Pancreas

Pancreas

1: Head of pancreas

2: Uncinate process of pancreas

3: Pancreatic notch

4: Body of pancreas

5: Anterior surface of pancreas

6: Inferior surface of pancreas

7: Superior margin of pancreas

8: Anterior margin of pancreas

9: Inferior margin of pancreas

10: Omental tuber

11: Tail of pancreas

12: Duodenum

Gray's subject #251 1199

Artery

inferior pancreaticoduodenal artery,

superior pancreaticoduodenal artery,

splenic artery

Veinpancreaticoduodenal veins, pancreatic

veins

Nerve pancreatic plexus, celiac ganglia, vagus [1]

Precursor pancreatic buds

MeSH Pancreas

Dorlands/Elsevier Pancreas

The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as an exocrine gland, secreting pancreatic juice containing digestive enzymes that pass to the small intestine. These enzymes help to further breakdown the carbohydrates, protein, and fat in the chyme.

Histology

Under a microscope, stained sections of the pancreas reveal two different types of parenchymal tissue.[2] Lightly staining clusters of cells are called islets of Langerhans, which produce hormones that underlie the endocrine functions of the pancreas. Darker staining cells form acini connected to ducts. Acinar cells belong to the exocrine pancreas and secrete digestive enzymes into the gut via a system of ducts.

Structure Appearance FunctionIslets of Langerhans

Lightly staining, large, spherical clusters

Hormone production and secretion (endocrine pancreas)

Pancreatic aciniDarker staining, small, berry-like clusters

Digestive enzyme production and secretion (exocrine pancreas)

Function

The pancreas is a dual-function gland, having features of both endocrine and exocrine glands.

Endocrine

Main article: Endocrine pancreas

The part of the pancreas with endocrine function is made up of approximately a million[3] cell clusters called islets of Langerhans. Four main cell types exist in the islets. They are relatively difficult to distinguish using standard staining techniques, but they can be classified by their secretion: α cells secrete glucagon (increase Glucose in blood), β cells secrete insulin (decrease Glucose in blood), δ cells secrete somatostatin (regulates/stops α and β cells), and PP cells secrete pancreatic polypeptide.[4]

The islets are a compact collection of endocrine cells arranged in clusters and cords and are crisscrossed by a dense network of capillaries. The capillaries of the islets are lined by layers of endocrine cells in direct contact with vessels, and most endocrine cells are in direct contact with blood vessels, by either cytoplasmic processes or by direct apposition. According to the volume The Body, by Alan E. Nourse,[5] the islets are "busily manufacturing their hormone and generally disregarding the pancreatic cells all around them, as though they were located in some completely different part of the body."

Regulation

The pancreas receives regulatory innervation via hormones in the blood and through the autonomic nervous system. These two inputs regulate the secretory activity of the pancreas.

Sympathetic (adrenergic) Parasympathetic (muscarinic)α2: decreases secretion from beta cells, increases secretion from alpha cells

M3[6] increases stimulation of alpha cells and beta cells

Anatomy

Position

It lies in the epigastrium & left hypochondrium areas of the abdomen

Parts

It consists of:

Head: Lies within the concavity of the duodenum Uncinate process: emerges from the lower part of head & lies deep to superior

mesenteric vessels Neck: The constricted part between the head and the body Body: It lies behind stomach Tail: It is the left end of the pancreas. It lies in contact with the spleen and runs in

the lienorenal ligament

Blood Supply

Arterial Supply

Superior pancreaticoduodenal artery from gastroduodenal artery Inferior pancreaticoduodenal artery from superior mesenteric artery

Both run in the groove between the pancreas & duodenum & supply the head of pancreas.

Pancreatic branches of Splenic artery. The largest of those branches is called arteria pancreatica magna, it's occlusion although rare is fatal.

Supplies the neck, body & tail of pancreas

Venous Drainage

From Body & Neck of pancreas drain into splenic vein. From head of pancreas drains into superior mesenteric vein & portal vein.

Lymphatic Drainage

splenic lymph nodes Celiac lymph nodes Superior mesenteric lymph nodes

Diseases

Main article: Pancreatic disease

Because the pancreas is a storage depot for digestive enzymes, injury to the pancreas is potentially very dangerous. A puncture of the pancreas generally requires prompt and experienced medical intervention.

