Animal and Human Physiology: Key Terms and Glossary

A red-cell metabolite that binds haemoglobin and lowers its oxygen affinity. It changes over days in hypoxia, not during one pass of a red cell through a capillary.

The red-cell carbohydrate antigens A and B. Plasma already contains antibody against whichever of those antigens the person's own cells lack.

The laboratory form of acclimatisation, a reversible change in one animal produced by a single imposed variable.

A reversible adjustment acquired by one individual over days or months, such as the ventilatory and red-cell changes at altitude. It is not a heritable evolutionary adaptation.

A heritable trait of a population, shaped across generations. In these notes the word is not used for a change one animal acquires in its own lifetime.

Antidiuretic hormone, made in the hypothalamus and released from the posterior pituitary. It inserts aquaporin-2 into the apical membrane of the collecting duct so that water can be reabsorbed.

The main catecholamine secreted into the blood by adrenal chromaffin cells, so that a sympathetic preganglionic signal becomes a circulating hormone.

Clumping of red cells when antibody meets the matching surface antigen.

The principal plasma protein, which provides most of the colloid osmotic pressure and binds many poorly soluble molecules.

The mineralocorticoid of the zona glomerulosa that increases principal-cell sodium reabsorption and potassium secretion by adding ENaC, sodium–potassium pumps, and apical potassium channels.

The relation that places alveolar PO2 from moist inspired PO2, alveolar PCO2, and the respiratory exchange ratio, so alveolar oxygen lies well below the inspired partial pressure.

The fresh-air volume that reaches exchanging lung each minute, equal to tidal volume minus dead space, multiplied by breathing frequency.

Urinary NH4+ generated from renal glutamine, which represents a net gain of bicarbonate only if the ammonium itself is excreted rather than reused in urea synthesis.

The peptide formed from angiotensin I that constricts resistance vessels, supports glomerular filtration, promotes proximal sodium reabsorption, and stimulates aldosterone, thirst, and ADH.

Plasma sodium minus the sum of chloride and bicarbonate. The gap widens when bicarbonate has been consumed and replaced by an unmeasured anion.

Atrial natriuretic peptide, released when the atrial wall is stretched. Through a guanylate-cyclase receptor it raises sodium excretion and opposes renin, aldosterone, and ENaC.

The glandular lobe derived from oral ectoderm, whose hormones are controlled by hypothalamic peptides delivered in portal blood.

A plasma inhibitor of thrombin and factor Xa, accelerated by heparan sulphate on intact endothelium so that clot formation is discouraged on healthy wall.

The collecting-duct water channel stored in vesicles and inserted into the apical membrane when ADH acts on the V2 receptor.

Slow passage of the impulse through the atrioventricular node, which lets the atria finish adding to ventricular filling before the ventricle contracts.

Local control that keeps blood flow, or glomerular filtration, nearly steady across a range of pressures, by myogenic contraction and by metabolites or tubuloglomerular feedback.

A stretch receptor in the carotid sinus or aortic arch that reports arterial pressure and corrects it within about a second. If pressure stays high, firing resets, so the reflex does not set the level over days.

A cholesterol-derived detergent that forms micelles with fat-digestion products and is reabsorbed in the terminal ileum for return to the liver.

The decrease in haemoglobin's oxygen affinity caused by raised CO2, H+, temperature, or red-cell 2,3-bisphosphoglycerate, which favours unloading in working muscle. It is not the effect of oxygenation on carbon dioxide carriage.

The hormone of thyroid C cells that inhibits osteoclasts when ionised calcium is high. In adult humans its day-to-day role is small beside PTH and vitamin D.

The active vitamin D hormone made by the kidney, which increases intestinal absorption of both calcium and phosphate.

The calcium-binding protein of smooth muscle. The calcium–calmodulin complex activates myosin light-chain kinase, and smooth muscle has no troponin switch.

The red-cell enzyme that hydrates carbon dioxide fast enough for bicarbonate to be formed during a single capillary transit.

