Editing Peritoneum (section)

==Structure==
===Layers===
The peritoneum is one continuous sheet, forming two layers and a [[potential space]] between them: the [[peritoneal cavity]].

The outer layer, the '''parietal peritoneum''', is attached to the [[abdominal wall]] and the [[pelvic walls]].<ref>{{cite book | vauthors = Tank PW | chapter = Chapter 4: The abdomen | chapter-url = https://books.google.com/books?id=JDC-dFMy-BIC&pg=PA99 |title=Grant's dissector |date=2013 |location=Philadelphia |isbn=978-1-60913-606-2 |edition=Fifteenth}}</ref> The [[tunica vaginalis]], the serous membrane covering the male [[testis]], is derived from the [[vaginal process]], an outpouching of the parietal peritoneum.

The inner layer, the '''visceral peritoneum''', is wrapped around the visceral organs, located inside the intraperitoneal space for protection. It is thinner than the parietal peritoneum. The [[mesentery]] is a double layer of visceral peritoneum that attaches to the [[human gastrointestinal tract|gastrointestinal tract]]. There are often blood vessels, nerves, and other structures between these layers. The space between these two layers is technically outside of the peritoneal sac, and thus not in the peritoneal cavity.

The potential space between these two layers is the [[peritoneal cavity]], filled with a small amount (about 50 mL) of slippery [[serous fluid]] that allows the two layers to slide freely over each other.

The right [[paracolic gutter]] is continuous with the right and left subhepatic spaces. The [[epiploic foramen]] allows communication between the greater sac and the lesser sac.<ref>{{Cite encyclopedia|last=Jones|first=J.|title=Epiploic Foramen {{!}} Radiopaedia.org|doi=10.53347/rID-6059|url=https://radiopaedia.org/articles/epiploic-foramen-1#:~:text=The%20epiploic%20foramen%20(also%20called,communication%20between%20these%20two%20spaces.|date=14 April 2009|access-date=21 May 2022|publisher=Radiopaedia|doi-access=free}}</ref> The peritoneal space in males is closed, while the peritoneal space in females is continuous with the extraperitoneal pelvis through openings of the [[fallopian tubes]], the [[uterus]], and the [[vagina]].<ref name="Tirkes 2012"/>

===Subdivisions===
[[Mesentery#Peritoneal folds|Peritoneal folds]] are omentums, mesenteries and [[ligament]]s; they connect organs to each other or to the abdominal wall.<ref name="Drake2009p295">{{cite book|last1=Drake|first1=R. L.|last2=Vogl|first2=A.W.|last3=Mitchell|first3=A.W.|chapter=Abdominal Viscera|chapter-url=https://books.google.com/books?id=_ozrqnzzhFwC&dq=These%20folds&pg=PA295|page=295|title=Gray's Anatomy for Students|date=4 April 2009|publisher=[[Elsevier Health Sciences]]|location=Philadelphia, PA|isbn=9781437720556|oclc=489070574}}</ref> There are two main regions of the peritoneal cavity, connected by the [[omental foramen]].
* The [[greater sac]], represented in red in the diagrams above.
* The [[lesser sac]], represented in blue. The lesser sac is divided into two "omenta":
** The [[lesser omentum]] (or ''hepatogastric'') is attached to the [[lesser curvature of the stomach]] and the [[liver]].<ref name="Tortora">{{cite book | vauthors = Tortora GJ, Anagnostakos NP |title=Principles of anatomy and physiology |date=1984 |publisher=Harper & Row |location=New York |isbn=978-0-06-046656-5 |edition=4th}}</ref>
** The [[greater omentum]] (or ''gastrocolic'') hangs from the [[greater curvature of the stomach]] and loops down in front of the [[intestines]] before curving back upwards to attach to the transverse [[colon (anatomy)|colon]].<ref name="Tortora" /> In effect it is draped in front of the intestines like an apron and may serve as an insulating or protective layer.<ref name="Tortora" />

The [[mesentery]] is the part of the peritoneum through which most abdominal organs are attached to the abdominal wall and supplied with [[blood]] and [[lymph]] vessels and nerves.