Pancreatic cancer, particularly cancers of the exocrine pancreas remain one of the most deadly cancers, and the mortality rate is very high.

Diabetes mellitus type 1 is a chronic autoimmune disorder in which the immune system attacks the insulin-secreting cells in the pancreas.

History

The pancreas was first identified for western civilization by Herophilus (335–280 BC), a Greek anatomist and surgeon. Only a few hundred years later, Ruphos, another Greek anatomist, gave the pancreas its name. The term "pancreas" is derived from the Greek πᾶν ("all", "whole"), and κρέας ("flesh").[7] – presumably because of its fleshy consistency.

Embryological development

Schematic illustrating the development of the pancreas from a dorsal and a ventral bud. During maturation the ventral bud flips to the other side of the gut tube (arrow) where it

typically fuses with the dorsal lobe. An additional ventral lobe which usually regress during development is omitted.

The pancreas forms from the embryonic foregut and is therefore of endodermal origin. Pancreatic development begins the formation of a ventral and dorsal anlage (or buds). Each structure communicates with the foregut through a duct. The ventral pancreatic bud becomes the head and uncinate process, and comes from the hepatic diverticulum.

Differential rotation and fusion of the ventral and dorsal pancreatic buds results in the formation of the definitive pancreas.[8] As the duodenum rotates to the right, it carries with it the ventral pancreatic bud and common bile duct. Upon reaching its final destination, the ventral pancreatic bud fuses with the much larger dorsal pancreatic bud. At this point of fusion, the main ducts of the ventral and dorsal pancreatic buds fuse, forming the duct of Wirsung, the main pancreatic duct.

Differentiation of cells of the pancreas proceeds through two different pathways, corresponding to the dual endocrine and exocrine functions of the pancreas. In progenitor cells of the exocrine pancreas, important molecules that induce differentiation include follistatin, fibroblast growth factors, and activation of the Notch receptor system.[8] Development of the exocrine acini progresses through three successive stages. These include the predifferentiated, protodifferentiated, and differentiated stages, which correspond to undetectable, low, and high levels of digestive enzyme activity, respectively.

Progenitor cells of the endocrine pancreas arise from cells of the protodifferentiated stage of the exocrine pancreas.[8] Under the influence of neurogenin-3 and Isl-1, but in the absence of Notch receptor signaling, these cells differentiate to form two lines of committed endocrine precursor cells. The first line, under the direction of Pax-0, forms α- and γ- cells, which produce the peptides glucagon and pancreatic polypeptide, respectively. The second line, influenced by Pax-6, produces β- and δ-cells, which secrete insulin and somatostatin, respectively.

Insulin and glucagon can be detected in the fetal circulation by the fourth or fifth month of fetal development.[8]

In animals

Pancreatic tissue is present in all vertebrate species, but its precise form and arrangement varies widely. There may be up to three separate pancreases, two of which arise from ventral buds, and the other dorsally. In most species (including humans), these fuse in the adult, but there are several exceptions. Even when a single pancreas is present, two or three pancreatic ducts may persist, each draining separately into the duodenum (or equivalent part of the hindgut). Birds, for example, typically have three such ducts.[9]

In teleosts, and a few other species (such as rabbits), there is no discrete pancreas at all, with pancreatic tissue being distributed diffusely across the mesentery and even within

other nearby organs, such as the liver or spleen. In a few teleost species, the endocrine tissue has fused to form a distinct gland within the abdominal cavity, but otherwise it is distributed amongst the exocrine components. The most primitive arrangement, however, appears to be that of lampreys and lungfish, in which pancreatic tissue is found as a number of discrete nodules within the wall of the gut itself, with the exocrine portions being little different from other glandular structures of the intestine.[9]

The Pancreas in Popular Culture

The second track on "Weird Al" Yankovic's album, Straight Outta Lynwood, entitled "Pancreas", centers around the pancreas and lists a summary of its functions.

Additional images

Accessory digestive system. Digestive organs.

The celiac artery and its branches; the stomach has been raised and the peritoneum removed.

Lymphatics of stomach, etc. The stomach has been turned upward.

Transverse section through the middle of the first lumbar vertebra, showing the relations of the pancreas.

