Undertstand The Main Structures And Layers Of Skin And Their Functions

Question 1

What are the nerve supply in the subcutaneous tissue?

Answer 1

Cutaneous nerve

Question 2

What are the 5 layers of the epidermis? Start with the lowest layer.

Answer 2

1. Stratum Basale (lowest layer)
2. Stratum Spinosum
3. Stratum Granulosum
4. Stratum lucidum
5. Stratum corneum (most superficial)

Question 3

Describe the stratum basale. Describe merkel cells and melanocytes.

Answer 3

• deepest layer
• attaches the epidermis to the basal lamina, below this lies the layers of the dermis
• they attach via collagen fibres intertwining to the basement membrane. Dermal papilla are found in the superficial portion of the dermis to help increase the connection & strength between the epidermis and dermis.
• it’s a single layer of basal cells made from keratinocytes and stems cells of the epidermis dividing repeatedly.
• other cells like merkel cells are receptors and responsible for stimulating sensory nerves that the brain perceive as touch.
• melanocytes produce melanin, giving skin & hair it’s pigment and help protect DNA in the nuclei from UV damage.

Question 4

Describe stratum spinosum

Answer 4

• provides strength and flexibility to skin
• 8 to 10 layers of keratinocytes formed because of cell division in the stratum basale.
• keratinocytes begin the synthesis of keratin and release water repelling glucolipids, making skin water proof.
• the new keratinocytes are pushed up from the stratum basale and into the stratum spinosum, the keratinocytes in the stratum spinosum are moved into the stratum granulosum.
• alongside the keratinocytes are dendritic cells called LANGERHANS cells. These function as a macrophage engulfing bacteria, foreign particles and damaged cells. These cells are from bone marrow and participate in the immune system,

Question 5

Describe stratum granulosum

Answer 5

• 3 to 5 layers of flat dying cells that show nuclear degeneration.
• contain lamellar granules that release lipids to repel water
• contain dark staining keratohyalin granules, keratohyalin converts tonofilaments into keratin.
• these 2 proteins make up the keratinocyte mass in the stratum granulosum and give its grainy appearance.

Question 6

Describe stratum lucidum

Answer 6

• smooth almost translucent layer. Only found in thick skin of palms, digits and soles of feet.
• keratinocytes are packed with eleidin ( a clear protein rich in lipids produced from keratohyalin & provide barrier to water ).
• keratinocytes produce the protein keratin, which helps protect the skin and underlying tissue from heat, microbes and chemicals and lamellar granules which release a waterproof sealant.
• contains the precursor to keratin

Question 7

Describe the stratum corneum

Answer 7

• most superficial epidermis layer
• 25 to 30 layers of keratinocytes, they are dry and dead filled with keratin and surrounded by lipids, helps prevent microbes and dehydration of deeper tissue.
• provides a mechanical and protective layer against abrasion, light, heat and chemicals
• regular shedding of cells and replaced by new cells that are pushed upwards
• lamellar granules in this layer help make the skin water repellant.

Question 8

Explain keratinisation and growth of the epidermis

Answer 8

1. Stem cells divide to produce keratinocytes
2. As keratinocytes are pushed up towards the surface, they fill with keratin.

Keratinisation is replacement of cells contents with the protein keratin; occurs as cells move to the skin surface over 2-4 weeks in 1mm of skin

Epidermal growth factors and other hormones like proteins play a role in epidermal growth.

Nutrients & oxygen diffuse to the avascular epidermis from blood vessels of dermis.

Question 9

Describe the dermis

Answer 9

• contains dermal papillae which anchors the epidermis and dermis.
• in the fingers, soles and feet dermal papillae are arranged in parallel lines given a ridged appearance = finger prints
• it’s tough and elastic: connective tissue and collagen fibres interlaced with elastic fibres.
• dermal cells: fibroblasts, macrophages and mast cells
• dermal structures: small blood & lymph vessels, sensory nerve endings, sweat glands and ducts, hair, arrector pili muscles & sebaceous glands.
• sub-cutaneous layer in under the dermis.

Question 10

Describe the sensory receptors in the skin

Answer 10

• meissners corpuscle = light pressure
• pacinian corpuscle = deep pressure
• free nerve ending pain

Information travels from these receptors to the spinal cord by sensory nerves & conducted to the sensory area of the cerebrum where they are perceived.

Question 11

Describe sweat glands

Answer 11

• eccrine : open, watery substance. Not fully active in infants. Presents on palms, soles of feet, axillae and groins.
• apocrine : sweat glands develop/ activate during puberty and secrete alongside hair follicles, mix with bacteria on skin = body odour
• subaceous gland : secrete into the hair follicles, scalp, face, axillae and groin. Waterproof barrier, bactericidal and fungicidal, prevents cracking and drying on exposure to heat and sunlight.
  Less active in elderly and infants = skin prone to mace ration from moisture.

Question 12

Explain skin and ageing

Answer 12

• changes may be caused by genetic, sun and weather exposure.
• aging = both the skin & mucous membranes becomes thin and fragile. The dermis is thinner & subcutaneous tissue is disminished.
• fewer capillaries & cell proliferation is decreased, resulting in slower wound healing and atrophy of the glands.
• number of sensory receptors in the skin and mucosa decline = increased susceptibility to injury, bruising occurs frequently, and the mucosal membranes become inflamed or ulcerated.
• the skin is often dry and appears wrinkled as elastic fibres are reduced & collagen fibres become less flexible
• melanocytes decrease causing greying of hair and skin

Question 13

Explain skin in a developing foetus.

Answer 13

• epidermis develops from a single layer of ectoderm to which layers are added.
• at 4 weeks, a thin outer layer of flattened cells covers the embryo
• Brown adipose tissue develops from 17-20 weeks gestation. Helps baby after birth thermoregulate.
• At 18 weeks, foetus is covered in vernix caseosa ( a protective layer )
• At 20 weeks, the foetus is covered in fine downy hair called lanugo.