Evolution of blood circulation types
The structure and function of various animal circulatory systems can be summarized as table 1. No matter single-celled organisms or multicellular organisms, including plant cells, we can see the simplest form of circulation-cytoplasmic flow, that is, protoplasm flow.
The separation of birds' and mammals' hearts and the separation of pulmonary circulation and systemic circulation are complete. This will produce an important result: the blood pressure in pulmonary circulation is much lower than that in systemic circulation. People's pulmonary artery pressure does not exceed 20 ~ 30mm Hg, which is about 65,438+0/5 of systemic arterial pressure. If the separation between the two is not complete, there can be no such big difference. After complete separation, the arteriovenous blood is no longer mixed and the aorta is filled with oxygen-enriched blood. In this way, various tissues can get more oxygen, improve the metabolic level and greatly enhance their ability to adapt to the environment. Most birds and mammals are warm-blooded animals, which is related to the improvement of circulatory system.
Structure and function of the heart
Structure and function of vascular system
The blood vessel wall is rich in elastic fibers and smooth muscle, which enables blood vessels to passively expand and actively contract. Arteries, veins and capillaries all have their own structural characteristics. Compared with the corresponding vein, the wall of the artery is thicker, and there are more elastic fibers and smooth muscles in the aorta. With the gradual tapering of arterial branches, the proportion of smooth muscle in the vessel wall is increasing. Capillary is the smallest blood vessel in the vascular system and consists of a layer of cells. The exchange of substances between blood and tissues is carried out through capillaries. The total cross-sectional area of mesenteric capillaries in dogs is about 800 times that of aorta. Starting from venules, the number of venous tubes decreases gradually, and the total cross-sectional area decreases accordingly, until the cross-sectional area of vena cava is the smallest, but slightly larger than that of aorta. The blood volume of venous system (680ml) is about 3.6 times that of arterial system (190ml). Because the venous blood system has the largest capacity, it is also called volume blood vessel. Arteries and arterioles are also called resistance vessels, because their tension changes play the greatest role in the change of peripheral resistance.
People who circulate blood and store blood account for about 6-8% of their body weight. Not all the blood in the whole body flows in the cardiovascular system, but some blood that flows very slowly or even stagnates is stored in the spleen, liver, skin, lungs and other parts. Blood that flows is called circulating blood, and blood that does not flow or flows slowly is called blood storage. Those organs that store blood are called blood banks or blood banks for short. Blood bank can regulate the circulating blood volume, in which the spleen plays the most important role. At rest, the spleen is relaxed, completely isolated from the circulating blood, and can store about 1/6 of the total body blood volume. Among them, the hematocrit is large, and the number of blood cells can reach about 1/3 of the total red blood cells in the whole body. When strenuous exercise, massive hemorrhage, asphyxia or blood hypoxia occur, under the adjustment of neurohumoral factors, the spleen contracts and releases a large amount of blood containing many blood cells (40% more than circulating blood) to increase the circulating blood volume of the cardiovascular system to meet urgent needs. However, both circulating blood and stored blood are affected by changes in blood volume. Excessive blood volume and blood cells can cause adverse reactions and even pathological changes.
The blood storage function of spleen, liver, lung and skin can stimulate visceral nerves to make the spleen contract rapidly and strongly, and the volume is obviously reduced? T 跹跹跶 跶 跶 跶 跶 跶 跶 跶 跶 跶 跶 跶 跶 跶 跶 跶 跶 Friends of dog porcelain (4)? I leaned against the plaque? ⒃ ⑿ ⑿ ⑿ ⑿ ⑿ ⑿ ⑿? "Meteorite attack school? What's the matter? 929)。 The conditioned reflex of spleen contraction can be established on the basis of unconditional reflex of spleen, thus clarifying the regulatory effect of cerebral cortex on spleen activity. The liver and lungs also have the function of blood bank. Although they are not completely isolated from the circulating blood flow, they can be regarded as blood banks because of their slow flow. The contraction of hepatic vein makes the inflow blood volume greater than the outflow blood volume in a certain period of time, and the stored blood is distributed in the dilated blood vessels in the liver. Depending on the degree of pulmonary vasodilation, like the liver, the lung can store more or less blood.
