Rectal Valve Research Articles

Is There a Precise Correlation between the Lengths of the Peritoneal Reflection and the Middle Rectal Valve?

Abstract Introduction Pelvic anatomy remains a challenge, and thorough knowledge of its intricate landmarks has major clinical and surgical implications in several medical specialties. The peritoneal reflection is an important landmark in intraluminal surgery, rectal trauma, impalement, and rectal adenocarcinoma. Objectives To investigate the correlation between the lengths of the middle rectal valve and of the peritoneal reflection determined with rigid sigmoidoscopy and to determine whether there are any differences in the location of the peritoneal reflection between the genders and in relation to body mass index (BMI) and parity. Design We prospectively investigated the location of the middle rectal valve and of the peritoneal reflection via intraoperative rigid sigmoidoscopy in colorectal cancer patients undergoing elective colorectal surgery. Results We evaluated 38 patients with a mean age of 55.5 years old (57.5% males) who underwent colorectal surgery at the coloproctology service of the Hospital Santa Marcelina, São Paulo, state of São Paulo, Brazil. There was substantial agreement between the lengths of the middle rectal valve and of the peritoneal reflection (Kappa = 0.66). In addition, the peritoneal reflection was significantly lower in overweight patients (p = 0.013 for women and p < 0.005 for men) and in women with > 2 vaginal deliveries (p = 0.009), but there was no significant difference in the length of the peritoneal reflection between genders (p = 0.32). Conclusion There was substantial agreement between the lengths of the peritoneal reflection and of the middle rectal valve, and the peritoneal reflection was significantly lower in overweight patients and in women with more than two vaginal deliveries.

ID: 3523296 COMBINED FORWARD AND RETROFLEXION WITHDRAWAL DURING COLONOSCOPY USING A SECOND-GENERATION SHORT-TURN RADIUS COLONOSCOPE

Colonoscopy is the screening method to prevent colorectal cancer; however, polyps and adenomas are missed indivertibly. Factors such as the location of polyps on difficult areas (proximal side of the ileocecal valve, haustral folds, flexures, or rectal valves). We aimed to evaluate the impact of combined forward and retroflexion withdrawal using a second-generation short-turn radius colonoscope during colonoscopy.

Interaction between Radioadaptive Response and Radiation-Induced Bystander Effect in Caenorhabditis elegans : A Unique Role of the DNA Damage Checkpoint.

Although radioadaptive responses (RAR) and radiation-induced bystander effects (RIBE) are two important biological effects of low-dose radiation, there are currently only limited data that directly address their interaction, particularly in the context of whole organisms. In previous studies, we separately demonstrated RAR and RIBE using an in vivo system of C. elegans . In the current study, we further investigated their interaction in C. elegans , with the ratio of protruding vulva as the biological end point for RAR. Fourteen-hour-old worms were first locally targeted with a proton microbeam, and were then challenged with a high dose of whole-body gamma radiation. Microbeam irradiation of the posterior pharynx bulbs and rectal valves of C. elegans could significantly suppress the induction of protruding vulva by subsequent gamma irradiation, suggesting a contribution of RIBE to RAR in the context of the whole organism. Moreover, C. elegans has a unique DNA damage response in which the upstream DNA damage checkpoint is not active in most of somatic cells, including vulval cells. However, its impairment in atm-1 and hus-1 mutants blocked the RIBE-initiated RAR of vulva. Similarly, mutations in the atm-1 and hus-1 genes inhibited the RAR of vulva initiated by microbeam irradiation of the vulva itself. These results further confirm that the DNA damage checkpoint participates in the induction of RAR of vulva in C. elegans in a cell nonautonomous manner.

