The development and structure of the mesentery.

The position of abdominal organs, and mechanisms by which these are centrally connected, are currently described in peritoneal terms. As part of the peritoneal model of abdominal anatomy, there are multiple mesenteries. Recent findings point to an alternative model in which digestive organs are connected to a single mesentery. Given that direct evidence of this is currently lacking, we investigated the development and shape of the entire mesentery. Here we confirm that, within the abdomen, there is one mesentery in which all abdominal digestive organs develop and remain connected to. We show that all abdominopelvic organs are organised into two, discrete anatomical domains, the mesenteric and non-mesenteric domain. A similar organisation occurs across a range of animal species. The findings clarify the anatomical foundation of the abdomen; at the foundation level, the abdomen comprises a visceral (i.e. mesenteric) and somatic (i.e. musculoskeletal) frame. The organisation at that level is a fundamental order that explains the positional anatomy of all abdominopelvic organs, vasculature and peritoneum. Collectively, the findings provide a novel start point from which to systemically characterise the abdomen and its contents.

Post-Surgical Peritoneal Scarring and Key Molecular Mechanisms.

Post-surgical adhesions are internal scar tissue and a major health and economic burden. Adhesions affect and involve the peritoneal lining of the abdominal cavity, which consists of a continuous mesothelial covering of the cavity wall and majority of internal organs. Our understanding of the full pathophysiology of adhesion formation is limited by the fact that the mechanisms regulating normal serosal repair and regeneration of the mesothelial layer are still being elucidated. Emerging evidence suggests that mesothelial cells do not simply form a passive barrier but perform a wide range of important regulatory functions including maintaining a healthy peritoneal homeostasis as well as orchestrating events leading to normal repair or pathological outcomes following injury. Here, we summarise recent advances in our understanding of serosal repair and adhesion formation with an emphasis on molecular mechanisms and novel gene expression signatures associated with these processes. We discuss changes in mesothelial biomolecular marker expression during peritoneal development, which may help, in part, to explain findings in adults from lineage tracing studies using experimental adhesion models. Lastly, we highlight examples of where local tissue specialisation may determine a particular response of peritoneal cells to injury.

The relationship between the testis and tunica vaginalis changes with age.

BACKGROUND/AIM: Anatomy of the testis and tunica vaginalis (TV) is taught to pediatric surgeons from adult postmortem material. Textbooks describe the testis as 'behind' the TV, but at pediatric orchidopexy it appears to be inside the TV. We aimed to study whether testis and TV anatomy changes with age. METHODS: After ethical approval, postmortem photographs and measurements of testis length, width, and mesenteric attachment length (mm) in 37 adults (22-92years), one infant (4/12), and one fetus (19/52) were compared with intraoperative orchidopexies (x6) after opening TV (n=4; 7/12-14years). Testis length, area and perimeter and ratios for mesentery attachment were plotted against age. RESULTS: The fetal and pediatric testes were intraperitoneal with a mesentery (mesorchium), but after 50years secondary adhesions between TV and testis obliterated the mesorchium, so in advanced age the testis appeared to be behind the TV. DISCUSSION: These results show that in childhood testes were 'intraperitoneal', but after 50years of age the TV progressively shrinks and adheres to the testis, making it appear to be behind the TV. This difference between anatomical texts and childhood anatomy suggests that pediatric surgery may need anatomy texts that specifically highlight age differences.

Epithelial-mesenchymal transition of rat peritoneal mesothelial cells via Rhoa/Rock pathway.

The objective of this study was to investigate the role of the RhoA/Rock signaling pathway in the epithelial-mesenchymal transition (EMT) of rat peritoneal mesothelial cells (RPMCs). Primary SD rat peritoneal mesothelial cells were cultured in vitro. RPMCs were randomly assigned to four groups: group A (control), group B (TGF-ß1, 10 µg/L), group C (10 µg/L TGF-ß1 + 10 µmol/L Y-27632, an inhibitor of Rock that was pre-applied for 2 h before TGF-ß1 stimulation), and group D (Y-27632 alone, 10 µmol/L). Our results were as follows: (1) TGF-ß1 stimulation elicited a robust increase in RhoA activity in a time-dependent manner; the increase was 2.57 ± 0.52 times larger than the activity observed for the control group (P < 0.05) after 10 min of stimulation. RhoA activity peaked at 1 h and was 4.35 ± 0.41 times the value observed for the control group (P < 0.05). (2) TGF-ß1 up-regulated mRNA and/or protein expression of α-SMA, vimentin, and collagen and down-regulated mRNA and protein expression of E-cadherin in RPMCs. (3) The Rock inhibitor Y-27632 effectively reduced TGF-ß1-induced expression of α-SMA, collagen, and vimentin; the mRNA levels of α-SMA and collagen decreased by 53.8% and 55.7%, respectively, and the protein levels of α-SMA, vimentin, and collagen decreased by 42.6%, 60.1%, and 58.1%, respectively, as compared to TGF-ß1-stimulated groups (P < 0.05). However, the Rock inhibitor Y-27632 had no effect on the level of E-cadherin. In conclusion, the RhoA/Rock signaling pathway may mediate EMT induced by TGF-ß1 in rat peritoneal mesothelial cells. The RhoA/Rock pathway may be a potential therapeutic target for the treatment of peritoneal fibrosis.

Growth of the rat gubernaculum in vitro and localisation of its growth centre.

