Lecture 14: Human skin biology

Question 1

How much percent body weight is skin

Answer 1

7-16%

Question 2

What is the Total body surface area of skin

Answer 2

average 2m squared

Question 3

How thick are eyelids

Answer 3

0.5 mm thick

Question 4

How thick can palms and soles of feet be

Answer 4

4 mm or thicker

Question 5

How does skin thermoregulate

Answer 5

Thermoregulation - evaporation of sweat, constriction or vasodilation of blood vessels in the dermis decrease or increase heat loss

Question 6

List the functions of skin

Answer 6

Thermoregulation, blood reservoir, protection/barrier, detecting sensation, synthesis of vitamin D.

Question 7

How much blood can the skin hold

Answer 7

8-10% of the total blood volume

Question 8

What does the corneocytes and lipid bilayer of skin help protect against

Answer 8

Environment, chemicals. pathogens, heat, UV damage and water/blood loss.

Question 9

What types of sensation does the skin detect

Answer 9

Touch, pressure, pain and temperature

Question 10

What role does skin do in Vitamin D synthesis

Answer 10

Vit. D precursor requires modification by UV before active form can be made in the liver

Question 11

What are the three parts of the skin structure looked at in this lecture

Answer 11

Epidermis (turnover/barrier function), Dermis (structural strength, elasticity) and pigmentation (melanocytes)

Question 12

What are the types of cells in the epidermis and what are their function and where in the epidermis are they found

Answer 12

Keratinocytes -Melanocytes (produce melanin, intraepidermal macrophage (Langerhans) cells, Tactile epithelial (Merkel) cell.

Question 13

What is the general structure features of the epidermis: what layer, mainly consists of, provides, no

Answer 13

Top layer of skin, mainly consisting of keratinocytes

Provides barrier for continued renewal and no structural strength

Question 14

Name the stratified layers of the epidermis from top to bottom including the extra layer for thick skin on soles, fingertips and palms.

Answer 14

All start with stratum corneum, ((lucidum for thick)), granulosum, spinosum, basale

Question 15

How does the nutrient supply and waste removal happen for epidermis

Answer 15

It is avascular so it has diffusion through the dermis which is vascular.

Question 16

What is the function and location of keratinocytes

Answer 16

produce keratin for protection and lamellar granules for waterproofing. Found in the 4/5 distinct layers of strata in epidermis

Question 17

What is the function and location of melanocytes

Answer 17

Produce the pigment melanin, contacting on average 36 keratinocytes and transferring melanosomes to them
Found at the basement membrane.

Question 18

What is the function and location of Langerhans cells

Answer 18

Intraepidermal macrophages surveil the epidermis for foreign organisms, helping other cells to identify and destroy invading microbe

Question 19

What is the function and location of Merkels cells

Answer 19

Tactile epithelial cells are least numerous. they contact the flattened process of a sensory neuron called tactile disc, detect touch sensations.
Found in the statum basale.

Question 20

Why is stratification of epidermis important

Answer 20

Crucial for barrier function and continued renewal of the epidermis.

Question 21

Tell me about the Stratum basale: layers, whats happening there

Answer 21

Single layer of cuboidal/columnar cells, containing keratinocyte stem cells that stay at the basement membrane and have one half of their divisions forming the transit amplifying keratinocytes which proliferate heaps and fill up the strata

Question 22

Tell me about the stratum spinosum: layers, whats happening there

Answer 22

8-10 layers thick. Keratinocytes start to flatten out as they go through the stratification process. Their nuclei start to part. Keratin intermediate filaments start to form which hold cells together through desmosomes.