The duodenum and pancreas.

The pancreatic duct.Pancreas of a human embryo of five weeks.

Pancreas of a human embryo at end of sixth week.

Front of abdomen, showing surface markings for duodenum, pancreas, and kidneys.

Dog pancreas magnified 100 times.

FROM: http://www.medterms.com/script/main/art.asp?articlekey=4743

Pancreas: A fish-shaped spongy grayish-pink organ about 6 inches (15 cm) long that stretches across the back of the abdomen, behind the stomach. The head of the pancreas is on the right side of the abdomen and is connected to the duodenum (the first section of the small intestine). The narrow end of the pancreas, called the tail, extends to the left side of the body.

The pancreas makes pancreatic juices and hormones, including insulin. The pancreatic juices are enzymes that help digest food in the small intestine. Insulin controls the amount of sugar in the blood.

As pancreatic juices are made, they flow into the main pancreatic duct. This duct joins the common bile duct, which connects the pancreas to the liver and the gallbladder. The common bile duct, which carries bile (a fluid that helps digest fat), connects to the small intestine near the stomach.

The pancreas is thus a compound gland. It is "compound" in the sense that it is composed of both exocrine and endocrine tissues. The exocrine function of the pancreas involves the synthesis and secretion of pancreatic juices. The endocrine function resides in the million or so cellular islands (the islets of Langerhans) embedded between the exocrine units of the pancreas. Beta cells of the islands secrete insulin, which helps control carbohydrate metabolism. Alpha cells of the islets secrete glucagon that counters the action of insulin.

FROM: http://pathology.jhu.edu/pc/BasicOverview1.php

What is the pancreas?

A simple answer is that the pancreas is an oblong flattened gland located deep in the abdomen. Most people don't know as much about the pancreas as they do about other parts of their bodies. In fact, this gland is an integral part of the digestive system that often goes unnoticed until problems occur. If you are concerned about pancreas cancer, you will want a lot more information.

Where is the pancreas?

The pancreas is located deep in the abdomen, sandwiched between the stomach and the spine. It lies partially behind the stomach. The other part is nestled in the curve of the duodenum (small intestine). To visualize the position of the pancreas, try this: Touch the thumb and "pinkie" finger of your right hand together, keeping the other three fingers together and straight. Then, place your hand in the center of your belly just below your lower ribs with your fingers pointing to the left. Your hand will be at the approximate level of your pancreas.

Because of the pancreas' deep location, tumors are rarely palpable (able to be felt by pressing on the abdomen.) It also explains why many symptoms of pancreatic cancer often do not appear until the tumor grows large enough to interfere with the function of nearby structures such as the stomach, duodenum, liver, or gallbladder.

Fig. 1-1

Parts of Pancreas

The pancreas is made up of glandular tissue and a system of ducts. The main duct is the pancreatic duct which runs the length of the pancreas. It drains the pancreatic fluid from the gland and carries it to the duodenum. The main duct is about one-sixteenth of an inch in diameter and has many small side branches. The pancreatic duct merges with the bile duct to form the ampulla of Vater (a widening of the duct just before it enters the duodenum.)

Your doctor will probably refer to different parts of the pancreas when discussing your situation. The part of the pancreas that a tumor arises in will effect how it is treated. For

descriptive purposes, there are two ways the pancreas is divided into parts: by parts of the overall shape and by the function of its cells. Fig. 1-2

The Shape of the Pancreas

uncinate process

The part of the gland that bends backwards and underneath the body of the pancreas. Two very important blood vessels, the superior mesenteric artery and vein cross in front of the uncinate process.

headThe widest part of the gland. It is found in the right part of abdomen, nestled in the curve of the duodenum which forms an impression in the side of the gland.

neck The thin section between the head and the body of the gland.

bodyThe middle part of gland between the neck and the tail. The superior mesenteric blood vessels run behind this part of the gland.

tailThe thin tip of gland in the left part of abdomen in close proximity with the spleen.

Pancreas Function

The pancreas can also be thought of as having different functional components, the endocrine and exocrine parts. Tumors can arise in either part. However, the vast majority arise in the exocrine (also called non-endocrine) part. Since the parts have different normal functions, when tumors interfere with these functions, different kinds of symptoms will occur.

