How our brain capillaries spit to survive.

Sometimes a science report headline will grab my attention because it sounds so quirky and this one certainly hit the spot.“Tiny Blood Vessels In Brain Spit to Survive”

I was intrigued, so I read on.

It turns out that capillaries, our really small blood vessels have a unique way of clearing out debris such as blood clot, cholesterol and calcium plaque out of harms way.

In the larger veins and arteries there is sufficient blood pressure to both push against a clot and break it into smaller pieces, or the body’s enzymes in the blood help to break it down. In the capillaries the role of blood pressure is much less effective and for debris (other than clot) such as cholesterol, because it is difficult to dissolve. Prolonged obstruction in a capillary will reduce the supply of oxygen and nutrient to a particular area of brain tissue, which if not cleared quickly enough can then cause cell death.

The really neat thing that has been observed in mice studies was that the brain capillaries have devised a unique way to clear out obstructions. What happens is that the clot or debris becomes enveloped in a membrane produced by the capillary vessel wall. The outer original vessel wall then opens up and literally ejects or spits the debris out into the brain tissue. The envelope, which had covered the clot, then becomes the new vessel wall and the blood flow is restored. Clever!

The study also showed that the capillaries ability to perform this diminishes with age, which may be relevant when we are looking at what causes brain age related cognitive decline. The process may be up to 30 to 50% slower in older brains. If the obstruction is not removed this can lead to damage or death of the affected brain tissue and capillary. Small brain infarcts are associated with the onset of vascular dementia, the second most common form of dementia after Alzheimer’s disease.

So there we have it. A fascinating tale of how our spitting brain capillaries clear out the rubbish.

Ref: Carson K. Lam, Taehwan Yoo, Bennett Hiner, Zhiqiang Liu, Jaime Grutzendler. Embolus extravasation is an alternative mechanism for cerebral microvascular recanalization. Nature, 2010; 465 (7297): 478 DOI: 10.1038/nature09001