Stomach and Spleen.pdf

Gastrointestinal System The Stomach and Spleen We are now ready to discuss the abdominal organs, and where better to start than with the stomach and spleen, two of the organs of the upper abdominal cavity.  Learning Outcomes After this lecture you sho...

Gastrointestinal System The Stomach and Spleen We are now ready to discuss the abdominal organs, and where better to start than with the stomach and spleen, two of the organs of the upper abdominal cavity.  Learning Outcomes After this lecture you should be able to: ▪ Give an account of the position and form of the stomach and know its parts ▪ Know the locations of the greater and lesser omenta ▪ Give an account of the functions of the stomach ▪ List the layers of the stomach wall ▪ List the relations of the stomach ▪ Give an account of the arterial supply, venous and lymphatic drainage of the stomach and spleen ▪ Describe the nerve supply of the stomach ▪ Know the position and form of the spleen, and understand the principles of examination of the abdomen for splenomegaly Here are the learning outcomes for this lecture.  Gastrointestinal System The Stomach and Spleen 1. Stomach Location and Parts 2. The Stomach and Its Relations 3. Neurovasculature 4. The Spleen There are 4 parts to this lecture.  Gastrointestinal System The Stomach and Spleen Part 1: Stomach Location and Parts In this first part we’ll consider the parts of the stomach and give an account of the normal size shape and position of this organ.  Learning Outcomes After this lecture you should be able to: ▪ Give an account of the position and form of the stomach and know its parts ▪ Know the locations of the greater and lesser omenta ▪ Give an account of the functions of the stomach ▪ List the layers of the stomach wall ▪ List the relations of the stomach ▪ Give an account of the arterial supply, venous and lymphatic drainage of the stomach and spleen ▪ Describe the nerve supply of the stomach ▪ Know the position and form of the spleen, and understand the principles of examination of the abdomen for splenomegaly The learning outcomes for this part of the lecture are that afterwards you should be able to: Give an account of the position and form of the stomach and know its parts Know the locations of the greater and lesser omenta Give an account of the functions of the stomach The remaining outcomes will be given in the subsequent sections.  General Guide to Viscera It is worth stating before we begin, that for every organ that we will discuss in this lecture and the others to follow, there is a standard set of things that we need to consider.  General Guide to Viscera ▪ We need to know; » Their size, shape and position » Their relations (compressions and spread of disease) » Their parts (for descriptive purposes) » Their functions (in brief) » Their blood supply, venous and lymphatic drainage » Their innervation (when relevant) » Their clinical symptoms following disease We need to know; Their size, shape and position, so that we can recognize any pathological sizes and shapes, and abnormal positions. Their relations so that we can appreciate compression from tumours or understand how enlargement of nearby organs can affect the functioning of the organ. We can also appreciate how infections can spread to and from the organs. Their parts so that we can pinpoint problems and direct more specific treatments. We can also communicate this more effectively. Their functions, but we will only do that briefly. Their blood supply, venous and lymphatic drainage (the latter two are important for cancer and infection spread). Their innervations, although that isn’t always important. We’ll highlight this when it is relevant to know. And lastly, their clinical symptoms following disease. And of course, try to make sense of those as much as we can.  Location and Shape of the Stomach OK then, we begin with the stomach. The stomach is the most dilated part of the alimentary canal. It is located between the oesophagus and the small intestine. In the supine position, it is usually located in the left upper quadrant, where it occupies parts of the epigastric, umbilical, and left hypochondriac regions. However, as the stomach is an intra-peritoneal organ, it is mobile. Its top and bottom ends are relatively fixed, as the oesophagus is firmly anchored to the diaphragm above, whilst the pyloric end is tethered to the relatively immobile duodenum. Indeed, the latter is said to lie at the transpyloric plane, one of the defining boundaries of the sub- divisions of the abdomen.  Hypertonic Stomach (not for inclusion in the lecture presentation) The mobile portion however will have a position dependent upon the tone of its muscular wall. If there is too much tone, the stomach will be shorter and flatter. This is hypertonia.  