(Source: shialablunt, via this--too--shall--pass)


Otter pup cuteness (by Paul Stevenson)

who said med school professors don’t have a sense of humor :)


Saltwater Crocodile embryos. Image 1 15 days after fertilisation. Image 2 just prior to hatching. 

The saltwater crocodile (Crocodylus porosus) is the largest of allcrocodilians, and the largest reptile in the world, with unconfirmed reports of individuals up to an impressive eight to ten metres in length, although a maximum of five to six metres is more usual(2) (3) (5). The species has a relatively large head, with a pair of ridges that run from the eye along the centre of the snout. Adults are generally dark in colour, with lighter tan or grey areas, and dark bands and stripes on the lower flanks. The underside is creamy yellow to white, becoming greyer along the tail. The juvenile is usually pale tan, with black stripes and spots on the body and tail, which gradually fade with age, although never disappear entirely. Female saltwater crocodiles grow to a smaller size than males, normally reaching a maximum length of 2.5 to 3 metres (3).

With its long, powerful tail, webbed hind feet, and long, powerful jaws, the saltwater crocodile is a superbly adapted aquatic predator. As in all crocodilians, the eyes, ears and nostrils are located on top of the head, allowing the crocodile to remain almost totally submerged when lying in water, helping to conceal it from potential prey, while a special valve at the back of the throat allows the mouth to be opened underwater without water entering the throat (2) (6). The saltwater crocodile is considered to be more aquatic than most crocodilians, and is less heavily armoured along the back and neck (3).


Why don’t our arms grow from the middle of our bodies? The question isn’t as trivial as it appears. Vertebrae, limbs, ribs, tailbone … in only two days, all these elements take their place in the embryo, in the right spot and with the precision of a Swiss watch. …During the development of an embryo, everything happens at a specific moment. In about 48 hours, it will grow from the top to the bottom, one slice at a time — scientists call this the embryo’s segmentation. “We’re made up of thirty-odd horizontal slices,” explains Denis Duboule, a professor at EPFL and Unige. “These slices correspond more or less to the number of vertebrae we have.”Every hour and a half, a new segment is built. The genes corresponding to the cervical vertebrae, the thoracic vertebrae, the lumbar vertebrae and the tailbone become activated at exactly the right moment one after another. “If the timing is not followed to the letter, you’ll end up with ribs coming off your lumbar vertebrae,” jokes Duboule. How do the genes know how to launch themselves into action in such a perfectly synchronized manner? “We assumed that the DNA played the role of a kind of clock. But we didn’t understand how.”When DNA acts like a mechanical clockVery specific genes, known as “Hox,” are involved in this process. Responsible for the formation of limbs and the spinal column, they have a remarkable characteristic. “Hox genes are situated one exactly after the other on the DNA strand, in four groups. First the neck, then the thorax, then the lumbar, and so on,” explains Duboule. “This unique arrangement inevitably had to play a role.”The process is astonishingly simple. In the embryo’s first moments, the Hox genes are dormant, packaged like a spool of wound yarn on the DNA. When the time is right, the strand begins to unwind. When the embryo begins to form the upper levels, the genes encoding the formation of cervical vertebrae come off the spool and become activated. Then it is the thoracic vertebrae’s turn, and so on down to the tailbone. The DNA strand acts a bit like an old-fashioned computer punchcard, delivering specific instructions as it progressively goes through the machine."A new gene comes out of the spool every ninety minutes, which corresponds to the time needed for a new layer of the embryo to be built," explains Duboule. "It takes two days for the strand to completely unwind; this is the same time that’s needed for all the layers of the embryo to be completed."This system is the first “mechanical” clock ever discovered in genetics. And it explains why the system is so remarkably precise.…The Hox clock is a demonstration of the extraordinary complexity of evolution. One notable property of the mechanism is its extreme stability, explains Duboule. “Circadian or menstrual clocks involve complex chemistry. They can thus adapt to changing contexts, but in a general sense are fairly imprecise. The mechanism that we have discovered must be infinitely more stable and precise. Even the smallest change would end up leading to the emergence of a new species.”
(via From blue whales to earthworms, a common mechanism gives shape to living beings)
This is why developmental biology (and evolution and molecular biology and everything) is awesome.

Rainbow ‘bird’s nest’ MRI reveals how a heart beats

(Image: Laurence Jackson)
This is not a colourful bird’s nest: it is the collection of muscle fibres that work together to make a mouse heart beat.
The vivid MRI picture was captured using diffusion tensor imaging, which tracks the movement of fluid through tissue, using different colours to represent the orientation of the strands.
The fibres, which spiral around the left ventricular cavity, curve in different directions around the inside and outside walls of the chamber. When the fibres pull against one another, the result is an upwards twisting motion that forces blood to be pumped out.
The image, which was the overall winner of the Research Images as Artcompetition at University College London last year, is currently on display at the Summer Science Exhibition taking place at the Royal Society in London. It is part of an exhibit showcasing future imaging techniques that will allow us to peer inside the body.

Bat Embryo Skeleton
The blue stains show the cartilage

Human embryo at 7 weeks gestation, measuring approximately 14 mm (crown to rump). the fingers and face are developing and growing rapidly but are still forming their shape. It is possible to clearly see the formation of the skull, which begins to close, which will form the fontanelle (“soft spots”) that subsequently shut as children grow, creating a suture in the skull. This openness facilitates at birth in normal delivery, and allows the growth of the child’s brain.Photo: Ralph Hutchings/Getty images via https://www.facebook.com/vidabiologia