All species, including humans, require food for development, restoration, and proper bodily function. Animal nutrition comprises nutritional requirements, food intake methods, and food use in the body. Carbohydrates are complex molecules that are found in food. Animals cannot use these complicated chemicals as they are. As a result, they are subdivided into simpler substances. Digestion refers to breaking down complex dietary constituents into simpler ones. After digestion, the body absorbs the nutrients for nutrient utilisation. The way food enters the body differs amongst animals. Grass-eating animals swiftly consume it and deposit it in the rumen, a section of the stomach. They later chew a part of the food. This process is called rumination.

Mode of food intake

The mode of consuming food differs from one organism to another:

• Bees and hummingbirds suck out nectar from plants
• Snakes swallow their prey
• Humans, just like animals, are fed milk by their mothers
• Aquatic animals feed on tiny food particles in the water

Nutrition utilisation

It is challenging to consume complex substances, so they are broken down into simpler substances before nutrition utilisation. For instance, carbohydrate is broken down into glucose, fatty acid, glycerol, and amino acid. This breaking down process is called digestion.

Digestion in humans

After the mouth consumes the food, some are digested, and some unused parts are defecated. The main parts of the digestive system include the Alimentary canal and Secretory glands.

• The alimentary canal or digestive tract starts from the buccal cavity and ends at the anus. It has the following parts:

1. Buccal cavity
2. Food pipe
3. Stomach
4. Small intestine
5. Large intestine
6. Anus

• The secretory glands that are responsible for secreting digestive juices are:

 1. Liver

 2. Salivary Glands

 3. Pancreas

Animal nutrition consumption occurs through ingestion, digestion, absorption, assimilation, and egestion. Where digestion of carbohydrates starts from the buccal cavity, protein digestion starts from the stomach. The liver secretes bile, pancreas-pancreatic juice, and intestine-digestive juice to carry out the process. Next, the digested food is absorbed by the blood vessels.

Food pipe

The food pipe or oesophagus helps pass the swallowed food into the stomach.

Stomach

The stomach, a J-shaped thick wall bag present in our body, further receives the food and passes it down to the small intestine for further secretion.

• Inside the stomach, hydrochloric acid, mucus, and digestive juices take place
• Mucus protects the inner wall of the stomach
• The acid kills any bacteria that may be present in food
• The digestive juice breaks protein into simple compositions

Small intestine

The small intestine is 7.5m long and highly coiled. It lets the pancreas and liver secretion enter and mix with its juice for further digestion.

Liver

The reddish-brown gland secretes bile juice stored in the gallbladder to digest the fats.

Pancreas

The cream-coloured gland below the stomach releases pancreatic juice for further breaking down carbs, fats, and protein. So, after the food reaches the small intestine and mixes with intestinal juice, the digestion process completes.

Absorption in the small intestine

• When nutrition from food sweeps down the blood vessel of the small intestine, the process is absorption
• Villus (finger-like outgrowths) present in the intestine’s inner wall helps absorb by increasing surface area
• After absorption, the nutrition is transported from the vessels to the organ, called assimilation
• The undigested food is transferred to the large intestine

Large intestine

The large intestine is 1.5m long. Its task is to absorb salt and water from undigested food and pass the remaining to the rectum. The process where the faecal matter is excreted out of the body from the anus is called egestion.

Digestion in grass-eating animals

Grass-eating animals like cows often swallow the grass and store a part in their stomach called the rumen. It is then partly digested (cud), and the remaining is sent to the mouth for chewing. This is known as rumination.

Animals like rabbits have caecum, a sac-like structure for digestion. The food is digested by bacteria that are not present in humans.

Digestion in Amoeba

They are microscopic plants that do not have a digestive system.

• They push out one or more finger-like projections (pseudopodia) to capture food
• They consume some microscopic organism that is trapped in the food vacuole
• Secretion of digestive juices takes place in the vacuole
• Gradually some foods are absorbed, and the vacuole expels others

Conclusion

Animal nutrition includes nutritional requirements, food intake methods, and food use in the body. The alimentary canal and secretory glands make up the human digestive system. It comprises the buccal cavity, the oesophagus, the stomach, the small intestine, the large intestine terminating in the rectum, and the anus. The salivary glands, liver, and pancreas are the primary digestive glands that release digestive fluids. The stomach and small intestine walls also produce digestive fluids. Distinct organisms have different eating mechanisms.