Structure and Function of the Skin

Question 1

What is the Integument?

What are the main functions of the skin?

Answer 1

• Skin, Hair, Nails; largest organ

- • Protection against Dehydration, Infection, Injury/Abrasion, Solar radiation
• Thermoregulation (homeostasis)
• Sensation
• Repair
• Vitamin D production

Question 2

What are the 3 layers of the skin?

Epidermis:
How does it differ around the body?

What are the 4 layers of the epidermis? Describe their structure (Top to bottom)

What other cells are present in this layer?

Answer 2

• Epidermis, Dermis, Hypodermis
• Thin in some areas (e.g. abdomen), Thick in others (e.g. heel)
• • CORNIFIED Layer (Stratum Corneum) - Very thick layer of non-nuclei squamous cells that are full of KERATIN with non-polar lipids between cells; makes it waterproof
• GRANULAR Layer (S. Granulosum) - 1-4 layers of cells rich with Keratohyalin granules (precursor of keratin), and lamellar bodies with lipids inside; prevents water evaporation
• SPINY Layer (S. Spinosum) - Cells have many strong desmosomes (junctions) between cells; look like spines under a microscope
• BASAL Layer (S. Basale) - 1 layer of stem cells which differentiate as they move upwards to shed from the outer surface; 20-50 days
• • Melanocytes (produce melanin and transfer it into basal keratinocytes)
  • Langerhans cells (defence; APCs in the skin)
  • Merkel cells (sensation)

Question 3

Dermis:
Describe its structure

How does its structure change with age?

What’s its function?

What does this layer carry?

Answer 3

• Dense, irregular connective tissue with Collagen and Elastin; Finger-like dermal papillae projecting into epidermis
• More UV damage = Loss of elastic fibres and Elasticity (wrinkles)
• Tensile strength for protection against abrasion/impact
• Blood and nerve supply for epidermis

Question 4

Hypodermis:
What are other names for it?

What is it composed of?

How does its thickness vary?

What’s its function?

Answer 4

• Fascia, Subcutis
• Fat/Adipocytes; Contains glands, Hair follicles, Nerves, Blood vessels
• Varies with Age, Area in body, Diet
• Insulation, Cushioning, Energy storage

Question 5

Where is Vitamin D produced?

What does it require for production?

Where is it converted to its active form?

Answer 5

• BASAL and SPINY layers in Epidermis
• UV light; the darker the skin, the more light needed
• Liver and Kidney

Question 6

What are the 2 types of Sweat glands?

What are Sebaceous glands?

Answer 6

• • Eccrine; normal sweat glands of watery secretion onto the skin to cool body down by evaporation
  • Apocrine; secrete into hair follicles and are found in armpit and anogenital region. Bacteria acts on it to give off body odour.
• Secrete oily sebum into hair follicles, which conditions the hair and skin to prevent dryness and flaking

Question 7

Where and What are nails composed of?

What is the area between the overhanging nail and skin called? What’s its clinical significance?

Answer 7

• Formed by Nail Matrix, formed of HARD KERATIN

- Hyponychium; Common site for infection

Question 8

What are the Sensory innervators in the skin? Function?

Answer 8

• Thermoreceptors
• Meissner’s corpuscle - Touch, Vibration
• Nociceptor - Pain (free nerve endings)
• Pacinian corpuscle - Pressure (mechanoreceptor)