The Collegian
Wednesday, September 28, 2022

Students study lymphatic hearts in different species

Collegian reporter

Gary Radice's biology class was studying the anatomy of tadpoles when a student asked what the pumping organ was. Radice told her it was the tadpole's heart. That is, until he saw that there were two beating organs on the tadpole's back.

Since that day 10 years ago, Radice has been studying the pulsatile organ - called a lymphatic heart -- found in reptiles, birds and amphibians.

"I'm interested in how the embryo builds the 3-D body plant, and how the animal regulates how many lymphatic hearts it has," said Radice, who studies the hearts in South African clawed frogs.

Species can have two to 200 lymphatic hearts, Radice told students at the Research Introduction Series on Nov. 6. Salamanders have 200, one in between each body segment, while frogs have three or four pairs near their spines.

"It's kind of like why do we only have two arms and legs when other animals have more?" Radice said.

While lymphatic fluid moves passively in mammals, reptiles aren't as active and the fluid would pool without these hearts pumping it, he said. Human feet swell from lack of movement because of accumulating lymphatic fluid. A frog similarly blows up like a balloon if its lymphatic heart is cut out, Radice said.

Radice said he wanted to determine if the muscles in the blood and lymphatic hearts were the same.

"It's interesting because lymphatic hearts have a type of muscle, and it's not skeletal, smooth or cardiac," said Carolyn Marks, the director of biological imaging.

Senior Matt Counihan , who has been studying the hearts with Radice since last spring, extracts the organ from euthanized tadpoles and uses electron microscopy to characterize them.

"It's a lot of trial and error to dissect the tissue," said Counihan, who is a biology major. "Trying to keep your hands as steady as possible is the biggest issue."

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Though the tadpole's skin is transparent, the heart is a mere 1/250th of an inch. Radice said he peeled the skin off the top of the tadpole to expose the lymphatic heart.

"Right now, we're trying to crack through the middle and get images of the inside of the heart," Counihan said.

A scanning electron microscope provides vivid images of the organ's surface structure, but a transmission electron microscope delves through the top layers to show internal processes at work. The TEM looks at samples of tissue embedded in plastic and sectioned off. It's cut with a diamond or freshly cut glass and put on tiny copper circles with an eyelash, Marks said. The section is a fraction of a wave length of light.

"The problem is that the lymphatic heart is small, fragile and loose like a tumbleweed," she said. "It looks like some crumbs and dust on one of these stubs. The cells make a chamber that's hollow and pumps fluid, so when you dissect it, you have to be careful not to destroy it."

Future research will look at how species determine the number of lymphatic hearts needed and the right places for them, Radice said.

"I would love to have more students help," he said.

Contact reporter Jenn Hoffman at jenn.hoffman@richmond.edu

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