Integumentary System I (The Skin)

Question 1

What are the functions of the skin?

Answer 1

Protective outer layer
Regulates body temperature
Energy storage (in adipose tissue)
Excretion of wastes
Vitamin D3 synthesis
Sensation
Defense against pathogens, skin cancer
Indicative of other problems (skin colour, hair loss, etc.)

Question 2

What are the three layers of the skin (top down)?

Answer 2

Epidermis (stratified squamous epithelium - flat, irregular shaped cells arranged in multiple layers with only one layer making contact with basal lamina; mostly keratinocytes)
Dermis (deeper, two layers of vascularized connective tissue)
Hypodermis (subcutaneous layer, often not considered part of the skin, connective tissue rich in adipocytes)

Question 3

Describe the characteristics of epithelium

Answer 3

Regenerative
Sits on a basal lamina
Cells are tightly adhered to one another
Cells are arranged in layers of single of multiple sheets
Not well vascularized

Question 4

What are the layers of epidermis in thick and thin skin?

Answer 4

4-5 layers total
Thick skin: Stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum
Thin skin: Same as above but without stratum lucidum

Question 5

Describe the stratum basale (base layer)

Answer 5

Epidermis = mainly keratinocytes
Germinative layer of stem cells (basal cells); fixed to basal lamina
Divides to produce keratinocytes
Keratinocytes move to more superficial layers with continued division of basal cells
Over next 15-30 days, new keratinocytes become keratinized (fill with keratin filaments; anucleate, with no organelles)

Question 6

Describe the stratum spinosum

Answer 6

Keratinization begins here - synthesize keratin proteins, bundles of keratin (tonofibrils) to stretch across cell, anchor desmosomes, and link adjacent keratinocytes (desmosomes anchor each cell to all of its neighbours - provides strength)
Langerhan’s cells are found here - phagocytic immune cells of the skin; pathogens, skin cancer

Question 7

Describe the stratum granulosum

Answer 7

Synthesis of keratohyalin granules (main identifier of stratum granulosum) - facilitate bundling of keratin filaments into tonofibrils (increases epithelium strength)
Synthesis of lipid coating - makes keratinocytes water-resistant, impedes exchange of nutrients and waste (cell death), cells start to lose nuclei, organelles

Question 8

Describe the stratum lucidum

Answer 8

Only in thick skin

Keratinocytes are flattened, anucleate, no organelles

Question 9

Describe the stratum corneum

Answer 9

Protective layer
Cells are fully keratinized, flattened, with very think plasma membrane
Few cell layers in thin skin, many in thick
Cells slough off after around 2 weeks, replaced with cells from deeper epidermal layers

Question 10

What are epidermal ridges?

Answer 10

Mounds/ridges of epidermis which project into the dermis (project down)
Met with upward-projecting dermal papillae
Increase area of contact between epidermis and dermis - anchors epidermis
Provide friction for hands and feet

Question 11

Describe the dermis

Answer 11

Papillary layer (loose connective tissue)
Reticular layer (dense irregular connective tissue with collagen (strength) and elastic (stretch) fibres) - when elastic fibres break, stretch marks occur; wrinkles occur due to thinning or decreased elasticity due to sun exposure

Question 12

Describe the hypodermis

Answer 12

Loose connective tissue rich in adipocytes (store energy as fats)
Anchors dermis to deeper structures

Question 13

What three main factors influence skin colour?

Answer 13

Melanin (black or brown-black pigment synthesized by melanocytes)
Carotene (yellow-orange pigment from diet; collects in keratinocytes and adipose tissue)
Blood supply (oxygenated Hb (pinkish colour to skin); deoxygenated Hb (bluish colour to skin))

Question 14

What are melanocytes?

Answer 14

Found in deeper layers of epidermis
Synthesize melanin in vesicles called melanosomes which are phagocytosed into keratinocytes
More melanocytes = darker skin colour
Skin colour within a person = number of melanocytes
Skin colour between people = amount of melanin produced by a similar number of melanocytes
Albinism = melanocytes don’t synthesize melanin

Question 15

Why is UV radiation required for synthesis of Vitamin D3?

Answer 15

Converts cholesterol precursor (7-dehydrocholesterol) to vitamin D3
Vitamin D3 then converted by other organs to useable form by body for regulation of calcium

Question 16

What supplies blood to the skin?

Answer 16

Cutaneous plexus (network of interconnecting blood vessels in hypodermis - do not enter epidermis as this is avascular)
Papillary plexus is found in dermis

Question 17

What are the three different types of skin cancers?

Answer 17

• Basal cell carcinoma
• Malignant melanoma (melanocyte damage)
• Squamous cell carcinoma

Question 18

Function of sensory innervation at the skin

Answer 18

Allows detection of touch, pressure, temperature, pain, detects movement of hair

Question 19

Function of autonomic innervation at the skin

Answer 19

Regulates blood flow, exocrine secretion, piloerection