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MD2001 > Strucure and Function of the Skin > Flashcards

Strucure and Function of the Skin Flashcards

1
Q

Which type of epithelial is the epidermis ?

A

Keratinised stratified squamous epithelium

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2
Q

What is the function of this keratinised layer ? What is it made of ?

A

Protection + waterproof function

Dead cells containing keratin

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3
Q

What are the main characteristics of the epidermis ?

A

Avascular epithelium
Undergoes proliferation
Synthesises keratin

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4
Q

What are the main characteristics of the dermis ?

A

Vascular, thick CT
Contains: i. Blood vessels, lymphatics, and cutaneous nerves ii. collagen and elastin which are not replaced with age

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5
Q

What are the main characteristics of the hypodermis ?

A

Vascular, loose CT and adipose tissue
Superficial fascia of varying thickness (less thick then dermis)
Contains: i. Blood vessels, lymphatics, cutaneous nerves
ii. Fatty tissue
iii. Skin ligaments, loose skin or taut skin

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6
Q

What are the main functions of skin ?

A 
1. Hemostasis
Internal homeostasis (water, electrolytes, macromolecules) 
Temperature regulation (vasoldilation, sweating, fat store, hairs)
Metabolic (vitamin D, fat store (may release product of fat breakdown as energy supply))
  1. Sensory Info
    Sensation (pain, P, temperature, touch, vibration)
    Psychosocial signals (visual like blushing, chemical like pheromones)
  2. Protection (UV-melanin, organisms- immune system, chemicals, water, mechanical-keratin)
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7
Q

What are the layers of the epidermis ? What does each contain/what goes on in each ?

A
  1. S. corneum- waterproof cell ghosts. Cell nuclei have disappeared. All is left is dead keratinised cell (cornified layer).
  2. S Lucidum - Specilised cell death programme (not much functional significance). Appears as pale layer.
  3. S Granulosum - Ketohyaline granules present. Intermediate keratin filaments begin to aggregate.
  4. S Spinosim - Intermediate keratin filaments linkage via desmosomes responsible for strength of epithelium.
  5. S basale- where differentiation and proliferation of stem cells leads to the formation of the S spinosum. Also forms interface with dermis.
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8
Q

How does the Stratum basale form the interface with the dermis ?

A

Through hemidesmosomes anchoring basal cells to BM.

Collagen VII plays role of anchoring fibrils

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9
Q

What is dystrophic epidermolysis bullosa ?

A

Mutation causing decreased levels of collagen VII leading to blistering and excessive sloughing off of skin (due to poor link between cells and BM)

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10
Q

What is the pattern of keratin expression in skin ?

A

Keratin K1/K10 expressed from S. spinosum to S. corneum
Keratin KS/K14 expressed in S. Basale
Flaggerin (protein found in ketohyaline granules expressed as cells get older, important in causing aggregation of keratin) appears slightly before S. granulosum starts and is expressed as the process of cell death begins. Expression of it ends in middle of S. corneum.

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11
Q

What is the precursor of filaggrin ?

A

Profilaggrin

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12
Q

What are the functions of filaggrin and profilaggrin in preventing disease ?

A
  • Maintain skin barrier by aiding keratin filament aggregation
  • Inhibit water loss (filaggrin cleaved into AAs which aid in maintaining moisture)
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13
Q

What are possible results of mutations affecting keratinisation ?

A
  • Icthyosis vulgaris (cornified skin elements in patches)
  • Eczema (damage is done mechanically but without filaggrin, repair is hindered)
  • Asthma (in null mutations of filaggrin)
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14
Q

What are the other two very important cells in the Epidermis ?

A

Melanocytes and Langerhan cells

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15
Q

Where is melanocyte found exactly ?

A

In the basal layer of epidermis

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16
Q

What is the function of melanocytes ?

A

Synthesise and release brown pigment melanin into keratinocytes (after which they are transferred to all cells, hence homogenous)

17
Q

What is melanin’s function ?