Postoperative complications in the treatment of rectal neoplasia by transanal endoscopic microsurgery: a prospective study of risk factors and time course

Transanal endoscopic microsurgery (TEM) is a safe and efficient minimally invasive treatment for rectal benign and early malignant neoplasia, but postoperative complications may be severe. We aimed to evaluate the risk factors related to the incidence, severity, and time course of postoperative complications of TEM. This is a prospective study of postoperative complications in 53 patients (>18 years old) with benign or early rectal neoplasia who underwent TEM with curative intention or, for higher stages, palliation. Outcome measures included age, sex, American Society of Anesthesiologists score, neoadjuvant chemoradiotherapy, lesion height and size, pathologic margins, tumor histology, and suture type. Overall morbidity was 50 %. Temporary fecal incontinence was the most frequent complication (17.3 %). Complication rates of Clavien-Dindo grades I and II were 21.1 % and those of grades III and IV 3.8 %. Of patients with complications, more had lesions under the first rectal valve than over the first valve (61.54 % vs 38.46 %, p = 0.04). Patients submitted to chemoradiotherapy had a 24-fold greater chance of presenting grade II complications (p = 0.002). When the surgical defect was treated using the TEM device to perform the suture, the chance of having grade III complications was reduced 16-fold (p = 0.04). Fifty-three percent of complications occurred in the first 10 days and 95 % within 20 days. Postoperative complications after transanal endoscopic microsurgery for the treatment of rectal neoplasia are frequent, acceptable, and usually controllable with pharmacologic treatment. Over time the nature of complications is continuous, centered on the first 20 days after surgery.

The rectal valve in Curculionoidea (Insecta: Coleoptera).

A rectal valve is known from Bostrichiformia (e.g. Dermestidae, Bostrichidae, Ptinidae), Cucujiformia (e.g. Chrysmeloidea, Cleridae, Curculionoidea, Endomychidae, Tenebrionidae) and Buprestidae, associated with the cryptonephridial system for water recovery from fecal matter. The valve is probably homologous in at least the Bostrichiformia and Cucujiformia although the form it takes may not be. It comprises a sclerotized band lying in the wall of the rectum where this meets the perinephric membrane. The valve is plesiomorphically a narrow crimped ring, probably acting as a sphincter to retain fecal matter for water extraction. Apomorphically it extends longitudinally along the rectum and supports the perinephric chamber; this state has probably arisen independently several times. Larval and adult morphology may be similar or different. Within the Curculionoidea different apomorphic forms suggest monophyly of groups within the Anthribidae and Dryophthoridae, and within the curculionid subfamilies Entiminae, Mesoptiliinae, Molytinae and Cossoninae + Scolytinae, although limited weight should be placed on a single character. No support is provided for a relationship between the Platypodinae and Scolytinae. The genera Cylindrotypetes Zimmerman 1942 and Edaphotrypetes Morimoto 1995 are transferred from Molytinae: Phoenicobatini to Cossoninae: Pentrarthini.

A comparison of the usage of anal verge and dentate line in measuring distances within the rectum

IntroductionThe anal verge is key in determining measurement-based suitability for neoadjuvant radiotherapy in rectal cancer. The dentate line is a distinct anatomic landmark and may permit more accurate measurement for rectal lesions. This study aimed to establish measurative ranges for distances of the rectal valves from the dentate line and the anal verge and to compare variability between the two. MethodsPatients (n = 104) undergoing colonoscopy and sigmoidoscopy were prospectively accrued. The distances of rectal valves were measured from the anal verge and the dentate line respectively by using a vector subtraction-based approach. Distances were correlated with gender, age and body mass index. Standard deviation was the measure of variability. ResultsThe gross topography of the rectum was remarkably consistent with three valves identifiable in the majority (99 of 104) of patients. The median distance between the dentate line and the anal verge was 2.0 cm. The distances of each rectal valve (proximal to distal) to the anal verge and dentate line were 11.4 ± 2.0 cm, 8.6 ± 2.0 cm, 6.0 ± 1.7 cm and 9.1 ± 1.6 cm, 6.3 ± 1.6 cm, 3.7 ± 1.5 cm, respectively. Between-group variability was minimally reduced when using the dentate line as a reference point. Obesity was associated with an increased distance of the proximal rectal valve from the anal verge and the dentate line (p = 0.004 and 0.015 respectively). ConclusionsRectal valve anatomy is remarkably consistent. Both dentate line and anal verge are reliable landmarks from which distances can be measured within the rectum.

Real-time measurement of rectal mucosal microcirculation during cardiopulmonary bypass.