Subcapillary vascular plexus can store a large amount of blood (up to 1 liter) when it is relaxed. The blood flow here is very slow, even stagnant. When the arteriovenous anastomosis in many parts of the skin is relaxed, a large amount of stored blood is temporarily isolated from the circulating blood flow. The decrease of circulating blood volume during standing may be caused by a considerable amount of blood flowing into the vascular plexus of lower limbs.
Neuroregulation of vascular movement
The contraction and relaxation of blood vessels are called vasomotor nerves, which control vasomotor nerves. The nerve that constricts blood vessels is called vasoconstrictor nerve, and the nerve that relaxes blood vessels is called vasodilator nerve, which is called vasodilator nerve. Arteriovenous blood vessels have nerve distribution, among which arterioles, arterioles and arteriovenous anastomosis branches have the densest nerve distribution, all blood vessels have vasoconstrictive nerve fibers, and some blood vessels have both systolic and diastolic nerve fibers.
Vasoconstriction Nerve viscera and skin blood vessels have the greatest vasoconstrictive effect. When the visceral nerve, the main vasoconstrictive nerve in abdominal cavity, is stimulated, the visceral vascular bed contracts widely, leading to a significant increase in blood pressure. Vasoconstructive nerve belongs to the sympathetic nervous system and consists of adrenergic fibers (fibers that release norepinephrine at the distal end). The contraction of blood vessels and nerves is of great significance to the regulation of arterioles, because it can keep the arterial blood pressure constant, thus ensuring adequate blood supply to various organs and tissues. The contraction of vascular nerves can keep vascular smooth muscle in a certain state. This is because it has a persistent nerve impulse. There are vasoconstrictive fibers in the blood vessels of various organs, but the frequency of nerve impulses is different. The tension release of sympathetic nerve fibers in visceral vessels is the highest; There is moderate tension release in skin and skeletal muscle blood vessels, and the lowest tension release in brain vasoconstrictor fibers, so the cerebral vessels are less affected by vasoconstrictor nerves and are often in a relaxed state.
Gotz, a German physiologist, found in a chronic experiment that after a few days' stimulation after cutting off sciatic nerve, you can see obvious relaxation reaction of blood vessels in hind limbs. Takhanov stimulated the distal end of sciatic nerve immediately after cutting it, but what he got was vasoconstriction. Therefore, because there are both contraction fibers and relaxation fibers in the sciatic nerve, the response is different. After stimulation, the role of relaxed fibers is generally inhibited, showing only contraction reaction. However, the vasoconstrictor fiber degenerates rapidly, losing its excitability 3-4 days after being cut off, while the vasodilator fiber can still be excited 6- 10 days after being cut off, so the mixed nerve will relax after being stimulated for 3-4 days in chronic experiments. Generally, the efferent nerve contains two kinds of fibers: vasodilatory fibers and contractile fibers. The origin of relaxing blood vessels and nerves is very complicated, and there are three kinds of * * *:
Parasympathetic nerve is the main vasomotor nerve. Among them, the relaxation fibers of facial nerve (ⅶ) and swallowing nerve (ⅸ) dominate the blood vessels in salivary gland, lacrimal gland, tongue and oropharyngeal mucosa. The parasympathetic nerve of pelvic nerve relaxes the blood vessels that dominate the rectum, bladder and external genitalia, making them relax. The transmitter released from the distal end of vasodilator fiber is acetylcholine, which is called cholinergic fiber. C Bernard1854 thinks that chorda tympani nerve is a vasomotor nerve, which has been confirmed for nearly 100 years. Later, German physiologist R.P.H. Heidenhain questioned this for the first time in 1872, and thought that the vasodilation of submandibular gland caused by chorda tympani nerve could not be blocked by atropine. 194 1 year, British physiologist J. Barcroft proposed that this relaxation reaction of submandibular gland blood vessels may be caused by the metabolites of gland cells. This view was confirmed by S.M. Hilton and G.P. Lewis in 1955; They found that stimulating chorda tympani nerve can make submandibular gland cells secrete lysyl bradykinin, which can quickly become bradykinin, both of which are strong vasodilators. Therefore, the conclusion that chorda tympani nerve is vasomotor nerve is denied.
