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Historical term for an excess of white blood corpuscles, especially the persistent organ-associated disorders subsequently classified as leukaemia. The old term does not make every raised white count malignant.

A cancer of blood-forming cells, commonly involving bone marrow and blood. Abnormal cell populations can interfere with normal blood production without forming a single solid mass.^[ref]

A leukocyte, or white blood cell, is a biological cell involved in immune defence. The category includes lymphocytes and cells such as macrophages and neutrophils, whose recognition and effector mechanisms differ. Many leukocytes circulate in blood but act within tissues, so a blood count samples only part of their distribution. Unlike the name might suggest, the category describes cellular identity rather than requiring a visibly white individual cell. ^[ref]

A Leydig cell is a steroid-producing biological cell in the interstitial tissue between seminiferous tubules of the testis. Adult Leydig cells produce testosterone, with their activity regulated in part by luteinizing hormone. They are anatomically and functionally distinct from the Sertoli cells supporting developing germ cells inside the tubules.

A 2014 adult-mouse experiment showed that this distinction does not make the populations independent. Selective removal of Sertoli cells was followed by a major decline in Leydig cell number. Yet average circulating testosterone was not significantly reduced in the same simple proportion, and the high values associated with pulses were largely absent. Cell number, average hormone level and the pattern of hormone release were therefore different observations.^[ref]

For an illustrative accounting model, total production is cell number multiplied by mean production per cell. Halving cell number need not halve total production if remaining cells change their activity. A circulating concentration additionally depends on removal from the blood. This explains why one hormone measurement cannot serve as a direct count of Leydig cells.

The ligamentum arteriosum is the postnatal fibrous remnant of the fetal ductus arteriosus connecting pulmonary and aortic regions. Its position records a former circulatory connection. The remnant is anatomically important even though it normally no longer conducts blood.

A lipoprotein is an assembly of lipids and proteins; in blood transport, the term commonly means a particle with a hydrophobic lipid core and an amphipathic surface containing apolipoproteins. This arrangement permits poorly water-soluble cargo to travel through an aqueous environment. Chylomicrons transport dietary lipid, while other classes differ in composition and route. Particle abundance, size and cholesterol content are distinct quantities. ^[ref]

The liver integrates metabolism, synthesis, storage, detoxification and biliary secretion. Its hepatocytes receive blood from both portal and arterial routes, while bile flows through a separate collecting pathway. This spatial organization connects processing of absorbed material to systemic distribution and excretion.

A liver function test measures selected substances in blood to investigate aspects of liver activity or injury. Common panels include albumin, bilirubin and enzymes associated with liver cells.

The components reflect different processes: protein production, handling of breakdown products and release of enzymes need not change together. Consequently the panel's name does not make every component a direct measurement of one overall liver function. The pattern and its clinical context contribute to clinical diagnosis; an abnormal value alone does not identify a unique disease.^[ref]

Post-mortem pooling of blood in dependent body regions. Its appearance must be distinguished from a living response to injury.

A lumen is the internal space of a hollow organ or vessel. In a blood vessel, the lumen contains the flowing blood and is bounded by endothelium. In the small intestine, the lumen contains material being digested and is bounded by an epithelium. The space, its contents and its surrounding wall are distinct anatomical objects.^[ref]

A transverse section makes the distinction visible. Model a circular tube with inner radius $r$ and outer radius $R$, where $R>r$. The luminal cross-sectional area is $\pi r^2$, whereas the wall occupies $\pi (R^2-r^2)$. If $R=2r$, the wall's cross-sectional area is three times the luminal area. Measuring the outside of a tube therefore does not directly measure its internal opening.

For a lining epithelium, the apical membrane faces the lumen; its opposite side faces underlying tissue. This orientation explains why transport into the lumen and transport into the surrounding interstitial fluid are physiologically different directions, even when the same substance moves across the same layer of biological cells.^[ref]

A lung contains branching airways and an extensive thin surface for gas exchange with blood. In humans, the right lung usually has three lobes and the left two. Airway transport, alveolar exchange and vascular flow are interacting functions rather than interchangeable measures of lung performance.^[ref]

A luteal cell is a biological cell belonging to the corpus luteum; in endocrine descriptions, the term usually emphasizes its steroid-producing populations. These cells arise as follicular tissue undergoes luteinization and contribute progesterone. The whole corpus luteum also contains vessels and other supporting cells, so an endocrine-cell count is not a count of every cell in the structure.^[ref]

Functional diversity can persist within the steroid-producing population. In 1982, researchers separated larger and smaller luteal cells from sheep by a flow-based separation procedure. For equal cell counts, unstimulated progesterone release from the larger-cell preparation was about twenty times that from the smaller-cell preparation. The result concerns the tested ewe preparation and conditions, not a universal ratio for all mammals.^[ref]

For an illustrative accounting model, ten cells each secreting one unit per hour and ten cells each secreting twenty units per hour contribute ten and two hundred units per hour respectively. Equal cell numbers need not imply equal endocrine contributions. Actual circulating progesterone additionally depends on distribution and removal from the blood.

