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Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries, small arterioles and veins. The process is the opposite of vasodilation

Vasodilation

Vasodilation refers to the widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large arteries, smaller arterioles and large veins. The process is essentially the opposite of vasoconstriction, or the narrowing of blood vessels. When...

, the widening of blood vessels. The process is particularly important in staunching hemorrhage and acute blood loss. When blood vessels constrict, the flow of blood is restricted or decreased, thus, retaining body heat or increasing vascular resistance

Vascular resistance

Vascular resistance is a term used to define the resistance to flow that must be overcome to push blood through the circulatory system. The resistance offered by the peripheral circulation is known as the systemic vascular resistance , while the resistance offered by the vasculature of the lungs...

. Cutaneously

Skin

-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...

, this makes the skin 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

Mean arterial pressure

The mean arterial pressure is a term used in medicine to describe an average blood pressure in an individual. It is defined as the average arterial pressure during a single cardiac cycle.-Calculation:...

.

Substances causing vasoconstriction are called vasoconstrictors, vasopressors, or simply "pressors". 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

Pupillary response or dilation of the pupil is a physiological response that varies the size of the pupil of the eye via the iris dilator muscle...

. Medications that cause vasoconstriction include antihistamines, decongestants and stimulants used to treat ADHD.

General mechanism

The mechanism that leads to vasoconstriction results from the increased concentration of calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

(Ca²⁺ 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 pharmokinetic components are more physiologically relevant. Two common stimuli for eliciting smooth muscle contraction is circulating epinephrine

Epinephrine

Epinephrine is a hormone and a neurotransmitter. It increases heart rate, constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the sympathetic nervous system. In chemical terms, adrenaline is one of a group of monoamines called the catecholamines...

and activation of the sympathetic nervous system

Sympathetic nervous system

The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...

(through release of norepinephrine

Norepinephrine

Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...

) that directly innervates the muscle. These compounds interact with cell surface adrenergic receptors. Such stimuli result in a signal transduction

Signal transduction

Signal transduction occurs when an extracellular signaling molecule activates a cell surface receptor. In turn, this receptor alters intracellular molecules creating a response...

cascade that leads to increased intracellular calcium from the sarcoplasmic reticulum through IP3

Inositol triphosphate

Inositol trisphosphate or inositol 1,4,5-trisphosphate , together with diacylglycerol , is a secondary messenger molecule used in signal transduction and lipid signaling in biological cells. While DAG stays inside the membrane, IP3 is soluble and diffuses through the cell...

mediated calcium release, as well as enhanced calcium entry across the sarcolemma

Sarcolemma

The sarcolemma is the cell membrane of a muscle cell . It consists of a true cell membrane, called the plasma membrane, and an outer coat made up of a thin layer of polysaccharide material that contains numerous thin collagen fibrils...

through calcium channels. The rise in intracellular calcium complexes with calmodulin

Calmodulin

Calmodulin is a calcium-binding protein expressed in all eukaryotic cells...

, which in turn activates myosin light chain kinase. This enzyme is responsible for phosphorylating

Phosphorylation

Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes....

the light chain of myosin

Myosin

Myosins comprise a family of ATP-dependent motor proteins and are best known for their role in muscle contraction and their involvement in a wide range of other eukaryotic motility processes. They are responsible for actin-based motility. The term was originally used to describe a group of similar...

to stimulate cross bridge cycling.

Once elevated, the intracellular calcium concentration is returned to its basal level 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.

Factors and individual mechanisms

Factors that trigger vasoconstriction can be of exogenous or endogenous origin. Ambient temperature is an example of the former. Cutaneous vasoconstriction will occur because of the body's exposure to the severe cold. Examples of endogenous factors include the autonomic nervous system

Autonomic nervous system

The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...

, circulating hormones and intrinsic mechanisms inherent to the vasculature itself (also referred to as the myogenic

Myogenic

Myogenic contraction refers to a contraction initiated by the myocyte cell itself instead of an outside occurrence or stimulus such as nerve innervation.- Unstable Membrane Potentials :...

response).