Hypotonic stomach (not for inclusion in the lecture presentation) Loss of tone will allow the stomach to sag in the abdominal cavity. This is hypotonia and is referred to as “dropped stomach”, or “stomach ptosis”.  Atonic Stomach (not for inclusion in the lecture presentation) There can be a complete loss of tone to the muscular wall and this is atonia. The stomach may drop down into the pelvis. The position of the stomach will also depend upon the state of filling due to the ingestion of a meal (or 10 pints of beer on a Friday/Saturday night!).  Body Morphism and the Stomach (not for inclusion in the lecture presentation) Of course, the stomach shape is also dictated by body shape, so someone who is tall and thin (i.e. an ectomorph) will have a tall and thin stomach, whilst someone who is short and fat (i.e. an endomorph) will have a short stumpy stomach which lies more horizontally. Such individuals are said to have a steer-horn stomach. Have you seen a steer-horn?  Steerhorn Stomach (not for inclusion in the lecture presentation) This is one. You can see from this X-ray, where the stomach has been filled with a contrast medium, that the shape of the stomach is similar to the steer-horn and it lies almost horizontally within the cavity.  The Stomach on X-Ray (not for inclusion in the lecture presentation) Here is a normal contrast X-ray for comparison. Note the more usual J- shape.  Functions of Stomach (not for inclusion in the lecture presentation) Temporary storage of chyme Holds from 75mls (empty) - 2 litres (or more, full) Breakdown begins Churning Pepsin - breakdown of proteins HCL – allows action of pepsin and destruction of bacteria Secretions Gastrin, Intrinsic Factor Absorption H2O, electrolytes Alcohol, aspirin Food remains in stomach about 4 hours The adult volume of the stomach is approximately 1000 mls but can be double that after a hearty meal. The breakdown of the food begins with the release of pepsin and hydrochloric acid, which are mixed with the contents of the stomach by movements of the stomach wall. The pH can be as low as 1 in the stomach lumen, and gastric mucus is almost certainly one of the mechanisms protecting the gastric epithelium from this environment: the pH at the epithelial surface of the mucus is approximately 6. Obviously, since gastro-enteritis is common, this "acid sterilisation" is not a completely successful strategy. The body also secretes gastrin and intrinsic factor. The latter is to enable the absorption of vitamin B12. Absence of intrinsic factor is the cause of primary pernicious anaemia. Gastrin stimulates gastric acid secretion. Although absorption of nutrients occurs mostly in the intestines, the stomach wall is capable of the absorption of water and electrolytes as well as alcohol. That’s why you are advised not to drink on an empty stomach, otherwise the alcohol is absorbed too quickly. The other thing that is absorbed by the stomach wall is aspirin, which helps it get into the bloodstream quickly. However, there is a downside in that it can cause the stomach wall to bleed and cause peptic ulcers in some people. The process of digestion in the stomach takes about 4 hours which is enough time to break the meal down into chyme and also remove most ingested bacteria or viruses.  Parts of the Stomach The J-shape is created by the expansion of this organ to the left during development. It is connected above to the oesophagus and below to the duodenum. These parts are relatively fixed, so the stomach has to adapt its shape to fit. The oesophagus is slightly on the left, whilst the duodenum is on the right, hence the stomach hangs between these two organs on the left side. The stomach has 5 regions. There is a cardiac region (the orifice of which receives the oesophagus), a fundus (where gas bubbles are trapped), a body (which together with the fundus contain numerous glands to aid digestion), and a pyloric portion (containing an antrum or swelling, and a canal with a sphincter).  Angles of the Stomach Since the oesophagus enters the right side of the stomach, there is an angle between the cardia and the fundus and this is known as the cardial notch. There is another angle between the pyloric antrum and body on the lesser curvature of the stomach, and this is known as the incisura angularis.  