteomalacia and in children it is called rickets.
