SFP: histology of the skin

Question 1

What are the main functions of the epidermis

Answer 1

-Protection (physical barrier)
-Thermoregulation
-Sensory (interacting w environment)
-Metabolism (regulating electrolytes via sweat)
-Sexual signaling (visual indicator of health and attractiveness; pheromone production)

Question 2

What are the layers of the skin

Answer 2

Epidermis, dermis, subcutis

Question 3

Name the layers of the epidermis from superficial to deep

Answer 3

-Stratum corneum
-Stratum lucidum
-Stratum granulosum
-Stratum spinosum
-Stratum basale

Corny little grandpa sings badly

Question 4

Which cells make up the majority of the epidermis

Answer 4

keratinocytes

Question 5

Describe the stratum basale: general structure, connection to the basement membrane, function, other elements found

Answer 5

A single layer of cuboidal cells attached to the basement membrane via hemidesmosomes. They are the progenitor cells of the epidermis, so there is a lot of mitosis here. We can often find cytoskeletal keratins and melanocytes

Question 6

Describe the stratum spinosum

Answer 6

Has lots of keratinocytes connected by desmosomes. Keratin is synthesized in the cytoplasm and assembled into tonofibrils

Question 7

Describe the stratum granulosum

Answer 7

3-5 layers of flattened keratinocytes undergoing keratinization. The cytoplasm has keratohyaline granules with filaggrin and Golgi-derived lamellar granules containing lipids and glycolipids

Question 8

Describe the stratum lucidem

Answer 8

Only found on thick skin and is composed of flattened eosinophilic keratinocytes held together by desmosomes

Question 9

Describe the stratum corneum

Answer 9

15-20 layers of keratinized squamous cells with no nucleus. They’re filled with filamentous keratin and typically arranged in a basket weave pattern.

Question 10

Describe melanocytes

Answer 10

They are dendritic cells found in the basal layer that make melanin to give to keratinocytes

Question 11

What is the major function of melanin

Answer 11

Protect us from UV damage

Question 12

What is eumelanin

Answer 12

Brown-black pigment

Question 13

What is phaeomelanin

Answer 13

Melanin pigment found in red headed individuals

Question 14

Describe melanin synthesis

Answer 14

-Tyrosine is converted to 3,4 DOPA
-DOPA is polymerized into melanin
-Melanin accumulates in vesicles to form melanosomes
-Melanosomes are transported via kinesin to tips of dendrites
-Keratinocytes phagocytose melanosomes and are transported to the nucleus by dynein

Question 15

Describe Langerhans cells

Answer 15

They are dendritic cells that serve as antigen-presenters and are found in the stratum spinosum; they’re basically epidermal macrophages

Question 16

Describe Merkel cells

Answer 16

They’re epithelial tactile cells that can sense gentle touch

Question 17

Briefly describe the dermis

Answer 17

A layer of connective tissue that supports the epidermis, vasculature, and adnexal structures

Question 18

What are the layers of the dermis

Answer 18

Papillary dermis and reticular dermis

Question 19

Describe the papillary dermis

Answer 19

Loose connective tissue with type I and III collagen

Question 20

Describe the reticular dermis

Answer 20

Thicker connective tissue with type I collagen and elastic fibers

Question 21

What are the layers of the vascular plexus

Answer 21

Superficial: capillaries just below the epidermis

Deep: larger vessels and lymphatics

Question 22

What are the unencapsulated receptors

Answer 22

Merkel cells, free nerve endings, and root hair plexus

Question 23

meissner corpuscle: encapsulation and function

Answer 23

encapsulated and responds to light touch; found in the papillary dermis

Question 24

pacinian corpuscle: encapsulation and function

Answer 24

encapsulated; pressure and vibration

Question 25

krause end bulbs: encapsulation and function

Answer 25

encapsulated; low frequency vibration. found in the penis and clitoris

Question 26

ruffini corpuscle: encapsulation and function

Answer 26

encapsulated; senses tissue distortion (ex: edema)

Question 27

Describe the subcutis

Answer 27

Layer of fat between the dermis and superficial fascia; thickness is variable

Question 28

Describe hair follicles

Answer 28

Specialized invaginations of the epidermis

Question 29

What is the arrector pili muscle

Answer 29

Smooth muscle that can control hair position

Question 30

Name the 3 phases of the hair growth cycle

Answer 30

-Anagen: growth, 2-7 year duration, 85% of hairs

-Catagen: 2-3 weeks duration, less than 15% of hairs

-Telogen: resting and shedding, 100 day duration, less than 1% of hairs

Question 31

What is the dermal papilla

Answer 31

It inserts into the hair bulb at the base of the follicle. The cells here divide rapidly and keratinize here

Question 32

Where does hair acquire melanin

Answer 32

cortex

Question 33

What are the three layers of hair

Answer 33

-Medulla: in the center and made of moderately keratinized cells
-Cortex: heavily keratinized cells surrounding medulla
-Cuticle: thin outer layer of heavily keratinized squamous cells

Question 34

What are sebaceous glands

Answer 34

Sweat glands associated with hair follicles; found everywhere but palms of hands and soles of feet. They’re acinar glands comprised of sebocytes that converge on a duct that empties into the follicle

Question 35

What is the method of secretion in sebaceous glands

Answer 35

Holocrine; the cells proliferate, accumulate lipids, kill themselves and puke out their contents

Question 36

Describe eccrine sweat glands

Answer 36

The most numerous; they’re responsible for sweating. They utilize merocrine secretion. Their ducts absorb sodium ions to prevent excessive water loss.

Question 37

What are the cell types found in eccrine glands

Answer 37

Clear cells: product sweat
Dark cells: filled with eosinophilic granules that undergo merocrine secretion
Myoepithelial cells: contract to move secretions

Question 38

Describe apocrine glands

Answer 38

Limited to the axilla and groin; associated with smelly sweat

Question 39

Label the basic components of the nail unit

Answer 39

Nail plate: hard keratin derivative
Nail matrix: specialized cells divide and become keratinized and mature into nail plate
Nail bed: epithelium below nail plate