The Cardia Cardia Mucus secretion The cardia or cardiac region is ill-defined. There are no identifying landmarks externally to say where the oesophagus end and the cardia begins, and there is no defining boundary between the cardia and the body. Indeed, it is rather puzzling as to why it has this name at all. Cardiac of course refers to the heart. The naming of this dates back to Galen in 160s AD, where he likened symptoms of disease of this area to that of heart conditions. This is a very tentative connection. Back in Galen’s day, the stomach only had two parts, a cardia and a pylorus. Hence Galen probably wasn’t making any specific reference to the cardia of today. Nevertheless, we often make reference to ‘heart-burn’ as a pain in the ‘pit’ of the stomach, caused by acid reflux into the lower oesophagus. The main role of the cardia is to increase mucus secretion to reduce the effect of reflux of acid into the oesophagus. Although there are no identifying features of the cardia externally, there is one internally. This is the gastro-oesophageal junction.  Gastro-Oesophageal Junction At this junction there is a sharp transition from the stratified squamous epithelium of the oesophagus (shown here on the left) to the simple columnar epithelium of the stomach (shown on the right).  The Fundus Cardia Mucus secretion Fundus Storage of air The fundus is normally full of air. It rises to the level of the 5th intercostal space immediately below the diaphragm. It can readily be seen on chest or abdominal X-rays, even without contrast.  The Body Cardia Mucus secretion Fundus Storage of air Body Storage, mucus, HCl, pepsinogen, intrinsic factor The body of the stomach is a storage site for the ingested food, which is broken down by hydrochloric acid and pepsinogen, released from the stomach wall.  Gastric Glands (not for inclusion in the lecture presentation) The gastric glands in the body of the stomach contain goblet cells which secrete mucus. This mucus protects the stomach wall from the hydrochloric acid produced by the parietal cells. This acid is used by the stomach to digest the food and turn it into chyme. Parietal cells also secrete intrinsic factor. This has an important role in the absorption of vitamin B12 in the intestine, and failure to produce or utilize intrinsic factor results in the condition pernicious anaemia. There is also pepsinogen released by chief cells, and this helps to digest the proteins contained with the bolus of food. D cells secrete somatostatin which inhibits acid secretion. Finally, in the base of the gastric pit are G cells which stimulate acid secretion by the production of gastrin.  The Pyloric Region Cardia Mucus secretion Fundus Storage of air Body Storage, mucus, HCl, pepsinogen, intrinsic factor Pyloric Antrum Mixing/grinding, gastrin ▪ Pylorus The pyloric antrum is the first part of the pyloric region. The second part is the pylorus. There is often a groove between the antrum and the pylorus but not always. The antrum has a high proportion of gastrin secreting cells, and gastrin increases the motility of the intestines. There is a lot of mixing and grinding of the chyme here, as there are peristaltic waves pushing the chyme towards the pylorus.  The Pyloric Canal The word pylorus means ‘gatekeeper’ in Greek hence the pylorus contains a sphincter to control what leaves the antrum. The sphincter is very large and is formed of a ring of smooth muscle. The gap between the sphincteric muscle is called the pyloric canal. When this sphincter contracts it closes the pyloric canal and prevents the entry of chyme into the duodenum. We can see that animated here. The chyme in reality is not as fluid as the animation would have us believe.  The Greater and Lesser Omentum Finally, here is a reminder that the stomach is an intraperitoneal organ. Attached to the lesser curvature is the lesser omentum which connects to the liver. The greater curvature of the stomach is the outside of the “J”, and this gives rise to the greater omentum.  Formation of the Lesser Sac (not for inclusion in the lecture presentation) These omenta are part of the mesenteries which wrap around the stomach, posteriorly forming the anterior layer of the lesser sac.  Gastrointestinal System The Stomach and Spleen Part 2: The Stomach and Its Relations Welcome to the second part of this lecture on the stomach and spleen. In this section, we’ll cover the wall of the stomach and then consider the relations of this organ.  Learning Outcomes After this lecture you should be able to: ▪ Give an account of the position and form of the stomach and know its parts ▪ Know the locations of the greater and lesser omenta ▪ Give an account of the functions of the stomach ▪ List the layers of the stomach wall ▪ List the relations of the stomach ▪ Give an account of the arterial supply, venous and lymphatic drainage of the stomach and spleen ▪ Describe the nerve supply of the stomach ▪ Know the position and form of the spleen, and understand the principles of examination of the abdomen for splenomegaly The learning outcomes for this part of the lecture are that afterwards you should be able to: List the layers of the stomach wall List the relations of the stomach The remaining outcomes will be given in the subsequent sections.  