Physiology Flashcards
What percentage of the population have a skin condition?
> 25%
What is the skin?
- epidermis
- dermis
- non hairy and hairy skin
Describe the structure of the epidermis
- stratified cellular epithelium
- outer layer
- 95% of the epidermis is keratinocytes
- movement from basement membrane
- four defined layers
- other cells; melanocytes, langerhans cells and merkel cells
Describe the structure of the dermis
- beneath epidermis
- connective tissue
- thick coat of collagen fibres
What is the epidermis derived from?
- ectoderm cells form a single layer periderm
- gradual increase in layers of cells
- periderm cells cast off
What is the dermis derived from?
Formed from mesoderm below ectoderm
What are melanocytes?
Pigment producing cells from neural crest
When does gastrulation take place?
Between days 7 and 10
Describe the skin development at four weeks
- periderm
- basal layer
- dermis (corium)
Describe the skin development at 16 weeks
- keratin layer
- granular layer
- prickle cell layer
- basal layer
- dermis
What are blaschkos lines?
- developmental growth pattern of skin
- not following vessels, nerves of lymphatics
When a pattern runs across the blaschkos lines, what does this indicate?
It is a genetic problem, inborn error
What does the skin consist of?
- epidermis
- appendages; nail, hair, glands, mucosae
- dermo-epidermal junction
- dermis; connective tissue, less cellular
- subcutis - predominantly fat
What is pilum?
Hair in latin
What is a pilosebaceous unit?
Hair and a sebaceous gland
What do keratinocytes contain?
Structural keratins
Name the four cell layers of the epidermis
- keratin layer
- granular layer
- prickle cell layer
- basal layer
Describe the structure of sebaceous glands
Torturous tubes filled with grease
Describe the regulation of epidermal turnover
- balance between cells in and out
- control by; growth factors, cell death, hormones
- loss of control in; skin cancer, psoriasis
Most of the dermis is what?
Collagen fibres - produced by fibroblasts
Describe differentiation of the epidermis
- keratinocytes migrate form basement membrane
- continuous regeneration of epidermis
- 28 days from bottom to top
- they proliferate much faster in psoriasis
Describe the basal layer of the epidermis
- usually one cell thick
- small cuboidal
- lots of intermediate filaments (keratin)
- highly metabolically active
Describe the prickle cell layer of the epidermis
- larger polyhedral cells
- lots of desmosomes (connections)
- intermediate filaments connect to desmosomes
What are desmosomes?
Cell to cell contacts that allow both adhesion (to impart stability) and flexibility (so cells can move upwards)
Describe the granular layer of the epidermis
- 2 to 3 layers of flatter cells
- large keratohyalin granules, contain structural filaggrin and involucrin proteins
- odland bodies (lamellar bodies)
- high lipid content
- origin of cornified envelope
- cell nuclei lost
Name the key feature of the short filaggrin breakdown products?
They retain water
Describe the keratin layer of the epidermis
- corneocytes, overlapping non-nucleated cell remnants
- insoluble cornified envelope
- 80% keratin and filaggrin
- lamellar granules release lipid
- tight waterproof barrier
Human papilloma virus infection affects which type of skin cell?
- keratinocytes
- virus infection of keratinocytes causes warts
Describe the mucosal membrane
- highly specialised for function (eyes, mouth, nose, genito-urinary and GI tracts)
Describe the oral mucosa
- masticatory; keratinised to deal with friction/ pressure
- lining mucosa; non keratinised
- specialised mucosa; tongue papillae, taste
Describe ocular mucosa
- larcimal glands
- eye lashes
- sebaceous glands
True or false?
Mucosal surfaces can also be affected by skin diseases
True
Becomes white as keratin builds up
Name the epidermal cells
- 95% of epidermal cells are keratinocytes
- melanocytes (basal and suprabasal)
- langerhans cells (suprabasal)
- merkel cells (basal)
Where do melanocytes orginate?
Migrate from the neural crest to the epidermis in the first 3 months of foetal development
Where are melanocytes found?
