Physiology Flashcards
What are skin appendages
Addition to the skin layers
Includes: hair follicles, melanocytes, glands etc
What are Blaschko’s lines
Show the developmental growth pattern of skin
Does not follow vessels or nerves
What can happen if there is a malformation in a Blaschko line
Disease can present in the segment that that line covers
Allows you to determine that the skin abnormality was developmental
What does the skin consist of
Epidermis = 5 layers
Dermo-epidermal junction
Dermis = connective tissue
Sub-cutis = mostly fat
Also appendages - nails, hair etc
What is the function of the dermis
Structural rigidity
Blood vessels, lymphatics, glands and follicles are found here
Also contains numerous nerve endings - sensory functions
Are the epidermal layers the same across the whole body
NO
They vary depending on functions
E.g. Thicker keratin layer on palms and soles
Differences in number of hair follicles and sweat glands
What controls epidermal turnover
Growth factors
Cell death
Hormones
What can occur if there is loss of control of epidermal turnover
Skin cancer
Psoriasis - cycle is accelerated
Describe the basal layer (stratum basal)
4th layer of epidermis Usually one cell thick
Small cuboidal cells
Lots of intermediate filaments
Highly metabolically active - divide all the time
Contains the Merkel Cells
Describe the prickle cell layer (stratum spinosum)
3rd layer of epidermis Large polyhedral cells
Lots of desmosomes - connections
Move up through layers erratically
Describe the structure of the granular layer
2nd layer of epidermis 2-3 layers of flatter cells Large granules containing structural filaggrin and protein Have lamellar bodies High lipid content Cell nuclei lost
What is the function of the granular layer
Goes on to form the ‘glue’ that seals the skin
The cells shrink and die, releasing their granules
Lipids and proteins released seal the skin
What is the function of the keratin layer
Forms a tight waterproof barrier
Describe the structure of the keratin layer (stratum corneum)
Made up of overlapping cell remnants - corneocytes
Cells have lost their nucleus and cytoplasm
80% keratin and filaggrin
What causes warts
Infection that affects the keratinocytes
Viruses infect the cells and cause increased proliferation
Tries to push infected cells out but just forms a thickened layer on top = wart
What is the function of melanocytes
Creates melanin pigment by converting tyrosine - occurs in melanosomes
This absorbs light so works as a natural sun protection
Forms a cap over the nucleus to protect DNA
Describe the structure of melanocytes
Have long dendrites
Forms synapses with the basal layer to produce pigment
Found in the keratin layer
What causes melanin to be produced
Exposure to UV light
Hormones
What causes vitiligo
T cells attack melanocytes
Causes loss of pigmentation
Autoimmune condition
What is albinism
Genetic condition
Melanocytes don’t produce pigment
What is Nelson’s syndrome
A disorder where melanin stimulating hormone is produced in excess by the pituitary gland
Causes hyperpigmentation
Sometimes occurs as result of a tumour
What is a tumour of the melanocytes called
Melanoma
Malignant
What is the function of Langerhan’s cells
Part of skin immune system
Pick up antigens in skin and transport them to the lymph nodes
Act as antigen presenters
Describe Merkel cell cancer
Malignant transformation of the merkel cells
Very dangerous cancer with high mortality - 90%
Describe the structure of a pilosebaceous unit
Has an epidermal component plus dermal papilla
Contains specialised keratins
Has an adjacent sebaceous gland - moisturises skin
Melanocytes above papilla give hair colour
Which hormones can influence hair growth
Androgens
Thyroxine
What is Virilisation
Excess hair growth in male pattern due to excess androgen
May be due to an androgen-producing tumour
What is alopecia areata
Autoimmune condition where T lymphocytes attacks the hair follicle
Causes hair loss
Describe the structure of the nails
Contains specialised keratins
Come from specially differentiated skin cells
Nail plate of hard keratin sits on nail bed
Matrix contains dividing cells which grow the nails
Firm and rigid
If bed is damaged it is often irreversible and the nail will continue to grow in a abnormal way
What can happen if the DEJ fails
The skin can slip, split and blister
What is Bullous Pemphigoid
A skin condition where antibodies form against parts of the dermo-epidermal junction
Causes large blisters
Seen in elderly patients
What is epidermolysis bullosa
A genetic condition caused by a mutation in one of the proteins of the DEJ
Skin is extremely fragile and blisters/falls off easily
Can be life threatening
What makes up the dermis
Ground substance
Cells: mainly fibroblasts (connective tissue), macrophages, mast cells, lymphocytes and langerhans cells
