polygonmedical:

Hair Growth - Medical Illustration

Hair is made up of a protein called keratin (the same protein as in nails) produced in hair follicles in the outer layer of skin. As follicles produce new hair cells, old cells are pushed out through the surface of the skin. The visible hair is in fact a string of dead keratin cells. Each follicle has a life cycle that can be influenced by age, disease, and other factors:

Anagen (active hair growth) which lasts between 2 to 6 years. Catagen (transitional stage) which lasts two to three weeks, and Telogen (resting phase). At the end of the resting phase (two to three months) the hair is shed and the growing cycle begins again to make new hair to replace it.

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humananatomyphysiology:

Thick skin

1. Found on palms of hand and soles of feet.

2. All five strata are found here (basale, spinosum, granulosum, lucidum, and corneum).

3. Contains sweat glands but no hair follicles or sebaceous glands

Thin skin

1. Covers most of the body

2. Lacks stratum lucidum

3. Contains hair follicles, sebaceous glands, and sweat glands

biomedicalephemera:

Top: Hand of a day-laborer who had been drowned 24 hours prior
Bottom: Hand of a drowned person submerged in running water for several weeks

The process of tissues decomposing and sloughing off in animals generally reaches its peak around three to four weeks, in a moderate climate. However, in running water, the washing away of the acids from the liquefied fats and proteins, and the lack of insect activity, can often significantly retard or alter the decomposition.

Because of this, it can often take several extra weeks for tissues submerged in running water to separate from the body, and when they do separate, they don’t so much slough off when their substrate is consumed, but “slip” off, often in large sheets. The dermis of the hand is well-connected to itself, but less well-connected to its substrate, and as such is often subject to a phenomenon called “gloving” - where the skin slips off in, you guessed it, a “glove”.

Atlas of Legal Medicine. Dr. Eduard von Hofmann, 1898.

umzoology:

William T. Hornaday:  Taxidermy and Zoological Collecting

Here’s another spoiler for our 1st floor exhibit case: Dave brought this beautiful book from his home to go in our display among our information about William T. Hornaday.  This book, Taxidermy and Zoological Collecting, was published in 1891 during his term as Chief Taxidermist for the Smithsonian National Museum of Natural History.  

From an artistic, historical, and biological standpoint, this book is absolutely fascinating to look through!  In so many aspects was Hornaday ahead of his time in regards towards animal preparation and taxidermy, and this book discusses some techniques which we still employ in our museum today.  In many aspects of his personal life, however, Hornaday was a controversial and stubborn figure, but nevertheless passionate about wildlife and working ultimately towards its conservation.  Someday I’ll tell you all about the time he put a pygmy person from the Congo named Ota Benga on display in the National Zoo in the primates exhibit as a way to illustrate convergent evolution, but that is totally another story.  

radioretaliation:

Such a cool cake!

biomedicalephemera:

Tinea versicolor

Top: Manifestation in 18-year-old male
Bottom: Causative yeast cells

Unlike the other skin mycoses (called tinea - from Latin, “meaning a gnawing moth, or bookworm”), tinea versicolor is not caused by the same dermatophytes of the genus Ascomycota that most “ringworm”-type afflictions belong to.

Tinea versicolor is a yeast, which is a fungus of the phylum Basidiomycota, and a fairly common condition. Between 2 and 8% of people in the United States express this condition, especially during the summer months, as tinea versicolor thrives in hot and humid conditions when there is excess skin oil and dead skin cells to consume. Among young adults and adolescents, this condition affects almost 10% of individuals.

These yeasts (Malassezia furfur and Malassezia globosa) are not considered harmful, and are generally asymptomatic aside from its dermatological manifestation. When the condition recurs during multiple summers, the source of the yeast is generally high environmental concentrations of the spores; unlike many vegetable or animal parasites, the yeasts that cause tinea versicolor are not known to lay dormant on humans for more than a few weeks.

The original cures for this condition included both oral and topical mercury treatments - needless to say, topical mercury did kill the fungus, but you can’t exactly justify the harm done, just to clear up a harmless condition that isn’t all that disfiguring to begin with. These days, tolnaftate (brand name Tinaderm) and selenium sulfide (like in Selsun Blue shampoo) are used to treat the condition, and can generally clear up the condition. However, when the source is due to high environment concentrations, it can often recur, especially while one is maturing, and skin oil/dead skin cells are more prevalent than usual.

Treatise on Diseases of the Skin, for the use of Advanced Students and Practitioners. Henry W. Stelwagon, 1914.

biomedicalephemera:

Sweat glands in the human epidermis:

Diagrammatically represented (top)
Isolated vertical cross-section (Right)
Isolated horizontal cross-section (left)

Staying cool this ridiculous summer, fellow North Americans? Even if you’re hot and miserable and sweaty, your body knows how to keep its organs at the optimal temperature - that’s why you sweat in the heat in the first place!

Unlike other mammals that sweat for thermoregulation (such as oxen and horses), humans largely sweat from their eccrine sweat glands, which are not directly connected to hair follicles. Eccrine sweat glands secrete mostly water, with a few electrolytes (mostly NaCl, which is why sweat tastes salty). The amount we sweat is regulated by the hypothalamus and the contraction of cells surrounding the eccrine glands, and is influenced by hormone release and internal body temperature.

The water secreted by the eccrine sweat glands utilizes a process called evaporative cooling to reduce the surface temperature of the skin, which in turn reduces the temperature of the blood flowing through the expanded arterioles near the skin surface, and that blood flows through the body and keeps the organs and muscles at a relatively constant temperature. Sweat glands are coil-shaped, with a bulbous sac at the bottom that filters blood plasma to produce sweat. When the cells surrounding the sac and coil are triggered, they contract, pushing that sweat to the surface of the skin.

We also have apocrine sweat glands (the only functional thermoregulatory glands in horses and other sweaty mammals), but they’re largely restricted to the armpits, areola, and perianal region. Their secretions are not as simple as eccrine sweat glands - they’re typically milky-white and contain hormones and additional components of blood plasma that bacteria *love* to chow down. Those bacteria produce stinky excretions of their own, and that’s what causes smelly armpits!

When you use deodorant, the substance you apply works by breaking down the components excreted by bacteria that cause the smell, and masking any residual stink that can’t be broken down. Antiperspirants function by plugging the openings of the sweat pores, so that sweat can’t escape. This is usually done with small particles of aluminum. Despite misconceptions, blocking the sweat glands does not cause breast cancer, though some people experience adverse effects due to allergies to aluminum or other ingredients.

Images:

Top: Anatomy, Descriptive and Applied. Henry Gray et al, 1910.
Bottom: Diseases of the skin; a text-book for students and practitioners. J.M.H. Macleod, 1920.

fuckyeahmedicaldiagrams:

TAKE OFF YOUR SKIN shirt by Night Channels

bioguru:

Photomicrograph of human scalp (top) and thick skin (bottom), showing the layers of the epidermis, the dermis, the subcutaneous layer (hypodermis), hair shafts, hair follicles, adipose tissue, blood vessels, arrector pili, and sebaceous glands. Can you identify them all?

1, 2, 3, 4

howstuffworks:

Do you smell that…? Here’s How Body Odor Works!

(via discoverynews)