Physiology

How the body works, topic by topic: what happens, why, how it is measured and what goes wrong in disease. With interactive diagrams you can touch (the oxygen curve, the cardiac cycle, the pressure–volume loop, the nephron, the hormone axes), linked to the 3D anatomy, biochemistry, pharmacology and DurgiPedia's conditions.

238 topics

• Interactive diagrams
• Cardiovascular
• Renal, fluids and acid–base
• Respiratory
• Endocrine
• Neurophysiology
• Gastrointestinal
• Cell and membrane
• Nerve and muscle
• Reproduction, pregnancy and the fetus
• Blood, hemostasis and basic immunity
• Temperature, exercise and metabolism
• A to Z

Interactive diagrams

Move the controls or tap the parts: we draw every diagram from data.

• Hormone axes and feedbackActions of cortisol
• The nephron: segments, transporters and diureticsADH, thirst and water balance
• Oxygen–hemoglobin dissociation curveAnemia physiology and compensation
• Left-ventricular pressure–volume loopCardiac output and what sets it
• Lung volumes and capacitiesDead space and alveolar ventilation
• Electrocardiogram: a normal beat in lead IIECG basics: waves, intervals and leads
• Cardiac cycle (Wiggers diagram)Heart sounds and where they come from
• Starling forces along a capillaryHow edema forms
• Action potentialImpulse conduction and myelin

Cardiovascular

The heart as a pump, the ECG, hemodynamics and how blood pressure is controlled.

• Cardiac output and what sets itCardiac output is how much blood the heart pumps each minute: beats per minute times the volume of each beat.Regulation · ★
• ECG basics: waves, intervals and leadsThe ECG records the heart's electrical activity from the skin; each wave shows a part of the heart activating or recovering.Measurement · ★
• Heart sounds and where they come fromThe 'lub-dub' you hear is the sound of heart valves snapping shut; extra sounds can mean the heart is filling against stiffness or overload.Mechanism · ★
• How edema formsSwelling appears when more fluid leaves the blood vessels than the lymph can carry back.Mechanism · ★
• Shock physiologyShock is when the circulation cannot deliver enough oxygen to the organs; cells switch to inefficient energy and start to fail.Mechanism · ★
• Starling forces at the capillaryBlood pressure pushes fluid out of capillaries and blood proteins pull it back in; the lymph carries away what is left over.Mechanism · ★
• Systolic, diastolic, mean and pulse pressureBlood pressure has a top number when the heart pushes, a bottom number when it rests, and an average that keeps organs perfused.Measurement · ★
• The baroreceptor reflexPressure sensors in the neck and aorta tell the brain about blood pressure each second, and the brain adjusts heart and vessels to keep it steady.Regulation · ★
• The cardiac conduction systemA wiring path carries each beat from the top of the heart to the bottom, with a short pause so the atria empty before the ventricles squeeze.Concept · ★
• The cardiac cycleOne heartbeat is a fixed sequence: the heart fills, squeezes with closed valves, ejects, relaxes, and fills again.Mechanism · ★
• The Frank–Starling mechanismThe more the heart is filled, the harder it squeezes, so it pumps out whatever blood comes back to it.Mechanism · ★
• The renin–angiotensin–aldosterone systemWhen blood pressure or salt falls, the kidney releases renin, starting a chain of hormones that tightens vessels and holds salt and water.Regulation · ★
• The SA node pacemaker potentialCells in the sinus node slowly charge themselves up until they fire, which sets the heart rate without any nerve signal.Mechanism · ★
• The ventricular action potentialEach ventricular muscle cell fires a long electrical signal with a plateau, so the heart squeezes fully and cannot be tetanized.Mechanism · ★
• The ventricular pressure–volume loopPlotting the ventricle's pressure against its volume in one beat draws a loop whose shape shows how well it fills and pumps.Measurement · ★
• Cardiac excitation–contraction couplingHow each beat's electrical signal becomes force: a small calcium influx triggers a much larger calcium release inside the cell.Mechanism
• Central venous pressure and the jugular pulseCentral venous pressure is the pressure of blood entering the right heart; the internal jugular vein shows it in the neck.Measurement
• Coronary circulation and myocardial ischemiaThe heart feeds mostly in diastole and already extracts almost all its oxygen at rest: if it needs more, it can only get more flow.Concept
• Flow, pressure and resistance: Poiseuille and turbulent flowBlood flows from high to low pressure; narrow vessels resist flow enormously, and fast, disturbed flow becomes noisy and turbulent.Concept
• Heart failure physiologyIn heart failure the heart cannot pump enough at normal filling pressures; the body's rescue hormones help at first, then make things worse.Mechanism
• How arrhythmias ariseAbnormal heart rhythms come from cells that fire on their own, beats that trigger extra beats, or a signal that loops in a circle.Mechanism
• Local and humoral control of blood flowEach tissue adjusts its own arterioles to get the blood it needs, even when arterial pressure changes.Regulation
• Long-term blood pressure control by the kidneyIn the long run, blood pressure is set by the kidneys: if pressure rises, they excrete more salt and water until it comes back down.Regulation
• Murmurs and the hemodynamics of valve diseaseA murmur is the sound of blood flowing turbulently through a narrow valve, a valve that does not close, or an abnormal opening.Mechanism
• Muscle blood flow and the cardiovascular response to exerciseDuring exercise the heart pumps up to four or five times more blood and the working muscles take almost all of it.Regulation
• Nervous control of the circulation and the CNS ischemic responseThe brain raises or lowers blood pressure within seconds through the sympathetic nerves and the vagus.Regulation
• Physiology of congenital shuntsA hole between the two halves of the heart or the great vessels lets blood flow from the high-pressure side to the low-pressure side.Mechanism
• Physiology of hypertensionHypertension is sustained high blood pressure; almost always, a kidney needs more pressure to get rid of salt.Mechanism
• Preload, afterload and contractilityHow much each beat pumps depends on how full the heart is, how hard it must push, and how strong the muscle is.Concept
• The cardiac electrical axisThe axis is the average direction in which ventricular depolarization travels; you work it out from the QRS in the limb leads.Measurement
• The ECG in ischemia and infarctionWhen heart muscle runs short of blood, the ST segment, T wave and Q wave change, and point to the wall and the artery involved.Measurement
• The ECG in potassium and calcium disordersPotassium and calcium reshape the cardiac action potential, and it shows in the T wave, the QRS and the QT interval.Measurement
• The response to standing upWhen you stand, blood drops into the legs; fast reflexes speed the heart and tighten the vessels so the brain keeps its supply.Regulation
• Vascular compliance and capacitanceArteries are elastic and cushion each beat; veins are so stretchy that they hold most of the body's blood.Concept
• Venous return and the Guyton curvesThe heart can only pump the blood that reaches it. Venous return depends on the gap between venous pressure and right atrial pressure.Mechanism
• How the lymphatic system worksLymphatics collect the fluid and proteins that leak out of capillaries and return them to the blood.Concept
• Skin blood flowSkin gets far more blood than it needs for its own nutrition, because its flow is mostly used to control body temperature.Regulation

Renal, fluids and acid–base

Glomerular filtration, clearance, tubular transport, water, sodium, potassium and acid–base balance.

