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Biomedical subjects

R O'Rahilly

Publications and source records attributed to R O'Rahilly.

15 recordsLinked to original sources
PubMed1991

Development of anencephaly and its variants.

Extreme variants of anencephaly in two human embryos of the same stage, namely 22 (54 days), shed new light on problems such as craniocerebral interrelationships and the timing of developmental events. Embryo X had a chondrocranium that possessed features typical of a holoacranial anencephalic skull and an extremely well-preserved brain, in which some of the neural tracts were comparable to those in a normal control. On the other hand, embryo Y of the same stage had a completely degenerated brain, although the chondrocranium was more nearly normal and represented the precursor of a meroacranial skull. A comparison of the two cases seems to indicate a certain independence between skull and brain. Moreover, it appears possible that the disturbances are related primarily to the skeletal, and only secondarily to the nervous, component. Comparisons with experimental data allow the conclusion that the maldevelopment involves mostly paraxial mesenchyme and little or no disturbance of neural crest. The timing of the mesenchymal defect is probably as early as stages 8 and 9 (18-20 days). This is also the time at which mesenchymal defects can result in failure of the neural tube to close.

Abnormalities, Multiple↗
PubMed1979

Early human development and the chief sources of information on staged human embryos.

In a brief historical survey, the importance of Wilhelm His, senior, to human embryology is emphasized. He provided the impetus to Mall to establish the Carnegie Embryological Collection, which serves as a 'Bureau of Standards' for early human development. The Carnegie system of 23 stages for the embryonic period proper (first 8 postovulatory wk) is outlined, and some common misusages are noted. Finally, because of the difficulty in tracking down data based on staged human embryos, an annotated list of more than 40 key references is provided.

Embryology↗
PubMed1979

The initial development of the human brain.

An account of the early development of the human brain has been prepared from the data available for the Carnegie Collection, as well as from published information from other sources. Although the site of the neural plate can be discerned at stage 7, the first visible indication of the nervous system is the neural groove in certain embryos of stage 8, in which the embryonic disc measures more than 1 mm and the notochordal process at least 0.3 mm. The progressive fusion of the neural folds during stage 10, and the closure of the rostral and caudal neuropores at stages 11 and 12, respectively, are detailed with further precision than hitherto. It is emphasized that the major subdivisions of the human brain do not begin as vesicles, but as enlargements of the open neural folds at stage 9. The relationships of the neuromeres to the otic region, the somites, and the neural crest are clarified and illustrated. The early appearance of the telencephalon medium (before cerebral vesicles have formed) is stressed, and the terminological implications for the subdivisions of the brain are discussed.

Brain↗
PubMed1979

Types of neural cells in the spinal ganglia of human embryos and early fetuses.

Spinal ganglial of human embryos and fetuses ranging in C.-R. length from 15 to 74 mm and in age from 6 1/2 to 11 postovulatory weeks were studied by light and electron microscopy. A sequence of events in differentiation and maturation enabled five types of cells to be distinguished: 1. apolar, undifferentiated neuroblasts are the main cells at 6 1/2 to 7 1/2 weeks; 2. early bipolar neuroblasts (strictly speaking, types 2 to 5 are immature neurons) predominate at the end of the embryonic period proper (8 postovulatory weeks); 3. intermediate bipolar neuroblasts are characteristic of the early fetal period; 4. late bipolar neuroblasts, in which two proceses arise separately from one pole of the cell, appear at about 10 postovulatory weeks; 5. unipolar neuroblasts are found within another week and, by that time, cells of types 1 and 2 are no longer present.

Cell Differentiation↗
PubMed1978

The timing and sequence of events in the development of the human digestive system and associated structures during the embryonic period proper.

A documented scheme of the early development of the human digestive system is presented. It is based on (1) reports of workers who personally studied staged embryos, and (2) personal observations and confirmations. The necessity of studying staged embryos in order to determine the precise sequence of developmental events is stressed.

Digestive System↗
PubMed1977

The assessment of prenatal age from the crown-rump length determined ultrasonically.

Crown-rump lengths determined ultrasonically in vivo and in utero in cases of known postovulatory age (33-86 days) agree well with those in length/age tables in current embryological usage. Within the embryonic period proper, however, for a given age, the ultrasonic lengths are usually 1 to 5 mm longer than those of fixed specimens. The probable reasons for this are discussed.

