The morphometric and immunocytochemical analysis of the human carotid body.
thesisposted on 19.11.2015, 08:51 by Muzaffer. Seker
The carotid bodies are paired organs located at the bifurcation of the common carotid arteries. Together with the aortic bodies they constitute the major arterial chemoreceptors that monitor the partial pressure of oxygen, carbon dioxide, and pH of arterial blood. The carotid body consists of groups of specific cells located in a rich vascular connective tissue including many nerve fibres. The functional unit of the organ: the cell clusters or glomoids, consists of two different cell types, namely the Type I cells and Type II cells. The thesis reviews previous work on the structure of human carotid body (HCB) and experimental studies so far on the organ including histopathological studies. In this thesis the following four types of study are reported: 1-General histology and ultrastructure of the normal human carotid body; 2-Postmortem changes in rat and human carotid bodies, the distribution of Type I cells in different pathological conditions and after different postmortem delays in fixing the tissue; 3-Quantitative studies of the human carotid body using morphometric and stereological techniques in various pathological conditions especially chronic obstructive pulmonary diseases "COPD", Essential hypertension (EH), Diabetes mellitus (DM), Thoracic carcinoma (THC); 4-The analysis of cell constituents of human carotid body using immunocytochemical (ICC) techniques. The following antibodies were studied: Neurofilament (for nervous constituents), S100 protein (for Type II and Schwann cells), Synaptophysin (for Type I cells). Von Willebrand Factor (to outline blood vessels), and Vimentin (for cells of mesencyhmal origin). Their immunoreactivity in different pathological conditions are also discussed. The carotid bodies in experimental animals contain only one variety of Type I cells whilst in the human carotid body three varieties of this cell type have been described (namely light, dark and pyknotic cells). The present study provides data, obtained from different postmortem human material, showing that the three different varieties of Type I cell are the effect of delays in fixation (autolytic changes) on the cell structure. The quantitative study of the distribution of cells, ultrastructural observation, and ICC analysis of the organ all together provide data that to perform an adequate human carotid body study it is essential that specimens should be obtained within 8 hours for light microscopy and immunocytochemistry and within 3 hours for electron microscopy. It has been reported that in chronic hypoxia and EH there is an increase in the size of the organ. The present work confirms these reports and in addition, provides stereological data that DM,THC, and chronic infection also alter HCB structure (hypertrophy and/or hyperplasia). The ICC study of COPD cases shows very variable results: in some cases the classic picture of the structural changes could not be observed whilst in others it was very strong. It was observed that there is an increase in the number of blood vessels and the volume of vasculature in COPD, EH, and DM. The morphological and ICC data presented provide new insight into the structure of human carotid body and advance the postmortem study of the organ. The changes in the structure of the human carotid body in different pathological conditions also provide better understanding of the condition of the organ in health and disease. It is also postulated that the previous experimental animal studies which were exposed to "long term hypoxic conditions" may not have been sufficiently exposed. This is essential to obtain similar structural changes that match human observations. It might be interesting to study much longer periods of hypoxia on experimental animals in order to see whether these longer exposures result ultimately in Type II cell hyperplasia.