Lecture 22, The Integumentary System

Question 1

The Integumentary System (function and what is consists of)

Answer 1

the largest organ system in the body is the integumentary system, which includes the skin and all of the supporting structures associated with the skin
- the primary function is to protect the internal environment (internal structures and fluids) from harmful microorganisms and toxins present in the external environment
- provides the body with overall protection; protection against injury, protection against pathogens and regulation of body temperature
- contains several sensory, autonomic and sympathetic nerve fibers
the integumentary system consists of:
- cutanenous membrane = skin (epidermis and dermis layers)
◦ the epidermis – most superficial layer of the skin
that is made of closely packed epithelial cells
◦ the dermis – lies beneath the epidermis, and is
made of densely packed connective tissue, blood
vessels, glands
accessory structures = hair follicles, nails, exocrine glands (very distinct from endocrine glands as exocrine will be exposed to external environment)

Question 2

Anatomy of the Skin

Answer 2

• the epidermis is a superficial tissue composed of stratified squamous epithelium
• the dermis lies beneath the epidermis, and is composed of areolar tissue and a reticular layer of dense irregular connective tissue
  underneath the dermis is the hypodermis (subcutaneous layer)
• composed of loose connective tissue and adipose tissue
• is not part of the integument, but contains tissue fibers that are interwoven into the dermis

Question 3

Skin Function (8)

Answer 3

1. protection: from trauma (impact, abrasion, distortion), fluid loss, chemicals, pathogens
2. excretion: salts, water and organic wastes
3. body temperature regulation: the dermis and hypodermis are well-vascularized
4. vitamin D synthesis:
   A. vitamin D is a steroid that can be converted into
   calcitriol, which is a hormone that is required for
   enhanced Ca2+ absorption from the GI tract
5. lipid storage (adipose tissue)
   A. fat stored in the hypodermis can be used for
   insulation (thermoregulation), energy stores, and
   protection from physical trauma
   B. location of fat distribution within the hypodermis
   or viscera depends on hormones and genetic
   factors
6. sensation: contains various tactile receptors
7. melanin production: protects the DNA within cells from UV damage
   A. melanin production is stimulated by exposure to
   UV, and provides the appearance of darker skin
   tones
   B. beneficial in protecting cells, but may impede
   Vitamin D production
8. keratin production: protecting cells from dehydration

Question 4

The Epidermis

Answer 4

the epidermis is a stratified squamous epithelium, and is avascular (not well vascularized)
- primary composed of cells called keratinocytes (epithelial cells that contain keratin)
- keratinocytes are formed at the bottom layer of the epidermis, and gradually move up to the most superficial layer over time
the epidermis may have either 4 or 5 layers of keratinocytes
- thin skin contains 4 layers and covers most of the body, thick skin contains 5 layers and covers the palms of the hands and the soles of the feet
finger nails are also made of epidermal tissue, and contain keratin that has stiffened
the surface of the skin follows the contours of epidermal ridges
- ensures good grip of fingers and toes, and results in fingerprints

Question 5

Layers of the Epidermis (1)

Answer 5

the five layers of the epidermis, from deep to superficial are:
1. stratum germinativum (or basale)
◦ attaches the epidermis to the basal lamina
◦ contains germinative cells (a type of stem cell),
melanocytes (melanin/pigment producing cells),
and merkel cells (sensory receptors)
◦ Most germinative cells will turn into keratinocytes

Question 6

Layers of the Epidermis (2 and 3)

Answer 6

2. stratum spinosum (spiny layer)
   ◦ contains 8-10 layers of keratinocytes, connected
   together by desmosomes
   ◦ also contains phagocytes and langerhans cells,
   which protect against microorganisms and
   superficial skin cancer
3. stratum granulosum (grainy layer)
   ◦ 3-5 layers of keratinocytes, which contain large
   amounts of keratin
   ◦ contains keratohyalin*, which accumulates in
   granules, and promotes dehydration
   ◦ as cells move up in this layer, they become more
   flattened, thinner, and begin to die
   *keratohyalin is non-water-soluble, and helps create an impermeable layer that prevents the passage of unwanted substances or pathogens

Question 7

Layers of the Epidermis (4 and 5)

Answer 7

4. stratum lucidum
   ◦ only in the palms and soles
   ◦ keratinocytes are densely packed with keratin,
   and do not contain organelles
5. stratum corneum
   ◦ 15-30 layers of keratinized dead cells, lightly
   interconnected by desmosomes
   ◦ cornification = increased keratinization
   ◦ water resistant – prevents dehydration of
   underlying tissues
   ◦ the most superficial layer of cells shed
   periodically, and are replaced by underlying cells
   * the entire layer is replaced every ~4 weeks

Question 8

Epithelial Pigments (melanin and carotene)

