Duplications of the alimentary tract
Prem Puri in Newborn Surgery, 2017
The most satisfactory of several theories of the origin of GI duplications is that relating to the development of the neurenteric canal. Saunders,15 in 1943, noted that thoracic duplications are frequently associated with abnormalities of the cervical and thoracic vertebrae. These duplications may be attached to the vertebral bodies or connected to the spinal canal. These findings gave rise to the Bentley and Smith split-notochord theory.16–18 The embryo initially has two layers: ectoderm and endoderm. Mesoderm forms between the two, but for a short time, these two layers remain adherent. A transient opening (the notochordal plate) appears, connecting the neural ectoderm with the intestinal endoderm. This notochordal plate normally migrates dorsally and becomes “pinched” off from the endoderm by the ingrowth of mesodermal cells from each side. If the notochordal plate fails to migrate as a result of adhesions to the endodermal lining, the spinal canal cannot close ventrally, and a tract resembling a diverticulum is established with the primitive gut. This tract may remain open, leaving a fistula between the gut and the spinal canal, or close, leaving only a fibrous tract. However, in the majority of cases, it disappears completely, leaving only the duplication of the GI tract. This theory explains the formation of thoracic and caudal duplications, which may be associated with vertebral anomalies. However, the absence of spinal defects in many alimentary tract duplications makes this theory less tenable as a unifying model of their origin.
The Many Faces of Neoplasia
Jeremy R. Jass in Understanding Pathology, 2020
The majority of cancers may be ascribed to one of the three cancer types: carcinoma, sarcoma and lymphoma. This classification has an embryological basis. When an ovum is fertilised by a sperm, the result is a single cell or zygote (from the Greek word meaning joined together). The zygote carries the potential to form all the cells of the body. At first this totipotential cell divides to form two, then four, then eight cells and so on. At this early stage the ball of cells may be disaggregated and could in theory form a clone of two, four, eight or sixteen identical individuals. The embryo starts to form when groups of cells become committed to a particular line of tissue differentiation, of which there are three major types. Ectoderm forms the skin and nervous system, endoderm forms the epithelial lining of internal hollow organs (e.g. gut) and associated glandular organs (e.g. liver and pancreas), and mesoderm forms all the rest (muscle, bone, bone marrow, cartilage, lymphoid system and connective tissue). As a general rule carcinomas arise from ectoderm or endoderm, whereas sarcomas and lymphomas arise from mesoderm.
Anatomy
Peter Sagar, Andrew G. Hill, Charles H. Knowles, Stefan Post, Willem A. Bemelman, Patricia L. Roberts, Susan Galandiuk, John R.T. Monson, Michael R.B. Keighley, Norman S. Williams in Keighley & Williams’ Surgery of the Anus, Rectum and Colon, 2019
Defective midgut embryological development accounts for a variety of abnormalities of location and fixation of the colon (from aberrant rotation); intestinal atresias and stenoses (from imbalances in the relative amounts of cell proliferation and apoptosis in the endoderm tube) and persistence of vestigial structures (e.g. Meckel’s diverticulum). With the exception of rotational abnormalities (which cover a wide spectrum, ranging from complete non-rotation or reversed rotation to varying degrees of malrotation), midgut anomalies tend to primarily interfere with small intestinal development and are therefore not covered in detail here. The vast majority of hindgut developmental anomalies are located in the anorectal region and result typically from failure of normal development of the urorectal septum.
The mesentery: an ADME perspective on a ‘new’ organ
Published in Drug Metabolism Reviews, 2018
Aneesh A. Argikar, Upendra A. Argikar
The development of mesentery during and after the embryonic stage has been covered in great detail elsewhere (Martini and Tallitsch 2014). To summarize the embryonic development, the endoderm forms the hindgut and the foregut. During the initial months of the embryo, the gut is just a simple tube. This simple digestive tube is suspended by the mesentery. After gradually disappearing, the ventral mesentery remains in two places, on the ventral surface of the stomach known as lesser omentum and between the liver and anterior abdominal wall known as falciform ligament. The lesser omentum provides stability to the stomach and also provides a way for the blood vessels and other structures to enter and leave the liver. As the embryo grows, the dorsal mesentery enlarges and forms a pouch called the greater omentum. The literature on the expression of enzymes and transporters in the embryonic and fetal mesentery was not available.
Tissue engineering approaches and generation of insulin-producing cells to treat type 1 diabetes
Published in Journal of Drug Targeting, 2023
Mozafar Khazaei, Fatemeh Khazaei, Elham Niromand, Elham Ghanbari
The pancreas and liver develops embryonically from the endoderm appendages. Later, the liver and pancreas were separated during organogenesis; both organs had multipotent cells capable of producing both hepatic and pancreatic cell lineages. This common embryonic origin raises the interesting speculation that liver cells may convert to pancreatic Endocrine cells (ECs) (Figure 3). Previous investigations have shown that biliary epithelial cells and foetal or adult hepatocyte are able of reprogramming into IPCs by stimulating the endocrine pancreas-specific gene expression. In vivo results indicated that these hepatic cell-derived IPCs might reduce hyperglycaemia after being implanted into diabetic mice. When these livers cell-derived IPCs were implanted into diabetic mice, the in vivo results indicated that they could reduce hyperglycaemia [113–117].
Advances in understanding vertebrate nephrogenesis
Published in Tissue Barriers, 2020
Joseph M. Chambers, Rebecca A. Wingert
Vertebrate development entails the formation of three germ layers, the ectoderm, mesoderm, and endoderm, which provide cellular blueprints for embryonic organogenesis. Ectoderm gives rise to the central nervous system and skin cells, and endoderm derivatives encompass cells that line the respiratory and digestive tracts. The mesoderm, or middle layer, produces cells that are most abundant in the human body constituting skeletal muscle, cartilage, heart, gonads, and blood, among other tissue types.1 This review will focus on a member of the mesoderm lineage: the kidney. Much of our understanding about kidney development stems from rodent models, but also has benefited from studies in other vertebrates such as fish, frogs, and birds.2The inception of mesoderm development begins with the differentiation of pluripotent epiblast cells into a transient ‘primitive streak’ zone.1Position along the anterior-posterior embryonic axis and other instructive signals regulate the regionalization of paraxial, intermediate, and lateral plate mesoderm.3