Anatomy of the Skin Flashcards
% body weight occupied by the skin
16%
Define the epithelium of the skin
Stratified squamous epithelium, keratinized
Layer beneath the dermis
Hypodermis
Main type of connective tissue in the dermis
Dense irregular connective tissue
Main type of connective tissue in the hypodermis
Loose connective tissue
Contents of hypodermis
Adipose tissue (unilocular adipocytes; fat cells)
What is the hypodermis continuous with?
The deep fascia surrounding nerves and bones
Describe the epithelium of the wet surface of the oral cavity
Stratified squamous epithelium, non-keratinized
5 functions of the skin
- Protection from injury and dessication
- Receive stimuli from the environment
- Excretion of various substances
- Participation in thermoregulation and maintenance of water balance
- Cutaneous immunigenicity
What mediates the skin function of protection from injury and dessication?
Keratinocytes of the epithelium
What mediates the skin’s ability to receive stimuli from the environment?
- Merkel cells within the epithelium
- Nerve endings in and beneath the epithelium
What mediates the excretion of substances from the skin?
- Sebaceous glands associated with the hair
- Sweat glands
What mediates thermoregulation and maintenance of water balance by the skin?
- Insulating properties of secretion by keratinocytes that act as hydrophobic barriers to water
- Shivering mechanism related to “goose-bumps”
What mediates cutaneous immunogenicity by the skin?
Langerhans cells within the epithelium acting as antigen-presenting cells
From what are the appendages of the skin derived?
The epithelium of the skin
4 appendages of the skin
- Nails
- Hair
- Sebaceous glands
- Sweat glands
2 layers of the dermis
- Papillary layer
- Reticular layer
Describe the composition of the papillary layer of the dermis
- Composed of finger-like projections of epidermis (rete pegs) into the dermis
- Can be thought of conversely as finger-like projections of loose connective tissue from the dermis into the epidermis
From what embryologic germ layer is the keratinizing system derived?
Ectoderm
2 distinct cell lineages which compose the stratified squamous epithelium of the skin
- Keratinocytes
- Melanocytes
Fibrous protein produced by keratinocytes
Keratin
Function of keratin
Transforms the keratinocytes into a dead cell layer (keratinized/cornified layer)
Typical time length of cytomorphosis of a keratinocyte
15 - 30 days
Function of melanocytes
Produce pigment (melanin) to protect against UV radiation
Embryological origin of melanocytes
Neural crest
When do the melanocytes invade the skin during development?
3rd to 6th month in utero
2 cells of the epidermal epithelium that do not belong to either the keratinizing system nor the pigmentary system
- Langerhans cell
- Merkel cell
5 layers of the epidermis from the innermost to the outermost layer
- Stratum Basale/Germinativum (Basal Layer)
- Stratum Spinosum (Spiny Layer)
- Stratum Granulosum (Granular Layer)
- Stratum Lucidum (Clear Layer)**
- Stratum Corneum (Cornified Layer)
NOTE: Stratum lucidum is not in ALL epidermises
4 examples of structures derived from the ectoderm
- Lining of oral and nasal cavities
- Cornea
- Skin epidermis
- Glands of skin
4 examples of structures derived from the endoderm
- Lining of the GI tract
- Lining of the respiratory tract
- Liver
- Pancreas
3 examples of structures derived from the mesoderm
- Renal tubules
- Lining of the reproductive tract
- Lining of blood vessels
Shape of keratinocytes
Cuboidal
When do mitoses occur in the stratum basale of the epidermis?
Mostly at night
Purpose of hemidesmosomes
Cell-matrix adhesions
Protein associated with hemodesmosomes
Integrins
Purpose of desmosomes
Cell-cell adhesion
Protein associated with desmosomes
Cadherins
Connective tissue type of the epidermal basement membrane
Collagen IV and Laminin
Type of collagen that comprises the anchoring fibrils contained in the papillary layer of the dermis
Collagen VII
Type of collagen that comprises the reticular fibril found in the papillary layer of the dermis
Collagen III
Intermediate filaments of the stratum spinosum
Tonofilaments
Number of keratin genes (cytokeratins) in epidermis
14
Number of diseases identified with mutated keratin genes
70
Location of keratins in the stratum spinosum and where they insert
In the spiny processes; insert into desmosomes
Where is the stratum lucidum found?
Skin that is very thick (i.e. sole of foot)
Thickness of stratum granulosum
3 - 5 layers of cells
Describe the cells of the stratum lucidum
No organelles (not even nucleus); dead
Full of keratin tonofibrils
3 constituents of the stratum granulosum
- Large keratohyalin granules (filaggrin protein) associated with tonofibrils
- Increased number of lamellated bodies/granules
- Increased transglutaminase crosslinking
What do the cells of the stratum spinosum secrete?
Distinct lamellated granules (membrane coating granules)
What are the lamellated granules of the stratum spinuson ccomprised of?
Glycolipids (NOT phospholipids)
2 proteins deposited under the membrane as a cell envelope in the stratum corneum
Involucrin
Loricrin
What occupies the intercellular space in the stratum corneum?
Lipids
How does desquamation occur in the stratum corneum?
Desmosomal attachments are released
Define epidermolysis bullosa
Blistering in response to minor trauma
Cause of epidermolysis bullosa
Defective epidermal cell adhesion (acantholysis)
Describe basal cell carcinoma
Basal cells affected, but not metastatic
Cells affected by squamous cell carcinoma
Keratinocytes
Cause of psoriasis
7x increased cell proliferation (i.e. turnover of skin is less than 30 days) and T-cell activation (autoimmune)
Define warts
Benign infection with papilloma viruses
Define blisters
Separations between keratinocytes due to trauma
Define ichthyosis
Abnormal keratinization or glycolipid processing/release (i.e. filaggrin and transglutaminase mutations)

