Following the Body’s Connections: Its Words, Its Routes, and Its Big Ideas
by Professor Stephen T. Abedon Steve Abedon, Ph.D., has taught well over 100 individual classes and ~10 individual courses (including introductory biology, microbiology, physiology, biochemistry, etc.) over his 30+ years as a college professor. He has over 150 publications, including multiple monographs, and is ranked in the top 1 or 2 percent among researchers of all disciplines worldwide. His research focuses on bacteriophage biology and phage therapy. (abedon.1@osu.edu)
phage.org | phage-therapy.org | biologyaspoetry.org | abedon.phage.org | google scholar | publications
Jump to: 📋 Overview | 🔎 Explore | 🛤️ Trace a Route | ✂️ Cut or Block | 🔤 Word Parts | 🧭 Directions and Regions | 🧅 Layers | 💪 Muscles and Bones | 📨 Hormones | 💡 Big Ideas | 🐀 Human and Specimen | 🎯 Practice | 🧾 About the Data | 🧮 More Calculators
biologyaspoetry.org/laboratories/anatomy/ · Abedon’s Books
How can I improve this page? contact: anatomy@biologyaspoetry.org
Anatomy is the study of the structure of the body: what its parts are, where they are, and how they are put together. A first course in human anatomy asks you to learn several thousand names, which can feel like memorizing a telephone book. Two facts make the job smaller than it looks.
The first fact is that the names are built from parts. Brachiocephalic looks like one long, strange word, but it is three short ones: brachio- (arm), cephal (head), and -ic (having to do with). The brachiocephalic trunk is the artery that supplies the right arm and the right side of the head. A few hundred word parts, mostly Greek and Latin, build most of the names you will meet, and once you know a part you know it in every name that uses it.
The second fact is that the structures are connected. A vessel carries blood from one place to the next; a nerve runs to particular muscles; a duct empties into a particular part of the gut. A list of names gives you no way to check yourself, but a set of connections does: if you know where blood goes after the left ventricle, and where it goes after that, you can work out a route you have never seen written down.
Every name, description and connection in this laboratory’s data files was written by an AI (Claude, made by Anthropic) and has not been checked by a person. The data were written to the level of a first college course in human anatomy, using the names and conventions most textbooks use, and the page runs automatic checks on them. Those checks can catch a route that leads nowhere, but not a route that leads somewhere wrong.
Use this page to practice and to see how the pieces fit together, and treat your textbook, your instructor and your laboratory specimen as the authorities. Where they disagree with this page, they are probably right. Every structure’s description ends with a link for reporting a problem, and the About the Data tab says more about what was checked and how.
Here are three kinds of connection that this laboratory follows, from the most literal to the least.
Every structure named on the page is a link. Click one to see what it is, where it sits, and what it is connected to; each of those is a link in turn, so you can walk through the body one connection at a time.
Your answers are kept as you go. In most browsers they are still here if you leave and come back on the same device, though a private window, a different device, or cleared browser data will start you fresh. When you are done, download a summary to hand in or keep. It lists your answers and, for each, whether it was right the first time.
Choose an organ system, or type part of a name, and pick a structure. Its card says what it is and where it sits, then lists everything it connects to: where blood or air or food comes from and goes next, which nerve runs it, what it is part of and what its parts are. Every name in a card is a link, so you can walk from one structure to the next.
Here are the five parts of a structure’s card, from the top down.
The dot on the body figure shows roughly where the structure is. The figure is a guide to position, not a drawing of the structure: a dot on the abdomen marks a kidney even though the kidneys lie toward the back.
Choose what moves, where it starts and where it ends, or click a suggested route. The page finds the route in the data, lists each structure along the way and draws it on the body.
The structures along part of a route are shuffled below. Click them in the order in which they are passed, from first to last, then press Check. Click a structure you have placed to take it back.
Blood is always red. It is bright red when it carries a lot of oxygen and a darker red when it carries less, because hemoglobin, the protein in red blood cells that carries oxygen, changes color slightly as it picks oxygen up and gives it off. Diagrams draw oxygen-rich blood in red and oxygen-poor blood in blue to make the difference easy to see, and this page does the same.
Blood changes from one to the other in the capillary beds, the networks of tiny vessels where materials pass between the blood and the tissues around it. In the capillaries of the body’s organs and muscles, blood gives up some of its oxygen and picks up carbon dioxide, so it leaves them oxygen-poor. In the capillaries of the lungs, blood picks up oxygen and gives off carbon dioxide, so it leaves them oxygen-rich. “Oxygen-poor” does not mean empty: blood returning to the heart still carries a good share of its oxygen, just less than it set out with.
