Study Guide

Animal Nutrition and Digestion Terms

Animal Nutrition and Digestion Terms

Active Transport

A rapid transport of nutrients that comes with a cost: the need to burn energy in the form of adenosine 5'-triphosphate (ATP, the energy transport molecule). Active transport occurs independently of the concentration gradient, and is a mechanism to build up the nutrient concentration.


Stimulated by angiotensin II and released by the adrenal glands, aldosterone causes the nephron's distal tubule to reabsorb more NaCl and water to increase blood volume and pressure. Think of it as the hormone that tells the kidney it was born to be a sponge.

Alimentary Canal

Most animals have this digestive tube that flows from the oral cavity to the anus, including people. No gondolas in this canal though; just keeping things simple. Food goes in one end and comes out the other. Flatworms are an exception…way to be unique, guys.

Antidiuretic Hormone (ADH)

Hormone secreted from the pituitary gland in response to hyperosmotic blood. ADH will increase water solubility in the nephron's collecting duct and lower blood osmolarity. If things are bad enough, it'll make you thirsty too.

Atrial Natriuretic Peptide (ANP)

Released by the heart atria in response to high blood pressure and/or volume. ANP is renin's worst nightmare, since it blocks its release and reduces aldosterone release to effectively lower blood pressure and volume. Too much blood means the body will try to dry things out a bit.


Bad mood; annoyance OR pretty gross green substance

Bowman's Capsule

The filtered stuff (the proteins, ions, nutrients) from the blood enters Bowman's capsule, a hollowed out space where pee starts to look like pee.


An animal that just relies on eating other animals for its nutrition. If you offer one a salad, even if it's drenched in Ranch dressing and bacon bits, it will be more interested in munching on you instead.


Organisms, including bacteria, which get all their energy through biological reactions, like moving electrons around. When they get a little low on energy, they're not looking to call the local pizza place.

Chief Cell

Present in the stomach, chief cells secrete pepsinogen, which is converted into pepsin once it joins the acid pool party in your tummy.


Hormone secreted when fats and amino acids hit the small intestine. It stimulates the release of bile so the fats can finally get digested. Breaking down fats, it might as well be the body's personal trainer—complete with neon stretch pants and some Cyndi Lauper on the Walkman.


Water-soluble groups of triglycerides (groups of three fatty acids), formed within the epithelial cells of the small intestine. They are too large to pass into the blood stream directly, so they sneak in through the back door via the lymphatic system before making their way back to the blood.


Essentially "food goo." Chyme is what kicks around in your tummy early on in the digestion process. It's a joyous mixture of gastric juices and partially digested food. Don't be embarrassed; everyone has partially digested goop in his or her stomach at some point.

Collecting Duct

At the collecting duct, the filtrate's trip is almost complete. This is the nephron's last-ditch-effort to conserve water and salt before the filtrate leaves the body as urine. Antidiuretic hormone increases water permeability here.


Whether we are talking about the kidney or the brain, the cortex is the outer part of the organ. But here we're all about the kidneys, and the outer cortex for that pink pair of organs is where the majority of the nephron is located.

Countercurrent Multiplier System

The teamwork of salt, water, and both the up-and-down portions of the Loop of Henle causes hyperosmotic medullary (see medulla) interstitial fluid. Its ultimate goal is to create concentrated urine. Some folks want to be astronauts; others want to create concentrated urine. Either way, it's good to have goals.


The process by which food is broken down into simple compounds that can be taken up by the blood stream or used by cells. Digestion primarily takes place in the small intestine where carbohydrates, proteins, and fats are broken down into sugar, amino acids, and fatty acids so they can be sucked up by the body and put to good use. It's the reason we're all able to do what we do, and it's the reason you get to enjoy a greasy slice of pizza whenever your stomach starts growling.

Distal tubule

After the ascending Loop of Henle, filtrate flows into the distal tubule where K+ and NaCl concentrations are regulated.

Essential Amino Acids

Small nitrogen-containing compounds that are an essential component in forming protein, but like essential nutrients, they need to be obtained via the diet. There's no magic button hidden deep in your small intestine to make the amino acid valine, so listen to your mom the next time she orders you to eat those beans. She's not just a great cook; she's got your back.


Fluid that ultimately becomes urine. Consider it "pre-pee." The filtrate flows through the tubules of the nephron (part of the kidney) until it gets to the ureter, the tube that connects the kidney to the bladder where it awaits excretion.


Hormone secreted when peptides reach the stomach. Gastrin stimulates the stomach's parietal cells to produce HCl (that's hydrochloric acid) and aid in digestion.


When this stomach-released peptide reaches the brain, it stimulates hunger, making high calorie foods extremely appealing. We may be dating ourselves here at the Shmoop mothership, but one way to remember what ghrelin does is to think back to the 1980s cult classic, Gremlins. Don't worry; you can still eat after midnight with only heart burn to show. Just don't feed the gremlins.


