Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Our Bodies and Their Systems A Model for Society Our Bodies and Their Systems In our divided society, we are called to be healers. As healers, we need to envision society in a new way with systems that work together in harmony. Our own human bodies provide an insightful model of how natural systems can function with each other in proper ways. We contend that the systems of society— health care, education, judicial, political, economic, transportation, communication, and all the others—should interact with each other in the same way that the systems of a healthy body operate. In healthy individuals, all of their organ systems operate in harmony with each other. They should serve as the model for a healthy society. The Cell – the Fundamental Unit of Life Systems thinking is holistic thinking. Consideration of biological systems starts with the cell, the fundamental unit of life. A microcosm of the whole organism, each cell contains specialized parts called organelles that work together to carry out all the fundamental tasks of life for each particular cell. Each organelle carries out a unique function: some parts help generate the energy required to power the cell; others transport vital substances from one part of the cell to another; still other organelles function like manufacturing plants, churning out the raw materials needed for a cell to work properly; certain other parts of the cell assemble and customize these raw materials so that they are best suited to carry out their tasks; other parts help defend the cell and maintain a proper internal environment. The cell, then, is very much like a miniature city—a society that functions in concert to carry out the specialized tasks the cell is designed to do. Helping to orchestrate and coordinate all of the dynamic functions of the cell is the main information bank of the cell, the nucleus. Here, in the center of the cell, is stored the DNA of the cell. DNA—deoxyribonucleic acid— is the material that encodes all the genetic information for the cell and for the whole body. Each of the 3 trillion cells in the human body, except for the specialized sex cells, contains an identical set of DNA. The genetic material in the nucleus of a cell is organized into long and twisted strings called chromosomes. The typical human cell has 46 chromosomes in it. Each chromosome is a long string of DNA organized into thousands of genes. A gene is a section of the string of DNA that encodes a particular bit of genetic information. There are about 30,000 genes in a human being. The Human Genome Project has been working on deciphering the massive amount of information contained in the DNA of human cells. DNA is a blueprint. Each gene is a set of directions for assembling a certain protein. Proteins are the building blocks that cells use for constructing its constituent parts and carrying out its intended functions. Not all of the genes in a person’s DNA are active in every cell. The particular combination of genes used by a cell determines the cell’s purpose. The Process of Development – from Conception to Baby The sperm and egg are cells of the body that each only contains half of the genetic material that other body cells do—they have 23 chromosomes. When the sperm and egg are united together in the process of fertilization, the full suite of genetic material—46 chromosomes—is restored. Fertilization occurs after sperm—about 3 million of them—are deposited in the woman’s cervix, the opening of the womb. Of these millions of sperm, usually only one of them will reach an egg that has been released from the ovary. When more than one arrives simultaneously, twins can develop. The sperm penetrates the outer layers of the egg and fuses with the egg, joining their genetic material. The new cell, created by the union of the sperm and egg, then begins an intricate process of development, culminating in the creation of a new baby. The first step in the process of development is cellular division: one cell becomes two; two becomes four, and so on, resulting in the formation of a clump of cells. These early cells are stem cells. Each one has the potential to give rise to any cell type in the body. As development proceeds, the growing cells each become more and more specialized, and less able to change its type of cell. Cells multiply in at least 260 varieties, and there are billions of cells in a human body. A complex set of instructions, relayed by chemical signals inside and around the growing cell, directs the future development of an individual cell. These instructions guide the cell to turn on and off different genes, which encode specific proteins that allow the cell to grow more and more specialized. Other chemical messages serve as a road map for the subsequent development of the cell’s offspring. Two basic messages are told to the cell and its descendants: what to grow into, and where to go in the developing organism. In this way, many different kinds of cells grow together to create a body with a unique form, that of the human body. Cells don’t develop by themselves. Millions of cells follow similar trajectories in their lives. Similar cells then become tissues; tissues develop into organs; organs function together in systems of the body. From the earliest stages of cells dividing in the newly formed embryo, body systems are beginning to develop. With each passing week of gestation, the fetus becomes more and more developed, and what originates as a clump of dividing cells begins to look distinctively human. By the end of the first trimester, all of the organs of the body have been roughly formed, and throughout the remainder of the pregnancy, systems of organs begin to interact with each other: blood cells begin to form and are pumped through the developing circulatory system; the brain and nervous system begin to control certain body functions; the musculoskeletal system begins to allow the fetus to move around in the uterus. When gestation comes to an end and the baby is born, the systems of the body continue to develop. The central nervous system, in particular, continues to develop in profound ways after the individual is born, and is influenced by both genetics and the surrounding environment. Early experiences affect the development of the brain and lay the foundation for intelligence, emotional health, and moral development. Healthy early development of the brain is vitally dependent on nurturing and dependable relationships. The Wisdom of the Body Knowing structure