Anatomy of the Skin - Part 1

Question 1

Describe the functions of the integumentary system (skin + the accessory parts)

Answer 1

• Protects underlying tissues and organs from abrasions, fluid loss, chemicals etc.
• Excretes salt, water and organic wastes using glands
• Temperature regulation by insulation or evaporative cooling as required
• Produces melanin: protects underlying tissues against UV
• Produces keratin: protection against abrasions and water repellant
• Synthesise Vitamin D3 (steroid) converted to calcitriol: a hormone important for blood calcium homeostasis
• Lipid storage in adipocytes, some in the dermis and mostly in adipose tissues in the hypodermis
• Detect touch, temperature, pain and pressure stimuli and real the information to the nervous system

Question 2

What are the four tissue types and their basic function?

Answer 2

Epithelial tissue (covers exposed surfaces, lines internal passageways and chambers, forms secretory glands), connective tissue (fills internal spaces, provides structural support, stores energy), muscle tissue (contracts to produce movement) and nervous tissue (conducts electrical impulses and carries information)

Question 3

Describe the three primary layers of the skin and their roles

Answer 3

1. Epidermis: stratified (layered) barrier, mostly keratinocytes, avascular
2. Dermis: protein fibres for strength, vascular
3. Hypodermis: adipose tissue

Epidermis and dermis make up the cutaneous membrane/layer, and the hypodermis makes up the subcutaneous membrane/layer.

Question 4

What tissue type is predominant in epidermis?

Answer 4

Epithelial tissue, as its role is protection

Question 5

What are the types of epithelia?

Answer 5

Simple epithelia = single:
- squamous, cuboidal, columnar

Stratified epithelia - stacked:
- squamous, cuboidal, columnar

The epidermis is mostly made of stratified squamous epithelium.

Question 6

Describe the layers of the epidermis and their properties (from outermost to innermost)

Answer 6

Stratum corneum (spiky layer):
- dead, dried out hard cells without nuclei
- has the most cells

Stratum granulosum (granular layer):
- contain granules that promote dehydration of the cell, cross linking of keratin fibre
- waxy material is secreted into the intercellular spaces

Stratum spinosum (spinous, or prickly cell layer):
- intercellular bridges called desmosomes link the cells together
- the cells become increasingly flattened as they move upwards

Stratum basale (basal layer):
- columnar (tall) regenerative cells
- as the basal cell divides, a daughter cell migrates upwards to replenish the layer above.
- this is the layer of the epidermis, it is made of stem cells that divide into the layer above and push upwards to the surface of the skin

Question 7

Describe desmosomes and hemidesmosomes

Answer 7

Desmosomes: anchors adjacent/neighbouring cells in epidermis

Hemidesmosomes: anchors stratum basal (basal layer) to the dermis

Question 8

What are the differences between thick skin and thin skin?

Answer 8

• Thick skin has a layer called stratum lucidum that is between the stratum corneum and the stratum granulosum.
  (to remember the order of skin layers go: Come Lets Get Some Burgers)
• thick skin is present in places like the palms of hands and soles of feet
• thick skin has no hair

Question 9

What are the purposes of dermal papilla and epidermal ridges?

Answer 9

They stop the epidermis from sliding off the dermis by providing ridges that increase the surface area and grip/anchoring between the layers

Question 10

Describe the dermis

Answer 10

• Situated below the epidermis and anchors via hemidesmosomes
• Does NOT SHED
• Divided into two layers:
  - Papillary layer (upper dermis): consists of highly vascularised tissues (for nourishment)
  - Reticular layer (lower dermis): ‘mesh like’ structure of collagen and elastin fibres (for strength)

Note: both layers contain blood vessels, lymphatics, sensory nerve fibres and accessory structures

Question 11

Describe the two plexuses of the dermis

Answer 11

Cutaneous plexus:
- Network of blood vessels present at the junction of dermis/hypodermis
- Supplies the hypodermis, deeper dermis, including the capillaries for hair follicles and sweat glands

Subpapillary plexus:
- Branches from the cutaneous plexus
- its deep to the papillary layer of the dermis
- Network of blood vessels providing O2 and nutrients to the upper dermis and epidermis.

Note: plexus refers to a network of blood vessels or nerves

Question 12

Describe the hypodermis

Answer 12

• The ‘subcutaneous’ layer
• Not considered part of the skin
• Dominated by adipocytes that produce subcutaneous fat
• The subcutaneous fat stores energy and provides insulation
• Common site of injections using hypodermic needles

Question 13

Describe first degree burns

Answer 13

• Superficial. ie. only involve the outer layers of the epidermis
• Red/pink, dry, painful - this is called Erythema
• Usually no blisters. eg. mild sunburn
• Skin remains a water and bacterial barrier
• Usually heals 3-10 days

Question 14

Describe second degree burns

Answer 14

Normal 2nd degree burns:
- Epidermis + varying amounts of dermis burnt off
- Painful, moist, red and blistered
- Usually heal in approx 1-2 weeks (needs good dressing)

Deeper 2nd degree burns:
- may include whitish, waxy (from the granules) looking areas
- Hair follicles, sweat glands, may remain intact
- Usually heal in 1 month
- May have some loss of sensation and scarring

Question 15

Describe third degree burns

Answer 15

• Full thickness burns. ie, extend into subcutaneous tissue and may involve muscle and bone (epidermis, dermis and hypodermis destroyed along with some muscle and sometimes can extend to the bone beneath).
• Varied colour from waxy white through to deep red or black
• Hard, dry and leathery skin
• No pain in these areas as sensory nerve endings destroyed
• May require skin grafting
• Weeks to regenerate + scarring