Blood vessel

The blood vessels are part of the circulatory system and function to transport blood throughout the body. The most important types, arteries and veins, are so termed because they carry blood away from or towards the heart, respectively.

Physiology

Blood vessels do not actively engage in the transport of the blood (they have no appreciable peristalsis), but arteries - and veins to a degree - can regulate their caliber by contraction of the muscular layer. This determines the blood flow to particular downstream organs, and is determined by the autonomic nervous system. Vasodilation and vasoconstriction are also used antagonistically as a method of thermoregulation in homeotherms.

Related Topics:
Peristalsis - Autonomic nervous system - Thermoregulation - Homeotherms

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Oxygen (bound to hemoglobin in red blood cells) is the most critical nutrient carried by the blood. In all arteries apart from the pulmonary artery, hemoglobin is highly saturated (95-100%) with oxygen. In all veins apart from the pulmonary vein, the hemoglobin is desaturated at about 70%. (The values are reversed in the pulmonary circulation.)

Related Topics:
Oxygen - Hemoglobin - Red blood cell

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The blood pressure in blood vessels is traditionally expressed in millimetres of mercury (1 mmHg = 133 Pa). In the arterial system, this is usually around 120 mmHg systolic (high pressure wave due to contraction of the heart) and 80 mmHg diastolic (low pressure wave). In contrast, pressures in the venous system are constant and rarely exceed 10 mmHg.

Related Topics:
Blood pressure - Millimetres of mercury - Pa - Systolic - Diastolic

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Vasoconstriction is the constriction of blood vessels (narrowing, becoming smaller in cross-sectional area) by contracting the vascular smooth muscle in the vessel walls. It is regulated by vasoconstrictors (agents that cause vasoconstriction). These include paracrine factors (e.g. prostaglandins), a number of hormones (e.g. vasopressin and angiotensin) and neurotransmitters (e.g. adrenalin) from the nervous system.

Related Topics:
Vasoconstriction - Vascular smooth muscle - Vasoconstrictor - Paracrine - Prostaglandin - Hormone - Vasopressin - Angiotensin - Neurotransmitter - Adrenalin

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Vasodilation is a similar process mediated by antagonistically acting mediators. The most prominent vasodilator is nitric oxide (termed endothelium-derived relaxing factor for this reason).

Related Topics:
Vasodilation - Nitric oxide - Endothelium-derived relaxing factor

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Permeability of the endothelium is pivotal in the release of nutrients to the tissue. It is also increased in inflammation in response to histamine, prostaglandins and interleukins, which leads to most of the symptoms of inflammation (swelling, redness and warmth).

Related Topics:
Endothelium - Inflammation - Histamine - Prostaglandin - Interleukin

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