Stratified Squamous Epithelium Research Articles

Histological Study for Skin of Horse

The present study was done on skin of horse,samples are taken from six animals after anaesthetized the animals and slaughttered . Samples are taken from dorsal back area ,the collected tissues were fixed in 10% formalin for 24 hrs. tissue was prepared for light microscopic examination . the result showed skin of horse composed of Epidermis & dermis .epidermis are keratinized stratified squamous epithelium ,that divided into four cellular layers from the top (stratum corneum ,granulosum ,spinosum and basale), stratum basale are consist of simple cubiodal epithelium cells were rest on the basement membrane, Melanocytes cells are located in stratum basale .Dermis composed of papillary layer and dermal papilla. Papillary layer composed of bundles of collagenouse fibers with fibroblast. Primary hair follicles. primary hair follicle which surrounded by sweat glads and sebaceous glands. sweat glands was simple tubular gland which lined by simple cuboidal epithelium, the alveoli of sweat gland that surrounded by Myoepithelial cells. Sebeceous gland, Like double saccule, lined by simple cubiodal epithelium cells that contain fat dropletes. Primary hair follicle, that consist of Hair shaft in the center which represented the medulla, it was enclosed by cortical layer of stratified squamous epithelium.The primary & secondary hair follicle were attached to the smooth muscle bundles, was represented the arector pilli muscles. Small artery near the hair follicle that supply the oxygen and nutrient to the skin.

Preparation of IgE Antibody and Distribution of IgE+ Secretory Cells in the Palatine Tonsil of Bactrian Camel.

Allergic diseases induced by dust have seriously threatened human health, while Bactrian camels can live in a sandy environment for a long time. To prepare rabbit anti-Bactrian camel IgE antibody and explore the distribution characteristics of IgE+ secretory cells in the palatine tonsils, which lays a theoretical foundation for the distribution of local antibodies in the palatal tonsils of Bactrian camel and the study of immune function. In this study, the amino acid sequences of Bactrian camel IgE, IgA, IgM and IgG heavy chain constant regions were compared, and a specific IgE gene fragment were selected (447 bp). The recombinant plasmid pET-28a-IgE was induced in Escherichia coli BL21(DE3) by IPTG and its expression conditions were optimized. The antibody was prepared by immunizing rabbits with purified IgE recombinant protein, its titer and specificity were detected by indirect ELISA and Western blotting. Immunohistochemical and statistical methods investigated the distribution of IgE+ secretory cells in the palatine tonsils. The IgE recombinant protein was expressed in the form of inclusion bodies with a size of 16 kDa. The optimal IPTG induction concentration was 0.7 mmol/L and the induction time was 8 h. The titer of the antibody was 1:16000 by ELISA, and the antibody could specifically bind to the recombinant protein by Western blotting. IgE+ secretory cells were mainly distributed in the subepithelial compartments of reticulated crypt epithelium of the palatine tonsil of the Bactrian camel, followed by the subepithelial compartments of stratified squamous epithelium and occasionally in the extrafollicular region. The rabbit anti-Bactrian camel IgE polyclonal antibody was successfully prepared. It is confirmed that IgE exists in the palatine tonsils of Bactrian camels under normal living conditions. In addition, IgE+ secretory cells are mainly distributed in the subepithelial compartments of reticulated crypt epithelium of the palatine tonsil, which is consistent with the distribution characteristics of IgG+ and sIgA+ secretory cells in the palatal tonsils of the Bactrian camel.

Unusual presentation of ameloblastoma in a nasal polyp with a review of tumour behaviour

Ameloblastoma is a benign odontogenic tumour occurring primarily in the mandible with a peak incidence in the fourth and fifth decades of life. We report a case of an ameloblastoma presenting as a polypoidal mass in the right nasal cavity of a 72-year-old woman. The polypoidal mass was lined by stratified squamous epithelium, with tumour cells composed of palisading hyperchromatic columnar cells with reverse polarity present within the polyp stroma. Subsequent imaging study showed a mass lesion involving the right maxilla.

Epidermal Cyst in an Intrapancreatic Accessory Spleen.

