BIOL 1030 / Topic 4: Animal Digestion & Waste Management

What kind of heterotrophs are animals?

Ingestive.

There are four different things that animals consume in order to live. Name these things and explain what they are or what they are used for.

• Carbon compounds, which are used for ATP and macromolecule synthesis.

• Essential nutrients, which are some amino acids and fatty acids, with the first being amino acids we can’t synthesize in our bodies.

• Vitamins, which are organic compounds.

• Minerals, which are inorganic compounds.

What happens if you miss any one of the dietary components required?

You get malnourished, the state of unhealthiness. You might even crave for a specific dietary component because it’s your body’s response telling you to eat that specific dietary component.

There are four steps to food processing. Name ‘em, and define ‘em.

1. Ingestion, wherein you’re physically changing the state of the food.

2. Digestion, wherein you’re breaking down the food into small pieces, with the help of enzymes performing hydrolysis.

3. Absorption, wherein the nutrient molecules enter body cells.

4. Elimination, wherein you feed your toilet with all the waste product remaining from what you fed yourself.

List down the common carbohydrates we eat!

Starch, sucrose, and lactose.

Can we absorb polymers, i.e. can we absorb carbs as whole polysaccharides? Why or why not?

No, because they’re too big to absorb.

There are four strategies of ingestion. What are they?

• Suspension feeding, a.k.a. filter feeding.

• Substrate feeding.

• Fluid feeding.

• Bulk feeding.

Suspension feeding

Ingestion wherein the food is suspended in the water and is eaten.

E.g. Blue whales, forcing water across their baleen and trapping food, are an example of suspension feeding.

Substrate feeding

Ingestion wherein the food is the organism’s own environment, burrowing and eating at it.

E.g. A maggot (fly larva) that eats as it borrows through a carcass is an example of substrate feeding.

Fluid feeding

Ingestion wherein food is fluids in animals and nectar in plants.

E.g. A female mosquito that feeds on blood is an example of fluid feeding.

Bulk feeding.

Ingestion wherein the food is prey, consumed in one piece or many pieces.

E.g. A hyena that swallows its food in pieces is an example of bulk feeding.

For bulk feeding, ingestion of pray as a WHOLE requires what?

• Expandable soft body.

• Expandable modified jaws.

For bulk feeding, ingestion of pray IN PIECES requires what?

• Modified appendages.

• Modified teeth.

In bulk feeding, why is eating prey in pieces more efficient, i.e. increasing the SA:V?

Increasing the surface area to volume ratio (SA:V) is like cutting food into smaller pieces. This makes it easier for digestive enzymes to reach and break down more of the food, in turn making it faster for absorption of nutrients and energy, overall making the digestive system work more effectively.

Let’s talk digestion, which can only work when enzymes are present. Where can digestion happen? Be specific!

• Intracellular digestion within food vacuoles.

• Extracellular digestion within chambers.

In regards to intracellular digestion, there are two different types of enzymes for two different groups in the kingdom Animalia. What can each of these enzymes be called, and where are they found?

• Lysosomal enzymes in choanocytes and amoebocytes of Parazoa.

• Cytoplasmic enzymes in epithelial cells of Eumetazoa, which digest by phagocytosis.

In regards to extracellular digestion, how does it work?

Enzymes are secreted into places where digestion can take place, such as the gastrovascular cavity, and are then mixed with food.

There are three types of digestive systems found in animals. What are they, and where are they generally found?

• Gastrovascular cavity, which is a space with only one way to go both in and out, found in phyla Platyhelminthes and Cnidaria.

• Alimentary canal, which is a space with two openings, leading from the mouth to the anus, passing multiple organs with specialized functions, found in most animals.

• Tegument, which is skin itself absorbing nutrients of host in digestive system, specifically the small intestine, found in tapeworms.

There are several adaptations of digestion throughout evolution, with three types adaptations being formed and thus three different types of animals based on this. What are they?

• Omnivores, consuming plants and animals.

• Herbivores, consuming plants and plant-based food.

• Carnivores, consuming animals and animal-based food.

Animals, based on their dietary adaptation, have different dentition, i.e. arrangement of teeth. What is the dentition of carnivores?

Incisors: Large and pointed, to kill prey and rip pieces of flesh.

Canines: Large and pointed, to kill prey and rip pieces of flesh.

Premolars: Jagged to crush and shred food.

Molars: Jagged to crush and shred food.

Animals, based on their dietary adaptation, have different dentition, i.e. arrangement of teeth. What is the dentition of herbivores?

