Lecture Tuesday August 28: intro to Abdomen

Peritoneum
The peritoneum is a serosal membrane, which is composed of a single layer of flat mesothelial cells supported by submesothelial connective tissue.



In this subserosal tissue there are fat cells, lymphatics, blood vessels and inflammatory cells like lymphocytes and plasma cells.
The visceral peritoneum lines all the organs that are intraperitoneal.
The parietal peritoneum lines the anterior, lateral and posterior walls of the abdominal cavity.

Mesenteries
The mesentery is a double fold of the peritoneum.
True mesenteries all connect to the posterior abdominal wall.
These are:
- The small bowel mesentery
- The transverse mesocolon
- The sigmoid mesentery (or sigmoid mesocolon)

Specialized mesenteries do not connect to the posterior peritoneal wall.
These are:
- The greater omentum: connects the stomach to the colon
- The lesser omentum: connects the stomach to the liver
- The mesoappendix: connects the apendix to the ileum



Retroperitoneal organs:
- Kidneys, ureters, bladder and adrenal glands
- Aorta
- Inferior vena cava
- Duodenum (second and third segment)
- Pancreas
- Ascending colon
- Descending colon
- Rectum

Inguinal Canal
4 cm long tube like space within the lower lateral part of abdominal wall. It is here that the testis, which develop in the abdominal cavity, descend down into the scrotum. Because the testis go through this region, this stretches and pulls this area of the abdominal wall, and makes it weaker. Especially at the areas of the entrance and exit to the canal, the inguinal rings. Hernias are when any tissue or organ, most commonly, loops of the intestines, protude through the adbominal wall. Because females have no testis that descend in this region, their abdominal wall is not as weak as in males, though they do have structures that pass through this region (round ligament of the uterus). Therefore, males are more likely to have abdominal hernias than females.

Borders:
Superior = inferior border of internal oblique & transverse abdominis muscles.
Inferior = Inguinal ligament (from ASIS → Pubic tubercle, is an extension of the external oblique aponeurosis)
Anterior = Aponeurosis of External & Internal abdominal oblique m.
Posterior = Transversalis fascia and Conjoint tendon (the two tendons of Internal oblique & Transverse abdmoninis m. combined).

Entrance – Deep Inguinal Ring
Slit in the transversalis fascia
Located 1cm above and lateral to midpoint of inguinal ligament
Lateral to the Inferior epigastric a/v

Exit – Superficial Inguinal Ring
Triangular shaped slit above and just lateral to pubic tubercle
is an opening in the external oblique aponeurosis

Contents:
Male : Spermatic cord, Ilioinguinal n, genital branch of genitofemoral n, Lymph vessels
Female: Round ligament of uterus, Ilioinguinal n, genital branch of genitofemoral n, lymph vessels

Clinical Note: Hernia – Direct v. Indirect

Direct Inguinal Hernia – Protrudes through the superficial inguinal ring, directly through the abdominal wall. Medial to inferior epigastric vessels.

Indirect Inguinal Hernia – protrudes through the deep inguinal ring, going through the inguinal canal (and pushing on structures within) and emerging through the superficial inguinal ring. More common than direct. Lateral to inferior epigastric vessels.

Realize that all of the blood drained from the GI tract and associated organs must first pass through the liver before entering the general/systemic venous system. This is via the PORTAL venous system.

Realize that there are 3 clinically important sites where the portal and systemic venous systems anastomose:
1. Gastric veins (portal) with esophageal/azygous veins (systemic): esophageal varices

2. Superior rectal veins (portal) with middle and inferior rectal veins (systemic): hemorrhoids

3. Paraumbilical veins around ligamentum teres (portal) with superficial veins of abdominal wall (systemic): captut medusae

Much of the remainder of this lecture you will learn in doing the TBL objectives, looking at the handouts and doing the dissection in the lab.


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