Histology of Skin Flashcards
1
Q
What are some functions of the skin?
A
- functional part of the integumentary system
- largest organ
- protects from external environment
- thermoregulation
- forms continous layer with mucous membranes & covers all body surfaces
2
Q
Describe the Integumentary System
A
- consists of skin, hair, nails, nerves & glands
- primary function = barrier to protect the body from the external environment
- also functins to retain body fluids, protect against disease/infection
3
Q
What are the 3 layers of the skin?
A
- Epidermis
- Dermis
- Subcutaneous tissue
4
Q
Describe the Epidermis
A
- outermost layer of skin
- most cosmetically important
- consists of stratified squamous epithelium tissue
- most prominent cell = Keratinocytes
- other cells present = melanocytes, Merkel cells & Langerhans cells
5
Q
Describe Keratinocytes
A
- synthesise keratin
- associated with the 4 layers of the epidermis, and travel through these layers during their life cycle
6
Q
Describe Merkel cells
A
- mechanosensitive cells that plays a role in our sense of touch
- found in digits, lips, oral cavity & hair follicles
- when local keratinocytes deform, they stimulate Merkel cells to secrete chemicals that generate an action potential in local afferent neurons
7
Q
Describe Langerhans cells
A
- an immunoloigically active cell that plays a role in allergy & immune response
- involved in T cell response
- present in all 4 layers of epidermis but most abundant in squamous cell layer
- during skin infection the Langerhans cells process microbial antigens
8
Q
What 4 layers make up the epidermis ?
A
- cornified cell layer (stratum corneum)
- granular cell layer (stratum granulosum)
- squamous cell layer (stratum spinosum)
- basal cell layer (stratum basale)
(basement membrane)
9
Q
Describe the Basal Cell layer of the epidermis in relation to keratinocytes
A
- keratinocytes start their journey & proliferate
- keratinocytes appear column shaped & attached to the basement membrane
- they also have elongated nuclei & support squamous cells
10
Q
Describe the Squamous Cell layer of the epidermis in relation to keratinocytes
A
- keratinocytes take on a flattened shape & appear ‘squamous’
- they become flatter as they travel to the top of layer
- they also contain lamellar granules which contain hydrolytic enzymes
- keratin fibres are formed around the nuclei
11
Q
Describe the Granular cell layer of the epidermis in relation to keratinocytes
A
- keratinocytes in granular layer contain lots of keratohyline granules in cytoplasm
- these cells are key players in keratinisation
- eventual terminal differentiation removes organelles from cells
12
Q
Describe the Cornified cell layer of the epidermis in relation to keratinocytes
A
- keratinocytes terminally differentiate to corneocytes & they provide a barrier to external environment & stop excessive water loss
13
Q
Describe Keratins
A
- epithelial cells synthesise at least one type I & one type II keratin
- Type I & II keratins copolymerise to form filaments
13
Q
What are hard keratins used for ?
A
- mix of type I & II keratins are used for hair, nails & horns
14
Q
What are soft keratins used for ?
A
- mux of type I & II keratins are abundant in cytoplasm of eptihelial cells
15
Q
What keratins are important for mechanical stability & integrity of epithelial cells & tissues?
