50 Fun Facts About Lymphatic System

The lymphatic system is considered part of which other body system?

It works alongside the circulatory system, returning fluid to the blood while filtering out bacteria and damaged cells.

Unlike the closed circulatory system, the lymphatic system is described as what kind of system?

Lymph starts as fluid that leaks out of blood capillaries into the tissues and is only later collected by blind-ended lymph vessels.

Lymph originates from which fluid that leaks out of blood into the tissues?

That fluid delivers nutrients to cells and collects waste, bacteria and damaged cells before draining into the lymph vessels.

Roughly how many litres of blood does the circulatory system filter through capillaries daily?

About 17 litres are reabsorbed straight back into the blood vessels, and the lymphatic system returns the remaining 3.

About how many litres of fluid a day does the lymphatic system return to the blood?

It is the leftover after most filtered plasma is reabsorbed directly, so the lymphatics act as an accessory return route.

Lymph is described as very similar to which component of blood?

Like plasma it carries waste products, cellular debris, bacteria and proteins; its cells are mostly lymphocytes.

Where in the body are lymphocytes initially generated?

B cells mature there too, while T cell precursors leave for the thymus to finish their training.

Mature naive lymphocytes are maintained and activated in which class of lymphoid organ?

The lymph nodes and spleen are the classic examples; activation there leads to clonal selection and affinity maturation.

What does the acronym MALT stand for?

It is the loosely organised lymphoid tissue found in mucosal linings such as the gut, tonsils and adenoids.

The large left lymphatic duct draining most of the body is known by what name?

The much smaller right lymphatic duct drains only the right upper side of the body.

The lymph ducts empty into which veins to return lymph to the bloodstream?

Those veins sit just under the collarbones, which is why the ducts finish their journey at the base of the neck.

With no central pump, what mainly moves lymph through the human body?

Some vertebrates, unlike humans, have a dedicated lymph heart that pumps lymph into the veins.

In which century was the lymphatic system first described as a system?

Olaus Rudbeck and Thomas Bartholin worked independently, and their near-simultaneous claims led to a bitter priority dispute.

Which two organs make up the primary lymphoid organs where lymphocytes are produced?

Secondary lymphoid organs such as the lymph nodes and spleen are where mature lymphocytes later meet their antigens.

Birds have an extra primary lymphoid organ that mammals lack. What is it called?

It sits near the cloaca and is where B cells were first identified; the 'B' in B cell traces to this organ.

Developing T cells undergo positive selection in which part of the thymus?

Only T cells able to recognise self-MHC molecules survive; those that bind too weakly die off before reaching the medulla.

Roughly what share of developing T cells survive both selection tests and reach maturity?

Positive selection keeps cells that recognise self-MHC; negative selection removes those that bind self-antigens too strongly.

During which life stage does the thymus begin to atrophy and fill with fatty tissue?

Some T cell production continues throughout adulthood, but the gland's most active years are the neonatal and pre-adolescent periods.

Where in the body is the thymus located?

Its lobules are divided by septa and built from epithelium, which is unusual for a lymphoid organ.

What does the absence of the thymus result in?

Without it, T cells never become immunocompetent, leaving the body highly susceptible to infection.

Which part of the spleen synthesises antibodies and houses its lymphocytes?

The other pulp, the red one, is where macrophages clear aged red blood cells and pathogens.

A 2009 mouse study found the spleen holds what fraction of the body's monocytes in reserve?

Those reserve monocytes move to injured tissue such as the heart and become dendritic cells and macrophages.

Until which month of prenatal development does the human spleen make red blood cells?

After birth the bone marrow takes over blood cell production entirely.

What does the spleen do during acute blood loss?

It can store up to a quarter of the body's lymphocytes too, ready for an emergency.

The spleen breaks down haemoglobin from old red cells into what reusable building blocks?

The spleen recycles some erythrocyte components and discards others.

Roughly how many lymph nodes are in the human body?

Around 300 of them are packed into the head and neck alone.

