АНГЛЗАЧЕТ. Reveal striated поперечнополосатый
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The walls of the blood vessels are contracting or expanding when they respond to certain chemicals in the blood or in response to the effect of temperature but we cannot deliberately cause them to lift our arm or open our mouth. For this reason, we may call them involuntary muscles. Smooth muscle tissue consists of long cells. Smooth muscle fibres are bound (связаны) into bundles by connective tissue which contain blood vessels and nerves. 4. Striated muscle tissue consists of large fibres in the form of bundles. Striated muscles are most necessary for manipulation of the bones of the skeleton. Those are the muscles necessary for walking, running, turning the head and so on. That's why we sometimes call them skeletal muscles. This type of muscle tissue includes the large muscle masses of the body, the muscles of the arms, legs, back etc.1 It includes all those muscles which must react quickly to changes in the environment, i.e.2 those that become active through an effort of will. For this reason, we call striated muscles voluntary muscles. 5. Cardiac (heart) muscle is, in a sense, a cross between the previous two. A characteristic feature of cardiac muscle is that fibres have neither a beginning nor an end. In other words, the heart is simply a huge net of muscles in which all elements are continuous with each other. Cardiac muscles («heart» - Greek) have the strength and force of contraction of the skeletal muscle. Cardiac muscle is under complete involuntary control. In that, it resembles visceral muscle. Text В Skeletal and Smooth Muscles Muscle are the active part of the motor apparatus: their contractions are producing various movements, when they are active. Functionally all muscles are divided into two groups: voluntary and involuntary muscles. Voluntary muscles consist of striated muscle tissue and contract by the will of the man. This group includes all the muscles of head, trunk and extremities, i.e., the skeletal muscles, as well as those of some internal organs (tongue, larynx, etc.). The skeletal muscles are the organs of the muscular system. There are more than 400 skeletal muscles in the human organism: in adults they make up about two-fifths of the total body weight. Each skeletal muscle has an arterial, venous, lymphatic and nervous supply. Muscles must always act in groups. Skeletal muscles are complex in structure. They consist of muscle fibers of different length (up to 12 cm); the fibers are usually parallel to each other and are united in bundles. Each muscle is composed of many such bundles. There are tendons at the ends of muscles by means of which they are attached to bones. Smooth muscles form the muscular coat of internal organs such as esophagus, stomach and intestines, bladder, uterus and so on. They also form the part of the capsule and the trabeculae of the spleen; they are present as single cells or as little cylindrical bundles of cells in the skin. They also form the walls of arteries, veins and some of the larger lymphatics. Smooth muscles are not rich in blood vessels, as are striated muscles. A smooth muscle is capable of spontaneous contraction and can contract in two ways. Firstly, individual cells may contract completely and secondly, a wave of contractions may pass from one end of the muscle to the other. Smooth muscle cells are usually elongated cells. In the skin and intestines they are long and thin, but in the arteries they are short and thick. They vary in length from 12-15 mm in small blood vessels to 0.5 mm in the human uterus but their average length in an organ such as the intestine is about 200 mm. These cells have an oval nucleus that encloses nucleoli, and when the cell is contracting the nucleus may become folded or twisted. Muscles have both motor and sensory nerve fibres. Impulses (signals) about the state of the muscle reach the brain along the sensory fibres. The nerve impulses which cause the muscle to contract come from the brain along the motor fibres. Injury to the nerves which innervate muscles causes disturbances in voluntary movements (muscular paralysis). Text А The Circulatory (Cardiovascular) System 1.The cardiovascular system is the system of blood circulation. By the cardiovascular system we mean the heart, the arteries, the veins and the capillaries of the human body. 2.The centre of the circulatory astern is the heart. The human heart is a cone-shaped organ, about 5 fnches1 long and 3 1/2 inches broad. It weighs about in the adult male, 6 ounces in the female. It lies in the thoracic cavity, just behind the breastbone and between the lungs. The heart is a hollow muscle which four chamber. The right heart consists of an upper chamber, the atrium or the auricle and a lover chamber ventricle. Between these two chambers is a one-way valve, the tricuspid valve. The left heart has two chambers, but the valve that separates its chambers we call the mitral valve. Although the heart is a unit, anatomically and functionally, we may think of it as of two pumps - the «right heart» and the «left heart». The right heart receives blood from the veins and pumps it into the lungs by way of the lesser circulatory system. In the lungs the blood receives oxygen. Then it moves into the left heart. From the left heart the well-oxygenated blood moves into a large artery, the aorta. The blood returns to the heart by means of the veins. The walls of the capillaries are so thin that the dissolved nourishment that has come from the digestive system and the oxygen that has come from the lungs can pass through them into the tissues of the body and so nourish it. The capillaries form a close network all over the body. They gradually join together and get larger, and become veins. 