TEAS Human anatomy and physiology study guide

What this topic actually asks of you

Human anatomy and physiology is one of the twelve sub-content areas of the ATI TEAS, and it is the largest sub-content area in Science — and one of the two largest on the whole exam, tied with numbers and algebra: ATI publishes it as 12% of the exam and 18 of the 44 scored science questions, the same 18 that numbers and algebra carries in math. The whole Science section is 50 items (44 scored, 6 unscored) and is timed separately — 60 minutes.

Three things follow, and they shape how to study it.

• It is twelve short subjects, not one big one. ATI's objective list walks the body system by system. Each system has its parts (anatomy: what is there, and where) and its one working mechanism (physiology: how the parts make the job happen — the path air takes, the path blood takes, the path food takes). Learn a system as a list of parts plus one path, and the questions stop being a memory test.
• Most of the points are recall; the mechanism items are where items get harder. Naming the chamber that pumps blood to the body is one fact. Putting the stations of a pathway in order, or saying what happens when one station is blocked, is several facts used together — that is where the exam separates a learner who memorized a diagram from one who understood it.
• One arithmetic family, and it is small. Cardiac output is heart rate × stroke volume. That is the whole calculation in this topic; everything else is words. The words are the trap: ureter and urethra, bronchus and bronchiole, afferent and efferent, sympathetic and parasympathetic, innate and adaptive.

Our practice items are single-answer and text-only. The real ATI TEAS also uses other item types: ATI's own content outline lists multiple-choice, multiple-select, fill-in-the-blank numeric, hot spot and ordered-response items. Elk Ridge Academy's practice items are single-answer only, and they carry no pictures or diagrams — a pathway is written as text — so treat the method, not any one format, as the thing you are drilling.

ATI's anatomy-and-physiology objectives. ATI's Content Outline names what this topic measures, and every practice item below maps to one of them: S.1.1 the general orientation of human anatomy · S.1.2 the respiratory system · S.1.3 the cardiovascular system · S.1.4 the digestive system · S.1.5 the nervous system · S.1.6 the muscular system · S.1.7 the male and female reproductive system · S.1.8 the integumentary system · S.1.9 the endocrine system · S.1.10 the urinary system · S.1.11 the immune system · S.1.12 the skeletal system.

How to read this guide

This guide takes ATI's objectives in ATI's order: orientation first, because every other section uses its words ("the superior vena cava", "a medial structure", "a cut across the thorax"), then the systems one by one. Each section has the same three things:

1. The parts, in a reference table — what each part is and what it does.
2. The mechanism, as a path you can say out loud (air, blood, food, urine, a nerve impulse).
3. A worked example, showing how one question in that section is answered.

One thing this guide does not reteach: the levels of organization. Cell → tissue → organ → organ system is science biology's material (cell organization); here it appears once, as the sentence that explains why an organ system is "a group of organs with a shared job". If tissues and organs are the missing piece for you, read the Biology guide first.

Every table here restates OpenStax Anatomy and Physiology, 2nd edition (2022, CC BY 4.0, openstax.org — chapters 1, 5–6, 10–11 and 17–28) in our own words, with our own examples; nothing is copied and no figure is reproduced. The foot of this page carries the full source list.

S.1.1 — Orientation: naming where a structure is

Before a single organ, learn the vocabulary of position. Every later question is easier when "superior" and "medial" are automatic.

Anatomical position is the reference point. A body in the anatomical position is standing upright, face forward, feet flat and slightly apart, and arms at the sides with the palms facing forward and the thumbs pointing away from the body. Every directional word below assumes that position: in it the palm faces anteriorly, even if a hand is turned palm-back.

Directional terms come in pairs. Learn them as opposites, and remember that they describe the body's own directions, not the page: "medial" means toward the body's midline even when the body is drawn sideways.

Table 1 — The directional terms, as pairs.

Three planes cut the body. A plane is a flat surface the body is viewed or cut through. The name says which way the cut runs; that is the whole question — which plane is named?

Table 2 — The body planes and the body cavities.

1. Orientation terms — which directional word fits

Which directional term describes the relationship of the elbow to the wrist on the same arm?

1. Both points are on the same limb, so the pair that only moves toward the head or the feet — superior/inferior — says nothing about them.
2. The elbow is closer to the trunk than the wrist; the wrist is farther down the limb.
3. Closer to where the limb joins the trunk is proximal, so the elbow is proximal to the wrist, and the wrist is distal to the elbow.

The trap: reading proximal/distal as "up and down" instead of "along the limb". Up and down is superior/inferior; along a limb is proximal/distal.

2. Body planes — name the cut

A cut divides the body into an upper part and a lower part. Which plane is it?

1. Read what the cut separates: left from right is sagittal; front from back is frontal.
2. This cut separates upper from lower — neither of those.
3. A plane that divides the body into upper and lower parts is a transverse plane (a cross-section) — the plane a body scan slices the trunk in.

The trap: "frontal" sounds like the front of the body, but the frontal plane divides front from back. The name describes the cut, not the surface you end up looking at.

3. Body cavities — which cavity holds what

The heart and lungs sit in which body cavity?

1. The body has two main cavities: dorsal (the brain and the spinal cord) and ventral (everything at the front of the trunk).
2. The heart and lungs sit at the front, not the back, so the dorsal cavity is out.
3. The front-of-trunk cavity is the ventral cavity, and the heart and lungs occupy its upper division, the thoracic cavity, separated from the abdomen below by the diaphragm.

The trap: putting the heart and lungs in the dorsal cavity — they are posterior to the sternum, but the dorsal cavity is the name of one compartment, the one holding the brain and spinal cord. Being posterior to the sternum does not put an organ in the dorsal cavity, and dorsal as a direction does mean posterior.

S.1.2 — The respiratory system

The respiratory system does two jobs at once: it moves air and it exchanges gases. The parts are one tube that branches over and over until it ends in millions of tiny sacs, each wrapped in capillaries.

The parts, from the outside in. Air is warmed, moistened and filtered as it passes the nose. The pharynx is the throat shared with food; the larynx is the voice box, where the vocal cords sit and the epiglottis keeps food out of the airway. The trachea (windpipe) carries air to the chest, held open by C-shaped cartilage rings — and it sits anterior to the esophagus, so food passes behind the airway. The trachea divides into the bronchi (one per lung), which divide again into bronchioles, which end in the alveoli — thin-walled air sacs where gas exchange happens.

Table 3 — The parts of the respiratory system.

