Normal Skin Structure & Function I and II Flashcards
What features of the skin provide resistance to abrasion?
- keratinocytes
- desmosomes
- keratin filaments
- dermal CT
What features of the skin provide resistance to infection?
- keratinocytes
- Langerhans cells
- WBCs in dermis
What features of the skin provide prevention of dehydration?
- keratinocytes
- stratum granulosum
- lamellar bodies
What features of the skin provide protection of underlying tissue from UV light?
- keratinocytes
- melanocytes
What features of the skin provide synthesis of vitamin D?
keratinocytes
What features of the skin provide thermoregulation?
- sweat glands & hair
- dermal blood vessel distribution and regulation
What features of the skin provide excretion?
sweat glands
What features of the skin provide sensation of temperature, pressure, pain?
- sense organs including hot and cool receptors?
- Meissner’s corpuscles and Pacinian corpuscles (will be covered in neuro)
What two kinds of skin are recognized histologically?
- thick skin
- thin skin
Where is thick skin found?
- palms of the hands
- soles of the feet
Where is thin skin found?
everywhere besides palms of the hands and soles of the feet
What are the main cells found in the epidermis?
- keratinocytes
- melanocytes
- Langerhans cells
What type of epithelium makes up the epidermis?
stratified squamous epithelium
The keratin of keratinocytes are particularly rich in which three amino acids?
- cysteine
- lysine
- histidine
*amino acids involved in forming crosslinks within and between protein chains
Keratin filaments connect at the plasma membrane to what structure that attaches adjacent keratinocytes?
desmosomes
Keratin filaments connect at the plasma membrane to what structure that attaches keratinocytes to the basal lamina?
hemidesmosomes
The stratified squamous epithelium of the skin is composed of what 5 recognizable layers (sometimes 4)?
- basal layer (stratum basale, stratum germinativum)
- spinous layer (stratum spinosum)
- granular layer (stratum granulosum)
- clear layer (stratum lucidum) - found in thick skin
- cornified layer (stratum corneum)
The youngest keratinocytes are found in which layer of the skin?
basal layer (stratum basale, stratum germinativum)
The youngest keratinocytes, found in the basal layer, are what type of cells?
cuboidal or columnar
Hemidesmosomes are the target of immune destruction in which autoimmune disease?
bullous pemphigoid
Desmosomes are the target of immune destruction in which autoimmune disease?
pemphigus vulgaris
What do basal keratinocytes secrete?
Type VII collagen
Type VII collagen is important for what?
Type VII collagen is the main component of anchoring fibrils which reinforce the connection of epidermal basal lamina with underlying dermis
What type of collagen underlies several kinds of epidermolysis bullosa (a family of genetic blistering diseases)
Type VII collage
Cells from the basal layer migrate upward into the ______ layer and differentiation into keratinocytes called ______.
Cells from the basal layer migrate upward into the SPINOUS layer and differentiation into keratinocytes called PRICKLE CELLS.
Prickle cells from large numbers of ______ with adjacent cells.
desmosomes
What is the function of tonofibrils and in what cell do you find them?
Prominent bundles of tonofibrils internally reinforce prickle cells. Tonofibrils are made up of keratin filaments.
Why are the keratinocytes of the spinous layer called prickle cells?
Shrinkage of the cell cytoplasm away from the desmosomes during post-mortem fixation gives the cells the appearance of being prickly
Where is Vitamin D synthesized?
in the plasma membranes of spinous layer keratinocytes (prickle cells), in response to UV light
The granular layer consists of _____ cells containing _____ _____.
The granular layer consists of FLATTENED cells containing KERATOHYALIN GRANULES.
What are keratohyalin granules?
They are basophilic granules that contain profilaggrin, a precursor of filaggrin.
They are found in the flattened keratinocyte cells of the granular layer.
What is the importance of profilaggrin in skin?
It cross-links keratin filaments and organizes them into reinforced bundles in corneocytes (cells of the cornified layer).
What is the importance of filaggrin in skin?
Filaggrin is a hygroscopic (absorbs moisture from air) molecule that acts as a natural moisturizer and helps to keep overlying keratinocytes of the cornified layer hydrated.
Genetic defects in filaggrin can result in what?
increased permeability of the skin to allergens, and this is emerging as a causative factor in atopic eczema
Breakdown products of filaggrin _____ the stratum corneum and may contribute to ______ to colonization by some potential pathogens.
Breakdown products of filaggrin ACIDIFY the stratum corneum and may contribute to RESISTANCE to colonization by some potential pathogens.
Breakdown products from what substance can acidify the stratum corneum?
Filaggrin
Acidifying the stratum corneum has what effect?
It contributes to resistance to colonization by some potential pathogens
What are lamellar bodies? Where are they found?