The volume of blood ejected by one ventricle in a minute, the product of heart rate and stroke volume. Over time the right and left outputs must match.

The main peripheral chemoreceptor in humans. It senses dissolved arterial PO2, together with PCO2 and pH, and is not driven by a low oxygen content when PO2 itself is normal.

A medullary sensor of brain extracellular pH. Carbon dioxide crosses into that fluid and acidifies it; H+ itself does not cross promptly, so metabolic acidosis is not an immediate stimulus here.

Feed-forward drive from higher centres that raises heart rate and ventilation at the start of exercise, before metabolites from the muscle have reached the blood.

Exchange, on band 3, of bicarbonate leaving the red cell for chloride entering, so that plasma carries most of the bicarbonate formed from CO2.

The duodenal hormone released by fat and protein-digestion products. It contracts the gallbladder and, in humans, promotes pancreatic enzyme secretion largely through a vagal reflex.

An adrenal-medullary cell, equivalent to a postganglionic sympathetic neuron, that secretes catecholamine into the blood when preganglionic acetylcholine arrives.

The triglyceride-rich particle, carrying apolipoprotein B-48, that enterocytes release into lymph, so most absorbed fat bypasses the liver on its first circuit.

The plasma volume completely freed of a substance per unit time, UV/P, where U and P are the urine and plasma concentrations and V is the urine flow.

The force of cardiac contraction at a given end-diastolic length. Sympathetic stimulation raises this force without requiring a change in filling, which is the distinction from Frank–Starling.

The endocrine remnant of the ovulated follicle, secreting progesterone and oestradiol under LH, which regresses after about two weeks unless pregnancy maintains it.

The glucocorticoid of the zona fasciculata, secreted under ACTH. It supports hepatic glucose production and is required if catecholamines are to maintain vascular tone under stress.

Antiparallel flow of the two exchanging streams, as in a fish gill, which keeps an oxygen gradient along the whole surface. It is the wrong description of the bird lung.

The loop-of-Henle mechanism in which the water-impermeable thick ascending limb deposits salt, and the hairpin multiplies that single effect into a steep medullary osmotic gradient.

The bird arrangement in which successive capillaries meet through-flow parabronchial air at different points along the tube, rather than running antiparallel to the whole stream as gill blood does.

The partial pressure of a gas equals its mole fraction times the total pressure, so a lower barometric pressure lowers inspired PO2 even though the oxygen fraction is unchanged.

Ventilated volume that does not exchange gas, chiefly the conducting airways, which is subtracted from tidal volume before alveolar ventilation is obtained.

An enzyme that converts T4 to active T3 or, in the case of the type 3 enzyme, to inactive reverse T3.

The muscle, gland, or organ that changes a regulated variable after the sensor's report has been compared with the defended value.

The epithelial sodium channel of the principal-cell apical membrane, increased by aldosterone and inhibited by ANP.

The myenteric and submucosal plexuses, which can still produce a coordinated gut reflex after connections to the central nervous system are cut.

The duodenal brush-border enzyme that cuts trypsinogen to trypsin, after which trypsin activates the other pancreatic proteases in the lumen.

The hormone released by renal interstitial fibroblasts when local oxygen delivery falls, which increases red-cell production.

Control that responds to a predicted disturbance, before the regulated variable has actually changed. The prediction can be wrong, so feedback is still required.

Positive feedback in labour: cervical stretch releases oxytocin, contraction increases the stretch, and delivery of the fetus removes the stimulus so the loop stops.

Production of oestrogen that requires an androgen precursor from the fetal adrenal and aromatase in the placenta, so the output depends on fetus and placenta together.

The osteocyte hormone that increases phosphate excretion and suppresses the renal step that makes calcitriol.

The polymer formed from fibrinogen and cross-linked by factor XIIIa, which stabilises the platelet plug.

Conservation applied to oxygen: cardiac output equals whole-body oxygen uptake divided by the arteriovenous difference in oxygen content.