Table 4 — The path air takes, nose to blood.

Breathing is a pressure story. The diaphragm contracts and flattens while the ribs lift: the chest gets bigger, the pressure inside falls, and air flows in. Breathing out is mostly passive — the diaphragm relaxes back into its dome, the chest gets smaller, pressure rises above the outside pressure, and air leaves. Nothing has to be pumped out.

Table 5 — Breathing: inhale and exhale.

Gas exchange is diffusion, one direction per gas. In the alveolus, oxygen is high and in the arriving blood it is low, so oxygen moves from the air into the blood; carbon dioxide is high in the blood and low in the air, so it moves from the blood into the air you breathe out. Most oxygen then rides on hemoglobin inside red blood cells; most carbon dioxide travels in the plasma as bicarbonate, with a little riding on hemoglobin too.

Table 6 — Gas exchange, and how each gas travels.

4. Respiratory organs — the part that keeps the airway open

Which structure keeps the trachea from collapsing as air moves through it?

1. The airway must stay open while air moves in and out under changing pressure.
2. The trachea's wall carries C-shaped rings of cartilage — firm, but open at the back, where the esophagus can bulge as food passes.
3. So the structure holding the trachea open is its cartilage rings — the same job cartilage does in the nose and in the bronchi.

The trap: treating the rings' shape ("C-shaped") as a separate structure, or swapping the trachea's position with the esophagus behind it.

5. The air pathway — put the stations in order

Which list is the correct path of air from the outside to the exchange surface?

1. Air enters at the nose, and the throat and voice box follow: pharynx, then larynx.
2. From the larynx the air goes down the trachea, which branches into the bronchi, and those branch into the bronchioles inside the lung.
3. The smallest airways end in the alveoli, where the gas exchange happens — so the order is nose → pharynx → larynx → trachea → bronchi → bronchioles → alveoli.

The trap: putting the bronchioles before the bronchi. The branches get smaller as you go in; a bronchiole is the small end of a bronchus.

6. Breathing mechanics — what the diaphragm does

What happens to the diaphragm during inspiration?

1. Inspiration means air is flowing in, which needs the space inside the chest to get bigger.
2. The diaphragm contracts, and a contracted diaphragm flattens downward.
3. A flattened diaphragm increases the volume of the thoracic cavity, which lowers the pressure inside the chest below the outside pressure — so air flows in.

The trap: reversing the direction. Contracting and flattening brings air in; relaxing back into a dome pushes air out.

7. Gas exchange — which way each gas goes

At the alveolus, which way does carbon dioxide move?

1. The alveolus is the air side; the capillary wrapped around it is the blood side.
2. The body's cells produce carbon dioxide, so the arriving blood carries more of it than the air in the alveolus holds.
3. A gas diffuses from where it is more concentrated to where it is less, so carbon dioxide moves from the blood into the alveolus — and leaves the body on the next exhale.

The trap: swapping the two gases' directions. Oxygen goes into the blood and carbon dioxide leaves it; both move toward the lower concentration, which is why neither gas needs a pump.

S.1.3 — The cardiovascular system

This is the topic's biggest system, and the one an exam likes best, because it has one path to learn and a handful of structures that are easy to confuse. Learn the path once and most of the section answers itself.

The heart is two pumps side by side. The right side receives oxygen-poor blood from the body and pumps it to the lungs; the left side receives oxygen-rich blood from the lungs and pumps it to the whole body. A wall called the septum separates the two sides, so oxygen-poor and oxygen-rich blood do not mix. Each side has an upper chamber (atrium, which receives) and a lower chamber (ventricle, which pumps) — and because the left ventricle pushes blood through the entire body, its wall is the thickest of the four chambers.

Valves keep the flow one-way. A valve sits between each atrium and ventricle (tricuspid on the right, bicuspid or mitral on the left), and one sits at each exit into a great vessel (pulmonary semilunar and aortic semilunar). A valve's job is always the same: it stops blood flowing backwards, and when it closes is the part to keep straight — the AV valves (tricuspid and bicuspid) close when the ventricles contract, and the semilunar valves close when the ventricles relax.

Table 7 — The heart: chambers, valves and vessels.

Table 8 — The path blood takes through the heart, the lungs and the body.

The heart has its own electrical path, which is why it beats without your deciding to beat it. The signal starts in a patch of specialized cells in the right atrium and travels down and out; that order is why the atria contract first and the ventricles second.

Table 9 — The heart's own electrical path (conduction).

Blood vessels come in three kinds, and one question — which direction is the blood going? — decides between them. Arteries carry blood away from the heart (under the highest pressure, so they have thick muscular walls and no valves); veins carry blood toward the heart (under the lowest pressure, so they have thinner walls and valves that stop the blood sliding back); capillaries are one cell thick, which is what lets exchange happen.

Table 10 — Blood vessels compared.

Blood is tissue, not just liquid. Slightly over half of it is plasma — the liquid that carries dissolved substances, including carbon dioxide as bicarbonate. The rest is cells and cell fragments: red blood cells (which carry oxygen on hemoglobin), white blood cells (which defend the body) and platelets (which help it clot). This section names what each part does, not how many of each — cell counts are a lab test, not an entrance-exam fact.

Table 11 — The parts of blood.

The cardiac cycle is one beat, in two halves. In diastole the chambers relax and fill; in systole they contract and push the blood out. Cardiac output is the volume the heart pumps in a minute, and it is the one calculation in this topic: heart rate × stroke volume.

Table 12 — The cardiac cycle, and cardiac output.

8. Heart structures — which chamber does which job

Which chamber of the heart pumps oxygen-rich blood to the whole body?

1. Trace the blood: the body's blood returns oxygen-poor to the right side, so the right atrium and right ventricle cannot be the answer.
2. The left side receives the oxygen-rich blood coming back from the lungs, into the left atrium first.
3. The chamber that pumps from there is the left ventricle — and it is the thickest-walled chamber precisely because its blood goes everywhere.

The trap: choosing the left atrium (which receives oxygen-rich blood) instead of the left ventricle (which pumps it). Receiving and pumping are the two jobs the four chambers split between them.

9. The blood path — put the stations in order

Which list is the correct path of blood through the heart, starting from the right atrium?

