Histology of the Skin Flashcards
What is the largest organ of the body?
Skin
What percentage of body weight does the skin make?
15%
What is the thickness range of skin?
1.5-5mm
List the functions of the skin.
Protective - barrier against microbial organisms - against mechanical, chemical, osmotic, thermal, UV, radiation damage - immunological response Biomedical synthesize - vit D under influence of UVB Homeostasis - controlling body temp - sweating - sweat glands Major sensory organ - touch, temperature, pain
What is the epidermis?
Self-renewing stratified epithelia tissue
What is the predominant cell in the epidermis?
Keratinocytes
List the other types of cells found in the epidermis.
Langerhans cells - immune function
Merkel cells - sensory nerve ending
Melanocytes - produce melanin pigment
What mediates the turnover of keratinocytes?
Stem cell - basal layer
Describe the renewal of keratinocytes.
Undergo continuous renewal throughout life
List the layers of the epidermis.
Cornified layer (Stratum corneum) Clear layer (Stratum lucidum) Granular layer (Stratum granulosum) Spinous/prickle cell layer (Stratum spinosum) Basal layer (Stratum basale)
Where are the keratinocyte stem cells found?
Basal layer
What shape are keratinocytes?
Columnar in shape
What is the basal layer the site of?
Epidermal cellular proliferation
What is the function of desmosomes?
Connect plasma membranes of basal keratinocytes
Name the function of hemidesmosomes.
Connect basal keratinocytes to basal lamina.
What does the basal layer cytoplasm consist of?
Melanosomes and keratin filament bundles (keratin tonofilaments)
What are the basal keratinocytes in contact with?
Basal lamina (lamina lucida and lamina densa)
What other cells are present in the basal layer?
Melanocytes
Langerhans cells
Merkel cells
What does the prickle/spiny cells layer consist of?
Closely packed keratinocytes (connected to each other by desmosomes which provides tensile strength)
What does the cytoplasm of the spiny cell layer consist of?
Melanosomes
What cells are also present in the spiny layer?
Langerhans cells
NO MERKEL CELLS
What does the granular layer consist of?
3-4 layers of flattened cells
What happens to nuclei and organelles in the granular layer?
Become disintegrated
What makes up the water barrier of the granular layer?
Densely stained keratocyte hyaline granules
Describe what happens to the cytokeratin filament bundles in the granular layer.
Cytokeratin filament bundles become more compact
What does the cornified layer consist of?
Closely packed/flattened cells/ corneocytes
Packed with keratin filaments
What do the cells of the cornified layer lack?
Lack nucleus & membranous organelles
List qualities of melanocytes.
Present at the basal lamina
Produce melanin pigment
Lack desmosome connections with keratinocytes
Present hemidesmosomes connection with basal lamina
Describe the characteristics of langerhans cells.
Immune function
Distributed in both basal and spiny layers
List the qualities of merkel cells.
Present in basal lamina
Sensory nerve ending (touch sensation)
Has desmosomes connections to keratinocytes
What is the dermis made up of?
Irregular, moderately dense CT
Meshwork of collagen (tensile strength) and elastin (stretch/recoil) fibres
Ground substance (glycosaminoglycans, glycoproteins and water)
What does the dermis contain?
Fibroblasts, plasma cells, macrophages, blood vessels, nerves, lymphatics, epidermal appendages (hair, sweat galnds and sebaceous glands)
Name the two regions of the dermis.
Reticular layer
Papillary layer
Describe the differences between the papillary layer and reticular layer.
Papillary Layer
- immediately next to the epidermis
- can find rete ridges which interdigitate with rete pegs
- predominantly consist of collagen type III and some elastic fibres
- fine and loosely packed collagens
- sensory receptors (Meissner’s corpuscles)
Reticular Layer
- no proper boundary between papillary and reticular layer
- absent
- collagen type II with some elastin fibers
- thick, irregular bundles of collage
- sensory receptors (Pacinian corpuscles) - also present in hypodermis
What is the hypodermis made up of?
Layer of connective tissue of variable thickness, deeper to dermis Mainly consists of adipose tissue Blood vessels (BV), nerves and lymphatics travel through it
What is the function of the hypodermis?
Increase morbidity of skin
Adipose - thermal insulation, shock absorber, store metabolic energy
Name the accessory structures & their function.
Hair - sensory/thermoregulation
Sebaceous glands - produce sebum, epidermal barrier
Sweat glands (apocrine, eccrine/regular) - thermoregulation
Sweat glands (Eccrine)
Secretions from the secretory cells will be passed to the eccrine duct
Duct is deeply stained
What do the sensory receptors detect?
Touch
Pressure
Temp
Pain
Where are meissner corpuscles found?
Dermal papillae
What is the function of the meissner corpuscles?
Rapidly adoptive mechanoreceptor
Sensitive to touch
Where are Pacinian corpuscles found?
Deep in dermis & hypodermis
List the functions of the Pacinian corpuscles and associated features.
Rapidly adapting mechanoreceptors
Sensitive to pressure & vibration
Has a capsule, intermediate zone and a central core
Central core contains an axon terminal
