Histology of Skin and Appendages Flashcards
What are the layers formed in skin?
Epithelial layer, epidermis, dermis, hypodermis
What is the structural organisation of the epidermal-dermal junction?
Folded into ridges and the papillae rase the epidermis up.
- dermal papillae
- epidermal ridges
What are the 7 functions of the skin? State which layer performs this function.
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.
What is the difference between thick skin and thin skin?
Thick skin = keratinised layer and lacks hair follicles
Thin skin = thin cornified layer, generally contains hair follicles
Outline the appearance of the epidermis under the microscope
- stratified squamous epithelium (squashed cells)
- keratinised
- principle cell type = the keratinocyte
- Cornified layer (dead cells) with no nuclei present
What does the basal layer (innermost layer of epidermis) look like under the microscope?
Cuboidal or columnar cells.
Site of cell division so lots of cells can be seen doing this.
What does the prickle cell layer found in the epidermis look like under the microscope?
Cell tightly attached by desmosomes. Cells enlarged and accumulated.
How are keratin proteins organised?
They are organised into filaments (10nm) and form bundles that converge on desmosomes.
How much of the epidermis do keratinocytes make up?
90%
How does keratinisation occur in the granular layer?
In the cornified layer?
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.
How does a permeable layer form in the skin?
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.
How are cells replaced in the skin?
Division of undifferentiated stem cells.
Cell division is cornified almost entirely to the basal layer.
What cells protect the skin from UV?
Melanocytes which produce melanin.
These are mainly in the basal layer.
Melanin accumulates into melanosomes and these are endocytose by keratinocytes.
Name 2 other cells of the epidermis and state the roles of these cells
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.
Describe the organisation of the dermis.
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
What layer of the skin do each of these sit?
- Papillary loops
- Sebaceous gland (secrete semen to lubricate and waterproof the skin)
- Sweat gland
- Arterial supply & venous drainage
1 = epidermis 2 = dermis 3 = hypodermis 4 = hypodermis
In relation to each other, where do the Meissner’s corpuscles and Pacininan corpuscles sit and why?
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.
What does the secretory portion of the sweat gland do? Location? Structure?
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.
What does the excretory duct do? What is the structure of it?
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)
Describe the hypodermis
Loose connective tissue, abundant fat cells, allows mobility of skin, bundles of collagen are transverse through the hypodermis
What are the two types of glands? Explain the function of each
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
Where is the arrector pili muscle present in the skin?
What is it responsible for?
Inserts into the connective tissue sheath and into the papillary layer of the dermis.
It is responsible for raising the hair.
How is a hair follicle distinguishable under a microscope?
Ring structure
What is distinguishable layer of a hair follicle?
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.
What is a hair papilla?
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.
What is the growth period and quiescence period of hair in the scalp? body hair?
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.