Arteries are named for the direction in which they carry blood, away from the heart, not for how much oxygen the blood holds; veins carry blood toward the heart. Most arteries carry oxygen-rich blood, but the pulmonary arteries are the exception: they carry oxygen-poor blood from the right ventricle to the lungs. The pulmonary veins, in turn, bring oxygen-rich blood from the lungs back to the left atrium. Before birth the lungs are not yet in use and the placenta takes their place, so the umbilical vein carries oxygen-rich blood toward the fetus’s heart.
How the page decides: blood leaving the lungs (or, before birth, the placenta) is drawn red until it passes through a capillary bed somewhere else; blood leaving any other capillary bed is drawn blue. The glomerulus of the kidney is treated as an exception, because blood leaves it through an arteriole with most of its oxygen still on board. Before birth, oxygen-rich and oxygen-poor blood partly mix inside the heart, so there the two colors are a simplification.
The data list connections, one at a time: each one says that something moves directly from one structure into another (blood from the left ventricle into the aorta through the aortic valve, for example). A route is a chain of these connections. The page looks for the chain with the fewest steps, using these three rules.
The route shown is the one that the data’s connections allow; it is not a claim about how much blood actually takes it. Blood leaving the heart goes into every branch of the aorta at once, and where two routes are equally short the page shows only one of them. Use By way of to make the route pass through a structure of your choosing.
Choose a scenario, a structure or a spinal nerve root. The page works out from the data what depends on it: muscles that lose their nerve, tissues that lose their blood or cannot drain, bones that come loose, and hormones that are lost.
Signals from the eyes reach the brain by a pathway that partly crosses over. The diagram shows it from above, with the eyes at the top: the person’s left is on your left. Click a ✂ to cut the pathway there and see what each eye can still see.
Colors in the diagram:fibers carrying what you see on your leftfibers carrying what you see on your right. Gray marks fibers whose signals no longer arrive.
The rule behind every pattern: light from the left half of what you see falls on the right half of each retina, and fibers from the right half of each retina end on the right side of the brain. To get there, fibers from the inner half of each retina (the half nearer the nose) cross to the other side at the optic chiasm; fibers from the outer half do not cross. So each side of the brain sees the opposite half of the world, with both eyes.
A cut rarely affects only the structure that was cut. Here are the four ways its effects spread.
A real body often does better than these rules suggest, because small connections, other nerves and other glands can take over part of the work. The page shows what the data’s connections imply, not how much function a particular person would keep.
Type an anatomical word, or choose one of the suggestions that appear as you type, and see the pieces it is built from. Each piece is a prefix (a beginning), a root (the core of the meaning) or a suffix (an ending); the last section on this tab explains them. You can also choose a structure and take its whole name apart, one word at a time. The figure marks the structures that carry the word in their names.
The box gives the literal meaning of a word, piece by piece. Click the pieces that build the word, in order, then check your answer. If you are stuck, show the meaning of every piece and choose by meaning.
Here is every word part in the data, with its meaning, the language it came from (where the data say), and a few words that use it. Example words that name a structure are links to that structure. Type in the box to search forms and meanings at once: try heart or cardi.
Most anatomical names are put together from a few kinds of pieces. Here are the four, in the order they usually come in a word.
Before a suffix that begins with a vowel, the connecting vowel is usually dropped: the stomach root gastr plus -itis gives gastritis, not gastroitis. A long word is often easiest to read from its end. The suffix says what kind of word it is, and the pieces before it say what it is about: pericardium is peri- (around) + cardi (heart) + -um (a noun ending), the sac around the heart.
Anatomy borrowed from both Latin and Greek, so many body parts have two roots, one from each language. Here are three pairs. As a loose rule, the names of structures often use the Latin root and many medical terms the Greek one, but there are plenty of exceptions.
Underlined words in this section are in the data’s word list; click one to take it apart at the top of the tab.
Every direction word in anatomy assumes that the body is in one standard pose, called anatomical position. Here are its five parts.
The direction words keep their meaning whatever the body is actually doing. A person lying face down is still described as if standing in anatomical position, so the back is still the posterior side, even though it now faces the ceiling.
Right and left always mean the person’s own right and left, never yours. In a front view, like the figure, the person faces you, so the person’s right is on your left; the R and L at the top of the figure are the person’s. Click Back above the figure to turn it around: in a back view, the person’s right is on your right.
Directional terms say where one structure is compared with another, always with the body in anatomical position. Most come in pairs of opposites: if the heart is superior to (above) the liver, then the liver is inferior to (below) the heart. Try the questions first; the table of terms is below them.
The page works out each answer from the data: from where the two structures sit on the figure, from their order along a limb or in a list of layers, or from statements in the data such as “the sternum is anterior to the heart”. It asks only when the answer is clear.
