World Library  
Flag as Inappropriate
Email this Article

Arteriole

Article Id: WHEBN0000479444
Reproduction Date:

Title: Arteriole  
Author: World Heritage Encyclopedia
Language: English
Subject: Artery, Arteriolosclerosis, Capillary, Venule, Blood vessel
Collection: Angiology
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Arteriole

Arteriole
Simplified illustration of capillary system - arteries give rise to arterioles, venules from capillaries form veins.
Rabbit arteriole at 100X
Details
Latin arteriola
Anatomical terminology

An arteriole is a small diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries.[1]

Arterioles have muscular walls (usually only one to two layers of smooth muscle) and are the primary site of vascular resistance. The greatest change in blood pressure and velocity of blood flow occurs at the transition of arterioles to capillaries. The decreased velocity of flow in the capillaries reduces the pressure and increases exchange of gas and nutrients. Arterioles receive autonomic nervous system innervation and respond to various circulating hormones in order to regulate their diameter. Retinal vessels lack a functional sympathetic innervation.[2] Further local responses to stretch, carbon dioxide, pH, and oxygen also influence arteriolar tone. Generally, norepinephrine and epinephrine (hormones produced by sympathetic nerves and the adrenal gland medulla) are vasoconstrictive acting on alpha 1-adrenergic receptors. However, the arterioles of skeletal muscle, cardiac muscle, and pulmonary circulation vasodilate in response to these hormones when they act on beta-adrenergic receptors. Generally, stretch and high oxygen tension increase tone, and carbon dioxide and low pH promote vasodilation. Pulmonary arterioles are a noteworthy exception as they vasodilate in response to high oxygen. Brain arterioles are particularly sensitive to pH with reduced pH promoting vasodilation. A number of hormones influence arteriole tone such as angiotensin II (vasoconstrictive), endothelin (vasoconstrictive), bradykinin (vasodilation), atrial natruretic peptide (vasodilation), and prostacyclin (vasodilation).

Blood pressure in the arteries supplying the body is a result of the work needed to pump the cardiac output (the flow of blood pumped by the heart) through the vascular resistance, usually termed total peripheral resistance by physicians and researchers. An increase in the media to lumenal diameter ratio has been observed in hypertensive arterioles (arteriolosclerosis) as the vascular wall thickens and/or lumenal diameter decreases.

Contents

  • Physiology 1
  • Clinical relevance 2
    • Disease 2.1
      • Arteriosclerosis 2.1.1
      • Arteritis 2.1.2
    • Medication 2.2
  • Metarterioles 3
  • See also 4
  • References 5

Physiology

The up and down fluctuation of the arterial blood pressure is due to the pulsatile nature of the cardiac output and determined by the interaction of the stroke volume versus the volume and elasticity of the major arteries.

In a healthy vascular system the endothelium lines all blood-contacting surfaces, including arterioles, arteries, veins, capillaries, and heart chambers. This healthy condition is promoted by the ample production of nitric oxide by the endothelium, which requires a biochemical reaction regulated by a complex balance of polyphenols, various nitric oxide synthase enzymes and L-arginine. In addition there is direct electrical and chemical communication via gap junctions between the endothelial cells and the vascular smooth muscle.

Clinical relevance

Arteriole diameters decrease with age and with exposure to air pollution.[3] [4]

Disease

Any pathology which constricts blood flow, such as stenosis, will increase total peripheral resistance and lead to hypertension.

Arteriosclerosis

Arteriolosclerosis is the term specifically used for the hardening of arteriole walls. This can be due to decreased elastic production from fibrinogen, associated with ageing, or hypertension or pathological conditions such as atherosclerosis.

Arteritis

Medication

The muscular contraction of arterioles is targeted by drugs that lower blood pressure (antihypertensives), for example the dihydropyridines (nifedipine and nicardipine), which block the calcium conductance in the muscular layer of the arterioles, causing relaxation.

This decreases the resistance to flow into peripheral vascular beds, lowering overall systemic pressure.

Metarterioles

A "metarteriole" is an arteriole which bypasses capillary circulation.[5]

See also

References

  1. ^ Maton, Anthea; Jean Hopkins; Charles William McLaughlin; Susan Johnson; Maryanna Quon Warner; David LaHart; Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey: Prentice Hall.  
  2. ^ Riva, CE; Grunwald, JE; Petrig, BL (1986). "Autoregulation of human retinal blood flow. An investigation with laser Doppler velocimetry". Invest Ophthalmol Vis Sci 27: 1706–1712. 
  3. ^ Adar, SD; Klein, R; Klein, BE; Szpiro, AA; Cotch, MF (2010). "Air Pollution and the microvasculature: a crosssectional assessment of in vivo retinal images in the population based multiethnic study of atherosclerosis (MESA)". PLoS Med 7 (11): e1000372.  
  4. ^ Louwies, T; Int Panis, L; Kicinski, M; De Boever, P; Nawrot, Tim S (2013). "Retinal Microvascular Responses to Short-Term Changes in Particulate Air Pollution in Healthy Adults". Environmental Health Perspectives.  
  5. ^ Physiology: 3/3ch9/s3ch9_2 - Essentials of Human Physiology
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.