and functions of the body’s organs isn't enough. They are connected to each other as organ systems which must work in harmony with each other to maintain a steady internal environment in which the body's 75 to 100 trillion cells can thrive. Our bodies are surrounded by the external environment, but they also have an internal environment, which was described in the late 19th century by the French physiologist Claude Bernard (1813-1878). He noted that body cells remained healthy only when the temperature, pressure, and chemical composition of the internal environment of the body remained relatively constant. The American physiologist, Walter B. Cannon (18711945), coined the term "homeostasis" to describe this phenomenon. From the two Greek words, "homeo" meaning the same, and "stasis," meaning standing, homeostasis describes the tendency of the body to maintain a certain balance or equilibrium. As Cannon emphasized, homeostasis does not mean something fixed and unchanging that remains the same all the time, but rather "a condition that may vary, but which is relatively constant." He called this "The Wisdom of the Body." In health, all of the body’s systems are aligned, constantly interacting to maintain an optimal internal environment for all of the body’s individual cells, regardless of the hostility of the external environment. There is no such thing as winners and losers among the body’s organ systems. In the healthy body, ALL of its components thrive, not just some of them. This, indeed, is the wisdom of the body. The Body’s Systems There are many systems in the body, and together they can seem somewhat overwhelming. What follows is a brief introduction to each of the major systems of the body, including a description of their primary components and functions. Understanding the many systems of the body can help us envision how the systems of society should function together. Nervous system The nervous system is the body's primary control system. Composed of the brain, the spinal cord, and nerves, it sends, receives, and processes nerve impulses throughout the body. Sensory experiences—gathered by the eyes, ears, skin, and other specialized structures—are transmitted by nerves to the brain and spinal cord. There, millions of bits of information are integrated and processed, and the brain generates appropriate nerve impulses to respond to the incoming stimuli. These nerve impulses tell muscles and organs what to do and how to adapt to the environment. There are three parts of the nervous system that work together: the central nervous system, the peripheral nervous system, and the autonomic nervous system. The central nervous system consists of the brain and spinal cord. It sends out nerve impulses and analyzes information from the sense organs, which inform the brain about things you see, hear, smell, taste and feel. The peripheral nervous system includes the nerves that branch off from the brain and the spinal cord. It carries the nerve impulses from the central nervous system throughout the body to the muscles and glands. The autonomic nervous system regulates involuntary action, such as heartbeat and digestion. Endocrine System Along with the nervous system, the endocrine system is one of the body’s vital communication and control systems. The endocrine system acts to regulate body processes that go on for relatively long periods of time, including: sexual development; growth; mobilizing the body against stress; maintaining nutrient, electrolyte and water balance in the blood; and regulation of cellular metabolism. This system is made up of a group of glands spread throughout the body, including the pituitary gland, thyroid gland, parathyroid glands, adrenal glands, thymus gland, pineal body, pancreas, ovaries, and testes. The glands produce hormones, releasing them directly into the bloodstream. Hormones are the body's long-distance messengers, chemicals that operate in feedback loops to directly change the activity of cells. These hormones are transported to specific organs and tissues throughout the body and help organs adapt to changing internal and external environments. They also help orchestrate the interactions of different body systems. Circulatory System The cardiovascular or circulatory system is the body's transport system. It is made up of a group of organs that transport blood throughout the body. The heart pumps the blood through blood vessels, including arteries and veins, transporting it to all the cells and tissues of the body. Oxygen-rich blood leaves the left side of the heart and enters the biggest artery, called the aorta. The aorta branches into smaller arteries, which branch further into even smaller vessels that travel all over the body. The smallest blood vessels are called capillaries and are found in body tissues. Within capillaries, a vital exchange takes place: blood brings nutrients and oxygen to the cells and removes carbon dioxide, water, and other waste products of metabolism. The blood, which no longer contains oxygen and nutrients, then goes back to the heart through veins. Veins carry waste products away from cells and bring blood back to the right side of the heart. From the right heart, blood is pumped to the lungs, where a reverse exchange occurs: the waste product carbon dioxide is eliminated, and the blood becomes restored with oxygen. As the body’s transport system, the cardiovascular system needs to be responsive to the changing metabolic needs of the body. To meet the increased physiologic demands placed on the body by exercise, for example, complex control mechanisms are put into action. As a result, the heart beats faster and more forcefully, and certain blood vessels constrict while others expand, preferentially shunting nutrient-rich blood to areas of high demand like the muscles. Respiratory System The respiratory system ensures that the body is supplied with oxygen and that carbon dioxide is expelled from the body. Oxygen is critical to the basic processes of cellular metabolism that sustain life, while carbon dioxide is a waste product of metabolism. The respiratory system includes the nose, trachea, and lungs. When signals from the respiratory center of the brain instruct the diaphragm to activate, inspired air enters through the nose or mouth, traveling down a long tube called the trachea. The trachea branches into two bronchial tubes, or primary bronchi, which direct air to the lungs. The primary bronchi branch off into even smaller bronchial tubes, or bronchioles. The bronchioles branch further, ultimately