Histology: Glands, Hair, and Nails Flashcards
Introduction to Glands
Glands and hair have stem cells used to regenerate the skin especially during burns
Glands are derived from epithelium
Cannalized/lumen formed and cells can secrete specific products attached to surface = exocrine gland
No lumen that is secreted into but directly into blood = endocrine gland
Parenchyma: cells that are doing the secreting of specialized product; determines the type of gland
Stroma: CT or supportive tissue cells
Merocrine, Apocrine, and Holorcrine Glands
Merocrine/Eccrine: exocytosis of secretory products from vesicles via fusion with membrane; sweat, salivary
Apocrine: ceruminous (ear wax) and mammary; the products are in vesicles, and the vesicles + apical part of the cell are secreted; fairly limited in body
Holocrine: will oily/sebum into vesicles, but cell will fill with the product and undergo apoptosis and disintegrate for release; sebaceous
Merocrine, Apocrine, and Holorcrine Glands Locations
Apocrine: open to hair shaft and not found all over body; coiled
Merocrine/Eccrine: coiled and open directly to skin
Holocrine/Sebaceous: secreting onto hair shaft, but lower down than apocrine glands near erector pili muscles; found all over the body where there is hair
Eccrine Sweat Gland
Merocrine; coiled tubular gland throughout most of the body
Sweat is 99% water withpH = 4-6 acid mantle to inhibit bacterial growth on skin
Thermoregulation
Some excretion: NaCl, urea, uric acid, ammonia
Secretory portion in dermis/hypodermis
Sympathetic innervation (cholinergic) aka ACh
Eccrine Gland: Secretory vs. Excretory Portions
Secretory portion (dermis): secrete H2O, salt, urea, ammonium; lighter cells Myoepithelial cells - contractile
Excretory (duct) portion: smaller diameter & lumen; stratified cuboidal epithelium; smaller, darker cells; reabsorb NaCl to make hypotonic sweat
No myoepithelial cells
Eccrine Gland Cell Types
- Clear cell (C): water & NaCl of sweat; rich in mitochondria, glycogen
- Dark cell (D): line the lumen; rER makes glycoprotein; apical granules
Mode of secretion: merocrine via exocytosis - Myoepithelial Cells: contractile for secretory portion of gland
In between the cells, there are spaces called intercellular canaliculus where secretory products can go before secreted into the lumen
CF and Sweating
Stratified cuboidal cells: modify salt content as the secretions pass by
In normal sweat glands, there is a Cl- channel that absorbs Cl- and Na+ back into body to make hypotonic sweat; this channel is mutated in those with CF
In the skin, a defect in the CF transmembrane conductance regulator channel in the sweat gland duct causes increased concentration of Cl- and Na+ in sweat by decreased reabsorption of NaCl from the lumen. This the basis of high salt content of sweat clinically diagnostic in CF
Apocrine Sweat Gland
In axillary, areolar, pubic, perianal regions Ducts: open into hair follicle and superior to sebaceous duct Sympathetic innervation (adrenergic) aka NE
Scent glands – respond to stress, emotional & sensory stimuli via pheromones; no thermoregulation; no resorption; have myoepithelial cells
Wider lumen than eccrine sweat gland
Simple cuboidal/columnar epithelium
Apical blebs: merocrine mode of secretion
Protein-rich secretion; more viscous & milky than eccrine sweat; odorless until skin bacteria degrade it
Active at puberty
Sebaceous Gland
Also called holocrine
In the stratum basale and opens directly onto lumen of hair follicle
Outgrowth of basal cells in upper 1/3 of hair follicle
Abundant sER for lipid synthesis
Secretes oily sebum
Active at puberty, respond to sex hormones
Hair Structure
Infundibulum: base of sebaceous duct; hair follicle that extends from the epidermis to the opening of the sebaceous gland duct; lumen of the infundibulum normally contains the hair shaft, keratin material and sebum
Isthmus: shortened segment of the hair follicle, extending from the attachment of the erector pili muscle (bulge rgion) into the entrance of the sebaceous gland duct
Below insertion of erector pili muscle (smooth muscle) = inferior segment
Dermal papilla – CT w/ BVs, nerves; nourishes matrix: secretes growth factors
Bulge Region
Where arrector pili muscle attaches;
Stem cells
Burn Victims
Epidermal water barrier = lose water through this structure with burn victims
Hair Follicles
Invaginations of the epidermis into dermis
Glassy membrane ~ basement membrane
Papillary layer of dermis ~ CT dermal sheath; loose CT and type I collagen
Above level of sebaceous duct: all layers of epidermis present
At sebaceous level, loses str. corneum and granulosum to leave a space where products go and coat the shaft with the sebum
At sebaceous level and deeper, only str. basale and spinosum present = Outer/External Root Sheath
Inner root sheath (IRS) - below duct of sebaceous gland
Dermal Papilla
Matrix cells surrounding DP proliferate and undergo keratinization to form hair shaft and Internal Root Sheath
Matrix Cells
The only living cells are in and near the bulb.