1. Blood enters the right atrium from the body, and the first valve it crosses is the tricuspid, into the right ventricle.
2. From the right ventricle the blood leaves through the pulmonary semilunar valve into the pulmonary artery, and goes to the lungs to pick up oxygen.
3. It returns through the pulmonary veins to the left atrium, crosses the bicuspid valve into the left ventricle, leaves through the aortic semilunar valve into the aorta, and goes out to the body — so the order is right atrium → right ventricle → pulmonary artery → lungs → pulmonary veins → left atrium → left ventricle → aorta.

The trap: sending the blood from the right ventricle straight to the aorta, or from the left ventricle to the lungs. The right side goes to the lungs and the left side goes to the body — never the reverse.

10. Blood vessels — artery or vein

Which feature belongs to veins rather than arteries?

1. Both carry blood, so the useful question is which way and under what pressure: arteries leave the heart at high pressure, veins come back at low pressure.
2. A vessel that carries blood back at low pressure needs something to stop the blood sliding backwards, because nothing is pushing it.
3. That something is valves, which are found in veins — arteries have none, and instead carry a thick, muscular wall to take the pressure.

The trap: "artery = oxygen-rich and vein = oxygen-poor". It is usually true in the body but false in the pulmonary vessels, where the pulmonary artery carries oxygen-poor blood to the lungs and the pulmonary veins carry oxygen-rich blood back. Direction, not oxygen, defines the vessel.

11. Blood components — which part carries oxygen

Which part of the blood carries oxygen to the tissues?

1. Plasma is the liquid part, and it carries dissolved substances — but oxygen does not dissolve well enough to supply the body.
2. Oxygen is carried bound to a protein called hemoglobin.
3. Hemoglobin sits inside the red blood cells, so that is the part that carries oxygen.

The trap: naming plasma because it is the largest part of the blood, or naming white blood cells because "blood cell" sounds like the oxygen job. White cells defend; red cells carry.

12. The heart's conduction path — put the stations in order

Which list is the correct order of the heart's own electrical signal?

1. Each beat starts in the SA node, the pacemaker in the wall of the right atrium.
2. The signal reaches the AV node at the atrial–ventricular boundary, where it is delayed so the atria finish emptying before the ventricles squeeze.
3. It then travels down the AV bundle (the bundle of His) into the bundle branches and out through the Purkinje fibers, which is why the ventricles contract from the bottom up — so the order is SA node → AV node → AV bundle → bundle branches → Purkinje fibers.

The trap: putting the AV node before the SA node, or the Purkinje fibers before the bundle branches. The signal always starts at the SA node (the pacemaker) and ends at the muscle.

13. Cardiac output — heart rate × stroke volume

A heart beats 72 times per minute and ejects 65 mL of blood with each beat. What is the cardiac output?

1. Cardiac output is the volume pumped in one minute, so every quantity has to be per minute or per beat — and here both already are.
2. Multiply: heart rate × stroke volume = 72 beats per minute × 65 mL per beat.
3. The beats cancel, leaving 4,680 mL per minute — that is the cardiac output.

The trap: adding the two numbers instead of multiplying them, or dividing the stroke volume by the heart rate. Cardiac output is a product: more beats per minute or more blood per beat, either one, raises it.

S.1.4 — The digestive system

The digestive system is a tube with helpers hanging off it. Food travels the tube in one direction while the body breaks it into molecules small enough to absorb; the helpers add the chemicals the tube cannot make for itself.

Table 13 — The parts of the digestive system.

Table 14 — The path food takes, mouth to anus.

Digestion happens in stages, and the stage is the question. A carbohydrate starts breaking down in the mouth (saliva) and is finished in the small intestine; a protein starts in the stomach (acid and enzymes) and is finished in the small intestine; a fat is hardly digested at all before the small intestine — there it is emulsified by bile and broken down. Absorption is just as orderly: most nutrients are absorbed in the small intestine, but into two different places — the sugars and amino acids cross into the blood capillaries of the villi, and most of the fat crosses into the villi's lymph vessel, the lacteal, and reaches the blood from there. Much of the water is absorbed along the same stretch. The water that is left is reclaimed by the large intestine, which is also where the waste is formed into feces.

Table 15 — Where each nutrient class is digested, and where it is absorbed.

Table 16 — The accessory organs: the helpers that are not the tube.

The pancreas is the clearest example of a structure that belongs to two systems at once (the diaphragm, the pharynx and the gonads are others). The digestive pancreas releases enzymes into the small intestine; the endocrine pancreas releases hormones into the blood (that is S.1.9's material). An exam question about it will name either the system or the function — read which one it named.

14. Digestive organs — the organ that absorbs most nutrients

Most of the nutrients from a meal are absorbed where?

1. The stomach churns food and begins protein digestion, but very little absorption happens there.
2. The small intestine is the long, folded tube whose villi give it an enormous surface.
3. Surface is what absorption needs, so most nutrients are absorbed in the small intestine — and the water that the body keeps comes with them, along the same stretch. What is left for the large intestine is the water still in the waste, which it reclaims before forming it into feces.

The trap: choosing the large intestine because it is late in the path, or the stomach because it is where food stops being food. Finishing digestion and absorbing nutrients are the small intestine's jobs.

15. The food pathway — put the stations in order

Which list is the correct path of food through the digestive tube?

1. A swallow sends the food from the mouth to the pharynx, and the esophagus carries it down with peristalsis.
2. The stomach churns it, and then the small intestine finishes digesting it and absorbs the nutrients.
3. What is left passes to the large intestine, then the rectum and the anus — so the order is mouth → pharynx → esophagus → stomach → small intestine → large intestine → rectum → anus.

The trap: putting the large intestine before the small one. Food takes the small intestine first; the large intestine is the last stretch of the tube, and water is what it reclaims.

16. Digestion and absorption — where a class is digested

Where does most of the digestion of fat happen?

1. Fat does not dissolve in the watery contents of the mouth or the stomach, so only a little of it is digested before the small intestine.
2. Fat has to be broken into droplets first, and the substance that does that is bile.
3. Bile is released into the small intestine, so most fat digestion happens there — not in the mouth like starch and not in the stomach like protein.

The trap: assuming every nutrient is digested in one place. Starch starts in the mouth, protein in the stomach, and most fat is digested in the small intestine — and each of those three is a favorite exam question.

17. Accessory organs — who adds what

Which organ makes bile?

1. Bile is made for fat digestion and it is stored before it is used, so making and storing are two different organs.
2. The liver is the organ that makes bile.
3. The gallbladder only stores it and releases it into the small intestine.

The trap: naming the gallbladder because that is where bile waits. Making and storing are the liver's and the gallbladder's jobs respectively — the same trap as the pancreas's two jobs.