Body Height↗
PubMed1976

The onset of ossification in the human calcaneus.

A (silver) radiographic and microscopic study of the onset of ossification in the calcaneus of 177 human fetuses between 49 and 150 mm C.-R. length has revealed the presence of two independent and developmentally different ossific sites. A lateral locus, intramembranous (parachondral) in origin and precocious in appearance, was observed in slightly over 16% of the fetuses examined between 93 mm (the first appearance of this bone) and 150 mm C.-R. It occupied the vascular connective tissue within the anterior portion of a distinct groove on the inferolateral wall of the cartilaginous calcaneus between the retrotrochlear eminence anterosuperiorly, and the lateral process of the tuber posteroinferiorly. A centrally situated, primary ossific centre, endochondral in origin, was detected in only 11% of the fetuses between 118 mm (the initial appearance of this centre) and 150 mm C.-R. It was situated in the centre of the anterior third of the cartilaginous calcaneus in relation to the sustenaculum tali medially and to a distinct cartilaginous prominence on its lateral surface. Only four fetuses possessed both ossific sites (lateral and central): at 122, 143, 145, and 150 mm C.-R., and in only one of these was continuity established between them. One fetus (122 mm) possessed two independent endochondral centres (superior and inferior).

Calcaneus↗
PubMed1976

The nerve supply and conducting system of the human heart at the end of the embryonic period proper.

The nerve supply and conducting system were studied in a stage 23 human embryo of exceptional histological quality. The nerves on the right side arose from cervical sympathetic and from cervical and thoracic vagal filaments. Out of their interconnexions vagoxympathetic nerves emerged, which (1) sent a branch in front of the trachea to the aorticopulmonary ganglion, thereby supplying arterial and venous structures, and (2) formed the right sinal nerve, which supplied the sinu-atrial node, and gave filaments to the interatrial septum which could be traced to the atrioventricular node and pulmonary veins. The nerves on the left side arose similarly from cervical sympathetic and from cervical and thoracic vagal filaments. These formed several descending, ganglionated, vagosympathetic filaments that descended to the right of the arch of the aorta and entered the aorticopulmonary ganglion. Filaments leaving the ganglion supplied the pulmonary trunk, ascending aorta, interatrial septum, pulmonary veins, and, as the left sinal nerve, the fold of the left vena cava. The thoracic vagal filaments descended to the left of the arch of the aorta and supplied chiefly the arterial end of the heart. No thoracic sympathetic cardiac filaments were found. The sinu-atrial node began as a crescentic mass in front of the lower part of the superior vena cava. It gradually extended on each side of the superior vena cava and came to form its posterior wall at a more caudal level. The atrial myocardium that formed the septum spurium, venous valves, and interatrial septum could be traced from the sinu-atrial to the atrioventricular node. Myocardium also encircled the atrial aspects of the atrioventricular orifices, and could be traced caudally to the atrioventricular nde. The atrioventricular node was a conspicuous mass in the anterior and lower part of the interatrial septum, from which a clearly defined bundle left to enter the interventricular septum. Right and left limbs were observed, the former being a rounded bundle that passed immediately in front of the root of the aorta.

Atrioventricular Node↗
PubMed1975

The Dandy-Walker and Arnold-Chiari malformations. Clinical, developmental, and teratological considerations.

Five patients with the Dandy-Walker syndrome had dysgenesis of the cerebellar vermis, cystic dilatation of the fourth ventricle, and a high position of the tentorium cerebelli. When only these features are present, the patient may lead a normal life. Additional defects usually account for the prominent clinical and pathological features of this syndrome. In this series, one patient had aqueductal stenosis, four had agenesis of the corpus callosum, two had hydrocephalus, one had cerebral abiotrophy, and one (a 72-year-old man) had no additional defects and no symptoms from his Dandy-Walker syndrome. An analysis of development and teratological considerations indicates that the Dandy-Walker and Arnold-Chiari malformations are complex disorders that have different causes and mechanisms and begin at different times in the emryonic period. The causes are still unknown.

Adolescent↗