Matrix cells, mitotically active; give rise to keratinized cells in shaft and IRS.
Keratinization – occurs shortly after cells leave the matrix.
Inner root sheath – soft keratin
External root sheath – NOT involved in hair formation, just part of hair follicle from epidermal cells
Hair Shaft
Hair Shaft (inner to outer):
medulla - present only in thick hairs
cortex – widest; hard keratin
cuticle - squamous cells
Hard keratinization only in these layers
Scattered melanocytes in the germinative layers
Inner Root Sheath
Derived from matrix cells in bulb
More cellular deeper, but more keratinization superficially
Indicating differences in distance from the bulb
Hair Follicle Layers
5 from inner to outer:
Medulla (not shown here) – core of shaft; moderately keratinized
Cortex (Cx) – widest; hard keratin
Cuticle (Cu) – thin plates of keratin
Internal Root Sheath – lightly keratinized; derived from matrix cells; disintegrates at level of sebaceous duct
External Root Sheath – downgrowth of surface epidermis; str. Basale & spinosum only; not involved in hair formation
Hair Cycle: Anagen
Growth Phase
Prominent hair bulb
Well-formed dermal papilla
Duration depends on location: scalp 2-6 yrs; eyebrows 3 months
Initiated by growth factors: FGF -7 & sonic hegdehog factor (dermal papilla) and IGF-1 (bulge & dermal papilla)
Will get so long and then fall out and start regrowth process
Hair follicle itself is growing downwards and dermal papilla bring in capillaries and nerves, which is deeper as anagen phase goes on; lasts as hair shaft grows longer
Hair Cycle: Catagen
Apoptosis and Regression
2-4 weeks
FGF -5 (dermal papilla) stops anagen; turns off mitosis all cells of lower follicle undergo apoptosis
Follicle shortens to the bulge, leaves dermal papilla & its trophic factors behind so no longer as nutrients
Club hair = dead hair in follicle
Hair Cycle: Telogen
Resting phase
Lasts a few months
Hair bulbs small w/ no DP
Club hair falls out (50-100/day)
At end of telogen, dermal papilla gets drawn back up to base of follicle
If not, follicle dies forever.
FGF-7, SHH, and IGF-1 are secreted mitosis new hair grows
Bulge – stem cells proliferate; travel downward; push DP deeper
Lanugo Hair
Fetal hair; fine, downy, unpigmented; shed before or shortly after birth. Replaced by vellus
Vellus Hair
Fine, pale hair in most of skin of children, 2/3 of hair of women, and in bald skin; short, plump follicles
Terminal Hair
adult type, coarser, usually more pigmented; longer, straighter follicles
Scalp, eyebrows & lashes, axillary, pubic.
Club Hair
A terminal hair which is no longer connected to base of follicle.
May occupy follicle with a newly growing hair shaft.
Baldness
Androgenetic alopecia: can occur in both sexes but patterned in males
Fewer and shorter follicles causes thinner vellus hairs
susceptibility of dermal papilla to androgens:
Testosterone causes anagen phase to shorten so only vellus remains
Rogaine (minoxidol) thought to lengthen anagen phase
Hair Texture and Color
Straight hair: round cross section Oval cross section = wavy hair Eumelanin = dark hair Pheomelanin = red hair Medulla of hair shaft is filled with air and no coloration = gray hair
Nail Lunula and Eponchium
Plates of hard keratin – densely packed kertain bundles; high sulfur content contributes to hardness
Lunula = opaque layer of partially keratinized matrix cells
Eponychium – a fold of skin stratum corneum; protects matrix
Nail Body, Bed, Matrix, Hypoychium
Nail body – fully keratinized, more transparent
Nail bed = str. basale & spinosum only
Matrix = growth zone; cell mitoses for nail formation & growth
Hyponychium – str. corneum; protects nail bed from bacterial & fungal invasion
More keratinized superiorly because the cells lose their nuclei and other organelles and can see vessels underneath the nail
Nail Matrix
Germinative zone; growth zone;
Thickened str. Basale under eponychium;
Cells: stem, epithelial, Langerhans, Merkel, melanocytes
Stem cells divide, migrate toward root, produce keratin; continuous growth; no cycling; slows with age due to reduced circulation
Nail Plate
Corneocytes - thin, dead, scaly, densely packed cells lacking nuclei and organelles but filled with parallel fibers of hard keratin (high sulfur content)
More keratinization = more transparency;
Takes on color of underlying vascular bed (dermis)
Muehrcke Lines
Transverse lines that signify an abnormality in the vascular bed of the nails.
Occur in association with several conditions including pellagra, Hodgkin disease, renal failure, sickle cell anemia, others.
They persist with chronic hypoalbuminemia but the exact pathogenesis has not been clearly explained.