Sympathetic vasodilator nerves innervate the sympathetic trunk of skeletal muscle blood vessels, and there are vasodilator fibers besides vasoconstrictor fibers. Although the source of this fiber is sympathetic nerve, it can relax blood vessels, and its transmitter is acetylcholine, so it is called cholinergic sympathetic vasodilator fiber.
The vasodilation effect of dorsal root reverse conduction cuts off the dorsal root of spinal nerve and stimulates its distal end, and the impulse can be transmitted back to the distal end to cause vasodilation in the skin. This phenomenon may be abnormal, but in 190 1, the British physiologist Bayless thinks that the axons of afferent neurons in the dorsal root can be divided into two branches, one leading to the receptor and the other leading to the blood vessel wall, which makes the blood vessel relax after being stimulated. This branch can also reach the walls of arterioles and anterior capillaries, causing their relaxation reaction. This reverse conduction leads to the response of effector called axonal reflex. Stimulating a small piece of skin can relax the skin blood vessels far away from the stimulation site, and this reaction can still occur after cutting off all nerves leading to this area. This is an important evidence for the existence of axonal reflex. However, a few days after the nerve was cut off, the reaction disappeared because the nerve fibers had degenerated.
Vasodilator center
The group of nerve cells that regulate vascular movement in the central nervous system is called vascular movement center. Its high-level center is in the cerebral cortex, and its low-level center is under the cortex from hypothalamus to spinal cord. There is a close relationship between vascular movement center and heartbeat regulation center, and they often appear at the same time in the reflection of cardiovascular system. Cardiac acceleration reflex is often accompanied by vasoconstriction reflex; Bradycardia reflex is often accompanied by vasodilation reflex. This is because these centers are close to each other in the brain and spinal cord.
The lower center of spinal vascular movement is located between thoracic 1 and lumbar 2 segments of spinal cord. The experiment of spinal cord transection found that the higher the transection site, the more the blood pressure dropped. Stimulation at the transection of thoracic spinal cord leads to an increase in blood pressure. After cervical spinal cord amputation, blood pressure first decreased and then rose again soon. The spinal cord was completely destroyed, and the blood pressure dropped beyond recovery. The vasoconstrictor center of the spinal cord is composed of thoracic and lumbar sympathetic and vasoconstrictor neurons, which can integrate various nerve impulses and have intense activities to maintain hypertension in spinal animals (animals that only keep the spinal cord). Vascular architecture fibers originated from thoracic and lumbar segments of spinal cord. In the whole body, the activity of spinal cord vasoconstriction center is controlled by higher centers such as medulla oblongata.