Incisors: Small but modified for cutting vegetation.

Canines: Small but modified for cutting vegetation. Absent in some herbivores.

Premolars: Broad, rigid surfaces to grind vegetation.

Molars: Broad, rigid surfaces to grind vegetation.

Animals, based on their dietary adaptation, have different dentition or arrangement of teeth. What is the dentition of omnivores?

Incisors: Bladey for biting.

Canines: Pointy for tearing.

Premolars: Used for grinding.

Molars: Used for crushing.

What are the special ways that herbivores eat plants, which contain cellulose, which is hard to digest because of its nature as a structural carb?

Ruminant digestion and coprophagy.

What are ruminants, and how do they consume cellulose?

Cud-chewing animals, e.g. deer, sheep, and cattle, which have symbiotic relationships with bacteria and protists that have cellulase.

Explain the stepwise process of ruminant digestion.

1. Chewed food first enters rumen and reticulum, wherein microorganisms digest cellulose via their cellulase.

2. Cow periodically regurgitates and rechews cud.

3. Reswallowed cud passes in the omasum, where some water is removed, and into the abomasum, wherein cows digest their food with the broken down cellulose with their own enzymes.

The more you chew, the more surface area.

Coprophagy

The digestion of feces.

Why do herbivores that perform coprophagy perform the process itself?

According to the alimentary canal, in order, you have the small intestine, the cecum, and the large intestine. It is in the small small intestine where the absorption of the food occurs, and it is in the cecum and large intestine that microorganisms with cellulase are present. During the first round of digestion, not all food particles are absorbed, because not all of the food was broken down by the enzymes, which is further down the canal. So, in the second round of digestion, these herbivores can eat their feces, which already have the broken down nutrients they need.

Compared to carnivores, herbivores have proportionately bigger cecum and large intestine and smaller small intestine, why is that?

Herbivores have a bigger cecum and large intestine and smaller small intestine because that’s where the cellulase-containing microorganisms are! If they have organs of this size, it gives more time to that breakdown of cellulose.

How do animals adapt to maximize efficiency of absorption of nutrients?

• For animals with small intestine, they evolved over time with the increase of large folds with villi in order to absorb nutrients more.

• For animals without small intestines, such as tapeworms, their epithelia absorbs nutrients.

• For animals that have small intestine and skin available to absorb nutrients with… they just absorb it through both their small intestine and skin, simple as that. It maximizes efficiency regardless.

Some proteins, amino acids, nitrogenous bases, and nucleic acids are not needed. Collectively, in regards to animal digestion and waste management, what are they known as?

Nitrogenous wastes.

There are three types of nitrogenous wastes that are excreted by animals. Name these three types of N-waste and from which animals they are excreted.

• Ammonia, excreted by most aquatic animals, including bony fishes.

• Urea, excreted by most mammals, most amphibians, sharks, and some bony fishes.

• Uric acid, excreted by birds and many reptiles, insects, and land snails. Completely non-toxic because it’s completely insoluble.

How does nitrogenous waste removal generally work?

1. FILTRATION, wherein water and solutes diverge into the excretory tubule with filtrate and the capillaries with blood.

2. REABSORPTION, wherein the capillary gets back the useful stuff from the tubule to make up the entire thing it has called body fluids.

3. SECRETION, wherein the capillary removes useless stuff, e.g. toxins and excess ions, from the body fluids and into the tubule.

4. EXCRETION, wherein the filtrate, which can now be called urine because it’s mostly made of urine, is excreted.

What is protonephridia, and how does it work?

Protonephridia are excretory organs of flatworms, wherein the beating of cilia within bulb-like structures called flame bulbs draw fluid outside of cells from surroundings, and in the tubules reabsorption and secretion occur, and via an excretory pore excretion occurs.

What is metanephridia, and how does it work?

Metanephridia are excretory organs of annelids, wherein the beating of ciliated funnels draws in coelomic fluid into the tubule, and the general process of waste removal continues with capillaries wrapped around the tubules.

What are malpighian tubules, and how do they work?

Malpighian tubules are exretory organs in insects and terrestrial arthropods, wherein epithelia on the tubules secrete solutes into the lumen from the hemolymph (filtration), and as it passes through the alimentary canal, reabsorption into the hemolymph occurs, and then excretion occurs via the anus.

What are kidneys and nephrons, and how do they work?

The kidneys are excretory organs for mammals. Kidneys are made of nephrons. Nephrons are essentially a complex of tubules and filters responsible for waste removal.