The Gut Wall The gut wall has a general organisation which applies along the entire length of the gastrointestinal tract. We’ll look at the specialisations of the stomach later, but for now let’s look at the general plan. The wall is made up of 4 layers as we can see in this step-wise illustration. Let’s look at these layers one by one.  Mucosa Duct of accessory gland GALT (e.g. pancreas, liver) (gut-associated lymphoid tissue) Mucosa: Epithelium Lamina Propria Muscularis Mucosa Sub-mucosal gland Mucosal gland The first layer from the lumen outwards is the mucosa or mucous membrane. This consists of the gut epithelium, the lamina propria which is the loose connective tissue immediately beneath the epithelium, and the muscularis mucosa. The latter is a thin sheath of smooth muscle, whose contractions serve to take up the slack in the mucosa and control its local pleating. There are several ducts that traverse this layer on their way to the lumen. Firstly, there are the ducts of accessory glands such as the liver and pancreas. Next there are ducts of the mucosal and submucosal glands. These mostly secrete mucus. The lamina propria also contains the gut‐associated lymphoid tissue (GALT), nodules of lymphatic tissue bearing lymphocytes and macrophages that protect the GI tract wall from bacteria and other pathogens that may be mixed with food.  Submucosa Submucosal (Meissner’s) Plexus Submucosa: Loose CT Blood Vessels Lymphatics Nerves Glands Sub-mucosal gland The 2nd layer is the submucosa - a layer of loose connective tissue carrying many blood vessels, lymphatics and nerves. The nerves form an intrinsic plexus here, called the submucosal plexus. These nerves control the secretion of the glands within the mucosa and submucosa. They also control the contractions of the muscularis mucosa. These nerves have their own autonomy, that is they offer control without any external influence, although they do have the option of being influenced by the parasympathetic nerves of the vagus or pelvic splanchnic nerves. This plexus is part of the enteric nervous system. It is likened to the gut having its own brain.  Muscularis Externa Myenteric (Auerbach’s) Plexus Muscularis Externa: Outer Longitudinal Inner Circular Stomach – additional inner oblique layer The powerful muscularis externa usually comprises an inner circular layer and an outer longitudinal layer of smooth muscle. The muscularis externa generates the peristaltic contractions that propel food down the tract, as well as the movements that churn the contents of the stomach and those that expel faeces from the bowel. The movements of this layer are controlled by the myenteric (of Auerbach) plexus of nerves. This is also part of the enteric nervous system, and again can function independently of any external influence. It is stimulated however by the vagus or pelvic splanchnic nerves.  Adventitia or Serosa Adventitia or Serosa: Connective Tissue or Peritoneum Extrinsic nerves Blood Vessels The final layer is an adventitia for the retroperitoneal parts of the gut, or a serosa for the intraperitoneal parts. This layer carries blood vessels and extrinsic nerves.  The Enteric Nervous System The enteric nervous system provides a direct control over gut secretions via the submucosal plexus and gut motility via the myenteric plexus. There are also nerve cells within the myenteric plexus which can influence the activity in the submucosal plexus and vice versa. There are sensory nerves within this plexus that respond to local factors within the wall of the gut and the gut lumen. Like the brain and spinal cord there are reflex pathways that respond to sensory stimuli.. However, the brain and spinal cord are able to take control when required. Parasympathetics stimulate the effect of these plexuses, whilst sympathetics inhibit these.  The Stomach Wall The wall of the stomach is specialised. We have already witnessed the elaborate nature of the gastric glands in the mucosa. The muscularis externa of the stomach is also a little unusual. It is made up of three coats of muscle; an inner oblique layer, a middle circular layer and an outer longitudinal layer. The oblique layer is unique to the stomach. The circular layer is increased massively at the pyloric sphincter, to control the release of gastric content into the duodenum. Much is made of the fact that there is a distinct muscle around the lower end of the oesophagus, and this has been referred to as the lower oesophageal sphincter. However, this is not a true sphincter, and the control of reflux of gastric secretions into the oesophagus is controlled largely by the muscular fibres of the diaphragm, particularly from the right crus, which loops around the oesophagus at this point. Another important factor is the angulation that the oesophagus makes with the cardia. This produces a functioning flap-valve, preventing reflux into the oesophagus.  