Answer-choice strategies: three moves for a path item

Pathway questions (air, blood, food) look harder than they are, because every choice is a version of the same list: reordered, or with a station left out. Do these three things and the answer appears.

1. Find the start and the end in the stem. "Starting from the right atrium…" and "…before it reaches the body" tell you the first and last stations. Cross out any choice whose first or last station is wrong. In many items every choice shares the same first and last station, and then the middle is the whole question: go to move 3.

2. Say the direction out loud, not the order. Every pathway in this topic has a direction sentence: air goes in through the nose; the right side of the heart sends blood to the lungs and the left side sends it to the body; food goes down and urine goes out; an impulse travels from the dendrites toward the axon terminals. If a choice reverses a direction, it is gone, however plausible its middle looks.

3. Hunt the swap. The most common wrong choice is the correct order with two neighboring stations swapped — bronchioles before bronchi, the AV node before the SA node, the large intestine before the small one. Read the choice one station at a time rather than recognizing the set of names; recognizing the names is exactly what the item is built to punish.

And one move for a naming item: when a structure belongs to two systems (the pancreas, the diaphragm, the ovary, the testes), read whether the stem named the system or the function, and answer that one. If the stem asks what the liver does for digestion, do not answer with the liver's other job.

S.1.5 — The nervous system

The nervous system is the body's wiring and its control room: cells that carry an electrical signal fast, and organs that decide what the signals should say. It is the system whose vocabulary trips people up most, because it comes in pairs — central and peripheral, somatic and autonomic, sympathetic and parasympathetic, sensory and motor.

A neuron is one cell with three working parts plus its output. Dendrites receive signals and carry them toward the cell body; the cell body holds the nucleus and decides whether to pass the signal on; a single long axon carries the signal away from the cell body; and the axon terminals pass it to the next cell — another neuron, a muscle or a gland.

Table 17 — The parts of a neuron.

The impulse travels one way, in one order. A signal arrives at the dendrites, reaches the cell body, travels down the axon, and leaves at the axon terminals — and a neuron with a myelin sheath carries it faster, because the signal can jump between the gaps in the wrapping instead of crawling along every millimeter of the membrane.

Table 18 — The path of a nerve impulse, one neuron long.

The wiring comes in two divisions, and then the second one splits again. The central nervous system (CNS) is the brain and the spinal cord — the control room. The peripheral nervous system (PNS) is everything else: the nerves that carry information in and commands out. The PNS itself has a voluntary part — the somatic nervous system, which moves your skeletal muscles — and an involuntary part, the autonomic nervous system, which runs the organs you do not consciously control.

Table 19 — The divisions of the nervous system.

The brain's three big regions have three different jobs. The cerebrum is the folded upper part: thinking, memory, language, and the conscious control of movement. The cerebellum sits at the back underneath: coordination, balance and smooth movement. The brain stem is the stalk below: the involuntary functions that cannot pause — breathing, heart rate, blood pressure.

Table 20 — The regions of the brain.

18. Neuron parts — which end receives, which end sends

Which part of a neuron receives signals from other cells?

1. A neuron has one output fiber and one receiving zone, so the question is which is which.
2. The axon is the output: it carries the signal away from the cell body to its terminals.
3. The receiving zone is the dendrites — the branched endings that carry signals toward the cell body.

The trap: swapping the two. Dendrites receive; the axon sends. A question that says "away from the cell body" is describing the axon.

19. The impulse path — put the stations in order

Which list shows the order in which a nerve impulse travels through one neuron?

1. The signal arrives from another cell, so it enters where signals enter: the dendrites.
2. From the dendrites it reaches the cell body, which sums what arrived and starts a new impulse if the signal is strong enough.
3. The impulse then travels down the axon and leaves at the axon terminals — so the order is dendrites → cell body → axon → axon terminals.

The trap: running the impulse backwards, or putting the terminals before the axon. A neuron is a one-way street, and the direction is written into its parts.

20. The nervous-system divisions — which one is voluntary

Which division of the nervous system carries the commands to the muscles you decide to move?

1. Start with the two big divisions: the CNS (brain and spinal cord) and the PNS (all the nerves).
2. The brain decides, but the nerves that carry the command to a muscle belong to the peripheral system — and inside it, the division serving skeletal muscle is the somatic one.
3. So the voluntary commands run through the somatic nervous system, while the heart, glands and gut are run by the autonomic system without your deciding.

The trap: reading "central" as "the part you control", and "autonomic" as "automatic movement". Autonomic means automatic organs; somatic means the muscles you move on purpose.

21. Brain regions — which part does which job

A person's balance and coordination are affected. Which region of the brain is most involved?

1. Balance and coordination are not thinking or memory, so the cerebrum is not the region in question.
2. The region behind and beneath the cerebrum, specialized for coordination and balance, is the cerebellum.
3. The brain stem is the other candidate — but it runs breathing, heart rate and blood pressure, not balance.

The trap: picking the brain stem because it sounds like the "basic" part of the brain. Breathing and heart rate are the brain stem; balance and smooth movement are the cerebellum.

S.1.6 — The muscular system

Muscle does one thing: it pulls, and it pulls by shortening. Every question about muscle is really one of three: which kind of muscle is this, how does it shorten, and which muscle does this movement.

Three kinds of muscle, told apart by three questions. Is it voluntary? Is it striated (banded under a microscope)? Where is it? Skeletal muscle is voluntary, striated, and attached to bone. Smooth muscle is involuntary, not striated, and sits in the walls of hollow organs and vessels. Cardiac muscle is involuntary but striated, and is found only in the heart wall.

Table 21 — The three muscle types.

How a muscle shortens: the sliding-filament idea. A skeletal muscle fiber is full of two protein filaments — thin actin and thick myosin. When a signal arrives, calcium is released inside the fiber, and the myosin heads pull the actin filaments toward the center of the sarcomere. The filaments themselves do not get shorter; they slide, so the whole fiber shortens and pulls on what it is attached to. The pull needs ATP as its energy, and when the signal stops, the calcium is pumped away and the muscle relaxes.

Table 22 — How a muscle contracts and relaxes (the level the exam uses).

Muscles work in pairs, and the words for them come in pairs too. A muscle's origin is the end that stays put; its insertion is the end that moves. A flexor bends a joint; an extensor straightens it. The muscle doing the movement is the agonist; the one that relaxes to let it happen (and does the opposite movement) is the antagonist. Muscle is tied to bone by a tendon; bone is tied to bone by a ligament — that pair is a favorite question.