Fibres: collagen and elastin - given tensile strength and elasticity
Muscles, blood vessels, lymphatic system and nerves
Describe the fibres found in the dermis
Most are collagen which provides strength and support
Elastin provides skin elasticity
Becomes less functional as we age
What is photo ageing
Exposure to UV light can attack the fibres in the dermis and cause ageing - more wrinkles etc
Smoking can also have this effect
Why does the skin have more blood supply than necessary
Partly due to role in thermoregulation - arteriovenous anastomoses are particularly important in this
What is an angioma
Benign overgrowth of blood vessels
Presents as large purple patches
Describe the nerves within the skin
Somatic sensory
- free nerve ending for pain and heat
- Pacinian (pressure) receptors
- Meissners (vibration) corpuscles
Autonomic nerves
- for blood vessels, nerves and glands
What is the function of the sebaceous gland
Lubricate and moisturise hair and skin
May offer immune protection by preventing bacteria from entering the follicle
What can cause acne
Overproduction of sebum by sebaceous glands
Blocks the pores
Occurs during puberty due to hormones
Describe apocrine sweat glands
Part of pilosebaceous unit - open into hair follicle
Activated during puberty - androgen dependent
Produce oily fluid that starts to smell
Found in axillae, nipple and genitals
What is the function of eccrine sweat glands
Produce sweat to cool us down - regulate heat and salt loss
Moistens palms
On the soles they improve grip
Where are eccrine glands found
Over the whole body
Axilla palms and soles in particular
Not in lips and genitals
What are the functions of the skin
Barrier Metabolism and detoxification Fluid balance Thermoregulation Immune defense Communication - sensory function
What is toxic epidermal necrolysis
Drug causes failure of cohesion between the epidermis and dermis - usually across 90% of the body
Increases infection risk, pain, loss of moisture and protein
What does the skin act as a barrier against
Friction, mechanical trauma, UV
Irritants, allergens, toxins
Bacteria, viruses, fungi
What is the function of vitamin D
Calcium absorption
What can vitamin D deficiency cause
Rickets in children
Osteoporosis in the elderly
How does the skin help with thermoregulation
Has thermoreceptors
This will induce behavioural changes
Blood vessels dilate or constrict to control heat
Sweating cools us down
How does the skin act in immune defence
Langerhan’s and T cells are important
An intact dermis & epidermis are key
What are the sensory functions of the skin
Touch, pressure and vibration
Pain and itch
Temperature
The epidermis is composed primarily of which cell type
Keratinocytes
Where are keratinocytes produced
In the basal layer of the epidermis
They then undergo a process of migration starting from the basal layer, upwards to the stratum corneum
What are the 5 layers of the epidermis from top to bottom
Stratum corneum Stratum lucidum Stratum granulosum Stratum spinosum Stratum basal
What are the two main layers of the dermis
Papillary dermis - loose CT and lots of cells
Reticular dermis - denser CT and fewer cells
Do people with darker skin tones have more melanocytes
No - we all have the same number
Darker skin has larger melanosomes containing more melanin and the melanosomes degrade slowly compared to fair skin
How does the keratin layer differ in dark skin
Keratin layer in darker skin tones is more compact
Why are those with darker skin at higher risk of keloid scars
Larger and more numerous fibroblasts
The higher fibroblast activity increases keloid risk
List the 3 phases of the hair cycle
Anagen – growth phase, 2-7years, most hairs in this phase 85%
Catagen – transitional stage, 2 weeks, hair detaches from the blood supply
Telogen - approx 3 months, hair falls out, ‘released from the follicle’ and new hair grows behind it
Which parts of the body lack sebaceous glands
Palms and soles
Name the muscles associated with hair follicles
Arrector pili
Can pull the hair perpendicular to the skin during cold / fright ( goose bumps)
Meissener’s corpuscles detect what
Tactile sensation
Found in dermis
Pacinian corpuscles detect what
Deep pressure
Found in dermis
What is primary intention healing
When the edges of a wound are brought together - leads to rapid healing
Usually with stitches etc
What is healing by secondary intention
Wound is left open and heals from the bottom up
Inflammation then granulation then tissue remodelling
Used for for larger wounds that are too tight to stitch, or areas where direct closure would cause significant distortion
Describe the different degrees of burn
First degree: epidermis only.
Second degree/Partial thickness: epidermis and dermis.
Third degree/ Full thickness: extends beyond dermis
