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Blood vessels are the tubular structures of a circulatory system that transport blood throughout a vertebrate's body. Blood vessels transport blood cells, nutrients, and oxygen to most of the tissues of a body. They also take waste and carbon dioxide away from the tissues. Some tissues such as cartilage, epithelium, and the lens and cornea of the eye are not supplied with blood vessels and are termed avascular.
The sympathetic nervous system is one of the three divisions of the autonomic nervous system, the others being the parasympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vessels. The process is particularly important in controlling hemorrhage 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 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.
Vasodilation, also known as vasorelaxation, is the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins, large arteries, and smaller arterioles. Blood vessel walls are composed of endothelial tissue and a basal membrane lining the lumen of the vessel, concentric smooth muscle layers on top of endothelial tissue, and an adventitia over the smooth muscle layers. Relaxation of the smooth muscle layer allows the blood vessel to dilate, as it is held in a semi-constricted state by sympathetic nervous system activity. Vasodilation is the opposite of vasoconstriction, which is the narrowing of blood vessels.
An arteriole is a small-diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries.
Vascular resistance is the resistance that must be overcome for blood to flow through the circulatory system. The resistance offered by the systemic circulation is known as the systemic vascular resistance or may sometimes be called by another term total peripheral resistance, while the resistance caused by the pulmonary circulation is known as the pulmonary vascular resistance. Vasoconstriction increases resistance, whereas vasodilation decreases resistance. Blood flow and cardiac output are related to blood pressure and inversely related to vascular resistance.
In haemodynamics, the body must respond to physical activities, external temperature, and other factors by homeostatically adjusting its blood flow to deliver nutrients such as oxygen and glucose to stressed tissues and allow them to function. Haemodynamic response (HR) allows the rapid delivery of blood to active neuronal tissues. The brain consumes large amounts of energy but does not have a reservoir of stored energy substrates. Since higher processes in the brain occur almost constantly, cerebral blood flow is essential for the maintenance of neurons, astrocytes, and other cells of the brain. This coupling between neuronal activity and blood flow is also referred to as neurovascular coupling.
The tibial nerve is a branch of the sciatic nerve. The tibial nerve passes through the popliteal fossa to pass below the arch of soleus.
Hyperaemia is the increase of blood flow to different tissues in the body. It can have medical implications but is also a regulatory response, allowing change in blood supply to different tissues through vasodilation. Clinically, hyperaemia in tissues manifests as erythema because of the engorgement of vessels with oxygenated blood. Hyperaemia can also occur due to a fall in atmospheric pressure outside the body. The term comes from Greek ὑπέρ (hupér) 'over' and αἷμα (haîma) 'blood'.
Vasomotor refers to actions upon a blood vessel which alter its diameter. More specifically, it can refer to vasodilator action and vasoconstrictor action.
Iloprost, sold under the brand name Ventavis among others, is a medication used to treat pulmonary arterial hypertension (PAH), scleroderma, Raynaud's phenomenon, frostbite, and other conditions in which the blood vessels are constricted and blood cannot flow to the tissues. Iloprost is a prostacyclin mimetic.
Angiokeratoma is a benign cutaneous lesion of capillaries, resulting in small marks of red to blue color and characterized by hyperkeratosis. Angiokeratoma corporis diffusum refers to Fabry's disease, but this is usually considered a distinct condition.
In medicine, hepatopulmonary syndrome is a syndrome of shortness of breath and hypoxemia caused by vasodilation in the lungs of patients with liver disease. Dyspnea and hypoxemia are worse in the upright position.
The axon reflex is the response stimulated by peripheral nerves of the body that travels away from the nerve cell body and branches to stimulate target organs. Reflexes are single reactions that respond to a stimulus making up the building blocks of the overall signaling in the body's nervous system. Neurons are the excitable cells that process and transmit these reflex signals through their axons, dendrites, and cell bodies. Axons directly facilitate intercellular communication projecting from the neuronal cell body to other neurons, local muscle tissue, glands and arterioles. In the axon reflex, signaling starts in the middle of the axon at the stimulation site and transmits signals directly to the effector organ skipping both an integration center and a chemical synapse present in the spinal cord reflex. The impulse is limited to a single bifurcated axon, or a neuron whose axon branches into two divisions and does not cause a general response to surrounding tissue.
Rombo syndrome is a very rare genetic disorder characterized mainly by atrophoderma vermiculatum of the face, multiple milia, telangiectases, acral erythema, peripheral vasodilation with cyanosis, and a propensity to develop basal cell carcinomas.
The hunting reaction or hunting response is a process of alternating vasoconstriction and vasodilation in extremities exposed to cold. The term Lewis reaction is used too, named after Thomas Lewis, who first described the effect in 1930.
The triple response of Lewis is a cutaneous response that occurs from firm stroking of the skin. This produces an initial red line, followed by a flare around that line, and then finally a wheal.
Microvasculature comprises the microvessels – venules and capillaries of the microcirculation, with a maximum average diameter of 0.3 millimeters. As the vessels decrease in size, they increase their surface-area-to-volume ratio. This allows surface properties to play a significant role in the function of the vessel.
In physiology, acute local blood flow regulation refers to an intrinsic regulation, or control, of the vascular tone of arteries at a local level, meaning within a certain tissue type, organ, or organ system. This intrinsic type of control means that the blood vessels can automatically adjust their own vascular tone, by dilating (widening) or constricting (narrowing), in response to some change in the environment. This change occurs in order to match up the tissue's oxygen demand with the actual oxygen supply available in the blood as closely as possible. For example, if a muscle is being utilized actively, it will require more oxygen than it was at rest, so the blood vessels supplying that muscle will vasodilate, or widen in size, to increase the amount of blood, and therefore oxygen, being delivered to that muscle.
Skin temperature is the temperature of the outermost surface of the body. Normal human skin temperature on the trunk of the body varies between 33.5 and 36.9 °C, though the skin's temperature is lower over protruding parts, like the nose, and higher over muscles and active organs. Recording skin temperature presents extensive difficulties. Although it is not a clear indicator of internal body temperature, skin temperature is significant in assessing the healthy function of skin. Some experts believe the physiological significance of skin temperature has been overlooked, because clinical analysis has favoured measuring temperatures of the mouth, armpit, and/or rectum. Temperatures of these parts typically are consistent with internal body temperature.
References
- ↑ Chaurasia, B. D.. (2015). BD Chaurasia's handbook of general anatomy (Fifth ed.). New Delhi: CBS Publishers & Distributors Pvt Ltd. p. 166. ISBN 978-81-239-2620-9.
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