فایل صوتی ندارد
The human body is truly one of the wonders of nature. Gaining an understanding human anatomy is an important scientific goal, and it is obviously of crucial significance for medicine. Although the human body is extremely complex, consisting of a vast array of interdependent parts, several “systems” can be identified and studied individually. We will consider each of these major systems very briefly. The skeleton is made up of bones, joints, and cartilage. The skeleton serves as a frame that supports the body, and as a hard shell that protects organs. The various bones of the skeleton are fitted together at the joints, with cartilage acting as a cushioning material. Red blood cells are produced within the marrow at the center of the bones. The muscles, many of which are attached to the skeleton, allow the body to move and to apply force to external objects, and also to perform some vital functions. Some muscles are under voluntary control, but other muscles?such as the heart and the muscles of some internal organs?operate without our conscious control.
The respiratory system is responsible for breathing and for the supply of oxygen. Air is inhaled through the nose and mouth, and sent down the wind-pipe (or trachea) to the lungs. Within some very small spaces inside the lungs, oxygen is absorbed into the bloodstream. At the same time, carbon dioxide is released and exhaled. The circulatory system is responsible for supplying needed materials throughout the body, and for removing unwanted materials. These materials are carried in the blood, which is pumped through arteries and veins by the contraction of the heart. The blood also contains substances that help to defend the body against infections. Another fluid, known as lymph, is also transported within the circulatory system. The digestive system is responsible for extracting nutrients from food. Food is chewed in the mouth, and then sent down the esophagus to the stomach. Within the stomach, food is broken down and sent on to the small intestine, where nutrients are absorbed. These digestive processes are aided by substances that are released by other organs, such as the pancreas and liver.
Undigested material then goes to the large intestine, where water is re-absorbed. Waste is then excreted through the colon and finally the anus. The urinary system allows the body to maintain proper levels of water and other molecules, such as sodium and potassium. Blood is sent through the kidneys, which then filter the blood to remove unneeded materials. This waste liquid is sent through tubes called ureters to the bladder, where it is stored and then expelled through another tube, the urethra. The endocrine system contains the glands that release many substances, called hormones, that control the body’s activity. Various glands release hormones that regulate activities such as growth, sexual development, and the breakdown of sugar and starch. The nervous system is also heavily involved in the regulation of the body’s activities. Sensory information is sent via the nerves and spinal cord to the brain. The brain processes information, and transmits instructions via the spinal cord and nerves to the rest of the body.
The skin is the largest organ of the body. It is responsible for covering and protecting the body’s other organs, and it helps to regulate body temperature and hydration. Hair and nails are actually parts of the skin. The reproductive system differs between men and women. The reproductive organs of men include the testicles, which produce sperm cells, and the penis, which is used in sexual intercourse. In women, the reproductive organs include the ovaries, where egg cells are produced, the uterus (or womb), where the fetus develops, the clitoris, which is involved in sexual response, and the vagina, which is involved in both sexual intercourse and in the birth of the baby. Women also possess developed mammary glands that produce milk after childbirth. To understand the workings of the human body in detail, many years of study are required. But we can all gain and appreciate a basic understanding of how this amazing machine is put together.