Spleen

Key takeaways

Spleen belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Spleen to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Spleen from memory before moving on to harder problems.

Reference excerpt

The spleen (from Anglo-Norman espleen; ult. from Ancient Greek σπλήν, splḗn), or milt, is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The spleen plays important roles in regard to red blood cells (erythrocytes) and the immune system. It removes old red blood cells and holds a reserve of blood, which can be valuable in case of hemorrhagic shock, and also recycles iron. As a part of the mononuclear phagocyte system, it metabolizes hemoglobin removed from senescent red blood cells. The spleen is a center of activity of the mononuclear phagocyte system and is analogous to a large lymph node, as its absence causes a predisposition to certain infections. The globin portion of hemoglobin is degraded to its constitutive amino acids, and the heme portion is metabolized to bilirubin, which is removed in the liver. The spleen contains red and white pulp, which have distinct purposes contributing to adaptive and innate immunity. The white pulp houses T lymphocytes in periarteriolar lymphoid sheaths (PALS) situated around central arterioles and B lymphocytes in follicles adjacent to PALS. This positioning allows the B lymphocytes to encounter blood-borne antigens, which activate B cells to differentiate into plasma cells. Plasma cells then secrete antibodies, such as IgM antibodies and later IgG antibodies. Antigen-specific responses by B cells exemplify the spleen's role in the adaptive immune system. The red pulp surrounds the white pulp and marginal zone, consisting of venous sinuses and splenic cords called the cords of Billroth. Blood traveling through the red pulp is "filtered" as it encounters actively phagocytic macrophages, which remove old or damaged red blood cells as well as other antibody-coated cells and pathogens. The red pulp also stores monocytes, which can be mobilized to travel to sites of tissue injury (such as the heart after myocardial infarction) where they differentiate into dendritic cells and macrophages and help promote tissue healing. Quick and non-specific phagocytic functions occurring in the red pulp and its storage of monocytes, which can respond to sites of tissue injury, demonstrate the role of red pulp in innate immunity. In humans, the spleen is purple in color and is in the left upper quadrant of the abdomen. The surgical process to remove the spleen is known as a splenectomy.

Structure In humans, the spleen is underneath the left part of the thoracic diaphragm, and has a smooth, convex surface that faces the diaphragm. It is underneath the ninth, tenth, and eleventh ribs. The other side of the spleen is divided by a ridge into two regions: an anterior gastric portion, and a posterior renal portion. The gastric surface is directed forward, upward, and toward the middle, is broad and concave, and is in contact with the posterior wall of the stomach. Below this it is in contact with the tail of the pancreas. The renal surface is directed medialward and downward. It is somewhat flattened, considerably narrower than the gastric surface, and is in relation with the upper part of the anterior surface of the left kidney and occasionally with the left adrenal gland. There are four ligaments attached to the spleen: gastrosplenic ligament, splenorenal ligament, colicosplenic ligament, and phrenocolic ligament.

Measurements

The spleen, in healthy adult humans, is approximately 7 to 14 centimetres (3 to 5+1⁄2 inches) in length. It weighs between 30 and 230 grams or 1 and 8 ounces (standard reference range), correlating mainly to height, body weight and degree of acute congestion but not to sex or age.

Blood supply

Near the middle of the spleen is a long fissure, the hilum, which is the point of attachment for the gastrosplenic ligament and the point of insertion for the splenic artery and splenic vein. There are other openings present for lymphatic vessels and nerves. In addition to the splenic artery, collateral blood supply is provided by the adjacent short gastric arteries. Like the thymus, the spleen possesses only efferent lymphatic vessels. The spleen is part of the lymphatic system. Both the short gastric arteries and the splenic artery supply it with blood. The germinal centers are supplied by arterioles called penicilliary radicles.

Nerve supply The spleen is innervated by the splenic plexus, which connects a branch of the celiac ganglia to the vagus nerve. The underlying central nervous system processes that coordinate the spleen's function seem to be embedded into the hypothalamic–pituitary–adrenal axis, and the brainstem, especially the subfornical organ.

Development The spleen is unique in respect to its development within the gut. While most of the gut organs are endodermally derived, the spleen is derived from mesenchymal tissue. Specifically, the spleen forms within, and from, the dorsal mesentery. However, it still shares the same blood supply—the celiac trunk—as the foregut organs.

Function

Pulp

Other Other functions of the spleen are less prominent, especially in the healthy adult:

Spleen produces all types of blood cells during fetal life Production of opsonins, properdin, and tuftsin. Release of neutrophils following myocardial infarction. Creation of red blood cells. While the bone marrow is the primary site of hematopoiesis in the adult, the spleen has important hematopoietic functions up until the fifth month of gestation. After birth, erythropoietic functions cease, except in some hematologic disorders. As a major lymphoid organ and a central player in the reticuloendothelial system, the spleen retains the ability to produce lymphocytes and, as such, remains a hematopoietic organ. Storage of red blood cells, lymphocytes and other formed elements. The spleen of horses stores roughly 30 percent of the red blood cells and can release them when needed. In humans, up to a cup (240 ml) of red blood cells is held within the spleen and released in cases of hypovolemia and hypoxia. It can store platelets in case of an emergency and also clears old platelets from the circulation. Up to a quarter of lymphocytes are stored in the spleen at any one time.

Clinical significance

Enlarged spleen

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Spleen

Start with the simplest possible case. Write down what Spleen claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Spleen before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Spleen ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Spleen

In research: Spleen appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Spleen in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Spleen is common in secondary-school and first-year university syllabi. It links to neighbouring topics Abdomen, Glands, Immune system, so understanding it makes those chapters shorter.
In everyday life: Look for Spleen outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Spleen in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Spleen means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Spleen out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Spleen in simple terms?

The spleen (from Anglo-Norman espleen; ult. from Ancient Greek σπλήν, splḗn), or milt, is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter.

Why does Spleen matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Spleen?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Spleen.