Mesenteric ischemia is still a fatal event after cardiac procedures. No adequate intraoperative methods are available to monitor the gastrointestinal mucosal microcirculation in real-time conditions. The aim of the study was to assess a newly designed microprobe using laser Doppler flowmetry and remission spectroscopy. One-group, prospective, nonrandomized, open, pilot diagnostic study. Monocenter university hospital. 50 patients (n = 38 males, 67±6 years) scheduled for cardiopulmonary bypass (CPB) were prospectively included. During anesthetic induction, the transrectal microprobe (30×15 mm) was positioned between the inferior and middle rectal valve (5-8 cm). Time periods were summarized at T1 = pre-CPB, T2 = CPB, T3 = post-CPB. In 39 of 50 patients, data recruitment with the microprobe was successful. Measurement failures were due to fecal contaminations and probe dislocations. Rectal blood flow and velocity significantly decreased after bypass initiation (T2). Lowest flow rates were recorded after cross-clamp removal and did not recover at the end of bypass (T3). No side effects of the probe were noted. The new microprobe allows reproducible, safe, intraoperative, real-time evaluation of the rectal mucosal microcirculation. It could be a useful diagnostic tool to prevent mesenteric ischemia by optimizing extracorporeal circulation in future studies. However, first correlation of rectal blood flow and postoperative events (eg, ischemia, lactate) in a large cohort are necessary.

Spiral rectal valves: Anatomy, eponyms, and clinical significance.

Rectal wall valves are obscure anatomic parts that rarely are considered in current medical practice. Yet from the seminal analysis of them in the early nineteenth century by the Irish anatomist and surgeon, John Houston, their structure, purpose, and clinical significance were topics of surprising disagreement. Were they true structures? What function might they have? Did disease originate in rectal valves? Were special operations required for any such diseases? Because Houston's anatomic analyses of rectal valves were substantiated, they came to be known in the English literature as the Spiral Rectal Valves of Houston. In the mid-nineteenth century, a single mid-rectal valve was described by the Hanoverian, Otto Kohlrausch., creating confusion with the established eponym "Houston's Valves." Many hypotheses about rectal valves have been discredited; and their physiologic functions are still unknown.

Local resection for small rectal cancer

Rectal resection with total mesorectal excision is the standard treatment for rectal cancers. Local excision represents an alternative with less post-operative mortality and morbidity and preservation of intestinal and bladder function. However, local excision cannot provide adequate nodal staging. Presently, endorectal ultrasound and magnetic resonance imaging are used to select the appropriate patients for local excision, those with limited T1 rectal tumors. There is general agreement that the ideal tumors for local excision are less or equal to 3 cm in diameter, superficial (usTis and/or usT1N0), infra-peritoneal, located below the middle rectal valve, and involving no more than 40% of the rectal circumference. Transanal tumor excision is suitable for distal tumors and transanal endoscopic microsurgery for mid and upper lesions. The principles of adequate resection margin, non-fragmentation, and full-thickness excision are similar to those for any cancer resection. Unfavorable pathologic criteria, as assessed on the fixed rectal specimen, include depth of tumor invasion (submucosal [T1sm3] or muscular [T2]), positive resection margins, vascular and/or lymphatic invasion, and poor differentiation. Further radical surgery is required in case of unfavorable criteria. Simple surveillance may be advised for superficial tumors (T1sm1) without any unfavorable criteria. Management of T1sm2 tumors without any unfavorable criteria should be discussed on a case-by-case basis.

Mo1596 Impact of Prototype Extra-Wide-Angle-View Colonoscope in the Adenoma Detection Rate: A Multicenter Randomized Controlled Trial

Screening colonoscopy has been shown to decrease colorectal cancer incidences as well as mortality, not only by identifying cancers at an early stage, but also more so because of the detection and removal of adenomas as precursor lesions. For standard colonoscopy, however, it has been shown that a 15-28% miss rate for adenoma detection occurs in clinical practice. A major contributing factor may be undetected lesions located behind haustra folds, flexures or rectal valves. The aim of this study is to assess the efficacy of a novel prototype extra-wide-angle view colonoscope that provides a simultaneous lateral-backward view that complements the forward view of the colonoscope for polyp detection.

