How Does the Body Know a Finger is Fully developed?

When a baby is being developed inside the womb,

1) how does the baby's body know a finger, or any other part of the body, has been fully developed?

2) following question, how does it "stop" the development of that part? What kind of signals are being communicated here?

3) I have hairy arms. The length of the hair is almost the same length if i don't cut it. If it breaks, it grows back almost the same length. How does the body know the current length and how to stop when it reaches the "target length"? Is it the same "procedure" as the development of parts inside the womb?

Fetal development: Your baby's arms and legs, fingers and toes

Your baby's movements start with uncoordinated flutters between 7 and 8 weeks of pregnancy, and progress to flips, jabs, and kicks in the second and third trimesters. You'll probably begin to feel these movements between 16 and 22 weeks, and they may be strong enough for others to feel through your belly by around 24 weeks. Meanwhile, 10 tiny fingers and 10 tiny toes will have developed before the end of the first trimester.

Male vs. Female Proportions

Male and female proportions are so different that even a skeleton (or certain parts of it) betrays its sex. Bear in mind, however, that on a vertical axis there is no real difference: the joints don't move up or down. The variations are almost entirely on the horizontal axis, i.e. in the width of certain parts of the body. So how do we feminize or masculinize our basic figure? On the structural level we're still working on, there's actually just one big difference to master, and the rest are small helpful details.

The Shoulders/Hips Ratio

The primary difference is the relationship of shoulder width to hips. Women have a much broader pelvic bone than men, since they need to be able to bear and give birth to a child. This one, central fact has consequences throughout the body. It means that in women the hip line is the broadest part of the body, and a narrower waist appears by contrast, while in men the broadest part is the shoulder line, and the waist is hardly different from the hips. The overall female silhouette, then, is an hourglass as opposed to the male trapeze shown below.

To give an idea of measurement (take these with a grain of salt because the impression of the overall silhouette trumps accurate measurements every time), on our basic figure below (middle) I have dropped down guidelines from the sides of the head, and then again from a distance equivalent to one head from the central axis. These lines define two yellow zones where the figure's shoulder and hip bones are contained.

To make this neutral figure female, the pelvic bone is broadened so that the hip joints are closer to the outer side of the yellow area. The shoulders may vary but always within this zone. (Notice what this does to the legs: the thighs taper in much more from the hips to join the knees, which haven't changed position. Men's legs look more vertical relative to women's).

To make the neutral figure male, the pelvic bone remains narrow while the shoulders joints are actually just outside the yellow area. Here again they can vary but they'll always tend to the outer side of the yellow area. This again translates in the way the two sexes hold their arms, which you can glimpse in the previous image and observe in daily life: women's elbows tend to be held close to the body, and the arms at rest naturally follow the body's contours. A woman has to deliberately hold her arms away from her body. Meanwhile, men's shoulders being "further out", the arm at rest dangles away from the body and is not naturally held close.

Your body recycling itself -- captured on film

Our bodies recycle proteins, the fundamental building blocks that enable cell growth and development. Proteins are made up of a chain of amino acids, and scientists have known since the 1980s that first one in the chain determines the lifetime of a protein. McGill researchers have finally discovered how the cell identifies this first amino acid -- and caught it on camera.

"There are lots of reasons cells recycle proteins -- fasting, which causes loss of muscle, growth and remodeling during development, and normal turnover as old proteins are replaced to make new ones," explained lead researcher, Dr. Kalle Gehring, from McGill's Department of Biochemistry. "One way that cells decide which proteins to degrade is the presence of a signal known as an N-degron at the start of the protein. By X-ray crystallography, we discovered that the N-degron is recognized by the UBR box, a component of the cells' recycling system."

The powerful technique can pinpoint the exact location of atoms and enabled the team to capture an image of the UBR box, providing insight to this incredibly tiny yet essential part of our bodies' chemical mechanics.

Aside from representing a major advance in our understanding of the life cycle of proteins, the research has important repercussions for Johanson-Blizzard syndrome, a rare disease that causes deformations and mental retardation. This syndrome is caused by a mutation in the UBR box that causes it to lose an essential zinc atom. Better understanding of the structure of the UBR box may help researchers develop treatments for this syndrome.

The research was published in Nature Structural & Molecular Biology and received funding from the Canadian Institutes of Health Research.