Basal layer and above
Describe the function and structure of melanocytes
- pigment producing dendritic cells
- contains organelles; melanosomes
- convert tyrosine to melanin pigment; eumelanin (brown or black), phaeomelanin (red, yellow)
- melanin absorbs light (neutral density filter)
- full melanosomes (melanin granules) transferred to adjacent keratinocyte via dendrites
- form protective cap over nucleus
Melanin is derived from what?
Tyrosine
Melanin is hormonally driven by what?
- alpha melanocyte stimulating hormone (aMSH)
What is vitiligo?
An autoimmune disease with loss of melanocytes
What is albinism?
A genetic disorder where there is a genetic partial loss of pigment production
What is nelsons syndrome?
A disorder in which melanin stimulating hormone is produced in excess by the pituitary
What is a malignant melanoma?
A tumour of the melanocyte cell line - always deadly if not treated
Describe langerhans cells of the skin
- mesenchymal origin; bone marrow
- prickle cell level in epidermis
- also found in dermis and lymph nodes
- involved in the skin immune system; antigen presenting cells, pick up antigen in skin and circulate to lymph nodes via lymphatic system - a type of dendritic cell
Describe merkel cells
- basal
- between keratinocytes and nerve fibres
- mechanoreceptors
What is merkel cell cancer?
- rare
- caused by viral infection - high mortality
Describe pilosebaceous units (hair follicles)
- epidermal component plus dermal papilla
- specialised keratins
- adjacent sebaceous gland
- hair pigmentation via melantocytes above dermal papilla
What is natures own emollent?
Sebum greasy wax (ceramides), greases the epidermis
What are the three phases of growth of hair follicles?
- anagen; growing
- catagen; involuting
- telogen; resting
Name the types of hair follicle
- lanugo (in utero)
- vellus
- terminal
Name some hormonal influences on hair growth
- thyroxine
- androgens
Is human hair growth synchronous or asynchronous?
Asynchronous
What is hirutism?
Virilisation due to excess androgen from a tumour
What is alopecia areata?
Autoimmune hair loss
Describe the structure of nails
- specialised keratins
- nail matrix / root similar to hair bulb
- growth rate 0.1mm per days
- some drugs increase nail / hair growth
Where is the nail matrix located?
Underneath the nail proximal to the bed
Describe the cuticle
A protective layer
What is luluna?
Keratin
What does clubbing of the nails affect?
Stem cells affected in the keratin layer
Where are the stem cells located in the nail
In the nail matrix
What are the three plates of nail growth?
- dorsal
- intermediate
- ventral
What are the divisions of the matrix?
- dorsal
- intermediate
- ventral
Describe the dermo-epidermal junction
- interface between epidermis and dermis
- key role in epithelial - mesenchymal interactions
- support, anchorage, adhesion, growth and differentiation of basal cells
- semi-permeable membrane acting as barrier and filter
The dermis contains what?
- ground substance
- cells; mainly fibroblasts, macrophages, mast cells, lymphocytes and langerhans cells
- fibres; collagen, elastin
- muscles; blood vessels, lymphatics, nerves
What percentage of the dermis is collagen based?
90%
Describe the flow of blood vessels
- arteriole
- precapillary sphincters
- arterial
- venous capillaries
- post capillary venules
- collecting venules
Where are deep vessels found?
In the subcutaneous fat
The papillary dermis supplies what with blood?
- the epidermis
- materials diffuse across the dermis epidermis junction
Describe the lymphatic vessels
- sub epidermal meshed networks
- smaller noncontractile vessels»_space;> larger contractile lymphatic trunks
- continual drainage of plasma proteins, extravasated cells and excess interstitial fluid
- important immune functions; immune surveillance by circulating lymphocytes and langerhans cells, channelling of micro-organisms / toxins
What are the special receptors of the skin?
- pacinian (pressure) corpuscles
- meissners (vibrations) corpuscles
Are pacinian and meissners corpuscles somatic sensory or autonomic nerve supply?
Somatic sensory
What type of nerve senses light touch sensation?
