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Heterotrophs have diverse adaptations for acquiring food. Once captured or ingested, food is digested extracellularly by secreted enzymes to release nutrients that are absorbed into the animal’s body, usually via a tubular gut. The gut microbiome plays a role in digestion.
learning outcomes
You should be able to:
Compare the feeding and digestive adaptations of different species.
Relate structural features of animal guts to their functions and adaptive significance in digestion.
Describe digestive enzymes that are present in animal guts.
Explain the importance of the microbiome in the digestion of food.
Why do herbivores typically spend more time feeding than do carnivores?
Herbivores must spend much time feeding because their food has low energy content and requires considerable processing both mechanically (chewing) and chemically (digestion).
What do the actions of all digestive enzymes have in common?
All of the digestive enzymes act through hydrolysis of their substrates.
Why is it common for individuals to have digestive problems after antibiotic therapy?
Antibiotic therapy can greatly diminish or alter the gut microbiota and therefore result in altered digestion.
When people with celiac disease eat food containing gluten, their immune system damages their intestinal villi. If undiagnosed, such people are likely to experience bloating, abdominal pain, diarrhea, fatty stool, loss of body weight, and iron deficiency. Why do these symptoms occur?
The symptoms are due to damage to the villi. Damaged villi are less effective at absorbing the products of digestion and therefore contribute to undernutrition and even lack of micronutrients such as iron. Unabsorbed digestive products pull water into the gut, resulting in diarrhea, and also support microbial metabolism, leading to bloating. Damaged villi compromise the surface area available for digestion, affecting fat absorption as well as absorption of nutrients that require transport. The undigested fat results in fatty stools.
Once ingested by an animal, food may be fragmented and moved into the gut for digestion by hydrolytic enzymes. The processes of digestion release nutrients that are absorbed into the animal’s body. Next we will focus on how those processes occur in vertebrates.