Magic embryology: special macrophages thin heart valves (Introduction)

by David Turell , Sunday, February 24, 2019, 01:47 (2100 days ago) @ David Turell

How heart valves are made so thin is discovered. It shows how complex embryological processes are:

https://www.sciencedaily.com/releases/2019/02/190221130250.htm

"UCLA researchers have identified for the first time the origin of an immune cell that plays a critical role in the formation of healthy heart valves.

"'Ever since we discovered that the heart tube produces some blood progenitor cells, we have been trying to figure out why," Nakano said. "Blood progenitor cells are generated in much greater numbers in other parts of the developing embryo. Having the heart tube produce blood progenitor cells is like having a small, not-very-productive factory just down the street from a larger, more productive factory. If both factories produce the same thing -- in this case blood progenitor cells -- why not just have one big factory?"

***

"Macrophages ("big eaters" in Greek) reside in tissues and travel around the body in the blood, seeking out and consuming harmful, damaged or unnecessary cells. Previous research had shown that macrophages exist in the heart valves, but Nakano's team was the first to discover their role there: eating up excess cells to make the valves paper-thin and hyper-efficient. This process begins in the developing embryo and continues after birth; the macrophages remain in the valves to help keep them in shape throughout the lifecycle.
"Macrophages were known to exist in heart valves, but nobody had nailed down when they arrived there and where they came from until we watched them develop in the heart tube," Nakano said.

"To test just how essential heart-derived macrophages are to valve formation and remodeling, the scientists blocked their production to see if it had any effect. They found that the other macrophages in the body -- those from circulating blood -- traveled to the heart, but they weren't very effective at remodeling the valves. Without the heart-derived macrophages, the heart valves remained thick and unwieldy.

"'This showed us that the macrophages that are generated in the heart tube are particularly adept at eating up excess tissue," Nakano said. "This makes them essential not just to heart valve formation, but to heart valve maintenance throughout life.'"

Comment: Early evolution had fluids moving around body cavities due to organ movements such as muscles. Later as heart tubes developed they contracted to move fluid. Eventually those tubes were twisted and eventually formed chambers to manage a back and forth circulation . Valves had to be added to control flow in one circular direction, with the delicate valves leaflets paper thin to move very quickly because the heart beats are timed by the second. Most human pulses average rest rates that are an average 70 per minute. I can't image all of this complexity happened by chance.