Anatomy clinical correlates: Peritoneum and diaphragm

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Introduction0:00–0:31

The peritoneum is a transparent serous membrane that lines the abdominal cavity and covers the abdominal organs, whereas the diaphragm is a skeletal muscle that separates the thoracic cavity from the abdominal cavity and plays an important role in respiration.
Understanding the anatomy of these structures allows us to better understand the unique clinical conditions that affect them.
Let’s start off by reviewing the innervation of visceral and somatic pain in the abdomen. The peritoneum is made up of two continuous layers, the visceral peritoneum and parietal peritoneum.

Visceral and somatic pain0:31–4:06

The inner visceral layer mainly covers the abdominal organs and has a visceral nerve supply, where the outer parietal layer mainly covers the internal surface of the abdominopelvic walls and has a somatic nerve supply.
Furthermore, both the visceral and somatic nerve supply of the peritoneum sense pain during different clinical conditions; however, the way in which they sense pain is different.
The visceral peritoneum is innervated by the autonomic nervous system. When the visceral peritoneum is irritated, pain sensation is detected by visceral afferent fibers which travel with the autonomic nerves, mainly sympathetic nerve fibers, back to the spinal cord.
Visceral pain is typically sensed as a diffuse, dull pain which is not very well localized, and the pain is often referred to the midline region of the dermatomal areas of the same spinal level as the autonomic nerve supply.
Typically, pain sensed by the foregut visceral peritoneum is referred to the epigastric region, midgut visceral pain is referred to the umbilical region, and hindgut visceral pain is referred to the hypogastric region.
Patients who experience visceral pain may also present with nausea, vomiting, or sweating due to activation of the autonomic nervous system.
On the other hand, the parietal peritoneum has a somatic nerve supply, which is the same as the adjacent abdominopelvic wall in which it lines.
When the parietal peritoneum is irritated, pain sensation travels back with these somatic nerves to the spinal cord. Somatic pain is typically sensed as a sharp, localized pain specific to the spinal level innervating that irritated area.
To illustrate these types of pain, let’s use appendicitis as an example, where appendicitis refers to inflammation of the appendix, and can cause both visceral and somatic pain.
Visceral pain occurs due to irritation of the visceral peritoneum of the appendix and surrounding areas which travel with sympathetic fibers back to the level of T10.
As a result, there may be vague pain in the right lower quadrant where the appendix is, as well as anywhere along the T10 dermatome level, frequently being felt around the umbilicus.
As the appendix becomes more and more inflamed, it can also irritate the parietal peritoneum, causing somatic pain; specifically, a sharp, localized pain to the right lower quadrant over the appendix to an area classically known as McBurney point.
The McBurney point is situated at two-thirds of the distance between from the umbilicus to the anterior superior iliac spine, and tenderness due to palpation over this area is a classic sign of appendicitis.
In addition to appendicitis, there are many situations that can cause irritation and inflammation of the peritoneum, and this is called peritonitis.

Peritonitis4:06–5:54

Often, peritonitis is the result of bacterial contamination, such as during open surgery; when the gut is penetrated during trauma; or as the result of a ruptured internal organ, such as the appendix.
This exposes the peritoneum to gas and fecal matter which is usually contained within the gastrointestinal tract, and allows bacteria to enter the otherwise sterile peritoneal cavity, leading to infection and subsequent inflammation of the peritoneum.
Peritonitis causes intense pain in the abdomen and results in increased tone of the anterolateral abdominal muscles, which is a mechanism that aims to protect the contents of the abdominal cavity.
Therefore, on examination the abdomen is extremely tender to palpation, resulting in patient discomfort and voluntary guarding.
Other signs include abdominal wall rigidity which is due to involuntary increased muscle tone as we just mentioned, as well as another clinical sign called rebound tenderness.
Rebound tenderness is when you slowly perform deep palpation on the abdomen, and then quickly remove your hand which elicits a stabbing pain over the area of palpation, resulting in a ‘rebound’ tenderness indicating peritonitis.
Symptoms of peritonitis include severe abdominal pain, nausea, vomiting, fever and constipation. Now, if the peritoneum is damaged or infected because of trauma, surgery or peritonitis, fibrin starts to deposit on the inflamed peritoneal surface which results in fibrous tissue formation during healing.

Peritoneal adhesion5:54–7:10

This fibrous tissue, often referred to as scar tissue, can lead to the formation adhesions, which are abnormal fibrous attachments between the visceral peritoneum of nearby organs or between the visceral peritoneum of an organ and the parietal peritoneum of the nearby abdominal wall.
Abdominal adhesions are often the result of an abdominal operation such as an appendectomy, and adhesion formation can limit the normal movements of the abdominal viscera.
Adhesions can cause chronic pain, or complications such as intestinal obstruction as the intestine can become tethered or twisted around to an adhesion, and can also result in a potential volvulus.
This is one reason why less invasive surgical techniques, such as laparoscopy, are preferred to open surgery, when possible.
Before we move on, we can’t discuss the peritoneum without mentioning how one of its really cool features is that it can be used for peritoneal dialysis!

