arteriole

Examples of arteriole in the following topics:

• Arterioles

  • An arteriole is a small diameter blood vessel in the microcirculation system that branches out from an artery and leads to capillaries.
  • An arteriole is a small-diameter blood vessel which forms part of the microcirculation that extends from an artery and leads to capillaries.
  • The microcirculation involves the flow of blood in the smallest blood vessels, including arterioles, capillaries, and venules.
  • Arterioles have muscular walls that usually consist of one or two layers of smooth muscle.
  • Arterioles are part of the microcirculation system, along with capillaries, arteries, veins, venules, and tissue cells.

• Local Regulation of Blood Flow

  • Blood flow is regulated locally in the arterioles and capillaries using smooth muscle contraction, hormones, oxygen, and changes in pH.
  • As such arterioles are the main part of the circulatory system in which local control of blood flow occurs.
  • Arterioles contain smooth muscle fibers in their tunica media, which allows for fine control of their diameter.
  • Pulmonary arterioles are a noteworthy exception as they vasodilate in high oxygen.
  • Brain arterioles are particularly sensitive to pH, with reduced pH promoting vasodilation.

• Supply of Blood and Nerves to the Kidneys

  • The renal arteries split into several segmental arteries upon entering the kidneys, which then split into several arterioles.
  • These afferent arterioles branch into the glomerular capillaries, which facilitate fluid transfer to the nephrons inside the Bowman's capsule, while efferent arterioles take blood away from the glomerulus, and into the interlobular capillaries, which provide tissue oxygenation to the parenchyma of the kidney.
  • The renal plexus are the source of nervous tissue innervation within the kidney, which surround and primarily alter the size of the arterioles within the renal cortex.
  • Input from the sympathetic nervous system triggers vasoconstriction of arterioles in the kidney, thereby reducing renal blood flow into the glomerulus.
  • The kidney also receives input from the parasympathetic nervous system, by way of the renal branches of Vagus nerve (Cranial nerve X), which causes vasodilation and increased blood flow of the afferent arterioles.

• Muscular Arteries

  • Muscular or distributing arteries are medium-sized arteries that draw blood from an elastic artery and branch into resistance vessels, including small arteries and arterioles.
  • The splenic artery branches off to the stomach and pancreas before reaching the spleen and gives rise to arterioles that directly supply capillaries of these organs.

• Glomerular Filtration

  • Blood plasma enters the afferent arteriole and flows into the glomerulus, a cluster of intertwined capillaries.
  • The size of the filtration slits restricts the passage of large molecules (eg, albumin) and cells (eg, red blood cells and platelets), which are the non-filterable component of blood, which then leave the glomerulus through the efferent arteriole, which becomes capillaries meant for kidney oxygen exchange and reabsorption before becoming venous circulation.
  • Diagram showing the afferent and efferent arterioles bringing blood in and out of the Bowman's capsule, a cup-like sac at the beginning of the tubular component of a nephron.

• Blood Pressure

  • Blood flows to the arterioles (smaller arteries) where the rate of flow is slowed by the narrow openings of the arterioles.
  • Throughout the cardiac cycle, the blood continues to empty into the arterioles at a relatively even rate.
  • Blood pressure is related to the blood velocity in the arteries and arterioles.

• Capillaries

  • Capillaries form a network through body tissues that connects arterioles and venules and facilitates the exchange of water, oxygen, carbon dioxide, and many other nutrients and waste substances between blood and surrounding tissues.
  • A capillary bed can consist of two types of vessels: true capillaries, which branch mainly from arterioles and provide exchange between cells and the circulation, and vascular shunts, short vessels that directly connect arterioles and venules at opposite ends of the bed, allowing for bypass.
  • When blood pressure increases, the arterioles that lead to the capillary bed are stretched and subsequently constrict to counteract the increased tendency for high pressure to increase blood flow.

• Regulation of Glomerular Filtration Rate

  • The increased blood volume with its higher blood pressure will go into the afferent arteriole and into the glomerulus, resulting in increased GFR.
  • Pressure changes within the afferent and efferent arterioles that go into and out of the glomerulus itself, will also impact GFR.
  • Vasodilation in the afferent arteriole and vasconstriction in the efferent arteriole will increase blood flow (and hydrostatic pressure) in the glomerulus and will increase GFR.
  • Conversely, vasoconstriction in the afferent arteriole and vasodilation in the efferent arteriole will decrease GFR.

• Glomerular Diseases

  • A glomerulus receives its blood supply from an afferent arteriole of the renal circulation.
  • Unlike most other capillary beds, the glomerulus drains into an efferent arteriole rather than a venule.
  • The resistance of these arterioles results in high pressure within the glomerulus.

• Distribution of Blood

  • Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries and small arterioles.
  • Vasodilation refers to the widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large veins, large arteries, and smaller arterioles.
  • Therefore, dilation of arterial blood vessels (mainly the arterioles) causes a decrease in blood pressure.