Histology - Skin Flashcards
Label the structures in this image and state their functions.
- Dermal papillae / epidermal ridges –> increase surface area of attachment between dermis and epidermis allowing for greater resistance to frictional forces (shear) that would pull try to separate the 2 layers
- Papillary dermis –> contains blood supply that delivers nutrients and oxygen to epidermis, contains sensory structures to provide feedback to CNS
- Reticular dermis –> dense CT, has a lot of collagen and elastin fibers, provides strutural support for epidermis
How is the epidermis connected to the dermis?
Hemidesmosomes link the intermediate filaments of the dermal cytoskeleton into the basal lamina. In addition, focal adhesions anchor dermal actin filaments into the basal lamina.
Papillary Dermis
- Is this above or below the reticular dermis?
- What is the classification of this tissue type?
- What types of fibers are found in this layer?
- How does this area of the skin change with age?
- More superficial layer (above)
- Loose connective tissue (more cellular than fibrous)
- Elastin, as well as type I and type III collagen
- The number and diameter of collagen fibers decreases with age and the ratio of type III to type I collagen increases
Reticular Dermis
- What is the size and cellularity of this layer compared to reticular dermis?
- What is this type of tissue?
- What type of fibers are found in this layer?
- What is the orientation of these fibers?
- What is the clinical significance of this orientation?
- It is always considerably thicker and less cellular than the papillary layer
- Dense irregular CT
- Thick, irregular bundles of mostly type I collagen and coarser elastic fibers
- The collagen and elastic fibers are not randomly oriented but form regular lines of tension in the skin called Langer lines.
- Skin incisions made parallel to Langer lines heal with the least scarring
Hypodermis
- Where is this located?
- What is its function?
- Deep to the reticular layer is a layer of adipose tissue
- This layer serves as a major energy storage site and also provides insulation.
What are langerhan’s cells?
Langerhans cells are dendritic-appearing, antigen-presenting cells in the epidermis.
Where do langerhan’s cells originate from?
They originate from common lymphoid progenitor (CLP) cells in the bone marrow, migrate via the bloodstream, and ultimately enter the epidermis where they differentiate into immunocompetent cells.
How do langerha’s cells function as immune cells?
Langerhans cells are specialized at “sensing” the microenvironment of the epidermis by extending their processes through intercellular tight junctions to sample the outermost layers of the skin (stratum corneum). Once antigen is phagocytized, processed, and displayed on the surface of the Langerhans cell, the cell migrates from the epidermis to a regional lymph node. Within the lymph node, interaction of Langerhans cells with T lymphocytes initiates instruction of the adaptive immune system toward either immune tolerance or immune activation and response to the antigen.
What is the effect of UV radiation on langerhan’s cell activity?
Exposure to UV radiation causes depletion of Langerhans cells and decreases their ability to present antigen
Do langerhans cells have desmosomal attachments to neighboring cells?
Langerhans cells do not form desmosomes with neighboring keratinocytes
What classes of MHC are expressed by langerhans cells?
Langerhans cells express both MHC I and MHC II molecules, which are essential for presentation of antigen to cytotoxic CD8+ and helper CD4+ lymphocytes
In addition to MHC, what other important immune receptors are present on the surface of Langerhans cells?
Fc receptors for IgG
Complement C3b receptors
What type of hypersensitivity reaction are langerhans cells involved in?
Involved in delayed-type hypersensitivity reactions (type 4) (e.g., contact allergic dermatitis and other cell-mediated immune responses in the skin) through their recognition of antigens in the skin and their transport to the lymph nodes.
Merkel cells
- What type of cells are these?
- Where are they located in the layers of the skin?
- What types of skin possess the most of these structures?
- What cell junctions do they have?
- What substance do they have in their cytoplasm?
- How is their nucleus shaped?
- What is the function of these cells?
- Dendritic cells
- Stratum basale
- Most abundant in skin where sensory perception is acute, such as the fingertips and lips
- Bound to adjoining keratinocytes by desmosomes
- Contain keratin in their cytoplasm and dense-cored neurosecretory granules
- The nucleus is lobed
- Sensitive mechanoreceptor
- Where can you find free nerve endings (c-fibers) in the skin?
- What signals are they sensing?