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Materials provided by McGill University. Note: Content may be edited for style and length.

Strengths and Weaknesses

Irken skin can kill parasites such as lice, possibly by secreting some sort of protective substance. However, while safe from such pests, their skin cannot tolerate Earth meat, water, or beans, the former burning them terribly and sometimes even fusing to their skin. They also have negative reactions when exposed to Earth liquids (namely water), though Zim didn't exhibit this weakness when splashed with punch.

As confirmed by Jhonen in the commentary for "The Wettening", it's the pollutants in Earth water that causes the burns rather than the water itself. Paste suffices to completely nullify the effects of tainted Earth liquids. It seems that there is nothing that can protect them from Earth's meat, however.

They sweat similarly to humans, and can get pimples when the skin is scrubbed by an oily substance (such as cheese or bacon). However, unlike human zits, they can grow to enormous size (as big as a classroom when fully swollen), are translucent, and filled with a vast amount of pus. Irken zits also have hypnotic powers when shaken, though it's possible this may just be an allergic reaction to certain chemicals, such as a combination of cheese, bacon, and Acne Blast.

Most Earth foods will make an Irken sick, although foods such as waffles, rich in sugar and carbohydrates, seem to be fine if eaten in moderation. It's seen in certain episodes that an appendage can fall off or be removed and that it has no real influence.

As seen in "Dib's Wonderful Life of Doom" and "Planet Jackers". They can heal at incredibly fast rates, which is why Zim said to Dib in "Halloween Spectacular of Spooky Doom": "As soon as my skeleton stops being broken, I will destroy you!".

Zim's eyes have been seen falling out of their sockets before, although they can usually be simply popped back in without irritation or injury. While capable of sleep, Irkens don't seem to sleep, as confirmed in "Roboparents Gone Wild", and their PAKs may just keep recharging even when functioning so that they don't have to.

Despite their decades of military training, few Irkens show much prowess in the way of physical strength although he is only a child, Dib has been shown to be more than capable of pinning Zim down. Therefore, with this in mind, it's possible that Irkens rely on their wits, technology, and sheer numbers when it comes to battling, rather than by actual physical prowess.

However, Zim has, on occasion, shown feats of uncanny strength, an example of which being when he bodyslammed a human in "Attack of the Saucer Morons". Irkens also are shown to have incredible agility on Earth, and this may be due to (a) Irk's massive size and gravity, (b) genetic enhancements, (c) all of the above, or (d) the way Zim and Tak are animated. Dib also seems to have this miraculous agility, but that might be due to the fact that he was created/built much like Irkens are or the way he is animated.

In spite of their apparent weaknesses, however, Irkens have extremely long lifespans compared to normal humans. Zim and Tak looked the same in a flashback that took place fifty years ago as they do today, and Jhonen Vasquez confirmed that Zim is almost two centuries old. It has also been said that a year on Irk is equivalent to ten Earth ones, meaning that Irk's axial rotation must be super-slow or the planet is somewhat far from its home star.

However, this could also be in reference to an Irken's lifespan, meaning that in comparison to the average human lifespan of approximately 80 years, Irken live to be approximately 800 years old.

New wearable device turns the body into a battery

Researchers at the University of Colorado Boulder have developed a new, low-cost wearable device that transforms the human body into a biological battery.

The device, described today in the journal Science Advances, is stretchy enough that you can wear it like a ring, a bracelet or any other accessory that touches your skin. It also taps into a person's natural heat -- employing thermoelectric generators to convert the body's internal temperature into electricity.

"In the future, we want to be able to power your wearable electronics without having to include a battery," said Jianliang Xiao, senior author of the new paper and an associate professor in the Paul M. Rady Department of Mechanical Engineering at CU Boulder.

The concept may sound like something out of The Matrix film series, in which a race of robots have enslaved humans to harvest their precious organic energy. Xiao and his colleagues aren't that ambitious: Their devices can generate about 1 volt of energy for every square centimeter of skin space -- less voltage per area than what most existing batteries provide but still enough to power electronics like watches or fitness trackers.

Scientists have previously experimented with similar thermoelectric wearable devices, but Xiao's is stretchy, can heal itself when damaged and is fully recyclable -- making it a cleaner alternative to traditional electronics.