The pattern of sympathetic nerves and adrenal adrenaline, established within seconds, that speeds and strengthens the heart, redirects blood flow, and mobilises fuel. Cortisol supports fuel supply and vascular responsiveness later; it is not that fast limb.

The fall in shortening speed as load rises, from a maximum at no load to zero when the force is isometric, so that power is greatest at an intermediate load.

The rise in stroke volume, within limits, as diastolic filling increases cardiac fibre length, which lets each ventricle pump the blood it receives.

Local metabolites in working muscle overriding sympathetic vasoconstriction, so flow to that muscle can increase while other beds constrict.

The size of the correction a feedback loop produces for a given error.

The antral hormone that stimulates acid secretion, chiefly by causing enterochromaffin-like cells to release histamine onto the parietal cell.

Glomerular filtration rate, the volume of plasma filtered at the glomeruli per unit time, equal to the clearance of inulin.

Glucose-dependent insulinotropic polypeptide, the incretin from upper-intestinal K cells. It amplifies insulin secretion when glucose is already high and does little when glucose is low.

Glucagon-like peptide-1, the incretin from distal L cells. It amplifies insulin secretion only when glucose is elevated, suppresses glucagon, and slows gastric emptying.

An episodic burst of gonadotrophin-releasing hormone, about once an hour in an adult man. Continuous exposure desensitises the gonadotroph, and LH and FSH then fall.

The apical pump of the gastric parietal cell, which secretes H+ into the lumen in exchange for K+.

The fraction of blood volume that is occupied by red cells.

Haemolysis of fetal red cells by maternal IgG, classically anti-D made after an earlier Rh-positive pregnancy. The sensitising pregnancy is usually spared, because that antibody response comes too late to destroy the fetal cells of that pregnancy.

The effect of oxygenation on carbon dioxide carriage: deoxyhaemoglobin binds H+ and forms carbamino compounds more readily than oxyhaemoglobin. It is not the Bohr effect.

Human chorionic gonadotrophin, secreted by the syncytiotrophoblast, which binds the LH receptor and keeps the corpus luteum secreting until the placenta can maintain the pregnancy steroids itself.

The amount of a gas in solution equals its solubility times its partial pressure. Dissolved oxygen is therefore only a small part of arterial oxygen content.

The vein that delivers blood from the gut, pancreas, and spleen into a second capillary bed in the liver, so the liver sees absorbed sugars and amino acids before the rest of the body.

In this course, the paracrine amplifier of gastric acid, released from enterochromaffin-like cells onto H2 receptors of the parietal cell.

Cannon's name for the active defence of the internal environment by coordinated, often opposing, effectors, aimed at a range in which cells can work rather than at one unmoving number.

Insulin-like growth factor 1, made in the liver and locally in cartilage, through which growth hormone drives lengthening at the epiphyseal plate before that plate closes.

A gut hormone that makes an oral glucose load release more insulin than the same amount of glucose given into a vein.

The part of a control loop that compares the sensor's report with the value currently being defended.

The junction between cardiac muscle cells that couples them mechanically and, through gap junctions, electrically, so the myocardium contracts as a sheet.

A substance that is freely filtered and neither reabsorbed nor secreted, so its plasma clearance equals GFR.

A smooth-muscle state in which dephosphorylated cross-bridges remain attached and hold force with very little ATP use.

The dependence of active force on sarcomere length through the overlap of thick and thin filaments. Skeletal muscle in the body sits near the plateau, whereas ordinary cardiac filling sits on the ascending limb, which is why extra filling raises stroke volume.

The testicular cell that secretes testosterone under the control of LH.

The ovulatory burst of LH released when oestradiol has been high for long enough, and progesterone is still low, to flip feedback from negative to positive. Ovulation removes that oestradiol signal, and rising progesterone restores inhibition.

Cells of the distal nephron that sense NaCl delivery. High delivery constricts the afferent arteriole; low delivery promotes renin release.