A 59-year-old asymptomatic woman with no disease history presented to our institution for investigation of a pancreatic tail mass. Hematological parameters were within normal ranges, including serum carcinoembryonic antigen levels and carboxyhydrate antigen 19-9. Computed tomography revealed a strongly enhanced solid peripheral mass with an intracystic component in the pancreatic tail (Figure A, arrow). Magnetic resonance imaging revealed a cystic lesion on the T2 image surrounded by a solid component with density and intensity levels similar to those in the spleen parenchyma (Figure B, arrow). Endoscopic ultrasonography showed a solid hyperechoic 20-mm mass and an intracystic hypoechoic component showing stronger enhancement by Sonazoid (MSD Inc) than the pancreatic parenchyma (Figure C, arrow). Laparoscopic distal pancreatectomy was used for diagnosis. Pathological examination revealed a white and red sinus of the ectopic spleen in the pancreatic tail, with a unilocular cyst lined with stratified squamous epithelium, indicating an epidermal cyst in the intrapancreatic accessory spleen (Figure D, arrows). Most epidermal cysts in the intrapancreatic accessory spleen cases are found incidentally, typically as single monolobular cystic lesions in the pancreatic tail with a thickened cystic wall or solid components identical in density to the spleen on imaging examinations, making a definite preoperative diagnosis extremely difficult, resulting in unnecessary surgical intervention.

Polarity in skin development and cancer.

The epidermis is a stratified squamous epithelium that forms the outermost layer of the skin. Its primary function is to act as a barrier, keeping pathogens and toxins out and moisture in. This physiological role has necessitated major differences in the organization and polarity of the tissue as compared to simple epithelia. We discuss four aspects of polarity in the epidermis - the distinctive polarities of basal progenitor cells as well as differentiated granular cells, the polarity of adhesions and the cytoskeleton across the tissue as keratinocytes differentiate, and the planar cell polarity of the tissue. These distinctive polarities are essential for the morphogenesis and the function of the epidermis and have also been implicated in regulating tumor formation.

Epidemiologic and histopathological evaluation of unclassified gingival papules in Urmia, Iran.

Unclassified gingival papules might be mistaken with other malignant lesions as they resemble some other oral lesions. The present study demonstrates epidemiologic and histopathological characteristics of the gingival unclassified papules in the patients referred to Urmia Dental School, Iran. A cross sectional descriptive study design was conducted among 500 pateints in Urmai university of medical sciences, Iran. The participant's demographic data and medical history were obtained using clinical examinations and a questionnaire. Histopathological assessments were done in two specimens. The effect of the possible factors on the incidence of gingival papules was statistically assessed by Fisher's exact test. Among 500 participants, 340 (68%) demonstrated unclassified gingival papules (40.9% males, 59.1% females; mean age of 34.9 years). No significant differences were found regarding the effect of gender, smoking, mouth breathing, history of skin disease or pregnancy on the incidence of gingival papules. However, the breastfeeding females (P < 0.004) or those using contraceptive pills (P < 0.02) showed lower frequency of papules' incidence. Among 340 papules, 332 (97.6%) were white in color, 337 (99.1%) were well defined and 331 (97.3%) were observed in the keratinized gingiva. 207 (60.9%) were multiple and 133 (39.1%) were single lesions. The papules showed healthy tissues similar to gingival tissue; however, abundant collagen bundles were irregular and close to the surface, which was covering by stratified squamous epithelium. Gingival papules are common findings in patients referring to Urmia Dental School; the lesions were almost white in color, well defined and appeared in the keratinized gingiva. The lesions were a variation of normal oral structures with no treatment requirements.

Lymphangiectasia Mimicking Lichenoid Contact Reaction

Lymphangiectasia, otherwise known as acquired lymphangioma, is unusual to occur in the oral cavity. Among the frequently recognised forms of congenital and acquired entities, the acquired form of the lymphangiectasia may be caused due to trauma or obstruction to the lymphatic system. Commonly, this condition is asymptomatic; however, the needs of aesthetics and functions warrant treatment. This was a case report of a 55-year-old male patient, who came with a chief complaint of burning sensation in his left cheek region for the past three weeks. Clinically, silver amalgam restoration was evident in relation to the tooth numbers 26,27,36 and 37. Soft tissue examination revealed evidence of greyish radiating striae interspersed with hyperpigmentation on the left buccal sulcus and left lateral border of the tongue. Considering the clinical features, a working diagnosis of lichenoid contact reaction was proposed. Further, an incisional biopsy was performed. Histopathological examination showed thin stratified squamous epithelium with vacuolar spaces, which strongly supported the diagnosis of lymphatic malformation. The patient was symptomatically managed with topical triamcinolone acetonide 0.1% twice daily for two weeks. At two weeks follow-up, the patient was symptom-free and hence the medication was withdrawn. The patient is currently under regular follow-ups.

