#digestive physiology

[scienceguy22]

The sloth poop gambit.

Sloths poop once every 5-7 days, descending 5-30 ft (1.8-9 m) from its safe canopy to the forest floor. They then dig a small depression, perform their famous "poop dance" (a rhythmic wiggle), & defecate up to 1/3 of their body weight. If humans emulated sloths in this regard, an average man would expel 50 lb (23 kg) of feces all at once, while an average woman would expel 43 lb (20 kg). This is (thank God) biologically impossible for humans. It is during sloths' poop time that 50% ofsloth predation occurs. From a survival standpoint, this behavior is absurd, considering they are the slowest mammals on Earth, moving at a ground speed of 0.3 mph (0.05 km/h). They then have to climb back up at 0.06 mph (0.1 km/h); they burn precious calories descending & climbing back up. Sloths burn calories at 1/2 the rate predicted for their size. They have a leaf-based diet, which is low in calories, & low calories mean a low energy budget. They have very slow digestion, up to 2 weeks. On the ground, there are jaguars, ocelots & large constrictor snakes, & even harpy eagles that love a grounded sloth.

Despite being the slowest mammal, 50% of sloths survive their bathroom break because they are camouflaged, covered in algae. They barely move. Predators detect movement. Nevertheless, they are at their most exposed, they are unbearably slow & are near-defenseless. They could simply poop from trees, so why keep doing it? It turns out they do it because of a unique symbiotic cycle involving sloth fur, moths, algae growth & nutrient recycling—all of which ultimately boost sloth nutrition. The nutritional payoff appears to outweigh the risks. Sloth fur hosts specialized moths that live nowhere else on Earth except in the fur of sloths. After sloths do their business, moths leave the fur & lay eggs in the fresh dung. Larvae feed on the dung, mature & fly back to the sloth. Adult moths die & decompose in the sloth's fur. Their nitrogen enriches the fur. Nitrogen boosts algae growth, & the sloths eat the algae, giving them extra nutrients. A win-win for all involved.

Eating the algae provides sloths with extra lipids, extra nitrogen, extra calories & a rare protein boost. This may be the difference between life & death. They have to poop even if they don't want to because holding it in for a week leads to constipation danger. The fecal mass can reach up to 2.5 lb (1.1 kg) in a 9-lb (4 kg) sloth. If algae boosts fitness even slightly, natural selection can preserve the behavior despite the risk. Evolution is not about perfection—it's about advantage. Risk now, nutrients later, survival overall.

[scienceguy22]

The most underrated organ in the history of life—the anus.

First off, yes, the anus is an organ. It includes sphincter muscles, mucosal lining, nerves, blood vessels & connective tissue. It's not just a hole but a multi-tissue functional complex. 640 mya, for the first time ever, anuses are about to evolve & change the course of history & life on Earth forever. To fill in the gaping hole of knowledge of the anus, let's go back 3.7 million years, when life on Earth began with protocells, formed either in the intense heat of geothermal vents or arrived on Earth from an asteroid. These protocells eventually evolved into cyanobacteria, which began to transform radiation from the Sun into chemical energy. They extracted electrons from the hydrogen using the sun's energy & released oxygen into the atmosphere, known as "the great oxygenation." There was a great boom in life after that with mosses, ferns, plants & animals, following around 640 mya, beginning with the sea sponge. They were largely static, but they fell off in polyps that would then begin to move & traverse the sea bottom, where plenty of food & detritus littered the ocean's floor.

The theory goes that around 541 mya, when there was a great Cambrian explosion, it was likely due to the creation of animals now having a head & more importantly, an anus. We know they existed from fossils from that era. You cannot evolve a head that eats without also evolving a direction of travel. Once you have forward motion (a front end that encounters food first), you need a backend to expel waste behind you. It's all about movement, & the ability to move is all about getting food. This movement is related to our nervous systems & our brains in animals & of course, in humans. So, for us to gain a brain that could have consciousness, we first needed to get an anus. Without it, animals would have stayed tiny, simple & energetically limited. The anus enabled constant nutrient intake, longer digestive tracts, bigger bodies, more cell types & tissues & more active lifestyles. Energy is the currency of evolution; the anus massively increases the "budget." The anus forms first in the human embryo.

Put simply, without the anus, no through-gut, no high-energy animals, no big brains—and no humans.

[scienceguy22]

Science of Valentine's Day, Part 2.

Yesterday, I teased you with what the biggest gift for Valentine's Day would be. I'm sure most of you guessed correctly that it was chocolates. Let's get into the science. It all started with the ancient Mayans in Mexico, the earliest chocolate makers, around 1,500-1,000, who made the 1st chocolate beverage by 600-400 BCE. The Aztecs, who lived in the Mexican highlands, later imported it from southern Mexico in the 1500s. Both cultures used cacao as currency, denominating one cacao bean as the basic value, which could buy 1 tomato or 1 tamale; 2 beans could buy 1 large chili pepper; 3 for 1 avocado or 1 turkey egg; 30 beans got them 1 rabbit & 100 beans would purchase 1 turkey hen. When Hernán Cortés arrived in 1519, landing on the Yucatán coast, he met the beautiful Mexican princess, Doña Marina, & she introduced him to a drink called "xocolatl," made from the pods of a tree the Aztecs called cacashuatl cuahultl, literally "cacao tree." Its scientific name is Theobroma cacao, which translates into "food of the gods." The drink was laced with hot chili peppers. She told Cortes that the drink would "stimulate amorous adventures." He must have been impressed by its effects because on his return to Spain, he presented Emperor Charles V with a sample of cocoa.

Within a few years, Europeans were indulging in the joys of chocolate & singing its praises. Everyone but nuns, that is. They were forbidden to partake of chocolate due to the belief that it was an aphrodisiac. The myth can be attributed to chocolate's natural stimulants: caffeine, theobromine, & the newly discovered anandamide. Anandamide is also found in cannabis, but cannabis has thousands of times more than chocolate, which has only trace amounts, so no psychoactive effects are seen with chocolate. Chocolate contains more than 300 chemical compounds, but the one most strongly associated with love is phenylethylamine (PEA). PEA is an amphetamine-like substance, alluringly called the "chemical of love" or sometimes called the "infatuation molecule" because people in love actually have higher levels of PEA in their brains. So people thought, "Well, chocolate contains PEA; therefore, it must help make people fall in love. However, PEA is in very small amounts in chocolate, and besides, it never reaches the brain because it's broken down by the digestive tract & eliminated. In fact, sauerkraut has 10-50X more PEA than chocolate does but doesn't make nearly as appropriate a gift as chocolate.

Although chocolate does contain fat, it is stearic acid & is not the type to raise blood cholesterol. Chocolate also contains antioxidants in the form of phenolic acids in the same amounts you would find in a glass of red wine. In lab studies, these can prevent the oxidation of LDL cholesterol (low-density lipoprotein—the so-called "bad" cholesterol). This can help prevent damage to the coronary arteries. Human studies showed that about 35 grams of defatted cocoa (the kind found in Fry's cacao) had the greatest health benefits, but you'd have to drink 7 cups of hot cocoa to match that result. Another intriguing study from Yale University found that students who were studying for an exam recalled the material better when exposed to the smell of chocolate while writing the exam. And a Chicago neurologist, Alan Hirsch, put cuffs on the penises of volunteers to measure blood pressure & blood flow, & he found that chocolate increased pressure & blood flow to the penis more than kissing when measured by a penile plethysonograph. Chocolate aroma also produced the same results. So ladies, make sure you share that delicious box of chocolates you will receive this Valentine's Day.