Lecture 14: Human skin biology Flashcards
How much percent body weight is skin
7-16%
What is the Total body surface area of skin
average 2m squared
How thick are eyelids
0.5 mm thick
How thick can palms and soles of feet be
4 mm or thicker
How does skin thermoregulate
Thermoregulation - evaporation of sweat, constriction or vasodilation of blood vessels in the dermis decrease or increase heat loss
List the functions of skin
Thermoregulation, blood reservoir, protection/barrier, detecting sensation, synthesis of vitamin D.
How much blood can the skin hold
8-10% of the total blood volume
What does the corneocytes and lipid bilayer of skin help protect against
Environment, chemicals. pathogens, heat, UV damage and water/blood loss.
What types of sensation does the skin detect
Touch, pressure, pain and temperature
What role does skin do in Vitamin D synthesis
Vit. D precursor requires modification by UV before active form can be made in the liver
What are the three parts of the skin structure looked at in this lecture
Epidermis (turnover/barrier function), Dermis (structural strength, elasticity) and pigmentation (melanocytes)
What are the types of cells in the epidermis and what are their function and where in the epidermis are they found
Keratinocytes -Melanocytes (produce melanin, intraepidermal macrophage (Langerhans) cells, Tactile epithelial (Merkel) cell.
What is the general structure features of the epidermis: what layer, mainly consists of, provides, no
Top layer of skin, mainly consisting of keratinocytes
Provides barrier for continued renewal and no structural strength
Name the stratified layers of the epidermis from top to bottom including the extra layer for thick skin on soles, fingertips and palms.
All start with stratum corneum, ((lucidum for thick)), granulosum, spinosum, basale
How does the nutrient supply and waste removal happen for epidermis
It is avascular so it has diffusion through the dermis which is vascular.
What is the function and location of keratinocytes
produce keratin for protection and lamellar granules for waterproofing. Found in the 4/5 distinct layers of strata in epidermis
What is the function and location of melanocytes
Produce the pigment melanin, contacting on average 36 keratinocytes and transferring melanosomes to them
Found at the basement membrane.
What is the function and location of Langerhans cells
Intraepidermal macrophages surveil the epidermis for foreign organisms, helping other cells to identify and destroy invading microbe
What is the function and location of Merkels cells
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.
Why is stratification of epidermis important
Crucial for barrier function and continued renewal of the epidermis.
Tell me about the Stratum basale: layers, whats happening there
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
Tell me about the stratum spinosum: layers, whats happening there
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.
Tell me about the stratum granulosum: layers, whats happening there
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
Tell me about the stratum Lucidum: layers, whats happening there
only present in thick skin. 4-6 layers. additional toughness
Tell me about the stratum corneum: layers, whats happening there
25-30 layers of flattened dead keratinocytes. Thin membrane enclosed keratin overlap like snake scales. shed by epidermis
What is the process of stratification
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
list three features of the stratification process
Changes in gene expression distinct between layers. A defined and controlled process. Complete epidermal turnover once a month.
What is the general structure features of the dermis: formed from, consists of, thickness, strength, stability
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
What is the difference between the reticular and papillary layers of dermis
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.
What are the rete ridges/ papillae
Small ridges on the interface between the epidermis and dermis provides resistance to shear force. Increases surface area for diffusion
What are fibroblasts
Long spindley cells that produce collagen for strength and elastins for elasticity –> the extracellular matrix.
What cells are present in the dermis
Fibroblasts, immune cells, nerve cells, vasculature
What is the function of vasculature
to supply nutrients and remove waste for both the dermis and epidermis
What are the two types of melanin and what is the function of melanin
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.
What are the three main types of wounds
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.
How are superficial wounds healed
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.
How are partial thickness wounds healed- 4 phases
- Inflammatory phase where immune cells come to eliminate microbes, foreign material.
- Migratory phase where keratinocytes migrate from the wound edge and appendages. Fibroblasts migrate into the clot make collagen fibres to make a scar.
- Proliferative phase- keratinocytes proliferate and undergo stratification
- Maturation phase, the scab falls off.
Why are full thickness wounds harder to repair
All the reservoirs of epidermal stem cells have been destroyed.
Current full thickness wound treatment is … How does this work. and how long does it take to heal.
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
what is the problems with current gold standard treatment for full thickness wounds
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.
What is the new alternate way to treat full thickness wound
A small piece of patient skin, isolate the cells in skin and then grow enough to cover their wounds.
What is the work being done by Upside biotechnologies to supplement thick skin grafting.
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.
