Histology of Skin and Appendages

Question 1

What are the layers formed in skin?

Answer 1

Epithelial layer, epidermis, dermis, hypodermis

Question 2

What is the structural organisation of the epidermal-dermal junction?

Answer 2

Folded into ridges and the papillae rase the epidermis up.

• dermal papillae
• epidermal ridges

Question 3

What are the 7 functions of the skin? State which layer performs this function.

Answer 3

Protection (epidermis) - barrier to infection and UV radiation.
Prevention of desiccation (water loss) in epidermis.
Sensation to touch, heat, pressure in dermis.
Thermoregulation (dermis and hydodermis).
Metabolic (fat stores in hypodermis).
Vitamin D (all layers)
Excretion (urea and ammonia) in dermis.

Question 4

What is the difference between thick skin and thin skin?

Answer 4

Thick skin = keratinised layer and lacks hair follicles

Thin skin = thin cornified layer, generally contains hair follicles

Question 5

Outline the appearance of the epidermis under the microscope

Answer 5

• stratified squamous epithelium (squashed cells)
• keratinised
• principle cell type = the keratinocyte
• Cornified layer (dead cells) with no nuclei present

Question 6

What does the basal layer (innermost layer of epidermis) look like under the microscope?

Answer 6

Cuboidal or columnar cells.

Site of cell division so lots of cells can be seen doing this.

Question 7

What does the prickle cell layer found in the epidermis look like under the microscope?

Answer 7

Cell tightly attached by desmosomes. Cells enlarged and accumulated.

Question 8

How are keratin proteins organised?

Answer 8

They are organised into filaments (10nm) and form bundles that converge on desmosomes.

Question 9

How much of the epidermis do keratinocytes make up?

Answer 9

90%

Question 10

How does keratinisation occur in the granular layer?

In the cornified layer?

Answer 10

Granular layer = cells flatten and keratohyaline granules appear. Protein profilaggrin produced to bundle keratin together.

Cornified layer = cells become extremely squashed, pertains become cross-linked by disuphide bridges, cells die and lose nuclei and other organelles, dehydrated which packs the keratin filaments together.

Question 11

How does a permeable layer form in the skin?

Answer 11

Cells ascend to the prickle cell layer and membrane coated granules appear.
These are released into the intercellular space and fuse to form multiple lipid bilayers arranged in sheets. This seals gaps between clues to make a water-tight barrier.

Question 12

How are cells replaced in the skin?

Answer 12

Division of undifferentiated stem cells.

Cell division is cornified almost entirely to the basal layer.

Question 13

What cells protect the skin from UV?

Answer 13

Melanocytes which produce melanin.
These are mainly in the basal layer.
Melanin accumulates into melanosomes and these are endocytose by keratinocytes.

Question 14

Name 2 other cells of the epidermis and state the roles of these cells

Answer 14

Langerhan Cells - found in the upper prickle cell layer. They form part of the immune system and are macrophage like. They play an important role in immunological response.

Merkel Cells - small number in basal layer of epidermis. They are touch receptors and are involved in sense perception.

Question 15

Describe the organisation of the dermis.

Answer 15

It is dense, irregular connective tissue.
It consists of a papillary and reticular layer.
Conveys blood vessels, lymphatics and nerves.
Consists of parallel bundles of collagen fibres

Question 16

What layer of the skin do each of these sit?

1. Papillary loops
2. Sebaceous gland (secrete semen to lubricate and waterproof the skin)
3. Sweat gland
4. Arterial supply & venous drainage

Answer 16

1 = epidermis
2 = dermis 
3 = hypodermis 
4 = hypodermis

Question 17

In relation to each other, where do the Meissner’s corpuscles and Pacininan corpuscles sit and why?

Answer 17

Meissner corpuscle sit just under the epidermis as they are triggered by light touch.
Pacinian corpuscles sit deeper in the hypodermis as they respond to coarse touch and pressure.

Question 18

What does the secretory portion of the sweat gland do? Location? Structure?

Answer 18

Secretes isotonic fluid (water and ions).
Located at the junction of dermis and hypodermis.
It is highly coiled and a single layer of cuboidal cells + single layer of myoepithelial cells.

Question 19

What does the excretory duct do? What is the structure of it?

Answer 19

The duct moves through the dermis and corkscrews through the epidermis and this portion is impermeable.
There is a double layer of cuboidal cells present and its job is to absorb NaCl to produce hypotonic sweat (lower concentration of electrolytes)

Question 20

Describe the hypodermis

Answer 20

Loose connective tissue, abundant fat cells, allows mobility of skin, bundles of collagen are transverse through the hypodermis

Question 21

What are the two types of glands? Explain the function of each

Answer 21

Apocrine sweat glands -
tips of cell bud off to form vesicles containing the secretion and cytoplasm.

Sebaceous gland - discharge into middle portion of hair follicles, secretes sebum

Question 22

Where is the arrector pili muscle present in the skin?

What is it responsible for?

Answer 22

Inserts into the connective tissue sheath and into the papillary layer of the dermis.
It is responsible for raising the hair.

Question 23

How is a hair follicle distinguishable under a microscope?

Answer 23

Ring structure

Question 24

What is distinguishable layer of a hair follicle?

Answer 24

Medulla - lightly keratinised, large cells
Cortex - heavily keratinised
Cuticle - highly keratinised
Inner root sheath - degenerates at level of sebaceous glands to form a space into which sebum is discharged. Forms the channel for the growing hair.
Outer root sheath - continuous with epidermis, reservoir of stem cells to regenerate the epidermis.

Question 25

What is a hair papilla?

Answer 25

It is the large structure at the base of the hair follicle. It is formed of connective tissue and has a role in directing hair formation. It is is destroyed, no hair will grow back.

Question 26

What is the growth period and quiescence period of hair in the scalp? body hair?

Answer 26

Scalp - Growth period is years and quiescence is 3 months.
Body hair - Growth period is months and quiescence is years.

The base of the follicle identifies whether it is quiescent or not.