Islets of Langerhans

These are the endocrine (endo= within) cells of the pancreas that produce and secrete hormones into the bloodstream. The pancreatic hormones, insulin and glucagon, work together to maintain the proper level of sugar in the blood. The sugar, glucose, is used by the body for energy.

Acinar cells

These are the exocrine (exo= outward) cells of the pancreas that produce and transport chemicals that will exit the body through the digestive system. The chemicals that the exocrine cells produce are called enzymes. They are secreted in the duodenum where they assist in the digestion of food.

What function does the pancreas serve?

The pancreas is an integral part of the digestive system. The flow of the digestive system is often altered during the surgical treatment of pancreatic cancer. Therefore it is helpful to review the normal flow of food before reading about surgical treatment.

Food is carried from the mouth to the stomach by the esophagus. This tube descends from the mouth and through an opening in the diaphragm. (The diaphragm is a dome shaped muscle that separates the lungs and heart from the abdomen and assists in breathing.)

Immediately after passing through the diaphragm's opening, the esophagus empties into the stomach where acids that break down the food are produced. From the stomach, the food flows directly into the first part of the small intestine, called the duodenum. It is here in the duodenum that bile and pancreatic fluids enter the digestive system.

What is bile?

Bile is a greenish-yellow fluid that aids in the digestion of fats. After being produced by cells in the liver, the bile travels down through the bile ducts which merge with the cystic duct to form the common bile duct. The cystic duct runs to the gallbladder, a small pouch nestled underneath the liver. The gallbladder stores extra bile until needed. The common bile duct actually enters the head of the pancreas and joins the pancreatic duct to form the ampulla of Vater which then empties into the duodenum. Flow of bile indicated by green arrows.

What is pancreatic fluid?

Instead of carrying bile, the pancreatic duct carries the pancreatic fluid produced by the acinar cells (exocrine) of the pancreas. The pancreatic duct runs the length of the pancreas and joins the common bile duct in the head of the pancreas. These ducts join to form the ampulla of Vater which then empties into the duodenum. Flow of pancreatic fluid indicated by dark yellow arrow.

The food, bile and pancreatic fluid travels through many more feet of continuous intestine including the rest of the duodenum, jejunum and ileum which comprise the small intestine, then through the cecum, large intestine, rectum, and anal canal

SpleenFrom Wikipedia, the free encyclopedia

Spleen

Spleen

Laparoscopic view of a horse's spleen (the purple and grey

mottled organ)

Latin splen, lien

Gray's subject #278 1282

Artery Splenic artery

Vein Splenic vein

Nerve Splenic plexus

PrecursorMesenchyme of dorsal

mesogastrium

MeSH Spleen

Dorlands/Elsevier Spleen

The spleen (from Greek "σπλήν" - splen[1]) is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system.[2] In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock while also recycling iron.[3] It synthesizes antibodies in its white pulp and removes antibody-coated bacteria along with antibody-coated blood cells by way of blood and lymph node circulation. The spleen is purple and gray.[3][4] Recently, it has been found to contain in its reserve half of the body's monocytes within the red pulp. These monocytes, upon moving to injured tissue (such as the heart), turn into dendritic cells and macrophages while promoting tissue healing.[5][6][7] It is one of the centers of activity of the reticuloendothelial system and can be considered analogous to a large lymph node, as its absence leads to a predisposition toward certain infections.[8]

Anatomy

The spleen, in healthy adult humans, is approximately 11 centimetres (4.3 in) in length. It usually weighs 200 grams (7.1 oz) and lies beneath the 9th to the 12th thoracic ribs.[9]

Like the thymus, the spleen possesses only efferent lymphatic vessels.

The spleen is part of the lymphatic system.

The germinal centers are supplied by arterioles called penicilliary radicles.[10]

The spleen is unique in respect to its development within the gut. While most of the gut viscera are endodermally derived (with the exception of the neural-crest derived suprarenal gland), the spleen is derived from mesenchymal tissue.[11] 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

Area Function Composition

red pulp

Mechanical filtration of red blood cells. Reserve of monocytes [5]

"sinuses" (or "sinusoids") which are filled with blood

"splenic cords" of reticular fibers

"marginal zone" bordering on white pulp

white pulp

Active immune response through humoral and cell-mediated pathways.