Histological and histochemical characteristics of the esophagus in local breed donkey (Equus asinus).

Certain advantages of donkeys are still not listed as for other equine species. Moreover, donkeys lack comprehensive scientific studies. The present study examines the histological architecture and histochemical characteristics of the esophagus in the Iraqi local breed donkey (Equus asinus). Eight esophagus samples were collected from a local breed donkey. Tissue specimens (~1 cm3) were collected from the cervical, thoracic, and abdominal regions of the esophagus and processed via routine histological technique. The tissue sections were stained with hematoxylin and eosin, Massons Trichrome, and combined Alcian blue (pH 2.5) plus PAS (AB-PAS). The esophagus of the local breed donkey had folded mucosa wrapped by thin non-keratinized stratified squamous epithelium. The heights of epithelia of the cervical and thoracic regions of the esophagus were significantly higher than that of the abdominal regions. The lamina propria consisted of dense fibrous tissue that appeared thickest in the thoracic and abdominal regions of the esophagus. The muscularis mucosa disappears at the cervical region, while the thoracic and abdominal regions of the esophagus contain thick, scattered, interrupted bundles of smooth muscle fibers. Tunica submucosa was very thick at the thoracic and abdominal regions of the esophagus, composed of loose connective tissue filled with compound tubular mucoserous esophageal glands. Using a combined AB-PAS stain, mucous alveoli within the esophageal glands indicated strong acidic mucopolysaccharide. Tunica muscularis of the cervical and thoracic regions was built up by striated muscle fibers and turned into smooth type at the abdominal region of the esophagus. The esophagus of the local breed donkey shows considerable histological similarities with the other mammals that make this species reliable as an experimental model of digestive tissue.

Concurrent Occurrence of Nasopharyngeal and Disseminated Cutaneous Rhinosporidiosis: A Rare Presentation.

Concurrent Occurrence of Nasopharyngeal and Disseminated Cutaneous Rhinosporidiosis: A Rare Presentation.

Analiza limfocitarnog infiltrata kao prediktivnog faktora pojave metastaza na vratu kod oralnog skvamocelularnog karcinoma

Introduction: Carcinoma of the stratified squamous epithelium of the oral cavity - oral squamous cell carcinoma (OSCC) is an invasive pathological lesion of the epithelium with varying degrees of squamous differentiation. It is characterized by early and extensive metastases, infiltration of adjacent anatomical structures, frequent recurrences, and a relatively low five-year survival rate of less than 50%. The aim of the study to determine the correlation between the analysis of the lymphocytic infiltrate of biopsy specimens with pathohistologically proven metastases of oral squamous cellular carcinoma on postoperative neck dissection specimens. Material and methods: The study included 42 patients with pathohistologically verified oral squamous cellular carcinoma who underwent surgery at the Department of Maxillofacial Surgery of the Clinic of Dental medicine in Niš in the period from 2018 to 2022. The histopathological analysis included the depth of tumor invasion, histopathological analysis of the lymph nodes of neck dissections, analysis of lymphocytic infiltration, and presence of lymphovascularand perineural invasion. Results: It was determined that the depth of invasion is statistically significantly different regarding the degree of lymphocytic infiltration (p=0.004). Invasion of over 4mm was present in 20% of patients with high infiltration, 44.4% of patients with medium infiltration, and 85.7% of patients with low infiltration. Conclusion: Given that the results of the study indicate that the analysis of the lymphocytic infiltrate can be a reliable predictive factor of the appearance of metastases in the lymph nodes of the neck, further research should be directed toward as sociating lymphocytic infiltration with certain biochemical and genetic parameters based on which a plan can be created for neck treatment in the N0 stage of oral squamous cellular carcinoma.

Surgical management of a dermoid cyst with mandibular gland tissue in a Japanese Black calf.