Rugae The mucous membrane is thrown into large longitudinal folds, called rugae. These produce a characteristic appearance on contrast X-rays of the stomach. The purpose of the gastric rugae is to allow for expansion of the stomach after the consumption of foods and liquids. It can also allow the stomach to adapt to movements of the stomach wall caused by contraction of the muscularis mucosa and peristalsis in the muscularis externa. Here we can see an animation of these peristaltic waves driving the pyloric sphincter to open.  Relations of the Stomach There are a number of important relations of the stomach, and most of these lie posteriorly on what is known as the bed of the stomach. There is one key structure though that crosses the stomach anteriorly.  Relations of the Stomach: Liver That is the left lobe of the liver, which crosses the cardiac region and the fundus. Relations of the Stomach: Diaphragm These regions are also in close contact with the left dome of the diaphragm. To the left and behind the stomach is the spleen, and hence this is also an important relation. It isn’t shown on this illustration, but we’ll discuss this relationship in the final section of this lecture.  Relations of the Stomach: Pancreas On the stomach bed, the body and pyloric region are closely related to the pancreas.  Relations of the Stomach: Renal And the left kidney and left suprarenal gland are also related to the body of the stomach.  Relations of the Stomach: DJF The duodenum turns a sharp corner to become the jejunum, and this is the duodenojejunal flexure. This is also a relation of the distal part of the body or proximal part of the pyloric antrum.  Relations of the Stomach: Vessels Lastly, the coeliac trunk originates at the level of T12, close to the incisura angularis of the stomach. Running behind the stomach towards the spleen is the splenic artery. The hepatic portal vein lies behind the pyloric region of the stomach.  Gastrointestinal System The Stomach and Spleen Part 3: Neurovasculature Welcome back to this lecture on the stomach and spleen. We have now reached part 3 in which we will discuss the neurovasculature of these organs.  Learning Outcomes After this lecture you should be able to: ▪ Give an account of the position and form of the stomach and know its parts ▪ Know the locations of the greater and lesser omenta ▪ Give an account of the functions of the stomach ▪ List the layers of the stomach wall ▪ List the relations of the stomach ▪ Give an account of the arterial supply, venous and lymphatic drainage of the stomach and spleen ▪ Describe the nerve supply of the stomach ▪ Know the position and form of the spleen, and understand the principles of examination of the abdomen for splenomegaly The learning outcomes for this part of the lecture are that afterwards you should be able to: Give an account of the arterial supply, venous and lymphatic drainage of the stomach and spleen Describe the nerve supply of the stomach The remaining outcome will be given in the subsequent sections.  Coeliac Trunk The coeliac trunk is the key artery of the foregut, and hence supplies all of the upper abdominal organs. It arises from the anterior aspect of the abdominal aorta, shortly after the aorta appears through the aortic opening in the diaphragm. This is at the vertebral level of T12. There are 3 branches, a large one for the liver heading to the right. The is the common hepatic artery. This becomes the proper hepatic before dividing into left and right hepatic arteries. There is also a large branch destined for the spleen on the left. This splenic artery is characteristically tortuous. The other organ that needs a supply from the coeliac trunk is the stomach, hence there is a left gastric artery for this purpose. The thing is though, this artery is quite small hence the stomach has to take part of its supply from the common hepatic and splenic branches. Branches of the Coeliac Trunk to Stomach The lower half of the stomach takes branches of the common hepatic, whilst the upper half is mostly from the splenic. The upper part of the lesser curvature and cardiac region is from the left gastric artery.  Branches of the Coeliac Trunk This diagram shows the detail of this supply. Information about each branch is given, but will not be given in the lecture. You will dissect these branches in the accompanying practical.  