= membrane-coating granules
They are membrane bound vesicles found in cells of the granular layer.
Lamellar bodies contain which glicolipid? Where is this glicolipid synthesized?
acylceramide, which is synthesized in the ER and is secreted by exocytosis
What is the importance of acyclceramide, the glicolipid found in lamellar bodies?
It is an important factor in waterproofing of the skin at the granular layer/cornified layer junction
What are the living cell layers of the epidermis?
- basal
- spinous
- granular
*these are collectively known as the stratum Malpighi
As cells from the granular layer migrate outward, they die and lose their nuclei. This process is evident in a very thin transparent layer known as what?
the clear layer - stratum lucidum
usually seen in thick skin, not thin skin
Which layer of skin is in contact with the air?
cornified layer (stratum corneum)
In the cornified layer, cells have lost their organelles and all that remains is a layer of dead cells containing _____ ___ _____. The cells are still attached to each other by _____.
In the cornified layer, cells have lost their organelles and all that remains is a layer of dead cells containing CROSS-LINKED SOFT KERATIN. The cells are still attached to each other by DESMOSOMES.
What cell is the source of skin pigment?
Melanocytes
Where do melanocytes originate?
they originate in neural crest and migrate to the skin during development
What is the function of melanocytes?
Melanocytes synthesize the pigment, melanin, which can to some extent shield the dividing cells of the skin and underlying tissues form the damaging effects of ultraviolet radiation.
Melanocytes are satellite cells (very roughtly star-shaped) situated among cells of the stratum germinativum.
In what layer of the epidermis are melanocytes found?
stratum germinativum - stratum basale - basal layer
Where is melanin synthesized?
in the RER of melanocytes form the amino acid tyrosine
What amino acid is melanin synthesized from?
tyrosine
Melanin-containing granules migrate out to the tips of melanocyte processes, from where they are transferred to ______ in a process known as _____ secretion.
Melanin-containing granules migrate out to the tips of melanocyte processes, from where they are transferred to KERATINOCYTES in a process known as CYTOCRINE secretion.
What is the process of cytocrine secretion from melanocytes to keratinocytes?
the keratinocytes engulf melanocyte processes containing melanin granules
*this is why in pigmented skin, most melanin granules are present in keratinocytes and not in melanocytes
What is a characteristic feature of albinism?
absence of melanin pigment - generally due to a lack of or defect in the tyrosinase enzyme required to synthesize melanin
What is vitiligo?
a condition in which patchy areas of depigmentation occur in otherwise pigmented skin
- caused by localized death of melanocytes, at least in part because of autoimmunity
A lack of or defect in the tyrosinase enzyme required to synthesize melanin causes what?
albinism
Localized death of melanocytes causes what?
patchy areas of depigmentation in oetherwise pigmented skin - a condition called vitiligo
What are Langerhans cells and where are they produced?
- cells of the immune system
- produced in the bone marrow
- they derive from the monocyte-macrophage lineage
- involved in processing and presenting of antigens entering through the skin to lymphocytes in the epidermis and dermis so that an immune response can be generated
What are Merkel cells and where are they present?
- present mainly in the thick skin of the palms of the hand and soles of the feet
- they contain keratin filaments and are abound to keratinocytes by desmosomes
- intimately associated with free nerve endings in the epidermis and play a role in mechanoreception
Desmosomes bind Merkel cells to what other cells?
keratinocytes
Merkel cells contain _____ filaments.
keratin
The dermis underlies the epidermis and does what for it?
- supports the epidermis mechanically
- supplies it with blood vessels, lymphatic vessels, and nerves
What is the dermis composed of?
- collagen and elastic fibers
- resident connective tissue cells, including fibroblasts, mast cells, and macrophages
- small blood vessels and lymphatic capillaries
- a rich nerve supply
- sensory structures, including receptors for temperature, pressure, and pain
What are the resident connective tissue cells?
- fibroblasts
- mast cells
- macrophages
What are the two layers of the dermis?
- papillary layer
- reticular layer
What layer of the dermis lies directly under the epidermis?
the papillary layer
What is the function of the papillary layer?
to provide mechanical, immunological, and metabolic support to the epithelium
What are dermal papillae and what layer of the dermis are they a part of?
- projections of the dermis into the epidermis
- located in the papillary layer
Dermal papillae interdigitate with epidermal spines or rete ridges for what purpose?
to increase surface area, both for adhesion, and for metabolic exchange between the epithelium and the dermal capillaries
What are rete ridges?
projections of the epidermis into the dermis
Connective tissue cells in the papillary layer of the dermis produce signaling molecules that determine what?
the phenotype of the overlying epidermis, and of epidermal derivatives such as hair and nails
Where in the dermal layer is the reticular layer and what distinguishes it from the papillary layer?