A

Absorbing UV-B and preventing DNA damage to underlying cells of hypodermis (more melanin = lower incidence of skin cancer)

18
Q

What is Melanoma ?

A

Tumour of melanocytes, due to exposure to UV radiation.

19
Q

How are melanocytes derived ?

A

Melanocytes are derived from neural crest cells which originate near the developing NS and spread into the embryo (become mesodermal in nature).
Then, they synthesise specialised lyosomes which can undergo exocytosis (=melanosomes).
Melanosomes then transferred to keratinocytes.

20
Q

What is the function of Langerhan cells ? How does their shape aid this function ?

A
  1. Antigen capturing, processing and presentation (sentinel). Once activated in skin, can migrate to lymph nodes (through BM and to lymphatic vessels first) where is may stimulate immune system.
  2. Can degrades viruses such as HIV by expressing Langerin which degrades viruses in specialised endosomes called Birbeck granules.
    They are dendritic in shape, their processes await contact.
21
Q

Where are Langerhan cells derived from ?

A

Derived from monocytes

22
Q

Where are Langerhan cells found ?

A

In the S. Spinosum mostly

23
Q

What are the different layers of the dermis ?

A

Dermo-epidermal junctions- complex to prevent shearing.

Papillary dermis- Comprises fine collagen and elastic fibres, small blood vessels and nerves. Papillae flatten with age so skin becomes more vulnerable.

Reticular dermis- Comrpises coarser collagen and elastic fivres and larger blood vessels and nerves.

24
Q

What are the components of the hypodermis (/structures the hypodermis supports)?

A

Loose CT and adipose tissue

Deepest part of the hair follicles + eccrine and apocrine glands

25
Q

What is the main function of the hypodermis ?

A

Vitamin D production

Role in motility (ligaments)

26
Q

What are sweat glands ? Where are they located ?

A

Simple coiled tubular glands which secrete a watery fluid (reaches surface of the skin through duct opening into pore)
In dermis and hypodermis.

27
Q

How are sweat glands regulated ? When would they need to be activated ?

A 
Through the SNS. 
For thermoregulation (too warm) or in response to fear
28
Q

Which types of sweat glands are there ?

A

Apocrine- Found in axillae and genital regions, open into the hair follicles and release milky secretion containing pheromones.
Eccrine/merocrine-

29
Q

What are hair follicles ? Where are they located ?

A

Cylindrical, epithelial structures.

Anchored in the hypodermis.

30
Q

What are the different components of the hair follicle ?

A

The bulb- where the hair shaft grows from
Hair shaft
Root sheath (“derived from epidermis”)

31
Q

What are associated structures with the hair follicle ?

A

Sebaceous gland open into the follicle and secrete sebum (fatty substance) to lubricate skin and adjacent skin.
Arrector pili muscle attached to sheath of follicle and to papillary dermis may contract to pull hair upright (controlled by SNS)

32
Q

What are the components of the pilosebaceous unit ?

A

Hair follicle + sebaceous glands + hair shaft + arrector pili

33
Q

What are other major skin appendages (outside of sweat gland and hair follicles) ?

A

Mammary glands- Modified appocrine sweat glands (under hormonal control)
Nails- Nail plate on nail bed. Growth from nail root (deep in dermis)
Teeth- Enamel develops from epithelium. Dentine, pulp and periodontal membrane (between teeth and skull) is mesodermal

34
Q

What are each of these sensed by ?

A

-Pain- free nerve endings (nociceptors fire when tissues being damaged or close to being damaged)
-Temperature- free nerve endings (seperate receptors for cold and heat)
(These free nerve endings usually close to epidermis and end in dermal papillae)

  • Touch- Meissner’s corpuscles (just beneath epidermis in dermal papillae) and Merkel cells (in S. basale)
  • Pressure- Pacinian corpuscles (dermis)
  • Vibration- Meissner’s corpuscles and Pacinian corpuscles (dermis, although pacinian corpuscules are deeper)

MD2001 (35 decks)

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