Histology 3: Skin and Associated Structures

Question 1

What are the functions of the skin?

Answer 1

1. Protection against injury and bacterial invasion
2. Provides a cover for the underlying soft tissue
3. Sense organ (for touch, temperature and pain)
4. UV protection, carried out by melanocytes (skin pigment cells)
5. Thermoregulation via sweat glad evaporation and blood radiation
6. Excretion of water and heat via sweat glands
7. Absorption of solar UV radiation for Vitamin D synthesis

Question 2

What are the three main areas of the skin?

Answer 2

1. Epidermis
2. Dermis
3. Hypodermis

Question 3

What is the dermis?

Answer 3

A deeper connective tissue layer than the epidermis, composed of dense, irregular collagen that interdigitates (dermal papillae) with the epidermis.

Question 4

What is the hypodermis?

Answer 4

Technically not part of the skin, it is superficial fascia that covers the entire body, immediately deep to the skin, and contains a loose connective tissue with large, varying amounts of fat

Question 5

What is the name given to ‘normal’ skin?

Answer 5

Stratified, squamous, keratinised epithelium

Question 6

What are the four types of cells that comprise the epidermis?

Answer 6

1. Keratinocytes (skin cells)
2. Melanocytes
3. Langerhans cells
4. Merkel Cells

Question 7

Skin can be classified as thick or thin depending on the thickness of the epidermis. What are some features of each?

Answer 7

Thick skin (covers the palms and soles)

• 400-600um
• No hair follicles
• No arrector pili muscles
• Sweat glands

Thin Skin (covers most of the remainder of the body)

• 75-150um
• Has a thin stratum corneum
• No definite stratum lucidum
• Has hair follicles, arrector pili muscles, sebaceous and sweat glands

Question 8

What are the five epidermal layers?

Answer 8

1. Stratum Corneum
2. Stratum Lucidum (only in thick skin)
3. Stratum Granulosum
4. Stratum Spinosum
5. Stratum Basale

Question 9

What are the features of Stratum Corneum?

Answer 9

1. The most superficial layer of skin
2. Composed of layers of flattened, keratinised cells
3. Cells lack nuclei and organelles but have numerous keratin filaments embedded in an amorphous matrix (non living tough shells) and are eventually shed

Question 10

What are the features of Stratum Lucidum?

Answer 10

1. A clear later of flattened cells
2. Lack organelles and nuclei, but contain keratin filaments orientated parallel to the skin surface and eleiden (a transformation product of keratohyalin).

Question 11

What are the features of Stratum Granulosum?

Answer 11

1. Consists of 3-5 layers of flattened keratinocytes
2. the most superficial (thin) layer of the epidermis
3. Cells possess many nuclei
4. Enzymes (release by lysosomes) digest the organelles and the nucleus of keratinocytes as they move through the layer

Question 12

What are the features of Stratum Spinosum?

Answer 12

1. The thickest layer of the epidermis
2. Composed of more flattened cells containing bundles of tonofilaments, which attach adjacent cells to each other by desmosomes.
3. (ABOVE) causes cells to have a ‘prickle-cell’ appearance

Question 13

What are the features of Stratum Basale?

Answer 13

1. The deepest layer of the epidermis
2. Keratinocytes are a single layer of mitotically active, cuboidal cells
3. When new cells are formed, they are pushed upwards to become the stratum spinosum, where the cells begin to flatten and the filaments accumulate
4. Process from basal layer to surface takes 20-30 days

Question 14

What are the other three cells of the dermis?

Answer 14

1. Melanocytes
2. Langerhan Cells
3. Merkel Cells

Question 15

What are melanocytes?

Answer 15

1. Melanocytes sit in the stratum basale and produce melanin (a brown pigment giving skin colour). They put melanin inside the keratinocytes, by a melanocyte dendritic process whereby melanosomes transfer the melanin into the cytoplasm of keratinocytes.
2. Melanocytes absorb UV light and protect the skin, as the sun damages the collagen in the dermis

Question 16

What are Langerhan cells?

Answer 16

Part of the immune system, and scattered throughout the epidermis (but found mainly in the SS) they are antigen-presenting cells, which ‘creep’ around the epidermal cells looking for antigenic invaders (bacteria etc.). They then migrate to nearby lymph nodes where they present epitopes of processed foreign antigens to T cell lymphocytes

Question 17

What are Merkel cells?

Answer 17

Found among the keratinocytes of the SB and especially numerous in the fingertips, they function as mechanoreceptors and pressure receptors

Question 18

What is the thickness of the dermis?

Answer 18

It varies from 0.6mm (in the eyelids) to 3mm (palms and soles)

Question 19

What are some of the more important features of the papillary level of the dermis?