"Whenever you use a battery, you're depleting that battery and will, eventually, need to replace it," Xiao said. "The nice thing about our thermoelectric device is that you can wear it, and it provides you with constant power."

High-tech bling

The project isn't Xiao's first attempt to meld human with robot. He and his colleagues previously experimented with designing "electronic skin," wearable devices that look, and behave, much like real human skin. That android epidermis, however, has to be connected to an external power source to work.

Until now. The group's latest innovation begins with a base made out of a stretchy material called polyimine. The scientists then stick a series of thin thermoelectric chips into that base, connecting them all with liquid metal wires. The final product looks like a cross between a plastic bracelet and a miniature computer motherboard or maybe a techy diamond ring.

"Our design makes the whole system stretchable without introducing much strain to the thermoelectric material, which can be really brittle," Xiao said.

Just pretend that you're out for a jog. As you exercise, your body heats up, and that heat will radiate out to the cool air around you. Xiao's device captures that flow of energy rather than letting it go to waste.

"The thermoelectric generators are in close contact with the human body, and they can use the heat that would normally be dissipated into the environment," he said.

Lego blocks

He added that you can easily boost that power by adding in more blocks of generators. In that sense, he compares his design to a popular children's toy.

"What I can do is combine these smaller units to get a bigger unit," he said. "It's like putting together a bunch of small Lego pieces to make a large structure. It gives you a lot of options for customization."

Xiao and his colleagues calculated, for example, that a person taking a brisk walk could use a device the size of a typical sports wristband to generate about 5 volts of electricity -- which is more than what many watch batteries can muster.

Like Xiao's electronic skin, the new devices are as resilient as biological tissue. If your device tears, for example, you can pinch together the broken ends, and they'll seal back up in just a few minutes. And when you're done with the device, you can dunk it into a special solution that will separate out the electronic components and dissolve the polyimine base -- each and every one of those ingredients can then be reused.

"We're trying to make our devices as cheap and reliable as possible, while also having as close to zero impact on the environment as possible," Xiao said.

While there are still kinks to work out in the design, he thinks that his group's devices could appear on the market in five to 10 years. Just don't tell the robots. We don't want them getting any ideas.

Coauthors on the new paper include researchers from China's Harbin Institute of Technology, Southeast University, Zhejiang University, Tongji University and Huazhong University of Science and Technology.

What does it mean if you're born with more than five fingers on a hand?

Polydactyly is a condition where someone is born with one or more extra fingers or toes. It can occur on one or both hands or feet.

The name comes from the Greek poly (many) and dactylos (finger). The extra fingers or toes are described as “supernumerary,” which means “more than the normal number.” For this reason, the condition is sometimes called supernumerary digit.

A range of treatments is available depending on the type of polydactyly, and the cause is often genetic.

Share on Pinterest Small finger duplication is the most common form of polydactyly.
Image credit: Radke / Otis Historical Archives of “National Museum of Health & Medicine”. (1979, September)

Polydactyly is a condition where a person is born with extra fingers or toes on one or both of their hands and feet.

The way polydactyly presents can vary. It may appear as a:

  • small, raised lump of soft tissue, containing no bones (called a nubbin)
  • partially formed finger or toe containing some bones but no joints
  • fully functioning finger or toe with tissues, bones, and joints

There are three main types including:

  • Ulnar or postaxial polydactyly or small finger duplication: This is the most common form of the condition, where the extra finger is on the outside of the little finger. This side of the hand is known as the ulnar side. When this form of the condition affects the toes, it is called fibular polydactyly.
  • Radial or preaxial polydactyly or thumb duplication: This is less common, occurring in 1 in every 1,000 to 10,000 live births. The extra finger is on the outside of the thumb. This side of the hand is known as the radial side. When this form of the condition affects the toes, it is called tibial polydactyly.
  • Central polydactyly: This is a rare type of polydactyly. The extra finger is attached to the ring, middle, or most often index finger. This form of the condition has the same name when it affects the toes.

Polydactyly may be passed down in families.

When polydactyly is passed down, it is known as familial polydactyly. This form of polydactyly typically happens in isolation, meaning a person may not experience any associated symptoms.

Polydactyly may also be associated with a genetic condition or syndrome, which means it may be passed down along with a genetic condition. If polydactyly is not passed down, it occurs due to a change in a baby’s genes while it is in the womb.

