Vasoconstriction is the narrowing of the
blood vessel
The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide awa ...
s resulting from contraction of the muscular wall of the vessels, in particular the large
arteries and small
arterioles
An arteriole is a small-diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries.
Arterioles have muscular walls (usually only one to two layers of smooth muscle cells) and are the pri ...
. The process is the opposite of
vasodilation, the widening of blood vessels. The process is particularly important in controlling
hemorrhage
Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, v ...
and reducing acute blood loss. When blood vessels constrict, the flow of blood is restricted or decreased, thus retaining body heat or increasing
vascular resistance. This makes the
skin
Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation.
Other animal coverings, such as the arthropod exoskeleton, have different ...
turn paler because less blood reaches the surface, reducing the radiation of heat. On a larger level, vasoconstriction is one mechanism by which the body regulates and maintains
mean arterial pressure
In medicine, the mean arterial pressure (MAP) is an average blood pressure in an individual during a single cardiac cycle. MAP is altered by cardiac output and systemic vascular resistance.
Testing
Mean arterial pressure can be measured direc ...
.
Medications causing vasoconstriction, also known as vasoconstrictors, are one type of
medicine used to raise blood pressure. Generalized vasoconstriction usually results in an increase in systemic blood pressure, but it may also occur in specific tissues, causing a localized reduction in blood flow. The extent of vasoconstriction may be slight or severe depending on the substance or circumstance. Many vasoconstrictors also cause
pupil dilation
Pupillary response is a physiological response that varies the size of the pupil, via the optic and oculomotor cranial nerve.
A constriction response (miosis), is the narrowing of the pupil, which may be caused by scleral buckles or drugs such ...
. Medications that cause vasoconstriction include:
antihistamines,
decongestants, and
stimulants. Severe vasoconstriction may result in symptoms of
intermittent claudication
Intermittent claudication, also known as vascular claudication, is a symptom that describes muscle pain on mild exertion (ache, cramp, numbness or sense of fatigue), classically in the calf muscle, which occurs during exercise, such as walking, an ...
.
General mechanism
The mechanism that leads to vasoconstriction results from the increased concentration of
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...
(Ca
2+ ions) within vascular
smooth muscle cells. However, the specific mechanisms for generating an increased intracellular concentration of calcium depends on the vasoconstrictor. Smooth muscle cells are capable of generating
action potentials, but this mechanism is rarely utilized for contraction in the vasculature.
Hormonal or pharmacokinetic components are more physiologically relevant. Two common stimuli for eliciting smooth muscle contraction are circulating
epinephrine and activation of the
sympathetic nervous system (through release of
norepinephrine
Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter. The name "noradrenaline" (from Latin '' ad ...
) that directly innervates the muscle. These compounds interact with cell surface
adrenergic receptors
The adrenergic receptors or adrenoceptors are a class of G protein-coupled receptors that are targets of many catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) produced by the body, but also many medications like bet ...
. Such stimuli result in a
signal transduction cascade that leads to increased intracellular calcium from the
sarcoplasmic reticulum through
IP3-mediated calcium release, as well as enhanced calcium entry across the
sarcolemma through
calcium channels
A calcium channel is an ion channel which shows selective permeability to calcium ions. It is sometimes synonymous with voltage-gated calcium channel, although there are also ligand-gated calcium channels.
Comparison tables
The following tables ex ...
. The rise in intracellular calcium complexes with
calmodulin, which in turn activates
myosin light-chain kinase
Myosin light-chain kinase also known as MYLK or MLCK is a serine/threonine-specific protein kinase that phosphorylates a specific myosin light chain, namely, the regulatory light chain of myosin II.
General structural features
While there ar ...
. This enzyme is responsible for
phosphorylating the light chain of
myosin to stimulate cross-bridge cycling.
Once elevated, the intracellular calcium concentration is returned to its normal concentration through a variety of protein pumps and calcium exchangers located on the plasma membrane and sarcoplasmic reticulum. This reduction in calcium removes the stimulus necessary for contraction, allowing for a return to baseline.
