Chapter 8: Gastrointestinal Digestive System Terminology

Mouth

or/o, stomat/o

Pharynx

pharyng/o

Esophagus

esophag/o

Stomach

gastr/o

Small Intestine

enter/o

Large Intestine

col/o, colon/o

Rectum and Anus

an/o, proct/o, rect/o

Liver

hepat/o

Gallbladder

Gallbladder

Pancreas

pancreat/o

an/o

anus, ring

chol/e

bile, gall

cholecyst/o

gallbladder

col/o

colon, large intestine

colon/o

colon, large intestine

-emesis

vomiting

enter/o

small intestine

esophag/o

esophagus

gastr/o

stomach, belly

hepat/o

liver

-lithiasis

presence of stones

-pepsia

digest, digestion

-phagia

eating, swallowing

proct/o

anus and rectum

rect/o

rectum, straight

sigmoid/o

sigmoid colon

Gastrointestinal tract

often called the GI tract is the long continuous tube of organs that forms the main part of your digestive system. The name breaks down simply, with "gastro" meaning stomach and "intestin" meaning intestine. This main tube works together with a few extra helper organs to process everything you eat.

Upper gastrointestinal (GI) tract

is the top portion of your digestive system made up of your mouth, throat, esophagus, and stomach. Its main job is to act as the entryway and highway for everything you swallow. It moves food down into your body and holds it right up until the process of digestion officially begins in the stomach.

lower gastrointestinal (GI) tract

often just called the bowels is the bottom portion of your digestive system made up of the small intestine, large intestine, rectum, and anus. This section takes over to finish up the entire process of digesting food and absorbing its nutrients. Once that job is done, it packages up all the leftover waste so your body can push it out.

Accessory organs

are a team of extra helper organs specifically the liver, gallbladder, and pancreas that support your main digestive tube. Even though food never actually passes through them, they create and store crucial chemicals like bile and enzymes. They pump these special fluids into your gut to help break down and process your food.

Oral cavity

plainly known as your mouth is the main opening where your digestive system begins. It is built from several key structures, including your lips, tongue, teeth, periodontium (the supporting gums and bone), and the hard and soft palates on the roof of your mouth. Together with the salivary glands, these parts work as a team to taste, break down, and lubricate food so you can easily swallow it.

The lips

also medically known as the labia are the fleshy structures that border and form the outer entrance to your mouth. During eating, they work alongside your cheeks and tongue like a sealed gate to keep food inside your mouth while you chew. Beyond eating, your lips play major roles in guiding airflow for breathing, shaping sounds so you can speak, and displaying facial expressions to convey emotions.

Hard palate

is the firm, bony roof toward the very front of your mouth right behind your teeth. It is covered in a specialized, durable lining called a mucous membrane that helps protect the mouth from constant rubbing and friction. This rigid structure acts as a solid surface so your tongue can comfortably press and mash food while you chew.

Soft palate

is the flexible, fleshy roof toward the back of your mouth right behind the hard palate. When you swallow, it sweeps upward like a trapdoor to seal off the back of your nasal passage. This key movement prevents food and liquids from accidentally shooting up into your nose while you eat or drink.

Uvula

is that little teardrop-shaped piece of tissue hanging down from the middle edge of your soft palate at the back of your throat. During swallowing, it swings upward right along with the soft palate to help seal off your nasal passage. It also plays a key role in helping shape certain speech sounds and vibrating to create the sound of snoring when you sleep.

Tongue

is a super strong, flexible muscle that stays firmly anchored at the back of your mouth while the front part moves around freely. This clever design lets it act like a built-in spatula to push food around while you chew and help you swallow. It also acts as your body's master talker, shifting shapes constantly to form clear sounds and words when you speak.

Upper surface

of the tongue medically called the dorsum is the top side of your tongue covered by a tough protective layer. It is covered in tiny bumps called papillae, which house your taste buds. These specialized sensory receptors allow you to detect different flavors every time you eat or drink.

Sublingual surface

of the tongue refers to the delicate underside of your tongue and the tissues directly beneath it. The term "sublingual" literally means under the tongue, and this area is lined with extremely thin tissue. Because it is highly vascular meaning packed with tons of blood vessels it can quickly absorb certain medications directly into your bloodstream.

Lingual frenum

is a small band of tissue located right under the middle of your tongue that connects it to the floor of your mouth. Its main job is to anchor your tongue in place while acting like a safety tether to limit how far it can move. This prevents your tongue from sliding too far back or moving around wildly, keeping it stable when you eat and talk.