The time-averaged arterial pressure that drives flow through the systemic resistance. At rest it lies closer to diastolic pressure than to the arithmetic midpoint, because diastole lasts longer.

A bile-salt aggregate that carries fatty acids and monoacylglycerols across the aqueous lumen to the brush border.

Bernard's internal environment: the extracellular fluid in which the cells of a multicellular animal live, rather than the outside world.

One motor neuron and all of the skeletal-muscle fibres it innervates.

Smooth muscle with little electrical coupling, each fibre more independently innervated and with little spontaneous activity, as in the iris and the large airways.

G-protein-coupled acetylcholine receptors on organs supplied by parasympathetic postganglionic fibres, distinct from nicotinic receptors at ganglia.

The enzyme, switched on by calcium–calmodulin, that phosphorylates smooth-muscle myosin so cross-bridges can cycle.

A control arrangement in which a rise in the measured variable produces a response that brings it back down.

Ligand-gated acetylcholine receptors that excite autonomic ganglion cells, chromaffin cells, and the skeletal muscle endplate.

The transmitter released by most sympathetic postganglionic fibres onto adrenergic receptors. Sweat glands are the exception: their sympathetic supply is cholinergic.

A hypothalamic nonapeptide released from the posterior pituitary. It strengthens uterine contraction in labour and ejects milk, but it does not synthesise the milk.

The electrocardiographic deflection produced by atrial depolarisation.

Para-aminohippurate, which is filtered and almost completely secreted, so its clearance approximates renal plasma flow.

A flow-through tube of the bird lung, ventilated in one direction by air-sac bellows during both inspiration and expiration. Exchange occurs in this tube, not in alveoli, which the bird lung does not use.

The intestinal brush-border transporter that takes dipeptides and tripeptides into the enterocyte together with H+.

A propulsive motor pattern, organised by the enteric plexuses, in which the gut contracts behind a bolus and relaxes in front of it.

An action that allows another hormone to work, as when cortisol must be present for catecholamines to maintain vascular tone in stress.

The high-energy store that creatine kinase uses to refill ATP during the first seconds of hard muscular work.

The protease, generated most effectively on fibrin itself, that cuts fibrin into soluble pieces and so removes clot locally.

The relation in which resistance of a rigid tube rises with viscosity and length and falls with the fourth power of radius. Blood and vessels depart from those assumptions, so the relation is used here as a qualitative guide.

Two capillary beds joined in series. The hypothalamic–pituitary version delivers releasing hormones to the anterior lobe before they are diluted in the general circulation.

A loop that amplifies a change. It is used for a transition that must run to completion, such as labour or the upstroke of an action potential, and each such loop contains its own stop.

Neural tissue of the pituitary that releases ADH and oxytocin made in hypothalamic cell bodies. Those hormones are not synthesised in the posterior lobe, and they have no releasing hormone.

The second neuron of an autonomic path, with its cell body in a ganglion and its axon ending at the organ.

The first neuron of an autonomic path, with its cell body in the brainstem or spinal cord and its synapse in a ganglion.

The anterior-pituitary hormone, held in check by dopamine, that maintains milk synthesis when suckling removes that inhibition. Ejection of the milk is oxytocin's job.

A protease activated when thrombin is bound to thrombomodulin. With protein S it destroys factors Va and VIIIa and so limits further thrombin generation.

Parathyroid hormone, released when ionised calcium falls. It increases bone resorption and renal calcium reabsorption, decreases phosphate reabsorption, and stimulates formation of calcitriol.

The electrocardiographic complex of ventricular depolarisation, kept short because the Purkinje system activates a large muscle mass together.

The band within which opposing effectors hold a variable, rather than a single value that is never allowed to move.

A hypothalamic peptide carried in portal blood to control secretion of an anterior-pituitary hormone.

The enzyme released from the kidney when perfusion pressure or macula-densa NaCl falls, or when renal sympathetic activity rises. It cleaves angiotensinogen to angiotensin I and thereby starts the cascade that retains sodium.