PURPOSE: Recent studies suggest that testicular descent is accomplished by outgrowth of the gubernaculum from the abdominal wall. The tip of the gubernaculum has been proposed as the primary site of growth, similar to an embryonic limb bud. We aimed to determine the maximum site of growth in organ culture. METHODS: Gubernacula from 1-day-old Sprague-Dawley rats (n = 40) were collected and divided into 4 groups as follows: whole gubernaculum (control), truncated gubernaculum (tip excised), gubernacular tip alone, and grafted gubernaculum with an extra tip on its side. Tissues were cultured with or without calcitonin gene-related peptide (CGRP) (714nmol/L) in medium for 24 hours. The area of each gubernaculum was determined by "Image J" analysis of digital photos collected via a Leica Wild M28 microscope (Leica Microsystems, Wetzler GmbH Germany) taken before and after culture. RESULTS: In organ culture, the neonatal rat gubernaculum normally shrank 10% to 15%, but this was prevented by the presence of exogenous CGRP (0.8% vs 11.8%; P < .003). By contrast, gubernacula with their tips excised were not affected by CGRP (3.4% vs 4.7%; not significant). Gubernacular tips alone did respond to CGRP (2.7% vs 13.5%; P < .03). Transplantation of the tip to another gubernaculum caused it to develop 2 tips. CONCLUSIONS: These results suggest that the rat gubernaculum contains a growth centre in its distal tip that can respond to CGRP. This is consistent with a limb bud model of gubernacular growth during the inguinoscrotal descent of the testis.

Phylogeny and ontogeny of the lymphatic stomata connecting the pleural and peritoneal cavities with the lymphatic system--a review.

This paper reviews the phylogeny and ontogeny of "lymphatic stomata" through which fluids and cells in the pleural and peritoneal cavities enter the lymphatic system. In amphibians, the pleuroperitoneal cavity is connected through numerous pores with the wide subvertebral lymphatic sinus corresponding to the thoracic duct in mammals. In reptiles, direct connections of the pleural and peritoneal cavities with the lymphatic system have been reported. In mammals, the pleural and peritoneal cavities are directly connected with lymphatics through lymphatic stomata. How do lymphatic stomata develop in mammals? In the rat, distinct lymphatics are noted in the subpleural space of the diaphragm periphery in 16 days old embryo. With age, the supleural lymphatics increase and form a polygonal network. They show a tubular appearance and possess many valves. Some of them become endowed with smooth muscle cells. In 19 days old embryos, some lymphatics appear in the subperitoneal space of the diaphragm. They extend centripetally and form many lateral projections that later elongate and connect with those from adjacent lymphatics, thus forming a lattice-like network or "lymphatic lacunae". During early postnatal days, the lymphatic lacunae project many bulges that subsequently come into contact with the pores among mesothelial cells lining the diaphragmatic peritoneum, thus forming lymphatic stomata. They increase until postnatal week 10. The lymphatic stomata in the costal pleura also develop during early postnatal days.

Progesterone receptor is constitutively expressed in chicken intestinal mesothelium and smooth muscle.

We have previously shown that progesterone receptor (PR) is expressed in the mesothelium of the chick oviduct and ovary and in the smooth muscle cells of the oviduct and the bursa of Fabricius. Here, we investigated the presence of PR in different parts of the peritoneum and abdominal organs using an immunohistochemical staining based on monoclonal antibodies against chicken PR. In 4-week-old sexually immature chicks, PR expression was located in the mesothelial cells of different parts of the peritoneum, in a thin layer of muscle cells of the ileum and throughout the muscle tissue of the colon and cloaca. In chicks of the same age treated with estrogen, PR was demonstrated similarly in the peritoneum and in the smooth muscle cells of the ileum, colon and cloaca. Using 25-week-old mature chickens, PR was also detected in identical tissues. Immunoblotting of the cloacal cytosol revealed the B form, but no A form of PR, both of which were found in the oviduct samples. Muscle cells of the duodenum and jejunum were not found to contain PR. Estrogen treatment was not needed to stimulate the production of PR in any of the tissues examined. We therefore conclude that the B form of PR is constitutively expressed in the mesothelial cells in different parts of the peritoneum and also in the smooth muscle cells of the ileum, colon and cloaca.

[Reactive growth of the mesothelium of the parietal leaf of the peritoneum]. / Reaktivnye razrastaniia mezoteliia parietal'nogo listka briushiny

In the process of reparative regeneration of the mesothelium caused by suturing of a portion of the jugular vein into the peritoneum defect the inflammatory mesothelial growings are formed. They have different configuration, consist only of the mesotheliumor the connective tissue covered with the mesothelium and are observed from the 4th day till 3 months after operation, being always faced to the abdominal cavity. The capacity of mesothelial cells to high mitotic activity and wedging out from the layer underlies the formation of posttraumatic structures of the mesothelium.

Mesothelial injury and recovery.

This paper describes the cytologic effects of drying or wetting of visceral peritoneum and the course of mesothelial regeneration. Using en face silver staining and electron microscopy, it was found that mesothelial cells disappeared from the surface after the cecum was either briefly dried or kept wet with isotonic saline for 30 minutes; the fibrin-slide technic showed that such injury caused a loss of the normal serosal fibrinolytic activity. In following the course of mesothelial regeneration using the same technics, it was apparent that free-floating peritoneal mononuclear cells settled on the denuded surface where they spread out, attached to one another, and developed features (eg, microvilli) typical of mature mesothelial cells; such new mesothelium showed a greatly enhanced fibrinolytic activity.