Periodontium

refers to all the structures that surround, support, and attach your teeth to your mouth, with "peri" meaning surrounding and "odonti" meaning teeth. This support system consists of both the solid jawbone of your dental arches and the surrounding soft tissues. Together, they act like a sturdy anchor system that holds your teeth tightly in place while you bite and chew.

Gingiva

more commonly known as your gums is a tough, specialized layer of mucous membrane that covers the jawbone in your mouth. It fits snugly and hugs tightly around the base or "neck" of each individual tooth like a protective collar. This tight seal acts as a barrier, safeguarding the underlying bone and tooth roots from bacteria and the daily friction of chewing.

Sulcus

is a tiny, shallow gap or pocket located between the surface of a tooth and the surrounding gum line. Because it acts like a little groove around the base of the tooth, food debris and bacteria can easily get trapped inside it if not brushed away. If that buildup sits in the sulcus for too long, it can lead to gum irritation, inflammation, and infection.

Dental arches

are the curved, bony structures located inside your mouth that make up your upper and lower jaws. Their main job is to act as a sturdy framework that holds all of your teeth firmly in place so they don't shift around. This solid setup gives your teeth the stable foundation they need to successfully crush food when you chew and help you speak clearly.

Maxillary arch

commonly known as your upper jaw is made up of the bone structures that form the lower part of your skull. Unlike your lower jaw, this arch is permanently fused to your skull and does not move at all when you open or close your mouth. Instead, it stays completely stationary while your lower jaw does all the moving work against it.

Mandibular arch

commonly known as your lower jaw is a single, separate bone attached to the base of your skull. It is the only part of your entire skull and jaw structure that can actually move around. Thanks to its flexible joints, it hinges up, down, and side-to-side so you can chew your food and talk freely.

Temporomandibular joint

commonly called the TMJ is the special hinge that connects your upper and lower jaws together right near the back of your mouth. It sits right where your fixed upper jaw (the maxillary arch) meets your moving lower jaw (the mandibular arch). This handy joint acts just like a door hinge, letting your jaw smoothly swing open, close, and slide around every time you speak or chew.

Dentition

is just the medical word for your full set of natural teeth arranged in your upper and lower jaws. Your front teeth called incisors and canines act like sharp little tools designed specifically for biting into and tearing your food. Meanwhile, your back teeth called premolars and molars use their flat surfaces as a heavy-duty grinder to crush and chew everything down into small, swallowable pieces.

Primary dentition

is the official medical name for your first set of 20 natural teeth, commonly known as your baby teeth. They come in during early childhood to help you chew and speak, then naturally fall out later in childhood to make room for your permanent adult teeth. This initial set includes eight incisors, four canines, and eight molars, but completely leaves out premolars.

Permanent dentition

is your complete set of 32 adult teeth that come in to replace your 20 baby teeth and add 12 extra back teeth to last you a lifetime. This adult set includes eight incisors, four canines, eight premolars, and 12 molars designed for biting, tearing, and grinding up your food. The very last of those molars to pop up at the way back of your jaw are your four wisdom teeth.

Crown

is the top part of your tooth that you can actually see poking out above your gums when you smile. It is completely coated in a super-tough armor called enamel, which is officially the hardest substance in the entire human body. This invincible outer layer protects the sensitive inside of your tooth from daily wear and tear every time you bite down on food.

Roots

are the hidden bottom portion of your tooth that anchors it deeply into your jawbone so it stays firmly in place. These buried roots are covered and protected by a specialized, bone-like layer called cementum. While cementum is quite tough and hard, it isn't quite as indestructible as the shiny enamel found on the top of your tooth.

Cervix

also known as the neck is the slightly narrowed area where the visible crown and the hidden root meet. It sits right at the gum line, serving as the anatomical transition zone between the top and bottom portions of the tooth. (As a side note, the term "cervix" simply means neck, which is why it is also used in female anatomy to describe the neck of the uterus.)

Dentin

is the hard, bone-like material that makes up the main bulk and inner core of your entire tooth. The part of this dentin that sticks up above your gums is safely covered by shiny enamel. Meanwhile, the part of the dentin hidden down in your roots is covered and protected by cementum.