Common Hepatic Artery (not for inclusion in the lecture presentation) The common hepatic artery travels to the right and divides into the proper hepatic artery and the gastroduodenal artery. The former heads upwards to the liver, and the latter travels downwards behind the duodenum. In this location the gastroduodenal artery is at risk of lesion following ulceration of the duodenum. The proper hepatic artery divides into right and left hepatic branches. The main trunk of the proper hepatic artery usually gives off the right gastric artery. It does so in approximately 55% of cases. This supplies the right side of the lesser curvature of the stomach. The origin of the right gastric artery though is highly variable. The gastroduodenal artery divides into the right gastroepiploic and the superior pancreaticoduodenal arteries. The former supplies the right side of the greater curvature of the stomach. The latter partly supplies the duodenum and pancreas.  Left Gastric Artery (not for inclusion in the lecture presentation) The left gastric ascends to the oesophagus and then supplies the lesser curvature of the stomach, anastomosing with the right gastric artery. It also gives oesophageal branches.  Splenic Artery (not for inclusion in the lecture presentation) The splenic artery follows a tortuous course along the upper border of the pancreas, which it supplies, and then reaches the spleen via the lienorenal ligament. It gives off pancreatic branches and the short gastric and left gastroepiploic arteries, which reach the stomach via the gastrosplenic ligament.  Venous Drainage of the Stomach Superior vena cava Azygos vein Oesophageal veins The venous drainage of the oesophagus is mostly into the azygos vein, which is a vein of the thorax terminating in the superior vena cava.  Portal System Azygos vein Oesophageal veins Gastric veins Hepatic portal vein Splenic vein Superior mesenteric vein The venous drainage of the stomach and spleen is via gastric, gastroepiploic and splenic veins. These all drain into the hepatic portal vein, which then reaches the liver. There is a rich anastomosis around the lower part of the oesophagus, and hence the oesophagus is partly connected with the portal venous system. Should venous drainage of the hepatic portal vein be impeded, then the tributaries of the portal system my attempt to return to the heart via the azygos system instead. Oesophageal veins may hence enlarge and become varicosed. These can rupture and cause the patient to vomit blood.  Lymphatics of the Stomach Gastric lymphatics are continuous at the pylorus with the duodenal lymphatics and the oesophageal lymphatics at the cardia. Lymph channels largely follow the blood vessels and 4 main groups have been identified. 1. Left Gastric nodes: drains the region supplied by the left gastric artery. 2. Pancreaticolienal nodes: drains the gastric fundus and body left of a vertical line drawn from the oesophagus. 3. Right Gastro-omental nodes: drains the greater curvature as far as the pylorus. These nodes drain into the pyloric nodes. 4. Right Gastric and Pyloric nodes: drains the pyloric part of the stomach. All the nodes eventually drain into the coeliac nodes (pre-aortic nodes) and from there to paraortic, cysterna chyli and thence to the thoracic duct. This latter statement is the only one regarding the lymphatics that need be committed to memory. Parasympathetic Supply of the Stomach Vagus » Motor and secretomotor Lastly, we need to consider the nerve supply to the upper abdominal organs. Parasympathetic innervation to most of the GI tract, from the stomach to the splenic flexure of the colon, is from the vagus nerves (CN X). The vagus gives many branches along its route which contribute to various plexuses in the thorax (e.g. oesophageal plexus, cardiac plexus and pulmonary plexus). The vagus nerves (right and left) lie behind the lung roots, but are then directed onto the oesophagus. The oesophageal plexus involves branches of both right and left vagi. The main parts of these nerves become twisted around the lower oesophagus as anterior and posterior vagal trunks. They pass through the oesophageal sphincter to lie anterior and posterior to the stomach respectively. Some of the fibres (particularly from the posterior vagus) then give branches to the plexuses of the abdomen (coeliac and superior mesenteric).  