- deep to the papillary layer
- it is much thicker and has coarser collagen bundles
The skin is supplied with blood through what two main plexuses of blood vessels?
- subpapillary plexus between the papillary layer and the reticular layer of the dermis
- cutaneous plexus, between the reticular layer of the dermis and the hypodermis
The two plexuses (subpapillary and cutaneous) are connected by what? What does this connection allow for?
they are connected by arteriovenous shunts that enable blood to bypass the papillary plexus to conserve heat
- important for thermoregulation
What does preferential shunting of blood into the subpapillary plexus of the dermis allow for?
It allows for the body to lose excess heat
What does shunting of blood into the cutaneous plexus do?
conserve heat
The epidermis of the skin gives rise to what three types of glands?
- sebaceous glands
- sweat glands
- mammary glands
Sebaceous glands are situated in the dermis and generally associated with what?
hair follicles
From what do sebaceous glands arise?
- they arise from the invaginated epidermis of the follicle along the side of the hair shaft
Describe the structure of sebaceous glands
- the glands have a lobular secretory portion which drains via a duct that opens onto the epidermis of the upper region of the hair follicle
- each lobule is made up of a layer of rapidly dividing basal cells which lie on the basal lamina, and their progeny, the sebaceous cells, which fill the lobule and are gradually pushed out through the duct by the continual addition of new cells from the base of the gland
What is the secretion from sebaceous glands called and what is it composed of?
Sebum, composed of:
- mainly lipid
- remnants of dead cells
Sebum serves as a natural emolliment and what else?
- emolliment: softening of the skin
- sebum may also help to reduce water loss from the skin, although the main protection against water loss is due to secretion of lipid from stratum granulosum
Sebaceous glands are responsive to what hormones and when do they become more active?
- responsive to sex hormones
- become more active after puberty
The main protection against water loss is due to secretion of what from the stratum granulosum?
lipid
Where are eccrine sweat glands found?
deep in the dermis, or in the hypodermis
What are eccrine sweat glands composed of?
secretory portion consists of a coiled tubule composed of myoepithelial cells and secretory cells
The fluid produced by the secretory portion of sweat glands is isotonic (equal osmotic pressure) with ______, but is made hypotonic (less pressure) by _______ of some of the electrolyte content by the _____ cells.
The fluid produced by the secretory portion of sweat glands is isotonic with PLASMA, but is made hypotonic by REABSORPTION of some of the electrolyte content by the DUCT cells.
What does sweat contain?
- water
- sodium chloride
- urea
- ammonia
- uric acid
What two functions are sweat glands essential for?
- thermoregulation
- play a significant role excretion
Sweat glands in thick skin increase their secretion in response to what?
- stress
- emotional stimuli
Sweat glands in thick skin decrease their secretion in response to what?
secrete little if at all in response to elevated tempratures
Sweat glands in thin skin respond mainly to what stimulus?
heat stress
How do apocrine sweat glands resemble eccrine sweat glands?
they are similar in structure to eccrine sweat glands int hat they are coiled tubular glands derived from the epidermis
Differ:
- their lumens are larger
- their secretory cells produce and secrete a proteinaceous material
- their ducts open into the upper part of hair follicles rather than onto the surface
- they do not begin to secrete until puberty
- found only in the axilla, the areola, and the circumanal region
In what three regions are apocrine sweat glands found?
- axilla
- areola (pigmented region around nipple)
- curcumanal region
The secretory cells of apocrine sweat glands produce and secrete what material?
proteinaceous material
The ducts of apocrine sweat glands open up to what?
their ducts open into the upper part of hair follicles
What sweat glands do not begin to secrete until puberty?
apocrine sweat glands
What is the nail?
It is a plate of hard keratin that lies on a stratified squamous epithelium called the nail bed
Where does the nail plate epithelium arise from?
the nail matrix, located at the proximal end of the nail
A fold of the stratum corneum of the epidermis covering the proximal end of the nail forms what nail-related structure?
eponychium (cuticle)
The whitish crescent visible at the proximal end of the nail plate is what structure?
the lunula (it is the visible part of the nail matrix)
The keratinocytes of what structures do not contain melanin?
- nail bed
- nail plate
Measuring the color of the nail bed is commonly used as an indicator for what?
indicator of the degree of oxygenation of the blood
oxygenated blood is red, deoxygenated blood is blue
Nails are important diagnostic indicators of what conditions?
systemic conditions
What is koilonychia and what is it associated with?
- spooning of the nails
- it is associated with iron deficiency
Splitting of the nail from the nail bed is characteristic of what kinds of disease?
some kinds of thyroid disease