Pulp cavity

is a hollow space tucked right inside the center of your tooth, completely surrounded by the hard dentin layer. Its main job is to safely cradle and protect the soft, delicate pulp tissue, which contains all the vital blood vessels and nerves. As this inner space travels down into the roots of your tooth, it narrows and stretches out into tiny tunnels known as root canals.

Saliva

is the clear fluid in your mouth that acts like a natural moisturizer to keep everything soft, wet, and healthy. It gets digestion started by coating and lubricating your food while you chew, making it easy and smooth to swallow. On top of that, it contains a special enzyme called amylase that begins chemically breaking down starches before the food even reaches your stomach.

Parotid glands

are the largest saliva-producing glands in your body, sitting on your face just in front of each ear. They pump fresh saliva into your mouth through small tubes that open on the inside of your cheeks right near your upper back molars. This extra splash of liquid helps keep your mouth wet and starts breaking down food while you chew.

Sublingual glands

are tiny saliva glands tucked away directly under your tongue on the floor of your mouth. Their small tubes, or ducts, open up underneath the front of your tongue to continuously release saliva. This steady stream of moisture helps keep your mouth lubricated and makes it easier to chew and swallow your food.

Submandibular glands

are walnut-sized saliva glands located toward the back of the floor of your mouth, right along your lower jawbone. Their tiny ducts run forward and open up underneath the front of your tongue to release a major supply of saliva. This constant release of liquid keeps your mouth well-moistened and helps break down food every time you eat.

Pharynx

called the throat serves as a shared hallway for both the air you breathe and the food you eat. It plays a crucial role in deglutition, which is simply the official medical term for the act of swallowing. Every time you swallow, a flap-like structure called the epiglottis snaps shut over your windpipe so food and liquid go down into your stomach instead of into your lungs.

Esophagus

is a muscular, sliding tube that acts like a food chute connecting your throat straight down to your stomach. Whenever you swallow a bite of food, its muscular walls squeeze and relax in a wave-like motion to push the meal safely downward. This clever delivery system ensures your food gets right where it needs to go without getting stuck along the way.

Lower esophageal sphincter

or cardiac sphincter, is a muscular ring that acts like a one-way trapdoor between your esophagus and stomach. When you swallow, this ring relaxes to let food pass safely into your stomach, then snaps tightly shut immediately after. Closing tight is crucial because it stops stomach acids and food from flowing backward or regurgitating up into your throat.

Stomach

is a large, stretchy, sac-like organ that holds your food and gets to work breaking it down after you eat. Its upper rounded part is called the fundus, the big middle section is known as the body, and the lower section is the antrum. Together, these three parts work as a holding tank that mixes up your meals before sending them further along your digestive tract.

Rugae

are the stretchy, accordion-like folds lining the inside wall of your stomach. They unpack and flatten out to let your stomach expand when you eat a big meal, then fold back up when it empties out. Tucked inside these exact folds are tiny glands that pump out powerful gastric juices to break down your food.

Gastric juices

are a powerful liquid mix of enzymes and hydrochloric acid that start dissolving your food into a liquid soup. Because this acid is strong enough to harm tissues, special glands in your stomach secrete a thick layer of mucus as a shield. This slimy protective coating coats the inside wall of your stomach so the harsh acid doesn't eat away at your own stomach lining.

Pyloric sphincter

is a muscular ring located right at the very bottom exit of your stomach. It acts like a strict security gate that opens and closes to control how fast food leaves your stomach. By letting out only small squirts of partially digested food at a time, it makes sure the small intestine doesn't get overwhelmed.

Pylorus

is a short, narrow tunnel that acts as the final exit hallway at the bottom of your stomach. It forms the direct bridge connecting your stomach cavity to the start of the small intestine. Everything your stomach digests has to squeeze through this tight passage before continuing its journey.

Small intestine

is a long, folded tube that stretches from the bottom of your stomach all the way to your large intestine. Even though it is called "small," it is actually a massive 20 feet long and wound up tightly inside your belly. This is where the magic happens, as it finishes digesting your food and sucks all the important nutrients right into your bloodstream.

Three sections of the small intestines are

duodenum is the short first section of your small intestine that hooks directly up to the exit of your stomach. Next comes the jejunum, which makes up the middle portion where most of your digested food nutrients get absorbed. Finally, the ileum is the longest and final segment that finishes absorbing nutrients before dumping what's left into the large intestine.

