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Y1 Fundamentals of Life Science > Histology of Skin > Flashcards

Histology of Skin Flashcards

1
Q

What is the skin and what are its main functions?

A
  • Largest organ in the body
  • Forms a boundary between the body and the external environment
  • Protection
  • Thermoregulation
  • Sensation
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2
Q

What is skin made up of?

A

An epithelium of keratinised stratified squamous cells on a base of connective tissue called the epidermis

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3
Q

What determines skin colour?

A

Amount of melanin pigment secreted by melanocytes of the epidermis

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4
Q

How does the degree of keritanisation in skin change?

A

Skin thickness changes depending on the level of mechanical stress (such as the skin on the sole of the foot)

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5
Q

What improves the ability of skin to grip? What are these also important for?

A
  • Dermal ridges
  • Important for texture recognition and touch
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6
Q

How does skin change as you age?

A
  • Elasticity is reduced
  • Skin is lined, sags and recovers poorly after deformation
  • Epidermal appendages, epidermis-derived downgrowths into the dermis become visible
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7
Q

What is the structure under nails?

A
  • Cover the dorsal aspects of the distal phalanges of the limbs
  • Provide a firm base for the finger or toe pulp
  • Nail bed appears pink due to the underlying capillaries supplying the dermis
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8
Q

What differs between regions of skin?

A
  • Hair density and coarseness
  • Palms of hands, soles of feet and eyelids are hairless
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9
Q

What are the types of sweat glands?

A
  • Eccrine
  • Apocrine
  • Sebaceous
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10
Q

What are eccrine sweat glands?

A
  • Cover the vast majority of the body
  • Simple tubular glands
  • Important in temperature control through evaporation
  • Activity is under the control of the sympathetic nervous system
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11
Q

What are apocrine sweat glands?

A
  • Large, and in humans are limited to the axilla, the anogenital region and the mammary areola
  • Their duct opens into a hair follicle
  • Saline-­based product is more viscous than the product of eccrine sweat glands
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12
Q

What are sebaceous sweat glands?

A
  • Present everywhere but the palm of the hand or sole of the foot
  • The sebum they produce provides a protective covering for the skin
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13
Q

How does the skin change with temperature?

A
  • Hot weather the skin is richly perfused
  • Cold conditions cutaneous blood supply is reduced through the activity of arteriovenous anastomoses
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14
Q

What are arteriovenous anastomoses?

A
  • Networks of vessels which allow the reduction of perfusion through the most superficial tissues
  • Conserves heat and protects the central portions of the body housing the vital organs
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15
Q

What is the function of the top most layer of the skin?

A
  • Physical protection
  • Protects against UV light and mechanical and chemical stress
  • Waterproof
  • Thermoregulation achieved through arteriovenous shunts
  • Sensations
  • Metabolic functions
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16
Q

What is the topmost layer of the skin formed of?

A
  • Keratin formed through keratinisation
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17
Q

Why does skin sometimes go red during exercise or when flushed?

A
  • Blood supply shifts towards the periphery of skin for heat loss
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18
Q

What is the main metabolic function of adipose tissue below the skin?

A
  • Subcutaneous fat or adipose tissue involved in production of vitamin D
  • Triglyceride storage
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19
Q

What are the histological layers of the skin?

A
  • Epidermis (most superficial and epithelial tissue)
  • Dermis
  • Hypodermis or subcutis (deepest layer)
20
Q

How is the epidermis viewed on a micrograph?

A
  • Purple H&E stain
  • Reflects the number of cells present
21
Q

What is the dermis?

A
  • Dense connective tissue (mainly dense irregular)
  • Some loose connective tissue underlying epidermis
  • Many collagen fibres present
22
Q

How is the dermis viewed on a micrograph?

A

Pale pink

23
Q

What is the hypodermis mainly formed of?

A
  • Adipose tissue
  • Connects underlying tissues
24
Q

What other structures does the hypodermis have?

A
  • Sweat glands
  • Ducts that secrete their sweat onto the surface
  • Hair follicles with some glands attached
25
Q

What is the full histological classification for epithelial tissue?

A

Keratin stratified squamous epithelium

26
Q

What is the main cell type in the epidermis? What is distinct about this?

