Areas - Peritoneum Flashcards
What is the peritoneum?
It is a continuous lining that lines the abdominal cavity and the abdominal viscera.
Function of the peritoneum?
It acts to support the abdominal viscera and provides pathways for blood vessels and lymph to travel to and from abdominal viscera.
There are two layers of the peritoneum. These are called…
1) Parietal peritoneum
2) Visceral peritoneum
These two layers are continuous with each other.
Both types are made up of a simple squamous epithelium, called the mesothelium.
What is the structure of the parietal peritoneum?
Embryological derivation?
It lines the internal surface of the abdominal pelvic wall.
It is derived from the somatic mesoderm in the embryo.
It receives the same somatio nervous supply as the region of the abdominal wall that it lines, therefore pain in the parietal peritoneum is well localised. This peritoneum is sensitive to pressure, pain, temperature and laceration.
What is the structure of the visceral peritoneum?
Embryological derivation?
The visceral peritoneum invaginates to cover the majority of the abdominal viscera.
It is derived from the splanchnic mesoderm.
The visceral nervous supply has the same autonomic nerve supply as the viscera it covers. Unlike the parietal peritoneum, pain from the visceral peritoneum is poorly localised.
The visceral peritoneum is only sensitive to stretch and chemical irritation.
Pain from the visceral peritoneum is referred to areas of skin (dermatomes) which are supplied by the same sensory ganglia and spinal cord segments as the nerve fibres innervating the viscera.
Peritoneal cavity
This is a potential space between the parietal and visceral peritoneum. It normally contains a small amount of lubricating fluid.
Clinical relevance: peritoneal adhesions
Damage to the peritoneum can be as a result of infection, surgery or injury.
The resulting inflammation and repair may cause formations of fibrous scar tissue. This can result in abnormal attachments between the visceral peritoneum of adjacent organs or between the visceral and parietal peritoneum.
These adhesions can result in pain, and complications such as volvulus, when the intestines become twisted around an adhesion resulting in a bowel obstruction.
The abdominal viscera can be subdivided into two groups: intraperitoneal and retroperitoneal organs. What is the difference?
Intraperitoneal organs are enveloped by visceral peritoneum, which covers the organs anteriorly and posteriorly. Examples include stomach, liver and spleen.
Whereas retroperitoneal organs are not associated with the visceral peritoneum. It is only associated with the parietal peritoneum that covers the anterior surface of that organ.
The retoperitoneal organs can be further subdivided into two groups based on their embryological development. Which organs belong to each group?
1) Primary retroperitoneal - organs are developed and remain outside of the parietal peritoneum. These are the oesophagus, rectum and kidneys.
2) Secondary retroperitoneal - organs were initially intraperitoneal and were suspended by the mesentery. Throughout embryological development they become retroperitoneal as there mesentery becomes fused with the posterior abdominal wall. Examples include the ascending and descending colon.
The following organs are retroperitoneal:
Pneumonic: SAD PUCKER
S - suprarenal (adrenal) glands
A - Aorta/IVC
D - Duodenum
P - Pancreas
U - Ureters
C - Colon
K - Kidneys
E - Esophagus
R - Rectum
There are a number of terms to describe the folds and spaces of the peritoneum. What are these terms?
1) Mesentery - a double layer of visceral peritoneum. It connects an intraperitoneal organ (usually) to the abdominal wall. It provides a pathway for nerves, blood vessels and lymphatics to travel from the body wall to the viscera.
The mesentery of the small intestine is simply called ‘the mesentery’. Mesentery related to other parts of the GI named according to the viscera it connects to - for example the ‘mesoappendix’.
2) Omentum - this can be subdivided into the greater and lesser omentum.
Where is the greater omentum?
What is its function?
Consists of four layers of visceral peritoneum. It descends from the greater curvature of the stomach and the proximal part of the duodenum, then folds back up and attaches to the anterior surface of the transverse colon.
It has a role in immunity and is somtimes called the ‘abdominal policeman’, because it can migrate to infected viscera or to the site of surgical disturbance.
Where is the lesser omentum?
It is a double layer of visceral peritoneum. It attaches from the lesser curve of the stomach and the proximal part of the duodenum to the liver.
It consists of two parts: the hepatogastric ligament (flat, broad sheet) and the hepatoduodenal ligament (the free edge, containing the portal triad).
Peritoneal ligaments
1) Peritoneal ligament - a double fold of peritoneum that connects viscera together or viscera to the abdominal wall.
e. g Hepatogastric ligament - a portion of the lesser omentum, connecting the liver to the stomach.
Clinical relevance - referred pain
Pain from the viscera is poorly localised. It is referred to areas of skin (dermatomes) which are supplied by the same sensory ganglia and spinal cord segments as the nerve fibres innervating the viscera.
Pain is referred according to the embryological origin of the organ. Thus pain from the foregut structures are referred to the epigastric region, midgut structures to the umbilical region, and hindgut structures to the pubic region.
- Foregut - oesophagus, stomach, pancreas, liver, gall bladder, and the duodenum (proximal to the entrance of the common bile duct).
- Midgut - duodenum (distal to the entrance of the bile duct), to the junction of the proximal 2/3 of the transverse colon with the distal 1/3.
- Hindgut - distal 1/3 of transverse colon to the upper part of the anal canal.
Pain in retroperitoneal organs (e.g. kidneys, pancreas) may present as back pain.
Irritation of the diaphragm (e.g. as a result of liver, gall bladder or duodenum) may result in shoulder tip pain.
Referred pain in appendicitis
Initially pain from the appendix (midgut structure) and its visceral peritoneum is referred to the umbilical region. As the appendix becomes increasingly inflamed, it irritates the parietal peritoneum, causing pain to localise in the lower right quadrant.
