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The fine structure of human digital arterio-venous anastomoses (Hoyer-Grosser's organs)
Insights
This study details the microanatomy of Hoyer-Grosser's organs in human digits, revealing the structure of arteriovenous (AV) anastomoses and associated nerve networks. Findings clarify the cellular composition and innervation of these vascular structures.
Area of Science:
- Vascular Biology
- Dermatology
- Microanatomy
Background:
- Hoyer-Grosser's organs are specialized arteriovenous (AV) anastomoses in digital skin.
- Their detailed microstructural organization and innervation remain incompletely understood.
Purpose of the Study:
- To elucidate the fine structure of Hoyer-Grosser's organs in human digital biopsies.
- To characterize the endothelial cells, smooth muscle cells, and nerve supply within these vascular structures.
Main Methods:
- Human digital biopsies were examined using electron microscopy.
- Detailed ultrastructural analysis of arterial and venous segments of AV canals was performed.
Main Results:
- Endothelial cells in AV canals contain abundant Weibel-Palade bodies.
- Ramified smooth muscle cells (RSM) form the epithelioid zone, with variations in myofilament content.
- Nerve fibers, including unmyelinated axons and potential sensory terminals, innervate the adventitia.
Conclusions:
- The study provides a detailed ultrastructural description of Hoyer-Grosser's organs.
- RSM exhibit diverse forms, likely correlating with light microscopic epithelioid cells.
- The innervation suggests a role in regulating blood flow and sensory perception.
Abstract:
Hoyer-Grosser's organs were studied in human digital biopsies. The fine structure of both the supplying arteries and collecting veins was found to be inconspicuous. Endothelial cells in the AV canals form a continuous layer. They are characterized by their rich content of specific organelles (Weibel-Palade bodies), especially in the venous segments. The epitheloid zone is composed of a variety of ramified smooth muscle cells (RSM). These appear either dense, when well provided with bundles of myofilaments, or clear, when including only a few myofilaments. The nuclei of dense RSM show condensed chromatin, while those of clear RSM are larger with loose chromatin texture. In addition, all transitional forms occur. Cell organelles are rarely seen within all types of RSM. The cytoplasmic processes reach other as well as endothelial cells. The preservation of our material did not allow observation of specialized membrane contacts in these zones. All RSM are invested with a regular basal lamina and well provided with surface vesicles. Profiles of free basal lamina material and faint collagen (argyrophil) fibers are seen in the wide intercellular spaces. RSM poor in myofilaments are interpreted to represent "epitheloid cells" of light microscopy. Their number constantly decreases from the arterial segment of the AV canal to the venous segment. Here the cytoplasmic processes of RSM become less pronounced and the wall of the anastomotic segment continuously changes to that of the collecting vein. Dense RSM rich in myofilaments are compared with pacemaker cells found inthe ureter. Both internal and external elastic membranes are absent in AV canals. A dense network of unmyelinated nerve fibers is found in the adventitial layer of the AV canal, especially in its arterial segment. The axons branch out from small dermal nerves which also contain two or three myelinated axons. The myelin sheaths terminate where the axons reach the adventitia of the AV canals. Axon varicosities filled with mitochondria are thought to be terminals of myelinated axons and are interpreted as receptory. Axon varicosities with synaptic-type vesicles are assumed to be terminals of sympathetic and para sympathetic fibers. All axon profiles are confined to the adventitial layer of the anastomotic segment.