A 131-day-old male Japanese Black calf presented with a swollen right cheek from birth. Imaging examination revealed a cyst under the right buccal area and debris-containing fluid inside the cyst, and puncture aspiration revealed a mildly cloudy fluid containing hair and tissue fragments. Histological examination of the excised cyst revealed stratified squamous epithelium with skin appendages in the cyst wall, which was diagnosed as a dermoid cyst. In addition, some submandibular gland tissue was found within the cyst wall. After removal of the cyst, there was swelling in the same area, which resolved with steroid administration. Surgical treatment of buccal dermoid cysts should be performed with caution to avoid damage to adjacent salivary gland tissue.

A rare case of congenital ectopic eyelid tissue

Ectopic eyelid, an extremely rare entity, is a congenital disturbance in embryogenesis in which lid tissue is present in an abnormal position near the eyelid. We herein report a case of a six-year-old child with a soft mass near the lateral canthus of the left eye having cilia overlying it, with a similar family history in her father. A surgical excision biopsy was performed under general anesthesia. A histopathology report revealed stratified squamous epithelium with numerous dermal pilous units consisting of a central hair shaft and clusters of Moll's glands, suggesting eyelid tissue. Therefore, an ectopic eyelid tissue can be considered a differential diagnosis for any congenital, non-progressive, soft tissue mass near the eyelid with overlying cilia. However, histopathology is required to confirm the diagnosis.

Mendacious conjunctival lesions – A tale of two cases

Presentation of conjunctival tumors ranges from benign lesions like pinguecula and pterygium to highly malignant tumors of melanocytic, lymphoid, and stratified squamous epithelium origin. A 30-year-old female presented with two brown-colored conjunctival lesions in her left eye extending from medial canthus to limbus. Lesions were excised and subjected to histopathologic examination (HPE), which came out to be pigmented squamous cell papilloma, a rare conjunctival lesion having potential to convert to malignancy. Another 50-year-old female presented with pinguicula-like lesions in both her eyes along with maculopapular rash on her forehead. Conjunctival lesions were completely excised HPE, revealed Spiegler–Fendt sarcoid, also known as lymphocytoma cutis, along with conjunctival tumor of lymphocytic origin. Spiegler–Fendt sarcoid is usually a benign lesion with potential for systemic involvement requiring holistic approach for the management of such patients.

Epidermoid cysts of the orofacial region: A clinico-pathological study of 13 cases with review of literature.

Epidermoid cysts (ECs) are uncommon benign cystic lesions derived from the germinative epithelium. Head and neck ECs constitute only 7% of all ECs whereas only 1.6% are seen intraorally. The floor of the mouth is the commonest intraoral site whereas tongue, lips, buccal mucosa, and jaws are less commonly involved intraoral sites. To date, very few large case series of ECs of head and neck have been published. To the best of our knowledge, this is the third-largest case series of 11 intraoral ECs along with 2 extra-oral cases in the pre-auricular region. To highlight the typical and atypical features of ECs in the common as well as rare sites and draw attention to its consideration as a differential diagnosis for head and neck masses. Archival data of 13 histopathological cases identified as ECs were analyzed from the Department of Oral Pathology at a tertiary dental hospital and college in New Delhi from 2007 to 2020. The demographic, clinical, radiographic, histopathological features, and treatment modalities were recorded and analyzed. Appropriate statistical tests were used. The study found strong male predilection in the ratio of 10:3 with an average age of presentation as 28 years. The pre-auricular region and floor of the mouth were the common sites involved followed by buccal mucosa, lips, and jaws. All patients presented with slowly growing swelling with dysphagia, dyspnea, and dysphonia seen in larger cysts on the floor of the mouth. Microscopically, all cases were lined with stratified squamous epithelium filled with laminated layers of keratin. Two cases showed the presence of melanin. One case showed recurrence even after complete surgical excision. ECs, though a rare entity, should be considered in differential diagnosis for head and neck masses and require close follow-up due to their potential for malignant transformation.

