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MSK Week 4 > Histology Of The Skin > Flashcards

Histology Of The Skin Flashcards

1
Q

What are the functions of the skin?

A
  1. Maintain body temperature
  2. Prevent excess loss of water and ions
  3. Vitamin D production
  4. Receive stimuli from external environment
  5. Protects body from mechanical trauma or UV radiation
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2
Q

What are the 3 layers of the skin?

A
  1. Epidermis (most superificial layer)
  2. Dermis
  3. Hypodermis (deepest layer)
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3
Q

What serves as the division between the dermis and epidermis?

A

The basement membrane

Note: the epidermis INCLUDES the entirety of your hair follicles

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4
Q

What structures can be found in the dermis?

A
  1. Hair follicles
  2. Sweat glands
  3. Sebaceous glands
  4. Pacinian corpuscle (sensory receptor)
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5
Q

What is the dermis mostly comprised of?

A

Collagen

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6
Q

What is another name for the hypodermis?

A

Aka subcutaneous tissue or superficial fascia

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7
Q

What is the hypodermis mainly made of?

A

Adipose tissue = fat

It’s also made of connective tissue, blood vessels and nerves

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8
Q

What is the function of the hypodermis?

A
  1. Shock absorber
  2. Thermal insulator
  3. Fat storage
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9
Q

How is the blood supply of the skin organized?

A
  1. Papillary plexus

the papillary plexus in the papillary layer of the dermis near its junction with the reticular layer

Papillary loops travel in dermal papillae and stem from the papillary plexus

  1. Cutaneous plexus

the cutaneous plexus is in the superficial aspect of the hypodermis = at the junction of the hypodermis with the reticular layer of the dermis

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10
Q

What is the function of the papillary loops?

A

Papillary loops travel in dermal papillae and stem from the papillary plexus

They are important for delivering nutrients to the a vascular epidermis — nutrients from the papillary loops diffuse superficially to supply the cells of the epidermis

The papillary plexus, in turn, receives arterial blood from and drains venous blood to the deeper cutaneous plexus

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11
Q

What is the difference between thick and think skin?

A

skin is largely classified as either thick or thin skin, according to the thickness of its epithelial layer

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12
Q

What’s another name for thick skin?

A

Glabrous skin

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13
Q

Where is glabrous skin found?

A

Strictly on the palms of our hands and on the soles of our feet

Also there is NO hair in thick skin

Thin skin is located on the rest of the body

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14
Q

What are the general characteristics of the epidermis no matter where it is found on the body?

A

Regardless of whether it is located in thin or thick skin, epidermis is:

  1. made up of stratified squamous keratinized epithelium
  2. It rests on a basement membrane
  3. is avascular
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15
Q

Where is thin skin the thinnest on the body?

A

Eyelids

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16
Q

What are the layers of the epidermis?

A
  1. Stratum corneum (superificial)
  2. Stratum granulosum
  3. Stratum spinosum (deepest)
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17
Q

What gives people darker vs. lighter skin?

A

Compared to a dark-skinned individual, a light- skinned individual has the same number of melanocytes

However, the melanocytes of a light-skinned individual produce a lesser amount of melanin and a different kind of melanin

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18
Q

What are the layers of the epidermis?

A
  1. Stratum corneum (most superficial)
  2. Stratum lucidum
  3. Stratum granulosum (with kekratohyalin granules)
  4. Stratum spinosum
  5. Stratum basale (with melanin pigment)

Basement membrane

**thin skin does NOT have a stratum lucidum layer; it’s completely absent!!!

***these layers are also the order of the birth to death of a keratinocyte

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19
Q

In what layer of the skin is melanin found?

A

In the stratum basale layer of the epidermis

20
Q

What are the characteristics of the stratum corneum? What is its function?

A
  1. It is comprised of flattened keratinocytes
  2. No nuclei are present in the keratinocytes of this layer

This layer of dying cells acts to protect against mechanical trauma, bacterial invasion and desiccation

This layer ranges in thickness from 20 to 40 cells thick — a very thick stratum corneum is diagnostic of thick skin

21
Q

What are the characteristics of the stratum lucidum? What is its function?

A

it is seen ONLY in thick skin and is absent in thin skin

it is only 1-2 cells thick

keratinocytes are beginning to flatten in this layer, so the stratum lucidum typically appears especially thin

nuclei are absent in keratinocytes of the stratum lucidum

22
Q

how does the stratum lucidum stain?

A

the stratum lucidum stains variably

it usually appears as a clear layer but can sometimes appear as a dark layer

23
Q

What are the characteristics of the stratum granulosum? What is its function?

A

it is a layer that is about 2-3 cells thick

it contains keratinocytes that have dark-staining keratohyalin granules in their cytoplasm

nuclei are present in keratinocytes of this layer

24
Q

What are the characteristics of the stratum spinosum? what connects the cells of this layer?

A

this layer contains polyhedral-shaped cells with a fuzzy gap between the edges of the cells

the “fuzz” are numerous desmosomes that connect adjacent cells with their numerous processes or “bridges”

desmosomes are also known as tight junctions and function to hold adjacent keratinocytes tightly together in order to protect underlying soft tissue from shearing force

25
Q

What are the characteristics of the stratum basale?

A

it’s the deepest layer of the epidermis and is located immediately superficial to the basement membrane

it is comprised of a single layer of cuboidal keratinocytes

this layer is where proliferation of new keratinocytes occurs

26
Q

what are the layers of the dermis?

A
  1. papillary layer (superficial)

2. reticular layer (deep)

27
Q

what is the organization of the dermis?

