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Cellular Pathology > Histology of Skin > Flashcards

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
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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
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3
Q

What are the 3 layers of the skin?

A
  1. Epidermis
  2. Dermis
  3. Subcutaneous tissue
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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
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5
Q

Describe Keratinocytes

A
  • synthesise keratin
  • associated with the 4 layers of the epidermis, and travel through these layers during their life cycle
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6
Q

Describe Merkel cells

A
  • mechanosensitive cells that plays a role in our sense of touch
  • make up 0.1% of total cell population of the epidermis
  • specialist cells 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
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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
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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)
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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
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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
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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
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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
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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
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13
Q

What are hard keratins used for ?

A
  • mix of type I & II keratins are used for hair, nails & horns
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14
Q

What are soft keratins used for ?

A
  • mux of type I & II keratins are abundant in cytoplasm of eptihelial cells
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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
  1. pigment globules are released from melanocytes dendrites into extracellular space
  2. are then captured by microvilli of keratinocytes
  3. transported in via protease activated receptor 2 (PAR-2) dependant mechanism
  4. membrane of pigment globule is degraded
  5. single melanosomes are released into a keratinocyte cytosol & go to perinuclear area
  6. 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
Q

What does connective tissue generated by dermal fibroblasts do?

A
  • supports the adhesion of the epidermis
25
Q

What happens to dermis as you age?

A
  • the quantity & quality of fibroblasts in the dermis deteriorate with age
26
Q

Describe the production of collagen by fibroblasts

A
  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
Q

Where does the production of collagen by fibroblasts occur ?

A
  • occurs in endoplasmic reticulum & cytosol
28
Q

Describe Collagen

A
  • 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
Q

How is collagen bound in the papillary dermis?

30
Q

How is collagen bound in the reticular dermis?

31
Q

What are GAGs ?

A
  • Glycosaminoglycans
  • carbohydrate polymers which attract positively charges Na+ & attract water molecules by osmosis
  • this keeps extracellular environment wet & make cell survival sustainable
32
Q

Describe Dermal Macrophages

A
  • most abundant inflammatory cells in the dermis
  • differ from Langerhans cells because the adult population their origin is bone marrow derived monocytes
33
Q

Describe the action of macrophages

A
  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
Q

Explain macrophage activity

A
  • 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
Q

What are mast cells ?

A
  • role in innate adaptive immunity
  • important in inflammatory & allergic reactions
  • release histamine & cytokines during these processes
36
Q

Describe the role of Mast Cells in skin irritation

A
  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
Q

Describe the Subcutaneous adipose tissue

A
  • 3rd layer of skin
  • layer of fat cells & offers layer physical/thermal protection & an energy store

Cellular Pathology (9 decks)

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