Composed of nodules, called Malpighian corpuscles. These are composed of:

"lymphoid follicles" (or "follicles"), rich in B-lymphocytes

"periarteriolar lymphoid sheaths" (PALS), rich in T-lymphocytes

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

Production of opsonins, properdin, and tuftsin. 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 an hematopoietic organ.

Storage of red blood cells and other formed elements. In horses roughly 30% of the red blood cells are stored there. The red blood cells can be released when needed.[12] In humans, it does not act as a reservoir of blood cells.[13] It can also store platelets in case of an emergency.

Storage of half the body's monocytes so that upon injury they can migrate to the injured tissue and transform into dendritic cells and macrophages and so assist wound healing.[5]

Effect of removal

See also: Asplenia

Surgical removal causes:[6]

modest increases in circulating white blood cells and platelets, diminished responsiveness to some vaccines, increased susceptibility to infection by bacteria and protozoa; in particular, there

is an increased risk of sepsis from polysaccharide encapsulated bacteria.

A 28-year follow up of 740 veterans of World War II found that those who had been splenectomised showed a significant excess of mortality from pneumonia (6 from an expected 1.3) and a significant excess of mortality from ischaemic heart disease (4.1 from an expected 3) but not from other conditions.[14]

Disorders

Main article: Splenic disease

Disorders include splenomegaly, where the spleen is enlarged for various reasons, and asplenia, where the spleen is not present or functions abnormally.

Etymology and cultural views

The word spleen comes from the Greek σπλήν, and is the idiomatic equivalent of the heart in English, i.e. to be good-spleened (εὔσπλαγχνος) means to be good-hearted or compassionate.[15]

In English the word spleen was customary during the period of the 18th century. Authors like Richard Blackmore or George Cheyne employed it to characterize the hypocondriacal and hysterical affections.[16][17]

In French, "splénétique" refers to a state of pensive sadness or melancholy. It has been popularized by the poet Charles Baudelaire (1821–1867) but was already used before in particular to the Romantic literature (18th century). The word for the organ is "la rate."

The connection between spleen (the organ) and melancholy (the temperament) comes from the humoral medicine of the ancient Greeks. One of the humours (body fluid) was the black bile, secreted by the spleen organ and associated with melancholy. In contrast, the Talmud (tractate Berachoth 61b) refers to the spleen as the organ of laughter while possibly suggesting a link with the humoral view of the organ. In the eighteenth- and nineteenth-century England, women in bad humour were said to be afflicted by the spleen, or the vapours of the spleen. In modern English, "to vent one's spleen" means to vent one's anger, e.g. by shouting, and can be applied to both males and females. Similarly, the English term "splenetic" is used to describe a person in a foul mood.

In Chinese, the spleen '脾 (pí)' counts as the seat of one's temperament and is thought to influence the individual's willpower. Analogous to "venting one's spleen", "發脾氣" is used as an expression for getting angry, although in the view of Traditional Chinese Medicine, the view of "脾" does not correspond to the anatomical "spleen". "脾" is a conceptual functional group that mainly has regards to digestion which, in some scholars' opinions, corresponds to the function of the pancreas.

The spleen also plays a part in Western/American humor, a joke being 'Aaaah! My spleen!' shouted by somebody being attacked/hurt. This is a recurring joke in the American comic Brewster Rockit—whenever the character Winky is sent out to fight a monster he is always hurt and always screams 'Aaaah! My spleen!' or such variations of the phrase.[citation needed] The spleen joke has also played a part in blonde jokes (usually having the blonde not know where her spleen is) as well in other humor occurrences.[citation

needed]

Variation among vertebrates

In cartilagenous and ray-finned fish the spleen is normally a somewhat elongated organ, consisting primarily of red pulp, with only a small amount of white pulp. In lungfish, the spleen is not a distinct organ as it actually lies inside the serosal lining of the intestine. In many amphibians, especially frogs, it takes on the more rounded form and there is often a greater quantity of white pulp.[18]

In reptiles, birds, and mammals, white pulp is always relatively plentiful, and in the latter two groups, the spleen is typically rounded, although it adjusts its shape somewhat to the arrangement of the surrounding organs. In the great majority of vertebrates, the spleen continues to produce red blood cells throughout life; it is only in mammals that this function is lost in the adult. Many mammals possess tiny spleen-like structures known as haemal nodes throughout the body, which presumably have the same function as the spleen proper.[18] The spleens of aquatic mammals are in some ways dissimilar to those of fully land dwelling mammals. In general the spleens of aquatic mammals are bluish in colour. In cetaceans and manatees it tends to be quite small, but in deep diving pinnipeds it can be quite massive, owing to its function of storing red blood cells.