Exogenous medications

Examples include amphetamine

Amphetamine

Amphetamine or amfetamine is a psychostimulant drug of the phenethylamine class which produces increased wakefulness and focus in association with decreased fatigue and appetite.Brand names of medications that contain, or metabolize into, amphetamine include Adderall, Dexedrine, Dextrostat,...

s, antihistamine

Antihistamine

An H1 antagonist is a histamine antagonist of the H1 receptor that serves to reduce or eliminate effects mediated by histamine, an endogenous chemical mediator released during allergic reactions...

s and cocaine

Cocaine

Cocaine is a crystalline tropane alkaloid that is obtained from the leaves of the coca plant. The name comes from "coca" in addition to the alkaloid suffix -ine, forming cocaine. It is a stimulant of the central nervous system, an appetite suppressant, and a topical anesthetic...

. Many are used in medicine to treat hypotension

Hypotension

In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...

and as topical decongestant

Topical decongestant

Topical decongestants are decongestants applied directly to the nasal cavity. By applying them directly to the site of action, topical decongestants relieve nasal congestion while reducing the side effects associated with systemically-acting decongestants, such as high blood pressure...

s. Vasoconstrictors are also used clinically to increase blood pressure

Blood pressure

Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...

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.

The routes of administration varies. They may be both systemic and topical. For example, pseudoephedrine

Pseudoephedrine

Pseudoephedrine is a sympathomimetic drug of the phenethylamine and amphetamine chemical classes. It is used as a nasal/sinus decongestant and stimulant, or as a wakefulness-promoting agent....

is available systemic (i.e. orally ingested tablets like Sudafed

Sudafed

Sudafed is a brand name and registered trademark for over the counter decongestants manufactured by McNeil Laboratories for sale in Australia, New Zealand, Canada, Ireland, the United Kingdom, and the United States...

), and topical (such as nose sprays like phenylephrine Neo-synephrine, and eye drops for pupil dilation purposes)

Examples include:

Vasoconstrictors
Amphetamine Amphetamine Amphetamine or amfetamine is a psychostimulant drug of the phenethylamine class which produces increased wakefulness and focus in association with decreased fatigue and appetite.Brand names of medications that contain, or metabolize into, amphetamine include Adderall, Dexedrine, Dextrostat,... s
antihistamines
Cocaine Cocaine Cocaine is a crystalline tropane alkaloid that is obtained from the leaves of the coca plant. The name comes from "coca" in addition to the alkaloid suffix -ine, forming cocaine. It is a stimulant of the central nervous system, an appetite suppressant, and a topical anesthetic...
LSD LSD Lysergic acid diethylamide, abbreviated LSD or LSD-25, also known as lysergide and colloquially as acid, is a semisynthetic psychedelic drug of the ergoline family, well known for its psychological effects which can include altered thinking processes, closed and open eye visuals, synaesthesia, an...
LSA Ergine Ergine, also known as d-lysergic acid amide , d-lysergamide, and LA-111, is an alkaloid of the ergoline family that occurs in various species of vines of the Convolvulaceae and some species of fungi...
Methylphenidate Methylphenidate Methylphenidate is a psychostimulant drug approved for treatment of attention-deficit hyperactivity disorder, postural orthostatic tachycardia syndrome and narcolepsy. It may also be prescribed for off-label use in treatment-resistant cases of lethargy, depression, neural insult and obesity...
Mephedrone
Oxymetazoline Oxymetazoline Oxymetazoline is a selective alpha-1 agonist and partial alpha-2 agonist topical decongestant, used in the form of Oxymetazoline hydrochloride, in products such as Afrin, Dristan, Nasivin, Logicin, Vicks Sinex, Visine L.R., Sudafed OM, and Zicam. It was developed from Xylometazoline at E.Merck...
Phenylephrine Phenylephrine Phenylephrine is a selective α1-adrenergic receptor agonist used primarily as a decongestant, as an agent to dilate the pupil, and to increase blood pressure...
Propylhexedrine Propylhexedrine Propylhexedrine is a stimulant drug related to methamphetamine. It is used mainly to provide temporary symptomatic relief of nasal congestion due to colds, allergies and allergic rhinitis...
Pseudoephedrine Pseudoephedrine Pseudoephedrine is a sympathomimetic drug of the phenethylamine and amphetamine chemical classes. It is used as a nasal/sinus decongestant and stimulant, or as a wakefulness-promoting agent....
Stimulant Stimulant Stimulants are psychoactive drugs which induce temporary improvements in either mental or physical function or both. Examples of these kinds of effects may include enhanced alertness, wakefulness, and locomotion, among others... s
Caffeine Caffeine Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants...
Tetrahydrozoline hydrochloride Tetrahydrozoline Tetrahydrozoline, a derivative of imidazoline, is found in over-the-counter eye drops and nasal sprays. Other derivatives include naphazoline, oxymetazoline, and xylometazoline. Poisoning can result from an overdose.... (in eye drops)
Psilocybin Psilocybin Psilocybin is a naturally occurring psychedelic prodrug, with mind-altering effects similar to those of LSD and mescaline, after it is converted to psilocin. The effects can include altered thinking processes, perceptual distortions, an altered sense of time, and spiritual experiences, as well as...