Causes
Factors that trigger vasoconstriction can be exogenous or endogenous in origin. Ambient temperature is an example of exogenous vasoconstriction. Cutaneous vasoconstriction will occur because of the body's exposure to the severe cold. Examples of endogenous factors include the
autonomic nervous system, circulating hormones, and intrinsic mechanisms inherent to the vasculature itself (also referred to as the
myogenic response).
Examples
Examples include
stimulants,
amphetamines, and
antihistamine
Antihistamines are drugs which treat allergic rhinitis, common cold, influenza, and other allergies. Typically, people take antihistamines as an inexpensive, generic (not patented) drug that can be bought without a prescription and provide ...
s. Many are used in medicine to treat
hypotension
Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure (the top number) and the di ...
and as
topical decongestants. Vasoconstrictors are also used clinically to increase
blood pressure or to reduce local blood flow.
Vasoconstrictors mixed with local anesthetics are used to increase the duration of local anesthesia by constricting the blood vessels, thereby safely concentrating the anesthetic agent for an extended duration, as well as reducing
hemorrhage
Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, v ...
.
The
routes of administration vary. They may be both systemic and topical. For example,
pseudoephedrine is taken orally and
phenylephrine is topically applied to the nasal passages or eyes.
Examples include:
Endogenous
Vasoconstriction is a procedure of the body that averts
orthostatic hypotension. It is part of a body negative feedback loop in which the body tries to restore homeostasis (maintain constant internal environment).
For example, vasoconstriction is a hypothermic preventative in which the blood vessels constrict and blood must move at a higher pressure to actively prevent a hypoxic reaction.
ATP is used as a form of energy to increase this pressure to heat the body. Once homeostasis is restored, the blood pressure and ATP production regulates. Vasoconstriction also occurs in superficial blood vessels of
warm-blooded
Warm-blooded is an informal term referring to animal species which can maintain a body temperature higher than their environment. In particular, homeothermic species maintain a stable body temperature by regulating metabolic processes. The on ...
animals when their ambient environment is cold; this process diverts the flow of heated blood to the center of the animal, preventing the loss of heat.
Pathology
Vasoconstriction can be a contributing factor to
erectile dysfunction.
[Richard Milsten and Julian Slowinski, ''The sexual ]male
Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization.
A male organism cannot reproduce sexually without access to ...
'', bc, main point W.W. Norton Company, New York, London (1999) An increase in blood flow to the penis causes an erection.
Improper vasoconstriction may also play a role in secondary
hypertension.
See also
*
Addison's disease
Addison's disease, also known as primary adrenal insufficiency, is a rare long-term endocrine disorder characterized by inadequate production of the steroid hormones cortisol and aldosterone by the two outer layers of the cells of the adrena ...
*
Inotrope
*
Hypertension
*
Nitric oxide
*
Pheochromocytoma
Pheochromocytoma (PHEO or PCC) is a rare tumor of the adrenal medulla composed of chromaffin cells, also known as pheochromocytes. When a tumor composed of the same cells as a pheochromocytoma develops outside the adrenal gland, it is referred t ...
*
Shock
Shock may refer to:
Common uses Collective noun
*Shock, a historic commercial term for a group of 60, see English numerals#Special names
* Stook, or shock of grain, stacked sheaves
Healthcare
* Shock (circulatory), circulatory medical emerge ...
*
Vasodilation
*
Postural orthostatic tachycardia syndrome
*
Hemostasis
In biology, hemostasis or haemostasis is a process to prevent and stop bleeding, meaning to keep blood within a damaged blood vessel (the opposite of hemostasis is hemorrhage). It is the first stage of wound healing. This involves coagulatio ...
References
External links
Definition of Vasoconstriction on HealthScoutCannabis arteritis revisited--ten new case reports
{{Cardiovascular physiology
Cardiovascular physiology