Sympathetic Supply of the Stomach Sympathetics (T6-T9) » Afferent – pain (epigastric) » Efferent – vasoconstriction and antiperistaltic Sympathetics to the upper abdominal organs are derived mostly from the greater splanchnic nerves (T6-T9) and are distributed via the coeliac plexus. These nerves cause vasoconstriction. They are also inhibitory to the intrinsic plexuses, and hence inhibit peristalsis. Pain fibres from the stomach (as well as from other foregut derived structures) also travel in the greater splanchnic nerves to reach the T6-T9 spinal roots. These incoming signals are interpreted by the brain as pain emanating from the epigastric region of the body wall. This is an example of referred pain. Sometimes an area between the shoulder blades at the back is also involved.  Nerve Supply to Stomach In order to reach the organs of the upper abdominal cavity, the preganglionic sympathetic nerves synapse in the ganglia located at the root of the coeliac trunk, and then the post-ganglionic neurons hitch-hike along the blood vessels destined for these organs. The vagus nerves carry the parasympathetic preganglionic fibres along the oesophagus and then give branches to each of the organs. The post-ganglionic parasympathetic nerves are located in the walls of these organs. The left vagus nerve forms the anterior vagal trunk for the stomach, whilst the right vagus nerve forms the posterior vagal trunk. There is however shared branches for each via a plexus of nerves around the oesophagus.  Gastrointestinal System The Stomach and Spleen Part 4: The Spleen Welcome to the last part of this lecture on the stomach and spleen. In the last 3 sections of the lecture we have focussed on the stomach, so now it is time to focus on the spleen.  Learning Outcomes After this lecture you should be able to: ▪ Give an account of the position and form of the stomach and know its parts ▪ Know the locations of the greater and lesser omenta ▪ Give an account of the functions of the stomach ▪ List the layers of the stomach wall ▪ List the relations of the stomach ▪ Give an account of the arterial supply, venous and lymphatic drainage of the stomach and spleen ▪ Describe the nerve supply of the stomach ▪ Know the position and form of the spleen, and understand the principles of examination of the abdomen for splenomegaly The learning outcome for this part of the lecture is that afterwards you should be able to: Know the position and form of the spleen, and understand the principles of examination of the abdomen for splenomegaly  The Spleen The spleen is the largest unit of lymphoid tissue in the body. It is about the size of a fist and lies in the upper left hypochondrium. The spleen contains macrophages which destroy ageing red blood cells, and liberated pigment is transported to the liver via the hepatic portal system. The spleen also produces lymphocytes (white blood cells) and erythrocytes (red blood cells), although the latter is confined to the infant. It is also a store for red-blood cells and platelets. Normally, the spleen acts as a reservoir for about a third of the total platelet count. Whilst in the spleen, old and damaged red blood cells and platelets may be removed and recycled. If the spleen enlarges (via liver disease or splenic cancer), this results in a greater number of platelets staying in the organ. This then causes a correspondingly low number of platelets in the blood, with a risk of excessive bleeding. The spleen responds to stimulation from sympathetic nerves and circulating adrenaline, by releasing its store of blood. This function is useful in response to low blood levels (e.g. following a haemorrhage) but is not considered essential. The adult spleen is not essential for life, although immune-deficiency will result from its absence.  Position of Spleen (Lateral View) The spleen lies along the axis of the 10th rib and sits between the 9th to the 11th ribs. There is a risk of rupture of the spleen following fracture of these ribs. The spleen is highly vascular, and its rupture may be life- threatening, since there will be a massive haemorrhage. The anterior boundary of the spleen is level with the mid-axillary line.  The Spleen in Situ The spleen has a number of important relations in the left hypochondrium. The diaphragm is a postero-lateral relation of the spleen, since the spleen lies under its left dome. It moves during breathing. The spleen is a 'floating' structure since it is an intraperitoneal organ. It is attached to the stomach via the gastrosplenic ligament and to the posterior abdominal wall and left kidney via the lienorenal ligament. Spleno- and lieno- can be used interchangeably. Splen is Greek and lien is Latin. Hence you could equally say the splenorenal ligament.  Surfaces and Borders of the Spleen Pancreas The spleen has a diaphragmatic surface and a visceral surface. There is a sharp superior and anterior border which is notched, and a smooth and rounded posterior or inferior border. There is some confusion over the naming of the surfaces amongst various textbooks (some label 3 borders, others 2, and the superior and anterior borders are sometimes the same), but if you consider just two borders (one notched and one not), this is all that matters clinically. The visceral surface has a notch for the stomach, the kidney, the splenic flexure of the colon and the tail of the pancreas.  