Week 6: Integument

Question 1

What are the main layers of the structure shown here?

Answer 1

From top to bottom: epidermis

dermis

skin appendages: hair, nails, glands

hypodermis

Question 2

What is a denticle and what is it composed of?

Answer 2

A dermal scale of ancient fish/amphibians, composed of dentin and enamel (like our teeth). These would evolve into epidermal scales (stratum corneum) in reptiles, feathers in dinosaurs and birds, epidermis (hair, nails) in mammals, and sweat/mammary glands in mamals

Question 3

What are the two classifications of skin and what do they contain?

Answer 3

Thin skin covers most of the body, and is made up of dermal and epidermal cells, including a stratum corneum. Thick skin is unique because it has a very thick stratum corneum, and has a layer called the stratum lucidum, which thin skin does not have

Question 4

What are the main cells of the epidermis? What are the other kinds?

Answer 4

Keratinocytes are the main kinds

Langerhan’s cells (skin monocytes)

Melanocytes produce melanin (pigmentation)

and Merkel’s cells are sensory, with nerve endings embedded

Question 5

How are keratinocytes attached to one another? What are the layers they form?

Answer 5

They attach via desmosomes, and have five main layers, top to bottom (Can Little Girls Strike Back):

stratum corneum

stratum lucidum

stratum granulosum

stratum spinosum

stratum basalis

Question 6

What is the mnemonic you use to identify the thick skin layers? What do each of these layers look like, generally?

Answer 6

Can Little Girls Strike Back

Corneum, Lucidum, Granulosum, Spinosum, Basalis

Corneum = very thick, keratinized layer (fibrous)

Lucidum = thin, clear-staining layer

Granulosum = flattened cells with small nuclei

Spinosum = larger, bulbous cells that flatten out towards the top

Basale = wave-like layers of cells that have amorphous appearance

Question 7

What is another name for the stratum basale? What is it composed of?

Answer 7

Desmosomes (cadherins), hemidesmosomes (integrins), and a basement membrane

Question 8

Why does the stratum spinosum appear “spiky” in slides, and what structures create this look?

Answer 8

The desmosomes that hold the cells together, as well as the tonofibrils (cytokeratin filaments) that secure the cytoplasm to the desmosomes attach cells to one another. Dehydration during slide preparation causes the cells to shrink while remaining attached, causing this “spiked” look

Question 9

What two kinds of granules are located in the stratum granulosum, and what is the function of each?

Answer 9

The keratohyalin granules (no membrane) contain filaggrin that binds keratin

Lamellar granules (membrane-bound) contain lipid sheets that are secreted to form intracellular “glue” that also acts as a barrier

Question 10

What form fingerprints and other unique structural elements of different individuals?

Answer 10

Dermatoglyphs, which are formed from undulations in the stratum granulosum and stratum corneum, form the unique dermatoglyphs of fingerprints

Question 11

What are the three main functions of the epidermis?

Answer 11

Abrasion resistance

Physical-chemical barrier

Waterproofing

Question 12

What are the two kinds of melanin, and what colors do they form?

Answer 12

Eumelanin (black pigmentation) and pheomelanin (red pigmentation)

Question 13

What chemical activity occurs as melanosomes mature? What happens once melanin granules are fully formed?

Answer 13

Melanosomes mature into melanin granules via the reduction by tyrosinase of DOPA into dopaquinone, then into melanin. Melanin granules then bud off into nearby keratinocytes to help protect the nuclear/DNA structures there.

Question 14

What is skin color dictated by? What is albinism?

Answer 14

Skin color is dictated by the amount of melanin and carotene–the activity of melanocytes, not the amount of them

Albinism is the lack of reductive tyrosinase activity in melanocytes, disallowing maturation of granules.

Question 15

What are Langerhan’s cells?

Answer 15

They are dendritic cells (monocyte-like) that are present in the skin. They act as antigen-presenting cells (APCs) for B and T cells.

Question 16

What are Merkel’s cells and what are their associated cell components?

Answer 16

Merkel’s cells are sensory cells above the stratum basalae, and are attached to a nerve ending (Merkel’s disc). They have dense core granules that contain neurotransmitter molecules.

Question 17

Describe the general pathologies of skin cancers

Answer 17

Over 2 million cases of skin cancer are found in the country each year. The main kinds are:

basal cell carcinoma (75%+ of all skin cancers)

squamous cell carcinoma (20%)

and melanoma (<5%)

Skin cancer is directly correlated to UV light exposure

Question 18

What proteins/glycoproteins form the main basal lamina structures?

Answer 18

Laminins, fibronectin, Type IV and VII collagen

Question 19

What are the two main layers of the dermis?

Answer 19

The papillary (upper) and reticular (lower) layers

Question 20

What does the papillary layer do as far as securing the skin?

Answer 20

It forms a peg-and-socket structure that prevents shear stress from sliding epidermis off the dermal layer

Question 21

Describe the main structures of the dermis, and explain the role it forms in wrinkle formation?

