Structure of Skin

Question 1

define the integument

Answer 1

the tissue surrounding an organism’s body or an organ within - skin, hair and nails as the integumentary system

Question 2

what are the three layers of the skin?

Answer 2

epidermis = outer epithelial layer
dermis = middle layer of connective tissue and collagen
hypodermis = inner fatty layer

Question 3

functions of the skin?

Answer 3

protection as a barrier against external insults
- keeps water in, prevents dehydration
- resident immune cells in skin protect against infection
- protect against injury and solar radiation

thermoregulation
sensation - skin has sensory receptors
repair
vitamin D production

Question 4

describe the use of the epidermis

Answer 4

• protects us from pathogens and the environment
• vitamin D production using UV light
• gives us our skin colour

Question 5

name the different layers of the epidermis from bottom to top

Answer 5

basal layer/ stratum basale
spiny layer/ stratum spinosum
granular layer/ stratum granulosum
(stratum lucidium) - not a main layer but is present in thick areas of skin (soles of feet)
cornified layer/ stratum corneum

keratinocytes are constantly differentiating and moving up through the layers, takes about 20-50 days

cells are constantly shed and constantly need replacing

Question 6

describe the basal layer

Answer 6

innermost layer, attached to dermis

has constantly mitotically proliferating basal keratinocyte stem cells

daughter cells move up through the different layers, differentiating through them

Question 7

describe the spiny layer

Answer 7

keratinocytes with many desmosomes between cells - white spiny projections/structures that hold the spiny layer and entire epidermis together

Question 8

describe the granular layer

Answer 8

keratinocytes with keratohyalin granules (containing precursor to keratin) and lamellar bodies (containing lipids)

keratinocytes undergo keratinisation
- keratinocytes flatten and die, produce lots of keratohyalin and glycolipids which are packaged into keratinocyte granules and lamellar bodies
- keratohyalin granules aggregate and form large keratin bundles
- lamellar bodies are secreted and stick on outer surface of keratinocyte
- cells lose nuclei, differentiate into cornified layer cells and move up

Question 9

describe the cornified layer

Answer 9

outermost layer of cornified/ keratinised keratinocytes
- flattened cells with no nuclei
- large keratinocyte granule = makes cell tough and resistant to injury
- non-polar lipids on outside of keratinocyte, between cells = make skin waterproof

Question 10

name other cells in the epidermal layer apart from keratinocytes

Answer 10

melanocytes
Langerhans cells
Merkel’s cells/discs

Question 11

describe melanocytes of the epidermis

Answer 11

melanocytes make melanosomes - pigment granules, which are transferred to basal keratinocytes through melanocytes long dendrites

basal melanocytes then position melanosomes distal to the nucleus as a cap - protects nucleus from UV damage, and provides pigment for skin

black people have more melanin than white people, more protection against UV damage

Question 12

describe Langerhans cells of the epidermis

Answer 12

antigen presenting immune cells that protect against microbes

as dendritic cells they form an immune network

hard to visualise with H&E staining, require an immunoperioxidase stain

Question 13

describe Merkel’s cells of the epidermis

Answer 13

sensory receptor cells - superficial, slow adapting and have a small receptor field

good for high resolution tactile discrimination

Question 14

how is vitamin D production related to the epidermis?

Answer 14

requires UV light from sunlight- vitamin D3 is converted in the liver and kidney to its active form

vitamin D3 as active vitamin D precursor is made mostly in the basal layer - needs UV light

melanin protects skin cells from UV light damage - black people are more protected as they have more melanin, but they need for UV light to make the same amount of vitamin D3

Question 15

describe the dermis

Answer 15

middle layer of dense, irregular connective tissue - made up of interconnected elastin and collagen fibres produced by dermal fibroblasts

responsible for tensile strength and elasticity - from collagen and elastin

has blood vessels, skin glands and sensory receptors - contains the blood and nerve supply for epidermis

Question 16

what are the two layers of the dermis?

Answer 16

thin papillary layer
deeper reticular layer = interconnected mesh of fibres running in all directions

Question 17

describe the structure of the dermal-epidermal border and its advantages

Answer 17

consists of dermal papillae and rete ridges

dermal papillae protrusions extend from dermal to epidermal tissue, rete ridges are extensions from the epidermal to dermal layer

wavy structure allows layers to resist sheer forces as they rub together, especially in thicker areas of skin

Question 18

describe the hypodermis

Answer 18

below the dermis, insulates deeper tissues and anchors skin to muscles with connective tissue

consists of well vascularised connective and adipose tissue - site for fat storage, contains fat glands = offers insulation and energy storage

also contains hair follicles, nerves and blood supply - vascularisation allows fats to be deposited and taken up

thickness varies with age, body state and nutrition, though it’s often the thickest layer of skin

Question 19

functions of each of the skin layers?

Answer 19

epidermis = protective barrier against pathogens, UV radiation and the environment

dermis = structural support, elasticity, tensile strength and blood & nerve supply to epidermis

hypodermis = insulates deeper layers, anchors skin to muscles with connective tissue
= site for fat storage with well-vascularised adipose tissue and fat glands.

Question 20

describe the structure and properties of hair

Answer 20

consists of hair shaft, root and bulb - hair bulb sits within a hair follicle, extends into the dermis

hair follicle interacts with apocrine and sebaceous glands, arrector pili muscles and nerve receptors

hair bulb contains hair matrix for hair growth and pigmentations - contains two types of cells:
1. follicular keratinocytes = produce hard keratin which fills follicular keratinocytes, flattens organelles and turns them into compact cells as they get pushed out of the hair follicle
- follicular keratinocytes only replicate in the hair bulb a set number of times before they stop and hair follicle falls out = baldness

2. melanocytes = produce pigment/melanin for hair colour, stop with age at which point hair starts turning white

Question 21

what causes baldness?

Answer 21

follicular keratinocytes in the hair matrix of the hair bulb only replicate a set number of times

hair follicle then falls out, causing baldness

Question 22

name the three types of sweat glands

Answer 22

eccrine seat glands, apocrine sweat glands and sebaceous glands

Question 23

describe eccrine sweat glands

Answer 23

produce water secretion as sweat on the surface of the skin, cools the body by evaporation

Question 24

describe apocrine sweat glands

Answer 24

secretes oily fluid in armpit and anogenital regions

unknown function, do contain pheromones and contribute to odour - active following puberty

Question 25

describe sebaceous glands

Answer 25

secrete oily sebum - antibacterial, conditioner for hair and skin to prevent dryness and flaking

function following puberty

Question 26

describe nail structure and features

Answer 26

nail structure:
- nail folds = sides of a nail
- eponychium/ cuticle = semi-circular layer of dead skin keratinocytes, prevents pathogen entry
- nail matrix = creates the nail plate, contains nerves, lymphatics and blood vessels supporting the nail

modified keratinocytes in the nail matrix replicate and undergo keratinization, forming the visible nail plate

Question 27

describe the two types of sensory receptors

Answer 27

1. free nerve endings = detect pain, thermal sensations, and light touch
2. encapsulated endings
   - Pacinian and Meissner’s = fast adapting; vibration and moving touch resp.
   - Merkel’s discs and Ruffini endings = slow adapting; sustained touch and skin stretch resp.
   - root hair plexus = fast adapting, for root hair displacement
   - Krause end bulbs = touch, pressure, maybe thermoreceptors

fast- adapting nerve fibres send information related to changing stimuli