Study Guide

Animal Nutrition and Digestion

Animal Nutrition and Digestion Introduction

They say what goes up must come down. When it comes to the food we swallow every day, what goes in must come out. You may or may not have noticed that you aren't filling the toilet with grape Kool-Aid and Krispy Kreme doughnuts, or whatever else you eat. That's because our food and drink change a lot in our bodies before we excrete them. Welcome to the wonderful world of digestion—a world full of bathroom humor opportunities. We'll try to contain ourselves.

Our food may come in all sorts of fancy packaging, and that bowl of Lucky Charms may be full of clover and star-shaped goodness. When it comes to digestion, we'll talk about various shapes and sizes that go way beyond marshmallow clovers and moons. We're taking this thing microscopic.

Carbohydrates, fats, and proteins are all nutrients our bodies break down and digest, and they provide us with critical substances and energy that keeps the body going. Whether we are eating a healthy portion of sautéed green beans or a shame-filled handful of Circus Peanuts, all food must undergo ingestion, digestion, and absorption. Once the body's guts have worked it over and wrung out every bit of nutritional goodness it can, it's stored up and eventually eliminated by our good friends Numbers 1 and 2. We're classy like that. We're wearing a monocle and a top hat as we type this, that's how classy we are.

When we're actually digesting food, our bodies attack it in multiple ways. We'll work over that chewed-up grub mechanically, by contracting muscles to squeeze it and churn it. We'll chemically blast the stuff with enzymes, acids, and other powerful stuff to break it down to its bare nutritional bones. In a way, we can think of the digestive process kind of like an employee at a recycling plant working through the city's refuse. As all the dirty bits and pieces pass by, it's his job to pull out the paper and plastic, all the useful stuff that can serve a purpose, while making sure the really nasty stuff like used diapers and coffee grounds just keep on trucking to be dumped off into a landfill somewhere. Hey, we never said it was a glamorous job, but someone's got to do it.

Beyond the crunchy and chewy solid food we nosh on, the other part of our diet comes in the form of liquid. Wouldn't you know it, our bodies have thought of everything; we also have a complex system that tackles the challenging job of regulating how much water we need to keep and how much we pee. That's the job of the excretory system, namely the kidney and its nephrons. The word "kidney" may bring to mind beans more than anything else, but don't sell that little pink pair of organs short. Through a series of winding, crazy-straw-like tubules and confusing concentration gradients, our bodies—via the kidneys—excrete just enough water and dissolved nutrients to make sure we can function properly. This happens whether we're in the middle of the sweltering jungle and are seriously considering wringing out our underwear for a quick drink, or in the middle of a water balloon fight in the rain forest. What? It could happen.

Never thought so much went into your bathroom breaks, now did you? Neither did Mike Rowe.

Animal Nutrition and Digestion Resources

Websites

All Want to Know About Kidneys
Website put together by the US Health and Human Services branch of the government. Answers many questions about kidneys and their function.

Kidney Slide Show
When in doubt, learn from How Stuff Works. They will never fail you. Not even when you are searching for how the kidney works.

Test Your Kidney Knowledge
The perfect website to test your knowledge about kidney structure and function!

What's Saliva For, Anyways?
Science Daily is a great place to find interesting, current research on a bunch of topics. We found this report that talks about our good ol' friend salivary amylase and all its importance.

Current Research

Current News in Osmoregulation
Research review on how marine mammals regulate salt and water balance. When it's in the Journal of Experimental Biology, you know it's bound to be a good read.

Videos

Bill, Bill, Bill, Bill
What do we love more than Bill Nye? Bill Nye talking about digestion, of course.

Digestion, Why Don't You Actually Work Like This?
Here's a cartoon video that describes digestion if it were run by microscopic bearded, British men.

A Walk-Through Tour of Osmosis
The Khan Academy is a non-profit organization whose mission is to give everyone a good education. They have a lot of great videos, and here's one on diffusion and osmosis.