- Free nerve endings in the epidermis terminate in the stratum granulosum
- Fine touch, heat, cold, and pain
[…] and […] are considered unencapuslated nerve endings in the skin
Merkel cells
Free nerve endings
What are the types of encapsulated sensory structures in the skin?
Pacinian corpuscle
Meissner’s corpuscle
Raffini corpuscle
Pacinian Corpuscle
- Where are these found in the skin?
- Describe their structure.
- What are their lamella composed of?
- What stimuli do they respond to?
- Found in the deeper dermis and hypodermis
- They are composed of a myelinated nerve ending surrounded by a capsule structure.
- Flattened cells that correspond to the cells of the endoneurium outside the capsule, fluid, collagen fibrils, and capillaries
- Pressure and vibration through the displacement of the capsule lamellae –> causes depolarization of the axon
Meissner’s Corpuscle
- What type of receptors are these?
- Where are they located in the skin?
- Touch receptors that are particularly responsive to low frequency stimuli in the papillary layer of hairless skin
- Meissner’s corpuscles are present in the dermal papillae just beneath the epidermal basal lamina
Ruffini Corpuscle
- What type of receptor is this?
- How does this structure sense its environment?
- Mechanoreceptors
- The axonal endings respond to displacement of internal collagen fibers induced by sustained or continuous mechanical stress; thus, they respond to stretch and torque
Hair distribution is influenced to a considerable degree by […]
sex hormones
What types of hair begin to develop during puberty?
- Pigmented facial hairs
- Pubic and axillary hair
How does hairline change with age?
Males: the hairline tends to recede
Both sexes: the scalp hair thins with age because of reduced secretion of estrogen and estrogen-like hormones
What gives hair its color?
Coloration of the hair is attributable to the content and type of melanin that the hair contain
What are the 4 regions of a hair follicle?
The infundibulum
- Extends from the surface opening of the follicle to the level of the opening of its sebaceous gland, part of the pilosebaceous canal
The isthmus
- Extends from the infundibulum to the level of insertion of the arrector pili muscle.
The follicular bulge
- Protrudes from the hair follicle near the insertion of the arrector pili muscle and contains epidermal stem cells
The inferior segment
What is the hair matrix?
Other cells forming the bulb, including those that surround the connective tissue dermal papilla, are collectively referred to as the hair matrix
What is the internal root sheath of hair?
The dividing matrix cells differentiate into the keratin-producing cells of the hair and the internal root sheath.
Humans of all race and genders have roughly the same number of melanocytes in their skin. Why then do we have a wide range in skin tone?
Although the number of melanocytes is essentially the same in all races, the fate of the melanin that is produced by the melanocytes differs.
- Because of the lysosomal activity of keratinocytes, melanin is degraded more rapidly in individuals with light skin than in individuals with dark skin.
- In lighter skinned people, melanosomes are concentrated in the keratinocytes nearest the basal layer and are relatively sparse in the midregion of the stratum granulosum. In contrast, dark skin may exhibit melanosomes throughout the epidermis, including the stratum corneum.
What is the role of Bcl2 in maintaining melanocytes in the skin and hair?
What are the clinical consequences of mutations or loss of function of Bcl2?
The expression of Bcl2 in melanocyte stem cells is essential to maintaining their population within the niche of the follicular bulge. Deficiency in Bcl2 expression causes apoptosis of melanocyte stem cells and a consequent decrease in the number of melanocytes. Melanocyte depletion occurs with age, resulting in a decreased rate of pigment donation to keratinocytes. Therefore, the skin becomes lighter with increased age, and the incidence of skin cancer also increases. Melanocyte depletion caused by defective self-maintenance of melanocyte stem cells is also linked to hair graying, the most obvious sign of aging in humans. Individuals with a mutation in the Bcl2 gene may become prematurely gray
- What is the follicular bulge?
- What is the role of the cells in this bulge?
- What is their role in skin maintenance ?
- Recent studies have identified the follicular bulge as a niche of epidermal stem (ES) cells.
- The ES cells can reside in this area indefinitely and undergo self-renewal or differentiation into specific cell lineages. Under normal conditions, ES cells are responsible for providing stem cells for the growth of hair follicles (the hair matrix, internal root sheath, cortex, and medulla) as well as sebaceous glands.