Free nerve endings
Give an example of a condition where the free nerve endings grow without ingivition
Neurofibromatosis
Which cells give pigmentation?
Melanocytes above the dermal papilla
Name a specialised keratin
Adjacent sebaceous gland
Where are the largest and most abundant pilo-sebaceous units found
In the face, upper back and upper chest
Describe involuted hairs
Hairs that are still embedded but are not growing
Describe a condition in which there is an attack on anagen hairs
Alopecia areata
What are the three skin glands?
- sebaceous
- apocrine
- eccrine
Which glands are involved in acne?
Sebaceous glands
Describe apocrine glands
- feed into the hair follicle
- most likely linked to pheromones
- develop as part of pilosebaceous unit
- axillae and perineum
- androgen dependent
- produce oily fluid»_space;> odour after bacterial decomposition
Which glands play a role in thermoregulation?
Eccrine glands
Describe sebaceous glands
- holocrine secretion opening into pilary canal
- widely distributed; largest glands face and chest
- hormone sensitive; quiescent pre-puberty
- produce sebum; squalane, wax esters, TG and FFA
- functions; control moisture loss, protection from fungal infection
Describe eccrine sweat glands
- whole skin surface; palms, soles and axillae in particular
- sympathetic cholinergic nerve supply; mental, thermal and gustatory stimulation
- ultrafiltration; can be >10L per day, NaCl and HCO3 reabsorbed, hypotonic fluid
- functions; cooling by evaporation, moisten palms and soles to aid grip
Name the functions of the skin
- barrier function
- metabolism and detoxification
- thermoregulation
- immune defence
- communication
- sensory functions
Describe the barrier function of skin
- two way barrier; epidermis
- physical; friction, mechanical trauma, UV radiation
- chemical; irritants, allergens, toxins
- pathogens; bacteria, viruses, fungi
Which UV causes the most damage?
UVA and UVB
What is the role of the superior cap of melanin pigment in basal cells?
Melanin absorbs UV rays to protect DNA in the cells nuclei
Describe metabolism and detoxification of the skin
- skin is metabolically active
- vitamin D metabolism
- thyroid hormone metabolism
- defence against chemicals, drugs, pollutants and sunlight
Vitamin D3 is stored as what in the liver?
Hydroxycholecalciferol
Vitamin D3 is converted to what in the kidney?
1,25-dihydroxycholecalciferol
Cholecalciferol is converted to vitamin D3 at what UV wavelength?
290 to 320nm
Where does thyroid hormone metabolism take place?
20% occurs in thyroid gland
80% in peripheral (to thyroid) tissues including skin
If there is less blood in the superficial plexus what is retained?
Heat
Name the sensory functions of the skin
- touch, pressure, vibration
- pain and itch
- heat and cold
- nerve endings and receptors in skin
Name the basic tissue groups found in the skin
- epithelium
- nervous tissue
- glands
- muscle
- hair
- adipose tissue
- connective tissue
The skin consists of what type of epithelium?
Stratified squamous epithelium
Blood vessels are lined with which type of epithelium?
Simple squamous epithelium
What gland is described?
Derived from epidermis. Lobulated masses in dermis which usually secrete an oily substance into hair follicle to coat hair and skin. Not present in palm and sole skin
Sebaceous glands
What gland is described?
Found over the whole body except the lips and genital. Coiled tubular structures which regulate heat and salt loss
Eccrine glands
What gland is described?
Limited to axillae/nipple/genitals. Develop at puberty and open into hair follicles
Apocrine glands
What is attached to hair follicles and can pull the hair perpendicular to the skin during cold
Arrector pilli
also present in the walls of blood vessels
What provides tensile strength and the elastic qualities of the skin?
Collagen fibres and elastic fibres present in the dermis
Where are meissners corpuscles found?
Present in the dermis, just beneath epidermis and abundant in tactile areas of fingers and toes
Where are pacinican corpuscles located?
Located in deep dermis and frequently seen in finger pulp sections
What senses;
- tactile sensation
- deep pressure
- pain
- meissners corpuscle
- pacinian corpuscles
- free nerve endings
What is a hair follicle?