• ADH, thirst and water balanceThe brain senses how concentrated the blood is. If it rises, you get thirsty and ADH tells the kidney to keep water. Blood sodium mirrors that balance.Regulation · ★
• Distal tubule and collecting ductThe end of the nephron does the fine tuning: how much salt, water, potassium and acid leaves in urine, under hormone control.Mechanism · ★
• Glomerular filtration: the barrier and its determinantsThe kidneys filter about 180 litres of plasma a day. How much they filter depends on pressures in the glomerulus and the tone of its two arterioles.Mechanism · ★
• Metabolic acidosis, the anion gap and compensationIn metabolic acidosis the blood loses bicarbonate or gains acid. The lungs breathe more to blow off CO₂ and the kidneys make new bicarbonate.Mechanism · ★
• Potassium balanceAlmost all potassium sits inside cells. Small changes in the blood upset the heart and muscles, so the body controls it closely.Regulation · ★
• Reading an arterial blood gas step by stepA blood gas shows the blood's pH, CO₂, bicarbonate and oxygen. Read in order, it tells you what is failing: the lungs, the kidneys or metabolism.Measurement · ★
• Reasoning through fluid and electrolyte imbalancesEach electrolyte problem makes sense with three questions: did it move into or out of cells, what did the kidney do, and which tissue suffers? Here is the map.Table to know · ★
• Renal clearanceClearance tells how much plasma the kidney cleans of a substance per minute. It measures filtration and shows whether the tubule reabsorbs or secretes.Measurement · ★
• Respiratory acidosis and alkalosisBreathing too little builds up CO₂ and acidifies the blood; breathing too much blows off CO₂ and makes it alkaline. The kidneys compensate over days.Mechanism · ★
• Sodium and extracellular volume regulation (with natriuretic peptides)The body's total sodium decides how much fluid sits outside the cells. The kidney adjusts it with hormones that keep or shed salt.Regulation · ★
• The countercurrent mechanism, urea recycling and urine concentrationThe kidney salts its medulla so it can pull water out of urine when needed. That lets urine be up to four times more concentrated than blood.Mechanism · ★
• Transport in the loop of HenleThe loop of Henle separates salt from water: one limb lets water out and the other pumps salt out. This dilutes urine and builds a salty medulla.Mechanism · ★
• Where and how diuretics actEach diuretic blocks a salt transporter in one stretch of the nephron. Knowing where it acts predicts how much urine forms and which electrolytes are lost.Mechanism · ★
• Buffers and the Henderson–Hasselbalch equationBuffers soak up surplus acid or base within seconds and stop blood pH from swinging sharply.Concept
• Dehydration and fluid overloadToo little or too much fluid changes blood pressure, pulse, urine and skin; the kidney tries to fix it by keeping or shedding salt and water.Mechanism
• Fluid shifts between compartmentsWater moves between cells and the fluid around them toward wherever more particles are dissolved.Mechanism
• Functional anatomy of the nephronEach kidney has around a million nephrons: a filter (the glomerulus) and a long tube that recovers what is useful and lets waste through.Concept
• Glucose transport maximum and renal thresholdThe kidney reclaims all filtered glucose up to a limit; when blood glucose goes past it, glucose spills into the urine.Measurement
• IV fluids: tonicity and where they goEach IV fluid ends up in a different part of the body depending on what is in it: in the plasma, across the extracellular space or inside cells.Concept
• Measuring GFR and plasma flow: inulin, creatinine, PAH and filtration fractionHow we measure how much the kidneys filter and how much blood they get, using substances the kidney handles in a known way.Measurement
• Metabolic alkalosis and its compensationWhen there is too much bicarbonate in the blood, pH rises; the lungs breathe less to compensate and the kidney decides whether to fix it or keep it.Mechanism
• Micturition and the bladder reflexThe bladder fills while relaxed and empties through a reflex coordinated by the sacral cord and brainstem, which the cortex allows or holds back.Regulation
• Mixed acid–base disordersSometimes two or three acid–base problems happen at once; they show up because the compensation doesn’t fit what is expected.Measurement
• Physiology of acute and chronic kidney failureWhen the kidneys filter too little, potassium, acid, water and wastes build up and kidney hormones fail; cause and speed shape the picture.Mechanism
• Proximal tubule transportThe first part of the tubule takes back two-thirds of the filtered salt and water and nearly all the glucose and amino acids.Mechanism
• Renal blood flow, autoregulation and tubuloglomerular feedbackThe kidney keeps its flow and filtration nearly constant even when blood pressure rises or falls a lot, by narrowing or widening its inflow arteriole.Regulation
• Renal handling of calcium, phosphate and magnesiumThe kidney decides how much calcium, phosphate and magnesium the body keeps; each one is reclaimed mainly in a different part of the tubule.Mechanism
• Renal handling of H⁺ and bicarbonateThe kidney reclaims all filtered bicarbonate and makes new bicarbonate by excreting the acid that metabolism produces.Mechanism
• Urine dilution, free water and osmotic diuresisThe kidney can excrete water without salt (dilute urine) or hold on to it; free-water clearance shows which way it is working.Measurement
• Tubular secretion of organic acids and basesThe proximal tubule pulls many drugs and wastes out of the blood and dumps them into urine, even those bound to proteins.Mechanism

Respiratory

Mechanics, volumes, ventilation/perfusion, gas transport and the control of breathing.

