2 THE OUTSIDE: SKIN AND HAIR Flashcards
What is the largest organ of the human body?
Skin
The skin is also known as the cutaneous system.
What are the two main layers of the skin?
Epidermis and dermis
The epidermis is the outer layer, while the dermis is the inner layer containing active systems.
What is the thickness of skin on the eyelids?
One-thousandth of an inch
This is the thinnest skin on the body.
What is the outermost surface of the epidermis called?
Stratum corneum
It is composed entirely of dead cells.
How many skin flakes do we shed approximately every hour?
Over a million
We shed around twenty-five thousand flakes a minute.
What are skin flakes properly called?
Squamae
The term means ‘scales.’
What substance are skin and hair largely made of?
Keratin
Keratin is a fibrous protein found in skin, hair, and nails.
What do sebaceous glands secrete?
Sebum
Sebum mixes with sweat to form an oily layer that keeps skin supple.
What is the condition known as when hair follicles become infected and inflamed?
Pimple
Chronic cases of pimples can lead to acne.
What are Meissner’s corpuscles responsible for?
Detecting light touch
They are abundant in sensitive areas like fingertips and lips.
What is the formal name for sunburn?
Erythema
It occurs when blood vessels in the skin become engorged.
What is melasma?
Darkening of the skin during pregnancy
It is due to increased melanin production.
What is the primary pigment responsible for skin color?
Melanin
Eumelanin is the most important type of melanin.
What is convergent evolution in the context of skin color?
Similar outcomes evolved independently in different locations
Example: Sri Lanka and Polynesia both have light brown skin.
How many genes are involved in pigmentation in mammals?
Over 120
This complexity makes understanding pigmentation difficult.
What can cause vitamin D deficiency in northern latitudes?
Insufficient sunlight exposure
Many people in these areas must rely on dietary sources for vitamin D.
What evolutionary change occurred about six thousand years ago regarding hair and eye color?
Lighter-colored eyes and hair evolved
This change occurred around the Baltic Sea.
What is phenotypic plasticity?
The ability of an organism to adapt its phenotype
This includes changing skin color due to environmental factors.
What physiological response causes blushing?
Increased blood flow to the face
The reason for this response is still a matter of study.
What is the evolutionary significance of skin color variation?
Adaptation to sunlight intensity
Different skin tones evolved to balance vitamin D synthesis and UV exposure.
What are the two varieties of skin?
Hairy skin and hairless skin
Hairless skin is referred to as glabrous.
What is the term for hairless skin?
Glabrous
Glabrous skin includes areas like lips, nipples, genitalia, and the bottoms of hands and feet.
What types of hair cover the human body?
- 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.
How many hairs are humans estimated to have?
Approximately five million hairs
The number of hairs varies with age and circumstances.
What is the process called when mammals get goose bumps?
Horripilation
This process occurs when muscles around hair follicles contract, making hair stand up.
What are the two main questions about human hair?
- When did humans become hairless?
- Why did we retain hair in specific areas?
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.
What are the functions of hair?
- Provides warmth
- Cushions the body
- Camouflage
- Shields from ultraviolet light
- Signals emotions
Some features of hair may not function effectively in nearly hairless humans.
What is the hypothesis regarding the purpose of pubic and underarm hair?
- Trapping or dispersing sexual scents
- Protecting skin from chafing
- Displaying sexual maturity
The existence of human pheromones is disputed, suggesting other functions for secondary hair.
What is the growth cycle of hair comprised of?
- Growing phase
- Resting phase
The duration of the cycle varies by hair type; for example, facial hair completes a cycle in four weeks.
When was the murder at 157 rue du Faubourg Saint-Honoré?
October 1902
This case involved the use of Alphonse Bertillon’s identification methods.
What system did Alphonse Bertillon invent for identifying criminals?
Anthropometry
This system became known as Bertillonage and included detailed measurements of physical attributes.
What was the purpose of Bertillon’s system?
To identify recidivists among criminals
The system was effective in catching repeat offenders.
Who established the uniqueness of fingerprints in the West?
Jan Purkinje
The Chinese had discovered this fact over a thousand years earlier.
What is the textbook name for fingerprints?
Dermatoglyphics
This term describes the patterns formed by papillary ridges on fingers.
What is the primary function of eccrine sweat glands?
To produce watery sweat
Eccrine glands are more numerous and are responsible for cooling the body.
What is the composition of sweat?
99.5% water, with the rest being half salt and half other chemicals
Salt loss can be significant, particularly in hot conditions.
What activates the sweat glands?
Release of adrenaline
This is why sweating can occur during stress, separate from physical exertion.
What are the two types of sweat glands?
- Eccrine glands
- Apocrine glands
Apocrine glands are primarily found in the groin and armpits and produce thicker sweat.
What is the condition called when someone is born with smooth fingertips?
Adermatoglyphia
This condition is associated with fewer sweat glands than normal.
What is the evolutionary significance of sweating in humans?
It allows for efficient heat dissipation
This adaptation has been crucial for human endurance and brain development.
How much water can a 155-pound man lose in a day under strenuous conditions?
10.5 to 12.5 quarts
Maintaining hydration is essential to prevent serious health risks.
What is the primary cause of body odor?
Bacteria acting on sweat
Sweat itself is odorless; bacteria produce isovaleric acid and methanediol, which cause the smell.
How many microbes are estimated to live on human skin?
About 100,000 microbes per square centimeter
These microbes are not easily eradicated and can increase after bathing.
What study found that most people have about 200 different species of microbes on their skin?
A study at New York University in 2007
Only four types of microbes were found on everyone tested.
What is the Belly Button Biodiversity Project?
A study that swabbed belly buttons to identify microbial species
It found 2,368 species of bacteria, with 1,458 unknown to science.
Fill in the blank: The problem with antibacterial soaps is that they kill ______ bacteria on your skin.
[good and bad]
True or False: Demodex folliculorum mites are harmful to humans.
False
They are generally harmless and have coexisted with humans for a long time.
What is pruritus?
The medical term for itching
Itching is confined to the outer layer of skin and certain moist areas.
What is a common side effect of chronic itching?
It can occur in various conditions, including brain tumors and autoimmune disorders
One form is phantom itching, which can occur after amputations.
What hormone is associated with hair loss as we age?
Dihydrotestosterone
This hormone affects hair follicles, leading to hair loss on the head.
On average, how many head hairs do people lose daily?
Between fifty and a hundred
Sometimes these hairs do not grow back.
What is the one known cure for baldness?
Castration
This is due to its effect on hormone levels.
True or False: Hair can decay quickly after a person dies.
False
Hair can last for thousands of years in graves.
What is the meaning of ‘corpuscle’?
A term meaning ‘little body’
It can refer to unattached cells or clumps of cells functioning independently.
