SKIN

Question 1

What did Virchow describe skin as?

Answer 1

Protective covering

Question 2

What functions does the skin have?

Answer 2

• Resists bacterial and fungal invasion
• It’s rich in antigen-presenting cells (Langerhans cells) for immune response
• Pigmentation from melanin provides protection from UV
• Facilitate synthesis of vitamin D3
• Skin helps thermoregulate via blood circulation in extremities and sweat
• Receptors for touch, pressure, pain and temperature

Question 3

What are the layers of the skin?

Answer 3

3 main layers,

• epidermis
• dermis
• subcutis

Question 4

What does the epidermis do?

Answer 4

Continuously multiplying stratified squamous epithelium which produces a non-living layer of keratin

Question 5

What types of cells does the epidermis contain?

Answer 5

• The epidermis contains
• keratinocytes (90%)
• melanocytes, which protect against sunlight
• Langerhans cells which recognise external antigens (immune response)
• Merkel cells which are sensory receptor cells
• inflammatory cells

Question 6

Why is keratinisation of the skin important?

Answer 6

its integral to skin renewal and healing

Question 7

How does the epidermis function?

Answer 7

• The layers of the epidermis continually move upward, flatten, build up at the surface and then slough off to make room for the cells behind them
• The epidermis is adapted to withstand constant abrasion and desiccation due to tough non-living surface layer composed of protein keratin wrapped in plasma membrane.
• the epidermis is avascular (it doesn’t contain any blood vessels) so its nourished by diffusion from the dermis.

Question 8

the dermoepidermal junction

Answer 8

is an area of tissue that joins the epidermis and the dermal layers

Question 9

what does the dermorpidermal juction contain?

Answer 9

• rete ridges: highly corrugated and many downward ridge like extensions of the epidermis
• dermal papillae: alternating, upward projections of dermis

Question 10

What are rete ridges?

Answer 10

Finger like projections in the junction that increase the surface area of the epidermis that is exposed to the blood vessels and the needed nutrients.
It is responsible for the change of nutrients from th epidermis to the dermis and without it the skin would suffer premature ageing and damage.

Question 11

What are the layers of the epidermis?

Answer 11

• keratin layer (stratum corneum)
• granular layer (stratum granulosum)
• prickle cell layer (stratum spinosum)
• basal layer (stratum basale)

Question 12

What layer does thick skin have that thin skin doesn’t have and what does it do?

Answer 12

• stratum lucindum, between stratum cornea and stratum granulosum
• its comprised of a few layers of tightly packed squamous cells that lack organelles and nuclei. Its translucent
• it reduces friction and shear forces between the surrounding layers of the epidermis

Question 13

Basal Layer (Stratum Basale)

Answer 13

• deepest layer of epidermis
• single layer of of closely packed basophilic cuboidal to columnar epithelial cells (kertainocytes) attached to the basement membrane on their dermal surface.

Question 14

How does the basal layer function?

Answer 14

Every hour, between 30,000 and 40,000 dead skin cells are shed. At the basal surface the cells in this layer are attached to the underlying basement membrane - the dermoepidermal junction.

Question 15

Prickle Cell Layer ( Stratum Spinosum)

Answer 15

Superficial to the stratum basale and forms the majority of the epidermis.
It consists of several layers of irregular, polyhedral cells that become flattened in the outermost layers.
The stratum spinosum made of:
- polyhedral-shaped keratinocytes
- round-oval nuclei
- prominent nucleoli and cytoplasm, forming a pavement-like pattern.

Question 16

Granular Layer (Stratum Granulosum)

Answer 16

3 to 5 layers of flattened cells, contain numerous basophilc granules (keratohyalin)
Begin to lose their polyhedral shape and become more flattened near the surface

Question 17

How does the granular layer function?

Answer 17

They acquire dense basophilic,keratohyaline, they undergo kertinisation as they progressing towards the surface, the cells lose their nuclei and cytoplasm, becoming flattened interconnectedkeratin squareswhich form the surface of the skin thestratum corneumC.

Question 18

Keratin layer (Stratum Cornuem)

Answer 18

• Outermost layer of the epidermis with the vital barrier function.
• Dead anucleate cornified cells, keratin replaces cytoplasm

Question 19

Whats the Malpighian layer?

Answer 19

the stratum basale and stratum spinosum layer are collectively known as the Malpighian layer

Question 20

What determines the colour of skin and hair?

Answer 20

Melanocytes are cells that produce melanin, however it is not the number of melanocytes but the activity that is affected by corticotropin from the pituitary.

Question 21

How many melanocytes occur per 1mm2 of epidermis?

Answer 21

1000-2000

Question 22

Where is melanin produced?

Answer 22

melanosomes = membrane-bound organelles

Question 23

What 2 major forms of melanin are found in humans?

Answer 23

• Eumelanin = brown to black

- Phenomelanin = yellow to red

Question 24

What is the purpose of melanin?

Answer 24

protection against damaging effects of UV radiation on DNA

Question 25

Where does a melanoma form from?

Answer 25

Mainly from frequent exposure to the sun | They develop from melanocytes in the skin and some in the mucous membranes, urea of the eye and meninges.