• CO₂ transport and the Haldane effectCO₂ travels in blood mostly as bicarbonate. When hemoglobin gives up O₂, it picks up more CO₂ and acid.Mechanism · ★
• Control of breathing, chemoreceptors and lung reflexesThe brainstem sets the rhythm of breathing. Blood CO₂ tunes it most; low O₂ only matters once it falls a lot.Regulation · ★
• Dead space and alveolar ventilationPart of every breath stays in the airway tubes and never reaches the alveoli. What matters for CO₂ is the air that does arrive.Concept · ★
• Lung volumes, capacities and spirometryThe lung has four basic volumes; their sums are the capacities. Spirometry measures most of them, but not the air that always stays inside.Measurement · ★
• Mechanics of breathing: pressures and musclesTo breathe in, muscles enlarge the chest, pressure inside the lungs drops and air flows in by itself. Quiet breathing out is passive.Mechanism · ★
• Obstructive and restrictive patterns, and flow–volume loopsIn obstruction the air comes out slowly; in restriction the lung is small. The FEV₁/FVC ratio tells them apart.Measurement · ★
• Oxygen transport and the dissociation curveAlmost all oxygen rides bound to hemoglobin. Its S-shaped curve explains why it loads in the lung and unloads in the tissues.Mechanism · ★
• Oxygenation: SpO₂, PaO₂, cyanosis and oxygen therapyA pulse oximeter shows how full of O₂ hemoglobin is; a blood gas measures O₂ pressure. Each has its traps.Measurement · ★
• The alveolar gas equation and the A–a gradientA formula estimates how much oxygen is in the alveoli. If arterial blood has much less, the problem is in the lung.Measurement · ★
• The causes of hypoxemiaThere are only a few ways to end up with too little oxygen in the blood. The A–a gradient and the response to oxygen tell you which.Mechanism · ★
• Ventilation–perfusion matching and West zonesTo exchange gas, air and blood must reach the same alveolus. If either is missing, that alveolus is wasted.Mechanism · ★
• Abnormal breathing patterns and sleep apneaHow someone breathes says a lot: cycles that swell and fade, deep breaths from acid, or pauses in sleep each have different causes.Regulation
• Airway resistanceThe narrower a tube, the harder it is to push air through. Halving the radius multiplies resistance by 16.Concept
• Carbon monoxide, methemoglobin and cyanideThree poisons starve tissues of oxygen even when the lungs work: two spoil hemoglobin and one stops cells from using oxygen.Mechanism
• Diffusion across the respiratory membrane and DLCOOxygen crosses from the air sac into the blood through a very thin wall. If the wall thickens or surface is lost, less gets through.Mechanism
• Hypoxemic and hypercapnic respiratory failureThe lungs can fail in two ways: they can't get oxygen into the blood (type 1), or they can't clear CO₂ because breathing is too weak (type 2).Mechanism
• Lung and chest wall complianceCompliance is how much the lung inflates for each unit of pressure. A stiff lung takes more work to fill.Concept
• Oxygen content, delivery and extractionTissues care not just about saturation but about how much oxygen the blood carries and how much blood arrives. Three numbers capture it.Measurement
• Physiology of pulmonary edemaWhen lung capillaries leak more fluid than the lymphatics can drain, the air sacs flood and oxygen can't get in.Mechanism
• Pleural fluid: formation and drainageA tiny layer of fluid between lung and chest wall lets them glide. It is made and drained all the time; if the balance fails, an effusion builds up.Mechanism
• Surface tension, surfactant and Laplace's lawA thin film of fluid lines the air sacs and pulls them shut. Surfactant is a natural detergent that weakens that pull and keeps them open.Concept
• The pulmonary circulation and hypoxic vasoconstrictionThe right heart pumps all the blood through the lungs at low pressure. Where oxygen is missing, the vessels narrow to send blood to well-aired areas.Regulation
• The work of breathingBreathing costs energy: the lung must be stretched and airway resistance overcome. In asthma or obesity it costs far more.Concept
• Airway defenses, cough and mucociliary clearanceThe nose filters, mucus traps, cilia sweep upward and cough throws it out: that is how the lung stays clean.Concept
• The bronchial circulationThe lung has two blood supplies: the pulmonary one to oxygenate blood, and the bronchial one that feeds the airways with blood from the aorta.Concept

Endocrine

The hypothalamic–pituitary axes, thyroid, adrenal, endocrine pancreas and calcium.

• Actions of cortisolCortisol is the lasting stress hormone: it raises glucose, damps inflammation and keeps blood pressure up.Mechanism · ★
• Actions of thyroid hormonesThyroid hormones set the pace of metabolism: with too much everything speeds up, with too little everything slows down.Mechanism · ★
• Aldosterone: actions and controlAldosterone makes the kidney keep sodium and excrete potassium and hydrogen. Angiotensin II and high potassium trigger it.Regulation · ★
• Calcium regulation: PTH, vitamin D and calcitoninWhen blood calcium falls, the parathyroid releases PTH, which pulls it from bone, saves it in the kidney and activates vitamin D.Regulation · ★
• Islets and insulin: secretion and actionsAfter a meal the pancreatic β cell releases insulin, which makes liver, muscle and fat store glucose and energy.Regulation · ★
• Physiology of diabetes and ketoacidosisIn diabetes insulin is missing or does not work well: glucose stays in the blood and, if insulin is gone, the body makes acids (ketones).Mechanism · ★
• The HPA axis and its circadian rhythmThe brain sends CRH, the pituitary ACTH and the adrenal cortisol. Cortisol is high on waking, low at midnight and rises with stress.Regulation · ★
• The hypothalamic–pituitary system: overviewThe hypothalamus gives orders to the pituitary, and the pituitary drives the thyroid, adrenals, gonads, liver and breast.Concept · ★
• The thyroid axis: reading TSH and free T4TSH is the thermostat: it rises when thyroid hormone is short and falls when there is too much. Free T4 tells where the fault is.Measurement · ★
• Appetite hormones: leptin, ghrelin and incretinsFat sends leptin to say «we have reserves»; the empty stomach sends ghrelin to say «eat»; the gut sends GLP-1 to say «enough».Regulation
• Blood glucose, glucose tolerance test and HbA1cThree tests show how well the body handles sugar: a fasting level, a curve after a sugary drink and HbA1c, the average of the last months.Measurement
• Bone remodelingBone is rebuilt all the time: some cells dig out old bone and others fill the hole with new bone. If digging wins, bone gets weak.Mechanism
• Glucagon and the counter-regulatory hormonesWhen glucose falls, glucagon and epinephrine raise it within minutes; cortisol and GH hold it up for hours.Regulation
• Growth hormone and IGF-1The pituitary releases growth hormone in pulses, mostly in deep sleep; the liver answers with IGF-1, which makes bones and tissues grow.Regulation
• Hormones: types, receptors and feedbackHormones are chemical messages in the blood. Protein hormones act at the membrane; steroid and thyroid hormones act inside the cell.Concept
• Measuring hormones: stimulation and suppression testsIf a hormone is thought to be missing, the gland is stimulated; if it is thought to be in excess, the test tries to suppress it.Measurement
• Prolactin and its control by dopamineProlactin makes the breast produce milk. The brain keeps it switched off with dopamine; take the dopamine away and prolactin rises.Regulation
• The adrenal cortex: zones, hormones and androgensThe outer layer of each adrenal gland has three zones: one makes the salt hormone, one the stress hormone and one weak male hormones.Concept
• The adrenal medulla and catecholaminesThe core of each adrenal gland is a nerve relay that pours adrenaline into the blood in seconds when the body faces danger or a drop in sugar.Regulation
• The endocrine stress responseIn injury, surgery or infection, the body releases cortisol, adrenaline and other hormones that raise sugar, hold water and burn its own protein.Regulation
• The physiological response to hypoglycemiaWhen blood sugar falls, the body first stops insulin, then releases glucagon and adrenaline, and only then do symptoms appear.Regulation
• The posterior pituitary: ADH and oxytocinThe posterior pituitary releases two hypothalamic hormones: ADH, which makes the kidney save water, and oxytocin, for birth and milk.Regulation
• Phosphate and FGF-23Phosphate builds bone and stores energy. Bone cells make FGF-23, a hormone that tells the kidney to throw out extra phosphate.Regulation
• The pineal gland and melatoninIn darkness the pineal gland releases melatonin, a signal that tells the body it is night. Light, especially blue light, switches it off.Regulation
• Thyroid hormone transport and deiodinasesAlmost all thyroid hormone travels attached to proteins; only a tiny free part works. Tissues turn T4 into the active T3 themselves.Mechanism

Neurophysiology

Synapses, sensation, pain, motor control, the autonomic system, special senses and sleep.