Sa1605 Prototype Extra Wide Angle View Colonoscope: A Randomized Controlled Multicenter Simulated Study Using Anatomic Colorectal Models

Prototype Extra Wide Angle View Colonoscope: A Randomized Controlled Multicenter Simulated Study Using Anatomic Colorectal Models Toshio Uraoka*, Shinji Tanaka, Takayuki Matsumoto, Takahisa Matsuda, Shiro Oka, Tomohiko Moriyama, Kazuhide Yamamoto, Yutaka Saito Division of Research and Development for Minimally Invasive Treatment, Cancer Center, Keio University School of Medicine, Tokyo, Japan; Department of Endoscopy, Okayama University Hospital, Okayama, Japan; Department of Endoscopy, Hiroshima University Hospital, Hiroshioma, Japan; Department of Medicine and Clinical Science, Kyushu University Graduate School of Medical Sciences, Fukuoka, Japan; Endoscopy Division, National Cancer Center Hospital, Tokyo, Japan; Department of Gastroenterology and Hepatology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan Background and Aim: Colonoscopy is the preferred screening method for colorectal cancer, but previously reported rates of undetected colorectal polyps have been approximately 25%. A major contributing factor may be that undetected lesions are located behind haustra folds, flexures or rectal valves. Several different techniques including chromoendoscopy, cap-fitted colonoscopy and retroflexion of the colonoscope have been used to improve polyp detection. The aim of this randomized controlled multicenter simulated study was to evaluate the efficacy of a prototype extra wide angle view colonoscope for polyp detection. Method: Two colonoscopes were used including a commercially available standard colonoscope with a 140°-angle lens; and the prototype colonoscope with a 144°-to-232°-angle lateral-backward view lens and a 140°angle forward view lens. Views from both lenses are simultaneously constructed and displayed on a video monitor as a single image. Two anatomic colorectal models were prepared each with eight polyps that were positioned in obvious locations and eight polyps that were placed behind folds. Thirty-two participating endoscopists from four institutions including 16 experienced endoscopists ( 5,000 colonoscopies) and 16 less experienced endoscopists ( 5,000 colonoscopies) conducted examinations of the two models in random order using the two colonoscopes. All polyps were 3mm or 5mm in diameter with a round shape and dark red in color, but varied in their individual markings. Insertion and withdrawal examination times and detected polyps were recorded by an independent observer. The primary outcome measurement was the detection rate of simulated colorectal polyps. Results: Although the mean withdrawal times were not significantly different for the two colonoscopes (6.5 vs. 6.7 minutes; p 0.60), the detection rate with the prototype colonoscope was significantly higher than the detection rate with the standard colonosocpe (68% vs. 51%; p 0.0001). While there was no statistical difference in the detection rate of polyps located behind folds between the two colonoscopes when used by experienced endoscopists (61% vs. 51%; p 0.11), the detection rate for such polyps with the prototype colonoscope was significantly higher than the detection rate with the standard colonosocpe (63% vs. 43%; p 0.003) when used by less experienced endoscopists. There were no significant differences in insertion times for the two colonoscopes even for less experienced endoscopists. Conclusion: Based on this study’s results, the prototype colonoscope may represent a considerable advancement in colorectal polyp detection particularly for less experienced endoscopists, but a randomized controlled multicenter trial should be conducted to fully evaluate its efficacy for screening and surveillance purposes.

Caenorhabditis elegans Galectins LEC-6 and LEC-10 Interact with Similar Glycoconjugates in the Intestine

Galectins are a family of metazoan proteins that show binding to various β-galactoside-containing glycans. Because of a lack of proper tools, the interaction of galectins with their specific glycan ligands in the cells and tissues are largely unknown. We have investigated the localization of galectin ligands in Caenorhabditis elegans using a novel technology that relies on the high binding specificity between galectins and their endogenous ligands. Fluorescently labeled recombinant galectin fusions are found to bind to ligands located in diverse tissues including the intestine, pharynx, and the rectal valve. Consistent with their role as galactoside-binding proteins, the interaction with their ligands is inhibited by galactose or lactose. Two of the galectins, LEC-6 and LEC-10, recognize ligands that co-localize along the intestinal lumen. The ligands for LEC-6 and LEC-10 are absent in three glycosylation mutants bre-1, fut-8, and galt-1, which have been shown to be required to synthesize the Gal-β1,4-Fuc modifications of the core N-glycans unique to C. elegans and several other invertebrates. Both galectins pull down the same set of glycoproteins in a manner dependent on the presence of these carbohydrate modifications. Endogenous LEC-6 and LEC-10 are expressed in the intestinal cells, but they are localized to different subcellular compartments that do not appear to overlap with each other or with the location of their glycan targets. An altered subcellular distribution of these ligands is found in mutants lacking both galectins. These results suggest a model where LEC-6 and LEC-10 interact with glycoproteins through specific glycans to regulate their cellular fate.