Large intestine

is a wider tube that stretches from the end of your small intestine all the way down to the anus, though it is much shorter in length. Even though it is only about a fourth as long as the small intestine, it is twice as wide and handles processing all your leftover food waste so it can leave the body. Its major parts include the cecum, colon, rectum, and anus, which all work together to prep and handle waste before excretion.

Cecum

is a small, pouch-like pocket sitting on the lower right side of your belly that acts as a meeting point for your digestive tract. It forms the bridge where your small intestine (the ileum) ends and your large intestine (the colon) officially begins.

Ileocecal sphincter

is a circular band of muscle that acts as a one-way doorway between your small and large intestines. It sits right where the ileum ends and the cecum begins to regulate the passage of digested material. By opening up to let waste through while staying tightly shut the rest of the time, it stops anything from backing up into your small intestine.

Vermiform appendix

called the appendix is a tiny, slender tube that dangles off the bottom of the cecum pouch. The word "vermiform" simply means it has a strange, worm-like shape that hangs down in your lower right abdomen. Even though it is part of your body's immune system tissue, it doesn't play a main role in digesting your food.

Colon

is the longest part of the large intestine and is split into four distinct sections to guide waste along. It starts with the ascending colon traveling upward, passes across the body as the transverse colon, and heads down the left side via the descending colon. Finally, it wraps up with the S-shaped sigmoid colon, which curves gracefully like the letter S to connect straight into the rectum.

Rectum

is the widest section at the very end of your large intestine, measuring about four inches long. It acts like a storage holding tank that collects solid waste right before it is ready to leave your body. This final stretch ends right at the anus, completing the journey through your digestive system.

Anus

is the final lower opening of your entire digestive tract where solid waste leaves your body. The release of this waste is tightly controlled by two powerful muscle rings called the internal and external anal sphincters. Working together, these muscles stay closed until you are ready to use the bathroom, ensuring your body maintains full control over waste elimination.

Accessory organs

are special helper parts that play a huge role in digestion even though food never actually travels directly through them. Instead, they sit right next to the main digestive tube and pump out important juices and chemicals to help break everything down. The main players that make up this helper team are your liver, gallbladder, and pancreas.

Liver

(hepat) is the body's largest organ that acts as its main fuel manager and filter, cleaning toxins from your blood while saving extra sugar (as glycogen) to release whenever your energy gets low. It also makes a digestive juice called bile(chol/e), which gets stored in your gallbladder to help break down the fats you eat. Lastly, it breaks down old blood components to make a yellowish pigment called bilirubin, which leaves the body through bile so it doesn't build up and make your skin turn yellow (jaundice).

Biliary tree

(bile) The network of vessels and ducts that carries bile from the liver and gallbladder into the small intestine to assist with digestion. Tiny channels inside the liver collect bile and flow together to form the common hepatic duct outside the liver. This fluid travels through the cystic duct into the gallbladder for storage and out again into the common bile duct, where it finally empties into the duodenum alongside pancreatic digestive juices.

Gallbladder (Cholecystic)

A small, egg-sized, pear-shaped pouch located beneath the liver that stores and concentrates bile until it is needed for digestion. When you eat, this organ contracts to squeeze the concentrated bile out through the biliary tree and into the small intestine. Cholecystic (cholecyst means gallbladder, and -ic means pertaining to).

Pancreas (Pancreatic)

A soft, six-inch-long gland positioned behind the stomach that plays essential roles in both the digestive and endocrine systems. In digestion, it creates and releases specialized juices filled with enzymes to break down food and sodium bicarbonate to neutralize harsh stomach acid. These digestive fluids travel out through the pancreatic duct, joining the common bile duct right before entering the small intestine.

Digestion

The biological process of breaking down complex food into basic nutrients that the body can absorb and use for energy, growth, and cell repair. Food flows sequentially through the digestive system as organs work together to mash, chemically alter, and extract useful components from what you eat. Whatever the body cannot convert into usable fuel is filtered out and eventually excreted as waste.

Digestive enzymes

are specialized substances that trigger chemical changes to break complex foods down into simpler nutrients. By acting like biological scissors, they chop food into small pieces that your body can easily absorb and use for energy. Without them, your body wouldn't be able to turn what you eat into usable fuel.

Nutrient

is a substance from food necessary for the body to function, categorized into macronutrients (carbs, fats, and proteins that provide energy-supplying calories) and micronutrients (vitamins and minerals required in small amounts).