• Adrenergic and cholinergic receptorsAdrenaline and acetylcholine act through different receptor types; knowing which type sits on an organ predicts what a drug will do.Table to know · ★
• Basal ganglia and movement controlDeep brain nuclei work as brake and accelerator for movement, letting the wanted action through. Dopamine keeps the balance.Regulation · ★
• Cerebral blood flow, brain metabolism and intracranial pressureThe brain uses a fifth of the body's oxygen and stores no fuel, so its blood flow is tightly controlled; swelling inside the closed skull is dangerous.Regulation · ★
• Motor cortex and the corticospinal tractThe motor cortex plans voluntary movement and sends the command down the corticospinal tract, which crosses in the lower brainstem.Concept · ★
• Pain and temperature: pathways and modulationPain starts at free nerve endings, rides two fibre speeds up the spinal cord, and the body can turn its volume up or down.Mechanism · ★
• Somatosensory pathways: dorsal column and anterolateralTouch, vibration and position travel up the cord in one bundle, pain and temperature in another. Where each crosses explains cord injuries.Concept · ★
• Spinal cord reflexesA reflex is a fast, automatic loop through the spinal cord: tap the tendon and the muscle jerks, with no decision from the brain.Regulation · ★
• Synaptic transmissionA nerve cell passes its signal to the next one by releasing a chemical messenger across a tiny gap: the synapse.Mechanism · ★
• The autonomic nervous system: organizationThe autonomic system runs the organs without conscious control: the sympathetic side prepares for action, the parasympathetic side for rest.Concept · ★
• Upper versus lower motor neuron lesionsWeakness from the brain or cord is stiff with brisk reflexes; weakness from the nerve or anterior horn is floppy, wasted and areflexic.Concept · ★
• Aqueous humor and intraocular pressureThe eye makes and drains a clear fluid all the time; if drainage fails, pressure rises and can harm the optic nerve.Regulation
• CSF and the blood–brain barrierThe brain floats in a clear fluid made inside its cavities, and a tight wall of vessel cells chooses what reaches the neurons.Concept
• Functions of the cerebellumThe cerebellum compares the movement that was planned with the one being made and corrects it, so motion is smooth, accurate and well timed.Regulation
• Functions of the hypothalamusA small region below the thalamus that keeps the body's settings: temperature, water, hunger, sleep, hormones and the stress response.Regulation
• Headache physiologyThe brain itself feels no pain; headaches come from the meninges, blood vessels, nerves and muscles around it.Mechanism
• Hearing: middle ear, cochlea and auditory pathwayThe ear turns sound waves into nerve signals: the middle ear boosts them, the cochlea sorts them by pitch.Mechanism
• Learning and memoryMemories are stored by strengthening the connections between neurons; the hippocampus files facts and events.Mechanism
• Muscle spindle and Golgi tendon organTwo sensors tell the spinal cord how long a muscle is and how hard it pulls, so movement stays smooth and safe.Mechanism
• Optics of the eye, accommodation and refractive errorsThe cornea and lens bend light onto the retina; if the eye is too long or too short, the image blurs.Concept
• Sensory receptors, coding and neuronal circuitsSense organs turn touch, light, sound or chemicals into nerve impulses; the brain reads which nerve fires and how fast.Concept
• Sympathetic and parasympathetic effects on each organThe sympathetic system prepares the body for action; the parasympathetic one for rest, digestion and repair.Table to know
• The main neurotransmittersNeurons talk with a small set of chemicals; each one has its own jobs, its source nuclei and the diseases that follow when it fails.Table to know
• The retina and phototransductionLight makes rods and cones go quiet; the retina turns that change into the signals the brain reads as sight.Mechanism
• The vestibular system, tone and postureSensors in the inner ear detect head turns and tilts, keep the eyes steady and keep the body upright.Mechanism
• The visual pathway, pupillary reflexes and eye movementsSignals go from the eye to the back of the brain; where the path is damaged decides which part of the view is lost.Concept
• Visceral and referred painOrgans hurt in a vague, deep way, and the brain often blames the skin that shares the same spinal segment.Mechanism
• Wakefulness, sleep, the EEG and seizuresThe brain cycles between waking, deep sleep and dream sleep; the EEG shows each state as a different rhythm.Regulation
• Taste and smellTaste buds detect five basic tastes; the nose adds thousands of smells. Together they make flavour.Mechanism
• The cerebral cortex and languageDifferent areas of the cortex handle movement, sensation and language; damage to each one causes a typical problem.Concept
• The limbic system, emotion and rewardA ring of brain structures links feelings, memory and motivation, and drives the body's emotional reactions.Concept

Gastrointestinal

Motility, secretions, gut hormones, digestion, absorption and the liver.

• Bile and the enterohepatic circulationThe liver makes bile to emulsify fat; almost all bile salts are reabsorbed in the ileum and return to the liver to be used again.Mechanism · ★
• Carbohydrate digestion and absorptionStarch and sugars are cut down to glucose, galactose and fructose; only those monosaccharides cross the gut wall.Mechanism · ★
• Fat digestion and absorptionBile disperses fat, lipase cuts it, micelles carry it to the wall, and it leaves the gut packed into chylomicrons through the lymph.Mechanism · ★
• Gastric acid secretionParietal cells pump acid into the stomach with the H⁺/K⁺ pump; the vagus, gastrin and histamine turn it on, and somatostatin turns it off.Mechanism · ★
• Gastrointestinal hormonesThe gut makes its own hormones: they report what food arrived and tune acid, enzymes, bile, emptying and appetite.Table to know · ★
• Water and electrolyte absorption and how diarrhea happensThe gut handles about 9 L of fluid a day and returns nearly all of it to the blood by following sodium; diarrhea is what happens when that balance fails.Mechanism · ★
• Absorption of iron, calcium and vitamin B12Iron and calcium are absorbed mainly in the duodenum; vitamin B12 needs intrinsic factor from the stomach and is absorbed at the end of the ileum.Mechanism
• Exocrine pancreatic secretionThe pancreas sends bicarbonate to the duodenum to neutralize acid, and enzymes that digest protein, fat and starch.Mechanism
• Functions of the liverThe liver processes what is absorbed, makes blood proteins, stores energy, clears toxins and produces bile.Concept
• Gastric motility and emptyingThe stomach stores food, grinds it and hands it to the duodenum in small portions, at the pace the gut can handle.Mechanism
• Protein digestion and absorptionProteins are cut in the stomach and duodenum down to amino acids and short peptides, which the gut absorbs with its own transporters.Mechanism
• Small bowel and colon motilityThe gut mixes its contents with segmenting contractions and moves them on with peristalsis; the colon dries them and pushes them with mass movements.Mechanism
• Splanchnic and portal circulationBlood from the gut, spleen and pancreas passes through the liver first via the portal vein; it is a large reservoir the body can mobilize.Regulation
• Swallowing and esophageal motilitySwallowing starts voluntarily and continues as an automatic reflex that seals the airway and pushes the bolus into the stomach in a few seconds.Mechanism
• The enteric nervous system, slow waves and GI controlThe gut has its own network of neurons: it sets the rhythm, mixes and pushes contents; the vagus and sympathetic nerves only adjust the volume.Regulation
• Vomiting and its controlVomiting is a protective brainstem reflex that expels stomach contents; losing a lot of acid upsets the electrolytes.Regulation
• Defecation and continenceWhen stool fills the rectum, a reflex opens the internal sphincter; the voluntary external sphincter decides whether it is time to go.Regulation
• Patterns of malabsorptionMalabsorption happens when luminal digestion, the absorbing mucosa or the lymphatic exit fails; each failure leaves its own footprint.Mechanism
• Salivary secretionThe salivary glands make 1 to 1.5 L of saliva a day to moisten food, start starch digestion and protect the mouth and teeth.Mechanism

Cell and membrane

Homeostasis, compartments, membrane transport and the membrane potential.