A
  • Keratinocyte
  • About 4/5 different discrete layers
27
Q

What cells are located at the basal layer of the epidermis? What is this layer called?

A
  • Cuboidal cells - layer which adheres to the basement membrane
  • Stratum basale
28
Q

What cells are the most superficial in the epidermis?

A
  • Flattened squamous cells
29
Q

Describe the basal layer

A
  • One cell thick
  • Attaches to the basement membrane via hemidesmosomes
  • Only layer where mitosis occurs - to replenish the above layers
  • Melanocytes only present in this layer
30
Q

Describe the layer above the basal layer?

A
  • Called the stratum spinosum
  • Around 8-10 layers thick
  • In a micrograph can sometimes see tiny spines connecting each cell together known as desmosomes
  • Involved in the production and maturation of keratin
31
Q

How is keratin formed?

A
  • Cytoskeleton protein called cytokeratin
  • In the stratum spinosum these cytokeratins aggregate as tonofibrils (collections of cytokeratin that are found attached to desmosomes)
  • Move upwards from the spinosum to the stratum granulosum as keratohyalin
  • Moves to stratum corneum as mature keratin (combination of keratohyalin and cytokeratin
  • Keratin so overproduced in the epidermis that the outermost layer of cells begin to die
32
Q

Describe the stratum granulosum

A
  • Characterised by basophilic (acidic) granules
  • These stain strongly with basic dye
  • With haematoxylin these stain very dark purple
  • Usually 3-5 cell layers thick
  • Granules packed full of keratohyalin
33
Q

Describe the stratum corneum

A
  • Mature keratin is overproduced here
  • Anuclear squames
34
Q

What happens to cells at the epidermis from overkeratinisation?

A
  • Cells begin to die
  • Kick out all the organelles
  • No nuclei present
  • Layers become known as squames which can flake off from your skin (dust)
35
Q

How often is the epidermis replenished?

A
  • Every 25-30 days
  • New skin cells come up from mitosis that occurs in the stratum basale
  • Mature as they move up the cell layers and become part of the stratum corneum where there are dead keratinocytes
36
Q

Describe the stratum lucidum

A
  • Found between the stratum granulosum and stratum corneum
  • Only in thick skin
  • Palms of hands, finger and soles of feet
  • Very thick layer of keratin
  • No hairs on this skin
  • Clearer on a micrograph
37
Q

What are melanocytes?

A
  • Only found in the basal layer
  • Long cellular processes that extend into the stratum spinosum
  • Involved in UV protection
38
Q

How can melanocytes be viewed on a micrograph?

A
  • Immunohistochemistry used to stain melanin
  • Can’t differentiate between keratinocytes and melanocytes using normal H&E stain
  • Can see individual cells when staining melanin
  • See cytoplasmic processes involved in transferring melanin to above layer of the stratum spinosum
39
Q

How are keratinocytes viewed on a micrograph?

A
  • Brown layer in melanin staining
  • Some melanin in the keratinocytes
40
Q

What is the function of melanin in keratinocytes/

A

Creates a barrier around the nucleus to protect from UV and involved in giving skin tones

41
Q

What are Merkel cells and their function?

A
  • Found in the stratum basale
  • Associate with free nerve involved in light touch
42
Q

What are Langerhans cells?

A
  • Immune cells
  • Act as an antigen presenting cell similar to macrophages or monocytes
  • Only found in the skin
  • Found in all layers of the epidermis and dermis
43
Q

What are the two sections of the dermis/

A
  • Papillary
  • Reticular
44
Q

Where is the papillary dermis found? How is it charcaterised?

A
  • Directly underneath the epidermis
  • Ridges and extension of the dermis into the epidermis called dermal papillae (elevations seen in micrographs)
  • Smaller layer than reticular and loose connective tissue
45
Q

What is the reticular dermis?

A
  • Dense irregular connective tissue
  • Larger layer than the papillary dermis
46
Q

How is the reticular dermis viewed on a micrograph with elastic van Gieson staining?

A
  • Black fibres of elastic tissue
  • Red is collagen
  • Densely arranged

Y1 Fundamentals of Life Science (25 decks)

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