Microanatomy of the Skin

Question 1

Primary functions of skin?

Answer 1

Barrier (retain water, prevent infection, absorb UV)
Production of Vitamin D
Thermoregulation
Secretion
Sensation

Question 2

Ectoderm: components

Answer 2

Epithelial: epidermis, pilosebaceous units, eccrine glands, apocrine glands
Neuroectoderm: melanocytes, nerves, Merkel cells

Question 3

Mesoderm components

Answer 3

1. Hematopoietic: mast cells, MØ, Langerhan’s cells, lymphocytes
2. Mesenchymal: fibroblasts (dermis), endothelial and pericytic cells (vessels), subcutaneous fat (adipocytes)

Question 4

Epidermis: layers

Answer 4

1. stratum basalis
2. stratum spinosum
3. stratum granulosum
4. stratum corneum

Question 5

Normal transit time from basalis layer to top of skin?

Answer 5

28 days

Question 6

Stratum basalis

Answer 6

• cells attach to basement membrane via hemidesmosomes
• basal layer: stem-like cells, highest proliferative index in unremarkable skin
• cells with perinuclear melanosomal cap protects from UV damage

Question 7

Stratum spinosum

Answer 7

• cells initiate terminal differentiation
• thickest part of dermis
• DESMOSOMES and ADHERINS junctions are prominent and give epidermis strength

Question 8

Stratum granulosum

Answer 8

• Keratohyaline granules (contain flaggrin-cross link keratin filaments)
• organelles, nuclei disappear

Question 9

Stratum corneum

Answer 9

• cell becomes network of cross-linked proteins and lipids

- secretion of protein-bound lipids (ODLAND BODIES) into intercellular space to enhance barrier

Question 10

How many types of keratins are there? What are they?

Answer 10

2; Type 1 (acidic) and Type 2 (basic)

Question 11

What are keratins?

Answer 11

1’ structural protein of keratinocytes, critical for barrier function

Question 12

What structures give the epidermis strength and integrity?

Answer 12

Desmosomes

Question 13

Basement Membrane

Answer 13

Organized structure of proteins forming bridge between dermis and epidermis; comprised of

1. Lamina lucida (laminin, ladinin)
2. Lamina densa (nidogen, Type IV collagen)
3. Sub-lamina densa (anchoring fibrils, type VII collagen)

Question 14

Rete

Answer 14

Downward invaginations that interdigitate with dermal papilla to form structure that provides mechanical integrity and immune surveillance

Question 15

Functions of Rete

Answer 15

1. Bring vasculature in close proximity to epidermis
2. Facilitate trafficking of immune cells
3. Lost during aging –> fragility
4. RESTORE LATERAL FORCES in the skin

Question 16

Melanocytes

Answer 16

NEURAL CREST-DERIVED, mature upon reaching epidermis, transfer melanosomes to keratinoytes

Question 17

Appearance of melanocytes on H&E

Answer 17

inconspicuous; may see brown nest on top (melanosomal cap)

Question 18

Melanocyte stain?

Answer 18

MART-1 (see dendritic tree of melanocytes)

Question 19

Langerhan’s Cells

Answer 19

BONE MARROW-DERIVED, professional APCs, usually located in stratum spinosum

Question 20

Role of Langerhan’s Cells

Answer 20

1. Prevent infection and neoplasia
2. Mediate allergic contact dermatitis
3. Traffic between epidermis and lymph nodes

Question 21

Langerhan’s Cells - stain?

Answer 21

CD1a

Question 22

Merkel Cell

Answer 22

NEUROEPITHELIAL ORIGIN - likely from epidermis

Question 23

Merkel Cell - function

Answer 23

sensation (likely)

Question 24

Merkel Cell - stain

Answer 24

CK 20

Question 25

Dermis ECM

Answer 25

- COLLAGENS provide durability, strength - ELASTINS - elasticity, tightness - MUCOPOLYSACCHARIDES - hyaluronic acid - resilience, fullness

Question 26

Skin appendages in dermis?

Answer 26

Pilosebaceous unit, eccrine gland, apocrine gland (axilla, groin)

Question 27

Where is eccrine gland located? What does it do?

Answer 27

Junction of dermis and subcutaneous fat, empties to skin - 2-4 million - involved in thermoregulation, sweat production - most abundant on foot, least on back - consists of secretory cell and duct - duct lined by MYOEPITHELIAL CELLS that help push sweat to skin surface

Question 28

What about apocrine glands?

Answer 28

A little bit bigger than sweat glands, drain into hair follicle - anogenital, areolae, eyelid, scalp, abdomen, EAM - glands in lower dermis, subcutis - enclosed by discontinuous myoepithelial cells that contract 2' to alpha-adrenergic agonists - originate from INFUNDIBULAR portion of hair follicle, found only on hairy skin - not responsive to heat

Question 29

...and sebaceous glands?

Answer 29

Near the skin surface, drain into hair follicle - produce SEBUM (fatty) - flows onto skin surface & mixes w/lipids

Question 30

Three cell types in eccrine glands?

Answer 30

1. Dark cell (CFTR, Cl- transporter) 2. Clear cell (secrete water, electrolytes) 3. Myoepithelial cells (contract)

Question 31

What are apocrine gland secretions?

Answer 31

-mixture of electrolytes & proteins (albumin, globulin, hexosamine, mucoprotein)

Question 32

Axillary odor...what gives?

Answer 32

Odor produced by bacteria acting on lipids in APOCRINE gland secretions

Question 33

Myoepithlial cell marker?

Answer 33

Anti-SMA (smooth muscle actin)

Question 34

Cells within dermis

Answer 34

1. FIBROBLASTS (produce collagen, elastin, mucopolysaccharides) 2. SMOOTH MUSCLE CELLS (pilar muscles) 3. ENDOTHELIUM (vascular, lymphatic) 4. MAST CELLS 5. NERVE CELLS

Question 35

Mast Cell

Answer 35

- hypersensitivity - located near vessels, nerves, lymphatics - granules contain TRYPTASE, CHYMASE - activated through Fc ER1 - SCF (c-Kit) agonist

Question 36

Subcutaneous Adipose Tissue

Answer 36

- composed of adipocytes | - functions: INSULATION, SHOCK ABSORPTION, ENERGY STORAGE, METABOLISM