• Body fluid compartmentsAbout two thirds of the body's water is inside cells and one third outside them, between cells and in the blood.Concept · ★
• Homeostasis and feedback controlThe body measures its variables (temperature, glucose, pressure) and corrects them when they drift from a target value.Concept · ★
• Membrane transport: diffusion, channels and carriersSubstances cross the cell membrane by dissolving in it, through channels, on carriers, or by spending energy.Mechanism · ★
• Osmosis, osmolarity and tonicityWater crosses a membrane towards the side with more dissolved particles; that is how cells swell or shrink.Concept · ★
• The resting membrane potentialThe inside of a resting cell is negative compared with the outside, mainly because potassium leaks out through its channels.Mechanism · ★
• Cell signaling for physiologyHormones and neurotransmitters bind receptors that switch on chains of signals inside the cell.Concept
• Diffusion and Fick's lawMolecules move from where there are more to where there are fewer; Fick's law says how fast.Concept
• Ion channels and gatingChannels are protein pores that open and close to let one specific ion through in microseconds.Concept
• Primary and secondary active transportCells spend energy to move substances against their gradient, using ATP pumps or riding on the sodium gradient.Mechanism
• The Nernst and Goldman equationsTwo formulas that work out a cell's voltage from the ion concentrations inside and outside it.Measurement
• Cell volume regulationCells guard against swelling or shrinking by moving ions and small molecules out or in, and water follows them.Regulation
• Endocytosis, exocytosis and vesiclesCells wrap particles in little membrane bags to bring them in (endocytosis) or to release their contents (exocytosis).Mechanism

Nerve and muscle

The action potential, the neuromuscular junction and contraction of skeletal, cardiac and smooth muscle.

• Impulse conduction and myelinMyelin wraps the axon like insulation so the signal jumps from gap to gap; that makes it many times faster and cheaper.Mechanism · ★
• Skeletal muscle excitation–contraction couplingThe electrical signal dives into the muscle fiber through tiny tubes and makes an internal store release calcium, which switches on contraction.Mechanism · ★
• Sliding filaments and the cross-bridge cycleMuscle shortens because tiny myosin heads grab actin, pull, let go and grab again, burning one ATP per stroke.Mechanism · ★
• The nerve action potentialA nerve signal is a brief, all-or-none flip of the voltage across the cell membrane, driven by sodium rushing in and potassium leaving.Mechanism · ★
• The neuromuscular junctionWhere a motor nerve meets a muscle fiber, it releases acetylcholine; each nerve impulse reliably fires one muscle impulse.Mechanism · ★
• Fast and slow fibers, energy and fatigueSlow red fibers run on oxygen and last for hours; fast white fibers are powerful but tire quickly. Muscles mix both.Concept
• Length–tension and force–velocity relationshipsA muscle is strongest at a middle length and when it moves slowly; stretched too much, squeezed too short or moving fast, it pulls less.Concept
• Motor units, recruitment and summationA muscle grades its force by switching on more nerve–fiber groups and by firing them faster until the twitches fuse into a steady pull.Concept
• Refractory periods and excitabilityRight after firing, a nerve cannot fire again for a moment. Blood potassium and calcium change how easily nerves and muscles fire.Concept
• Skeletal, cardiac and smooth muscle comparedThe body has three muscle types: skeletal for movement, cardiac for the heartbeat and smooth for organs and vessels. They switch on in different ways.Table to know
• Smooth muscle contractionSmooth muscle in vessels, airways and gut squeezes slowly and can hold tone for hours using very little energy.Mechanism
• Types of nerve fibersNerves carry fibers of different thickness: thick fast ones for movement and touch, thin slow ones for burning pain and temperature.Table to know
• Muscle hypertrophy, atrophy and remodelingMuscle grows with load and shrinks with disuse, illness or age, because it constantly builds and breaks down its proteins.Concept

Reproduction, pregnancy and the fetus

Male and female physiology, the menstrual cycle, pregnancy, lactation and the fetal circulation.

• Fetal circulation and the transition at birthBefore birth the placenta does the work of the lungs, so blood bypasses them through three shortcuts that close in the first hours and days of life.Mechanism · ★
• Maternal physiological changes in pregnancyIn pregnancy the mother's blood volume, heart output, breathing and kidneys all step up to feed the baby, and several lab values change.Regulation · ★
• The male gonadal axis and spermatogenesisThe brain sends pulsed signals to the testes, which make testosterone and, over about two and a half months, new sperm.Regulation · ★
• The menstrual cycle: ovary and endometriumAbout once a month the ovary ripens an egg and the uterine lining thickens; if no pregnancy occurs, hormones fall and the lining sheds.Regulation · ★
• Actions of estrogen and progesteroneEstrogen builds and grows female tissues and protects bone; progesterone prepares the uterus for pregnancy and keeps it quiet.Mechanism
• Fertilization and implantationA sperm meets the egg in the fallopian tube; the fertilized egg divides, travels to the uterus and burrows into its lining about a week later.Mechanism
• LactationAfter birth prolactin makes the breast produce milk and oxytocin squeezes it out when the baby sucks.Regulation
• MenopauseMenopause is the end of periods when the ovaries run out of follicles; estrogen falls and the brain's signals to the ovary rise.Regulation
• Newborn physiology and fetal maturationAt birth the baby must breathe, keep warm, feed and clear bilirubin on its own; the lungs, liver and kidneys are still maturing.Concept
• Oogenesis, follicles and ovulationGirls are born with all their eggs, paused halfway through division; each month one of them finishes maturing and is released.Mechanism
• Parturition: onset and uterine contractionAt term the quiet uterus switches on: hormones and stretch make it contract more and more strongly until the baby is born.Regulation
• PubertyPuberty begins when the brain restarts pulses of GnRH; the gonads wake up and the body matures sexually and grows fast.Regulation
• Testosterone and its actionsTestosterone builds male body features, muscle and sperm; part of it is turned into a stronger form (DHT) and part into estrogen.Mechanism
• The placenta and pregnancy hormonesThe placenta passes oxygen and food to the baby and works as a hormone gland that keeps the pregnancy going.Concept
• Erection and ejaculationErection is a blood-flow event controlled by parasympathetic nerves and nitric oxide; ejaculation is a sympathetic and somatic reflex.Mechanism
• Sex determination and differentiationA gene on the Y chromosome turns the early gonad into a testis; its hormones then build the male tract. Without them, the female pattern develops.Concept

Blood, hemostasis and basic immunity

Red cells and iron, white cells, blood groups, hemostasis and coagulation.

