Lecture 19 + 20 - Skin

Question 1

what are the general functions of the skin

Answer 1

A physical barrier to microbes, scratches, grazes, chemicals ect

prevention of fluid loss and entry (homeostasis)

thermoregulation
sweating

sensation , pressure, heat

synthesise vit D

Question 2

what is the structure of the skin ?

Answer 2

• Epidermis(4 layers) – Stratified squamous keratinised epithelium
• Stratum corneum(horny layer) –Dead squames of keratin
• Stratum granulosum(granular layer)
• Stratum spinosum(prickle cell layer)
• Stratum basale(basal layer) –Site of keratinocyte mitosis
• Dermis–Connective tissue layer (loose superficially, then majority is dense irregular)
• Blood vessels • Mechanoreceptors + nerves
• Hair follicles
• Sweat glands –Eccrine or apocrine
• Sebaceous glands –Produce sebum (oily substance) •

Hypodermis(subcutaneous tissue) –Adipose tissue and loose connective tissue

Question 3

skin histology ? do you know it ?

Answer 3

look it up

Question 4

what is psoriasis

Answer 4

Autoimmune condition

keratinocytes synthesis keratin this takes a transit time to the surface in 2-3 days in psoriasis instead of 28-40 days - highly proliferative epidermis

clinical features

silver scales - desquamating stratum corneum

ingrowth of blood vessels

Question 5

what is melanin and melanocytes ?

Answer 5

melanoctye is the mealnin porducing cell of the body
has many projections into the keratinocytes at the basal layer - it puts brown pigment into

melanin gives us colour

• Brown pigment -Absorbs UV light, therefore protecting against DNA damage
• Produced by melanocytes–In the basal layerof the epidermis
• Pigment donated to keratinocytes which migrate upwards
• Involves pinching off of melanosome which is endocytosed by keratinocytes

melanoctyes are not increase in darker skin, they simply are more active in porducing melanin

Question 6

causes of inflammation ?

Answer 6

1. could be vasodilation causing rubor and calor
2. could be influx of leucoctyes
3. tumor from increased microvasular permability

Question 7

what is the role of the hypodermis ?

Answer 7

Hypodermis(subcutaneous tissue) –Adipose tissue and loose connective tissue

thickness of the hypo varies in location and gender - woman hips men abdomen

Provides and energy store
insulatates
shock absorber
conncets skin to muscle and bone

Question 8

what is the role of the dermis ?

Answer 8

Location:
• Between epidermis and hypodermis

Structure:
• Three layers
• Papillary - upper
• Reticular - lower
• Dermal papillae – interdigitating

Functions:
• Contains hairs and sweat glands - thermoregulation
• Contains sensory structures – special senses - touch
• Gives structure to skin and so body shape

Thinning of this layer and hypodermis during ageing is also responsible for skin
wrinkling – less collagen and less elastin

Question 9

what is the role of the epidermis ?

Answer 9

Structure:
• Four layers of cells (thin skin)
• Five layers (thick skin)
• Held together by adherens junctions,
• Some terminal nerve endings
• NO blood vessels

Functions:
• Prevents water loss
• Prevents entry to bacteria and parasites
• Special cells that present pathogens to immune cells
• Synthesis of keratin
• Prevents tissue loss due to abrasion

Question 10

what are the layers of epidermis role and functions ?

you do not need all the details for this

Answer 10

Stratum corneum (horny cell layer):
• Outermost layer made of squames (dead keratinocytes)
• Thick on palms and soles of feet – prone to injury
• Continuously shed

Stratum lucidum (transparent layer):
• Only on palms and soles of feet

Stratum granulosum (granular layer):
• Stratified squamous epithelium
• Lamellar granules (filament-associated proteins that
assemble keratin fibrils and secrete it)
• Tonofibrils (bundles of keratin filaments and keratohyalin granules) made by lamellar bodies

Stratum spinosum (spinous layer):
• Cuboidal epithelium arranged in 3 layers(held together by desmosomes)
• Producers of lamellar bodies (keratin factories)
• First time Golgi apparatus appears

Stratum basale (basal cell layer)
• Tall columnar epithelial cells
• Constantly renew keratinocytes by cell division
• As daughter cells differentiate they move away from theepidermis-dermis junction
• These make keratin filaments (tonofilaments)
They lose their ability to divide
• Also home to the melanocytes – produce melanin

Question 11

what are the two (four) types of skin ? what variations do they have ?

Answer 11

Hairy skin - that is usually thin skin

Non Hairy Skin - that is usually thick skin
this lacks hair , pilli muscles , sebaceous glands

Question 12

what are the functions of hair ?

Answer 12

Thermoregulation
• Hair lays flat when body temperature is within normal range or elevated
• Hair stands erect when body temperature is lower than normal range
Arrector pili muscle contracts when stimulated by sympathetic fibres from the autonomic
nervous system
• Also acts a partial barrier to UV rays (scalp)

Sexual attraction

Sensation

Protection
• Eyelashes and nasal hair prevent dust and pathogens from entering the body
• Eyebrows reduce the amount of light and sweat from entering the eyes

Question 13

we also have mechanorecptors and nails

what are they ?

Answer 13

mechano - sensation - register pain, temp changes, vibrations ect

nails - keratin - protect the finger tip