Skin Physiology

Question 1

What are the various ways that we can lose heat from the body?

Answer 1

Question 2

What is normothermic heat transfer?

Answer 2

Question 3

What is hypothermic heat transfer?

Answer 3

Question 4

What is hyperthermic heat transfer?

Answer 4

Question 5

• When external temperature is < internal temperature, what will be the major mode of heat loss?
• When external temperature is > internal temperature, what will be the major mode of heat loss?

Answer 5

• Convective and radiative heat loss
• Evaporative heat loss (sweat)

Question 6

What is thermoregulation?

Answer 6

Alteration of the rate of heat loss via physiological responses in the skin in order to maintain homeostasis and avoid excessive hyper or hypothermia.

Question 7

What is the major regulator of body temperature?

Answer 7

Hypothalamus (integrator) –> effectors are components of the autonomic NS

Question 8

What is the body’s physiologic, vascular response to being cold?

Answer 8

Vasoconstriction

Question 9

What is the body’s physiologic and vascular response to being hot?

Answer 9

Vasodilation and sweating

Question 10

The […] nervous system controls both the skin vasculature and the sweat glands.

Answer 10

Sympathetic –> causes both vasoconstriction and vasodilation

Question 11

Under high body temperatures (e.g. during exercise), sympathetic centers are […] leading to vasodilation of cutaneous vasculature and heat dissipation.

Answer 11

inhibited

Question 12

Under low body temperatures (e.g. hypothermia), sympathetic […] of alpha-1 receptors leads to vasoconstriction of cutaneous vasculature and heat conservation by moving blood away from the surface to conserve heat in the body’s core.

Answer 12

Stimulation

Question 13

How does sweating lead to cooling of core body temp?

Answer 13

Sweating leads to evaporative cooling. Water molecules with greatest energy evaporate thereby lowering the average kinetic energy of the water and leading to lower temperature.

Question 14

What is another name for sweat glands?

What are the 2 components of their structure?

Answer 14

Eccrine

Contain a secretory coil and a straight duct

Question 15

Eccrine glands are composed of what 3 cell types?

Answer 15

Clear cells

Dark cells

Myoepithelial cells

Question 16

• Describe the affect of Ach on sweat glands
• Is sweat that is secreted hypertonic, hypotonic, or isotonic under normal conditions?

Answer 16

• Autonomic stimulation via acetylcholine (ACh) stimulates the eccrine glands to form an isotonic solution in the gland lumen.
• Due to the active resorption of electrolytes by the sweat gland, sweat secreted by eccrine glands is a hypotonic solution

Question 17

Apocrine Sweat Glands

• What are they?
• When do they become active?
• Where are they found?
• What causes this sweat to have an odor?

Answer 17

• Glands that secrete a milky viscous fluid into the infundibular portion of the hair follicle
• Inactive until puberty
• Axillae, areola, perianal region, external genitalia
• Apocrine sweat is initially odorless, and gains malodor with breakdown by bacteria

Question 18

• What is a sebaceous gland?
• Where are they found?

Answer 18

• Sebaceous glands are holocrine glands in the skin that secrete sebum to lubricate and waterproof the skin
• Face, scalp, all skin areas except palms of hands and soles of feet

Question 19

• What are the most common microorganisms found on the skin’s surface?
• What causes the skin flora to vary across the various parts of the body?

Answer 19

• Staphylococcus epidermidis, Staphylococcus aureus, Micrococci luteus, Diphtheroids (bacteria belonging to the genus Corynebacterium)
• According to the nature of secretions, normal clothing worn, and immediacy to mucus membranes

Question 20

What 2 hormones are responsible for sympathetic vasoconstriction in hypothermia?

Answer 20

Neuropeptide Y

Norepinephrine

Question 21

How does the sympathetic NS achieve both vasoconstriction and vasodilation?

Answer 21

It has separate parallel nerves that innervate the vasculature to send each signal separately in response to the appropriate stimuli

Question 22

Post-ganglionic sympathetic vasodilator nerves are […] and respond to […] and […]

Answer 22

cholinergic

Ach; vasoactive intestinal peptide (VIP)

Question 23

How does humidity affect the effectiveness of sweating?