• Anemia physiology and compensationAnemia means too little hemoglobin to carry oxygen. The body copes by pumping faster and letting go of oxygen more easily.Mechanism · ★
• Blood groups, transfusion and transfusion reactionsRed cells carry sugar and protein labels (A, B, Rh). Giving blood with the wrong label makes the patient's antibodies destroy it.Concept · ★
• Coagulation tests: PT/INR, aPTT and plateletsA few blood tests show which part of clotting is failing: the platelets, the extrinsic pathway (PT/INR) or the intrinsic one (aPTT).Measurement · ★
• Primary hemostasis and plateletsWhen a vessel is cut it narrows and platelets stick to the wound, forming a soft plug in seconds to minutes.Mechanism · ★
• The coagulation cascadeA chain of blood proteins turns on one after another to make thrombin, which weaves fibrin threads that hold the platelet plug.Mechanism · ★
• Body iron balanceThe body cannot get rid of extra iron, so it controls how much the gut absorbs. The liver hormone hepcidin is the gatekeeper.Regulation
• Erythropoiesis and erythropoietinThe kidney measures oxygen. When it is low, it releases erythropoietin, which tells the bone marrow to make more red cells.Regulation
• Fibrinolysis and natural anticoagulantsBlood has built-in brakes that keep clots small, and a cleanup enzyme, plasmin, that dissolves them once the vessel has healed.Regulation
• HematopoiesisAll blood cells come from a few stem cells in the bone marrow that copy themselves and mature into red cells, white cells and platelets.Concept
• Innate and adaptive immunity: overviewThe body has a fast, general defence (innate) and a slower, precise one with memory (adaptive). They work as a team.Concept
• The physiology of inflammationInflammation is the body's alarm: vessels widen and leak so defence cells and proteins reach the injury. That is why it gets red, hot, swollen and sore.Mechanism
• The red cell life cycle and the spleenA red cell lives about four months. Old, stiff cells are caught in the spleen, eaten, and their iron is reused; the rest becomes bilirubin.Concept
• Thrombosis and bleeding: Virchow's triad and hemostatic defectsClots form where blood is slow, the vessel wall is damaged or the blood clots too easily. Bleeding happens when platelets or clotting factors fail.Mechanism
• White blood cells: types and functionsWhite blood cells are the body's defence team. Each type has a job: eat bacteria, fight parasites, make antibodies or kill infected cells.Table to know
• Polycythemia: physiological causesPolycythemia means too many red cells. It is usually the body's answer to low oxygen, but it makes the blood thick.Mechanism
• Rh incompatibilityAn Rh-negative mother can make antibodies against her Rh-positive baby's red cells. In a later pregnancy they cross the placenta and destroy the baby's cells.Mechanism

Temperature, exercise and metabolism

Temperature and fever, energy metabolism, fasting, exercise, altitude and diving.

• Body temperature regulationThe brain keeps the body core near 37 °C: it sweats and opens skin vessels when hot, shivers and closes them when cold.Regulation · ★
• Exercise and training physiologyDuring exercise the heart pumps more, the lungs move more air and muscle pulls more oxygen; training improves every step.Regulation · ★
• Fed and fasting states: the hormonal switchAfter a meal insulin stores energy; when fasting, glucagon pulls it from stores so the brain never runs short of glucose.Regulation · ★
• FeverIn fever the brain turns its thermostat up: the body feels cold and makes heat until it reaches the new temperature.Mechanism · ★
• High altitude and acclimatizationAt altitude air has the same share of oxygen but less pressure; the body breathes harder and makes more red blood cells.Regulation · ★
• Physiology of the vital signs (including blood pressure measurement)Temperature, pulse, breathing, blood pressure and oxygen saturation: five numbers that sum up how the body is doing right now.Measurement · ★
• Energy balance, food intake and obesityWeight changes when what we eat differs from what we burn; the hypothalamus tries to keep that balance with hunger and fullness signals.Regulation
• Energy metabolism and basal metabolic rateThe basal metabolic rate is the energy the body burns at complete rest just to stay alive: most of what it spends each day.Measurement
• Heat exhaustion and heat strokeIn great heat and effort the body loses water and salt; if it can no longer cool down, temperature climbs out of control and damages organs.Mechanism
• Hypothermia and cold injuryIf the body loses heat faster than it makes it, core temperature falls below 35 °C and everything slows down.Mechanism
• Prolonged fasting and starvationWithout food the body spends glycogen, then fat, and spares muscle by switching the brain to ketones; in the end it burns vital protein.Regulation
• Vitamins and minerals: a physiological overviewVitamins and minerals are needed in small amounts, but without them blood, bones, nerves and the thyroid fail.Table to know
• Aviation and space physiologyIn flight the air has less pressure, accelerations move blood around, and in space the lack of gravity weakens bone and muscle.Concept
• Diving, decompression and hyperbaric oxygenUnderwater, pressure rises fast; gases are squeezed and dissolve more in blood, and on the way up they can form bubbles.Mechanism
• Nitrogen balance and body proteinComparing the nitrogen that comes in with food with the nitrogen lost in urine shows whether the body is gaining or losing protein.Measurement