Colonoscopy Peer Review Utilizing Automated Video Capture

Purpose: Colonoscopy is the screening modality of choice for detecting early colorectal cancer in the United States. Several retrospective reports show that colorectal cancers may appear within 3 years of a colonoscopy, suggesting some polyps or cancers are missed. Despite these findings, no standardized, validated method exists to objectively evaluate the skill set of an endoscopist. Aim: to evaluate an anonymous, automated video capture system used in conjunction with novel software to facilitate peer review of endoscopic performance, and to see if higher quality exams correlate with withdrawal time. Methods: Existing infrastructure and software were used to capture entire colonoscopies which were then stored as digital video files and reviewed anonymously. Video colonoscopy files were randomly obtained from 2 endoscopy suites at Mayo Clinic-Rochester over the course of 4 days in 2007. Three endoscopists with varied endoscopic experience (1 fellow, 1 junior staff and 1 senior staff) reviewed a set of 24 anonymous video colonoscopies, and provided feedback via a graphical user interface. The 3 reviewers were asked to assign numerical scores on several parameters: adequacy of colonic mucosal visualization including the proximal side of haustral folds, flexures, rectal valves and the ileocecal valve (0-100), adequacy of removal of fluid/feces during exam (0-10), and adequacy of luminal distention during exam (0-10). Additionally, reviewers identified key time points during each colonoscopy and a withdrawal time was calculated. Results: The panel of 3 individual reviewers demonstrated agreement when asked to evaluate 24 random colonoscopy video files of varied quality. Specifically, the intraobserver agreement for the visualization score (0-100) was good, reflected by a disagreement range of 19 ± 13 (Mean+SD). Similarly, scores for adequacy of fluid/feces removal (0-10) and adequacy of luminal distention (0-10), showed good agreement also reflected by low intra-observer disagreement; range 2.0 ± 1.3, and 2.1 ± 1.5 (Mean+SD), respectively. There was no relationship between visualization score and withdrawal time for each reviewed case: least squares analysis showed no correlation between the two (R2 = 0.04). Conclusion: Our results show that a standardized, anonymous method utilizing video capture and new software technology allows effective and consistent peer review of individual colonoscopies. The close agreement among reviewers suggests that this peer review method is independent of the evaluator's experience. Therefore, our method can be used to ensure that an endoscopist meets a minimal standard of quality, assessed in an anonymous and reproducible fashion. Our results question the utility of withdrawal time as a standard for quality. Disclosure: PC de Groen - stock in EndoMetric J Wong - stock in EndoMetric W Tavanapong - stock in EndoMetric J Oh - stock in EndoMetric.

A pilot study to assess the safety and efficacy of the Third Eye retrograde auxiliary imaging system during colonoscopy

Routine colorectal cancer screening, utilizing optical colonoscopy, has been shown to reduce the incidence and mortality rate of colorectal cancer. Despite its prevalence as the "gold standard" for neoplasia detection, the quality of colonoscopy screening is hindered by missed, undiagnosed lesions that may go undetected when located on the proximal aspect of haustral folds, rectal valves, the ileocecal valve, and/or flexures. The aim of this phase I feasibility trial is to assess the safety and efficacy of a new retrograde auxiliary imaging device, Third Eye Retroscope (Avantis Medical Systems, Inc., Sunnyvale, California, USA), used with optical colonoscopy to improve diagnostic yield. A total of 29 consecutive patients were enrolled in this phase I single-institution prospective series. Primary efficacy endpoint was identification of polyps in the retrograde image that were not identified in the antegrade image during colonoscope withdrawal. Of the 29 patients enrolled, 24 patients were treated and 34 out of a total of 38 polyps (classified as either adenoma or hyperplasia) were identified in the antegrade image. An additional four polyps, three hyperplastic and one adenoma, were identified in the retrograde image, and were detected on the proximal aspect of haustral folds during the colonoscope withdrawal, resulting in an 11.8% increase in diagnostic yield. No adverse events were encountered during the study. A retrograde auxiliary imaging device used in conjunction with a standard optical colonoscope proved to be safe, technically feasible, and clinically promising. A phase II multi-institutional study is currently underway to further evaluate this device.