Table 23 — The two muscle pairs the questions are built on.

The muscles worth recognizing. The same read-the-action rule answers a question about any named muscle, so know these by their job: the deltoid raises the arm out to the side; the pectoralis major pulls the arm forward and across the chest; the rectus abdominis bends the trunk forward; the trapezius raises and rotates the shoulders; the latissimus dorsi pulls the arm down and back; the gluteus maximus extends the hip; the gastrocnemius points the foot down, as in standing on tiptoe; and the diaphragm, the floor of the chest cavity, is the muscle whose contraction draws air in (S.1.2).

22. Muscle types — voluntary or not

Which muscle type is involuntary but striated?

1. Take the two questions in order: is it voluntary, and is it striated? Skeletal muscle is voluntary, so it is out.
2. Smooth muscle is involuntary — but it is not striated.
3. The muscle that is involuntary and striated is cardiac muscle, found only in the heart wall.

The trap: treating "striated" as a synonym for "voluntary". Cardiac muscle is the one type that is striated and still runs on its own.

23. Muscle contraction — what slides, and what is needed

In the sliding-filament model, what actually happens when a muscle fiber shortens?

1. The filaments that do the pulling are the thin actin and the thick myosin inside the fiber.
2. The myosin heads attach to the actin and pull the actin filaments toward the center of the sarcomere; the filaments slide past one another rather than shrinking.
3. The fiber shortens because the filaments overlap more, and the work is paid for with ATP — with calcium released to start it.

The trap: saying the filaments themselves get shorter, or that the muscle needs no ATP. Nothing inside shortens; things slide, and the energy bill is ATP.

24. Muscle actions — agonist and antagonist

The biceps brachii flexes the elbow. What does the triceps brachii do when the biceps contracts?

1. Muscles work in opposing pairs at a joint, so the partner of a flexor is an extensor.
2. Extending the elbow straightens the joint.
3. So while the biceps (the agonist) shortens, the triceps (the antagonist) relaxes and lengthens to let the movement happen — and does the opposite movement itself.

The trap: saying both muscles contract at once, or that the antagonist is the muscle that "helps". Helping is not the job of an antagonist; opposing is.

25. Major muscles — which muscle does this action

Which muscle extends the knee?

1. Extending the knee straightens the leg, and the muscles that do it sit on the front of the thigh.
2. The back of the thigh holds the hamstrings, which flex the knee — the opposite action.
3. The front-of-thigh group that straightens the knee is the quadriceps.

The trap: answering hamstrings by matching "thigh" to the word in the question. Read the action the question asks for — flex or extend — and then choose the side of the limb that performs it.

S.1.7 — The male and female reproductive systems

One objective covers two systems, so questions come in matched pairs: which structure is this, what does it make, and which hormone does the gonad release. Learn the two systems side by side and the pairs answer each other.

The male system makes sperm and delivers it. Sperm are made in the testes, which also release testosterone. Sperm then mature and are stored in the epididymis, travel up the vas deferens, and fluid from the seminal vesicles, the prostate and the bulbourethral glands joins them on the way out, forming semen — which leaves the body through the urethra, the tube that also carries urine.

Table 24 — The male reproductive structures.

The penis is the organ that delivers semen, the last station of the same route.

Three kinds of gland add the fluid, and each adds its own share. The seminal vesicles add the largest share; the prostate sits just below the bladder and surrounds the urethra, and adds fluid there; the bulbourethral glands add a small amount before the rest. Sperm plus that fluid is semen, and the glands' three jobs are a favorite exam trap: the question may name the gland and ask what it adds, or describe the fluid and ask which gland added it.

The female system produces eggs, receives sperm and houses development. Eggs are made in the ovaries, which also release estrogen and progesterone. An egg leaves an ovary and travels through a fallopian tube toward the uterus; the uterus is the organ where a fertilized egg implants and develops. The cervix is the narrow neck of the uterus, and the vagina is the passage that receives sperm and is the birth canal.

Table 25 — The female reproductive structures.

Both gonads make two things: a gamete and hormones. This is the one idea the two systems share, and it is the source of the section's most common distractor: the testes and the ovaries are named in the endocrine system too, so a question that asks about a hormone is not asking about a reproductive structure's shape.

Table 26 — The gametes, and the hormones the gonads make.

26. Male reproductive structures — where sperm mature

Where do sperm mature and wait before ejaculation?

1. Sperm are made in the testes, but they are not stored there.
2. The structure that sits on the back of each testis, where sperm mature and are kept, is the epididymis.
3. From there they travel up the vas deferens — so the vas deferens carries them, and the epididymis is where they were waiting.

The trap: naming the vas deferens for storage. The vas deferens is the road; the epididymis is the parking lot.

27. Female reproductive structures — where fertilization happens

In which structure does fertilization normally happen?

1. The egg leaves the ovary and is moved along by the fallopian tube toward the uterus.
2. Fertilization is the joining of sperm and egg, and it happens in the tube, not in the uterus itself.
3. The fallopian tube is therefore the site of fertilization; the uterus is where a fertilized egg implants and develops.

The trap: answering "uterus" because that is where development happens. The uterus houses the developing egg; the tube is where it is fertilized.

28. Gametes and gonadal hormones — which organ makes which

Which organ releases testosterone?

1. Both gonads make a gamete and hormones, so the question is which pair belongs to which organ.
2. The testes make sperm — and the hormone they release is testosterone.
3. The ovaries make eggs, and the hormones they release are estrogen and progesterone.

The trap: answering "the adrenal glands" because they also release a small amount of testosterone. The gonads are the primary source, and this system's questions are about the gonads.

S.1.8 — The integumentary system

The integumentary system is the skin and everything growing out of it — hair, nails, and the glands in the skin. The skin is the body's largest organ, and its functions are easy to take for granted: protection, temperature control, sensation, and vitamin D.

The skin is three layers, and each has a job. The epidermis is the thin outer layer — the barrier — and it has no blood vessels of its own, so it is fed by the layer beneath. The dermis is the thicker middle layer, and it holds what the skin needs to work: blood vessels, nerves, hair follicles and glands. The hypodermis (subcutaneous layer) is the deepest layer, just beneath the skin proper, and it is mostly fat: it insulates the body and anchors the skin to the tissue beneath.

Table 27 — The three layers of the skin.