A plane is an imaginary flat surface that slices through the body, the way a knife slices a loaf of bread. Pictures in an anatomy book are often slices, so it helps to know which way each one was cut. Click a plane to see it on two figures, one from the front and one from the side.
Anatomy names the surface of the body by regions, each with a term, usually an adjective such as brachial, and an everyday word such as arm. Click a dot on the figure, or a term in the lists, to see both. Use Front and Back above the figure to turn it around; some regions can be seen from one side only.
The brain, the spinal cord and the organs of the trunk sit in closed spaces called body cavities, and the larger cavities hold smaller ones. Click a cavity to see the organs that the data place in it; the figure marks them.
To say where something is in the abdomen, the front of the abdomen is divided in one of two ways: into four quadrants, by two lines that cross at the navel, or into nine regions, by two vertical and two horizontal lines, like a tic-tac-toe grid. Right and left are the person’s own: in this front view the person’s right is on your left, so the right upper quadrant is at the upper left of the drawing. Click a quadrant or a region to list the organs the data place in it.
Much of the body is built in layers: the wall of a blood vessel, the wall of the gut, the skin, the coverings of the brain. Choose a set of layers, then press Peel the next layer to uncover them one at a time, in the order the title gives (usually from the outside in). The layer just uncovered shows its description; click any other layer to show its own. Each layer's name opens its card. Tick Ask me first to guess each layer before you see it.
The layers of one set are shuffled below. Click them in order, from the first layer the title names to the last. A click on a layer that comes later does no harm: the layer stays, and you try again. Each set you finish is recorded in Your Work, with the number of wrong clicks.
The body reuses a few plans with small changes. An artery and a vein have the same three layers, in different thicknesses; the esophagus, the stomach and the small intestine share four main layers, each adjusted for its job. Choose any two sets of layers to compare them side by side. Structures that appear in both are highlighted.
Anatomy courses usually ask four things about each muscle: its origin (where it starts), its insertion (where it ends), its action (what it does) and its nerve supply. Pick a muscle to see all four, read from the data.
The pulsing dot marks the muscle. The line runs from its insertion (circle) to its origin (square), the direction in which it pulls. Muscles and bones are drawn on the person’s right side, and the dots show rough position only.
Choose a joint and a movement to list the muscles that produce it, or choose a muscle to list the movements it produces. Muscles that produce opposite movements at the same joint, such as bending and straightening the elbow, are called antagonists. The lists show the main movers recorded in the data, not every muscle that helps.
Textbooks usually say that an adult has 206 bones. Here the number is not taken on trust: it is added up from the data, one group of bones at a time. Each bone in the data carries a count (how many of that bone the body has: ×2 means two, usually one on each side), a group (cranium, face, upper limb and so on) and a division. The axial skeleton is the body’s central column: the skull, the spine and the rib cage. The appendicular skeleton is the limbs and the girdles of bone that attach them to it.
A joint is a place where two bones meet. Joints are sorted in two ways. The structural class says what holds the bones together, and the functional class says how much the joint moves. Click a joint in the table to see both, with the bones that meet there and the muscles that move it.
Here are the three structural classes, from the least movable to the most.
And here are the three functional classes: a synarthrosis does not move, an amphiarthrosis moves slightly, and a diarthrosis moves freely.
Each question is made fresh from the data. Choose a kind of question, or take them as they come. Your answers are kept in Your Work, on the Overview tab, and the Practice tab mixes these questions with those from the other tabs.
A hormone is a chemical message carried by the blood. Every message has a sender, the gland or cells that release it, and receivers, the targets: cells that carry receptors that fit it. Choose where to start (a gland, a hormone or a target) and the page lists every connection in the data. On the figure, senders and receivers are marked in two different colors, named in the key below it. To see what happens when a gland is lost, remove it on the Cut or Block tab.
Some glands take orders from other glands. The hypothalamus, at the base of the brain, releases hormones that act on the anterior pituitary; the anterior pituitary releases hormones that act on other glands; and those glands release hormones that act on the rest of the body. Choose a starting hormone and press Next step to follow its chain one link at a time. Watch for hormones late in a chain that act back on an earlier gland and slow it down. That is negative feedback, which keeps a hormone's level from climbing without limit.
The body solves the same few problems over and over, and it often solves them the same way in organ systems that have nothing else in common. Choose an idea below to read it and see its examples; the figure marks every example at once, so you can see one idea turning up all over the body.
Each question shows one example, or three examples, with the words that name the idea hidden. Decide which big idea the example shows. The names of the structures are left in, since recognizing the idea from the structures is the point.
Most anatomy courses that include dissection use a small mammal rather than a human body. A rat or a fetal pig is small, inexpensive and easy to obtain, so every pair of students can have one of their own.
