2 THE OUTSIDE: SKIN AND HAIR

Question 1

What is the largest organ of the human body?

Answer 1

Skin

The skin is also known as the cutaneous system.

Question 2

What are the two main layers of the skin?

Answer 2

Epidermis and dermis

The epidermis is the outer layer, while the dermis is the inner layer containing active systems.

Question 3

What is the thickness of skin on the eyelids?

Answer 3

One-thousandth of an inch

This is the thinnest skin on the body.

Question 4

What is the outermost surface of the epidermis called?

Answer 4

Stratum corneum

It is composed entirely of dead cells.

Question 5

How many skin flakes do we shed approximately every hour?

Answer 5

Over a million

We shed around twenty-five thousand flakes a minute.

Question 6

What are skin flakes properly called?

Answer 6

Squamae

The term means ‘scales.’

Question 7

What substance are skin and hair largely made of?

Answer 7

Keratin

Keratin is a fibrous protein found in skin, hair, and nails.

Question 8

What do sebaceous glands secrete?

Answer 8

Sebum

Sebum mixes with sweat to form an oily layer that keeps skin supple.

Question 9

What is the condition known as when hair follicles become infected and inflamed?

Answer 9

Pimple

Chronic cases of pimples can lead to acne.

Question 10

What are Meissner’s corpuscles responsible for?

Answer 10

Detecting light touch

They are abundant in sensitive areas like fingertips and lips.

Question 11

What is the formal name for sunburn?

Answer 11

Erythema

It occurs when blood vessels in the skin become engorged.

Question 12

What is melasma?

Answer 12

Darkening of the skin during pregnancy

It is due to increased melanin production.

Question 13

What is the primary pigment responsible for skin color?

Answer 13

Melanin

Eumelanin is the most important type of melanin.

Question 14

What is convergent evolution in the context of skin color?

Answer 14

Similar outcomes evolved independently in different locations

Example: Sri Lanka and Polynesia both have light brown skin.

Question 15

How many genes are involved in pigmentation in mammals?

Answer 15

Over 120

This complexity makes understanding pigmentation difficult.

Question 16

What can cause vitamin D deficiency in northern latitudes?

Answer 16

Insufficient sunlight exposure

Many people in these areas must rely on dietary sources for vitamin D.

Question 17

What evolutionary change occurred about six thousand years ago regarding hair and eye color?

Answer 17

Lighter-colored eyes and hair evolved

This change occurred around the Baltic Sea.

Question 18

What is phenotypic plasticity?

Answer 18

The ability of an organism to adapt its phenotype

This includes changing skin color due to environmental factors.

Question 19

What physiological response causes blushing?

Answer 19

Increased blood flow to the face

The reason for this response is still a matter of study.

Question 20

What is the evolutionary significance of skin color variation?

Answer 20

Adaptation to sunlight intensity

Different skin tones evolved to balance vitamin D synthesis and UV exposure.

Question 21

What are the two varieties of skin?

Answer 21

Hairy skin and hairless skin

Hairless skin is referred to as glabrous.

Question 22

What is the term for hairless skin?

Answer 22

Glabrous

Glabrous skin includes areas like lips, nipples, genitalia, and the bottoms of hands and feet.

Question 23

What types of hair cover the human body?

Answer 23

• Terminal hair
• Vellus hair

Terminal hair is the conspicuous hair found on the head, while vellus hair is the fine, downy hair on the skin.

Question 24

How many hairs are humans estimated to have?

Answer 24

Approximately five million hairs

The number of hairs varies with age and circumstances.

Question 25

What is the process called when mammals get goose bumps?

Answer 25

Horripilation ## Footnote This process occurs when muscles around hair follicles contract, making hair stand up.

Question 26

What are the two main questions about human hair?

Answer 26

* When did humans become hairless? * Why did we retain hair in specific areas? ## Footnote The exact timeline for hair loss in humans is unclear, but genetic studies suggest dark pigmentation dates from 1.2 to 1.7 million years ago.

Question 27

What are the functions of hair?

Answer 27

* Provides warmth * Cushions the body * Camouflage * Shields from ultraviolet light * Signals emotions ## Footnote Some features of hair may not function effectively in nearly hairless humans.

Question 28

What is the hypothesis regarding the purpose of pubic and underarm hair?

Answer 28

* Trapping or dispersing sexual scents * Protecting skin from chafing * Displaying sexual maturity ## Footnote The existence of human pheromones is disputed, suggesting other functions for secondary hair.