What is the depression on a lymph node's surface, where the efferent vessel exits, called?

It is what makes an otherwise spherical lymph node look bean-shaped; the node's arteries and veins pass through it too.

Vessels that bring lymph INTO a lymph node are described by which adjective?

Several of them feed each node, but only a single efferent vessel carries the filtered lymph out again.

In which part of a lymph node does the selection of B cells take place?

Lymph follicles swell dramatically when they encounter a foreign antigen.

Lymphocytes enter lymph nodes through what specialised blood vessels in the paracortex?

The paracortex surrounds the medulla and holds a mix of immature and mature T cells.

Which gut organ has colon-like mucosa that is heavily infiltrated with lymphocytes?

Peyer's patches in the small intestine are another gut outpost of mucosa-associated lymphoid tissue.

Tertiary lymphoid organs form in peripheral tissues under what condition?

They appear in chronic infection, rejected transplants, some cancers and autoimmune disease, and can predict how tumours respond to immunotherapy.

Researchers found functional lymphatic vessels lining which structures around the brain?

Before that discovery, the central nervous system was long thought to lack lymphatic drainage altogether.

Which two UVA researchers found vessels linking the brain directly to the lymphatic system?

Their finding was said to have 'redrawn the map' of the lymphatic system and may bear on diseases from multiple sclerosis to Alzheimer's.

Lymph capillaries are described as what kind of vessel, letting fluid enter but not flow back?

Anchoring filaments tug their valves open when tissue swells, so excess fluid drains in exactly when it is needed.

By the end of which week of embryonic development do lymphatic tissues begin to form?

The first structures are paired jugular lymph sacs at the junction of the jugular and subclavian veins.

The thymus develops as an outgrowth of which embryonic structure?

The spleen, by contrast, arises from mesenchymal cells between layers of the dorsal mesentery of the stomach.

What are the lymph vessels in the small intestine that absorb fats called?

Most nutrients go to the liver via the portal vein, but fats take the lymphatic route to the blood through the thoracic duct.

What name is given to the fat-enriched lymph that comes from the small intestine?

Medium-chain triglycerides are an exception: they diffuse straight into the portal system instead.

What term describes cancer cells spreading between body parts, often via the lymphatics?

Intervening lymph nodes can trap the travelling cells, which is why surgeons sample them when staging cancer.

What is the medical term for one or more enlarged lymph nodes?

When nodes in many regions swell at once it is called generalised, and causes range from mononucleosis to lupus.

Extreme lymphedema in which skin thickens like an elephant's limb is known as what?

A parasitic disease, lymphatic filariasis, is a classic cause of such severe lymphatic damage.

Which named cell is the microscopic hallmark of Hodgkin lymphoma?

Hodgkin lymphoma is linked to past Epstein–Barr virus infection and typically causes painless, rubbery swollen nodes.

Hodgkin lymphoma is staged using a system named after which US city?

Chemotherapy for it generally uses the ABVD combination, sometimes with radiotherapy.

Which ancient Greek physician mentioned the lymph nodes in a single sentence of On Joints?

Herophilos later described the lacteals in the 3rd century BC, wrongly concluding they drained into the liver.

In 1622, Gaspare Aselli identified the intestinal lymph vessels while dissecting which animal?

He named them venae albae et lacteae and called them a 'fourth kind of vessel' after arteries, veins and nerves.

Who in 1651 showed the intestinal lymph drains into the veins, not the liver?

He found a white fluid mixing with blood in a dog's heart and followed it back to a sac now called the cisterna chyli.

Olaus Rudbeck announced his lymphatic discoveries at the court of which monarch?

He then sat on the findings for a year, during which Thomas Bartholin published similar results and coined 'lymphatic vessels'.

Which anatomist is credited with coining the name 'lymphatic vessels'?

He also showed the vessels exist throughout the body, not just in the liver where Rudbeck had found them.

Which Latin word, meaning water, gives us both 'lymph' and the English word 'limpid'?

The y-and-ph spelling crept in through folk association with the Greek word for nymph.