ending in the alveoli, or air sacs. Air follows this path to the alveoli, where gas exchange occurs: oxygen passes through the walls of the air sacs and blood vessels into the blood stream while carbon dioxide passes back into the lungs and is exhaled. Digestive System The gastrointestinal or digestive system helps provide the body with energy necessary for life. It comprises organs that break down food into protein, vitamins, minerals, carbohydrates, and fats, which the body needs for energy, growth, and repair. After food is chewed and swallowed, it goes down the esophagus and enters the stomach, where powerful stomach acids further break it down. From the stomach the food travels into the small intestine. Chemicals secreted into the small intestine from the liver and pancreas help continue to break down the food into nutrients that can enter the bloodstream. Tiny hair-like projections in the walls of the intestines help transport the nutrients into the blood vessels surrounding the walls. The excess food that the body doesn't need or can't digest is turned into waste and is eliminated from the body. The liver, which plays an important role in digesting food, also helps store energy acquired from digested food, build important proteins for the body, and metabolize various substances in the bloodstream. Urinary System The urinary system eliminates waste from the body, in the form of urine. The kidneys remove waste from the blood, combining the waste with water to form urine. From the kidneys, urine travels down two thin tubes called ureters to the bladder. When the bladder is full, urine is discharged through the urethra. The kidneys also play an integral role in maintaining the delicate balance of fluids and electrolytes that allow cells to function properly. As blood is pumped through the kidneys, the composition of various electrolytes is adjusted, with extra salts and water being excreted in the urine. By altering the amount of water and solutes in the bloodstream, the kidneys also are critical in maintaining appropriate blood pressure throughout the body. Immune System The immune system is the body's primary defense system, protecting it against infections and diseases. This system is a complex network of specialized organs, tissues, and cells that work together to respond to external threats, including viruses, bacteria, fungi and other harmful substances that may enter the body from the environment. One of its primary functions is to distinguish between molecules inside the body that are native to the body or foreign invaders, called pathogens. The immune system protects the body in three overlapping ways: 1. Innate Immunity: Innate defenses act immediately in a non-specific way to deter the incursion of pathogens. General defenses include physical barriers (such as skin and cilia in mucous membranes) to prevent entry of threatening substances. Tears, nasal secretions and saliva contain bacteriadestroying enzymes. 2. The inflammatory system: When the general defenses are breached, special cells migrate to infected areas to engulf pathogens in an inflammatory response. This response helps detect and eliminate the invader before it can establish a foothold and begin reproducing. 3. The immune response: If an invading pathogen escapes the innate defenses, the body can launch an adaptive, or specific response against one type of antigen. White blood cells help orchestrate this process, in which different cell types secrete antibodies and other chemicals to fight disease. Lymphatic System The lymphatic system is also a defense system for the body. Consisting of a network of vessels, nodes and a few specialized organs, it has several key functions: filters out organisms that cause disease produces white blood cells generates disease-fighting antibodies distributes fluids and nutrients in the body drains excess fluids and protein so that tissues do not swell The lymphatic vessels are closely linked with the circulatory system, and help transport body fluids. These vessels carry excess fluid away from the spaces between tissues and organs and return it to the bloodstream. Lymph, the fluid inside these vessels, contains white blood cells that are transported in and out of the bloodstream as necessary. Reproductive System The reproductive system helps to maintain the continuity of life, allowing humans to produce children. Sperm from the male fertilizes the female's egg, or ovum, in the fallopian tube. The fertilized egg travels from the fallopian tube to the uterus, where the fetus develops over a period of nine months. Integumentary System The integumentary system provides the body's primary contact with the external environment. Comprising the skin (the largest organ of the body), the subcutaneous tissues and subcutaneous fat, this system serves several key roles: insulates the body, enabling it to maintain a normal core temperature in spite of variation of temperature of the external environment serves as a protective barrier for the body supports the removal of waste through dead skin cells and sweat maintains proper tissue moisture holds receptors for stimuli response Skeletal System The skeletal system provides much of the body’s infrastructure. Made up of bones, ligaments and tendons, the skeleton shapes the body and protects organs. The skeletal system works with the muscular system to help the body move. A less obvious function of the skeletal system is to serve as a production factory for valuable cellular material. Bone marrow is a soft, fatty tissue that is found inside bones where red blood cells, many white blood cells, and other immune system cells are produced and released into the bloodstream. Muscular System The muscular system is made up of tissues that work with the skeletal system to enable the body to move. While all muscles are under the control of the nervous system, some muscles are voluntary, meaning that you decide when to move them. Others are involuntary, meaning that they are controlled automatically by the nervous system and hormones without the input of conscious thought. Muscles function by contracting and expanding, thus allowing the body to move and function. There are three types of muscle tissue in the body: Skeletal muscles, which are voluntary, help the body move. These include muscles of the arms and legs, the face and head, and the trunk. Smooth muscles, which are involuntary, are located inside organs, such as the stomach and intestines. Cardiac muscle is found only in the heart. Its motion is involuntary.