Lecture Notes in Human Anatomy - Hryhorieva O.A., Svitlytskyi A.O. 2020

The Science of Viscera (Splanchnologia)
Anatomy of Internal Organs
Serous Membranes and Their Derivatives

Lecture outline:

1. Serous membrane

2. Peritoneum

3. Pericardium

4. Pleura

5. Tunica vaginalis Testis

The serous membrane (tunica serosa) is composed of Connective Tissue and a single layer of specialized Cells known as mesothelium. Serous membranes include the peritoneum, pleura, pericardium, and, in males, the tunica vaginalis testis.

The layers of the serous membranes (parietal and visceral) enclose serous cavities filled with a small amount of serous fluid.

This fluid reduces friction between Organs during their movement.

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Peritoneum. This is a serous membrane (tunica serosa) lining the walls of the Abdominal cavity (parietes cavitatis abdominis) and the organs located within it; therefore, it is correspondingly divided into:

- parietal peritoneum (peritoneum parietale);

- visceral peritoneum (peritoneum viscerale).

The transition from the parietal peritoneum (peritoneum parietale) to the visceral peritoneum (peritoneum viscerale) occurs via peritoneal derivatives:

- ligaments (ligamenta);

- mesenteries (mesenterium et mesocolon);

- omenta (omentum majus et omentum minus).

Functions:

✵ barrier (resistance to localized infection, etc.);

✵ secretory (fluid production, etc.);

✵ resorptive (fluid absorption, etc.);

✵ protective (reducing friction between organs, accumulation/storage of fat, etc.).

First of all, the lubricated, slippery surface of the peritoneum ensures the continuous physiological movement of mobile abdominal organs (loops of the Small Intestine, transverse and sigmoid colons, and PARTS OF THE Stomach). In addition, the peritoneum possesses significant bactericidal properties and The ability to localize inflammatory foci through adhesion formation. The free portion of the greater omentum is particularly active in this regard.

Vessels and nerves reach the abdominal organs via peritoneal folds (mesenteries, certain ligaments, and folds). Finally, the peritoneum, along with interperitoneal (fat tissue of the omentum and mesentery), subperitoneal, and retroperitoneal adipose tissue, plays a crucial role in fixing the abdominal organs in a specific position. This function becomes especially important in the upright posture (in humans, unlike quadrupeds, Internal Organs receive less support from the anterior abdominal wall).

Depending on their relationship to the peritoneum, the abdominal organs are classified as extraperitoneal, mesoperitoneal, and intraperitoneal.

Extraperitoneal organs are covered by the visceral peritoneum on only one side and lie in the retroperitoneal space: the duodenum, Pancreas, lower rectum, Kidneys, Ureters, Urinary Bladder (when empty), and Adrenal Glands.

Mesoperitoneal organs are covered by the visceral peritoneum on three sides: the ascending colon, descending colon, middle rectum, Uterus, urinary bladder (when full), and Gallbladder.

Intraperitoneal organs are covered by the visceral peritoneum on all sides: the cecum, sigmoid colon, upper rectum, stomach, jejunum and ileum, fallopian tubes, Spleen, Liver, and Appendix.

Depending on their relationship to the peritoneum, the abdominal organs are classified as extraperitoneal, mesoperitoneal, and intraperitoneal.

Intraperitoneally:

- stomach;

- small intestine;

- transverse colon;

- cecum;

- sigmoid colon;

- rectum (upper part);

- spleen;

- fallopian tube.

Mesoperitoneally:

- liver;

- ascending and descending colons;

- rectum (middle part);

- uterus.

Retroperitoneally:

- duodenum;

- pancreas;

- kidneys and adrenal glands;

- rectum (lower part);

- ureters;

- urinary bladder.

The peritoneum passes from the Inferior surface of the Diaphragm onto the superior surface of the liver, forming two ligaments: the falciform ligament (lig. falciforme) and the coronary ligament. Having covered the upper surface of the liver in the region of the porta hepatis, both peritoneal folds converge and descend as the hepatoduodenal ligament (lig. hepatoduodenale) and the hepatogastric ligament (lig. hepatogastricum).

These ligaments, together with a small gastrophrenic ligament, form the lesser omentum (omentum minus), whose layers attach to the lesser curvature of The Stomach and the superior margin of the superior part of the duodenum. At the lesser curvature of the stomach, the peritoneal layers of the lesser omentum diverge to cover the anterior and posterior walls of the stomach.

