ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
Three types of blood vessel are found: CAPILLARY, VEIN and ARTERY. Capillaries are the smallest and are composed of a thin layer of ENDOTHELIUM. Within tissues capillaries form networks known as CAPILLARY beds to facilitate interactions between blood and tissues. Veins and arteries are larger than capillaries and are both made in much the same way: they have three layers of tissue: an outer layer of connective tissue, an intermediate layer of smooth muscle and an inner layer of endothelium. Arteries always carry blood away from the heart (so the blood tends to be oxygen-rich) while veins always carry blood towards the heart (so veins tend to be oxygen-depleted). Of course, arteries do not narrow in a single step to become capillaries but instead narrow gradually. The intermediate portions are ARTERIOLES. Similarly, when blood is flowing away from capillary beds into veins, they pass through VENULES first, venules being wider than capillaries but narrower than veins. Arteries effectively pump blood through the body, having valves present to facilitate this. The flow is regular but discontinuous, reflecting the pumping of the ventricles: this pumping is effectively measured by taking one's pulse. Veins are less actively involved in moving blood, which tends to drain back to the heart rather than being actively pumped. Bodily movement works to keep blood moving in the veins.
Cardiovascular System and Muscle
George W. Casarett in Radiation Histopathology: Volume II, 2019
The venules, which are about 0.2 to 1.0 mm in diameter, have an intimai layer composed only of endothelium, without subendothelial connective tissue or an internal elastic membrane, a thin medial layer consisting of one to a few layers of muscle cells, and a relatively thick adventitial layer of homogenous connective tissue. In the small and medium-sized veins (1 to 10 mm in diameter) there is sometimes a thin layer of subendothelial connective tissue and sometimes a network of elastic fibers in the intima, the bundles of smooth muscles are separated by collagenous fibers and elastic networks in the media, and there is a relatively thick fibroelastic adventitial layer sometimes containing smooth muscle. In the large veins, e.g., the vena cava, portal vein, and main tributaries, the subendothelial connective tissue is thicker and may contain some bundles of smooth muscle, there is sometimes a thin internal elastic membrane, and the thick adventitial connective tissue layer usually contains bundles of smooth muscle. The valves which appear in many of the small or medium-sized veins are formed by foldings of the intimai layer.
Mechanisms of Fibril Formation and Cellular Response
Martha Skinner, John L. Berk, Lawreen H. Connors, David C. Seldin in XIth International Symposium on Amyloidosis, 2007
Amyloidosis is a progressive cumulative process. All systemic forms of amyloidosis are related to the cardiovascular system and become generalized via the bloodstream, while organ- or tissue-limited isolated amyloidosis is an extravascular phenomenon, not directly related to the systemic circulation and remains a localized process (7). With other words: the production of amyloid precursors connected to the cardiovascular system (for example SAA - serum amyloid A by the hepatocytes, in the liver, or immunoglobulin light chain: λ-chain, κ-chain by B-cells in bone marrow) is potentially always a systemic process; while the local production of immunoglobulin light chains, not related to the cardiovascular system (in case of organ- or tissue-limited plasmacytoma, or B-cell dyscrasia), is a localized one. The histology of amyloid deposits is practically the same in case of systemic AA, or systemic AL-a amyloidosis. The arterioles and small arteries are always involved, and less frequently the extravascular tissue structures of collagen and reticular fibers, or basal lamina (if it is present). The venules and small
Growth factor signaling pathways in vascular development and disease
Published in Growth Factors, 2019
In addition to promoting vessel growth, VEGFA triggers vessel permeability. Src phosphorylation of VE-cadherin in mature vessels in response to VEGFA weakens cell-cell junctions and increases vessel permeability (Schimmel and Gordon 2018; Sun et al. 2012) (Figure 2). Dismantling of VE-cadherin and junctions in response to VEGFA occurs in minutes (Honkura et al. 2018). Live-imaging of dermal vessel responses to VEGFA in vivo showed that VEGFA-induced permeability only occurred in vessels that were negative for the tight junction protein claudin 5 (Honkura et al. 2018). These vessels consisted of venules and certain capillaries, but not arterioles. VEGFA induces vasodilation as well as vessel permeability, but whereas vessel permeability caused by VEGFA is rapid and short lived, vasodilation persists well after its permeabilizing effect has resolved (Honkura et al. 2018). Similar to its function during angiogenesis, VEGFR3 determines vessel sensitivity to the permeabilizing effects of VEGFA by lowering VEGFR2 expression, thereby reducing the responsiveness of EC junctions to the destabilizing effects of VEGFA (Heinolainen et al. 2017).
Microvascular Network and Its Endothelial Cells in the Human Iris
Published in Current Eye Research, 2018
Hongfang Yang, Paula K Yu, Stephen J Cringle, Xinghuai Sun, Dao-Yi Yu
Using the Horton-Strahler’s nomenclature, the human iris vasculature was found to comprise 5.7 ± 0.48 (n = 10) orders of arteries and arterioles, 3 orders of veins and venules, and capillaries connecting the arterial and venous systems. Under close scrutiny, the trunk of arterial trees and venular trees were found to appear in pairs near the iris root. The diameter of each vascular segment is often relatively uniform along its path in the iris stroma. Iris vessel diameter of different vessel orders is shown in Table 2. The diameter of arteries was the greatest at the MAC (104.8 ± 10.64 µm (n = 10)), and decreased gradually with each bifurcation towards pupil margin. The arterial diameter was reduced by about 1/3 with every drop in order, till the pre-capillary artery (A1) with a diameter averaging 12.1 ± 1.10 (n = 10) µm. On the venular side, vessel diameter increased by almost 70% after each confluence of the same order of veins. The post-capillary venule is as narrow as 14.2 ± 1.28 µm (n = 10) and the largest vein is around 40.3 ± 4.56 µm (n = 10). Statistical analysis showed significant differences between diameter of each order of both arteries and veins (One-way ANOVA all with p ≤ 0.001).
Anatomic variations of the human falx cerebelli and its association with occipital venous sinuses
Published in British Journal of Neurosurgery, 2021
Safiye Çavdar, Bilgehan Solmaz, Özgül Taniş, Orhan Ulas Guler, Hakkı Dalçık, Evren Aydoğmuş, Leyla Altunkaya, Erdoğan Kara, Hızır Aslıyüksek
Falx cerebelli, is composed of fibroelastic, dense irregular connective tissue. The connective tissue consisted of cells predominantly of fibroblast which produced the ground substance and collagen fibers. Additionally, the connective tissue contained sensory nerve endings and blood vessels. The arterioles were composed of 1–2 layers of smooth muscle cells in the tunica media and the venules were composed of a single layer of endothelium with many erythrocytes in their lumens (Figure 10a). Furthermore, a large number of lymphatic vessels appeared to be undulated with a single layer of endothelium and a subendothelial layer (Figure 10b). Extravagated lymphocytes surrounding the lymphatic vessels were observed (Figure 10b). Near the vessels, a peripheral nerve characteristically formed a round bundle of nerve processes surrounded by connective tissue sheath perineurium was detected (Figure 10a).
Related Knowledge Centers
- Arteriole
- Basal Lamina
- Microcirculation
- Pericyte
- Vein
- Endothelium
- Connective Tissue
- Capillary
- Blood
- Biological Membrane