Question 26

How does a melanoma form?

Answer 26

Melanocyte transformation to melanoma is via radial and vertical growth phases: Melanocyte proliferation forming nevi with subsequent dysplasia, hyperplasia, invasion and metastasis

Question 27

How can we diagnose melanoma?

Answer 27

Skin biopsy determines diagnosis and disease severity. Melan-A and human melanoma black (HMB) immunohistochemistry is used to detect melanoma cells.

Question 28

What are Langerhans cells ?

Answer 28

They are monocyte-derived dendritic cells that reside in the epidermis

Question 29

What is the function of Langerhans cells?

Answer 29

- Phagocytic and antigen-processing and presenting cells. - They monitor and capture invading surface antigens, then migrate to regional lymph nodes. - Induce an immune response via antigen presentation to CD4+ and CD8+ T lymphocytes

Question 30

Where are Langerhans cells found?

Answer 30

Stratum spinosum and stratum granulosum

Question 31

What are Merkel cells? and what to they do?

Answer 31

They are intra-epidermal touch receptors and contain membrane-bound vesicles in their cytoplasm. Make synaptic junctions with their sensory nerves in the upper dermis.

Question 32

What are some epidermal skin appendages?

Answer 32

- Hair Follicles - Sebaceous glands - Eccrine (sweat) glands - Apocrine glands

Question 33

Hair Follicles

Answer 33

- produced in follicles, cylindrical shafts composed of keratin; hair shafts have a surface cuticle composed of a single layer of flattened keratin scales

Question 34

What are the function of hair follicles?

Answer 34

``` Thermoregulation Hair growth is cyclical w/ 3 phases: - long phase of active growth (anagen) - short phase of involution (catagen) - short inactive involuted phase (telogen) ```

Question 35

Where are sebaceous glands located?

Answer 35

Between a hair follicle and its arre ctor pili muscle in the dermis

Question 36

What is holocrine secretion?

Answer 36

Sebaceous glands produce sebum made of lipid-rich decomposed cells. They empty their secretions via duct into the upper part of the hair follicle near the hair shaft.

Question 37

What does each gland contain?

Answer 37

a peripheral layer of cuboidal cells with spherical nuclei resting on a thin basement membrane

Question 38

How does each gland function?

Answer 38

Active cells give rise to the larger sebum-producing cells. The larger cells are polyhedral with large amounts of lipid in the cytoplasm. Nuclei become pyknotic and cells gradually disintegrate, to the secretory product.

Question 39

What is an arrestor pili?

Answer 39

Sebaceous glands have a small bundle of obliquely arranged smooth muscle known as the arrector pili muscle. Contraction of this muscle compresses the gland and helps expel sebum into the follicle.

Question 40

Eccrine (sweat) glands

Answer 40

Eccrine sweat glands are simple, coiled tubular glands consisting of secretory and narrower excretory duct portions.

Question 41

What types of eccrine gland cells are there?

Answer 41

The tightly convoluted secretory part of a gland deep in the dermis consists of two types of cuboidal to pyramidal secretory cells—clear cells and dark cells.

Question 42

What do these cells do?

Answer 42

- Clear cells primarily secrete water and electrolytes - Dark cells secrete macromolecules. - Smaller, intensely eosinophilic myoepithelial cells, border the secretory cells. - Myoepithelial cells are mainly contractile and help expel sweat into the lumen

Question 43

What is the excretory duct?

Answer 43

The excretory duct is made of two layers of dark-staining cuboidal epithelial cells and has a smaller diameter than the secretory acinus and lacks myoepithelial cells.

Question 44

Where are apocrine glands found?

Answer 44

Apocrine glands are confined to a few localised areas, mainly in the axilla and groin. The secretory component is located in deep reticular dermis or subcutis

Question 45

What do apocrine glands look like and do?

Answer 45

Apocrine gland secretions in humans have no defined function. A duct system carries the secretion into the upper part of the hair follicle above the sebaceous duct. The secretory gland is a coiled tubular type with a widely dilated lumen. The secretory cells are usually low cuboidal with eosinophilic cytoplasm. They have a discontinuous layer of myoepithelial cells between the secretory cells and the basement membrane. The duct is histologically similar to that of eccrine sweat glands.

Question 46

What is the dermis?

Answer 46

The dermis is composed of bundles of collagen fibres and strands of elastic fibres embedded a small amount of acellular ground substance, There are a few fibroblasts which synthesise the collagen, elastic fibres and matrix.

Question 47

How many layer does the dermis have and what are they called?

Answer 47

2 layers: - Superficial papillary dermis (beneath the epidermis) - Deeper reticular dermis (borders the subcutis)

Question 48

What does the papillary dermis contain?

Answer 48

The papillary dermis is loose and contains very fine, interlacing collagen (red) and elastic fibres (black) in the EVG (elastin- Verhoeff Van Gieson) stain. It contains arterioles, capillary loops and venules, as well as lymphatics

Question 49

What is the reticular dermis?

Answer 49

The reticular dermis R, generally a much thicker layer. The interface may be poorly defined.