Question 29

What is the growth cycle of hair comprised of?

Answer 29

* Growing phase * Resting phase ## Footnote The duration of the cycle varies by hair type; for example, facial hair completes a cycle in four weeks.

Question 30

When was the murder at 157 rue du Faubourg Saint-Honoré?

Answer 30

October 1902 ## Footnote This case involved the use of Alphonse Bertillon's identification methods.

Question 31

What system did Alphonse Bertillon invent for identifying criminals?

Answer 31

Anthropometry ## Footnote This system became known as Bertillonage and included detailed measurements of physical attributes.

Question 32

What was the purpose of Bertillon's system?

Answer 32

To identify recidivists among criminals ## Footnote The system was effective in catching repeat offenders.

Question 33

Who established the uniqueness of fingerprints in the West?

Answer 33

Jan Purkinje ## Footnote The Chinese had discovered this fact over a thousand years earlier.

Question 34

What is the textbook name for fingerprints?

Answer 34

Dermatoglyphics ## Footnote This term describes the patterns formed by papillary ridges on fingers.

Question 35

What is the primary function of eccrine sweat glands?

Answer 35

To produce watery sweat ## Footnote Eccrine glands are more numerous and are responsible for cooling the body.

Question 36

What is the composition of sweat?

Answer 36

99.5% water, with the rest being half salt and half other chemicals ## Footnote Salt loss can be significant, particularly in hot conditions.

Question 37

What activates the sweat glands?

Answer 37

Release of adrenaline ## Footnote This is why sweating can occur during stress, separate from physical exertion.

Question 38

What are the two types of sweat glands?

Answer 38

* Eccrine glands * Apocrine glands ## Footnote Apocrine glands are primarily found in the groin and armpits and produce thicker sweat.

Question 39

What is the condition called when someone is born with smooth fingertips?

Answer 39

Adermatoglyphia ## Footnote This condition is associated with fewer sweat glands than normal.

Question 40

What is the evolutionary significance of sweating in humans?

Answer 40

It allows for efficient heat dissipation ## Footnote This adaptation has been crucial for human endurance and brain development.

Question 41

How much water can a 155-pound man lose in a day under strenuous conditions?

Answer 41

10.5 to 12.5 quarts ## Footnote Maintaining hydration is essential to prevent serious health risks.

Question 42

What is the primary cause of body odor?

Answer 42

Bacteria acting on sweat ## Footnote Sweat itself is odorless; bacteria produce isovaleric acid and methanediol, which cause the smell.

Question 43

How many microbes are estimated to live on human skin?

Answer 43

About 100,000 microbes per square centimeter ## Footnote These microbes are not easily eradicated and can increase after bathing.

Question 44

What study found that most people have about 200 different species of microbes on their skin?

Answer 44

A study at New York University in 2007 ## Footnote Only four types of microbes were found on everyone tested.

Question 45

What is the Belly Button Biodiversity Project?

Answer 45

A study that swabbed belly buttons to identify microbial species ## Footnote It found 2,368 species of bacteria, with 1,458 unknown to science.

Question 46

Fill in the blank: The problem with antibacterial soaps is that they kill ______ bacteria on your skin.

Answer 46

[good and bad]

Question 47

True or False: Demodex folliculorum mites are harmful to humans.

Answer 47

False ## Footnote They are generally harmless and have coexisted with humans for a long time.

Question 48

What is pruritus?

Answer 48

The medical term for itching ## Footnote Itching is confined to the outer layer of skin and certain moist areas.

Question 49

What is a common side effect of chronic itching?

Answer 49

It can occur in various conditions, including brain tumors and autoimmune disorders ## Footnote One form is phantom itching, which can occur after amputations.

Question 50

What hormone is associated with hair loss as we age?

Answer 50

Dihydrotestosterone ## Footnote This hormone affects hair follicles, leading to hair loss on the head.

Question 51

On average, how many head hairs do people lose daily?

Answer 51

Between fifty and a hundred ## Footnote Sometimes these hairs do not grow back.

Question 52

What is the one known cure for baldness?

Answer 52

Castration ## Footnote This is due to its effect on hormone levels.

Question 53

True or False: Hair can decay quickly after a person dies.

Answer 53

False ## Footnote Hair can last for thousands of years in graves.

Question 54

What is the meaning of 'corpuscle'?

Answer 54

A term meaning 'little body' ## Footnote It can refer to unattached cells or clumps of cells functioning independently.