These are blood vessels at the beginning of the nephron that are surrounded by Bowman's capsule. Blood is filtered through these blood vessels in the first step in making urine.


An organism that only eats tissue from autotrophic organisms, like plants and algae. Some examples of herbivores include members of the bovine family, like cows, bison, antelope, and sheep; members of the deer family, like moose, reindeer, and elk; and many insects, like leaf beetles, lady bugs, and aphids.


An organism that relies on ingesting food and carbon compounds to provide essential energy. We're talking about animals, people, basically anything that has to get its energy by ingesting food. This is opposed to plants, which can whip up their energy straight from the sun.


A solution that has a higher osmolarity than normal body tissue. If the membrane is permeable to water, it will flow into this solution in an effort to dilute it. Water always wants to go where it's needed most. Like Superman.


A solution that has a lower osmolarity than normal body tissue. When a solution is hypoosmotic, it will lose water to other solutions, making it more concentrated.


The medulla is the inside part of the kidney, where a journey within the Loop of Henle will take you.

Inorganic compounds

Compounds, like sodium chloride (NaCl), that lack the carbon atom. If it's got a carbon atom, the compound is organic.


Hormone released by fatty tissues that acts as an appetite suppressant when it reaches the brain. Leptin lowers hunger, and it's the thing that tells you that you really don't need another lap around the buffet.

Loop of Henle

The Loop of Henle is not some hot new indie band. Instead, it's a region of the kidney that makes a "U" shape. The descending part of the Loop is selectively permeable to water so filtrate osmolarity builds up. After the actual Loop, NaCl is selectively permeable in the ascending Loop, and osmolarity decreases. The Loop of Henle is critical in water conservation.


Part of the kidney that is responsible for excretion and urine production. There are millions of nephrons in each vertebrate kidney, and each nephron contains 6 parts: the glomerulus, Bowman's capsule, the proximal tubule, the Loop of Henle, a distal tubule, and the collecting duct.


These animals will eat both plants and animals to get all of their nutritional requirements. They get their name from the Latin phrase "omni," which means "all." Despite the fancypants Latin origin, we're pretty sure they aren't eating shoelaces and sunglasses for their high protein content.


The measure of solute concentration. For reference, blood's osmolarity is usually around 300 mOsm/L. It measures those compounds that become dissociated in water (like NaCl) and those that don't (like glucose).


Cell type within the brain's hypothalamus that sense changes in blood osmolarity. If blood is hyperosmotic, these cells will cause ADH release to decrease blood osmolarity to a set point.


The process by which solute and water concentrations are regulated to make sure everything stays in just the right ratio. Osmoregulation primarily takes place in the good ol' kidney.

Parietal Cell

These cells are present in the stomach and secrete HCl, making that acidic environment that's the perfect place for enzymes to break down chyme.

Passive Transport

A digestive process that allows nutrients to be absorbed without requiring the body to burn energy in the process. When separated by a permeable membrane, nutrients will flow down their concentration gradient (that is, from high concentration to low concentration) with passive transport. Think of it like a ball rolling down a hill.


Produced by the stomach's chief cells, these peptide-digesting enzymes break proteins down into smaller amino acids. Pepsin works only in acidic conditions, so it's mighty convenient that those parietal cells are handy to make a nice acidic pool for pepsin to work its magic.


Organisms who obtain their energy from the light, such as plants, trees, and glow-in-the-dark t-shirts.

Proximal Tubule

A part of the vertebrate nephron, where filtrate flows after the Bowman's capsule. At this stage, nutrients and other substances are reabsorbed from the filtrate back into the interstitial fluid, where they will return to the blood stream.


Hormone stimulated by high blood volume and/or pressure. Renin is produced in the juxtaglomerular apparatus (that's a real thing, it's in the beginning of the nephron) and stimulates the synthesis of angiotensin II. It is the first step in the renin-angiotensin II-aldosterone system (RAAS), which tells the blood volume to cool it and settle down.


When acidic chyme makes it way to the small intestine, secretin is released to stimulate the release of HCO3 to buffer the chyme to a more neutral pH, after it got itself all coated in acid in the stomach.

Vasa recta

Blood capillaries that follow the kidney's Loop of Henle, providing it with essential oxygen and nutrients. These blood vessels also help maintain the countercurrent multiplier system by preventing a washout of the medullary concentration gradient.

Roots of Common Terms in Animal Nutrition and Digestion


L = Latin, G = Greek


G: chole= "bile"; cysto = "sac"; kinin = "move"


L: diūrēticus; G: diourētikós = "to urinate"


G: gastr = "stomach"


G: huper = "over, above" 


G: hupo = "under" 


G: leptos = "thin"


L: omni = "all"


G: pepsis = "digestion"


G: photo = "light"; troph = "nutrition")

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