Answer 19

• Interdigitates with the epidermis, forming dermal ridges (papillae)
• It has loose connective tissue with thin type 3 collagen fibres (reticular fibres) and elastic fibres arranged in loose networks.
• Contains cells (fibroblasts, macrophages and mast cells as well as many capillary loops) which extend to the epidermis/dermis interface to regulate body temperature and nourish the cells of the avascular epidermis

Question 20

What are some of the more important features of the reticular level of the dermis?

Answer 20

• Has dense, irregular collagen which are packed into large bundles lying mostly parallel to the skin surface
• It has networks of elastic fibres amongst the collagen fibres

Question 21

Why are the collagen fibres in the dermis irregular?

Answer 21

Because the skin needs to move in many different directions

Question 22

What is the ground substance in the reticular layer of the dermis?

Answer 22

A gel like liquid that fills the spaces, which contains many chemical (like glycoamino glycans) that are used so that, if the skin is grazed, the chemicals can bind to water and use it up so that the ground substance can become more viscous and slow the bacteria down so that it buys time for the WBCs to arrive

Question 23

Are specialised cells found more in the reticular or papillary level?

Answer 23

Papillary level

Question 24

What are the three main receptors in the dermis?

Answer 24

1. Meissner Corpuscles (Papillary Layer)
2. Pacinian Corpuscle (Reticular Layer)
3. Ruffini Corpuscle

Question 25

What are Meissner Corpuscles?

Answer 25

Meissner corpuscles (shape like witchety grubs) are mechanoreceptors specialised to respond to fine, discriminative touch. They are found in the papillae of the dermis, and are common in areas sensitive to tactile stimulation (lips, external genitalia, nipples)

Question 26

What is a Pacinian Corpuscle?

Answer 26

An encapsulated receptor that responds to pressure and vibrations- It is concerned with deep, meaningful touch

Question 27

What is a Ruffini Corpuscle?

Answer 27

A receptor that responds to tension in the collagen

Question 28

What do the glands of the skin include?

Answer 28

1. Eccrine and apocrine sweat glands 2. Sebaceous glands 3. Mammary glands

Question 29

What are Eccrine sweat glands, and what are some of their features?

Answer 29

1. Eccrine sweat glands (normal sweat glands) are responsible for regulating temperature in production of fluid which evaporates on the body surface, thereby cooling that surface. 2. Around 0.4mm in diameter 3. Coiled, tubular glands are locate deep in the dermis or in the underlying hypodermis 4. Surrounded by myoepithelial cells on the basal lamina which produce contraction that help discharge secretion into the duct by squeezing them 5. Have small lumens in the secretors unit which make the sweat and the ducts which move them to the surface, both of which have an irregular stratified cuboidal appearance.

Question 30

What are Apocrine sweat glands, and what are some of their features?

Answer 30

1. Specialised sweat glands found in certain locations (the axilla, the eyelid, the nipple areola and the anal region) 2. Larger than eccrine gland (3mm) 3. Secretion influenced by hormones 4. Restricted to the axillae and perineum and produce a more protein-rich secretion with pheromonal properties. 5. Lumen of secretory portion is much larger than in eccrine glands, and their ducts open into hair follicles rather than to the epidermal surface.

Question 31

What are hairs?

Answer 31

Hard, keratinised structures that project from the epidermal surface of the skin.

Question 32

What are hair follicles?

Answer 32

The organs from which hairs develop, arise from invaginations of the epidermis invading the dermis, hypodermis, or both. They are surrounded by dense fibrous CT of the dermis. The expanded part of the hair follicle, the hair root, is indented to conform to the shape of the dermal papilla pushing into it. These 2 structures together are the hair bulb. Scattered among the matrix cells nearest the dermal papilla are melanocytes, which give hair a colour based on the amount of melanin present.

Question 33

What are the Arrector Pili muscles?

Answer 33

Strands of smooth muscle running from the dermal sheath and insert into the hair follicles. Under sympathetic nervous stimulation, they contract and pull the hair erect when the body is cold or one is suddenly frightened.

Question 34

What are nails?

Answer 34

Outgrowths of the epidermis (modification of the st. corneum) over the tips of the distal digits

Question 35

What is the nail matrix?

Answer 35

A region of the nail root, located beneath the proximal nail fold. Cells of the nail matrix proliferate and become keratinized

Question 36

What is the nail plate composed of?

Answer 36

Compacted, highly keratinized epithelial cells, lying on the epidermis (nail bed). The distal end of the nail plate is continuous with the skin of the finger (or toe) tip. Near this junction is an accumulation of St. corneum, called the hyponychium. The St. corneum of the proximal nail fold forms the eponychium (cuticle), which extends from the proximal end up on the nail for about 0.5 to l mm.