A to Z

• Abnormal breathing patterns and sleep apneaRespiratory · Regulation
• Absorption of iron, calcium and vitamin B12Gastrointestinal · Mechanism
• Actions of cortisolEndocrine · Mechanism
• Actions of estrogen and progesteroneReproduction, pregnancy and the fetus · Mechanism
• Actions of thyroid hormonesEndocrine · Mechanism
• ADH, thirst and water balanceRenal, fluids and acid–base · Regulation
• Adrenergic and cholinergic receptorsNeurophysiology · Table to know
• Airway defenses, cough and mucociliary clearanceRespiratory · Concept
• Airway resistanceRespiratory · Concept
• Aldosterone: actions and controlEndocrine · Regulation
• Anemia physiology and compensationBlood, hemostasis and basic immunity · Mechanism
• Appetite hormones: leptin, ghrelin and incretinsEndocrine · Regulation
• Aqueous humor and intraocular pressureNeurophysiology · Regulation
• Aviation and space physiologyTemperature, exercise and metabolism · Concept
• Basal ganglia and movement controlNeurophysiology · Regulation
• Bile and the enterohepatic circulationGastrointestinal · Mechanism
• Blood glucose, glucose tolerance test and HbA1cEndocrine · Measurement
• Blood groups, transfusion and transfusion reactionsBlood, hemostasis and basic immunity · Concept
• Body fluid compartmentsCell and membrane · Concept
• Body iron balanceBlood, hemostasis and basic immunity · Regulation
• Body temperature regulationTemperature, exercise and metabolism · Regulation
• Bone remodelingEndocrine · Mechanism
• Buffers and the Henderson–Hasselbalch equationRenal, fluids and acid–base · Concept
• Calcium regulation: PTH, vitamin D and calcitoninEndocrine · Regulation
• Carbohydrate digestion and absorptionGastrointestinal · Mechanism
• Carbon monoxide, methemoglobin and cyanideRespiratory · Mechanism
• Cardiac excitation–contraction couplingCardiovascular · Mechanism
• Cardiac output and what sets itCardiovascular · Regulation
• Cell signaling for physiologyCell and membrane · Concept
• Cell volume regulationCell and membrane · Regulation
• Central venous pressure and the jugular pulseCardiovascular · Measurement
• Cerebral blood flow, brain metabolism and intracranial pressureNeurophysiology · Regulation
• CO₂ transport and the Haldane effectRespiratory · Mechanism
• Coagulation tests: PT/INR, aPTT and plateletsBlood, hemostasis and basic immunity · Measurement
• Control of breathing, chemoreceptors and lung reflexesRespiratory · Regulation
• Coronary circulation and myocardial ischemiaCardiovascular · Concept
• CSF and the blood–brain barrierNeurophysiology · Concept
• Dead space and alveolar ventilationRespiratory · Concept
• Defecation and continenceGastrointestinal · Regulation
• Dehydration and fluid overloadRenal, fluids and acid–base · Mechanism
• Diffusion across the respiratory membrane and DLCORespiratory · Mechanism
• Diffusion and Fick's lawCell and membrane · Concept
• Distal tubule and collecting ductRenal, fluids and acid–base · Mechanism
• Diving, decompression and hyperbaric oxygenTemperature, exercise and metabolism · Mechanism
• ECG basics: waves, intervals and leadsCardiovascular · Measurement
• Endocytosis, exocytosis and vesiclesCell and membrane · Mechanism
• Energy balance, food intake and obesityTemperature, exercise and metabolism · Regulation
• Energy metabolism and basal metabolic rateTemperature, exercise and metabolism · Measurement
• Erection and ejaculationReproduction, pregnancy and the fetus · Mechanism
• Erythropoiesis and erythropoietinBlood, hemostasis and basic immunity · Regulation
• Exercise and training physiologyTemperature, exercise and metabolism · Regulation
• Exocrine pancreatic secretionGastrointestinal · Mechanism
• Fast and slow fibers, energy and fatigueNerve and muscle · Concept
• Fat digestion and absorptionGastrointestinal · Mechanism
• Fed and fasting states: the hormonal switchTemperature, exercise and metabolism · Regulation
• Fertilization and implantationReproduction, pregnancy and the fetus · Mechanism
• Fetal circulation and the transition at birthReproduction, pregnancy and the fetus · Mechanism
• FeverTemperature, exercise and metabolism · Mechanism
• Fibrinolysis and natural anticoagulantsBlood, hemostasis and basic immunity · Regulation
• Flow, pressure and resistance: Poiseuille and turbulent flowCardiovascular · Concept
• Fluid shifts between compartmentsRenal, fluids and acid–base · Mechanism
• Functional anatomy of the nephronRenal, fluids and acid–base · Concept
• Functions of the cerebellumNeurophysiology · Regulation
• Functions of the hypothalamusNeurophysiology · Regulation
• Functions of the liverGastrointestinal · Concept
• Gastric acid secretionGastrointestinal · Mechanism
• Gastric motility and emptyingGastrointestinal · Mechanism
• Gastrointestinal hormonesGastrointestinal · Table to know
• Glomerular filtration: the barrier and its determinantsRenal, fluids and acid–base · Mechanism
• Glucagon and the counter-regulatory hormonesEndocrine · Regulation
• Glucose transport maximum and renal thresholdRenal, fluids and acid–base · Measurement
• Growth hormone and IGF-1Endocrine · Regulation
• Headache physiologyNeurophysiology · Mechanism
• Hearing: middle ear, cochlea and auditory pathwayNeurophysiology · Mechanism
• Heart failure physiologyCardiovascular · Mechanism
• Heart sounds and where they come fromCardiovascular · Mechanism
• Heat exhaustion and heat strokeTemperature, exercise and metabolism · Mechanism
• HematopoiesisBlood, hemostasis and basic immunity · Concept
• High altitude and acclimatizationTemperature, exercise and metabolism · Regulation
• Homeostasis and feedback controlCell and membrane · Concept
• Hormones: types, receptors and feedbackEndocrine · Concept
• How arrhythmias ariseCardiovascular · Mechanism
• How edema formsCardiovascular · Mechanism
• How the lymphatic system worksCardiovascular · Concept
• Hypothermia and cold injuryTemperature, exercise and metabolism · Mechanism
• Hypoxemic and hypercapnic respiratory failureRespiratory · Mechanism
• Impulse conduction and myelinNerve and muscle · Mechanism
• Innate and adaptive immunity: overviewBlood, hemostasis and basic immunity · Concept
• Ion channels and gatingCell and membrane · Concept
• Islets and insulin: secretion and actionsEndocrine · Regulation
• IV fluids: tonicity and where they goRenal, fluids and acid–base · Concept
• LactationReproduction, pregnancy and the fetus · Regulation
• Learning and memoryNeurophysiology · Mechanism
• Length–tension and force–velocity relationshipsNerve and muscle · Concept
• Local and humoral control of blood flowCardiovascular · Regulation
• Long-term blood pressure control by the kidneyCardiovascular · Regulation
• Lung and chest wall complianceRespiratory · Concept
• Lung volumes, capacities and spirometryRespiratory · Measurement
• Maternal physiological changes in pregnancyReproduction, pregnancy and the fetus · Regulation
• Measuring GFR and plasma flow: inulin, creatinine, PAH and filtration fractionRenal, fluids and acid–base · Measurement
• Measuring hormones: stimulation and suppression testsEndocrine · Measurement
• Mechanics of breathing: pressures and musclesRespiratory · Mechanism
• Membrane transport: diffusion, channels and carriersCell and membrane · Mechanism
• MenopauseReproduction, pregnancy and the fetus · Regulation
• Metabolic acidosis, the anion gap and compensationRenal, fluids and acid–base · Mechanism
• Metabolic alkalosis and its compensationRenal, fluids and acid–base · Mechanism
• Micturition and the bladder reflexRenal, fluids and acid–base · Regulation
• Mixed acid–base disordersRenal, fluids and acid–base · Measurement
• Motor cortex and the corticospinal tractNeurophysiology · Concept
• Motor units, recruitment and summationNerve and muscle · Concept
• Murmurs and the hemodynamics of valve diseaseCardiovascular · Mechanism
• Muscle blood flow and the cardiovascular response to exerciseCardiovascular · Regulation
• Muscle hypertrophy, atrophy and remodelingNerve and muscle · Concept
• Muscle spindle and Golgi tendon organNeurophysiology · Mechanism
• Nervous control of the circulation and the CNS ischemic responseCardiovascular · Regulation
• Newborn physiology and fetal maturationReproduction, pregnancy and the fetus · Concept
• Nitrogen balance and body proteinTemperature, exercise and metabolism · Measurement
• Obstructive and restrictive patterns, and flow–volume loopsRespiratory · Measurement
• Oogenesis, follicles and ovulationReproduction, pregnancy and the fetus · Mechanism
