Digestive System Optimizes Performance

a large brown and black patterned snake rests on a log in murky waters with small rain drops

Biological Strategy

Indian python

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Image: Paul Asman and Jill Lenoble / Flickr / Some rights reserved

Optimize Shape/Materials

Resources are limited and the simple act of retaining them requires resources, especially energy. Living systems must constantly balance the value of resources obtained with the costs of resources expended; failure to do so can result in death or prevent reproduction. Living systems therefore optimize, rather than maximize, resource use. Optimizing shape ultimately optimizes materials and energy. An example of such optimization can be seen in the dolphin’s body shape. It’s streamlined to reduce drag in the water due to an optimal ratio of length to diameter, as well as features on its surface that lie flat, reducing turbulence.

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Modify Material Characteristics

The materials found in living systems are variable, yet often made from the same basic building blocks. For example, all insect exoskeletons consist of a material called chitin. Because material resources are limited, each material within or used by a given living system must frequently serve multiple purposes. Therefore, living systems have strategies to modify materials’ softness, flexibility, and other characteristics. To ensure survival, the benefits of these modifications must outweigh the living system’s energy and material expenditure to generate them. For example, spiders store the liquid components of spider silk in a gland, converting them into silk thread when needed. Some threads have different characteristics, such as elasticity and UV reflectance, than others.

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Regulate Cellular Processes

Cells are the basic building blocks of all living systems, so cellular processes dictate how physiological processes occur within those systems. Cells (whether entire unicellular organisms or parts of multicellular living systems) grow, metabolize nutrients (that is, chemically transform them), produce proteins and enzymes, replicate, and move. Cells as part of multicellular systems rarely act alone, instead having ways to signal to start and complete simple to quite complex interactions. How skin heals is a good example of the role of cellular processes. Blood cells called platelets release clotting factors to stop the bleeding; white blood cells rid the area of foreign materials and release molecules to coordinate healing; cells called fibroblasts start rebuilding using proteins called collagen; new blood vessels form; and skin cells called keratinocytes create the new surface.

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Reptiles

Class Reptilia (“creeping”): Lizards, crocodiles, turtles, snakes

Reptiles retain some of the key characteristics that first enabled vertebrates to live permanently on land. They have dry skin covered in scales made of keratin that help prevent water loss. (Amphibians still need to stick close to water to keep their skin moist.) Many reptiles reproduce by laying eggs that are watertight and have a yolk, so eggs can develop on land while staying moist and nourished. Reptiles are also ectotherms, meaning they don’t produce their own body heat. This means they burn through energy much more slowly than “warm blooded” creatures of the same size. It also means that they need to keep warm to keep active, which is why you might see them spending a seemingly inordinate amount of time simply basking in the sun.

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The gastrointestinal system in burmese pythons quickly regulates performance between fasting and feeding (leading to energy savings) thanks to cell plasticity.

“The morphology of the digestive system in fasting and refed Burmese pythons was determined, as well as the localization of the proton (H+, K+-ATPase) and sodium (Na+, K+-ATPase) pumps. In fasting pythons, oxyntopeptic cells located within the fundic glands are typically non-active, with a thick apical tubulovesicular system and numerous zymogen granules. They become active immediately after feeding but return to a non-active state 3 days after the ingestion of the prey. The proton pump, expressed throughout the different fasting/feeding states, is either sequestered in the tubulovesicular system in non-active cells or located along the apical digitations extending within the crypt lumen in active cells. The sodium pump is rapidly upregulated in fed animals and is classically located along the baso-lateral membranes of the gastric oxyntopeptic cells. In the intestine, it is only expressed along the lateral membranes of the enterocytes, i.e., above the lateral spaces and not along the basal side of the cells. Thus, solute transport within the intestinal lining is mainly achieved through the apical part of the cells and across the lateral spaces while absorbed fat massively crosses the entire height of the cells and flows into the intercellular spaces. Therefore, in the Burmese python, the gastrointestinal cellular system quickly upregulates after feeding, due to inexpensive cellular changes, passive mechanisms, and the progressive activation and synthesis of key enzymes such as the sodium pump. This cell plasticity also allows anticipation of the next fasting and feeding periods.” (Helmstetter et al. 2009:632)

Last Updated August 18, 2016

References

Journal article

Functional Changes with Feeding in the Gastro-Intestinal Epithelia of the Burmese Python ( Python molurus )

Zoological Science | 03/10/2009 | Cécile Helmstetter, Nathalie Reix, Mathieu T'Flachebba, Robert K. Pope, Stephen M. Secor, Yvon Le Maho, Jean-Hervé Lignot

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