====[[Omentum (disambiguation)|Omenta]]====
{| class="wikitable" style="width: 100%;"
 | '''Sources''' || '''Structure'''  || '''From'''  || '''To'''  || '''Contains '''
 |-
 | [[Dorsal mesentery]] || Greater omentum   || Greater curvature of stomach (and [[spleen]]) || Transverse colon  ||right and left gastroepiploic vessels and fat
 |-
 |  || [[Gastrosplenic ligament]]  || Stomach || Spleen || [[Short gastric artery]], [[Left gastroepiploic artery]]
 |-
 |  || [[Gastrophrenic ligament]] || Stomach || [[Thoracic diaphragm|Diaphragm]] || [[inferior phrenic arteries|Left inferior phrenic artery]]
 |-
 |  || [[Gastrocolic ligament]]  ||  Stomach || [[Transverse colon]]  || [[Right gastroepiploic artery]]
 |-
 |  || [[Splenorenal ligament]] || Spleen|| Kidney  || [[Splenic artery]], [[Tail of pancreas]]
 |-
 | [[Ventral mesentery]] || Lesser omentum || Lesser curvature of the stomach (and [[duodenum]])||Liver  ||The right free margin-hepatic artery, portal vein, and bile duct,lymph nodes and the lymph vessels,hepatic plexus of nerve,all enclosed in perivascular fibrous sheath. Along the lesser curvature of the stomach-left and right gastric artery,gastric group of lymph nodes and lyphatics, branches from gastric nerve.

 |-
 |  ||[[Hepatogastric ligament]]  || Stomach  ||  Liver  || [[Right gastric artery|Right]] and [[left gastric artery]]
 |-
 |  || [[Hepatoduodenal ligament]]  || Duodenum  || Liver  || [[Hepatic artery proper]], [[hepatic portal vein]], [[bile duct]], [[autonomic nerves]]
 |}

====[[Mesenteries]]====
{| class="wikitable" style="width: 100%;"
 | '''Sources''' || '''Structure'''  || '''From'''  || '''To'''  || '''Contains '''
 |-
 | Dorsal mesentery || Mesentery proper || [[Small intestine]] ([[jejunum]] and [[ileum]])  || Posterior abdominal wall  || [[Superior mesenteric artery]], accompanying veins, autonomic nerve plexuses, lymphatics, 100–200 lymph nodes and connective tissue with fat
 |-
 | || [[Transverse mesocolon]] || [[Transverse colon]]   || Posterior abdominal wall  || [[Middle colic]]
 |-
 |   || [[Sigmoid mesocolon]] || Sigmoid colon   || [[Pelvic wall]]  || [[Sigmoid arteries]] and [[superior rectal artery]]
 |-
 |  || [[Mesoappendix]] || Mesentery of ileum  || [[Vermiform appendix|Appendix]]  || [[Appendicular artery]]
 |}

====Other ligaments and folds====
{| class="wikitable" style="width: 100%;"
 | '''Sources''' || '''Structure'''  || '''From'''  || '''To'''  || '''Contains '''
 |-
 | Ventral mesentery || [[Falciform ligament]]  || Liver  || [[Thoracic diaphragm]], anterior abdominal wall  || [[Round ligament of liver]], [[paraumbilical vein]]
 |-
 | Left [[umbilical vein]] || [[Round ligament of liver]]  || Liver   || [[Navel|Umbilicus]] ||
 |-
 | Ventral mesentery || [[Coronary ligament]]  || Liver || Thoracic diaphragm  ||
 |-
 | [[Ductus venosus]] || [[Ligamentum venosum]]    || Liver  || Liver  ||
 |-
 |  || [[Phrenicocolic ligament]]  || [[Left colic flexure]]  || Thoracic diaphragm ||
 |-
 | Ventral mesentery || [[Left triangular ligament]], [[right triangular ligament]] || Liver  ||    ||
 |-
 |  || [[Umbilical folds]]  ||  [[Urinary bladder]] ||   ||
 |-
 |  || [[Ileocecal fold]] || Ileum || [[Cecum]]  ||
 |-
 |  || [[Broad ligament of the uterus]]   || [[Uterus]]  ||  Pelvic wall  || [[Mesovarium]], [[mesosalpinx]], [[mesometrium]]
 |-
 |  || [[Round ligament of uterus]] || Uterus || [[Inguinal canal]]  ||
 |-
 |  || [[Suspensory ligament of the ovary]] || [[Ovary]]  || Pelvic wall  || [[Ovarian artery]]
|}

