Skin Structure and Function

Question 1

Functions of Skin

Answer 1

• Thermoregulation: Vasodilation/vasoconstriction. Evaporation of sweat cools body by using latent heat from skin.
• Acts as a reservoir of blood- 8-10%.
• Protection: Physical barrier against water loss, pathogens, UV and heat. Secretes sebum to waterproof skin and kill bacteria.
• Detection of Stimuli: Corpuscles in the basement membrane detects heat and pressure.
• Excretion and absorption: Water soluble waste excreted via sweat. (Just remember absorption can occur-no examples.)
• Vitamin D synthesis: Precursor modified by UV before used to produce Vit D in liver.
  Enhances phagocytic activitiy, regulate immune response and reduce inflammation.

Question 2

How much skin per human? (Area and percentage body mass).

Answer 2

2M^2- 7%-16% of body mass

Question 3

Cells in the epidermis

Answer 3

Keratinocytes: Provide barrier function and has high turnover rate. Contains keratin intermediate filaments (tonofilaments) to provide structural integrity. Makes up 90% by cell number of epidermis.
Melanocytes: Produces and secretes melanin into nearby keratinocytes using projections.
Langerhans cells: Resident macrophages matured in red bone marrow and found in epidermis.
Merkel Cells: Forms a tactile disk at the lowest layer of epidermis to detect sensation.

Question 4

Stratum Basale/Germativum

Answer 4

A single layer of cuboidal/ columnar keratinocytes and stem cells, which divide to produce more keratinocytes. Has large nucleus, many free ribosomes, small Golgi, few mitochondria, some RER and tonofilaments.
Desmosomes hold the stratum together.

Question 5

Stratum Spinosum

Answer 5

8-10 layers of keratinocytes becoming more flattened towards the apical sides. Some retain ability to divide. In isolation, they form spine like projections with desmosomes at the ends to cling to other cells. In tissue these cells are rounded.

Question 6

Stratum Granulosum

Answer 6

3-5 layers of keratinocytes currently undergoing apoptosis and leaving behind tonofilament framework, which is assembled into keratin by keratohydralin granules.
Dying keratinocytes fuse with lamellar granules to release a lipid-rich secretion to waterproof the epidermis.

Question 7

Stratum lucidum

Answer 7

4-6 layers of dead keratinocytes found only in thick skin. High quantities of keratin and thickened cell membrane for protection.

Question 8

Stratum Corneum

Answer 8

25-30 layers of membranes containing keratin in an overlapping scale-like structure, where cells protect each other.

Question 9

Structure of Papillary Dermis

Answer 9

Contains thin collagen and elastin fibres in areolar connective tissue. Forms dermal papillae to increase surface area and fit with the epidermal ridges to resist shearing forces and hold epidermis to dermis. Epidermal ridges also form grooves in the epidermis to aid grip.
This layer also contains Meissner corpuscles and nerve endings.

Question 10

Structure of Reticular Dermis

Answer 10

Made of dense irregular connective tissue with thicker collagen and elastic fibres. Sweat and sebaceous glands are found between fibres.

Question 11

Pigmentation

Answer 11

Melanocytes can produce eumelanin (brown to black) or phenomelanin (red to yellow).
Tyrosinase converts tyrosine to melanin in a melanosome, a process that’s stimulated by UV. Melanin aggregates over keratinocyte DNA to form a protective cap to prevent DNA damage by UV.
Slight DNA damage by UV increases rate of melanin production.

Question 12

Epidermal Wound Healing

Answer 12

Cells in the stratum basale detach from the basement membrane and divide. The mass of cells spread along the membrane until they touch- contact inhibition.
Epidermal Growth Factor stimulate stem cells in the stratum basale to divide and reform the upper layers of epidermis.

Question 13

Deep Wound Healing

Answer 13

Inflammatory: Blood clot forms. Immune system stimulated to clean up pathogens and dying tissue. Blood vessel permeability increases to allow more freedom for WBCs to move. Mesenchymal tissue transported to wound.
Migratory: Blood clot turns into scab to cover cavity in the epidermis. Keratinotcytes starts to fill cavity be moving under the scab.
Fibroblasts produce glycoproteins and collagen to form scar tissue-fibrosis.
Dermal blood vessels start to reforms.
Proliferative: More keratinocytes and connective tissue form.
Maturation: Epidermis and dermis repair complete and scab is sloughed off.

Question 14

Types of Scar

Answer 14

Hypertrophic: Scar is raised but within wound boundary
Keloid: Scar exceeds wound boundary.