Conditions associated with polydactyly include:

  • syndactyly (webbed hands or feet)
  • asphyxiating thoracic dystrophy
  • Carpenter syndrome
  • Ellis-van Creveld syndrome (chondroectodermal dysplasia)
  • Laurence-Moon-Biedl syndrome
  • Rubinstein-Taybi syndrome
  • Smith-Lemli-Opitz syndrome
  • trisomy 13

Some types of polydactyly are more likely to be passed down. Others are more likely to be associated with a genetic condition.

Small finger duplication is often hereditary. This form of the condition is 10 times more common among African-American people than other groups.

In African-Americans, small finger duplication tends to occur in isolation, inherited from a specific dominant gene. In Caucasians, it is more likely to be associated with a genetic condition or syndrome.

Thumb duplication often occurs in isolation and on only one hand or foot.

The brains are constantly buzzing with electrical activity as neurons zap off signals to one another

Finally, the developing brains are enveloped in a blanket of jelly. “It’s the opposite of normal jelly – it starts off as a liquid which you pour on and it jellifies as it warms up in the incubator,” she says. The jelly mimics the tissue a brain would normally be surrounded with in an embryo – like a makeshift skull – and encourages them to develop relatively normally.

Then all you have to do is sit back and wait. Three months later, the finished product is about four millimetres across and contains around two million neurons. “A fully developed, adult mouse brain only contains four million, so you can do a lot with that number,” she says.

The brains are constantly buzzing with electrical activity as neurons zap off signals to one another – though Lancaster says this isn’t much of an achievement on her part. “It’s not very special but it does tell us that we are making functional neurons and that they are acting like neurons,” she says.

She compares it to the heart cells which scientists coaxed to beat inside a petri dish back in 2013 while heart cells are programmed to “want” to pump, neurons “want” to fire. “Even if you have a neuron by itself in a dish with no other neurons, it wants to fire so badly that it will connect to itself in order to fire,” she says.

Lancaster's team's mini brains have two million neurons - half that of a mouse (Credit: iStock)

At the moment, Lancaster’s brains aren’t thought to be able to think. Nobody understands how the activity of our brains gives rise to thoughts – and it’s surprisingly difficult to define what a thought actually is – but it might go something like this. Usually, when we’re exposed to stimulation from the outside world – smells, sounds, ideas – our brains store the information by strengthening the connections between our neurons or forming new ones. The average adult will have as many as 1,000 trillion, which together give our brains an equivalent processing power to a one trillion-bit-per-second computer.

And here’s the rub. Even with all the same components as regular brains, without a body to provide information about the world around them, the brains simply can’t develop normally. “The neurons are working but they aren’t really organised relative to one another,” she says.

Lancaster gives the example of people who are born blind. “Since they aren’t exposed to light, the part of the brain that [these signals] would normally connect up is actually not going to form,” she says.

Phase Three: Orgasm

This is the climax of the cycle. It is also the shortest of the four phases, usually only lasting a few seconds.

Men: First, seminal fluid collects in the urethral bulb. This is when a man may have the sensation that orgasm is certain, or "ejaculatory inevitability." Next, semen is ejaculated from the penis. Contractions occur in the penis during the orgasmic phase.

Women: The first third of the vaginal walls contract rhythmically every eight-tenths of a second. (The number and intensity of the contractions vary depending on the individual orgasm.) The muscles of the uterus also contract barely noticeably.

Both: Breathing, pulse rate and blood pressure continue to rise. Muscle tension and blood-vessel engorgement reach a peak. Sometimes orgasm comes with a grasping-type muscular reflex of the hands and feet.

Fingerprints and Bacteria

Researchers from the University of Colorado at Boulder have shown that bacteria found on the skin can be used as personal identifiers. This is possible because bacteria that live on your skin and reside on your hands are unique, even among identical twins. These bacteria are left behind on the items we touch. By genetically sequencing bacterial DNA, specific bacteria found on surfaces can be matched to the hands of the person from which they came. These bacteria can be used as a type of fingerprint because of their uniqueness and their ability to remain unchanged for several weeks. Bacterial analysis could be a useful tool in forensic identification when human DNA or clear fingerprints can not be obtained.