News on Health & Science

Why is the heart pear-shaped?

T.V. Jayan explains, with the help of a new study:  It’s often been said that there is no engineer quite like Mother Nature. A living organism ” with all its parts that fit in so smoothly  is after all an engineering marvel. But this near-perfect  manufacturing  skill of Nature has often fanned the debate on whether life was created, or evolved.


If the advocates of creationism are ready to swallow, however grudgingly, the theory that life originated from the amoeba eons ago, science has not been able to give convincing answers to a number of sub-questions. How does, for instance, a tiny, fragile fertilised egg grow into a body of full-blown organs without any “external” guidance? Why are the shapes of organs in a human being as they are? Why are our legs longer than our arms?

Ardent proponents of evolutionary biology, however, may no longer have to fumble for answers to many such questions. A team of scientists from the Skirball Institute of Biomolecular Medicine, affiliated to the New York University School of Medicine, recently proved that logic could explain some of these difficult questions. Led by Deborah Yelon, the scientists unravelled the factors governing the complex process of the formation of the heart, which is a simple tube in early development, growing into a four-chambered, intricate organ with a characteristic pear shape. The researchers published their study in the February 20 issue of PLoS (Public Library of Science) Biology.

The heart, like many other organs, undergoes dramatic changes in its three-dimensional form as the embryo develops and functional demands intensify. Before it becomes a multi-chambered organ, it exists as a simple tube made up of myocardium (muscle) lined by endocardium (endothelium). As this thin-walled tube bulges outward, the chambers emerge and eventually acquire the characteristic dimensions of curvature and thickness.

In an article in Current Biology (September 2005), Sheffield University scientist David Strutt wrote that in order to control the shape and size of an organ, it is necessary that the dimensions be measured as the organ grows, and growth stops in each axis at the appropriate time.

But how this is achieved largely remains a mystery.

Developing organs acquire a specific three-dimensional form that ensures their normal functioning. The unique shape of the heart in higher-order animals, too, is critical for proper functioning. It is composed of a series of chambers that rhythmically drive blood circulation. Each of the chambers is designed for its optimal functional capacity. The organ, which commences beating from approximately 21 days of conception, is responsible for pumping blood via blood vessels through repeated, rhythmic contractions. In the process, it picks up carbon dioxide from the blood and drops it off in the lungs in exchange for oxygen which is in turn circulated through the blood.

Organs acquire their characteristic shapes not simply as a consequence of the accumulation of cells that profusely divide and multipl  Shape is also a physical process during which tissues are pressed, pulled and moved,  the scientists said.

In the experiments using transgenic (containing genes transferred from another species) zebra fish in which individual cardiac cells can be watched, Deborah Yelon, her student Heidi Auman and others demonstrated that cells change size and shape, enlarging and elongating to form bulges in the heart tube and eventually the chambers. The big question was whether the function of the heart — that is, blood flow — too influences cell shape.

Their studies using zebra fish   genetically modified so that each fish has a functional defect — helped them to find out that both blood flow and contraction of the cardiac tissues play a role in shaping cardiac cells. The unique tools the researchers used helped to clearly show that blood flow affects form. Further, they could define this at the cellular level.

The contribution of individual cell morphology to the overall shape was not previously shown, particularly in relation to the impact on chamber morphogenesis (formation and shape), said Deepak Srivastava, director of the Gladstone Institute of Cardiovascular Disease, University of California, San Francisco.

“This is an important advance as although it has long been thought that blood flow does affect morphogenesis, the two have been difficult to isolate in a cause-and-effect manner,” Srivastava told KnowHow.

Moreover, the work is more rigorous and detailed than previous such exercises, he said.

However, Larry Taber, professor of biomedical engineering at Washington University, feels that the researchers are missing some key points. For example, he says, they talk about curvature (of the heart chambers) but never explicitly discuss looping, which causes the greatest changes during heart development. Looping, it may be mentioned, involves the bending and twisting of the heart tube to create asymmetry of the chambers as is required for optimal functioning.

There are a lot of misconceptions about looping among developmental biologists, including some propagated in this paper,  Taber, who has been studying heart formation in chicks for a couple of decades, told KnowHow.

He, however, said that the Skirball team’s conclusion that contraction and blood flow are important for chamber expansion seems plausible. He also said that cell shape changes can cause curvature changes as well. What he disagrees with is their implication that contraction and blood flow regulate looping.

The use of zebra fish with minor induced genetic defects helped the Skirball Institute scientists to show that slight abnormalities in cell morphology may lead to substantial changes in the shape and functioning of the cardiac chambers. This could probably explain aberrations observed in some types of heart disease.