A parasitic disease caused by Plasmodium, usually transmitted by infected mosquitoes. Distinct stages in the vector, liver and blood connect the organism’s life cycle with transmission and clinical illness.^[ref]

The median eminence is a region at the base of the hypothalamus where neurosecretory terminals release regulatory hormones near the first capillary bed of the hypophyseal portal system. It is an interface between hypothalamic neurons and the vascular route to the anterior pituitary. A GnRH terminal here is a site of release; the neuron's soma need not occupy the same location.^[ref]

Access to the capillaries also depends on neighboring glial cells, including tanycytes. In a 2004 study, female-rat tissue containing the median eminence was incubated for 30 minutes with or without added arginine, a substrate for nitric oxide production. Immunoelectron microscopy identified GnRH-containing terminals. In treated preparations, the investigators observed structural changes bringing terminals into direct contact with the space beside the capillaries. Complementary cell-culture experiments implicated signals from endothelium in glial remodeling.^[ref]

The comparison is illuminating because the route is more than a fixed pipe connecting two glands. The arrangement of neurons, glial cells and blood vessels can alter access to the release surface. A microscopic structural observation and a measurement of circulating hormone nevertheless remain different kinds of evidence: proximity alone does not quantify how much GnRH enters the blood.

A leech used in medicine, historically to remove blood locally. The category is functional and does not identify one particular species.

Menstruation is cyclic shedding of blood and endometrium tissue through the vagina. During a human menstrual cycle, ovarian hormones regulate the growth and maintenance of the endometrium; a decline in hormonal support is followed by shedding when a pregnancy has not become established.^[ref]

The first day of bleeding conventionally starts a new menstrual cycle. Menstruation describes a uterine event, whereas ovulation describes release of an oocyte from an ovary; treating the two as interchangeable obscures how the hypothalamic–pituitary–ovarian axis coordinates different organs.

Infection established at a site distant from its primary focus through spread of microorganisms, commonly through the blood.

Mixed venous oxygen content is the oxygen content of blood after the returning venous streams have mixed, representing whole-body venous return to the right side of the heart. It is the venous quantity required with arterial oxygen content in the whole-body Fick principle. A single regional vein need not have this content: different tissues remove different amounts of oxygen and return different blood flow rates.

The mixing rule follows from conservation of mass. If streams have blood flow rates $Q_i$ and venous oxygen content values $C_i$, with no oxygen exchange during mixing,For two constructed streams, $100$ mL/min at $0.05$ mL of oxygen per mL of blood and $50$ mL/min at $0.20$ mL/mL carry $5$ and $10$ mL/min of oxygen. Their mixture has content $15/150=0.10$ mL/mL, not the unweighted mean $0.125$ mL/mL. The correct weights are volume blood flow rates.

The right atrium receives several returns before blood passes through the right ventricle and pulmonary trunk.^[ref] A downstream sample can represent their mixture only to the extent that the streams have actually mixed and the sampling interval represents the desired state. Replacing that sample with one taken from a particular upstream vein introduces a representativeness assumption. Likewise, averaging oxygen saturation values is not generally an oxygen-content balance when hemoglobin concentrations differ. The whole-body balance is about amounts of transported oxygen, not averages of instrument displays.

Murray's law predicts $Q\propto R^3$ for an ideal blood vessel whose radius balances pumping power against the cost of maintaining its blood volume. Cecil D. Murray formulated this minimum-cost model in 1926. ^[ref]

Consider a cylindrical segment of fixed length $\ell$, prescribed positive volumetric flow rate $Q$ and constant dynamic viscosity $\mu$. The Hagen-Poiseuille equation gives pumping power $Q\Delta p=8\mu \ell Q^2/(\pi R^4)$. Adding a maintenance cost $b>0$ per unit volume per unit time givesDifferentiation givesThe pumping term diverges as $R\to 0$, while the maintenance term diverges as $R\to \infty$; the unique stationary radius is the minimum.

At an ideal bifurcation, conservation of mass for an incompressible flow gives $Q_0=Q_1+Q_2$. If the three segments have the same $\mu$ and $b$, their common proportionality constant cancels:Equal daughters therefore have $R_1=R_2=2^{-1/3}{R}_0$, approximately $0.794R_0$. This prediction depends on the model: pulsatile inertia, differing maintenance costs and radius-dependent apparent viscosity, including the Fahraeus--Lindqvist effect, can change the optimum.

A clonal disorder of blood-forming cells associated with ineffective production and abnormal maturation. Low circulating cell counts can coexist with an active marrow, distinguishing production failure from simple absence of precursor cells.