Body Removes Foreign Objects

Biological Strategy

Australian green treefrog

AskNature Team

Image: Jennifer Sophie / Shutterstock / Some rights reserved

Expel Solids

Living systems must often discharge solids–such as seeds, eggs, pollen, and mineral salts–for reproduction, protection, or other reasons. Solids can be easily moved when a living system applies force to them. But creating that force requires energy, so living systems must either have efficient strategies worth the energy investment or use an outside force (such as gravity). For example, a tropical mistletoe positions its pollen so that the weight of a bird landing nearby triggers the pollen’s release onto the bird’s forehead. The bird then fertilizes other mistletoes that it visits.

Search this Function

Amphibians

Class Amphibia (“to live a double life”): Frogs, salamanders, toads

Amphibians live a “double life” by being able to survive both on land and in water. Unlike reptiles with dry, scaly skin, amphibians have smooth skin that needs to be kept moist. Many live in the water through development and start life with gills, and then transition to breathing with lungs. They can get even more oxygen through cutaneous respiration, or breathing through their skin. This class represents the first animal group to be able to efficiently walk on land—aided by the well-defined limbs that gave them a “leg up” on their finned competitors.

Search this Living System

Foreign objects in the body cavity of some tree frogs can be absorbed into the urinary bladder and excreted.

“Plant thorns, spiny insects and even radio transmitters don’t stick
around for long inside tree frogs. Researchers have discovered that
these amphibians can absorb foreign objects from their body cavities
into their bladders and excrete them through urination…

“‘It strikes me as being a pretty incredible mechanism for getting stuff
out from the body cavity,’ says lead researcher Christopher Tracy of
Charles Darwin University in Darwin, Australia. By contrast, humans and
other mammals typically develop peritonitis, a potentially deadly
infection of the body-cavity membrane, if the membrane is punctured or
damaged by sharp objects…

“Tracy and his colleagues decided to look into the phenomenon. They kept
tree frogs and cane toads in the lab and surgically implanted beads in
their body cavities. Within 2–3 weeks, the beads appeared on the floor
of the frog cage. Only one cane toad out of five excreted a bead, but
Tracy opened some other toads after the surgery and caught them in the
act of enveloping the beads into their bladders. In just two days, the
bead was surrounded by a transparent tissue devoid of blood vessels,
which subsequently became vascularized and muscular…

“Although the study is the first to show an animal using its bladder to
expel foreign objects, researchers have observed similar phenomena in
other vertebrates. Several species of fish and snake absorb objects into
their intestines from the body cavity and expel them by defecation, for
instance.” (Borrell 2010)

http://www.nature.com/news/2010/100105/full/news.2009.1170.html?s=news_rss&utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+news%2Frss%2Fmost_recent+%28NatureNews+-+Most+recent+articles%29&utm_content=Google+Reader

AskNature