Endogenous

Vasoconstriction is a procedure of the body that avoids orthostatic hypotension

Orthostatic hypotension

Orthostatic hypotension, also known as postural hypotension, orthostasis, and colloquially as head rush or dizzy spell, is a form of hypotension in which a person's blood pressure suddenly falls when the person stands up or stretches. The decrease is typically greater than 20/10 mm Hg, and may be...

. It is a part of a body negative feed back loop in which the body tries to restore homeostasis.

For example, vasoconstriction is a hypothermic preventative in which the blood vessels constrict and blood must move at a higher pressure to actively avoid a hypoxic reaction. ATP

Adenosine triphosphate

Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...

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

The term warm-blooded is a colloquial term to describe animal species which have a relatively higher blood temperature, and maintain thermal homeostasis primarily through internal metabolic processes...

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.

Vasoconstrictor	Receptor (↑ = opens. ↓ = closes) On vascular smooth muscle cells if not otherwise specified	Transduction (↑ = increases. ↓ = decreases)
Stretch	↑Stretch-activated ion channel Stretch-activated ion channel Stretch-activated or stretch-gated ion channels are ion channels which open their pores in response to mechanical deformation of a neuron's plasma membrane. Stretch-activated channels were first observed in chick skeletal muscles by Falguni Guharay and Frederick Sachs in 1983 and the results were... s	depolarization Depolarization In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential... --> open VDCC Voltage-dependent calcium channel Voltage-dependent calcium channels are a group of voltage-gated ion channels found in excitable cells with a permeability to the ion Ca2+... s (primarily) --> ↑intracellular Ca²⁺ ↑Voltage-gated Na⁺ channels --> more depolarization --> open VDCC Voltage-dependent calcium channel Voltage-dependent calcium channels are a group of voltage-gated ion channels found in excitable cells with a permeability to the ion Ca2+... s --> ↑intracellular Ca²⁺ ↓Na⁺-Ca²⁺ exchanger Sodium-calcium exchanger The sodium-calcium exchanger is an antiporter membrane protein that removes calcium from cells. It uses the energy that is stored in the electrochemical gradient of sodium by allowing Na+ to flow down its gradient across the plasma membrane in exchange for the countertransport of calcium ions... activity --> ↑intracellular Ca²⁺
ATP Adenosine triphosphate Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism... (intracellular)	↓ATP-sensitive K⁺ channel
ATP Adenosine triphosphate Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism... (extracellular)	↑P2X receptor P2X Receptor P2X receptors are a family of cation-permeable ligand gated ion channels that open in response to the binding of extracellular adenosine 5'-triphosphate . They belong to a larger family of receptors known as the purinergic receptors...	↑Ca²⁺
muscarinic agonists e.g. acetylcholine Acetylcholine The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...	↑muscarinic receptor M₂ Muscarinic acetylcholine receptor M2 The muscarinic acetylcholine receptor M2, also known as the cholinergic receptor, muscarinic 2, is a muscarinic acetylcholine receptor.-Heart:...	Activation of G_i Gi alpha subunit Gi alpha subunit is a heterotrimeric G protein subunit that inhibits the production of cAMP from ATP.- Receptors :The following G protein-coupled receptors couple to the Gi subunit:* Acetylcholine M2 & M4 receptors... --> ↓cAMP Cyclic adenosine monophosphate Cyclic adenosine monophosphate is a second messenger important in many biological processes... --> ↓PKA activity --> ↓phosphorylation Phosphorylation Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes.... of MLCK --> ↑MLCK activity --> ↑phosphorylation of MLC Myosin light chain Myosin light chain is a subunit of myosin Myosin light chains are distinct and have their own properties, distinct from the heavy chains. They are not considered "myosins" but are components of the macromolecular complexes that make up the functional myosin enzymes.* Light chain: MYL1, MYL2, MYL3,... (calcium-independent)
NPY Neuropeptide Y Neuropeptide Y is a 36-amino acid peptide neurotransmitter found in the brain and autonomic nervous system."NPY has been associated with a number of physiologic processes in the brain, including the regulation of energy balance, memory and learning, and epilepsy." The main effect is increased food...	NPY receptor
