skin biology

Question 1

functions of skin: protection

Answer 1

protects body from heat, cold, chemicals, UV pollutants, bacteria and forms a very effective biological and physical barrier against water loss

Question 2

functions of skin: thermoregulation

Answer 2

the skin plays a significant role in regulation body temperature as 80% of heat is lost through skin

Question 3

functions of skin: cutaneous sensation

Answer 3

cutaneous sensation includes touch, pressure, vibration, tickle, temperature and pain. this sense is made possible by various cells and nerve endings in the skin, which sends impulses to our CNS

Question 4

functions of skin: excretion

Answer 4

metabolic waste products can be excreted from the body in small quantities via sweat

Question 5

functions of skin: adsorption

Answer 5

many lipid-soluble substances can enter the body via the skin (medical ointments)

Question 6

functions of skin: vitamin D synthesis

Answer 6

synthesis of vitamin D starts in the skin, triggered by UV light
(vitamin is essential in calcium metabolism and proper bone growth)

Question 7

what are the 3 layers of skin

Answer 7

1. epidermis
2. dermis
3. hypodermis (subcutaneous)

Question 8

main function of epidermis

Answer 8

protective barrier against moisture loss & penetration of particulate matter (includes cosmetic products) and micro-organisms

Question 9

four different types of cells in the epidermis

Answer 9

1. keratinocytes
2. langerhans cells
3. melanocytes
4. merkel (tactile) cells

Question 10

keratinocytes

Answer 10

produces keratin: tough and fibrous protein that serves to protect the skin
produce lamellar granules: release a water-repellent substance that helps waterproof the skin

Question 11

langerhans cells

Answer 11

responsible for skin immunology
- can recognise foreign microbes, engulf & destroy them.

Question 12

melanocytes

Answer 12

produce melanin: responsible for skin colour, also absorbs uv radiation, thereby protecting the skin from damage

Question 13

merkel cells

Answer 13

each merkel cell is associated with sensory nerve endings called a merkel disc, together they act as a slowly-adapting touch receptor

Question 14

5 layers of the epidermis

Answer 14

1. stratum corneum
2. stratum lucidium
   3.stratum ganulosum
   4.stratum spinosum
   5.stratum basale

Question 15

stratum basale:

Answer 15

deepest layer in the epidermis
- contains stem cells, keratinocytes, melanocytes
- new skin cells are produced and push the older cells towards the surface

Question 16

stratum corneum:

Answer 16

most superficial layer (top layer)
- horny layer consisting of 20-30 layers of dead keratinocytes
- dead cells have lost their organelles and become keratinized
- glycolipids present in this layer help waterproof the skin and prevent water loss

Question 17

keratinisation process:

Answer 17

process typically takes about 28 days
- desquamation takes place in the stratum corneum, where cells are dead, flattened and engorged with keratin. cells are then sloughed off and flake away
- balances proliferating keratinocytes that form in the stratum basale

Question 18

brick & motar structure for the stratum corneum

Answer 18

“brick” - staggered & layered lattice of keratinocytes
“motar” - intercellular lipid bilayer matrix
- mortar consists of top and bottom hydrophilic layer, middle lipophilic layer
- intercellular lipids -> cermaide, cholesterol, free fatty acids
- natural moisturising factor (NMF), hydrophillic layer -> amino acids, PCA, lactate, urea

Question 19

healthy vs eczema skin:

Answer 19

healthy:
- swollen skin cells and the extracellular lipids that surround them form the skin barrier
- water is attracted into and retained in the skin cells, causing them to swell and sit tightly together
- penetration of irritants, allergens and pathogens is blocked by the natural skin barrier

eczema skin:
- water is lost from the skin
- skin cells shrink and gaps form between them
- the extracellular lipid layers breakdown, causing cracks to form
- the breakdown of skin barrier means that irritants, allergens and pathogens can get into the skin, causing inflammation and itching

Question 20

what is the dermis made of

Answer 20

• connective tissues: collagen, elastin (proteins)
• most of the nerve endings, blood vessels, immune and lymphatic systems of the skin
• hair follicles and sweat glands

Question 21

collagen fibers & elastin fibers

Answer 21

collagen: imparts toughness and strength, asw as resistance to stretching forces

elastin fibers:
provides elasticity

Question 22

eccrine vs apocrine glands

Answer 22

eccrine:
- most abundant, palms & soles
- produce a clear, slightly salty fluid
- mainly water, inorganic cmpds (NaCl, K+, Ca2+, Mg2+) and organic cmpds (lactic acid, citric acid, formid acid)
- fluid produced is odorless
- cool the body and prevent overheating

apocrine:
- produce a milky fluid containing fatty acids
- water, proteins, carbohydrates, ammonium salts
- fatty organic cmpds broken down by bacteria living on the skin to produce a characteristic odor
- does not participate in thermoregulation