Digestive system in mammals

[Moreno]

What could be an evolutionary purpose to have digestive system strictly differentiated into the stomach, small intestine and large intestine? Is it too difficult to have a single organ which can perform the functions of all the three? For example something similar to a large intestine?

Edited June 17, 2019 by Moreno

[Dagl1]

It is a lot easier to make a system with compartmentalized functions. For instance, the stomach needs to both produce and be able to withstand large amounts of acidic material. The beginning of the small intestine subsequently neutralizes this acid and then starts to digest specific types of nutrients (proteins, fats and sugars) in an order (I can't remember what is taken up where, but each place is specialized to take up specific groups of nutrients). This then allows for specific groups of bacteria to sit in those niches helping the body even further. Lastly the water is taken up in the large intestine, something you wouldn't want to do before that as it would make it a lot more difficult to take up nutrients. Thus even if you would make 1 organ capable of doing all of these tasks, it would still follow the sequential nature of the current digestive track.

Food needs to first be made into pieces that are easily taken up.
Every nutrient type should be taken up as efficiently as possible.
Lastly water needs to be taken up.

Hope that helps

-Dagl

Edited June 17, 2019 by Dagl1

[Moreno]

Why small intestine needs to neutralize the acid?

[Sensei]

Quote

Digestive system in mammals

What could be an evolutionary purpose to have digestive system strictly differentiated into the stomach, small intestine and large intestine?

Not all mammals have stomach... egg laying mammals, platypus, monotremes etc. don't have stomach.

https://www.livescience.com/41661-why-platypus-wont-regain-stomach.html

 

"Since many animals have now had their genomes sequenced, researchers investigated 14 species with and without stomachs to see what genes they all might be missing. The scientists found that in all species examined, stomach loss was clearly linked with the complete loss of the genes responsible for pepsin and acid digestion."

[Dagl1]

30 minutes ago, Sensei said:

Not all mammals have stomach... egg laying mammals, platypus, monotremes etc. don't have stomach.

https://www.livescience.com/41661-why-platypus-wont-regain-stomach.html

 

"Since many animals have now had their genomes sequenced, researchers investigated 14 species with and without stomachs to see what genes they all might be missing. The scientists found that in all species examined, stomach loss was clearly linked with the complete loss of the genes responsible for pepsin and acid digestion."

I currently don't have the time to look into that but I am curious; how do these species then digest peptides and a lot of the relatively hard to eat food? If you don't have any idea I'll look it up later.
 

43 minutes ago, Moreno said:

Why small intestine needs to neutralize the acid?

Cause otherwise the stomach acid will "burn"/destroy the cells in the intestinal tract. 

-Dagl

[CharonY]

5 hours ago, Dagl1 said:

I currently don't have the time to look into that but I am curious; how do these species then digest peptides and a lot of the relatively hard to eat food? If you don't have any idea I'll look it up later.

The other major proteases are released in the intestine and work at higher pH (which is another functional reason for the need of neutralization).

[Dagl1]

8 hours ago, CharonY said:

The other major proteases are released in the intestine and work at higher pH (which is another functional reason for the need of neutralization).

Ahh my bad for being unclear; I understand that there are other enzymes which work in a redundant or (additional) manner, but my question is; the acidity of the stomach seems to quite essential for digestion, so is it the specific diet that these egg laying mammals have, which doesn't require the stomache or did they evolve some other digestion-related mechanisms instead?

 

[CharonY]

4 hours ago, Dagl1 said:

Ahh my bad for being unclear; I understand that there are other enzymes which work in a redundant or (additional) manner, but my question is; the acidity of the stomach seems to quite essential for digestion, so is it the specific diet that these egg laying mammals have, which doesn't require the stomache or did they evolve some other digestion-related mechanisms instead?

 

Acidification is generally speaking not that essential. (Over-) use of antacids where the stomach acidity is brought up close to neutral for example do not lead to noticeable changes in digestion itself. The acute effects seem more to be related to bacterial load and colonization. There are long-term effects, which are perhaps not surprising. But it appears that while a stomach and an acidic environment together with pepsins confer selective advantages, they are not fundamentally essential. I am not an expert, so I do not know whether there are specific modifications of the montreme GI, but I vaguely recall that at least on the macro level no specific genetic adaptations were reported to account for the reduced organ (things like dietary adaptations were part of the speculation). 

 

[Dagl1]

51 minutes ago, CharonY said:

Acidification is generally speaking not that essential. (Over-) use of antacids where the stomach acidity is brought up close to neutral for example do not lead to noticeable changes in digestion itself. The acute effects seem more to be related to bacterial load and colonization. There are long-term effects, which are perhaps not surprising. But it appears that while a stomach and an acidic environment together with pepsins confer selective advantages, they are not fundamentally essential. I am not an expert, so I do not know whether there are specific modifications of the montreme GI, but I vaguely recall that at least on the macro level no specific genetic adaptations were reported to account for the reduced organ (things like dietary adaptations were part of the speculation). 

 

Ahh that makes sense, I can imagine that if its more important for bacterial infections and such things that those animals who do not have a stomache have other measures of reducing infections and bacterial colonization (or they encourage it more, using even more bacteria within their GI tract). Thanks!

[John Cuthber]

One of the major  advantages to starting with an "acid bath" is that it kills things.

So, if there were insects in that apple- who cares? They aren't going to be causing trouble for long.

Pathogenic bacteria? Soon to become additional dietary protein.