hiussuonten

Hiussuonten is the Finnish term for capillaries, the smallest blood vessels in the circulatory system that form the microcirculation between arterioles and venules. They are key sites of exchange, allowing oxygen, carbon dioxide, nutrients, and waste products to move between blood and surrounding tissues.

Structure and types: Capillary walls consist mainly of a single layer of endothelial cells, supported by a basement membrane, and in many tissues are associated with pericytes. Their small diameter, typically around 5 to 10 micrometers, forces red blood cells to pass in single file. Capillaries are commonly categorized into three main types: continuous capillaries, which have uninterrupted endothelial lining; fenestrated capillaries, which contain small pores to enhance exchange; and sinusoidal (discontinuous) capillaries, which have larger gaps and a more porous lining found in organs such as the liver and bone marrow. The specific structure and permeability of capillaries vary by tissue to meet local functional needs.

Function and physiology: The primary role of hiussuonten is to mediate exchange between blood and tissues. Gases, glucose, amino acids, and other small molecules diffuse across the endothelial barrier, while larger molecules may be transported by vesicular mechanisms. Pericytes contribute to capillary stability and, in some areas such as the brain, help form the blood–brain barrier. Capillary density and flow dynamics adapt to metabolic demand, exercise, and tissue growth or repair.

Clinical relevance: Capillary function and density are altered in various diseases. Microvascular dysfunction is observed in diabetes and hypertension and can contribute to retinopathy, nephropathy, and poor wound healing. Inflammation increases capillary permeability, aiding leukocyte movement into tissues.

Development and regulation: Capillary formation is driven by angiogenic signals such as VEGF and modulated by Notch signaling, with remodeling influenced by tissue growth, injury, and systemic factors.