Bilateral Renal Agenesis

Ectopic Ureter

Mesenchyme to an epithelium for nephron formation is also mediated by the ureteric buds, in part through modification of the extracellular matrix. Thus fi-bronectin, collagen I, and collagen III are replaced with laminin and type IV collagen, characteristic of an epithelial basal lamina Fig. 14.7B . In addition, the cell adhesion molecules syndecan and E-cadherin, which are essential for condensation of the mesenchyme into an epithelium, are synthesized. Regulatory genes for conversion of the...

Development Of The Interventricular Septum

Endocardial Cushion Defect

Figure 11.16 Formation of the septum in the atrioventricular canal. A. From left to right, days 23, 26, 31, and 35. The initial circular opening widens transversely. B and C. Scanning electron micrographs of hearts from mouse embryos, showing growth and fusion of the superior and inferior endocardial cushions in the atrioventricular canal. In C, cushions of the ouflow tract arrow are also fusing. Figure 11.16 Formation of the septum in the atrioventricular canal. A. From left to right, days 23,...

Urethra Masculina

Androgen Insensitivity Syndrome

Figure 14.36 Development of the external genitalia in the female at 5 months A and in the newborn B . 14.36A urethral folds do not fuse, as in the male, but develop into the labia minora. Genital swellings enlarge and form the labia majora. The urogenital groove is open and forms the vestibule Figs. 14.34C and 14.36B . Although the genital tubercle does not elongate extensively in the female, it is larger than in the male during the early stages of development Fig. 14.34, A and B . In fact,...

Sulcus Of The Heart

Heart Tube Mouse Embryo

Dorsal view of a late presomite embryo approximately 18 days after removal of the amnion. Prospective myoblasts and hemangioblasts reside in the splanchnic mesoderm in front of the neural plate and on each side of the embryo. B. Transverse section through a similar-staged embryo to show the position of the blood islands in the splanchnic mesoderm layer. C. Cephalocaudal section through a similar-staged embryo showing the position of the pericardial cavity and cardiogenic field....

Clinical Correlates

Klinefelter Syndrome Birth Defects

Birth Defects and Spontaneous Abortions Chromosomal and Genetic Factors Chromosomal abnormalities, which may be numerical or structural, are important causes of birth defects and spontaneous abortions. It is estimated that 50 of conceptions end in spontaneous abortion and that 50 of these Figure 1.4 Events occurring during the first and second maturation divisions. A. The primitive female germ cell primary oocyte produces only one mature gamete, the mature oocyte. B. The primitive male germ...

Lateral Folding Of The Embryo

Embryo Liver Bud Lung

Remnant of the buccopharyngeal membrane Figure 5.16 Sagittal midline sections of embryos at various stages of development to demonstrate cephalocaudal folding and its effect on position of the endoderm-lined cavity. A. Presomite embryo. B. Embryo with 7 somites. C. Embryo with 14 somites. D. End of the first month. Note the angiogenic cell clusters in relation to the buccopharyngeal membrane. Amnionic cavity Surface ectoderm Amnionic cavity Surface ectoderm Figure 5.17 Transverse sections...

Environmental Factors

Fetal Alcohol Syndrome Vulva

Until the early 1940s it was assumed that congenital defects were caused primarily by hereditary factors. With the discovery by Gregg that German measles affecting a mother during early pregnancy caused abnormalities in the embryo, it suddenly became evident that congenital malformations in humans could also be caused by environmental factors. In 1961 observations by Lenz linked limb defects to the sedative thalidomide and made it clear that drugs could also cross the placenta and produce birth...

Human Blastocyst

Bilaminar Disc Epiblast

At the eighth day of development, the blastocyst is partially embedded in the endometrial stroma. In the area over the embryoblast, the trophoblast has differentiated into two layers a an inner layer of mononucleated cells, the cytotrophoblast, and b an outer multinucleated zone without distinct cell boundaries, the syncytiotrophoblast Figs. 3.1 and 3.2 . Mitotic figures are found in the cytotrophoblast but not in the syncytiotrophoblast. Thus, cells in the cytotrophoblast divide and migrate...