Introduction to the skin Flashcards
What is the largest organ in the human body?
- Skin: up to 16% of total body weight.
What does the cutis consist of?
- Epidermis and dermis.
What does the subcutis consist of?
- hypodermis (this is the buffer layer between skin and underlying material).
What are the functions of the skin?
- barrier (abrasion, fluid, immune).
- thermoregulation.
- VitD3 production.
- storage (fat and fluid).
- sensory information.
What is hirsute skin?
- Hairy skin.
What is glabrous skin?
- Hairless skin.
What is acral skin?
- Skin affecting body protrusions e.g. Finger tips, knuckles, elbows, knees.
- this skin will be hairless.
Where is hairless skin found?
- Acral skin: e.g. Fingertips, elbows etc.
- Epithelial transition zones of the lips and anus.
- Parts of outer genitals.
Name some appendages to skin.
- Nail, hair and glands (all epidermal in origin).
What are the three layers of skin?
- Epidermis (closest to surface), dermis and hypodermis (buffer layer between skin and underlying material).
Where do the nail, hair and glands originate?
- Although derived from the epidermis the base of all skin appendages is located in the lower dermis and subcutis.
What is the collective name for the skin + appendages?
- integument.
In wound healing can the appendages be restored?
- No.
What secretes next to the hair shaft?
- holocrine sebaceous glands.
- apocrine sweat glands.
What happens when the growing hair germ invades the underlying stroma?
- It forms a hair follicle with associated glands.
- it induces the formation of the arrector pili muscle.
What does the follicular unit (or pilo-sebaceous) consist of?
- Hair follicle + arrector pii muscle + sebaceous gland.
Name 2 procedures for hair restoration?
- Follicular unit extraction and transplantation.
What does a hair transplant consist of?
- Transplanted are small bundles consisting of 1-4 hair follicles and the sebaceous glands, arrector pii muscles and connecting tissue that accompany and support them.
What is an infundibulum?
- Cup or funnel in which a hair follicle grows, it’s continuous with surface, site where the ducts of the hair-associated glands end, initial site of inflammation.
What is acne?
- Result of blocked infundibulum (usually due to an initial plug of keratin and sebum).
Where are stem cells for hair located?
- In the bulge (of mature follicle).
What are the characteristics of a sweat gland?
- An eccrine germ invades the underlying stroma and forms an eccrine sweat gland .
- predominant type of sweat gland in primates.
- only gland not associated with hair, I.e. They have their own separate opening.
- have several million eccrine glands over the body surface.
- estimated aggregate mass of about 100 grams.
Name unusual apocrine glands.
- the glands of Moll at the eye lashes: active from brith.
- the ceruminous glands in the external ear canal, already active before birth.
- thought to have an antimicrobial function.
Name some hair germs that may develop into glands without associated hair.
- sebaceous meibomain glands forming the tarsal plate of the eyelids.
- apocrine mammary glands of the breast.
What are the five different cell types of the epidermis?
- keratinocytes (barrier) - 90%.
- melanocytes (uv protection) - pigment cells 5%.
- merkel cells (transduction of fine touch) mechanoreceptor cells 1%.
- T cells, NK cells (immune defence) patrolling lymphocytes.
- langerhans cells (immune defence) resident dendritic cells together about 4%.
What are the characteristics of skin cancer?
- Most common form of cancer, can derive from any epidermal cell type, each has a different prognosis and treatment.
Name different types of skin cancer.
- squamous cell carcinoma (20%).
- basalioma (75%) = slow but destructive.
- malignant melanoma (5%) = 75% of deaths.
- langerhans cell histiocytosis = rare, variable.
- cutaneous T cell lymphoma (type of non Hodgkin lymphoma) = relatively rare, variable.
- merkel cell carcinoma = very rare, highly aggressive.
What is a keratinocyte?
- Predominant cell type in the epidermis, the outmost layer of the skin, constituting 90% of cells found there.
- Primary function is the formation of a barrier against environmental damage by pathogenic bacteria, fungi, viruses etc.
- once pathogens invade the upper layers of epidermis keratinocytes react by inducing proinflammatory mediators e.g. Chemokines which attract leukocytes to the site of pathogen invasion.
When thinking about keratinocyte cross linking, explain epithelial sheet formation?
- Adherens junctions = actin- actin.
- Desmosomes = keratin-keratin.
When thinking about keratinocyte cross linking, explain anchorage and signalling?
Focal adhesions = actin - fibronectin
Hemi-desmosomes = keratin - laminin
Name the keratinocyte layers from outmost to innermost.
- Cornified layer, granular layer, spinous layer, basal layer.
What is proliferation?
- Constant cell renewal.
What is desquamation?
- Shedding of surface cells.
What are corneocytes?
- “Bricks”.
- Outer cell envelope: lipids (template for extracellular lipid bilayers).
- Inner cell envelope: insoluble proteins, structural stability of the individual cells.
What are extruded lipids?
- “Mortar” arranged in multi lamella membrane sheets.
What are corneodesosomes?
- “Rivets” hold the cellular sheet together - overall integrity.
Where do the keratinocytes form a waterproof barrier?
- In the granular layer this is one of the most important of all epidermal functions.
The cornified layer needs to be hydrated in order to retain water, how does it stay hydrated?
- Natural moisturising factor (NMF) is the collective term for filaggrin-derived cornification-specific compounds.
- They absorb water allowing the cornified layers to stay hydrated. As NMFs are water soluble, they easily leach from the cells upon water contact (I.e. Too much contact with water can actually make skin drier).