The only vertebrates lacking a spleen are the lampreys and hagfishes. Even in these animals, there is a diffuse layer of haematopoeitic tissue within the gut wall, which has a

similar structure to red pulp, and is presumably homologous with the spleen of higher vertebrates.[18]

Additional images

The celiac artery and its branches.

The celiac artery and its branches.

Horizontal disposition of the peritoneum in the upper part of the abdomen.

Transverse section through the middle of the first lumbar vertebra.

The duodenum and pancreas. The visceral surface

of the spleen.

Transverse section of the spleen, showing the trabecular tissue and the splenic vein and its tributaries.

Transverse section of the human spleen, showing the distribution of the splenic artery and its branches.

Section of the spleen, showing the termination of the small blood vessels.

Back of lumbar region, showing surface markings for kidneys, ureters, and spleen.

Side of thorax, showing surface markings for bones, lungs (purple), pleura (blue), and spleen (green).

Lymphatic system

FROM: http://www.mamashealth.com/organs/spleen.asp

What is the Spleen?

The human spleen is an organ that creates lymphocytes for the destruction and recycling of old red-blood cells. The spleen is also a blood reservoir. It supplies the body with blood in emergencies such as a bad cut. The spleen is also the location where white blood cells trap organisms.

The spleen is shaped like a loose fist and is tucked under the left side of the diaphragm .

The average weight of an adult spleen is 0.44 lbs. During and after digestion, the size of the spleen increases. Infection of malaria or mono can also cause the spleen to increase in size.

If the increase in size is significant, the spleen can rupture. If the spleen ruptures, immediate medical care is necessary. You may need emergency surgery to control the bleeding.

Other diseases that causes enlargement of the spleen are: rheumatoid arthritis, systemic lupus, sickle cell anemia, leukemia, lymphoma.

Where is the Spleen located?

The spleen is located in the upper-left part of your abdomen. It is protected by your rib cage.

Can the Spleen be removed?

Yes. If the spleen is ruptured, it can be removed. The spleen can also be removed because of certain kinds of cancers.

FROM: http://kidshealth.org/teen/your_body/body_basics/spleen.html

Spleen and Lymphatic System

The lymphatic system is an extensive drainage network that helps keep bodily fluid levels in balance and defends the body against infections.

The lymphatic system is made up of a network of lymphatic vessels. These vessels carry lymph — a clear, watery fluid containing protein molecules, salts, glucose, urea, and other substances — throughout the body.

The spleen is located in the upper left part of the abdomen under the ribcage. It works as part of the lymphatic system to protect the body, clearing worn-out red blood cells and other foreign bodies from the bloodstream to help fight off infection.

Why Are the Spleen and Lymphatic System Necessary?

One of the lymphatic system's major jobs is to collect extra lymph fluid from body tissues and return it to the blood. This process is important because water, proteins, and other substances are continuously leaking out of tiny blood capillaries into the surrounding body tissues. If the lymphatic system didn't drain the excess fluid from the tissues, the lymph fluid would build up in the body's tissues and they would swell.

The lymphatic system also helps defend the body against germs like viruses, bacteria, and fungi that can cause illnesses. Those germs are filtered out in the lymph nodes, which are small masses of tissue located along the network of lymph vessels. The nodes house lymphocytes, a type of white blood cell. Some of those lymphocytes make antibodies, special proteins that fight off germs and stop infections from spreading by trapping disease-causing germs and destroying them.

The spleen also helps the body fight infection. The spleen contains lymphocytes and another kind of white blood cell called macrophages, which engulf and destroy bacteria, dead tissue, and foreign matter and remove them from the blood passing through the spleen.