Metabolism

(metabol means change, and -ism means condition). is the condition of change that includes all the processes your body uses to handle and utilize nutrients, consisting of two parts

Absorption

is the process where fully digested nutrients are picked up and transported to cells all over your body. Once food is broken down into simple pieces, your body takes them in and moves them into your bloodstream. This delivery system ensures that every single cell gets the vital supplies it needs to function.

Villi

the inner lining of your small intestine is covered in tiny, finger-like projections that contain blood vessels and lacteals. These internal blood vessels absorb digested nutrients directly from your digestive tract into your bloodstream. From there, the bloodstream quickly delivers these vital nutrients to every single cell in your body.

Lacteals

are specialized lymphatic structures that absorb bulky fats and fat-soluble vitamins which cannot travel through regular blood vessels. They transport these nutrient packages through lymphatic vessels while lymph nodes filter them clean along the way. Finally, these filtered fats are delivered safely into the main bloodstream for the body to use.

Mastication

as chewing, is the physical process of breaking food down into smaller pieces using your teeth. At the same time, it mixes these food fragments with saliva to lubricate them thoroughly. This combined mechanical action turns your food into a soft mixture that is fully prepared for safe swallowing.

Bolus

is a rounded mass of chewed food that has been mixed with saliva and is ready to be swallowed. In medicine, this exact same term also refers to a concentrated dose of medication or liquid nutrition given all at once. Whether food in your mouth or medicine in a clinic, a bolus is simply a single, compact package ready for delivery.

Peristalsis

Food moves downward through the esophagus into the digestive system using a combination of gravity and peristalsis. Peristalsis is a series of wave-like contractions of smooth muscles moving in a single direction to push food forward. This automatic muscular motion ensures that food travels steadily along your digestive tract no matter your body position.

Role of stomach

continues breaking down food using gastric juices that contain hydrochloric acid and digestive enzymes. During this process, very few nutrients pass directly through the stomach walls into the bloodstream. Instead, its primary function is to act as a chemical mixing chamber that melts food down before it moves further along the digestive tract.

chyme

The physical churning action of the stomach works alongside gastric juices to turn solid food into a thick, soupy mixture called chyme. Once this semi-fluid blend is fully formed, it moves out of the stomach and passes through the pyloric sphincter valve. Finally, this mixture enters the small intestine so that the next stage of digestion and nutrient absorption can take place.

Duodenum

chyme mixes with pancreatic juice and bile so that large fat globules can be broken apart into smaller droplets. This crucial process of breaking down fats is called emulsification, which allows digestive enzymes in the pancreatic juice to successfully do their job. This entire preparatory step must be fully completed right here in the first part of the small intestine before any fat nutrients can be absorbed into the body.

Jejunum

is the middle section of the small intestine that takes over after food leaves the duodenum. In this region, the lining secretes large amounts of digestive enzymes to actively continue breaking down nutrients. This ongoing chemical processing ensures that food is thoroughly broken down into smaller components ready for absorption.

Ileum

is the final and longest section of the small intestine. Its primary function is to absorb remaining nutrients, vitamins, and bile salts from the digested food. Once this final absorption phase is complete, it passes the leftover waste material onward into the large intestine.

Role of large intestine

The large intestine receives leftover waste products from digestion and stores them until they are eliminated from the body. As this waste moves along, its walls reabsorb excess water back into the body to maintain proper fluid balance. The remaining solid material then forms into feces, which are safely stored until elimination occurs.

Feces

also called stool or solid body waste, consists of the leftover material that remains after digestion and water absorption are complete. This solid waste is held temporarily in the lower portion of the digestive tract until it is ready to leave the system. Finally, the body expels the feces out through the rectum and anus to complete the digestive process.

Defecation

also called bowel movement, is the physiological process of evacuating and emptying solid waste from the large intestine. During this final stage, the body coordinates muscular contractions to push stored waste through the rectum. This process successfully expels the waste material from the body to conclude the entire digestive journey.

Gut microbiota

refers to the billions of bacteria living in the large intestine that protect the body against infection and help maintain the immune system. Ongoing scientific studies continue to explore how these microorganisms are linked to various physical and mental health conditions. This internal community plays a vital role in keeping your overall body systems balanced and functioning properly.

Borborygmus

for the rumbling or gurgling noise caused by the movement of gas and fluid through the intestines. These distinct sounds happen as pockets of air and liquid are pushed along by muscular contractions in your digestive tract. It is a completely normal part of digestion, often becoming louder when your stomach is empty and gas has more open space to echo.