Wnt Signaling Positions Neuromuscular Connectivity by Inhibiting Synapse Formation in C. elegans

Nervous system function is mediated by a precisely patterned network of synaptic connections. While several cell-adhesion and secreted molecules promote the assembly of synapses, the contribution of signals that negatively regulate synaptogenesis is not well understood. We examined synapse formation in the Caenorhabditis elegans motor neuron DA9, whose presynapses are restricted to a specific segment of its axon. We report that the Wnt lin-44 localizes the Wnt receptor lin-17/Frizzled (Fz) to a subdomain of the DA9 axon that is devoid of presynaptic specializations. When this signaling pathway, composed of the Wnts lin-44 and egl-20, lin-17/Frizzled and dsh-1/Dishevelled, is compromised, synapses develop ectopically in this subdomain. Conversely, overexpression of LIN-44 in cells adjacent to DA9 is sufficient to expand LIN-17 localization within the DA9 axon, thereby inhibiting presynaptic assembly. These results suggest that morphogenetic signals can spatially regulate the patterning of synaptic connections by subdividing an axon into discrete domains.

A novel retrograde-viewing auxiliary imaging device (Third Eye Retroscope) improves the detection of simulated polyps in anatomic models of the colon

Colonoscopy is the "gold standard" for colorectal polyp and cancer detection, but important lesions may be missed on the proximal aspect of haustral folds, rectal valves, or flexures. Our purpose was to evaluate a prototype auxiliary imaging device that extends beyond the colonoscope's tip, providing a continuous retrograde view to detect lesions missed by the forward-viewing colonoscope. Three anatomic models of the colon were prepared with simulated polyps, 32% in obvious locations and 68% on the proximal aspect of folds. Six endoscopists examined each model with two methods. Method A used a standard video colonoscope. Method B involved an identical colonoscope with a retrograde-viewing auxiliary device positioned within its instrument channel. Order of testing was randomized and blinded. Laboratory bench. Detection rates for simulated polyps. Of 78 "obvious" polyps, 69 (88%) and 70 (90%) were detected by methods A and B, respectively (P > .9). In contrast, of 162 polyps on proximal aspects of folds, 20 (12%) and 131 (81%) were detected by methods A and B, respectively (P < .00001). Limitations resulted from (1) use of commercially available anatomic models in which haustral folds are less prominent and more rigid than in humans and (2) evaluation of a prototype device that had larger size and narrower angle of view than the planned production model and that was fixed in relation to the colonoscope. In simulated testing, a retrograde-viewing auxiliary imaging device used with a standard video colonoscope significantly improves detection rates of simulated polyps and promises to enhance the diagnostic yield of colonoscopy in humans.

Gut structure of two species of the neotropical genus Tauritermes Krishna (Isoptera: Kalotermitidae)

Gut morphology of two species of the neotropical genus Tauritermes Krishna was analyzed. Detailed description of the coiling gut and the cuticular armature of the gizzard and first and second proctodeal segments of pseudergates are given. The characteristics of Tauritermes gut followed the pattern previously known for the family, but some differences among this genus and other Kalotermitidae genera were: the length of the midgut, the structure and cuticular ornamentation of the first and second proctodeal segments, the junction of the third and fourth proctodeal segments and the armature of the rectal valve. Tauritermes was differentiated from other Kalotermitidae genera by means of the gut characters, currently used in termite systematics and phylogeny.

Anatomy of a hemiramphid pharyngeal mill with reference to Arrhamphus sclerolepis krefftii (Steindachner) (Teleostei: Hemiramphidae).