Peritoneal dialysis7:10–9:14

The peritoneum is a semipermeable membrane with a large surface area rich in blood and lymphatic capillary beds. The fact that the peritoneum is semipermeable means that it allows certain substances or molecules to be rapidly absorbed, just like how the information in this Osmosis video is absorbed into your brain!
Ok, maybe it’s not exactly the same but you get the point. Now, in individuals with end-stage renal disease, waste products like urea accumulate in the individuals blood and tissues because they cannot be excreted, causing signs and symptoms like nausea, vomiting, pruritus, mental status changes or even pulmonary edema.
If the individual is unable to overcome their renal dysfunction, dialysis may be needed. There are two main types of dialysis: peritoneal dialysis which takes advantage of the semipermeable peritoneal membrane, and hemodialysis where waste products are removed from the blood.
Peritoneal dialysis involves inserting a large indwelling catheter in the peritoneal space, where a dilute sterile solution is introduced in the peritoneum through the catheter which creates a concentration gradient between the blood and the fluid in the peritoneal cavity.
This concentration gradient pulls waste and excess fluid from the blood and into the peritoneal cavity, where the fluid is then removed through the indwelling catheter.
This procedure relies on the peritoneum’s large surface area and semipermeable membrane to eliminate waste. Quick quiz before we move on to the next section: what is the difference between visceral and somatic abdominal pain?Now let’s talk about one of the unknown heroes of the peritoneal cavity: the greater omentum.

Quiz9:14–9:27

Greater omentum9:27–10:25

The greater omentum is a large, four layered peritoneal fold containing a large amount of fat that hangs from the greater curvature of the stomach.
It is a very mobile structure which covers a large portion of the abdominal organs, and in doing so prevents the visceral peritoneum from sticking to the parietal peritoneum.
Furthermore, it has a protective mechanism where it can form adhesions and surround inflamed organs, such as the appendix, in order to wall them off and keep inflammation from spreading to other abdominal organs and viscera.
The greater omentum is also a cushion for the abdominal organs against injury and also forms insulation against loss of body heat.
Next up, there’s the hepatoduodenal ligament, which is the thickened free edge of the lesser omentum that extends between the liver and the superior part of the duodenum.

Pringle maneuver10:25–11:33

The hepatoduodenal ligament contains three very important structures: the hepatic artery, the portal vein and the common bile duct.
Due to the risk of hemorrhage during liver injury or hepatic surgery, the best way to prevent and control bleeding is to compress the hepatoduodenal ligament.
This can be done using the Pringle maneuver, which is clamping the hepatoduodenal ligament manually or with the use of a clamp.
During uncontrolled bleeding of the liver, the pringle maneuver can be used to help localize the source of bleeding. If the bleeding stops, then the source is likely from the hepatic artery or portal vein, and if it does not stop then bleeding is likely due to the inferior vena cava or hepatic veins.
Alright! Now let’s switch gears and discuss the clinical conditions affecting the diaphragm.

Referred pain from diaphragm11:33–13:26

The diaphragm receives most of its sensory supply from the phrenic nerves which carry signals to C3-C5 spinal nerves, where the periphery of the diaphragm receives sensory innervation from the T5 through T11 intercostal nerves and the subcostal nerves.
So, when there is irritation to the diaphragmatic peritoneum innervated by the phrenic nerve, this can result in referred pain to the dermatome area supplied by C3-C5.
This is because as the phrenic nerve is irritated, it sends this signal back to spinal level C3-C5, and our body confuses this for sensation at the C3-C5 dermatome levels.
This would manifest as shoulder tip pain and is referred to as Kehr’s sign. Can you recall another clinical condition that results in shoulder tip pain?
That's right, a myocardial infarction can, because the phrenic nerve also innervates the pericardium. Going back to the diaphragm, irritation of the peripheral portions of the diaphragm will lead to more localized pain over the costal margin and anterolateral abdominal wall as these areas receive sensation from the T5 - T12 spinal levels.
Irritation of the diaphragm can be the result of numerous clinical conditions, such as peritonitis which we already talked about, or other things such as splenic rupture or a hemoperitoneum.

Pneumoperitoneum13:26–14:38

Next up, let’s talk about something called a pneumoperitoneum, which is when there is free air located in the peritoneal cavity.
Free air is often recognized on clinical imaging, such as during an X-ray or CT scan. One of the classic signs is on x-ray where free air is seen underneath the diaphragm on an upright abdominal or chest radiograph as seen here.
A pneumoperitoneum is caused by any condition where air can leak into the peritoneal cavity, for example any perforation along the gastrointestinal tract, such as a perforated ulcer or perforated diverticulum.
Other causes include trauma, tumours, or even iatrogenic causes such as injury during endoscopy. Remember our earlier talk about diaphragmatic irritation and shoulder tip pain?
Well, free air under the diaphragm can also result in shoulder tip pain. Pneumoperitoneum is a sign of life-threatening intra abdominal condition and needs urgent surgical management.If you need a quick break, feel free to pause this video and see if you can recall what Kehr’s sign is!Moving on to something more annoying than dangerous, let's talk about hiccups.