In addition, in the [[pelvic cavity]] there are several structures that are usually named not for the peritoneum, but for the areas defined by the peritoneal folds:

{| class="wikitable" style="width: 100%;"
| '''Name''' || '''Location''' || '''Sexes possessing structure'''
 |-
 | [[Rectovesical pouch]] || Between [[rectum]] and urinary bladder || Male only
 |-
 | [[Rectouterine pouch]] || Between rectum and uterus || Female only
 |-
 | [[Vesicouterine pouch]] || Between urinary bladder and uterus || Female only
 |-
 | [[Pararectal fossa]]|| Surrounding rectum || Male and female
 |-
 | [[Paravesical fossa]] || Surrounding urinary bladder || Male and female
|}

===Classification of abdominal structures===
The structures in the abdomen are classified as intraperitoneal, mesoperitoneal, [[retroperitoneal]] or infraperitoneal depending on whether they are covered with visceral peritoneum and whether they are attached by mesenteries (mensentery, mesocolon).

{| class="wikitable" style="width: 100%;"
| '''Intraperitoneal''' 
|'''Mesoperitoneal'''|| '''Retroperitoneal ( or Extraperitoneal )''' || '''Infraperitoneal / Subperitoneal'''
 |-
 | Stomach, half of the first part of the duodenum [2.2&nbsp;cm], jejunum, ileum, cecum, [[Vermiform appendix|appendix]], [[transverse colon]], [[sigmoid colon]], rectum (upper 1/3)  
| || The rest of the duodenum, [[ascending colon]], [[descending colon]], rectum (middle 1/3) || Rectum (lower 1/3)
 |-
 | Spleen, [[pancreas]] (only tail)
|Liver|| Pancreas (except tail) ||
 |-
 | 
| || Kidneys, [[adrenal gland]]s, [[ureter|proximal ureters]], [[renal artery|renal vessels]]
|| Urinary bladder, [[ureter|distal ureters]]
 |-
 | In women: ovaries
| || ||Gonadal blood vessels, Uterus, Fallopian Tubes 
|-
 | 
| || [[Inferior vena cava]], [[aorta]] ||
|}

Structures that are ''intraperitoneal'' are generally mobile, while those that are ''retroperitoneal'' are relatively fixed in their location.

Some structures, such as the kidneys, are "primarily retroperitoneal", while others such as the majority of the duodenum, are "secondarily retroperitoneal", meaning that structure developed intraperitoneally but lost its mesentery and thus became retroperitoneal.

===Development===
The peritoneum develops ultimately from the [[mesoderm]] of the [[trilaminar embryo]]. As the mesoderm differentiates, one region known as the [[lateral plate mesoderm]] splits to form two layers separated by an [[intraembryonic coelom]]. These two layers develop later into the visceral and parietal layers found in all [[serous cavity|serous cavities]], including the peritoneum.

As an [[embryo]] develops, the various abdominal organs grow into the abdominal cavity from structures in the abdominal wall. In this process they become enveloped in a layer of peritoneum. The growing organs "take their blood vessels with them" from the abdominal wall, and these blood vessels become covered by peritoneum, forming a mesentery.<ref>{{cite web|url=http://healthoracle.org/downloads/P/Peritoneum.pdf | archive-url = https://web.archive.org/web/20160423062639/http://healthoracle.org/downloads/P/Peritoneum.pdf | archive-date = 23 April 2016 |title= Peritoneum |website=healthoracle.org|access-date=14 April 2018}}</ref>

Peritoneal folds develop from the [[ventral mesentery|ventral]] and [[dorsal mesentery]] of the embryo.<ref name="Drake2009p295"/>