Epidermoid cyst in submandibular region: a case report

The epidermoid cyst (EC) is a rare benign tumor that can develop in any region of the human body. About 7% of these cysts are located in head and neck. They are not frequent entities in cranio-facial region and in still more rare in oral cavity 1% statistically. Almost all of them occur in sublingual region, but there are rare case reports of occurrence in other sites. The epidermoid cysts is defined by a lined stratified squamous epithelium supported by an outer layer of collagenous-rich connective tissue. The detachment of keratin from the epithelial lining criates a soft white material rich in cholesterol crystals. This lipid rich content of the cyst may produce a vigorous inflammatory reaction if cyst rupture ocurrs. We report a case of epidermoid cyst (EC) located in submandibular region and the surgical removal procedure. This study was approuved by the Ferraz de Vasconcelos Regional Hospital (IRB) and the patient signed the Informed Consensus Files additionally. Clinical and radiographic examination revealed a movable swelling but hardened on palpation procedure. Histologic analisys of the excisional biopsy confirmed the initial hypotheses that it was an EC lesion. In spite of the EC being a rare benign lesion a differential diagnose is mandatory and it should not be underestimated due to its low but possible neoplasic transformation.

Expression of MUC-2, MUC-6, NAPE-PLD, IL-6 and IL-13 in Healthy and Metaplastic Bronchial Epithelium

Background: The normal tissue structure of the respiratory system is necessary to provide adequate protection of the airways and lungs. Prolonged exposure to trigger factors can result in adaptive mechanism activation and lead to the development of chronic pulmonary diseases or even dysplastic changes. Materials and methods: Respiratory system material with a pseudostratified ciliated epithelium was obtained from 12 patients (aged 16 to 95), and material with a stratified squamosa epithelium was obtained from six patients (aged 23 to 93). Routine staining was performed, and an immunohistochemistry was conducted for MUC-2, MUC-6, NAPE-PLD, IL-6 and IL-13. Results: Inflammatory processes were not detected in any of the specimens. A number of correlations were identified, with the most important being a strong positive correlation for IL-13 between the alveolar epithelium and alveolar macrophages and a strong positive correlation for IL-6 between the alveolar epithelium and alveolar macrophages in the stratified squamous epithelium group. We also detected a statistically significant difference in IL-6 in alveolar macrophages. Conclusions: There were no signs of dysplastic changes in either group. Increased secretion of IL-13 in the stratified squamous epithelium group shows its involvement in metaplastic changes in the bronchial epithelium. The secretion of atypical factors by hyaline cartilage demonstrates its plasticity and adaptability.

Modeling Oral-Esophageal Squamous Cell Carcinoma in 3D Organoids.

Esophageal squamous cell carcinoma (ESCC) is prevalent worldwide, accounting for 90% of all esophageal cancer cases each year, and is the deadliest of all human squamous cell carcinomas. Despite recent progress in defining the molecular changes accompanying ESCC initiation and development, patient prognosis remains poor. The functional annotation of these molecular changes is the necessary next step and requires models that both capture the molecular features of ESCC and can be readily and inexpensively manipulated for functional annotation. Mice treated with the tobacco smoke mimetic 4-nitroquinoline 1-oxide (4NQO) predictably form ESCC and esophageal preneoplasia. Of note, 4NQO lesions also arise in the oral cavity, most commonly in the tongue, as well as the forestomach, which all share the stratified squamous epithelium. However, these mice cannot be simply manipulated for functional hypothesis testing, as generating isogenic mouse models is time- and resource-intensive. Herein, we overcome this limitation by generating single cell-derived three-dimensional (3D) organoids from mice treated with 4NQO to characterize murine ESCC or preneoplastic cells ex vivo. These organoids capture the salient features of ESCC and esophageal preneoplasia, can be cheaply and quickly leveraged to form isogenic models, and can be utilized for syngeneic transplantation experiments. We demonstrate how to generate 3D organoids from normal, preneoplastic, and SCC murine esophageal tissue and maintain and cryopreserve these organoids. The applications of these versatile organoids are broad and include the utilization of genetically engineered mice and further characterization by flow cytometry or immunohistochemistry, the generation of isogeneic organoid lines using CRISPR technologies, and drug screening or syngeneic transplantation. We believe that the widespread adoption of the techniques demonstrated in this protocol will accelerate progress in this field to combat the severe burden of ESCC.