Accessory structures are the skin's tools. Hair grows from follicles in the dermis and helps with warmth and touch; nails protect the ends of the fingers and toes; sweat glands release sweat onto the surface, which cools the body as it evaporates; and sebaceous (oil) glands release oil that keeps the skin and hair from drying out.

Table 28 — The accessory structures of the skin.

Four functions, and each has a mechanism. The skin protects — it is a physical barrier, and its acid surface discourages microbes. It regulates temperature — sweating cools you, and the blood vessels in the dermis widen to release heat or narrow to keep it. It senses — the nerves in the dermis report touch, pressure, pain and temperature. And it makes vitamin D — when sunlight reaches the skin, the skin starts the reaction that produces it.

Table 29 — The functions of the skin.

29. Skin layers — which layer has the blood vessels

Which layer of the skin contains the blood vessels and nerves?

1. The outer layer is the epidermis, and it has no blood vessels of its own — which is why a scrape that stays in the epidermis does not bleed.
2. Beneath it sits the dermis, the thicker layer that carries the vessels, nerves, follicles and glands.
3. The hypodermis is deeper still, and mostly fat — it insulates rather than supplying.

The trap: putting the vessels in the epidermis because that is the layer you can see. The visible layer is the one with no blood supply at all.

30. Accessory structures — which gland does what

Which glands release oil that keeps the skin from drying out?

1. The skin has two kinds of gland, and they release different things: sweat glands release sweat, which cools the body.
2. Cooling is not the job described in the question — the question asks about oil.
3. The sebaceous (oil) glands release the oil; sweat glands release sweat.

The trap: answering "sweat glands" whenever a gland is mentioned. Ask what the question says the gland releases: sweat for cooling, oil for waterproofing the skin and hair.

31. Skin functions — how the body cools itself

On a hot day the body cools itself mainly by which mechanism of the skin?

1. The skin has four functions, so read which one the question names: cooling.
2. Protection, sensation and vitamin D production do not lower body temperature.
3. Sweating cools the body as the sweat evaporates from the surface — helped by the dermis's blood vessels widening to release heat.

The trap: naming "the blood vessels widening" alone. Widening the vessels helps too, but the question asks how the skin cools the body, and the mechanism that does it by name is sweating.

S.1.9 — The endocrine system

The endocrine system is the body's chemical messaging: glands release hormones into the blood, and each hormone travels to the cells that answer it. Beside the nervous system of S.1.5 it is slower to start and slower to stop — but it reaches everywhere the blood goes, and its effects last. The wiring is the nervous system; the broadcast is the endocrine system.

Every hormone question is three questions: which gland makes it, what it acts on, and what it changes. Learn each hormone as that sentence and this section stops being a list of names. It is also where this system crosses S.1.4 and S.1.7: the pancreas releases insulin and glucagon and adds digestive enzymes, and the ovaries and testes release the hormones S.1.7 already gave them. Read which of the two the question names — a question about the pancreas that asks about enzymes and food belongs to the digestive system, and one that asks about a hormone belongs here.

Table 30 — The endocrine glands, and the hormones each one releases.

Table 31 — What each hormone changes.

Two hormones in that table are a pair, and the pair is the question. Insulin and glucagon do opposite jobs to the same substance: insulin lowers the glucose level by moving glucose out of the blood and into the cells, and glucagon raises it by making the liver release glucose. Calcitonin and parathyroid hormone are the same shape of pair for calcium: calcitonin lowers the calcium level and parathyroid hormone raises it. The two hormones act on bone first, and also on the kidney (and, for parathyroid hormone, on the intestine too) — so calcium is the bone's store and the kidney's balance as well as the hormone pair's business. When a question names one of a pair, the other is the distractor — and the direction is the whole answer.

Table 32 — Negative feedback, worked with ADH.

That loop is what "negative feedback" means: the response cancels the change that started it, and because the body keeps checking the level, the release falls back as soon as the level is back. Almost every hormone in Table 31 is controlled this way — oxytocin is the exception: its loop pushes the level higher until the process it began is finished (positive feedback). The exam question is usually the last step — what happens to the gland once the level is back to normal? — and the answer is that the gland slows or stops releasing the hormone, not that it keeps going at the same rate.

32. Endocrine glands — which gland releases which hormone

The adrenal glands sit on top of the kidneys. Which two hormones do they release?

1. "Adrenal" names the gland's position, not its hormones, so the question is a recall of the pair — and the pair is the two stress hormones, not the two glucose hormones.
2. Cortisol works on stress that lasts, and epinephrine is the fast one: it speeds the heart and widens the airways in a moment.
3. So the answer is cortisol and epinephrine. Insulin and glucagon belong to the pancreas; ADH and oxytocin belong to the pituitary.

The trap: answering with the pair from another gland's row. Learn Table 30 one gland at a time — a question names the gland, and the gland's row is the answer.

33. Hormone action — what a hormone changes

After a meal, the glucose level in the blood rises. Which hormone answers it, and what does the hormone do?

1. The body keeps checking the glucose level, so read which way the level has moved: it has moved up.
2. The hormone that answers a raised glucose level is insulin, from the pancreas. Its partner, glucagon, is the hormone for the opposite direction.
3. Insulin moves glucose out of the blood and into the cells, which brings the level back down — and once the level is back, the pancreas slows or stops releasing it. That is the negative-feedback loop of Table 32.

The trap: naming glucagon because it is the pancreas's other hormone. Glucagon's direction is the opposite one — it raises the glucose level. Read the direction the question gives, and answer with the hormone that moves it back.

S.1.10 — The urinary system

The urinary system filters the blood and carries the waste out as urine — and on the way it decides how much water and salt the body keeps. That second job is why the system matters beyond waste: it is where the body's water balance is settled. The system's parts are a pair of filters and a one-way plumbing run, and a question about it is usually a question about which part, and which direction.

Table 33 — The urinary organs.

Table 34 — The path urine takes, out of the body.

Look at the two easy-to-confuse names in that path. The ureter carries urine from the kidney to the bladder; the urethra carries urine from the bladder out of the body. They differ by two letters and by one whole station, and swapping them is this system's signature mistake — a question usually settles it by naming the station on either side.

Table 35 — The kidney's three jobs, in outline.

Those three jobs are why urine is not simply filtered blood. Filtration is indiscriminate: it takes water and small molecules and leaves the cells and the large proteins behind. Reabsorption is the picky step that keeps what the body needs, and it is the step that makes the volume of urine a decision rather than a result. Secretion is the small top-up that moves a few wastes in the other direction. The exam asks which job does what: water kept → reabsorption, waste moved in → secretion, blood separated → filtration.

