Histology: Glands, Hair, and Nails

Question 1

Introduction to Glands

Answer 1

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

Question 2

Merocrine, Apocrine, and Holorcrine Glands

Answer 2

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

Question 3

Merocrine, Apocrine, and Holorcrine Glands Locations

Answer 3

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

Question 4

Eccrine Sweat Gland

Answer 4

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

Question 5

Eccrine Gland: Secretory vs. Excretory Portions

Answer 5

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

Question 6

Eccrine Gland Cell Types

Answer 6

1. Clear cell (C): water & NaCl of sweat; rich in mitochondria, glycogen
2. Dark cell (D): line the lumen; rER makes glycoprotein; apical granules
   Mode of secretion: merocrine via exocytosis
3. 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

Question 7

CF and Sweating

Answer 7

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

Question 8

Apocrine Sweat Gland

Answer 8

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

Question 9

Sebaceous Gland

Answer 9

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

Question 10

Hair Structure

Answer 10

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

Question 11

Bulge Region

Answer 11

Where arrector pili muscle attaches;

Stem cells

Question 12

Burn Victims

Answer 12

Epidermal water barrier = lose water through this structure with burn victims

Question 13

Hair Follicles

Answer 13

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

Question 14

Dermal Papilla

Answer 14

Matrix cells surrounding DP proliferate and undergo keratinization to form hair shaft and Internal Root Sheath

Question 15

Matrix Cells

Answer 15

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

Question 16

Hair Shaft

Answer 16

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

Question 17

Inner Root Sheath

Answer 17

Derived from matrix cells in bulb
More cellular deeper, but more keratinization superficially
Indicating differences in distance from the bulb

Question 18

Hair Follicle Layers

Answer 18

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

Question 19

Hair Cycle: Anagen

Answer 19

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

Question 20

Hair Cycle: Catagen

Answer 20

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

Question 21

Hair Cycle: Telogen

Answer 21

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

Question 22

Lanugo Hair

Answer 22

Fetal hair; fine, downy, unpigmented; shed before or shortly after birth. Replaced by vellus

Question 23

Vellus Hair

Answer 23

Fine, pale hair in most of skin of children, 2/3 of hair of women, and in bald skin; short, plump follicles

Question 24

Terminal Hair

Answer 24

adult type, coarser, usually more pigmented; longer, straighter follicles
Scalp, eyebrows & lashes, axillary, pubic.

Question 25

Club Hair

Answer 25

A terminal hair which is no longer connected to base of follicle.
May occupy follicle with a newly growing hair shaft.

Question 26

Baldness

Answer 26

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

Question 27

Hair Texture and Color

Answer 27

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

Question 28

Nail Lunula and Eponchium

Answer 28

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

Question 29

Nail Body, Bed, Matrix, Hypoychium

Answer 29

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

Question 30

Nail Matrix

Answer 30

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

Question 31

Nail Plate

Answer 31

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)

Question 32

Muehrcke Lines

Answer 32

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.