- The ES cells that normally reside in the follicular bulge do not contribute to the population of the basal stem cells of the epidermis. However, when the epidermis is injured or lost (such as in extensive skin burns and superficial skin wounds), the ES cells become reprogrammed, migrate toward the wound surface from their follicular niches, and participate in the initial resurfacing of the wound.
Describe the process of keratinization of hair.
Keratinization of the hair and internal root sheath occurs shortly after the cells leave the matrix in a region called the keratogenous zone in the lower third of the follicle. As the cortical cells pass through this zone, they differentiate, extrude their organelles, and become tightly packed with cross-linked keratin intermediate filaments. By the time the hair emerges from the follicle, it is entirely keratinized as hard keratin.
The arrector pili muscle is attached near the […]
follicular bulge
Sebaceous glands are usually found in association with […] in most areas of the body surface except for the […].
hair follicles
palms and soles
What is a pilosebaceous unit?
The hair follicle, hair shaft, arrector pili muscle, and sebaceous gland
The highest density of sebaceous glands is found on the […]
face
Sebaceous gland activity increases shortly after […] but then diminishes in the first few […]. Increased […] levels at […] coincide with an increase in sebaceous gland activity and sebum secretion
birth
postnatal months
androgen
puberty
[…] are the major cells within sebaceous glands that produce and accumulate lipids
Sebocytes
Describe how sebum is released from sebocytes.
Holocrine secretion - the entire cell produces and becomes filled with the fatty product while it simultaneously undergoes apoptosis. Ultimately, both the secretory product and cellular debris are discharged from the gland as sebum into the infundibulum of a hair follicle, which forms the pilosebaceous canal with the short duct of the sebaceous gland.
- How are new sebocytes produced?
- How are cells within the sebaceous gland connected?
- The basal lamina of the sebaceous gland is continuous with that of the […] and the […]
- New sebocytes are produced by mitosis of the basal cells at the periphery of the gland
- The cells of the gland remain linked to one another by desmosomes and gap junctions regardless of their differentiation stage.
- Epidermis; hair follicle
Describe the process of sebocyte maturation.
As the sebocytes move away from the basal layer and begin to produce their lipid secretory product, they become filled with numerous lipid droplets separated by thin strands of cytoplasm. Eventually they lose their nucleus and become only sebum. The sebum production process takes about 8 days from the time of basal cell mitosis to the secretion of the sebum.
What is sebum made of?
Triglycerides
Diglycerides
Free fatty acids
Wax esters
Squalene
Cholesterol
Cholesterol esters
Is everyone’s sebum the same?
No - due to its complex composition, human sebum is remarkably specific due to individual and provides each person with a highly individual and unique chemical signature.
What is the function of sebum?
- Contributing to the maintenance of a functional epidermal barrier
- May play a role in protection against ultraviolet irradiation
- May have immune and communication functions
- Antioxidants (especially vitamin E)
- Anti-inflammatory and proinflammatory substances
- Antimicrobial peptides
- Pheromones on the skin surface
- What compounds increase sebum production?
- What compounds decrease sebum production?
- Androgens, histamine, as well as dietary substances (e.g., free fatty acids, sugar, and fat)
- Estrogens
Eccrine sweat glands are / are not associated with hair follicles?
Are not
Describe how eccrine sweat glands are involved in temperature regulation.
Through the cooling that results from evaporation of water from sweat on the body surface. The secretory portion of the glands produces a secretion similar in composition to extracellular fluid (isotonic). Resorption of some of the sodium and water in the duct results in the release of a hypotonic sweat at the skin surface. This hypotonic watery solution is low in protein and contains varying amounts of sodium chloride, urea, uric acid, and ammonia.
What are the clear cells in eccrine sweat glands?
Clear cells are characterized by abundant glycogen. The morphology of these cells indicates that they produce the watery component of sweat.
What are dark cells in eccrine sweat glands?
They are the cells that are responsible for resorbing ions from the lumen of the gland. They contain many secretory granules that are moving ions from the luminal side of the cell to the apical side to be released back into the body.
What is the function of myoepithelial cells?
Contraction of these cells is responsible for rapid expression of sweat from the gland
[…] develop from the same downgrowths of epidermis that give rise to hair follicles.
Apocrine sweat glands
What is a distinguishing feature between apocrine and eccrine glands?
The most obvious difference, readily noted in the light microscope, is its very wide lumen
What type of secretion mechanism (merocrine, apocrine, holocrine) do eccrine glands utilize?