The D antigen of the Rh blood-group system. Anti-D is not present until a D-negative person is exposed, and the antibody that can then cross the placenta is IgG.

The duodenal hormone released when the lumen is acid, which drives a bicarbonate-rich secretion from the pancreatic ducts.

The fed pattern of alternating ring contractions in the small intestine, which mixes chyme and moves it little net distance.

The cell or receptor that reports a regulated variable, either as nerve impulses or as a hormone secretion.

The supporting cell of the seminiferous tubule, stimulated by FSH, which nurtures developing germ cells and secretes androgen-binding protein and inhibin.

A name for the value a control system is currently defending. It can move, as in fever or after baroreceptors reset, and it is not a fixed number inscribed in one neuron.

The sodium-coupled glucose transporters of the proximal tubule. SGLT2 reabsorbs most of the filtered glucose and SGLT1 recovers what remains.

The sodium-coupled transporter of the intestinal brush border that takes up glucose and galactose from the lumen.

Smooth muscle joined by gap junctions so that activity spreads through the sheet, which can contract on spontaneous slow waves, as in the gut.

The primary cardiac pacemaker, whose cells reach threshold by a slow spontaneous depolarisation and normally set the heart rate.

The recruitment order in which smaller motor neurons, innervating slow oxidative fibres, fire before larger neurons that supply fast, more fatigable fibres.

The balance of hydrostatic and oncotic pressures that decides whether fluid filters from a capillary into the interstitium. This is not the Frank–Starling relation of stroke volume to cardiac filling.

The volume of blood ejected by a ventricle in one beat, the difference between its end-diastolic and end-systolic volumes.

The electrocardiographic sign of ventricular repolarisation. It is upright because repolarisation finishes in the opposite order from depolarisation.

A sustained contraction produced when a second stimulus arrives before the twitch has relaxed, fused when the ripple disappears. Cardiac muscle cannot tetanise, because its refractory period outlasts the mechanical twitch and the ventricle must fill between beats.

The medullary segment that reabsorbs NaCl through the apical NKCC2 transporter and is impermeable to water, which both dilutes the lumen and powers the countercurrent multiplier.

The protease that converts fibrinogen to fibrin and, on the platelet surface, accelerates coagulation by activating upstream factors.

An endothelial protein that binds thrombin and redirects it to activate protein C, so thrombin on intact endothelium helps to stop the clot spreading.

An eicosanoid released by activated platelets that recruits further platelets into the haemostatic plug.

The large protein secreted into the thyroid follicle, on whose tyrosine residues iodine is attached and T4 and T3 are stored.

The protein on cells not normally in contact with blood that, with factor VIIa, starts the coagulation cascade at a wound.

Filtered buffer, chiefly phosphate, that carries secreted H+ out in the urine and thereby adds new bicarbonate to the blood.

The thin-filament complex of skeletal and cardiac muscle. Calcium binding to troponin C moves tropomyosin and allows cross-bridges to form.

The force transient that follows a single action potential, outlasting the electrical event because cross-bridge cycling and calcium removal are slower.

Oestradiol synthesis in which theca cells make androgens under LH and granulosa cells aromatise those androgens under FSH.

The human skeletal fibre classes: slow oxidative, fast oxidative-glycolytic, and fast glycolytic, brought in from fatigue-resistant towards fatigable as force rises.

Hairpin capillaries of the renal medulla that act as passive exchangers. They return solute to the interstitium and preserve the gradient only while their flow stays slow; they do not create the gradient.

The plasma protein that tethers platelets, through glycoprotein Ib, to exposed collagen, especially where shear is high.

The elastic-artery reservoir that stores part of the stroke volume in systole and recoils during diastole, so flow continues while the aortic valve is shut.

An inactive protease precursor. Pancreatic proteases are secreted in this form so that the activating cut occurs in the intestinal lumen rather than inside the gland.