The structure and function of the pharyngeal jaw apparatus (PJA) and postpharyngeal alimentary tract of Arrhamphus sclerolepis krefftii, an herbivorous hemiramphid, were investigated by dissection, light and scanning electron microscopy, and X-ray analysis of live specimens. A simple model of PJA operation is proposed, consisting of an adductive power stroke of the third pharyngobranchial that draws it posteriorly while the fifth ceratobranchial is adducted, and a return stroke in which the third pharyngobranchial bone is drawn anteriorly during abduction of the fifth ceratobranchial. Teeth in the posteromedial region of the PJA are eroded into an occlusion zone where the teeth of the third pharyngobranchial are spatulate incisiform and face posteriorly in opposition to the rostrally oriented spatulate incisiform teeth in the wear zone of the fifth ceratobranchial. The shape of the teeth and their pedestals (bone of attachment) is consistent with the model and with the forces likely to operate on the elements of the PJA during mastication. The role of pharyngeal tooth replacement in maintaining the occlusal surfaces in the PJA during growth is described. The postpharyngeal alimentary tract of A. sclerolepis krefftii comprises a stomachless cylinder that attenuates gradually as it passes straight to the anus, interrupted only by a rectal valve. The ratio of gut length to standard length is about 0.5. Despite superficial similarities to the cichlid PJA (Stiassny and Jensen [1987] Bull Mus Comp Zool 151:269-319), the hemiramphid PJA differs in the fusion of the third pharyngobranchial bones, teeth in the second pharyngobranchials and the fifth ceratobranchial face anteriorly, the presence of a slide-like diarthroses between the heads of the fourth epibranchials and the third pharyngobranchial, the occlusion zone of constantly wearing teeth, and the unusual form of the muscularis craniopharyngobranchialis. The functional relationship between these structures is explained and the consequence for the fish of a complex PJA and a simple gut is discussed.

Ultrastructure of the midgut and hindgut of Derocheilocaris remanei (Crustacea, Mystacocarida)

ABSTRACT Ultrastructural features and structure of the midgut and hindgut of Derocheilocaris remanei were studied. The large endodermal midgut is differentiated into an anterior midgut and a posterior midgut separated by a conspicuous constriction. Both circular and longitudinal striated muscle bands surround the midgut, while the hindgut only presents longitudinal muscles. The limit between the midgut and the cuticle-lined hindgut is marked by a rectal valve. In cross-section, the short hindgut is triradiate and has a distinct Y-shaped lumen. The hindgut cuticular lining appears interrupted at the tip of every branch of the Y. Three different cell types are found in the midgut epithelium: basally located undifferentiated cells that give rise to the other two specialized cell types; secretory zymogen-like cells responsible for extracellular digestion and located mainly in the anterior midgut; and vacuolated cells, distributed all along the midgut and appearing to have several functions, including absorption, intracellular digestion, and nutrient transport. A single basic cell type forms the hindgut epithelium. The suggested function for the hindgut is the transport and ejection of waste products. J. Morphol. 244:177–189, 2000 © 2000 Wiley-Liss, Inc.

Ultrastructure of the midgut and hindgut of Derocheilocaris remanei (Crustacea, Mystacocarida).

Ultrastructural features and structure of the midgut and hindgut of Derocheilocaris remanei were studied. The large endodermal midgut is differentiated into an anterior midgut and a posterior midgut separated by a conspicuous constriction. Both circular and longitudinal striated muscle bands surround the midgut, while the hindgut only presents longitudinal muscles. The limit between the midgut and the cuticle-lined hindgut is marked by a rectal valve. In cross-section, the short hindgut is triradiate and has a distinct Y-shaped lumen. The hindgut cuticular lining appears interrupted at the tip of every branch of the Y. Three different cell types are found in the midgut epithelium: basally located undifferentiated cells that give rise to the other two specialized cell types; secretory zymogen-like cells responsible for extracellular digestion and located mainly in the anterior midgut; and vacuolated cells, distributed all along the midgut and appearing to have several functions, including absorption, intracellular digestion, and nutrient transport. A single basic cell type forms the hindgut epithelium. The suggested function for the hindgut is the transport and ejection of waste products.