On the welcome page of the dictionary, three major sections are shown: Normal tissues, Cancer and Cell structure. Below the image of each section are links to introductory texts for i) normal tissue histology, ii) hallmarks of cancer, and iii) cell structure overview. For the cancer-section there is also a link to current cancer statistics (incidence, survival, etc) for Sweden and the rest of the world. Within each section there are direct links to histology descriptions of different tissue types and tumor forms as well as descriptions of cell structures.
For the 'Tissue & cell types' and 'Tumor' sections, tissue-slides stained with hematoxylin and eosin (HE) are shown at three different levels of magnification. On the top level, an overview of the whole tissue-sample is shown with boxes in black indicating where zoomed-in representative parts of the tissue are available for viewing. Clicking on these boxes will zoom in on that part to show tissue structures, cells and features in greater detail. Throughout these sections, arrows indicate relevant tissue structures, cell-types and other features.
For the 'Cell structure' section, immunofluorescent images of formaldehyde-fixed cell lines are shown. The various cell structures that are demonstrated are always shown in the green channel using an antibody found in the Human Protein Atlas. The antibody name is linked to the subcellular location summary page of the target gene. The other channels: nucleus, microtubules and endoplasmic reticulum, are always shown in the blue, red and yellow channels, respectively. The channels can be toggled on and off by clicking on the respective coloured button above the image. When applicable, the immunofluorescent images are complemented by immunohistochemically stained cells where the location of the particular cell structure is shown in brown.
A common feature for all sections is that a general descriptive text about the tissue, tumor-type or cell structure is provided when browsing a particular topic.
The lymphatic system forms the immunological fundament for the body?s defense system. A circulating pool of lymphocytes ensures a continuous immunologic surveillance of the entire body in order to protect against harmful invasion. These cells circulate between various lymphoid tissues, and the lymph and bloodstream. When certain lymphoid cells come in contact with their determined target antigens, these cells return to the lymphatic tissue to differentiate and proliferate.
Lymph vessels are present throughout the body and convey fluid from the extracellular space to eventually return the fluid to the vascular system. The walls of lymph capillaries are permeable and allow for the passage of relatively large substances such as cells and bacterial antigens into the lymphatic flow. As the lymph passes through lymph nodes, monitoring cells are able to detect antigens and initiate immune responses.
Lymph nodes are aggregates of lymphocytes organized in a reticular network consisting of reticular cells and reticular fibers enclosed by a dense connective tissue capsule. From the capsule connective tissue trabeculae penetrate into the organ. The lymph nodes receive lymph fluid through afferent lymph vessels. The lymph then passes through subcapsular sinuses, trabecular sinuses, medullary sinuses to eventually exit through an efferent lymph vessel. The sinuses within the lymph node are not open vascular spaces, instead cellular processes from surrounding macrophages and reticular cells intersect them, hampering flow through the node and enhancing filtration of lymph fluid and antigen detection. The sinuses are visible as white spaces within the lymph node.
Underlying the capsule is a darkly stained region termed the cortex, the center of the lymph node is termed the medulla, and stains lighter. The cortex is divided into a superficial and a deep cortex. Within the superficial cortex multiple spherical aggregations of lymphocytes are present. Aggregations of only small, dark lymphocytes are termed primary follicles. If the central region contains larger, paler cells they are termed secondary follicles. Secondaryfollicles are formed when a lymphocyte that has recognized its antigen returns to a primary follicle and starts proliferating, to form a germinalcenter. The less dark staining of immature B-cells is due to the less densely packed euchromatin in the corresponding cell nuclei. Lymph follicles are absent in the deep cortex, which is composed mainly of T-cells.
