Skin

Question 1

State the 5 functions of skin

Answer 1

Functions

Protective - against water, infection, UV, mechanical stimulus

Sensory - touch, temperature, pain

Interactive - Friction for grip, thermoregulation

Immune surveillance - entry of pathogens

Absorptive - skin patches

Question 2

Skin structure - Name 3 layers

Answer 2

Skin structure

Epidermis

Dermis

Hypodermis (subcutaneous loose connective tissue)

Question 3

Epidermis - Simply State 4 cells located in epidermis

Answer 3

Keratinocytes, Melanocytes, Langerhan’s, Merkel Cells

Question 4

Keratinocytes - Elaborate

Answer 4

Main cell type of skin

Undergo keratinisation - cells synthesise keratin and terminally differentiate

Form a barrier against microbes, water, heat, UV

Produce proinflammatory mediators in response to infection to attract immune cells to the tissue

Question 5

Melanocytes - Elaborate

Answer 5

Melanocytes

Responsible for forming melanin in melanosomes

Two types of melanosome: eumalonosomes and pheomelanosomes (latter are more red/yellow due to greater sulphation)

Melanosomes are transferred along cytoplasmic processes to the cytoplasm of basal and stratum spinosum keratinocytes

Question 6

Melanocytes - Clinical Relevance

Answer 6

Clinical relevance - Albinism

Defects in pathway to produce melanin pigments (tyrosinase enzyme)

Most common form affects P gene

Question 7

Langerhan’s - Elaborate

Answer 7

Tissue resident macrophages in the skin

Dendritic cells (take up and present microbial antigens to lymphocytes)

Question 8

Merkel Cells - Elaborate

Answer 8

Merkel cells

Sensory receptors in the skin which synapse with peripheral nerve endings

Either solitary cells or grouped in touch receptors related to hair discs

Contain neuroendocrine granules

Question 9

List the name of the epidermal layers

Answer 9

• Stratum Basale
• Stratum Spinosum
  -Stratum Granulosum
• Stratum Corneum

Question 10

Stratum Basale - elaborate

Answer 10

Stratum Basale (basal cell layer)

Sits on the basement membrane (on top of dermis), rete ridges for increased surface area

Columnar or cuboidal cells expressing keratin isoforms -> aggregate to form tonofilaments

Contains stem cells and daughter cells which divide to form keratinocytes + other cell types

Question 11

Stratum Spinosum - Elaborate

Answer 11

Stratum Spinosum (prickle cell layer)

High levels of keratin expression

Prickles are cellular extensions which permit attachment to neighbouring cells via desmosomes

Question 12

Stratum Granulosum (granular layer)

Answer 12

Stratum granulosum (granular layer)

High levels of keratin although synthesis is reduced

Numerous keratohyaline granules - proteins

Keratinosomes contain water repellent lipids

Contents of keratohyaline granules and keratinosomes together with tonofilaments are used to form mature cross-linked keratin - cornified envelope

Question 13

Stratum Corneum - Elaborate

Answer 13

Stratum corneum (cornified layer)

Remnants of dead keratinocytes and cornified envelope

Outer layers slough off (1.5g a day)

Waterproof effect due to hydrophobicity of glycophospholipids which stick the dead flakes of cells together

Question 14

Nails are a specialisation of the …..layer - keratin filled squames in layers

Answer 14

cornified

Question 15

Hair - elaborate

Answer 15

Hair grows from hair follicles - invaginations of epidermal tissue

Bulbous expansion at lower end = hair bulb, specialised dermis forms the hair papilla (containing blood vessels and nerve endings)

The hair itself is organised keratin

Arrector pili muscle under sympathetic control

Sebaceous glands around follicle secrete sebum - waterproofs + moisturises

Question 16

TO DO KERATIN SUBTYPES

Question 17

Keratinocyte maturation - elaborate

Answer 17

Takes roughly 30 days for cells to migrate from stratum basale to stratum corneum

Question 18

DERMIS

Answer 18

Following flashcards will cover for DERMIS the:
- composition
- sweat glands
-sebaceous glands
- blood supply of the skin
- apocrine glands
- nerve endings

Question 19

DERMIS
Composition - elaborate

Answer 19

Composition

Upper layer = papillary dermis - fine network of collagen and elastin with small blood vessels nerve endings and fibres

Lower layer = reticular dermis = dense type I collagen and long thick elastin fibres contains blood vessels, nerves and lymphatic vessels

Question 20

DERMIS
Sweat glands - elaborate

Answer 20

Sweat glands

Eccrine glands secrete sweat under cholinergic sympathetic control

Simple coiled tubular glands in superficial part of subcutis

Involved in thermoregulation and excretion

Question 21

DERMIS
Sebaceous glands - elaborate

Answer 21

Sebaceous glands

Around hair follicles + in regions adjacent to body tracts (e.g. Lips)

Secrete oily sebum - release lipids by cellular degeneration

Waterproofs and moisturises

Question 22

Dermis
Blood supply of the skin - elaborate

Answer 22

Blood supply of skin

Two vascular plexuses in the dermis

Cutaneous plexus - hypodermis/dermis junction

Subpapillary plexus - upper dermis - has superficial appendages - papillary loops

Thermoregulation - arteriovenous shunt, glomus bodies reduce blood flow to upper dermis

Question 23

Apocrine glands - elaborate

Answer 23

Apocrine glands

Axilla, anogenital region

Axilla = armpit

Question 24

Nerve endings
- name and elaborate

Answer 24

Free nerve endings in dermis - pain, itch, temperature

Merkel cells in epidermal basal layer - touch

Meissner’s corpuscles in dermis - light touch

Pacinian corpuscles deep in dermis - coarse touch, vibration and tension