Answer 23

Increased mositure in air makes it less favorable to excrete more moisture onto the skin surface

Question 24

What type of gland is shown?

Answer 24

Eccrine gland

Question 25

**Sebaceous Glands** * Where are they found? * What are the 4 structures of the gland? * Where is the highest density of these glands?

Answer 25

* Usually found in association with hair follicles in most areas of the body surface except for the palms and soles * They form the pilosebaceous units comprising four structures: the hair follicle, hair shaft, arrector pili muscle, and sebaceous gland * The highest density of sebaceous glands is found on the face

Question 26

Proliferation, differentiation, and metabolism of sebaceous glands are regulated by sex hormones, particularly [...]

Answer 26

androgens

Question 27

[...] are the major cells within sebaceous glands that produce and accumulate lipids.

Answer 27

Sebocytes

Question 28

Sebocytes secrete their oily and waxy sebum via holocrine secretion. What is holocrine secretion?

Answer 28

In this process, the entire cell produces and becomes filled with the fatty product while it simultaneously undergoes programmed cell death (apoptosis)

Question 29

What is sebum made of? Is this composition the same for everyone?

Answer 29

* Sebum represents a complex oily mixture that consists of triglycerides, diglycerides, and free fatty acids, wax esters; squalene; cholesterol; and cholesterol esters. * Due to its complex composition, human sebum is remarkably specific due to individual genetic variations in enzyme concentrations, pH, and temperature

Question 30

* Where does thermoregulatory sweat occur? How is this sweat controlled? * Where does emotional sweat occur? How is this sweat controlled?

Answer 30

* This thermoregulatory sweating first occurs on the forehead and scalp, extends to the face and to the rest of the body, and occurs last on the palms and soles. Control of thermoregulatory sweating is cholinergic. * Under conditions of emotional stress, however, the palms, soles, and axillae are the first surfaces to sweat. Emotional sweating may be stimulated by adrenergic portions of the sympathetic division of the autonomic nervous system.

Question 31

Where in the eccrine sweat gland are ions resorbed?

Answer 31

The resorptive duct

Question 32

Describe the changes in ion concetration that are occuring inside an eccrine sweat gland to produce sweat.

Answer 32

Question 33

Why is sweat hypertonic in patients with Cystic Fibrosis?

Answer 33

They have a mutation in CFTR receptor which disrupts ability to resorb Cl- from sweat and by association also Na+

Question 34

How do your eccrine glands adapt to sustained higher temps?

Answer 34

You sweat more but it is less salty. Adaptations mostly through Aldosterone acting on the duct portion of sweat gland and addition of more Na+ channels and Na+/K+ pumps

Question 35

What region of the DNA is particularly susceptible to damage from UVB radiation?

Answer 35

Telomeres (TTAGGG --\> thymine dimers)

Question 36

What is happening to your skin when you have a sunburn?

Answer 36

Inflammation caused by release of cytokines by keratinocytes or mast cells. This inflammation causes erythema due to vessel dilation.

Question 37

What is shown by the yellow arrows?

Answer 37

Sunburnt cells in the epidermis

Question 38

* What signaling pathway is activated when DNA is damaged from UV radiation? * What effect does this have on the skin?

Answer 38

* p53 * Tanning response --\> p53 turns on transcription factors that are involved in melanogenesis --\> produce more eumelanin --\> stabilize melanosomes --\> darken skin --\> more protection against UVB

Question 39

Is sun really the best way to get vitamin D?

Answer 39

No - in order to activate 7DHcholesterol, UVB radiation must be at specific wavelength of light (290-300nm). Depending on where you live (latitude), the radiation from the sun may not reach this wavelength year round (in CT it is only during June - August). As such, sun exposure outside these months is unlikely to produce active vitamin D so most people need supplementation if their diet is inadequate.

Question 40

What is the effect of skin color and vitamin D synthesis?

Answer 40

Lighter skin (types 2 and 3) are able to produce more active vitamin D3 compared to darker skin tones (4 and 5) --\> people with darker skin are more likely to be vitD deficient