Answer 8

melanin is the substance that gives skin and hair its pigment , and also serves to protect living epidermal cells from DNA damage due to UV exposure
- melanin is produced by melanocytes, packaged into vesicles (melanosomes), and passed on to keratinocytes
- in individuals with lighter skin, melanosomes tend to breakdown sooner, in the strata germinativum and spinosum
- in individuals with darker skin, larger melanosomes are produced, and travel farther up in the epithelial layers before they are broken down
- melanin production is stimulated by UV exposure
- lack of UV protection leads to damage to DNA in the stratum germinativum
carotene is another pigment found in the epithelium
- is an orange/yellow pigment also found in orange vegetables, and can be converted to vitamin A
◦ adds a yellow colour to the skin
◦ increased vegetable and fruit intake results in
increased carotenoid pigmentation of the skin
◦ too much carotene is not toxic, but can result in
carotenemia, which causes the skin to become
yellowish-orange

Question 9

Epitelial Pigments - Circulation

Answer 9

• oxygenated blood is bright red due to oxyhemoglobin; particularly noticeable during exercise or when flushed
• deoxygenated blood is dark red, but appears blue through pale skin = cyanosis
  extreme temperatures influence cutaneous blood flow
• cutaneous vasodilation during exercise and heat, to promote convective heat transfer from the core to the periphery
  ◦ flushed cheeks or skin
• cutaneous vasoconstriction during cold temperatures to prevent retain heat, and prevent heat dissipation from the skin
  ◦ pale, white skin, or blue in extreme cases
  ◦ skin can become red over time, as the body tries
  to maintain adequate blood flow to the periphery
  (initiate vasoconstriction followed by periodic
  vasodilation)
  the progression of frost bite begins with frostnip, where vasoconstriction causes numbness and impaired mobility
• superficial frostbite occurs when the red skin becomes white or pale, and ice crystals begin to form in the epidermis and dermis
• deep frostbite occurs when deep tissue damage occurs

Question 10

The Dermis (2 layers)

Answer 10

the dermis lies beneath the epidermis, and contains two layers:
- papillary layer: composed of areolar tissue
◦ forms dermal papillae
◦ contains capillaries, lymph vessels, and sensory
neurons
- reticular layer: composed of dense, irregular connective tissue
◦ also contains hair follicles, sweat and oil glands,
lymph vessels, and nerve fibers
the dermis contains both collagen and elastic fibers; collagen is very strong and resists stretching while elastic fibers are very stretchy
- the dermis is also well-vascularized, and contain vessels that extend into the papillae and supply the epidermis

Question 11

Integument accessory structures - hair

Answer 11

outside its role in self-expression, hair has integral physiological functions:
- insulates and protects the scalp (from UV damage, environmental factors)
- protects the nostrils and ear canals from pathogens
- detects movement via the root hair plexus
◦ sensory receptor function
- arrector pili muscle contraction results in goosebumps, and functions to generate and retain heat

Question 12

terminal hair

Answer 12

hair that grows from the scalp, face, armpits, pubic area, chest, and belly
◦ is very thick and coarse

Question 13

specialized terminal hair

Answer 13

eyelashes and eyebrows

Question 14

villus hair

Answer 14

body hair
◦ is generally very thin and fine
◦ is lighter and shorter than terminal hair

Question 15

lanugo hair

Answer 15

baby hair
◦ very fine, soft unpigmented hair that grows in
fetuses, newborns, and some disease states

Question 16

The Hair Growth Cycle

Answer 16

the growth of a hair follicle is cyclical
* the active phase of hair growth alternates with the resting phase of hair loss, and the follicle reactivation phase

Question 17

Integumentary Accessory Structures - Sweat Glands (merocrine glands)

Answer 17

sweat glands are called sudoriferous glands, and exist in two primary types:
1. merocrine glands are coiled tubular ducts that secrete sweat via exocytosis
A. sweat is secreted by merocrine gland cells into
the sweat pore, where it is transported to the
skin surface
B. secretion is watery and clear
- sweat released by merocrine glands function in thermoregulation, excretion of water and electrolytes, flushing chemicals present on the skin surface, and as an antibiotic (contains dermicidin, which inhibits microbial growth)

Question 18

Integumentary Accessory Structures - Sweat Glands (apocrine glands)

Answer 18

2. apocrine glands are also coiled tubular ducts that secrete sweat via exocytosis
   A. in this case, the sweat is secreted into the hair follicle, where it is transported to the surface of the skin
   B. secretion is cloudy, sticky, odorous
   * sweat released by apocrine glands is used as a nutrient for bacteria present on the skin, which produces pheromones (body odor)

Question 19

Integumentary Accessory Structures - Oil Glands

Answer 19

sebaceous (oil) glands are also a type of exocrine gland, and are relatively inactive until puberty
* the oil (sebum) produced by sebaceous glands functions to lubricate and waterproof the skin and hair
most sebaceous glands are associated with hair follicles
* produce and secrete sebum, which his composed of a mixture of lipids
* sebum lubricates the dead layer of skin cells in the stratum corneum
* sebum also has antibacterial properties, and prevents trans-epidermal water loss

Question 20

Integument Accessory Structures - Nails

Answer 20

finger and toenails function to protect the distal phalanx, the tip of the finger/toe, and surrounding soft tissue structures
* the nail body forms at the nail root, which has a matrix of proliferating cells from the stratum basale
* the lateral nail fold overlaps the nail on the sides, helping to anchor the nail body
* the nail fold that meets the proximal end of the nail body forms the nail cuticle, (eponychium)
* the nail bed is rich in blood vessels, making it appear pink, except at the lunala