Rumen Volatile Fatty Acids and Morphology of the Rumen Mucosa of Swamp Buffalo Raised under Semi-Intensive and Extensive System in Tropical Environment

Swamp buffaloes are mostly raised under an extensive system because they can adapt to the harsh environment. However, exploring the rumen mucosa (RM) morphology and volatile fatty acids (VFA) of swamp buffalo associated with different production systems is still lacking. This study evaluated the rumen VFA and morphology of RM between two groups of buffalo raised under semi-intensive (SI) and an extensive system (EX). VFA was analysed using gas chromatography. The morphology of rumen mucosa was evaluated macro and microscopically for papillae length and width, surface area, density, and muscle thickness, and the microscopic evaluation for stratified squamous epithelium (SSE) and keratin thickness. SI has a greater VFA concentration than the EX. The SSE layer on the dorsal region of the rumen was thicker in the EX group than in the SI group (p≤0.05). Within the group, the SSE of the dorsal region of rumen was thicker than the ventral region (p≤0.05) in the EX group. However, the ventral region of the rumen was thicker than the dorsal region in the SI group. The thickness of the keratin layer in the EX group was significantly thicker than the SI group (p≤0.05) only on the dorsal region. In conclusion, swamp buffalo from the SI production system has a greater concentration of volatile fatty acid than the EX-group contributed by feeding management under a semi-intensive system. Nevertheless, the advantage in VFA concentration alone is not sufficient to conclude semi-intensive production system exerts a favourable effect on the morphology of the rumen mucosa.

Distal phalanx intraosseous epidermoid inclusioncyst: A rare thing!

Pathological structures called epidermoid bone inclusion cysts are surrounded by a layer of stratified squamous epithelium that contains keratin debris. They go by the name epidermal bone cysts as well. Intraosseous epidermoid cysts are uncommon lesions that can develop as a result of trauma (puncture wound or pressure erosion). They typically affect the toes, phalanges, and head. The distal phalanx of the fingers is where phalangeal involvement most frequently occurs. Despite the fact that the cause of intraosseous epidermal inclusion cysts is still unknown, the majority of patients do recall a prior traumatic event, supporting the post-traumatic origin theory. Following digital trauma or surgery, it is hypothesised that surface epithelial cells are pushed into the underlying osseous compartment.Following the initiating event, symptoms may start to appear months to years later. It is challenging to distinguish intraosseous epidermoid inclusion cysts on radiographs from other radiolucent lesions, necessitating tissue diagnosis.We present a case of a 45-year-old man with right middle finger distal phalanx edoema for five months and a known history of minor blunt trauma. A well-defined expansile hypodense lytic lesion with eccentric phalanx erosion was discovered during radiological analysis. A creamy substance was found inside the lesion after surgery, and it was later determined by histology to be an epidermoid inclusion cyst.Gross examination of the surgical specimen indicated a cystic lesion with significant necrotic regions and pale, creamy material. A burst intraosseous epidermoid inclusion cyst was discovered upon microscopic inspection and was effectively removed.

Laparoscopic resection of an intra-abdominal esophageal duplication cyst in the ileum: a case report.

Esophageal duplication cyst (EDC) is a type of gastrointestinal duplication cyst that involves congenital malformations of the gastrointestinal tract. EDCs are frequently found in the mediastinum and thoracoabdominal region, but rarely occur in the abdominal cavity. However, intra-abdominal EDCs are frequently found in the upper abdomen near the abdominal esophagus. Here, we report, for the first time, a case of intra-abdominal EDC that occurred in the ileum. A 14-year-old female patient presented to our hospital with complaints of epigastric pain and vomiting. Abdominal computed tomography (CT) revealed a cystic tumor in the pelvis, suspected of ovarian origin. She was admitted to our gynecology department and underwent emergency surgery. The laparoscopic examination revealed that both ovaries were intact and that a primary tumor had developed from the ileal mesentery. Since the patient's condition was not urgent at the time of the gynecological surgery, the procedure was completed by only performing exploratory laparotomy; the patient was admitted to our department after the surgery. Pelvic magnetic resonance imaging performed on the next day revealed a cystic mass measuring 90 × 65mm with a smooth margin and homogeneous signal intensity, arising posterior to the uterus. The mass was suspected as an intestinal duplication cyst. On another day, after the examinations were completed, we resected the portion of the small intestine containing the tumor by laparoscopy. The patient had a successful postoperative course and was discharged on the 5th postoperative day. Histological examination showed that the cyst was lined by stratified squamous epithelium, contained esophageal glands, and had a two-layer muscularis propria. Therefore, a diagnosis of intra-abdominal EDC was performed. An intra-abdominal EDC cyst is relatively rare; this is the first case reported at the distal ileum.