The kidney's balance job is the other half of its work, and it is broader than water. Besides making urine, the kidney keeps the water, the salts and minerals and the acid of the body in range — and the calcium too, with the endocrine section's hormone pair setting how much of it is taken back. That is why the volume of urine rises and falls with what the body needs: the kidney is holding a level.

34. Urinary organs — which organ does which job

Urine is stored until it can be released. Which organ stores it?

1. The system has four parts, and each has one sentence: the kidney filters, the ureter carries, the bladder stores, the urethra releases.
2. Storage is the bladder's sentence.
3. So the answer is the bladder — a sac of muscle, which is why the urine leaves when that muscle contracts.

The trap: answering "the kidney" because the question is about urine. The kidney makes urine; the bladder keeps it.

35. The urine pathway — where urine goes next

Urine is made in a kidney. Which tube does it enter first, and where does that tube take it?

1. Two tubes leave the kidneys, one from each, and they are the ureters.
2. A ureter carries urine down to the bladder, where the urine waits.
3. From the bladder the urine leaves through the urethra — so the path is kidney → ureter → bladder → urethra, and the tube that leaves the kidney is the ureter, not the urethra.

The trap: the pair of look-alike names. If the sentence says "from the kidney", the answer is the ureter; if it says "out of the body", it is the urethra.

36. Urine formation — which job does what

Most of the water that is filtered out of the blood never leaves the body. Which job brings it back?

1. Filtration takes water and small wastes out of the blood and into the kidney's tubules — it does not bring anything back.
2. Reabsorption is the step that takes useful material back into the blood: most of the water, and the glucose and salts the body needs.
3. So the answer is reabsorption. Secretion runs the other way — the small top-up that moves a few wastes out of the blood and into the fluid that will leave.

The trap: reading "filtered out" as the whole story. Filtration makes a fluid that is mostly water; reabsorption is what turns it into the small volume of urine that leaves.

S.1.11 — The immune system

The immune system is the body's defense against what gets in — microbes, and anything else the body does not recognize as its own. Its innate defenses are the ones the body is born with, and they work in two steps: the barriers — the skin, the mucous membranes, the acid on the skin and in the stomach — and then a fast general response. Behind them sits the adaptive response, which is slower, targets one thing and remembers it. Three words carry the section: innate (general, no memory — the barriers and the fast response), adaptive (specific, with memory) and antigen (the part of a foreign cell or molecule the immune system recognizes).

Table 36 — The body's defenses, in three layers.

Memory is the difference the exam tests. The innate response meets a microbe it has never seen as though it had seen nothing at all. The adaptive response changes the body for a long time: the first meeting takes days, and the second meeting with the same antigen is fast and strong, because the memory cells are already there. That is what immunity means.

Table 37 — The lymphatic structures.

Table 38 — The white blood cells, and how antibodies work.

Antibodies do not eat anything; they mark and disable. An antibody fits one antigen — the fit is the specificity — and its work is to flag that antigen for the phagocytes and to stop it working. That is why the first meeting with an antigen is slow (the body has to find the right B cell) and the second is fast (the memory cells are already made and waiting).

37. Innate and adaptive immunity — which one remembers

A person meets the same microbe twice, and the second meeting is dealt with faster and more strongly than the first. Which part of the immune system explains that?

1. Split the system into its two working responses first: the innate response is general and keeps no memory, and the adaptive response targets one antigen and leaves memory cells.
2. The barrier layer cannot explain it — the barrier does not change when the same microbe returns.
3. The adaptive response explains it, because the memory cells left from the first meeting are already there, so the second answer needs no time to find the right B cell.

The trap: crediting the innate response with memory because it acted first. The innate response is the fast, general one; the remembering one is the adaptive response.

38. Lymphatic structures — where lymph is filtered

Which structure filters lymph, and holds the lymphocytes that meet what it carries?

1. Work out what the question asks the structure to filter: lymph or blood. Those are two different structures.
2. The structure that filters blood is the spleen. The lymph nodes are the ones that filter lymph.
3. So the answer is a lymph node — and the fluid it filters is the lymph collected from the tissues, traveling in the lymphatic vessels toward the heart.

The trap: answering "the spleen" for any question about filtering. The spleen filters the blood; the lymph nodes filter the lymph.

39. Antibodies and white cells — which cell does which

Which white blood cell engulfs a microbe, and which one makes antibodies?

1. Two jobs are in the question, and they belong to two different cells: engulfing is the innate response, and antibody-making is the adaptive one.
2. Phagocytes engulf and digest microbes and debris, and they act the same way on anything foreign.
3. B cells make the antibodies, and an antibody sticks to one specific antigen and marks it so a phagocyte can engulf it. So the engulfing cell is the phagocyte, and the antibody-maker is the B cell.

The trap: giving the phagocyte the antibody job. Antibodies are made by lymphocytes; phagocytes do the eating.

S.1.12 — The skeletal system

The skeleton is the body's frame, and it does four jobs: it supports the body, protects the organs inside, makes movement possible by giving the muscles something to pull on, and stores minerals — and the marrow inside some bones makes blood cells. Bones are also the body's calcium store, which is why the endocrine section's calcitonin and parathyroid hormone matter here.

The skeleton divides in two, and the division decides which bone belongs where.

Table 39 — The two divisions of the skeleton.

Table 40 — The named bones, and where each one sits.

Bones come in five broad shapes, and the shape follows the job. A long bone is longer than it is wide, with ends wider than its shaft — the femur and the humerus, which work as levers. A short bone is roughly cube-shaped, like the bones of the wrist and the ankle. A flat bone is thin and flat, and it often protects what lies beneath: the sternum, the ribs and the skull's bones. An irregular bone has no simple shape at all — the vertebrae are the example, and their shape is the point. A sesamoid bone forms inside a tendon, and the patella is the example.

Table 41 — Inside a long bone.

Bones meet each other at joints, and the joint's shape is the movement it allows. A ligament holds bone to bone at a joint, and a tendon — S.1.6's word — holds muscle to bone. That pair is what this system and the muscular system share, and it is a favorite question: ligaments join bone to bone, tendons join muscle to bone.

Table 42 — The joint types.

By structure, joints come in three kinds too: fibrous (the sutures, where the bones are held together by fibrous connective tissue), cartilaginous (held together by cartilage), and synovial — every freely movable joint in the table above.