An invagination of the epidermis
Describe hair structure
- central medulla containing soft keratin
- outer cortex and cuticle of hard keratin
- papilla (bulge at base) contains multiple vascular channels
- the hair bulb at the base of the follicle contains the hair matrix and dermal papilla
Nails are plates of cells filled with what?
Hard keratin
Describe the structure of nails
- nail plate; sits on the nail bed
- matrix; cells divide and then produce hard keratin
- cuticle; extension of the skin fold covering the nail root
- hyponychium; secures the free nail edge
Skin failure has what consequences?
- loss of thermoregulation; may contribute to cardiovascular instability
- increased risk of infection; bacterial and yeast infections may result in overwhelming sepsis
- failure of homeostatic function; enormous fluid and electrolyte losses, may result in cardiovascular instability
Name the requirements for healthy skin
- intact physical barrier ie good hydration, not broken infected or injured
- functioning immune system, both innate and adaptive
- functioning vasculature / adequate supply and drainage large and small arterial vessels - for oxygenation
- functioning venous return and lymphatic system, to avoid stasis
- means of temperature regulation; capillary dilatation / constriction, functioning sweat glands
- normal sensory nerve function to warn us about injury
- adequate nutrition
Many surgical wounds heal by means of what?
- primary intention
- the edges are approximated (brought together) by stitches leading to rapid healing
- can be compromised by haematoma, infection, poor suture technique or dehiscence
What is secondary intention healing?
- generally used for larger wounds that are too tight to stitch, or areas where direct closure would cause significant distortion of surrounding tissue
- has three stages
Name the three stages of secondary intention healing
- inflammation
- proliferation and tissue remodelling
- tissue remodelling
Describe the inflammatory phase of secondary intention healing
- platelets form the initial clot and release inflammatory mediators
- leucocytes debride the wound bed by phagocytosing bacteria and scavenging cellular debris
- inflammation gradually decreases as keratinocyte proliferation and new tissue formation become predominant
Describe the proliferation and tissue remodelling phase of secondary intention healing
- cells divide (proliferate) to re-epithelialise the wound surface
- granulation tissue formation is stimulated
- fibroblasts lay down matrix, and contract the wound (fibroplasia)
- endothelial cells develop into new blood vessels (angiogenesis)
Describe the tissue remodelling phase of secondary intention healing
- new tissue is converted into mature scar tissue over a period of months
- fibroblasts lay down collagen to improve the tensile strength of the scar and restore the normal dermal matrix
First degree burns affect which layer of skin?
Epidermis only
Second degree burns affect which layer(s) of the skin?
Epidermis and dermis
Third degree / full thickness burns affect which layer of the skin?
Goes beyond the dermis
Describe superficial burns
- erythematous
- wet
- extremely painful
Describe deep burns
- white or black and charred
- dry
- numb
Chronic wounds often exhibit surface what?
Slough - a mixture of dead cells, polymorphs and bacteria. It is yellow green in colour and may be quite adherent to the underlying tissue. Has an inhibitory effect on healing
How do chronic wounds tend to heal?
- from the edges
- increased risk of infection and slow resolution
What factors contribute to pressure sores?
- prolonged pressure over bony area
- lack of blood flow
- friction from bedding / clothing
- irritation from sweat / blood / urine / faeces
Describe the four stages of pressure sore development
- skin is unbroken but shows a pink or reddened area, may look like a mild sunburn. skin may be tender, itchy or painful
- skin is red, swollen and painful. blisters that may be broken or intact may be present. upper layers of skin begin to die
- sore has broken through the skin and wound extends down to deeper layers of skin tissue. crater-like ulcers are present. wound is prone to infection
- sore extends past the skin and into fat, muscle and bone tissue. blackened dead tissue called eschar may be seen in deep opened wounds
How might you ensure good healing of a laceration on a hand?
- clean wound (check for nerve / tendon / vessel damage)
- suture
- consider antibiotics
- tetanus prophylaxis