Define moles
Large aggregation of melanocytes
Location of cell body of melanocytes
Stratum basale
Contents of pre-melanosomes
Tyrosine
Describe how melanin is formed
- Melanosome is formed by tyrosinase vesicle + pre-melanosome
- Tyrosine activated by tyrosinase and UV
- Tyrosine –> Melanin

2 types of melanin and the colors associated with them
- Eu (dark brown)
- Pheo (red,yellow)
Method of melanin release to keratinocytes
Cytovrine
Location of melanin granules
Dendritic-like cell processes
Cause of albinism
Gene mutations in tyrosinase gene (complete or partial)
Risk associated with albinism
Increased risk of skin cancer
Role of Langerhans cell
Bind foreign substances (antigens) and migrate to lymph nodes to present to T lymphocytes (i.e. it’s an APC)
From where are Langerhans cells derived?
Bone marrow
Granules associated with Langerhans cells
Birbeck (vermiform) granules (NOTE: function unknown)
Granules associated with Merkel cells
Dense-cored granules (NOTE: function unknown)
8 functions of the extracellular matrix (ECM)
- Connecting and supporting (typically collagen fibrils)
- Signals for cell proliferation and differentiation
- Cell communication (outside-in/matrix-cell signalling)
- Cell protection
- Transmits and attenuates mechanical signals
- Compartment for blood vessels, lymphatics, nerves, etc.
- Transport system
- Controls diffusion of soluble growth factors
3 types influences on cells that can affect their fate
- Physical signals
- Soluble signals
- Cell-cell interactions
3 examples of soluble signals that can influence a cell
- Growth factors
- Cytokines
- Chemokines
6 examples of physical signals that can influence a cell
- Fibronectin
- Vitronectin
- Laminin
- Collagen
- Fibrillin
- GAGs, PGs
2 examples of cell-cell interactions that can influence the cell
- Cadherins
- CAMs
4 cell fate processes
- Replication
- Differentiation
- Migration
- Apoptosis
3 potential outcomes of cell signalling and coordinated functions
- Tissue formaiton
- Tissue homeostasis
- Tissue regeneration

2 types of connective tissue
- CT proper
- CT specialized
5 types of CT proper and their associated levels of cellularity
- Loose CT (very cellular)
- Loose CT (cellular)
- [Intermediate CT]
- Irregular dense CT (relatively acellular)
- Regular/oriented dense CT (relative acellular)
Define CT specialized
Basically, CT proper that has been mineralized
3 exampels of CT specialized
- Bone
- Cartilage
- Teeth (dentin, cementum)
6 major cell types of cennective tissue
- Mesenchymal cell
- Fibrobast/fibrocyte
- Adipocyte
- Macrophage/histiocyte
- Mast cell
- Plasma cell
Most abundant protein of the body
Collagen (20% of all proteins)
Structure of collagen fibrils
Triple helix of collagen alpha chains
Describe how scurvy is a collagen-related disease
Vitamin C deficiency –> lack of hydroxylation so no stable triple helix of alpha chain –> no ordered fibrils
Define Ehlers-Danios syndrome
Mutations in colalgen I, III, and V –> hyperextensive skin, hyper joint mobility and dislocation
3 fibres of the ECM
- Collagen (fibrillar)
- Reticular fibres
- Elastic fibres
Collagen types that are fibrillar (6)
- I
- II
- III
- V
- VII
- XI
Define amorphous ground substances (i.e. of the ECM)
Substances found between fibres that resist compressive forces
5 amorphous ground substances of the ECM
- Small proteoglycans
- Large proteoglycans
- Glycoproteins
- Water, metabolites, mineral ions, etc
- Plasma proteins
Describe how Marfan’s syndrome is an elastin-related disease
Fibrillin-1 gene mutation –> aortic aneurysm/rupture, lax joints and dislocations, and ectopia lentis
Define cutis laxa
Elastin and fibulin-5 mutations, and other elastic fibre degeneration events
Describe how mast cells release their secretory granules
After initial sensitization by antigens, degranulation after IgE binding to Fc receptors