adrenergic agonists e.g. epinephrine Epinephrine Epinephrine is a hormone and a neurotransmitter. It increases heart rate, constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the sympathetic nervous system. In chemical terms, adrenaline is one of a group of monoamines called the catecholamines... , norepinephrine Norepinephrine Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter... and dopamine Dopamine Dopamine is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this substituted phenethylamine functions as a neurotransmitter, activating the five known types of dopamine receptors—D1, D2, D3, D4, and D5—and their...	↑α₁ adrenergic receptor Alpha-1 adrenergic receptor The alpha-1 adrenergic receptor is a G protein-coupled receptor associated with the Gq heterotrimeric G-protein. It consists of three highly homologous subtypes, including α1A-, α1B-, and α1D-adrenergic...	Activation of G_q Gq alpha subunit Gq protein or Gq/11 is a heterotrimeric G protein subunit that activates phospholipase C . PLC in turn hydrolyzes Phosphatidylinositol 4,5-bisphosphate to diacyl glycerol and inositol triphosphate signal transduction pathway... --> ↑PLC Phospholipase C Phosphoinositide phospholipase C is a family of eukaryotic intracellular enzymes that play an important role in signal transduction processes. In general, this enzyme is denoted as Phospholipase C, although three other families of phospholipase C enzymes have been identified in bacteria and in... activity --> ↑IP₃ Inositol triphosphate Inositol trisphosphate or inositol 1,4,5-trisphosphate , together with diacylglycerol , is a secondary messenger molecule used in signal transduction and lipid signaling in biological cells. While DAG stays inside the membrane, IP3 is soluble and diffuses through the cell... and DAG --> activation of IP₃ receptor Inositol triphosphate receptor Inositol trisphosphate receptor is a membrane glycoprotein complex acting as Ca2+ channel activated by inositol trisphosphate . InsP3R is very diverse among organisms, and is necessary for the control of cellular and physiological processes including cell division, cell proliferation, apoptosis,... in SR --> ↑intracellular Ca²⁺
thromboxane Thromboxane Thromboxane is a member of the family of lipids known as eicosanoids. The two major thromboxanes are thromboxane A2 and thromboxane B2. The distinguishing feature of thromboxanes is a 6-membered ether-containing ring....	↑thromboxane receptor Thromboxane receptor The thromboxane receptor is a protein on the surface of cells in the endothelium of blood vessels and in the placenta which interacts with the eicosanoid lipid thromboxane. It is a G-protein coupled receptor coupled to the G protein Gq.-Gene:...
endothelin Endothelin Endothelins are proteins that constrict blood vessels and raise blood pressure. They are normally kept in balance by other mechanisms, but when they are over-expressed, they contribute to high blood pressure and heart disease....	↑endothelin receptor Endothelin receptor There are at least three known endothelin receptors, ETA, ETB1 and ETB2, all of which are G protein-coupled receptors whose activation result in elevation of intracellular-free calcium.-Clinical significance:... ET_A
angiotensin II	↑Angiotensin receptor 1	On smooth muscle cells: Activation of G_q Gq alpha subunit Gq protein or Gq/11 is a heterotrimeric G protein subunit that activates phospholipase C . PLC in turn hydrolyzes Phosphatidylinositol 4,5-bisphosphate to diacyl glycerol and inositol triphosphate signal transduction pathway... --> ↑PLC Phospholipase C Phosphoinositide phospholipase C is a family of eukaryotic intracellular enzymes that play an important role in signal transduction processes. In general, this enzyme is denoted as Phospholipase C, although three other families of phospholipase C enzymes have been identified in bacteria and in... activity --> ↑IP₃ Inositol triphosphate Inositol trisphosphate or inositol 1,4,5-trisphosphate , together with diacylglycerol , is a secondary messenger molecule used in signal transduction and lipid signaling in biological cells. While DAG stays inside the membrane, IP3 is soluble and diffuses through the cell... and DAG --> activation of IP₃ receptor Inositol triphosphate receptor Inositol trisphosphate receptor is a membrane glycoprotein complex acting as Ca2+ channel activated by inositol trisphosphate . InsP3R is very diverse among organisms, and is necessary for the control of cellular and physiological processes including cell division, cell proliferation, apoptosis,... in SR --> ↑intracellular Ca²⁺ On endothelium Endothelium The endothelium is the thin layer of cells that lines the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. These cells are called endothelial cells. Endothelial cells line the entire circulatory system, from the heart... : endothelin Endothelin Endothelins are proteins that constrict blood vessels and raise blood pressure. They are normally kept in balance by other mechanisms, but when they are over-expressed, they contribute to high blood pressure and heart disease.... synthesis
