Physiology

A chemoreceptor is a sensory cell or receptor system responding to chemical composition. In respiratory regulation, carbon-dioxide-related chemical signals contribute to feedback controlling ventilation. Blood transport and neural response introduce delays, so a lumped ventilation model may respond to past rather than present carbon-dioxide partial pressure.

The difference between total nitrogen intake and loss over a stated interval, equal to the change of nitrogen retained in the body when all routes are counted.

Deficiency of iodine that can affect thyroid function.

Insufficient vitamin C can produce the clinical syndrome scurvy. ^[ref]

A clinical consequence of vitamin C deficiency, with impaired collagen formation and fragile connective tissue. ^[ref]

A functional change in an organism following a stimulus. The response can occur remotely through reflexes without transport of the original stimulus to the responding tissue.

A valve limiting backward movement of lymph.

The main lymphatic channel delivering intestinal chyle and other lymph to the left jugulosubclavian region.

An inconstant enlarged origin of the thoracic duct in the upper lumbar region.

A central lymphatic capillary within an intestinal villus, receiving chylomicrons from intestinal absorption.

A region of an activated secondary lymphoid follicle in which B cells proliferate and undergo selection.

Lipid-rich intestinal lymph.

A muscular pump supporting blood circulation. Electrical activity, mechanical contraction and perception of heartbeat-related signals are distinguishable measurements.

The mitral valve separates the left atrium from the left ventricle. In a reservoir model with the atrium incorporated into the venous filling compartment, ideal one-way flow is $Q_v=[p_v-p_{LV}{]}_{+}/R_v$, where $[x{]}_{+}=\max (x,0)$ and $R_v$ is open-valve hydraulic resistance. The positive-part rule prevents reverse flow in this idealization.

Time-dependent elastance models the pressure generated by a cardiac ventricle at its current stressed volume. The reference $V_0$ is its zero-pressure volume. The inverse of elastance is compliance at fixed time. Rising elastance increases pressure without volume change during isovolumetric contraction; an approximately constant systolic value $E_S$ gives compliance $C_s=1/E_S$ during a simplified ejection stage.

If an open aortic valve equilibrates pressure much faster than peripheral outflow, the arteries and ventricle share a common pressure while their combined blood volume is conserved during the short adjustment. Let arterial vascular compliance be $C_a$ and systolic ventricular elastance be $E_s$. Equating the initial and final arterial-plus-ventricular stored volumes gives the displayed pressure. Subsequent peripheral drainage sees the combined compliance $C_a+1/E_s$; during filling a closed aortic valve removes the ventricular contribution.

After a rapid switch to systolic compliance $C_s$, negligible valve resistance equalizes arterial and ventricular pressures. Neglecting runoff during this short stage conserves combined stored volume and gives the displayed pressure. Thereafter, with closed mitral valve, negligible venous pressure and constant $C_s$, the pressure decays as ${\hat{p}}_a{e}^{-t/[R_c(C_a+C_s)]}$. At firing duration $\Delta t_F$, the stroke volume is $V^{+}-V_0-C_s{\hat{p}}_a{e}^{-\Delta t_F/[R_c(C_a+C_s)]}$. Each approximation follows from an explicit valve or time-scale separation condition.

Stroke volume is the volume expelled by a ventricle in one contraction. In a time-dependent ventricular elastance model, if end-ejection pressure is $p$ and systolic compliance is $C_s$, the remaining ventricular volume is $V_0+C_{s}p$. Subtracting that from the end-filling volume gives the ejected volume.

The recurrent sequence of contraction and relaxation during a heartbeat. Electrical activity, mechanical contraction and sensory afferent signals have related but different timings.

During this stage of the cardiac cycle, the ventricular inlet and outlet valves are both closed. Ventricular volume is fixed at its end-filling value $V^{+}$, while increasing ventricular elastance raises pressure as $p_{LV}=E_{LV}(t)(V^{+}-V_0)$. Arterial and venous pressures remain approximately fixed when the stage is short relative to their systemic resistance–compliance times.

The relaxation and filling phase of a cardiac cycle. In cardiac-phase experiments it provides a comparison period with different baroreceptor signalling.

The contraction phase of a cardiac cycle; ventricular systole includes ejection of blood. Timing a stimulus to systole can change its relation to cardiovascular afferent signals.

Delivery of blood through a tissue. Changes in perfusion can influence functional imaging and must be separated from changes in the computation of interest.

Movement of air into and out of the lungs. Changes in breathing can influence cardiac timing and can accompany emotion or nonemotional physical demands. Breathing must therefore be measured or controlled when interpreting appropriate psychophysiology recordings.

