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A historical condition attributed to excessive or overly abundant blood within humorism. It records an explanatory category of its period rather than a direct equivalent of a measured modern blood-volume or blood-cell disorder.

A portal system carries blood through two capillary beds in sequence before returning it to the heart. The connecting vessel sends material collected from the first bed to the second without first mixing it through the whole systemic circulation. In the hepatic example, the portal vein takes blood from digestive organs to the liver; the hypophyseal portal system connects the hypothalamus with the anterior pituitary.^[ref]

A simple transport calculation explains the advantage for chemical signaling. If a source adds a substance at rate $q$ to a steady blood flow $Q$, with negligible removal along the connection, its added concentration is $\Delta C=q/Q$. In a hypothetical example, $q=1\mathrm{pmol}\mathrm{mi}{\mathrm{n}}^{-1}$ and $Q=0.5\mathrm{mL}\mathrm{mi}{\mathrm{n}}^{-1}$ give $2\mathrm{pmol}\mathrm{m}{\mathrm{L}}^{-1}$. Mixing the same input into $500\mathrm{mL}\mathrm{mi}{\mathrm{n}}^{-1}$ instead gives $0.002\mathrm{pmol}\mathrm{m}{\mathrm{L}}^{-1}$. These are explanatory flow rates, not measured human values.

Direct sampling makes the portal route experimentally accessible. In a 1982 study, Iain J. Clarke and James T. Cummins measured GnRH in portal plasma and LH in peripheral plasma of conscious ewes while maintaining pituitary function. The paired pulses connected a local hypothalamic signal with the downstream pituitary response.^[ref]

The portal vein carries blood from major splanchnic drainage territories to the liver. Its branches distribute this blood into hepatic microvascular pathways. A portal vein connects two vascular beds in sequence, rather than returning its entire flow directly to the heart.

A postcapillary venule is a small venule immediately downstream of a capillary network. Its thin wall includes an endothelium supported by associated pericytes. It collects blood returning from exchange vessels and is an important site of leukocyte passage from the circulation into surrounding tissue.^[ref]

In a 2006 experiment, investigators followed neutrophils in inflamed mouse postcapillary venules using real-time and time-lapse intravital microscopy. After adhering, the neutrophils crawled along the luminal surface before leaving the vessel, sometimes moving against blood flow. Genetic perturbations separated effective adhesion from subsequent crawling.^[ref]

The time sequence matters: finding a neutrophil attached in one image does not establish that it has crossed the vessel wall. Following the same cell distinguishes arrest, active searching and exit, and shows why the number of adherent cells alone is an incomplete measure of recruitment.

The posterior interventricular sulcus is an external groove marking the meeting of the right ventricle and left ventricle on the posterior/inferior aspect of the heart. It provides a surface route for the posterior descending artery and middle cardiac vein toward the cardiac apex.^[ref]

Three objects must be distinguished when reading an anatomical drawing: the posterior interventricular sulcus is the groove, the vessels are structures within or along it, and the interventricular septum is the partition inside the heart. Following the groove toward the cardiac apex locates a ventricular boundary on the surface; it does not open a communication between the two ventricular cavities.

A useful dissection exercise is to identify the middle cardiac vein by tracing it back toward the coronary sinus, then compare its route with the neighboring posterior descending artery. The two vessels can occupy a common corridor while transporting blood in different directions. The origin of the posterior descending artery also varies with coronary dominance; the position of the groove does not by itself identify the supplying coronary artery. The posterior interventricular sulcus is therefore a stable anatomical landmark for describing a variable vascular network.

The posterior pituitary is the neural part of the pituitary gland. Peptide hormones made in the soma of hypothalamic neurons travel down their axons and are released from terminals into the blood. The location of release is therefore different from the location of synthesis.^[ref]

Its released hormones include oxytocin and vasopressin. The latter helps the kidneys conserve water. This is an example of a neuron producing an endocrine output: an electrical signal at its terminal can cause a chemical signal to enter the circulation.^[ref]

A biological or physical change occurring after death. Temperature change, tissue breakdown and blood redistribution can resemble or obscure ante-mortem findings, making timing and preservation important to interpretation.^[ref]

A pregnancy test detects or measures human chorionic gonadotropin in urine or blood. The placenta produces this hormone after implantation, giving the measurement its biological connection to pregnancy.