40. Skeleton divisions — which division is this bone in

The vertebrae are part of which division of the skeleton?

1. Split the skeleton into its two divisions: the axial skeleton is the head and the trunk, and the appendicular skeleton is the limbs and the girdles that attach them.
2. The vertebrae lie along the back, inside the trunk, and they protect the spinal cord — so they are not a limb and not a girdle.
3. They belong to the axial skeleton, with the skull, the ribs and the sternum.

The trap: sorting by "big bone" or "small bone" instead of by place. Sort by the division's sentence: head or trunk → axial; limb or girdle → appendicular.

41. Bone types and structure — what is inside a bone

Which part of a bone is the hard, dense outer layer, and what is the soft tissue inside it called?

1. A long bone is described in layers, from the outside in: the hard compact bone outside, the lighter spongy bone in the ends, and the marrow inside the shaft's central cavity.
2. The hard, dense outer layer is compact bone, and it is what gives the bone its strength.
3. The soft tissue inside is the marrow — the red marrow in the spongy bone makes the blood cells, and the yellow marrow in the shaft's cavity stores fat.

The trap: putting the marrow outside, or calling the whole bone solid. The outer layer is the dense one; the blood-making red marrow is the one inside the spongy bone at the ends.

42. Joints — which joint moves which way

Which kind of joint lets the shoulder move in every direction, and which kind is the elbow?

1. Read the movement the question gives, because a joint's kind is its movement: back and forth → hinge; every direction → ball-and-socket; turning → pivot; sliding → gliding; almost no movement → suture.
2. "In every direction, and round" is the ball-and-socket joint — the shoulder and the hip.
3. Back and forth, like a door, is the hinge joint — the elbow and the knee.

The trap: naming the joint by where it is rather than by how it moves. A knee is a hinge because of its movement, not because of its size.

The traps, collected

Most wrong answers in this topic's practice items are one of these.

• A part given another part's job: the gallbladder credited with making bile, the atrium with pumping, the epiglottis with warming the air.
• The right organ in the wrong system: the pancreas answered as an endocrine gland when the stem asked about digestion (or the reverse).
• A part named where a type was wanted: a tendon offered as a muscle type, or a named arm muscle offered where the stem asked for the type.
• A station moved one step: bronchioles before the bronchi, the large intestine before the small one, the AV node before the SA node, the bicuspid valve before the pulmonary valve.
• A direction reversed: air said to leave the alveolus as oxygen enters (the right way is oxygen in, carbon dioxide out); the diaphragm said to relax on inspiration; blood said to flow from the left ventricle to the lungs.
• A pair of look-alike words swapped: bronchus/bronchiole, ureter/urethra (S.1.10), artery/vein read as oxygen-rich/oxygen-poor rather than toward/away from the heart.
• Anatomical position ignored: a directional term read from the reader's viewpoint instead of the body's.
• A plane named by the surface it exposes: "frontal" taken as the front of the body rather than the cut that separates front from back.
• A nerve or a muscle given the other's job: a sensory structure credited with movement, an effector credited with sensation.
• The wiring read backwards: a command said to travel from the muscle to the brain, or an impulse said to start at the axon terminals and end at the dendrites.
• Somatic and autonomic swapped: the heart described as voluntary, or the skeletal muscles described as running on their own.
• Sympathetic and parasympathetic reversed: the sympathetic branch described as slowing the heart, or "rest and digest" attached to the wrong branch.
• A muscle pair read as both contracting: the antagonist said to shorten while the agonist shortens, or a flexor credited with straightening a joint.
• A muscle matched by where it is rather than what it does: the hamstrings chosen for "straighten the knee" because both the question and the answer say "thigh".
• A gonadal hormone on the wrong gonad: testosterone assigned to the ovaries, or estrogen to the testes.
• The skin's layers out of order: blood vessels put in the epidermis, or the hypodermis put outside the dermis.
• The two skin glands exchanged: oil credited to the sweat glands, or sweat credited with waterproofing the skin.
• A hormone given the other hormone's direction: insulin and glucagon swapped, calcitonin and parathyroid hormone swapped, or ADH said to make the kidneys release water.
• A gland given another gland's hormone: cortisol named for the thyroid, or insulin named for the pituitary — the question names the gland, and the gland's row in Table 30 is the answer.
• Negative feedback read as a switch that stays on: the gland said to keep releasing after the level is back to normal, instead of slowing or stopping.
• The urinary pair swapped: the ureter said to leave the body, or the urethra said to carry urine from the kidney. From the kidney → ureter; out of the body → urethra.
• The kidney's jobs confused: reabsorption credited with moving waste out, or secretion credited with keeping water. Water kept is reabsorption; waste moved in is secretion.
• The immune layers flattened: the innate response credited with memory, or a barrier credited with targeting one antigen — the specific, remembering response is the adaptive one.
• The lymphatic pair swapped: the spleen said to filter lymph, or a lymph node said to filter blood. Lymph nodes filter lymph; the spleen filters blood.
• The white cells swapped: antibodies credited to the phagocytes, or engulfing credited to the B cells. Phagocytes engulf; B cells make antibodies.
• A skeletal bone in the wrong division: the ribs or the vertebrae placed in the appendicular skeleton because they are not in a limb's name.
• A bone's inside and outside reversed: the marrow said to be the hard outer layer, or the compact bone said to make blood cells. Compact bone is outside and dense; red marrow makes blood cells.
• A joint named by where it is rather than how it moves: the knee called a ball-and-socket, or the shoulder called a hinge.
• Ligaments and tendons exchanged: a ligament said to join muscle to bone, or a tendon said to join bone to bone.

How to practice this

• Work the free Human anatomy and physiology practice set with a pencil, and write the path out each time a pathway item appears. Each option is a version of the same list, and writing the order is faster than reading each one.
• Drill the procedures you get wrong, not the ones you already know. Sorting your errors by procedure beats counting them.
• Read the explanation on every practice item, including the ones you got right. A right answer reached with the wrong reason comes back on test day.
• Re-attempt what you missed a day later, not immediately: a day later measures whether the fact stuck.

Where to go next

• Next topic — Biology
• The rest of the section — Biology, Chemistry, and Scientific reasoning.
• The reference table — the eleven body systems — each system's main parts and its primary function on one page.

This topic sits inside the Science section and carries ATI's published 12% of the exam and 18 of the section's 44 scored items — the blueprint's own split.