The vasomotor center of the medulla oblongata stimulates the left and right concave areas at the bottom of the fourth ventricle of the medulla oblongata with tiny needle electrodes in dogs, cats and other animals, which can increase the arterial blood pressure, which is called the compression area of the medulla oblongata, that is, the vasomotor center. This area can also cause sympathetic reactions such as cardiac acceleration, and it is the sympathetic center at medulla oblongata level. The compression area of the medulla oblongata includes most of the dorsal part of the reticular structure in the first two thirds of the medulla oblongata. Descending fibers reach vasoconstrictive neurons of spinal cord, medullary neurons are destroyed or descending fibers are cut off, and blood pressure drops. The nerve activity of vasoconstrictive neurons in spinal cord is caused by the nerve activity of neurons in the reticular structure of medulla oblongata. Some major vasomotor reflexes are also realized through these groups of neurons. From 1936 to 1938, China physiologists, such as Chen Meibo, Yi, etc., led by Lin Kesheng, made a systematic study on the vasomotor center of the medulla oblongata, and published a series of high-quality papers on the compression center (sympathetic nerve center) and decompression center (sympathetic inhibition center) in China Journal of Physiology. It is proved that there is a sympathetic nerve center between the voiceprint and fovea of the fourth ventricle of the medulla oblongata and near the vestibular nucleus, and the influence of the compressed area on visceral function is studied comprehensively. It is found that stimulating the compressed area can contract the blood vessels of the heart, intestine, kidney, uterus and legs, and can cause sympathetic reactions of various organs. In addition, the localization of ascending and descending bundles in sympathetic nerve center is also studied. It is proved that there is a sympathetic nerve inhibitory center (decompression area) in the medulla oblongata. Lin Kesheng and Lv Yunming studied the position of sympathetic nerve center in medulla oblongata of various vertebrates, including fish, toad, turtle, chicken, goat, guinea pig, pig, rabbit, cat, dog, hedgehog and monkey. It is found that the compression center of these animals is closely related to vestibular area. The compression area of lower vertebrates is on the head side of vestibular area, and that of mammals is on the tail side of vestibular area. The lower the animal, the lower the sensitivity of the compression zone to stimulation, and the less obvious the compression effect. The author thinks this is because their sympathetic nerves are not developed enough. Electrical stimulation of the medulla oblongata near the fourth ventricular latch causes hypotension, so it is called decompression zone. Including the vast area on the ventral side of the 1/3 reticular structure behind the medulla oblongata. The decompression effect of this region is not the result of the excitement of vasomotor nerves, but the inhibition of the activity of vasomotor centers. Excessive carbon dioxide in blood strengthens the excitement of vasoconstriction center, makes blood vessels contract and raises blood pressure; Too little carbon dioxide reduces the excitement of contraction center, vasodilation and blood pressure drop. Both medulla oblongata and spinal cord vascular motor center can produce pressor reflex to excessive carbon dioxide in blood, but medulla oblongata center is more sensitive than spinal cord center. All kinds of afferent impulses can affect the activity of vasoconstriction center of medulla oblongata, especially the decompression reflex of carotid sinus aortic arch, which is the most important in the mechanism of blood pressure regulation.
There are vascular motor centers in the midbrain and forebrain above the medulla oblongata. The S-shaped gyrus of dog brain can also cause decompression response when stimulated. Stimulating midbrain abdomen can cause typical pituitary pressor response. Cutting off the brain stem at the level of red nucleus causes significant changes in blood pressure (often related to respiratory changes). Stimulating cerebellum can also cause changes in blood pressure, which is related to the influence of cerebellum on sympathetic nerve. The hypothalamus of diencephalon is the advanced center of the whole autonomic nervous system, which can cause significant changes in blood pressure. In dogs with cerebral cortex removed and diencephalon preserved, the cardiovascular reflex is very complicated, and blood pressure often rises and the heart beats faster. In newborns with cerebral cortex hypoplasia, diencephalon plays a leading role in circulatory regulation. The well-developed cerebral cortex has the strongest effect on the regulation and integration of blood circulation. The cerebral cortex controls the activities of cardiovascular system through the establishment of conditioned reflex, so that blood circulation can quickly adapt to various complex living conditions.
Vascular motor reflex
Baroreceptors are distributed in many parts of the cardiovascular system. When stimulated mechanically, it can cause reflex motion of blood vessels, leading to changes in arterial blood pressure, among which carotid sinus and aortic arch are the most sensitive, and the second area can cause decompression reflex after stimulation. Smaller blood vessels and even general tissues have the distribution of baroreceptors, which can also cause reflex blood pressure drop (see blood pressure), but the response is weak.
Tam reflex1866 S. Tam found that when the afferent nerve of a limb or organ is stimulated, the blood vessels of the limb or organ expand while the blood vessels of other parts contract, and the arterial blood pressure increases at the same time. This phenomenon is called Tam reflex. For example, stimulating the dorsal nerve of the rabbit's foot makes the blood vessels in the lower limbs controlled by the nerve relax and increase in volume, while the blood vessels in other parts of the body contract, leading to pressor reflex, which has obvious effects on blood concentration to more active organs and blood redistribution.