3. Blood vessels that receive blood from the ventricle and lead it away from the heart and towards other organs are arteries («air duct» — Greek). The vessels received this name because the early anatomists assumed that they had been empty in dead persons and had carried air. The artery that takes up the blood from the right ventricle and carries it to the lungs is the («lungs» — Latin). The pulmonary artery divides in two - one branch leads to the right lung, the other — to the left. The arteries continue to divide and subdivide and form smaller and smaller vessels with thinner and thinner walls. The smallest arteries are the arterioles and these finally divide into capillaries («hairlike» — Latin). We name them so because of their fineness, though actually they are much finer than hairs. 4. Gradually the capillaries begin to join into larger vessels. Such larger blood vessels that carry blood to the heart from the organs are the veins. The smallest of these are the venules. 5. The particular vein into which the capillaries and venules of the lungs finally unite is the pulmonary vein. The pulmonary vein carries the freshly oxygenated blood to the left auricle. The pulmonary artery and pulmonary vein make up the pulmonary circulation. 6.The contraction of the left ventricle forces the blood through a one-way valve into the aorta («to lift up» — Greek). The aorta is the largest artery in the body. It moves upward at first (the ascending aorta), but then arches over dorsally (the arch of the aorta). In its downward course, the aorta passes through the diaphragm. 7. The blood is a red fluid, which coagulates when escapes, from a blood vessel. It consists of a colourless fluid, plasma or and many millions of minute bodies, the corpuscles. Text В Almost all parts of the body are vascular. Minute and very close-set canals, which have opened into one another traverse them and constitute a small-meshed network. The canals or rather tubes have distinct but very delicate walls. The walls contain a membrane that includes a number of thin epithelial cells, which are bound (связаны) together at their edges. There is a small oval nucleus in each of these cells. These tubes are the blood capillaries. They vary in diameter from 7 to 12 μηι. But there are certain parts of the body in which these blood capillaries have been absent. These are the epidermis and epithelium, the nails and hairs, the substance of the teeth and the transparent cornea of the eye. Tiny rings of muscles, precapillary sphincters, regulate the flow of blood into capillaries. The question of nervous control of the precapillary sphincters still remains the subject of the study. The capillary tubes contain the red fluid, blood. They join on opposite sides and form larger tubes, with thicker walls, which are the smallest arteries on the one side, and veins, on the other. These again join on to larger arteries and veins, which ultimately communicate by a few principal arterial and venous trunks with the heart. The mere fact that the walls of these vessels are thicker than those of the capillaries constitutes an important difference between the capillaries and the small arteries and veins. The most important difference between these vessels and the capillaries, however, is that their walls are not only thicker, but also more complex. They have got several coats, one, at least, of which has been muscular. The number and even nature of these coats differ according to the size because the vessels are not the same in the veins as in arteries, though the smallest veins and arteries resemble each other. The venous system starts with the venules into which the capillaries empty. Small veins join and form larger ones. The larger veins join and form the venae cavae. The superior vena cava collects the blood from the head, neck, arms, and thorax, and the inferior vena cava, from the legs and abdomen. Both empty into the right atrium. Pressure in the venous system is low. In the vein at the level of the heart the pressure would be more than 5-7 mm Hg. It is evident that in the erect position blood that returns to the heart from the feet has to overcome the force of gravity through a distance of about 4 ft. Veins, probably because of the low blood pressure and the absence of pulse waves, are in comparison to arteries, relatively immune to disease. Phlebitis sometimes occurs; this is the formaiton of blood clots within veins because of some infectious process in their walls. Text А The respiratory system Respiration occurs in all living things, both plants and animals.The proper function of this system is perhaps the most important one in the sustaining of life. Interruption of breathing for only a few minutes by suffocation or strangulation causes death. In the human organism, respiration consists of those processes by which the body cells and tissues make use of oxygen and by which carbon dioxide or the waste products of respiration are removed. Inhaled air contains about 20 per cent oxygen and four hundredths of one per cent carbon dioxide. Exhaled air consists of approximately 16 per cent oxygen and 4 per cent carbon dioxide. Nitrogen, which makes up about 79 per cent of the atmosphere, is not involved in the breathing process. When air is inhaled into the lungs, a portion of the oxygen is passing into the blood and is being circulated through the body. At the same time, carbon dioxide is being diffused out of the blood into the lungs and exhaled. Air is breathed through either the mouth or nose into the oral cavity, or pharynx. It then passes through the voice box, or larynx, into the windpipe, or trachea. The trachea ultimately divides into two smaller tubes, bronchi, one is going to each lung. The bronchi divide into tiny passage-ways that are named bronchioles, which lead directly to minute air sacs, or alveoli. The exchange of life-giving gases is effected through the walls of the alveoli. One must know that mechanisms in the ''upperres'piratory /tract ''serveto ''filter, and warm the ''airin its ''journeyto the \ lungs. | J The ''hairs, or ''cilia, in the nostrils partially ''filter out ''dustparticles as does ''stickyse'cretion, ''mucus, which has been pro'duced by ''mucous/cells. | It lines the /mouth, ''nasal/passages, | /pharynx | and \trachea. | | ''Ciliain the ''nasal''passagesand /trachea | are effective in helping to re'move ''foreign/particles | from the ''upperres'piratory \ tract. | | Other structures which have been connected with the system include: the laryngeal tonsils, which are masses of