A
- K5 & K14 = basal keratinocytes
- K1 & K10 = suprabsal keratinocytes
16
Q
Describe the function of lipids in the Stratum Corneum (cornified cell layer)
A
- lipids present (fatty acids, cholesterol & ceramides) all help prevent transepidermal water loss
17
Q
Describe Melanocytes
A
- pigment synthesising cells
- responsible for the production of melanin & its transportation to keratinocytes via melanosome
- larger melanosomes containing more pigment are found in heavily pigmented skin
-melanosomes are taken up into keratinocytes & protect them from UV radiation
18
Q
Describe Melanocyte/Keratinocyte Interactions
A
- pigment globules are released from melanocytes dendrites into extracellular space
- are then captured by microvilli of keratinocytes
- transported in via protease activated receptor 2 (PAR-2) dependant mechanism
- membrane of pigment globule is degraded
- single melanosomes are released into a keratinocyte cytosol & go to perinuclear area
- UV protection is offered to the cells nucelus by melanosomes
19
Q
Describe the Physiology of the Dermis
A
- contains fibrous, filamentous & amorphous connective tissues -> these tissues host fibroblasts, macrophages & mast cells
- thickest layer of the skin, gives skin its tensile strength & elasticity
- divided into 2 layers = papillary dermis & reticular dermis
- main component is collagen = 5 types present in dermis
- vascular portion of the skin
20
Q
Describe the Papillary Dermis
A
- uppermost layer of dermis - joined to basal membrane of epidermis
- contains loosely arranged collagen fibres
- papillae (finger like projections) that extend towards the epidermis contain capillaries & Meissners corpuscles
21
Q
Describe the Reticular Dermis
A
- lower layer of dermis - under papillary dermis
- consists of dense connective tissue -> densely packed collagen & elastic fibres
- contains roots of hair, sebaceous glands & sweat glands
22
Q
Describe the vasculature of the dermis
A
- dermal vasculature is made up of 2 plexus that connect ;
- sub-papillary plexus & lower plexus
23
Q
Describe Dermal Fibroblasts
A
- responsivle for production of important matrix proteins such as fibrillin, elastin & collagen
- most abundant cell type in dermis
- heavily involved in wound healing & generating connective tissue
24
What does connective tissue generated by dermal fibroblasts do?
- supports the adhesion of the epidermis
25
What happens to dermis as you age?
- the quantity & quality of fibroblasts in the dermis deteriorate with age
26
Describe the production of collagen by fibroblasts
1. ER - pre-procollagen is translated on ribosome & hydroxylation occurs
2. procollagen is released from ribosome
3. glycosylation occurs in cytosol
4. triple helix formation of procollagen strands
5. secretion from cell
6. removal of N- & C- terminals occurs in extracellular space
7. tropocollagen production & then cross link causes formation of collagen fibrills
27
Where does the production of collagen by fibroblasts occur ?
- occurs in endoplasmic reticulum & cytosol
28
Describe Collagen
- 15 types found in tbe dermis - most abundant = Collagen I & III
- biggest role in skin is to resist stress forces
- are always in state of flux- degraded by proteolytic enzymes in dermis & then remodelled
- makes up 70% of total weight of skin
29
How is collagen bound in the papillary dermis?
- loosely
30
How is collagen bound in the reticular dermis?
tightly
31
What are GAGs ?
- Glycosaminoglycans
- carbohydrate polymers which attract positively charges Na+ & attract water molecules by osmosis
- this keeps extracellular environment wet & make cell survival sustainable
32
Describe Dermal Macrophages
- most abundant inflammatory cells in the dermis
- differ from Langerhans cells because the adult population their origin is bone marrow derived monocytes
33
Describe the action of macrophages
1. macrophage moving towards bacteria
2. bacteria engulfed
3. bacteria contained within a vesicle
4. lysosome fusing with a vesicle & releasing phagocytic enzymes
5. bacteria being destroyed & digested
6. undigested remains of bacteria
34
Explain macrophage activity
- responsible for recognition & destruction of threats in skin
- 2 populations present in skin = M1 & M2
- M1 macrophages are more reactive to invasion & more involved in phagocytosis of microbes
- M2 macrophages are more active in wound healing response & produce polyamines to induce proliferation or proline to instigate collagen production
35
What are mast cells ?
- role in innate adaptive immunity
- important in inflammatory & allergic reactions
- release histamine & cytokines during these processes
36
Describe the role of Mast Cells in skin irritation
1. antigen/allergen is first presented to B cell
2. plasma cell is stimulated makes large amount of IgE antibody
3. IgE antibodies attach to mast cells - which are then primed for next exposure to allergen
4. IgE primed mast cells de-granulate & release histamine & cytokines
5. results in hives/allergic symptoms
37
Describe the Subcutaneous adipose tissue
- 3rd layer of skin
- layer of fat cells & offers layer physical/thermal protection & an energy store