The blood pressure of vagus nerve compression reflex vena cava decreases, which can stimulate vagus nerve compression fiber endings, cause extensive contraction of vascular bed and increase reflex blood pressure. This reflex is more common in massive blood loss, when the venous pressure is reduced, such as the vagus nerve is intact, so the arterial blood pressure cannot be reduced or not much. Blood pressure drops more after vagotomy. Applying cocaine to the right atrium has the same effect as cutting off the vagus nerve, which can inhibit the vagus nerve pressor reflex and lead to a greater drop in blood pressure during blood loss.
Regulation of vascular movement by higher central nervous system
Regulation of Cerebellum, Midbrain and Hypothalamus on Vascular Movement When the cerebellum and Midbrain are stimulated, they can all cause vascular movement reaction. Stimulating the frontal cortex of cerebellum can inhibit the vascular motor center and produce compression or decompression reflex. Hypothalamus is a more important autonomic nerve center. Electrical stimulation of the posterior hypothalamus of animals causes vasoconstriction of limbs; Thermal stimulation of the anterior hypothalamus leads to relaxation of blood vessels in limb skin. Hypothalamus is the center of thermoregulation, and its influence on vasoconstriction is an important part of thermoregulation mechanism. Thermal stimulation of hypothalamus relaxes skin blood vessels, helps to dissipate heat when the body temperature is too high, and plays an important role in keeping the body temperature constant. The cerebral cortex is the highest center for regulating and integrating vascular movement, and the so-called integration is an effective physiological process for integrating different physiological responses with each other. When cortical function weakens or even disappears, hypothalamus is the integration center of various plant sexual functions. Normally, it works under the control of the cerebral cortex. Only the cerebral cortex can highly unify the various functions of the body, including cardiovascular exercise, with the internal and external environment and complete the most complicated adjustment and integration. Electrical stimulation of the motor area of cerebral cortex and some areas of amygdala caused pressor response, and the heartbeat accelerated; Stimulating the orbital part of frontal lobe, anterior part of temporal lobe, piriform area and other parts of cortical amygdala causes low reactivity; Stimulation of cingulate gyrus, orbital gyrus and insula can cause obvious vascular response.
Regulation of cerebral cortex on vascular movement. Using plethysmography to record limb vascular movement can reveal the powerful control function of cerebral cortex. 19 18 years, Tsitovich first established vasoconstriction conditioned reflex by combining flute sound with skin cold stimulation, and only flute sound caused the same vasoconstriction reaction as cold stimulation. Later, A.A. rogov established conditioned reflex of vasoconstriction and vasodilation in human body and dog body respectively, and found that the reflection of conditioned reflex of vascular consolidation was not less than that of relevant unconditioned reflex, but it was often greater than the latter. Even in the experiment of human arm plethysmography, when the conditioned reflex of blood vessels is contrary to the unconditional reflex caused by strong stimulation, it can overwhelm the unconditional reflex; For example, skin pain stimulation at 63℃ causes obvious vasoconstriction, and after light is combined with skin thermal stimulation at 43℃ to form a consolidated vasodilation conditioned reflex, the response of conditioned stimulus light to skin pain stimulation at 63℃ is obvious vasodilation, and the vasoconstriction response of skin pain stimulation at 63℃ can completely disappear.
On the basis of very solid vascular conditioned reflex, we can establish second, third or even higher vasodilation conditioned reflex. Selective generalization from the first signal system (real stimulus) to the second signal system (abstract words) can occur; For example, words related to realistic conditional stimulation can cause corresponding positive vascular conditioned reflex and obvious differentiation phase, even accompanied by corresponding skin temperature feeling. Rushmeyer, an American scholar, and others saw that the same cardiovascular reaction, such as the change of electrocardiogram, appeared before the circuit was connected, which confirmed that dogs also had conditioned cardiovascular response from the electrophysiological point of view.