Quiz14:38–14:49

Hiccups14:49–15:27

Hiccups are involuntary and spasmodic contractions of the diaphragm that cause sudden inhalations of air being pushed against a closed larynx, creating a variety of funny sounding noises from person to person.
Hiccups are often the result of phrenic nerve irritation, and can be caused by things such as gastroesophageal reflux disease, diaphragmatic irritation as we mentioned before, or any thoracic or abdominal lesion disturbing the phrenic nerve.
Finally let’s talk about hernias! First, there are diaphragmatic hernias, which is when the abdominal viscera, for example the stomach or small intestine, can be forced into the thoracic cavity through any opening throughout the diaphragmatic surface.

Diaphragmatic hernias15:27–18:09

This can be due to congenital defects of the pleuroperitoneal membrane, or be the result of a blunt trauma to the abdomen which causes a sudden increase in intra abdominal or intrathoracic pressure resulting in a defect of the diaphragm throughout its surface or at its attachment points.
This increase in pressure leads to diaphragmatic rupture and herniation of contents through it. Now, diaphragmatic rupture occurs most often on the left hemidiaphragm, as the right hemidiaphragm is protected by the large mass of the liver.
Second, there are hiatal hernias, which are a type of diaphragmatic hernia, but occur when the upper part of the stomach pushes through the esophageal hiatus and extends up into the thoracic cavity.
There are two types of hiatal hernias: a sliding hernia and a paraesophageal hernia. A sliding hernia is more common, and is when the proximal stomach pushes into the thoracic cavity, or ‘slides’ into the thoracic cavity.
This is due to laxity of the phrenoesophageal membrane, which is a membrane that circumferentially attaches the distal esophagus to the diaphragm at the gastroesophageal junction.
Sliding hernias predispose individuals to reflux symptoms as gastric contents and acid can reflux proximally into the esophagus, leading to symptoms such as heartburn, indigestion, and epigastric or chest pain.
The second type of hiatal hernia is a paraesophageal hernia, which is when the fundus of the stomach bulges into the thoracic cavity adjacent to the esophagus due to a hole or defect in the phrenoesophageal membrane.
Large enough defects can even result in the additional herniation of the gastroesophageal junction, as well as other structures such as the spleen and bowel.
Paraesophageal hernias are less common than hiatal hernias, but have a higher risk of complications such as gastric obstruction, ulcerations, and even respiratory symptoms.

Review18:09–21:07

Alright, as a quick recap, the visceral peritoneum senses visceral pain which is diffuse and non-localized and often results in referred pain, while the parietal peritoneum senses somatic pain which is more sharp and well-localized.
During acute appendicitis, dull pain around the umbilicus is an example of visceral referred pain, where pain over McBurney point is an example of somatic pain.
Peritonitis is inflammation of the peritoneum where individuals can present with intense pain in the abdomen, nausea, and vomiting, and clinical signs include a tender, rigid abdomen with potential rebound tenderness.
When the peritoneum is damaged, the peritoneal surfaces can develop fibrous or scar tissue, leading to adhesions which can limit the movements of the abdominal viscera.
A Pringle maneuver is when the hepatoduodenal ligament, which contains the hepatic artery, the portal vein and the common bile duct, is compressed during hepatic surgery.The peritoneum can be used to remove toxic waste products in individuals with end-stage renal disease.
This is called peritoneal dialysis and is a temporary solution for individuals needing dialysis. Any intra abdominal or intrathoracic process which causes irritation of the phrenic nerve of the diaphragm can result in referred shoulder tip pain, referred to as Kehr's sign.
Diaphragmatic irritation can also result in irritating hiccups. A pneumoperitoneum occurs when free air accumulates in the abdominal cavity, and can be caused by things such as gastrointestinal tract perforation, trauma, or tumours and is classically seen as free air under the diaphragm on x ray.
Diaphragmatic hernias can result from congenital defects, or are acquired when an individual suffers blunt trauma to the abdomen typically affecting the left side of the diaphragm.
Finally, hiatal hernias are when the abdominal cavity contents herniate into the thoracic cavity through the esophageal hiatus.
Sliding hiatal hernias are more common and occur when the proximal stomach pushes into the thoracic cavity due to a weakened phrenoesophageal membrane, where paraesophageal hernias are typically when the fundus of the stomach bulges into the thoracic cavity due to a hole or defect in the phrenoesophageal membrane.