At the greater curvature of the stomach, the peritoneal folds approximate and descend as a broad " apron", which forms the anterior duplication of the greater omentum (omentum majus). Inferiorly, the anterior duplication turns and extends upward (the ascending duplication of the greater omentum), fusing with the transverse colon and its mesocolon. Near the posterior wall of the abdominal cavity, the layers of the ascending duplication diverge again: one layer ascends along the wall and merges with the posterior layer of the coronary ligament of the liver, while the second descends along the wall to become continuous with the posterior parietal peritoneum.

Adipose tissue is located between the peritoneal layers of the greater omentum. The upper compartment of the peritoneal cavity (cavitas peritonealis) lies between the diaphragm (diaphragma) and the transverse colon (colon transversum) along with its mesentery (mesocolon transversum).

It contains:

- liver (hepar);

- spleen (splen);

- stomach (gaster).

The duodenum is located retroperitoneally, meaning it lies extraperitoneally.

The upper compartment of the peritoneal cavity (cavitas peritonealis) contains the following structures:

- the hepatic bursa (bursa hepatica), which encloses the right lobe of the liver (lobus hepatis dexter) and the gallbladder (vesica biliaris);

- the pregastric bursa (bursa pregastrica), which is separated from the hepatic bursa (bursa hepatica) by the falciform ligament of the liver (lig. falciforme hepatis) and encompasses the anterior wall of the stomach (paries anterior gastris), the left lobe of the liver (lobus hepatis sinister), and the spleen (splen);

The pericardium, or The Heart sac (Fig. 188), is a double-walled closed sac that surrounds the heart on all sides, except for a small area at its base where the great Blood Vessels enter and leave the heart. The pericardium comprises two fused sacs: an outer layer—the fibrous pericardium (pericardium fibrosum)—and an inner layer—the serous pericardium (pericardium serosum). The latter consists of parietal and visceral (epicardium) layers. The slit-like pericardial cavity (cavitas pericardiaca) between them contains about 15–20 ml of serous fluid.

✵ The pericardium is bordered laterally and partially anteriorly by the mediastinal pleura (here, the phrenic nerves pass between the fibrous pericardium and the pleura), posteriorly by the Esophagus and the Thoracic Aorta; inferiorly, it is firmly fused with the diaphragm, and anteriorly it is anchored to the Sternum by sternopericardial ligaments.

The pleura (from the Greek for rib or side) is a connective tissue membrane lined with simple squamous epithelium that covers the Lungs and the inner surface of the thoracic cavity in humans and mammals. Similar to the peritoneum, the pleura (pleura) forms two layers: visceral and parietal. The visceral layer is tightly fused to the pulmonary tissue on all sides and extends into the fissures between the lobes. The parietal layer fuses with the thoracic cavity and mediastinal organs. Both layers are continuous, forming a complete double sac around the lungs. The pleura is a mesothelium-covered connective tissue plate. The parietal layer features costal, mediastinal, and diaphragmatic surfaces. The mediastinal surface fuses with the pericardium. In the region of the lung ROOT, this layer transitions into the visceral layer. The diaphragm is only partially covered by the pleura, as part of it is occupied by the pericardium.

The pleural cavity is a narrow, closed slit containing a small amount of serous fluid that lubricates the pleural layers.

The pleural cavity is a narrow, closed slit containing a small amount of serous fluid that lubricates the pleural layers. At the sites where the costal pleura transitions into the diaphragmatic and mediastinal pleura, recesses (sinuses) are formed (where lungs are absent): the costodiaphragmatic, phrenicomediastinal, and costomediastinal recesses.

The tunica vaginalis testis develops from the processus vaginalis of the peritoneum and forms a closed serous sac consisting of two layers: the lamina parietalis (parietal layer) and the lamina visceralis (visceral layer).

The visceral layer is closely fused with the tunica albuginea of the testis and also extends onto the Epididymis. Between the lateral surface of the testis and the middle part (body) of the epididymis, the visceral layer extends into the slit-like space between them, forming the sinus epididymidis. Along the posterior border of the testis, at the site where vessels emerge, the visceral layer transitions into the parietal layer.

A slit-like space—the cavum vaginale—lies between the apposed surfaces of the parietal and visceral layers; in pathological conditions, a large amount of serous fluid can accumulate here and cause hydrocele.