tissue in the nasopharynx or posterior portions of the nasal passages (adenoids are infected or diseased laryngeal tonsils); the sinuses, cavities in the bones in the front part of the skull that provide resonance to the voice, and the pleura, a double-walled membrane which surrounds the lungs. When the diaphragm contracts and flattens, it contributes to the extension of the vertical diameter of the thoracic cavity. Air is constantly renewing in the lungs. The capacity of the air passages is increasing. Any muscular effort, e.g. even standing up, increases the number of respirations. Text В Respiration The term «respiration» means the exchange of gases (oxygen and carbon dioxide) which takes place between the living organism and the environment. One must consider that in higher organisms this exchange takes place at several different levels. An initial exchange must occur between the air in the lungs, from which the oxygen is being continually taken up and into which carbon dioxide is being continually poured, and the external air. This is the process of external respiration. The composition of the air inside the lungs is different from that of the air which we inhale. The content of alveolar air is very constant, especially the one of carbon dioxide, the partial pressure of which is normally 40 mm of mercury. This constancy is the result of a self-regulating mechanism by which the respiratory activity is governed by the amount of carbon dioxide which has been eliminated from the organism. The exchange of gases varies according to the size and activity of the organism. In man at rest the absorption of oxygen reaches about 0.25 litre a minute and the elimination of carbon dioxide 0.2 litre. At a time of maximum muscular activity, the consumption of oxygen and the production of carbon dioxide may both exceed 4 litres a minute. The movement of air into the lungs is brought about by an increase in the volume of the thoracic cavity with the action of the respiratory muscles. The lungs follow this movement passively. Some of the inspiratory muscles have a fixed point on the ribs; when the ribs are being raised the muscles increase the anteroposterior and transverse diameters of the thoracic cavity (costal respiration). Another important muscle is the diaphragm, a thin dome-shaped «sheet», which closes the lower part of the thorax and separates it from the abdomen. The diaphragm contracts and flattens; it contributes in this way to the extension of the vertical diameter of the thoracic cavity and raises the ribs (abdominal respiration). At the time of expiration, the thorax returns to its initial position, and air is expelled through the same tracts that had been used by fresh air during inspiration. In an individual at rest the number of inspirations per minute is 10 to 15; the pulmonary ventilation, or the volume of air which passes through the respiratory system each minute, is about 6 litres per minute. During intense muscular activity the inspiration rate may rise to 50 and the ventilation to 150 litres or more per minute. Text A The Abdomen The abdomen is the largest cavity of the body. It is bounded above by the thorax or chest and below by two pelvic bones which meet in front. From the cavity of the thorax it is separated by the great muscle of respiration - the diaphragm. Laterally and in front it is enclosed by the lower ribs and abdominal muscles. Behind, it is supported by the spinal column. The organs of the abdominal cavity are the liver, the gall-bladder, the stomach, the intestines, the pancreas, the spleen, the kidneys and the bladder. The liver lies under the right ribs and extends across to the left of the epigastrium. The liver is a large organ that weighs about 1.5 kg. Everybody must know that the liver plays a very important role in the vital activities of the organism. It is the liver that secretes bile which participates in the digestive process and has a defensive function, i.e. some toxic substances are detoxified in the liver. The gall-bladder lies beneath the right lobe of the liver. The gallbladder serves as a bile reservoir. The stomach lies under the left ribs and extends across to the right. It is known that its smaller end situates in the epigastrium. The stomach serves as a container of food, which is partly digested in it. The size and shape of the stomach vary with any amount of food that is consumed and the extent of contraction of its wall. The stomach when it is filled with food is usually compared with a chemical retort. Its capacity is some 1-2 litres. The intestines («internal» - Latin) occupy chiefly the central portions of the abdominal cavity. From the stomach the food passes in small portions into the small intestine where it undergoes further mechanical and chemical changes. As the contents of the small intestine cannot move back they may freely pass into the large intestine. The «small» and «large» refers to the width, rather than the length. The small intestine is only 1.5 to 2 inches in diameter at the point where it leaves the stomach and it narrows somewhat thereafter. The large intestine is up to 2.5 inches wide. The Digestive System The digestive system consists of the digestive tract and digestive glands. The digestive tract is some 8-10 m long and is divided into the following parts: oral cavity, pharynx, oesophagus, stomach, small intestine and large intestine. The structures of the different parts of the tract have some special features. The wall of the greater part of the digestive tract consists of three coats: internal - mucous, middle - muscular, and the external - serous. The mucous coat is lined with the epithelium outside which is a connective tissue with a thin layer of smooth muscle fibres. The mucous coat is pink in colour because it has many blood vessels. The numerous small glands in this coat secrete a viscous coat of the digestive tract. It facilitates the movement of food and protects the mucous coat from the damage by solid particles of food and various chemical substances. One must remember that the mucous coat of the digestive tract begins with the esophagus, contains lymph nodules which also have a protective function. |