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,...

Abembryonic Pole

Decidual Lining Uterus Pregnancy

Figure 6.8 Structure of villi at various stages of development. A. During the fourth week. The extraembryonic mesoderm penetrates the stem villi in the direction of the decidual plate. B. During the fourth month. In many small villi the wall of the capillaries is in direct contact with the syncytium. C and D. Enlargement of the villus as shown in A and B, respectively. on the opposite side of the uterus and the two fuse Figs. 6.10 to 6.12 , obliterating the uterine lumen. Hence the only portion...

Monozygotic Twins

Conjoined Twins Cells Split

The second type of twins, which develops from a single fertilized ovum, is monozygotic, or identical, twins. The rate for monozygotic twins is 3 to 4 per 1000. They result from splitting of the zygote at various stages of development. The earliest separation is believed to occur at the two-cell stage, in which case two separate zygotes develop. The blastocysts implant separately, and each embryo has its own placenta and chorionic sac Fig. 6.18A . Although the arrangement of the membranes of...

Urethra Masculina

Adrenogenital Sindrom

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,...

Descent Of The Testes

Fascia The Peritoneal Cavity

Toward the end of the second month, the urogenital mesentery attaches the testis and mesonephros to the posterior abdominal wall Fig. 14.3 A . With degeneration of the mesonephros the attachment serves as a mesentery for the gonad Fig. 14.28B . Caudally it becomes ligamentous and is known as the caudal genital ligament Fig. 14.40A . Also extending from the caudal pole of the testis is a mesenchymal condensation rich in extracellular matrices, the guber-naculum Fig. 14.40 . Prior to descent of...

Sulcus Of The Heart

Cardiac Tube Formation Splanchnic

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...

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Human Circulation After Birth

Figure 11.48 Human circulation after birth. Note the changes occurring as a result of the beginning of respiration and interruption of placental blood flow. Arrows, direction of blood flow. Figure 11.48 Human circulation after birth. Note the changes occurring as a result of the beginning of respiration and interruption of placental blood flow. Arrows, direction of blood flow. The lymphatic system begins its development later than the cardiovascular system, not appearing until the fifth week of...

Lateral Folding Of The Embryo

Cephalocaudal Folding

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...

Neurocranium

Grow Neurocranium Bones

The neurocranium is most conveniently divided into two portions a the membranous part, consisting of flat bones, which surround the brain as a vault and b the cartilaginous part, or chondrocranium, which forms bones of the base of the skull. The membranous portion of the skull is derived from neural crest cells and paraxial mesoderm as indicated in Figure 8.3. Mesenchyme from these two sources invests the brain and undergoes membranous ossification. The result is formation of a number of flat,...

Environmental Factors

Thalidomide Infants

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...