Histology Of The Skin

Question 1

What are the functions of the skin?

Answer 1

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

Question 2

What are the 3 layers of the skin?

Answer 2

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

Question 3

What serves as the division between the dermis and epidermis?

Answer 3

The basement membrane

Note: the epidermis INCLUDES the entirety of your hair follicles

Question 4

What structures can be found in the dermis?

Answer 4

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

Question 5

What is the dermis mostly comprised of?

Answer 5

Collagen

Question 6

What is another name for the hypodermis?

Answer 6

Aka subcutaneous tissue or superficial fascia

Question 7

What is the hypodermis mainly made of?

Answer 7

Adipose tissue = fat

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

Question 8

What is the function of the hypodermis?

Answer 8

1. Shock absorber
2. Thermal insulator
3. Fat storage

Question 9

How is the blood supply of the skin organized?

Answer 9

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

2. 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

Question 10

What is the function of the papillary loops?

Answer 10

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

Question 11

What is the difference between thick and think skin?

Answer 11

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

Question 12

What’s another name for thick skin?

Answer 12

Glabrous skin

Question 13

Where is glabrous skin found?

Answer 13

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

Question 14

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

Answer 14

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

Question 15

Where is thin skin the thinnest on the body?

Answer 15

Eyelids

Question 16

What are the layers of the epidermis?

Answer 16

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

Question 17

What gives people darker vs. lighter skin?

Answer 17

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

Question 18

What are the layers of the epidermis?

Answer 18

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

Question 19

In what layer of the skin is melanin found?

Answer 19

In the stratum basale layer of the epidermis

Question 20

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

Answer 20

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

Question 21

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

Answer 21

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

Question 22

how does the stratum lucidum stain?

Answer 22

the stratum lucidum stains variably

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

Question 23

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

Answer 23

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

Question 24

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

Answer 24

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

Question 25

What are the characteristics of the stratum basale?

Answer 25

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

Question 26

what are the layers of the dermis?

Answer 26

1. papillary layer (superficial) | 2. reticular layer (deep)

Question 27

what is the organization of the dermis?

Answer 27

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

Question 28

what are dermal papillae? what is their function?

Answer 28

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

Question 29

what are langer lines?

Answer 29

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

Question 30

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

Answer 30

1. Meissner's corpuscles = papillary layer of the dermis | 2. Pacinian corpuscles = reticular layer or the dermis

Question 31

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

Answer 31

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

Question 32

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

Answer 32

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

Question 33

where are keratinocytes and melanocytes derived from embryologically?

Answer 33

keratinocytes = ectoderm melanocytes = neural crest

Question 34

what is a Langerhans cell?

Answer 34

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

Question 35

where are melanocytes found in the epidermis?

Answer 35

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

Question 36

what is a Merkel cell?

Answer 36

it is a mechanoreceptor responsible for deep touch, pressure and proprioception it is found strictly in the stratum basale

Question 37

what are the sensory receptors in the skin?

Answer 37

1. free nerve endings 2. Merkel cells 3. Meissner's corpuscles 4. Pacinian corpuscles 5. Ruffini corpuscles

Question 38

what is a Meissner's corpuscle?

Answer 38

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

Question 39

what is a Pacinian corpuscle?

Answer 39

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

Question 40

what is the integumentary system?

Answer 40

skin plus its appendages, i.e. glands, hair, and nails skin and all its appendages are derived from ectoderm

Question 41

what are the main types of glands in the skin?

Answer 41

1. sweat (apocrine and eccrine) 2. sebaceous 3. mammary each have a secretory and duct portion

Question 42

what is the structure of an eccrine sweat gland?

Answer 42

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

Question 43

what is the structure of an apocrine sweat gland?

Answer 43

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

Question 44

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

Answer 44

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

Question 45

what are sebaceous glands?

Answer 45

“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

Question 46

which structures have close proximity to hair follicles?

Answer 46

1. arrector pili muscle 2. apocrine sweat glands 3. sebaceous glands

Question 47

what are arrector pili?

Answer 47

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