Week 4 - Integumentary 2

Question 1

Skin colour

Answer 1

• Homeostatic imbalances
• Melanin
  ▪ Melanocytes (Same number in all people)
• 2 forms:
  ▪ Eumelanin – brownish black
  ▪ Pheomelanin – reddish yellow pigment
• Freckles, moles, age spots, anus, nipples etc. melanin is concentrated
• Carotene:
  ▪ Precursor of vitamin A
  ▪ Yellow to orange pigment
  ▪ Stratum corneum and dermis
  ▪ Most obvious in palms and soles of feet
• Haemoglobin
  ▪ Red pigment

Question 2

What are colour variations in skins?

Answer 2

Evolutionary pressures e.g. exposure to ultraviolet radiation (UV)

Question 3

What happens to skin that are exposed to too much UV?

Answer 3

Skin cancer and folic acid (a vitamin B) break down

Question 4

What happens to skin that are exposed to too little UV?

Answer 4

Vitamin D deficiency. Bone deformities (rickets) and other diseases

Question 5

Synthesising of vitamin D

Answer 5

• Involves organ interactions
  ▪ Keratinocytes use UV to convert a provitamin D3 to cholecalciferol
  ▪ Liver converts to calcidiol
  ▪ Kidneys converts to calcitriol (active Vitamin D)

Question 6

What does calcitriol do?

Answer 6

• Calcitriol raises blood calcium (Ca2+)
• Acts like a steroid hormone
  ▪ ↑Ca2+ absorption by small intestine
  ▪ ↑ Ca2+ release (resorption) from skeleton
  ▪ ↑ Ca2+ reabsorption by kidneys

Question 7

What is holocrine gland?

Answer 7

Cells accumulate a product and then disintegrate

Question 8

What is sebum?

Answer 8

• Released from the sebaceous gland
• Oily, dead cell fragments
• Secreted into hair follicle
• Lubricates and waterproofs
• Cells replaced by mitosis

Question 9

What is exocrine gland?

Answer 9

Secretory vesicles by exocytosis

Question 10

What is merocrine?

Answer 10

• Eccrine sweat glands
• Acidic sweat
• 99% H2O, NaCl, waste
• Duct to pore on skin surface
• Evaporative cooling
• 500 mL / day (insensible loss)

Question 11

What are apocrine sweat glands?

Answer 11

• Sweat contains lipids and protein
  ▪ Duct opens into hair follicle
  ▪ Axillary and genital areas (hair / pheromones)
  ▪ Little role in thermoregulation

Question 12

What are ceruminous glands?

Answer 12

Secrete cerumen (ear wax), buds off

Question 13

What are mammary glands?

Answer 13

• Secrete breast milk.
• Merocrine (exocytosis) and apocrine (budding off)

Question 14

What is hair?

Answer 14

• Protection, warmth, detection
• Columns of dead keratinised epithelial cells bonded together by extracellular proteins
• Produced by the hair follicle which is a fold in the epidermis down into the dermis

Question 15

What is a hair follicle?

Answer 15

• A dermal papillae projects into base of follicle
• Papillae contains capillaries that nourish growing (living) end of hair

Question 16

How does hair grow?

Answer 16

• Division (mitosis) of stratum basale cells (matrix) at base of follicle
• As cells get pushed upward they become keratinised and die

Question 17

What is the hair growth cycle?

Answer 17

• Growth phase: ~1 mm in 3 days, 6 to 8 years (short hairs less time)
• Regression phase: Atrophy of follicle, 2 to 3 weeks
• Resting phase: 1 to 3 months (Chemotherapy / cold caps ) (short hairs more time)
• Old hair pushed out by reactivated follicle

Question 18

What are the structures involved in hair growth?

Answer 18

Piloerector muscle:
- Smooth muscle.
- Pulls hairs upright when cold or frightened (sympathetic)
Hair receptors (touch):
- Knot of nerve endings around each follicle

Question 19

What are nails?

Answer 19

• Clear, hard derivatives of stratum corneum, heavily keratinized
• Nail plates extend at 1 mm/week, fingers 3x more than toes
  ▪ from stratum basale (nail matrix)

Question 20

What is the first stage of skin regeneration?

Answer 20

1) Broken blood vessels bleed into cut
- Antibodies, Clotting proteins, Erythrocytes, Leucocytes

Question 21

What is the second stage of skin regeneration?

Answer 21

2) Blood clot
- Haemostasis
- Macrophages digest debris

Question 22

What is the third stage of skin regeneration?

Answer 22

3) New dermis
- New fibroblasts (from mesenchymal stem cells)
- New collagen (fibrosis)
- New capillaries = Red granulation tissue

Question 23

What is the fourth stage of skin regeneration?

Answer 23

4) New epidermis
- New keratinocytes (from stem cells in stratum basale)
- Migrate along epithelial edge of wound = Pink epithelialisation tissue

Question 24

What is regeneration in tissues repairing?

Answer 24

Replacement with same kind of cells

Question 25

What is fibrosis in tissues repairing?

Answer 25

Repair by dense connective tissue (scar). Which used is determined by:
- Type of tissue damaged (Skin uses both)
- Severity of injury