Merocrine
What type of secretion mechanism (merocrine, apocrine, holocrine) do apocrine glands utilize?
Merocrine
Apocrine glands
- What is the secretion that is produced from apocrine glands?
- When secreted this substance is odorless. How does it get an odor?
- When do these glands become functional?
- What controls their development?
- What is their function?
- Secretion that contains protein, carbohydrate, ammonia, lipid, and certain organic compounds that may color the secretion
- Secretions vary with the anatomic location.
- Axilla - milky and slightly viscous
- Through bacterial action on the skin surface, it develops an acrid odor
- Apocrine glands become functional at puberty
- Development depends on sex hormones.
- It is generally believed that apocrine secretions may function as pheromones in humans
- Eccrine sweat glands are stimulated by the neurotransmitter […] by the […] nervous system
- Apocrine sweat glands are stimulated by the neurotransmitter […] by the […] nervous system
Acetylcholine (cholinergic); sympathetic
Norepinephrine (adrenergic); sympathetic
What is another name for fingernails and toenails?
What are nails attached to?
Nail plates
Strongly attached to underlying nail beds
The nail bed consists of epithelial cells that are continuous with the […] and […] of the epidermis
stratum basale
stratum spinosum
What is contained in the matrix of a nail?
The matrix contains a variety of cells, including stem cells, epithelial cells, melanocytes, Merkel’s cells, and Langerhans cells. The stem cells of the matrix regularly divide, migrate toward the root of the nail, and there differentiate and produce the keratin of the nail
The nail is made of […] keratin which [does/does not] desquamate.
Hard
Does not
- Fingernails grow […] mm / month and take […] months to regrow completely.
- Toenails grow […] mm / month and take […] months to regrow completely.
- 2 to 3 mm/month; 6 months
- 1 mm/month; 18 months
Whether skin is thick or thin is determined based on the thickness of the […]
Epidermis
Thick skin lacks what structures?
Hair follicles
Sebaceous glands
What types of cells are found in the:
- S. corneum
- S. Granulosum
- S. Spinosum
- S. Basale
- Flat, anucleated keratinocytes
- Keratinocyte with lamellar bodies
- Keratinocytes and langerhans cells
- Keratinocytes, melanocytes, stem cells, merkel cells
What are the “spines” that are seen in the s. spinosum under H&E staining?
Desmosomes that are seen due to being an artifact of fixation
The stem cells that become keratinocytes and traverse through the layers of the epidermis are connected to other cells via desmosomes and are attached to the basement membrane via hemidesmosomes. How then do they manage to migrate through the skin?
The bonds between cells and basement membrane are constantly being disrupted and reforming –> allows movement
How long does it take for a stem cell to differentiate into a keratinocyte and travel to the Stratum granulosum?
31 days
How long does it take for a keratinocyte to travel from the Stratum granulosum through the stratum corneum?
14 days
What type of tissue secretes substances via apocrine secretion?
Breast tissue
Why do the darker cells stain darker?
Darker cells = duct cells –> stain darker due to presence of lots of mitochondria
Describe the innervation of eccrine sweat glands
Postganglionic neuron releases acetylcholine (cholinergic) neurotransmitter onto sweat glands, which receive Ach with muscarinic receptors
What type of gland is shown?
Apocrine
What type of gland is shown?
What type of tissue is shown?
Nail
The deeper a sensory receptor is the […] its receptor field of action
Larger
What structure is shown?
What is it sensing?
What structure is shown?
What is it sensing?
The mammary gland is a modified […] gland
Apocrine
What factors lead to an increase in ductal and glandular tissue growth of breast tissue?
Pregnancy
Estrogen
Progesterone
Prolactin
Placental lactogen
[…] inhibits milk production until birth, when its levels decline and levels of […] rise resulting in lactation.
Progesterone
Prolactin
Secretion of breast milk has elements of what 2 kinds of secretion?
Merocrine (protein component)
Apocrine (lipid component)
Suckling by infant stimulates […] release, which acts on […] cells to cause contractiona nd expulsion of milk from breast.
Oxytocin
Myoepithelial cells
Lactiferous ducts of the nipple are lined by […] epithelium which transitions to […] epithelium as the duct exits onto the surface.
Stratified cuboidal
Stratified squamous
Which panel is inactive breast tissue? Why?