A qualitative result applies a detection rule, while a quantitative blood test estimates the hormone level. The sampling time and the test's detection capability therefore affect what a negative result can establish. Detection of a biochemical signal is one observation within clinical diagnosis, rather than a complete description of the pregnancy's development.^[ref]

Pressure-flow distinction in cardiovascular assessment is the separation of blood pressure, a mechanical loading quantity, from blood flow, a volume transported per unit time. Cardiac output is a flow rate. A pressure reading alone does not specify the volume of blood delivered by the heart.

In a simplified steady model,where $\Delta p$ is the pressure difference across the represented vascular region, $Q$ is its blood flow and $R$ its effective vascular resistance. The difference between upstream and downstream blood pressure matters, rather than one pressure considered in isolation. The pressure-gradient and resistance account is developed in the primary physiology text.^[ref]

An original counterexample holds the pressure difference fixed at 90 mmHg. With $R=18$ mmHg/(L/min), flow is 5 L/min; with $R=30$ mmHg/(L/min), flow is 3 L/min. The same driving pressure can accompany different delivery rates. Conversely, at fixed flow a higher measured pressure difference can represent a higher effective resistance.

The quantities also have different dimensions. The product $\Delta pQ$ has units of energy per time, describing a hydraulic rate of mechanical energy transfer in this model. A pressure alone has neither flow units nor power units.

A primary coronary thermodilution apparatus combined a pressure/temperature-sensing guidewire with a controlled infusion catheter; its flow estimate used infusion rate and temperature measurements.^[ref] The availability of pressure and thermal signals in one instrument does not make them the same observable. Finally, pulsatile circulation includes storage and changing vessel geometry, so the steady resistance relation is an explanatory approximation. Matching time averages, anatomical sites and model assumptions is part of interpreting pressure and flow together.

Progesterone is a steroid hormone produced prominently by the corpus luteum after ovulation and by the placenta during pregnancy. It helps transform and maintain the endometrium in a state that supports implantation and subsequent pregnancy. Its withdrawal, alongside other hormonal changes, contributes to menstruation when pregnancy is not established.^[ref]

Like other steroid signals, progesterone can act through a nuclear receptor to change gene expression. Its effect is therefore not merely the presence of a substance in blood: transport, receptor availability and tissue state shape the response. A post-ovulatory progesterone rise and an estrogen-driven proliferative phase describe different parts of the coordinated ovarian and uterine cycle.

A pulmonary artery carries blood from the right ventricle toward the lungs. Its relatively low oxygen content illustrates why artery and vein are directional terms. Branching distributes flow to exchanging regions where oxygenation occurs.

The pulmonary circulation carries blood from the right heart through the lungs and back to the left heart. It supports exchange of oxygen and carbon dioxide. Its pressure load differs from the systemic circulation even though long-term net flow through both circuits must balance.

Bleeding into lung tissue or air spaces. It differs from a blood collection in the pleural cavity and can impair gas exchange as well as cause visible haemoptysis.

The pulmonary trunk is the common artery leaving the right ventricle through the pulmonary valve before dividing into the vessels supplying the two lungs. It is the initial shared segment of the pulmonary artery route in the pulmonary circulation. The name artery describes flow away from the heart; the blood in the pulmonary trunk has not yet acquired oxygen in the lungs.^[ref]

At a junction with negligible storage, conservation of mass givesA constructed total blood flow of $5$ L/min could therefore divide into $3$ and $2$ L/min. Measuring the total does not establish equal flow to the two lungs. In a simple steady model with a common upstream and downstream pressure, branch blood flow rates depend on their respective vascular resistance values; the shared inlet does not force the resistances to be equal.

The pulmonary trunk also supplies an important distinction between two measurements. Right ventricular ejection fraction describes change in a chamber volume, whereas forward blood flow in the pulmonary trunk describes transport through a vessel. They agree through stroke volume and heart rate only under the relevant balance assumptions, including negligible backward flow. An anatomical connection is therefore the starting point for a flow model, rather than a substitute for its assumptions.

