Diabetes

What is colloquially known as diabetes is actually diabetes mellitus. In terms of word origins, diabetes means "running through" - the disease was given this name because those with diabetes urinate in greater volumes. The word mellitus means sweet since there's a lot of glucose (sugar) in the urine of diabetic.

There is another condition called diabetes insipidus (a vasopressin deficiency). These patients also urinate excessively, but their urine isn't sweet. Fun fact: in the past, doctors would actually drink a bit of urine to verify diagnosis! So while the word diabetes is used to refer to diabetes mellitus, this can be a bit confusing if you have the other condition.

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This Science Byte is focused on diabetes mellitus. I'll bet everyone reading this knows someone who has diabetes - it's fairly common. As you probably know, there are 2 types: type 1 & type 2.


A bit of background first: insulin. Insulin is a hormone that is secreted in response to elevated blood glucose (i.e. after you eat). It works to activate cells to uptake glucose, clearing it from the blood & storing it (or using it - glucose is the cell's main energy source). Diabetes is caused by a disruption of insulin's function (see below for the causes of both types). Diabetics prick their finger to measure their blood glucose - if it's too high or low, they could end up in a coma. Generally though, even with treatment, their glucose levels are higher than normal, eventually contributing to the side effects associated with diabetes (kidney failure, nerve damage, blindness, etc).


Type 1 diabetes: AKA insulin-dependent diabetes, childhood diabetes

People with type 1 diabetes are born with it - they cannot produce insulin (or don't produce nearly enough). This form is less common, comprising about 10% of diabetics in the US. Their immune system actually attacks the cells in the pancreas that secrete insulin (beta cells). The cause of this attack is unknown but thought to be autoimmune-related. So for type-1 diabetics, insulin therapy is necessary & injected daily. This on-going treatment is less than ideal however & cures are in the front line of diabetic research. Until recently, stem cell replacement was thought to be the best way to replace the damaged beta cells (though researchers still haven't found a way to control the insulin secreted by these stem cells). However, Nature Genetics just posted a cutting-edge report by Chutima Talchai, PhD, and Domenico Accili, MD, showing that resident progenitor cells in the gut of mice could be induced to differentiate into insulin-producing glucose-sensitive cells. While much research remains to be conducted to investigate the feasibility of performing these inductions in humans, it certainly provides a fresh new avenue for research.


Type 2 diabetes: AKA insulin-independent diabetes, adult-onset diabetes

Type 2 diabetes typically develops in overweight adults (& with the increasing prevalence of obesity, in teens & children now too). People with type 2 diabetes have normal (or above average) insulin levels in their blood. Instead, they have an insulin insensitivity - the body no long responds to it (or at least not as well as it should). Insulin therapy is therefore ineffective for type 2 diabetes. The causes of type 2 diabetes are not completely understood, but possibly relate to a decrease in the number of insulin-responsive glucose transporters on cells (proteins that take up glucose when stimulated by insulin) due to an excess of glucose (as in diet-induced obesity). Weight loss & exercise are the first line of treatment. Exercise actually increases these glucose transporters in cells. This isn't always enough though & a number of pharmacotherapies are available. All these drugs act to lower blood glucose levels (through different mechanisms I won't get into).

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My third cousin was born with type 1 diabetes & my grandpa developed type 2 diabetes. If you've somehow been touched by diabetes, I'd love to hear about it in the comments. Questions (or corrections) are welcome too!

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Today's Science Byte is brought to you by Vander, Sherman & Luciano's Human Physiology (p.619) & Science Daily.

Women in Science: Henrietta Swan Leavitt

The second female scientist I'm going to introduce is Henrietta Swan Leavitt. Her groundbreaking discovery forever changed our view of the Universe... have you heard of her?

If you haven't studied astronomy, chances are you aren't familiar with her name. She was a hard worker - never married, never had children - and in the end, like many females, she never received any recognition during her own lifetime.

• Henrietta Leavitt discovered Cepheid variables, which allowed Edwin Hubble to measure distances between stars, planets and galaxies. The Cepheid variables also enabled him to discover that other galaxies exist outside of ours, the Milky Way Galaxy.
• A Cepheid variable is actually a star. Variable stars pulsate, changing in size and luminosity (brightness). What makes a variable star a Cepheid is the relationship between the luminosity and period: the star will become brightest (and dimmest) at a distinct interval. It's like a sine (or cosine) curve, which I'm showing at the left. Imagine one of the lines as the luminosity: it always increases and decreases to the same level of brightness, and each cycle always takes the same amount of time. Somehow (I don't know the exact mechanics) this is used as a ruler to measure distances in the Universe.
• Henrietta discovered these stars while working at Harvard College Observatory. She was employed as a computer. That's right - before the PC, a computer was actually a job title. Henrietta was part of "Pickering's Harem," the first group of female computers (previously only a man's job). This of course freed the men to do more important (& fun) work, with telescopes, for example (which women were not allowed to use).
• Henrietta started working at the Observatory in 1893 & published her findings in 1908 - only 15 years, which is pretty impressive considering what she was doing. She measured and catalogued the brightness of stars from photographic plates. You can see an example of such a plate at the right. From these, she began to see a pattern, leading to her publication.
• After that, Henrietta's health declined. An illness left her almost completely deaf & she never fully recovered, probably due to the questionable medical practices at the time.
• She was appointed head of Stellar Photometry in 1921 by the new director of the Observatory, Harlow Shapley, but died later that year of cancer. Four years later, Gösta Mittag-Leffler of the Swedish Academy of Science contacted Shapley about Henrietta, intending to nominate her for the Nobel Prize in Physics. She never was, since the Nobel prize is not awarded posthumously, but the real insult came from Shapley, who suggested that he deserved the credit for the interpretation of her work.