Answer 21

The dermis contains fibroblasts, elastic fibers, Type I collagen in differential deposits. Irregular deposition is responsible for wrinkle formation.

Question 22

Which layer of skin contains the AV shunts? What is their function?

Answer 22

The papillary layer of the dermis contains the AV shunts of the skin, which are involved in thermoregulation. When it is cool, underlying blood vessels close off, preventing the shunting of warm blood to the surface and the loss of heat. When it is warm, the vessels open, allowing more blood to the surface to participate in evaporative cooling mechanisms.

Question 23

Where are Meissner’s corpuscles and what are they responsible for?

Answer 23

Meissner’s corpuscles are located in the papillary layer and are associated with light touch

Question 24

Where are the Pacinian corpuscles and what is their function?

Answer 24

The Pacinian corpuscles are located deep to Meissner’s corpuscles in the reticular layer, and are responsible for deep touch/pressure sensation.

Question 25

What is the hypodermis? Why is it different?

Answer 25

The hypodermis is NOT a part of the integument, and contains the superficial fascia

Question 26

Describe the structure of the epidermal nail

Answer 26

The eponychium is embedded in the skin, whereas the plate sits atop the nail bed, and the nail plate/hyponychium extends out over the tip of the finger

Question 27

Describer the structure and function of hair follicles

Answer 27

The hair bulb is rooted and attached to the papilla, with the follicle extending upwards through layers of skin. The “root” sits in the dermal layers of skin, whereas the shaft element begins near the surface/epidermal layer.

Question 28

What are the main components of the hair bulb? What element of the bulb usually causes hair to fall out during cancer treatment? What can prevent hair loss during chemo?

Answer 28

The germinal matrix (forms structural elements of hair), melanocytes (secrete pigment), hair papilla (the “post” that the hair grows around) and the blood vessels that fill the papillae. Germinal cells are destroyed by chemotherapy during cancer treatment, which targets fast-growing cells. Cooling the scalp to close off blood vessels allows fewer chemo molecules to reach the vessels there, preventing hair from falling out as readily.

Question 29

What are notable tissues and layers around the hair follicle?

Answer 29

The internal root sheath lies between the hair and the external root sheath, which is continuous with the epidermis. The arrector pili muscles help pull the skin around the hair, especially when cold or in the “fight or flight” response. Hair increases the “boundary layer” for heat, helping retain heat near your body. Sebaceous glands secrete oils that keep the hair moisturized.

Question 30

What are the three main layers of the hair shaft?

Answer 30

The medulla (center), cortex (middle portion) and cuticle (outer region that contains small barbs)

Question 31

What are the three main layers of hair moving internally to externally?

Answer 31

The hair shaft, the internal root sheath (inside the “tube”) and the external root sheath

Question 32

What are the two main growth methods of hair? What causes balding? What causes graying of hair?

Answer 32

Cyclic and asynchronous growth can occur. Balding is terminal and occurs both genetically and due to hormones. Graying occurs due to loss of melanin with age.

Question 33

What part of the hair follicle limits the growth of the internal root sheath?

Answer 33

The sebaceous gland

Question 34

What kinds of glands are sweat glands?

Answer 34

Simple branched acinar glands

Question 35

What do sebaceous cells secrete?

Answer 35

Lipid droplets and sebum via a holocrine mode of secretion. Sebum maintains the stratum corneum, and has weak antibacterial/antifungal activity.

Question 36

Describe the structure and function of eccrine sweat glands. What is another term for them?

Answer 36

Eccrine or merocrine sweat glands secrete onto the surface of the skin, releasing vesicles contianing water and salt. They consist of a duct, a secretory portion, myoepithelial cells, dark cells that secrete antibacterial mucous, and clear cells that produce sweat.

Question 37

What kinds of cells line eccrine sweat gland ducts?

Answer 37

Stratified cuboidal epithelium (rare)

Question 38

Why is “apocrine” sweat gland a misnomer?

Answer 38

“Apocrine” sweat glands secrete material in a merocrine mode of secretion, releasing material onto hair shafts.

Question 39

From a cross-section, how could you tell the difference between apocrine and eccrine sweat glands?

Answer 39

Eccrine sweat glands have much smaller ducts than “apocrine” sweat glands, which have much larger secretory portions. Apocrine sweat glands mostly release antibacterial material, as well as pheromones.

Question 40

Which type of gland secretes material onto the surface of the skin? What does that material contain? What glands secrete into the hair follicle? What do they mostly contain?

Answer 40

Eccrine sweat glands secrete sodium, chloride, and water onto the surface of the skin (clear cells), as well as mucous and antibacterial material (dark cells)

Apocrine and sebaceous glands secrete antibacterial mucous and sebum, respectively, into hair follicles. Sebum keeps the stratum corneum well-moisturized.