A

both layers of the dermis are made up of dense irregular connective tissue, meaning that they contain large bundles of collagen fibers that are tightly packed together and that are oriented in a haphazard, random manner

however, the papillary layer of the dermis often appears slightly lighter-staining compared to the reticular layer because its bundles of collagen fibers are smaller

so even though the collagen fibers of the papillary layer are not as densely packed as that of the reticular layer, the papillary layer is considered to be composed of dense irregular connective tissue as well

28
Q

what are dermal papillae? what is their function?

A

projections of dermis into the epithelium

in between dermal papillae are downward projections of epithelium into the dermis called epidermal ridges

the interdigitation of the dermal papillae and the epidermal ridges helps prevent the epidermis from being sheared off the dermis by shearing (horizontally-directed) forces

29
Q

what are langer lines?

A

he pattern created by collagen fibers of the reticular layer of the dermis

they are a reflection of the overall arrangement of collagen fibers in dense irregular connective tissue

30
Q

what receptors are in the skin and where are they found specifically?

A
  1. Meissner’s corpuscles = papillary layer of the dermis

2. Pacinian corpuscles = reticular layer or the dermis

31
Q

where are elastic fibers found in the skin? what is their function?

A

in the dermis interwoven between the bundles of collagen

elastic fibers enable the skin to return to its original position after being subjected to stress

elastic fibers cannot be seen on a standard H&E stain but rather only with a special elastic stain

32
Q

what are the 4 cell types that can be found int he epidermis?

A
  1. keratinocyte (most common type)
  2. melanocyte
  3. Langerhans cells
  4. Merkel cell
33
Q

where are keratinocytes and melanocytes derived from embryologically?

A

keratinocytes = ectoderm

melanocytes = neural crest

34
Q

what is a Langerhans cell?

A

a macrophage that is located throughout the epidermis but it is most readily seen in the stratum spinosum

35
Q

where are melanocytes found in the epidermis?

A

melanocytes are located strictly in the stratum basale and produce the pigment melanin

36
Q

what is a Merkel cell?

A

it is a mechanoreceptor responsible for deep touch, pressure and proprioception

it is found strictly in the stratum basale

37
Q

what are the sensory receptors in the skin?

A
  1. free nerve endings
  2. Merkel cells
  3. Meissner’s corpuscles
  4. Pacinian corpuscles
  5. Ruffini corpuscles
38
Q

what is a Meissner’s corpuscle?

A

it is an encapsulated sensory nerve ending that is responsible for discriminatory light touch

it’s oval-shaped, with its long axis oriented perpendicular to the external epidermal surface

a nerve fiber zig-zags within the corpuscle

it is found exclusively in dermal papillae of thick skin, i.e. in dermal papilla within the soles of our feet and palms of our hands, especially our fingertips

39
Q

what is a Pacinian corpuscle?

A

functions to responds to pressure, vibration and touch

looks like an onion

like a Meissner’s corpuscle, a Pacinian corpuscle is an encapsulated sensory nerve ending, is oval-shaped, and a single nerve fiber penetrates the core of the corpuscle

however, it is located deep in the dermis instead of in the superficial aspect of the dermis like a Meissner’s corpuscle – specifically, a Pacinian corpuscle is located at the junction of dermis and hypodermis

40
Q

what is the integumentary system?

A

skin plus its appendages, i.e. glands, hair, and nails

skin and all its appendages are derived from ectoderm

41
Q

what are the main types of glands in the skin?

A
  1. sweat (apocrine and eccrine)
  2. sebaceous
  3. mammary

each have a secretory and duct portion

42
Q

what is the structure of an eccrine sweat gland?

A

the secretory portion of eccrine sweat glands consists of a small, highly coiled, tube that is found at or near the junction of dermis and hypodermis

the duct of an eccrine sweat gland extends all the way to the external surface of the epidermis, where the sweat is deposited

43
Q

what is the structure of an apocrine sweat gland?

A

like eccrine sweat glands, the secretory portions of apocrine sweat glands are found at the junction of the dermis and hypodermis

also, the secretory portion of apocrine sweat glands is similarly comprised of coiled tubes

even though the name “apocrine sweat glands” suggests the apocrine mode of secretion, they use only the merocrine mode of secretion – in fact, merocrine secretion is used by both apocrine and eccrine sweat glands

44
Q

what’s the difference between an apocrine and eccrine sweat gland?

A

an apocrine sweat gland is much larger than an eccrine sweat gland, and the lumen of an apocrine sweat gland is larger than the lumen of an eccrine sweat gland

another difference is that apocrine sweat glands empty into hair shafts, in contrast to eccrine sweat glands, which empty their sweat onto the surface of the epidermis

45
Q

what are sebaceous glands?

A

“oil-producing” glands which secrete by the holocrine method

these glands are large, alveolar (sac or grape-like) structures which empty their degraded cellular product (sebum) into hair follicles

acne = infection of sebaceous glands

46
Q

which structures have close proximity to hair follicles?

A
  1. arrector pili muscle
  2. apocrine sweat glands
  3. sebaceous glands
47
Q

what are arrector pili?

A

small, thin bundles of smooth muscle cells

arrector pili course diagonally in the dermis

they are attached to hair follicles at one end and at the other end are attached to collagen and elastic fibers near the junction of the papillary and reticular layers of the dermis

they are innervated by sympathetic fibers –> when stimulated, these muscles pull hair shafts up so that they stand more vertically aka “goose bumps”,

goose bumps are are seen due to indentations in skin created when arrector pili “pull down” on areas of dermis where they are attached

MSK Week 4 (11 decks)

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