The pulmonary valve is the heart valve between the right ventricle and pulmonary trunk. During forward ventricular ejection it allows blood to enter the pulmonary circulation; closure limits return from the pulmonary trunk into the relaxing right ventricle.^[ref]

Its pocket-like cusps respond to the changing pressure difference. Unlike the tricuspid valve, the pulmonary valve has no attached chordae tendineae or papillary muscles.^[ref] Thus the same direction-control task is achieved by different supporting structures at the chamber inlet and outlet.

A deliberately idealized valve model sets forward blood flow to zero when the downstream pressure exceeds the upstream pressure, and permits positive flow when ventricular pressure exceeds trunk pressure. This model captures direction but omits the inertia and deformation of real cusps. It is useful for checking the sign of a flow term, not for predicting an exact opening time.

For example, if a constructed cycle sends 80 mL forward and 10 mL backward across the pulmonary valve, net transport is 70 mL. Counting only the positive part of blood flow overestimates net delivery. This is why stroke volume inferred from changing chamber volume and net forward flow in the pulmonary trunk require compatible assumptions about valve function.

A pulmonary vein returns blood from a lung to the left atrium. The pulmonary veins complete the return side of the pulmonary circulation, after blood has received oxygen in the lungs. They are veins because they carry blood toward the heart, even though their oxygen content is higher than that of the blood arriving through the pulmonary artery.^[ref]

Following a parcel of blood makes the sequence clear: right ventricle, pulmonary trunk, vessels of the lungs, pulmonary vein, left atrium, then left ventricle. The pulmonary vein connects the lung circuit to the receiving chamber of the left heart; it does not drain directly into the right atrium.

A simple oxygen balance illustrates why both content and flow matter. Suppose two returning streams have blood flow rates $Q_1,Q_2$ and oxygen contents $C_1,C_2$. If they mix without further oxygen exchange, the left atrium's inflow content isFor constructed values $Q_1=3$ L/min, $Q_2=2$ L/min, $C_1=0.20$ and $C_2=0.15$ mL/mL, this gives $0.18$ mL/mL. An unweighted average would give $0.175$ mL/mL. A specimen's vessel connections establish where the streams meet; conservation of mass establishes how their transported oxygen combines.

The pulmonary-vein backflow component comprises represented blood that leaves the left atrium through a pulmonary vein, toward the lungs. In atrial flow component analysis, the exit boundary distinguishes it from blood delivered through the mitral valve. The Bäck study includes both newly entering blood that returns to a pulmonary vein and previously resident atrial blood taking that exit.^[ref]

An original signed-flow example explains why forward and backward transport should be recorded separately. Orient a pulmonary vein's boundary normal toward the left atrium, so positive volumetric flow rate $Q(t)$ denotes inflow. Define gross entering and leaving volumes over an observation interval $I$ byThe net transferred volume is $V_{+}-V_{-}$. Constructed values $V_{+}=60$ mL and $V_{-}=5$ mL give 55 mL net inflow. Reporting only that net value hides the 5 mL reversal. Summing over all pulmonary veins gives a chamber-level boundary balance.

A boundary integral and a parcel history nevertheless answer different questions. If the same represented parcel crosses outward twice after re-entering, a gross boundary integral counts both crossings. A pathline-based component needs an explicit rule for repeated crossings and its observation window before its volume can be equated with that integral. Similarly, this route is not mitral regurgitation: the latter concerns reverse transport across the mitral valve, a different boundary. An outlet direction alone does not establish a diagnosis or the age of the blood taking that route.

RadiologyInfo.org is an institutional author of patient-oriented explanations of medical imaging and the work of a radiologist. Its professional-role material distinguishes interpreting images, helping choose an appropriate imaging method and communicating the resulting findings.^[ref]

Its procedure pages give useful physical examples. The venous ultrasonography explanation connects sound-based imaging with examination of blood vessels and measurement of moving blood. The magnetic resonance cholangiopancreatography explanation describes a specialized magnetic resonance imaging method for the biliary and pancreatic systems.^[ref][ref]

These are educational explanations of what an examination measures and how it is performed. Such a procedure description supplies context for interpreting a technique; it is a different kind of evidence from a controlled experiment comparing diagnostic performance in a defined population.

Increased pressure within the cranial compartment. Added tissue, blood or fluid can exceed compensatory capacity, connecting a confined space with impaired cerebral perfusion or tissue displacement.

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.