Human Systems - Human Systems
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Q: what are the systems found in the human body ?
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| 1 | Musculoskeletal System The human skeleton consists of 206 bones together by tough and relatively inelastic connective tissues called ligaments. The different parts of the body vary greatly in their degree of movement. Thus, the arm at the shoulder is freely movable, whereas the knee joint is definitely limited to a hinge like action. The movements of individual vertebrae are extremely limited; the bones composing the skull are immovable. Movements of the bones of the skeleton are effected by contractions of the skeletal muscles, to which the bones are attached by tendons. These muscular contractions are controlled by the nervous system. See Muscle; Skeleton. Nervous System The nervous system has two divisions: the somatic, which allows voluntary control over skeletal muscle, and the autonoinic, which is involuntary and controls cardiac and smooth muscle and glands. The autonomic nervous system has two divisions: the sympathetic and the parasympathetic. Many, but not all, of the muscles and glands that distribute nerve impulses to the larger interior organs possess a double nerve supply: in such cases the two divisions may exert opposing effects. Thus, the sympathetic system increases heartbeat, and the parasympathetic system decreases heartbeat, The two nervous systems are not always antagonistic, however. For example. both nerve supplies to the salivary glands excite the cells of secretion. Furthermore, a single division of the autonomic nervous system may both excite and inhibit a single eftecter, as in the sympathetic supply to the blood vessels of skeletal muscle. Finally, the sweat glands, the muscles that cause involuntary erection or bristling of the hair. the smooth muscle of the spleen, and the blood vessels of the skin and skeletal muscle are actuated only by the sympathetic division. Voluntary movement of head, limbs, and body is caused by nerve impulses arisitg in the motor area of the cortex of the brain and carried by cranial nerves or by nerves th | |
| 2 | Circulatory System In passing through We system, blood pumped by the heart follows a winding course through the right chambers of the heart, into the lungs, where it picks up oxygen, and back into the left chambers of the heart. From these it is pumped in to the main artery, the aota, which branches mo increasingly smaller arteries until it passes through the, smallest, known as arterioles. Beyond the arterioles, the blbod passes through a vast amount -p.f tiny, thin waIled structures called capillaries. Here, the blood gives up its oxygen and its nutrients to the tissues and absorbs from them carbon dioxide and oilier WWste products of metabolism.’ The blood completes its circuit by passing through small veins that join to tbrin increasingly larger vessels until it reaches the largest veins, the inferior and superior vcnae cavae, which return it to the right side of the heart. Blood is propelled mainly by contractions of the heart: contractions of skeletal muscle also contribute to circulation. Valves in the heart and in the veins ensure its how in one direction. Immune System The body defends itself against foreign proteins and infectious microorganisms by means of a complex dual system that depends on recognizing a portion of the surface pattern of the invader. The two parts of the system are termed cellular immunity. in which lymphocytes are the effective agent. and hunieral immun it, based on the action of anti body molecules. When particular lyniphocytes recognize a foreign molecular pattern (termed an antigen). they release antibodies iii great numbers; other lymphocytes store the memory of the pattern liar future release of antibodies should the molecule reappear. Antibodies attach themselves to the antigen and in that way mark them for destruction by’ other substances iii the body’s defense arsenal. These are primarily complement, a complex of enzymes that make holes in foreign cells, and phagocytes. cells that engulf and digest foreign matter. They are |
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