angiotensin II		open VDCC Voltage-dependent calcium channel Voltage-dependent calcium channels are a group of voltage-gated ion channels found in excitable cells with a permeability to the ion Ca2+... s --> ↑intracellular Ca²⁺
Asymmetric dimethylarginine Asymmetric dimethylarginine Asymmetric dimethylarginine is a naturally occurring chemical found in blood plasma. It is a metabolic by-product of continual protein modification processes in the cytoplasm of all human cells. It is closely related to L-arginine, a conditionally-essential amino acid...		Reduced production of nitric oxide Nitric oxide Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...
Antidiuretic hormone (ADH or Vasopressin) Vasopressin Arginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone , is a neurohypophysial hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue's...	Arginine vasopressin receptor 1 (V1) on smooth muscle cells	Activation of G_q Gq alpha subunit Gq protein or Gq/11 is a heterotrimeric G protein subunit that activates phospholipase C . PLC in turn hydrolyzes Phosphatidylinositol 4,5-bisphosphate to diacyl glycerol and inositol triphosphate signal transduction pathway... --> ↑PLC Phospholipase C Phosphoinositide phospholipase C is a family of eukaryotic intracellular enzymes that play an important role in signal transduction processes. In general, this enzyme is denoted as Phospholipase C, although three other families of phospholipase C enzymes have been identified in bacteria and in... activity --> ↑IP₃ Inositol triphosphate Inositol trisphosphate or inositol 1,4,5-trisphosphate , together with diacylglycerol , is a secondary messenger molecule used in signal transduction and lipid signaling in biological cells. While DAG stays inside the membrane, IP3 is soluble and diffuses through the cell... and DAG --> activation of IP₃ receptor Inositol triphosphate receptor Inositol trisphosphate receptor is a membrane glycoprotein complex acting as Ca2+ channel activated by inositol trisphosphate . InsP3R is very diverse among organisms, and is necessary for the control of cellular and physiological processes including cell division, cell proliferation, apoptosis,... in SR --> ↑intracellular Ca²⁺
	Arginine vasopressin receptor on endothelium	Endothelin Endothelin Endothelins are proteins that constrict blood vessels and raise blood pressure. They are normally kept in balance by other mechanisms, but when they are over-expressed, they contribute to high blood pressure and heart disease.... production
Products of platelet activation Endotoxin Endotoxin Endotoxins are toxins associated with some Gram-negative bacteria. An "endotoxin" is a toxin that is a structural molecule of the bacteria that is recognized by the immune system.-Gram negative:... Thrombin Thrombin Thrombin is a "trypsin-like" serine protease protein that in humans is encoded by the F2 gene. Prothrombin is proteolytically cleaved to form thrombin in the first step of the coagulation cascade, which ultimately results in the stemming of blood loss... insulin Insulin Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle.... Hypoxia Hypoxia (medical) Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise... Low shear stress Shear stress A shear stress, denoted \tau\, , is defined as the component of stress coplanar with a material cross section. Shear stress arises from the force vector component parallel to the cross section...	Various receptors on endothelium Endothelium The endothelium is the thin layer of cells that lines the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. These cells are called endothelial cells. Endothelial cells line the entire circulatory system, from the heart...	Endothelin Endothelin Endothelins are proteins that constrict blood vessels and raise blood pressure. They are normally kept in balance by other mechanisms, but when they are over-expressed, they contribute to high blood pressure and heart disease.... production

Pathology

Vasoconstriction can be a contributing factor to erectile dysfunction

Erectile dysfunction

Erectile dysfunction is sexual dysfunction characterized by the inability to develop or maintain an erection of the penis during sexual performance....

. An increase in blood flow to the penis causes an erection.

Improper vasoconstriction may also play a role in secondary hypertension

Hypertension

Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...