Source:The Telegraph (Kolkata,India)

News on Health & Science

Docs test heart implant to prevent strokes

At least 120,000 Americans a year suffer strokes because of a common irregular heartbeat  one that’s on the rise, hard to treat and can shoot deadly blood clots straight to the brain….click & see

Now doctors are experimenting with a new way to prevent those brain attacks: a tiny device that seals off a little section of the jiggling heart where the clots form.

If it works   and a major study is under way   the Watchman device might provide long-needed protection for thousands of people with atrial fibrillation, whose main hope now is a problematic blood-thinning drug that too many can’t tolerate.

“I don’t think I’m biased, but it could potentially revolutionise a-fib, which is a ton of people,”says Steven Almany, vice chief of cardiology at William Beaumont Hospital in Royal Oak, Michigan. He has implanted the Watchman into more than a dozen patients so far.

About 2.8 million Americans have atrial fibrillation, the most common type of irregular heartbeat. It is most common among the elderly, and cases are increasing as the population greys.

A-fib occurs when the heart’s top chambers, called the atria, get out of sync with the bottom chambers’ pumping. The atria speed up, sometimes so fast that they quiver like a bag of worms. Blood pools inside a pocket of the heart, allowing clots to form.

About 20% of the nation’s strokes are blamed on the condition, and they tend to be particularly severe. About a third of the victims die, and another third are significantly disabled.

The blood thinner warfarin, also called Coumadin, lowers the stroke risk dramatically. But it is very difficult to use    it can’t be taken together with dozens of other medicines. In addition, side effects include serious, even life-threatening, bleeding.

By some estimates, almost half the people who should take the drug can’t or won’t, and “there are lots of people out there on Coumadin who want off,”says William Gray, a cardiologist studying the Watchman at New York’s Columbia University Medical Center. “This provides the opportunity, hopefully, to get them off the drug.”

In atrial fibrillation, 90% of stroke-causing blood clots collect inside a jalapeno pepper-shaped flap of tissue that hangs off the edge of the left atrium. The Watchman physically seals off that flap, depriving clots of their staging area.

Source:The Times Of India

Healthy Tips

8 Ways to Burn Calories Without Noticing

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Add a little more activity into your daily routine.

1. Take the escalator — but climb the stairs while you ride. You’ll get there faster and use your muscles while you’re at it. Just 5 minutes of stair climbing burns 144 calories.

2. Instead of piling items on the stairs so you can take them upstairs at once, take them one at a time.

3. When cooling your heels while waiting in a doctor’s office, drugstore, or airport, stay on your feet– standing burns 36 more calories per hour than sitting.

4. Rake leaves instead of using a leaf blower: You’ll burn 50 more calories every half hour.

5. Scrub your floors more often. Putting some elbow grease into cleaning floors is more intense than vacuuming — and it makes your floors look better to boot.

6. Chew sugarless gum. Research has found that the action of jaw muscles alone burns about 11 calories an hour.

7. Wash your car by hand instead of taking it through the automatic carwash. You’ll burn an extra 280 calories in an hour.

8. Play with kids: Impromptu games of basketball, touch football, or tag — or just jumping rope or throwing a ball — will help you use energy and set a good example of active play for the children. Calories burned: 80 to 137 every 10 minutes.

From:    Change

Calculate your body mass index (BMI) and see if you are over weight

News on Health & Science

Protein find may be kye to cancer,eye disorder

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A protein that prevents blood vessels from forming in the cornea could become the basis of new treatments for cancer and macular degeneration, a leading cause of blindness in the elderly, scientists said.

The team of international researchers identified a protein called sVEGFR-1 and found that when levels are low, blood vessels begin to form in the eye, impairing vision.

They believe therapies that boost levels of the protein could prevent the formation of blood vessels, which are a component in the spread of cancers and the cause of macular degeneration.

“We have discovered what it is that keeps the cornea clear. It has no blood vessels — which allows us to see,”said Dr Jayakrishna Ambati, of the University of Kentucky in Lexington who headed the research team.

The cornea is the transparent front part of the eye. Scientists have wondered for centuries why it has no blood vessels.

What causes blood vessels to form is a fundamental question for vision and also for diseases like cancer.

“This finding teaches us what keeps the cornea clear and gives us the ability to exploit it in other diseases, both in the eye and systemically because now you have a protein that blocks blood vessel growth that the body itself makes,”added Ambati, who reported the findings in the journal Nature.

The lack of blood vessels has been perplexing researchers because the cornea contains vast amounts of a chemical called VEGF-A, which promotes blood vessel growth.

The new protein discovered by Ambati and researchers from the US, Japan, Italy and Australia provides the answer. It is produced in the cornea and acts like a mop, absorbing VEGF-A which would otherwise make blood vessels grow.

(As published in The Times Of India)