The Heart Essay Example | Topics and Well Written Essays - 1000 words

The Heart - Essay Example The arterial supply of the heart is built from the right and left coronary arteries, which arise from the aorta. The cardiac muscle is composed by specialized cells: cardiac myocytes. Kumar et al. (2005) describe five major components in the myocytes: cell membrane (sarcolemma) and T-tubules; sarcoplasmic reticulum; contractile elements; mitochondria; and nucleus. The sarcolemma and T-tubules enable impulse conductions, and the sarcoplasmic reticulum is a calcium reservoir needed for contraction. Mitochondria are crucial components, since they are involved in cardiac contraction by providing a constant supply of ATP to the sarcomeres. Mitochondria are abundant in cardiac tissue, constituting 20% to 40% of cellular volume in energy-demanding zones (Marin-Garcia 2005). Cardiac muscle is composed of sarcomeres, which are the contractile units with an arrangement of thin and thick myofilaments. The myocytes are composed of many parallel myofilaments arrays of sarcomeres in series, which are responsible for the striated appearance (Kumar 2005). Thin filaments are composed of various proteins named actin, tropomyosin, and troponin. Myosin is the thick filament, and possesses the cross-bridges that can attach to the actin. Au (2004) has described the various components of the sarcomere in great detail. Since cross-bridges possess ATPase activity, contraction may be explained as a continuous cycling of cross-bridges. Moreover, cardiac muscle fibers are joined together by junctional complexes called intercalated discs (Dunn 2004), so that the action potential is spread. The role of Calcium Calcium (Ca2+) regulates mechanical contractions and Vandenboom et al. (2005) have shown that "cross-bridge attachment increases thin filament activation dynamically and that this increase is proportional to the level of activation first established by Ca2+"; during membrane depolarization, a small amount of Ca2+ enters through specialized channels, and the influx triggers calcium release of the sarcoplasmic reticulum. Intracellular calcium binds to troponin C, which induces activation of the myofilaments and muscle contraction. Relaxation is initiated by dissociation of Ca2+ from troponin C, followed by its reuptake into the sarcoplasmic reticulum and removal through sodium/calcium exchangers (Chakraborti et al. 2007). Structure and Function Ventricular muscle contracts during systole and relaxes during diastole. The sarcomere length and sliding mechanism has been described by various researchers (Pollack et al 2005). The Frank-Starling mechanism depicts the relationship between structural components of the heart and its function: shorter sarcomeres have considerable overlap of actin and myosin filaments, reducing its contractile force, whereas longer lengths enhance contractility. In a normal heart, moderate dilation increases the subsequent force of contraction. With progressive dilation, however, there is a point at which effective overlap of filaments is reduced, and the force of contraction is reduced (Kumar 2005). The clinical consequences of

Buddhism Research Paper Example | Topics and Well Written Essays - 2000 words

Buddhism - Research Paper Example Siddhartha got distressed by all the sufferings around him and decided to leave his family and all the material comforts he possessed, and set out on a wondering life. It was in this journey that he sat under the Bodhi tree and staunchly decided not to move until he got enlightenment (Harvey 45). Buddha decided to leave the palace at the age of 29 on four different occasions to explore. During his first visit outside the palace, he witnessed an old man who was bent over and had problems walking when Siddhartha passed by; the man faced him, his red eyes squinting from his terribly wrinkled old face. In his second trip, he saw a sick man, crying in pain. On his third outing, Siddhartha came upon a corpse. He was saddened by these sights of sickness, old age and death. On his fourth outing, he met a monk who inspired him to leave the palace and all his mundane possessions, including his wife and son (Harvey 46). He sought to understand more about life and why human beings suffer, and ho w he would help in ending suffering in the world. During his enlightenment, he found the power to observe his former life, the power to see the rebirth of all forms, power to see death as well as the realization that he had left all the desires and ignorance that he had possessed. He had by all ways become a Buddha, meaning the â€Å"awakened one†. ... The Basic Tenets of Buddhism Reincarnation According to Buddhism, human beings possess the ability to get free from sufferings by observing, meditation and cultivating a lifestyle as prescribed by Buddha. Buddha gave a number of teachings known as Dharma. The wheel is a distinguished symbol in Buddhism since it depicts the perpetual cycle of life and death. According to Buddhism, after human beings die, they are born in a new form. They could either take the form of a deity, a human being, a ghost, an animal or even an inhabitant of hell. It is the belief that all the positive thoughts and people’s actions bring good karma, and may direct an individual into getting reborn in a higher form. The consequences caused by a person’s negative deeds, or evil karma, may lead to rebirth in a lower form (Gethin 22). Buddhism as a religion does not agree with the existence of a permanent self that will reincarnate from this life to the next. The assumption of an existing self gets created by the following five aggregates: Skandha, that suffers from a constant becoming and possesses a functional cause-effect relation; the body is the material form. Feeling, or Vedanta, is the sensation that develops from the sense organs in the body. Cognition, or sanna, is the process of classifying and labeling of experiences. Mental constructions, or Sankara, are the states that initiate action. Consciousness, or vijnana, is the awareness of a mental or sensory object. These five elements become impermanent, pass constant transformation, and have no abiding principle or the self. All human beings think that they got a self because of the consciousness. However, consciousness by being in a constant process of becoming and