As the opposite elements of this collection, this publish focuses on the chemical points of avian life – on this case, the chemistry of digestion.
Most meals birds eat is available in giant chunks – each on a macro degree (e.g., entire grains, giant items of meat) and on a micro degree (the person molecules are usually giant polymers, which means lengthy chains of comparable molecules linked by chemical bonds). The principle position of chemistry is to chop these lengthy molecules into small ones that may then be absorbed and digested.
The digestive chemistry of birds is dependent upon the precise location, so we want to check out the way in which meals passes by the our bodies of birds. There are 4 compulsory levels and two that solely apply to some birds.
Step 1: The Mouth (all birds)
This isn’t a serious focus of general digestion, however the saliva of some birds comprises amylase. That is an enzyme that begins breaking down carbohydrates, so it’s related for birds consuming grain (granivores and omnivores).
Chemical Response: Breaking down of bigger carbohydrates into smaller sugars, catalyzed by amylase.
Step 2: The Crop (some birds)
The crop is generally used for non permanent meals storage quite than for digestion. Nonetheless, in some birds, comparable to Hoatzins, there’s fermentation of meals within the crop, which entails enzymes that begin breaking down cellulose.
Chemical Response: Breaking down of cellulose into smaller sugars, catalyzed by enzymes.
Step 3: The Proventriculus, or Glandular Abdomen (all birds)
That is the place the chemical digestion actually begins. The abdomen comprises a powerful acid, hydrochloric acid, the identical as in human stomachs. Of their pure state, the proteins within the hen’s meals are lengthy chains of amino acids that fold into advanced shapes which can be stabilized by varied interactions which can be usually weaker than common chemical bonds (for instance, hydrogen bonds). The acid disrupts these different bonds, and because of this, the proteins unfold (you’ll be able to think about a ball of yarn being stretched out, although the analogy is a bit flawed).
As soon as the proteins have been unfolded, their lengthy (and now extra open) chains may be far more simply attacked by enzymes comparable to pepsin. By way of these assaults, the proteins are transformed into smaller peptides and amino acids, which the birds can immediately use.
There may be an fascinating facet story right here. The hen itself consists partly of proteins, so pepsin might begin attacking its personal proteins as nicely. Due to this fact, the abdomen doesn’t produce pepsin itself however solely an inactive precursor named pepsinogen. Pepsin is barely created by the response between pepsinogen and hydrochloric acid. The abdomen lining is then protected by mucus.
Chemical Reactions:
- Between proteins and hydrochloric acid, resulting in the straightening of the protein chains (“denaturation)
- Between hydrochloric acid and pepsinogen, resulting in the manufacturing of pepsin
- Between pepsin and long-chain proteins within the presence of hydrochloric acid, resulting in the manufacturing of smaller peptides and amino acids.
So, the proventriculus is nearly completely answerable for the digestion of proteins quite than the digestion of fat or carbohydrates, the opposite two essential meals elements. It’s thus much less essential for some households, comparable to hummingbirds, which primarily dwell on sugars.
Step 4: The Gizzard, or Muscular Abdomen (all birds)
The gizzard is a specialised abdomen with thick muscular partitions that’s used for grinding up meals, typically aided by particles of stone or grit. It’s thus much less related from a chemical standpoint, although the grinding of the meals enhances its floor space and thus will increase the floor accessible for chemical reactions.
Chemical Response: None.
Step 5: Small Gut (all birds)
That is the principle website of chemical digestion and absorption. Right here, the lengthy molecules of the three main teams of meals (carbohydrates, proteins, and fat) are cut up into small molecules and made absorbable. For every of the three teams, there are particular enzymes (biocatalysts) that facilitate the cut up into small molecules by letting them react with water (hydrolysis):
These enzymes are proteins delivered by the pancreas. They catalyze particular chemical reactions:
Amylase breaks down starch (a polysaccharide made from glucose) into maltose (a disaccharide) after which additional to glucose.
Chemical Response: Hydrolysis — amylase makes use of water to cleave the ?-1,4-glycosidic bonds in starch.
Proteases (trypsin, chymotrypsin) break down proteins into peptides after which amino acids. Much like the be aware about pepsin in step 3, these enzymes are secreted by the pancreas in an inactive kind (trypsinogen, chymotrypsinogen) to keep away from digesting the pancreas itself. Trypsinogen is activated to trypsin by enteropeptidase (one other enzyme, made by the intestinal lining). Trypsin then prompts extra trypsinogen and in addition chymotrypsinogen.
Chemical Response: Hydrolysis of peptide bonds (–CO–NH–) utilizing water.
Lipase breaks down triglycerides (fat) into glycerol + free fatty acids. It really works greatest when fats droplets are emulsified by bile salts (see under).
Chemical Response: Hydrolysis of ester bonds between glycerol and fatty acids.
The digestion of fat is supported by bile salts delivered from the liver (with or with out intermediate storage within the gallbladder, relying on species). Chemically, these bile salts are amphiphilic molecules, which means that they’re half hydrophilic (water-loving), half hydrophobic (fat-loving). They encompass giant fats globules and break them into smaller droplets, rising the floor space for lipase to behave. (Molecules in cleaning soap do the same job, serving to dissolve fats into water). Observe that this isn’t a chemical response.
Step 6: Ceca and Giant Gut (all birds, however giant variation in significance)
From a chemical standpoint, this step is of lesser significance. In some birds (primarily these consuming crops, the ceca have micro organism that ferment some plant materials into short-chain fatty acids, which may then be digested. In different birds with diets specializing in meat or nectar, the ceca are small.
The big gut is brief and primarily reabsorbs water. It’s current in all birds however is much less concerned in digestion.
Chemical Response: None.
Chook households differ considerably of their essential sources of meals, and these variations are additionally mirrored of their digestive system and their digestive chemistry. Beneath is the digestive focus of particular person households.
- Carnivores: Protein and the associated enzymes (pepsin, trypsin); low significance of carbohydrate enzymes
- Insectivores: Some protein digestion enzymes; an extra enzyme, chitinase, to digest insect exoskeletons
- Granivores comparable to pigeons: excessive amylase exercise; some cellulase (from intestine microbes)
- Nectarivores comparable to hummingbirds: excessive sucrase and maltase exercise to digest sugars shortly
- Frugivores comparable to toucans: solely reasonable amylase and sucrase exercise, as they primarily take in easy sugars.
- Herbivores such because the hoatzin: Giant fermentation chambers; excessive significance of microbial cellulase.
To summarize: birds flip to chemistry to chop the big molecules they get of their meals into small molecules that may be absorbed. These small molecules are then both burned for power or turned again into bigger molecules (i.e., change into a part of the hen’s physique). These two then once more are chemical reactions.