• Optics of the eye, accommodation and refractive errorsNeurophysiology · Concept
• Osmosis, osmolarity and tonicityCell and membrane · Concept
• Oxygen content, delivery and extractionRespiratory · Measurement
• Oxygen transport and the dissociation curveRespiratory · Mechanism
• Oxygenation: SpO₂, PaO₂, cyanosis and oxygen therapyRespiratory · Measurement
• Pain and temperature: pathways and modulationNeurophysiology · Mechanism
• Parturition: onset and uterine contractionReproduction, pregnancy and the fetus · Regulation
• Patterns of malabsorptionGastrointestinal · Mechanism
• Phosphate and FGF-23Endocrine · Regulation
• Physiology of acute and chronic kidney failureRenal, fluids and acid–base · Mechanism
• Physiology of congenital shuntsCardiovascular · Mechanism
• Physiology of diabetes and ketoacidosisEndocrine · Mechanism
• Physiology of hypertensionCardiovascular · Mechanism
• Physiology of pulmonary edemaRespiratory · Mechanism
• Physiology of the vital signs (including blood pressure measurement)Temperature, exercise and metabolism · Measurement
• Pleural fluid: formation and drainageRespiratory · Mechanism
• Polycythemia: physiological causesBlood, hemostasis and basic immunity · Mechanism
• Potassium balanceRenal, fluids and acid–base · Regulation
• Preload, afterload and contractilityCardiovascular · Concept
• Primary and secondary active transportCell and membrane · Mechanism
• Primary hemostasis and plateletsBlood, hemostasis and basic immunity · Mechanism
• Prolactin and its control by dopamineEndocrine · Regulation
• Prolonged fasting and starvationTemperature, exercise and metabolism · Regulation
• Protein digestion and absorptionGastrointestinal · Mechanism
• Proximal tubule transportRenal, fluids and acid–base · Mechanism
• PubertyReproduction, pregnancy and the fetus · Regulation
• Reading an arterial blood gas step by stepRenal, fluids and acid–base · Measurement
• Reasoning through fluid and electrolyte imbalancesRenal, fluids and acid–base · Table to know
• Refractory periods and excitabilityNerve and muscle · Concept
• Renal blood flow, autoregulation and tubuloglomerular feedbackRenal, fluids and acid–base · Regulation
• Renal clearanceRenal, fluids and acid–base · Measurement
• Renal handling of calcium, phosphate and magnesiumRenal, fluids and acid–base · Mechanism
• Renal handling of H⁺ and bicarbonateRenal, fluids and acid–base · Mechanism
• Respiratory acidosis and alkalosisRenal, fluids and acid–base · Mechanism
• Rh incompatibilityBlood, hemostasis and basic immunity · Mechanism
• Salivary secretionGastrointestinal · Mechanism
• Sensory receptors, coding and neuronal circuitsNeurophysiology · Concept
• Sex determination and differentiationReproduction, pregnancy and the fetus · Concept
• Shock physiologyCardiovascular · Mechanism
• Skeletal muscle excitation–contraction couplingNerve and muscle · Mechanism
• Skeletal, cardiac and smooth muscle comparedNerve and muscle · Table to know
• Skin blood flowCardiovascular · Regulation
• Sliding filaments and the cross-bridge cycleNerve and muscle · Mechanism
• Small bowel and colon motilityGastrointestinal · Mechanism
• Smooth muscle contractionNerve and muscle · Mechanism
• Sodium and extracellular volume regulation (with natriuretic peptides)Renal, fluids and acid–base · Regulation
• Somatosensory pathways: dorsal column and anterolateralNeurophysiology · Concept
• Spinal cord reflexesNeurophysiology · Regulation
• Splanchnic and portal circulationGastrointestinal · Regulation
• Starling forces at the capillaryCardiovascular · Mechanism
• Surface tension, surfactant and Laplace's lawRespiratory · Concept
• Swallowing and esophageal motilityGastrointestinal · Mechanism
• Sympathetic and parasympathetic effects on each organNeurophysiology · Table to know
• Synaptic transmissionNeurophysiology · Mechanism
• Systolic, diastolic, mean and pulse pressureCardiovascular · Measurement
• Taste and smellNeurophysiology · Mechanism
• Testosterone and its actionsReproduction, pregnancy and the fetus · Mechanism
• The adrenal cortex: zones, hormones and androgensEndocrine · Concept
• The adrenal medulla and catecholaminesEndocrine · Regulation
• The alveolar gas equation and the A–a gradientRespiratory · Measurement
• The autonomic nervous system: organizationNeurophysiology · Concept
• The baroreceptor reflexCardiovascular · Regulation
• The bronchial circulationRespiratory · Concept
• The cardiac conduction systemCardiovascular · Concept
• The cardiac cycleCardiovascular · Mechanism
• The cardiac electrical axisCardiovascular · Measurement
• The causes of hypoxemiaRespiratory · Mechanism
• The cerebral cortex and languageNeurophysiology · Concept
• The coagulation cascadeBlood, hemostasis and basic immunity · Mechanism
• The countercurrent mechanism, urea recycling and urine concentrationRenal, fluids and acid–base · Mechanism
• The ECG in ischemia and infarctionCardiovascular · Measurement
• The ECG in potassium and calcium disordersCardiovascular · Measurement
• The endocrine stress responseEndocrine · Regulation
• The enteric nervous system, slow waves and GI controlGastrointestinal · Regulation
• The Frank–Starling mechanismCardiovascular · Mechanism
• The HPA axis and its circadian rhythmEndocrine · Regulation
• The hypothalamic–pituitary system: overviewEndocrine · Concept
• The limbic system, emotion and rewardNeurophysiology · Concept
• The main neurotransmittersNeurophysiology · Table to know
• The male gonadal axis and spermatogenesisReproduction, pregnancy and the fetus · Regulation
• The menstrual cycle: ovary and endometriumReproduction, pregnancy and the fetus · Regulation
• The Nernst and Goldman equationsCell and membrane · Measurement
• The nerve action potentialNerve and muscle · Mechanism
• The neuromuscular junctionNerve and muscle · Mechanism
• The physiological response to hypoglycemiaEndocrine · Regulation
• The physiology of inflammationBlood, hemostasis and basic immunity · Mechanism
• The pineal gland and melatoninEndocrine · Regulation
• The placenta and pregnancy hormonesReproduction, pregnancy and the fetus · Concept
• The posterior pituitary: ADH and oxytocinEndocrine · Regulation
• The pulmonary circulation and hypoxic vasoconstrictionRespiratory · Regulation
• The red cell life cycle and the spleenBlood, hemostasis and basic immunity · Concept
• The renin–angiotensin–aldosterone systemCardiovascular · Regulation
• The response to standing upCardiovascular · Regulation
• The resting membrane potentialCell and membrane · Mechanism
• The retina and phototransductionNeurophysiology · Mechanism
• The SA node pacemaker potentialCardiovascular · Mechanism
• The thyroid axis: reading TSH and free T4Endocrine · Measurement
• The ventricular action potentialCardiovascular · Mechanism
• The ventricular pressure–volume loopCardiovascular · Measurement
• The vestibular system, tone and postureNeurophysiology · Mechanism
• The visual pathway, pupillary reflexes and eye movementsNeurophysiology · Concept
• The work of breathingRespiratory · Concept
• Thrombosis and bleeding: Virchow's triad and hemostatic defectsBlood, hemostasis and basic immunity · Mechanism
• Thyroid hormone transport and deiodinasesEndocrine · Mechanism
• Transport in the loop of HenleRenal, fluids and acid–base · Mechanism
• Tubular secretion of organic acids and basesRenal, fluids and acid–base · Mechanism
• Types of nerve fibersNerve and muscle · Table to know
• Upper versus lower motor neuron lesionsNeurophysiology · Concept
• Urine dilution, free water and osmotic diuresisRenal, fluids and acid–base · Measurement
• Vascular compliance and capacitanceCardiovascular · Concept
• Venous return and the Guyton curvesCardiovascular · Mechanism
• Ventilation–perfusion matching and West zonesRespiratory · Mechanism
• Visceral and referred painNeurophysiology · Mechanism
• Vitamins and minerals: a physiological overviewTemperature, exercise and metabolism · Table to know
• Vomiting and its controlGastrointestinal · Regulation
• Wakefulness, sleep, the EEG and seizuresNeurophysiology · Regulation
• Water and electrolyte absorption and how diarrhea happensGastrointestinal · Mechanism
• Where and how diuretics actRenal, fluids and acid–base · Mechanism
• White blood cells: types and functionsBlood, hemostasis and basic immunity · Table to know

Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.

Representative model, for educational purposes only.