Basic Anatomy

The lymphatic system is a network of very small tubes (vessels) that drain lymph fluid from all over the body. The major parts of the lymph tissue are located in the bone marrow, spleen, thymus gland, lymph nodes, and the tonsils. The heart, lungs, intestines, liver, and skin also contain lymphatic tissue.

One of the major lymphatic vessels is the thoracic duct, which begins near the lower part of the spine and collects lymph from the pelvis, abdomen, and lower chest. The thoracic duct runs up through the chest and empties into the blood through a large vein near the left side of the neck. The right lymphatic duct is the other major lymphatic vessel. It collects lymph from the right side of the neck, chest, and arm, and empties into a large vein near the right side of the neck.

Lymph nodes are round or kidney shaped. They can be up to 1 inch in diameter. Most of the lymph nodes are found in clusters in the neck, armpit, and groin area. Nodes are also located along the lymphatic pathways in the chest, abdomen, and pelvis, where they filter the blood. Inside the lymph nodes, lymphocytes called T-cells and B-cells help the body fight infection. Lymphatic tissue is also scattered throughout the body in different major organs and in and around the gastrointestinal tract.

The spleen helps control the amount of blood and blood cells that circulate through the body and helps destroy damaged cells.

How A Healthy Lymph System Typically Works

Carrying Away Waste

Lymph fluid drains into lymph capillaries, which are tiny vessels. The fluid is then pushed along through the capillaries when a person breathes or the muscles contract. The lymph capillaries are very thin, and they have many tiny openings that allow gases, water, and nutrients to pass through to the surrounding cells, nourishing them and taking away waste products. When lymph fluid leaks through in this way it is called interstitial fluid.

Lymph vessels collect the interstitial fluid and then return it to the bloodstream by emptying it into large veins in the upper chest, near the neck.

Fighting Infection

Lymph fluid enters the lymph nodes, where macrophages fight off foreign bodies like bacteria, removing them from the bloodstream. After these substances have been filtered out, the lymph fluid leaves the lymph nodes and returns to the veins, where it re-enters the bloodstream.

When a person has an infection, germs collect in the lymph nodes. If the throat is infected, for example, the lymph nodes of the neck may swell. That's why doctors check for swollen lymph nodes (sometime called swollen "glands" — but they're actually lymph nodes) in the neck when your throat is infected.

Things That Can Go Wrong With the Lymphatic System

Certain diseases can affect the lymph nodes, the spleen, or the collections of lymphoid tissue in certain areas of the body.

Lymphadenopathy. This is a condition where the lymph nodes become swollen or enlarged, usually because of a nearby infection. Swollen lymph nodes in the neck, for example, can be caused by a throat infection. Once the infection is treated, the swelling usually goes away. If several lymph node groups throughout the body are swollen, that can indicate a more serious disease that needs further investigation by a doctor.

Lymphadenitis. Also called adenitis, this inflammation of the lymph node is caused by an infection of the tissue in the node. The infection can cause the skin overlying the lymph node to swell, redden, and feel warm and tender to the touch. It usually affects the lymph nodes in the neck and is often caused by a bacterial infection that can be easily treated with an antibiotic.

Lymphomas. These cancers start in the lymph nodes when lymphocytes undergo changes and start to multiply out of control. The lymph nodes swell, and the cancer cells crowd out healthy cells and may cause tumors (solid growths) in other parts of the body.

Splenomegaly (enlarged spleen). In someone who is healthy, the spleen is usually small enough that it can't be felt when you press on the abdomen. But certain diseases can cause the spleen to swell to several times its normal size. Most commonly, this is due to a viral infection, such as mononucleosis. But in some cases, more serious diseases such as cancer can cause the spleen to expand.

If you have an enlarged spleen, your doctor will probably tell you to avoid contact sports like football for a while. If you're hit, the swollen spleen is vulnerable to rupturing (bursting). And if it ruptures, it can cause a huge amount of blood to be lost.

Tonsillitis. Tonsillitis is caused by an infection of the tonsils, the lymphoid tissues in the back of the mouth at the top of the throat that normally help to filter out bacteria. When the tonsils are infected, they become swollen and inflamed, and can cause a sore throat, fever, and difficulty swallowing. The infection can also spread to the throat and surrounding areas, causing pain and inflammation. Someone with repeated tonsil infections may need to have them removed in a procedure called a tonsillectomy.