Question 23

Tell me about the stratum granulosum: layers, whats happening there

Answer 23

3-5 layers of flattened keratinocytes starting to undergo apoptosis.
Lamellar granules in keratinocytes fuse with the plasma membrane and release lipid rich secretions that help to make waterproof barrier. The dark granules are from keratohyalin which help to form keratin intermediate filaments—-> Keratin

Question 24

Tell me about the stratum Lucidum: layers, whats happening there

Answer 24

only present in thick skin. 4-6 layers. additional toughness

Question 25

Tell me about the stratum corneum: layers, whats happening there

Answer 25

25-30 layers of flattened dead keratinocytes. Thin membrane enclosed keratin overlap like snake scales. shed by epidermis

Question 26

What is the process of stratification

Answer 26

Proliferating keratinocytes on the bottom of the epidermis push cells up and away from the dermis where the nutrients diffuse from. Further away means that keratinocytes are less metabolically active, then undergo apoptosis

Question 27

list three features of the stratification process

Answer 27

Changes in gene expression distinct between layers. A defined and controlled process. Complete epidermal turnover once a month.

Question 28

What is the general structure features of the dermis: formed from, consists of, thickness, strength, stability

Answer 28

It is a dense matrx made of collagen and elastin fibres. Consists of fibroblasts that secrete the fibres. Strong and supple. Thickness varies. Very stable with minimal turnover

Question 29

What is the difference between the reticular and papillary layers of dermis

Answer 29

Papillary is closer to epidermis and has high cell density -> more fibroblasts. Whereas Reticular is near the bottom, has low cell density, more collage and elastin fibres and extracellular matrix.

Question 30

What are the rete ridges/ papillae

Answer 30

Small ridges on the interface between the epidermis and dermis provides resistance to shear force. Increases surface area for diffusion

Question 31

What are fibroblasts

Answer 31

Long spindley cells that produce collagen for strength and elastins for elasticity –> the extracellular matrix.

Question 32

What cells are present in the dermis

Answer 32

Fibroblasts, immune cells, nerve cells, vasculature

Question 33

What is the function of vasculature

Answer 33

to supply nutrients and remove waste for both the dermis and epidermis

Question 34

What are the two types of melanin and what is the function of melanin

Answer 34

Pheomelanin is yellow-red. Eumelanin is brown -black. Melanin absorbs UV radiation preventing damage to epidermal cells. The melanosomes aggregate above the nucleus to protect the DNA.

Question 35

What are the three main types of wounds

Answer 35

Superficial - damage to epidermis only
Partial thickness- all epidermis lost, some of dermis destroyed
Full Thickness - all of epidermis and dermis destroyed. Hypodermis (adipose tissue) can also be destroyed exposing bone and muscle.

Question 36

How are superficial wounds healed

Answer 36

The migration of keratinocytes from the wound edge and dermal appendages (sweat glands, hair follicles and sebaceous glands). Once all the keratinocytes are in contact on all sides then stratification can occur.

Question 37

How are partial thickness wounds healed- 4 phases

Answer 37

1. Inflammatory phase where immune cells come to eliminate microbes, foreign material.
2. Migratory phase where keratinocytes migrate from the wound edge and appendages. Fibroblasts migrate into the clot make collagen fibres to make a scar.
3. Proliferative phase- keratinocytes proliferate and undergo stratification
4. Maturation phase, the scab falls off.

Question 38

Why are full thickness wounds harder to repair

Answer 38

All the reservoirs of epidermal stem cells have been destroyed.

Question 39

Current full thickness wound treatment is … How does this work. and how long does it take to heal.

Answer 39

Split thickness skin graft taking all the epidermis and part of the dermis from an undamaged donor site to cover the wound. Donor site repairs in 10-14

Question 40

what is the problems with current gold standard treatment for full thickness wounds

Answer 40

If >30% total body SA wounds then not enough undamaged skin to cover all wounds.
Requires multiple rounds of grafting. Long hospital stays for patients.

Question 41

What is the new alternate way to treat full thickness wound

Answer 41

A small piece of patient skin, isolate the cells in skin and then grow enough to cover their wounds.

Question 42

What is the work being done by Upside biotechnologies to supplement thick skin grafting.

Answer 42

Grow a full thickness skin, which is a permanent wound solution -> autologous. Skin grown fast- 100 fold return in 16 days. Reducing time to total wound closure.