Humoral regulation of vascular movement
Chemicals released into blood by some tissues and organs in animals can regulate the functional state of vascular system. Some of them are coordinated with vascular reflex under the control of nerves and become a link in the regulation of the whole circulatory system. In addition, some humoral factors are not controlled by nerves and are important factors for local blood flow regulation. To sum up, it can be divided into three substances: ① hormones secreted by endocrine glands, such as adrenaline and norepinephrine; ② Some chemicals released by tissues in some special activities can affect blood vessel movement, such as bradykinin, renin, serotonin and histamine. ③ General metabolites of tissues, such as adenine acid, the decomposition product of carbon dioxide, lactic acid and adenosine triphosphate. The first is controlled by nerves. The second and third types have little or no relationship with nerves (Table 3).
Adrenaline and norepinephrine are secreted by adrenal medulla, and their effects are similar to those of sympathetic nerve excitation. Both hormones can increase the metabolic rate of the heart; Accelerate and strengthen the heartbeat, and then increase cardiac output. Adrenaline has a strong effect on the heart. Norepinephrine has a strong effect on blood vessels. The combined effects of these two hormones on heart and blood vessels are to increase heart rate, cardiac output and systemic blood pressure.
Acetylcholine can relax small blood vessels and increase the blood flow of local tissues. Because it is easily destroyed by cholinesterase, it is impossible to have a large amount of acetylcholine in the blood under normal circumstances. Injecting a small amount of acetylcholine has a short-term antihypertensive effect. Its physiological significance lies in that it is the transmitter of cholinergic vasomotor fibers. When vagus nerve and other cholinergic vasomotor fibers are excited, the release of acetylcholine causes local vasodilation and cardiac arrest.
Vasopressin secreted by the posterior pituitary gland causes contraction of small blood vessels, including coronary vessels. For a long time, the endocrine function of the posterior pituitary gland was controlled by nerves. Stimulating the nerve center increases secretion, and vasopressin secretion in the posterior pituitary gland also plays a decisive role in pressor reflex caused by pain stimulation.
Renin and angiotensin partially block renal artery, resulting in insufficient blood supply to the kidney, which will cause renal hypertension in animals. The reason is that the decrease of blood sodium stimulates the cells around the glomerulus to release an enzyme called renin (angiotensinogen), which can hydrolyze plasma angiotensinogen (in α2 globulin) into a decapeptide called angiotensin I after entering the blood. When it passes through the pulmonary circulation, it is stripped of two amino acids by invertase and becomes angiotensin II. Angiotensin Ⅱ is hydrolyzed by aminopeptidase to heptapeptide angiotensin Ⅲ. Angiotensins ⅱ and ⅲ have high biological activities, especially angiotensin ⅱ is the strongest vasoconstrictor found at present. Angiotensin ⅲ mainly stimulates the adrenal cortex to secrete aldosterone, thus enhancing the reabsorption of sodium and water by renal tubules. Both angiotensin Ⅱ and angiotensin Ⅲ can raise blood pressure.
Local humoral regulators are mostly tissue metabolites such as carbon dioxide, lactic acid, hydrogen ions, potassium ions and adenosine triphosphate decomposition products such as adenine acid. It usually has the effect of local vasodilation and helps to increase the blood supply of active organs. Histamine is a decarboxylation product of histidine. Many tissues, especially skin, lung and intestinal mucosa, contain a large number of mast cells. When tissues are inflamed, injured and allergic, mast cells are released, which makes smooth muscles contract, but makes capillaries relax strongly, even causing damage, which leads to increased permeability of small blood vessels and a large amount of plasma exudation, thus reducing circulating blood volume and arterial blood pressure. These reactions have a destructive effect on blood circulation. Tryptophan-containing derivatives such as digestive tract, brain tissue and platelets are called serotonin (5-HT), which generally has vasoconstrictive effect, but a small amount relaxes muscle blood vessels. Prostaglandins are widely distributed in various tissues and can be released under physiological and pathological conditions, first in tissue fluid and then in circulating blood. Its composition is complex, some components have local vasoconstriction, but the main component prostaglandin causes vasodilation.