The substitute works because of how much we share with it. Humans, rats and pigs are all mammals, descended from a common ancestor, so their bodies are built on the same plan: the same organ systems, a heart with four chambers, a muscular diaphragm between the chest and the abdomen, and most of the same bones, muscles, nerves and vessels, usually under the same names. The differences are mostly in size and proportion, and in details that suit each animal’s diet and way of life.
The comparisons below cover the rat and the fetal pig because they are two of the most common choices. The specimen in your own course may be a different animal, and then some of these details will not apply to it; your laboratory manual is the guide to your specimen. Choose a topic to shorten the list.
Before birth, the lungs hold fluid rather than air, and a fetus gets its oxygen from its mother’s blood, through the placenta and the umbilical cord. A few vessels and openings found only before birth carry blood past the lungs and the liver. Soon after birth, as the lungs fill with air and the umbilical cord is cut, these shortcuts close, and what is left of each is usually a small dent or a cord of fibrous tissue. A fetal pig is a fetus, so its shortcuts are still open; an adult rat or an adult human has only what is left of them.
The directional terms of human anatomy were defined for a person standing upright in anatomical position. A rat or a pig stands on four legs, with its head forward and its back toward the sky, so two pairs of the human terms would point the wrong way. Anatomists who work with four-legged animals therefore use cranial and caudal for the head end and the tail end, and dorsal and ventral for the back and the belly. Those four words are tied to the body itself, so they point the same way in a human and in an animal.
Both bodies have the same two axes: head to tail (blue arrows) and back to belly (purple arrows). In a standing human the head-to-tail axis runs up and down; in a four-legged animal it runs from front to back.
Here are three more points that help at the dissecting table.
Choose your topics and press New question. Every question is worked out from the data files on the spot, so there is always another one; after a right answer, the explanation shows where the answer came from. Names in a question are links, and opening one does not count as an answer.
Here are three habits that research on learning supports, and that this tab is built to make easy.
A large review of ten common study techniques (Dunlosky and colleagues, 2013) rated practice testing and spreading practice out over time as the two most useful of the ten.
Two cautions. A question you got right only after a wrong try is worth another look later; the Your Work summary on the Overview tab lists which questions you got right on the first try. And a practice question checks what you can recall, not whether the data are right: the anatomy on this page was generated by an AI, so check anything surprising against your textbook.
The How to Study laboratory says more about studying this way.
The names, descriptions and connections were written by Claude, an AI made by Anthropic, at the level of a first college course in human anatomy. No person has checked them. An AI can state a wrong fact as confidently as a right one, and the errors it makes tend to be plausible ones: a vessel that drains into a neighbor of the right vein, a muscle credited to a nerve that runs nearby.
Your textbook, your instructor and your laboratory specimen outrank this page. If you find a disagreement, please report it; the address is at the bottom of this tab.
Why publish it anyway? Because the same data, right or wrong, can be checked in ways a list of names cannot. A route either reaches the heart or it does not; a muscle either has a nerve or it does not; the bones either add up to 206 or they do not. The page runs those checks on itself every time this tab opens, and each data file can be handed to another AI, or to a person, to be checked line by line.
The anatomy is stored in plain-text files in a format called JSON, one file for each organ system plus a few more. Each file lists structures (each with a name, a kind, a description and where it sits) and connections between them (blood flows from this into that; this nerve supplies that muscle; this muscle attaches to that bone). The page loads a file only when a tab needs it.
Here are six checks that the page runs on the data as soon as everything has loaded. The first column says what is checked, the second how many things were checked, and the third how many failed.
Passing these checks means the data hang together: no connection points to a structure that is missing, every route that should close does close, and the counts come out right. Passing does not mean the data are right. A vein that drains into the wrong vessel, as long as that vessel also reaches the heart, passes every check here. Only a reader who knows the anatomy, or a source that states it, can catch that kind of error.
Each data file has also been read in full by a separate AI that did not write it, looking for errors at the level of a first course in human anatomy: wrong connections, wrong names, and statements firmer than the evidence allows. The problems it found were corrected or, where the page simplifies on purpose, explained in a note. A second AI is no substitute for a person who knows the anatomy, though, because two AIs can share the same blind spots, so the warning at the top of this tab still applies.
A different AI, such as Google’s Gemini, can read a data file and point out what looks wrong. Here are four steps.
Two AIs trained on similar text can share the same mistakes, so agreement between them is weak evidence that something is right. Disagreement is more useful: it marks a place worth looking up.
Every structure’s card ends with a link, “Report a problem with this entry,” that opens an email with the structure’s name and data file already filled in. Say what seems wrong and, if you can, where the right information is (a textbook and page number is ideal). Reports go to the address for this page.
Here are the six conventions the data follow.