Hilum of the Spleen The hilum of the spleen is where the vessels enter and leave the organ on its visceral surface. Let’s now take a look at the section of the spleen in the location shown.  Cross-Section of the Spleen (not for inclusion in the lecture presentation) Here we can see the artery dividing within the substance of the spleen into smaller branches. It is important to appreciate that the splenic artery and vein do not form a continuous circulation. The capillaries of these arteries are open-ended, and blood cells escape these to be captured in venous sinusoids which then coalesce to form the splenic vein.  White Pulp vs Red Pulp (not for inclusion in the lecture presentation) The spleen substance is divided into two forms; red pulp and white pulp. Red pulp makes up about 75% of the total and consists of clusters of macrophages and red blood cells. This part of the spleen is essentially a place to filter and remove old or damaged red blood cells. White pulp makes up the remaining 25% and is characterised by the presence of lymphocytes suspended on a framework of reticular fibres, organised around the branches of the splenic artery. This is part of the immune defence system.  The Organisation of the Spleen (not for inclusion in the lecture presentation) The lymphocytes within white pulp are both T (mainly T-helper) and B- cells. The splenic artery branches to form central arterioles, and these become surrounded by a periarteriole lymphatic sheath. This is the location of the T-lymphocytes and some macrophages. Surrounding that is a marginal zone containing follicles where B-lymphocytes are generated. In this marginal zone there are also macrophages. Dendritic cells are brought to the spleen via the blood stream. These are antigen presenting cells, and these activate the T-cells in the periarteriole lymphatic sheath. In turn these activate the B-cells in the follicles turning them in plasma cells which release antibodies to the antigen. There are other immune responses in this tissue but we’ll keep this simple. The primary function of red pulp is to filter the blood of antigens, microorganisms, and defective or worn-out red blood cells. Within the red pulp are venous sinuses, and these have slit-like gaps in their walls. The red blood cells which are released from the arterioles try to gain access to the venous sinuses. Healthy ones will pass through easily but old or misshapen ones will not. These are then ingested by macrophages located in the cords of Billroth, and hence removed. These macrophages also remove blood-borne antigens and microorganisms. The venous sinuses lead to collecting veins which then coalesce to form the splenic vein.  Palpation of the Spleen (not for inclusion in the lecture presentation) The normal spleen is not palpable and can only be felt if the organ is enlarged. The patient is asked to take a deep breath in, and the descending diaphragm then pushes the enlarged organ below the costal margin.  Splenomegaly (not for inclusion in the lecture presentation) The notches on the anterior part of the superior border help to identify an enlarged spleen, since the notches persist even when the spleen is huge. Enlargement of the spleen is called splenomegaly. In such cases, the notched border of the spleen can be felt or even seen, as can be witnessed in this case presented here on the right.  Causes of Splenomegaly (not for inclusion in the lecture presentation) An enlarged spleen may be due to: infections inflammatory disease blood cell disorders abnormal blood flow and congestion (e.g. portal hypertension, cardiac failure) liver disease blood cancers (lymphoma, leukaemia, myelofibrosis) Gaucher disease (a lipid storage disease) Splenomegaly may be due to an immune hyperplasia, that is an increase in the immune response. It can also be a consequence of an increased need to remove damaged blood cells (e.g. anaemia or thalassemia). It can also enlarge during abnormal blood flows such as during organ failure (e.g. liver, heart) or as a consequence of venous congestion (e.g. portal hypertension). Finally, it may enlarge as a result of infiltration of infection or cancer (leukaemia or lymphoma). There are a few other causes, such as certain metabolic diseases, that need not concern us here.  Gastrointestinal System The Stomach and Spleen And that concludes this lecture on the stomach and spleen. In the next lecture we will consider the other main organ of the upper abdominal cavity – the liver.