A one-compartment carbon-dioxide balance couples metabolic production with pressure-dependent ventilatory removal. A positive-part response models a nonnegative threshold-linear respiratory drive, and a transport/response delay can destabilize negative feedback. With $T=t/\tau$, $P=P_0+[M/(G{P}_0)]p$, the scaled law is $p^{\prime }=\alpha [1-(1+\mu p)[p(T-1){]}_{+}]$, where $\alpha =\tau G{P}_0/K$ and $\mu =M/(G{P}_0^2)$. Its positive equilibrium is $2/[1+\sqrt{1+4\mu }]$; $1/(1+\mu )$ is only its first-order small-$\mu$ approximation.

For $K\dot{p}=M-pV(p(t-\tau ))$ and a positive steady state, linearization gives $\dot{z}=-Az-Bz(t-\tau )$, where $A=V(p^{\ast })/K$ and $B=p^{\ast }{V}^{\prime }(p^{\ast })/K$. Splitting the characteristic equation of a delay differential equation at an imaginary root yields ${\omega }^2=B^2-A^2$ and the displayed first critical delay. The root crosses into the unstable half-plane with real derivative ${\omega }^2/[(1+A{\tau }_c{)}^2+{\omega }^2{\tau }_c^2]>0$. If $A\ll B$, the period near onset is approximately $4{\tau }_c$. For a Hill equation response, $B/A=n{\theta }^n/({\theta }^n+(p^{\ast }{)}^n)$ identifies whether delayed gain can exceed instantaneous damping.

A longer circulation time increases the delay between gas exchange and its sensed feedback. The American Thoracic Society's documented case relates a change in breathing pattern during one night to a longer estimated circulation time; the simple scalar model isolates a possible feedback mechanism rather than representing every determinant of that observation.^[ref]

Suspension of breathing. In nineteenth-century accounts it can include the developing asphyxial condition; its meaning must be established from context rather than automatically identified with a modern sleep-disorder diagnosis.

A lung-inflation reflex carried through vagus nerve sensory pathways that inhibits inspiration. It was described in 1868 by Ewald Hering and Josef Breuer, after the 1867 examination.

Entry of material into the airways from the mouth, pharynx or stomach.

A tube placed in the trachea to provide an airway or a connection to respiratory recording apparatus.

Respiratory mechanics relates the movements of the thorax and respiratory diaphragm to pressure changes and airflow.

Distending pressure difference between alveolar pressure and pleural pressure.

Air pressure inside a pulmonary alveolus.

Pressure within the pleural cavity; it is distinct from alveolar pressure.

Recording electrical activity associated with muscle activation. Surface recording electrodes sample activity near the skin; electrode position and movement affect the signal.

A muscle response following stimulation of a motor pathway. Its amplitude indexes excitability under specified recording conditions, rather than directly measuring the activity of a single mirror neuron.

Recording electrical activity over facial muscle regions, such as the cheek and brow. It can detect small facial responses that are not obvious to an observer. A response compatible with a smile or frown does not by itself establish the corresponding subjective emotion.

A state variable involving activation and responsiveness. Its sensory, motor, autonomic and cognitive components need not vary together, and it can confound an interpretation based on reward or threat alone.

Bodily activation measured through specified physiological variables, such as heart rate or skin conductance. Physiological arousal, subjective distress and catastrophic interpretation are distinct measurements.

Variation in the intervals between successive heartbeats. Its interpretation depends on the time scale, breathing and recording conditions; it is not a context-free measure of a particular emotion.

Coordinated tissue repair involving growth, migration, matrix remodelling and immune responses. Persistent deployment of related activities can support a tumour without constituting productive repair.

An electrochemical approach measuring rapid changes in oxidation/reduction currents. Chemical identification, calibration and electroactive interferents matter when interpreting a signal as a particular neurotransmitter.

A physiological response to challenge or disturbance. Its cause, duration and measured consequences should be specified rather than inferred from one behavioural change.

Capacity to sustain oxygen-dependent energy metabolism, commonly assessed through maximum oxygen consumption in a specified activity or condition.

A contractile muscle class whose cells lack the conspicuous sarcomeric striations of skeletal and cardiac muscle. Differentiated smooth-muscle layers can also mechanically constrain neighbouring growing tissues.

A historical name for a crystalline material isolated from human faeces. Early descriptions and formulas are not sufficient to establish that every preparation was one pure modern compound.

The continuous digestive passage through which ingested material travels.