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WHY IS OUR IMMUNE SYSTEM IMPORTANT? One of the best known examples of the importance of the immune system is the “Bubble Boy” or David Vetter. David was born on September 21, 1971. Even before he arrived, his parents and physicians were making extraordinary arrangements for his life. David had an older brother who died of Severe Combined Immune Deficiency (SCID) before David was born. SCID is a complete absence of an immune system. After the birth and death of one son with SCID, the Vetters opted to try a new approach to ensure David's well-being until an effective scientific option to reconstitute his immune system became available. They agreed to place David into a specially designed plastic-enclosed environment immediately after birth. The bubble was complete with filtered air and strict antiseptic precautions to ensure no germs could enter and infect David. The plastic incubator (later replaced by a plastic-enclosed "room") became popularly known as David's "bubble," and David was thus referred to as "the Bubble Boy." INTRODUCTION TO PROTECTION & CONTROL • What if diseases from all over the world were to attack your body and your body was not about to fight them? You would probably die within seconds or minutes. • However, there is no reason to worry about such an occurrence because our body has a highly specialized mechanism called the immune system, which declares war on all disease causing organisms called pathogens. The structure of our immune system is divided into two specially unique defense armies. • These are the Non-Specific defenses and the Specific defenses. NON-SPECIFIC DEFENSE MECHANISMS • The Non-Specific defense mechanisms is a defensive action that works against a wide variety of invaders. Some apparent symptoms relating to this response are redness, heat, swelling, and pain. • These are the defence mechanisms that we are born with...that come standard in our bodies. These include the barrier formed by our skin; chemicals in perspiration, skin oil, saliva, tears, etc.; the hairs in our nostrils; the ciliary escalator (the cilia and mucus that clean out dust and debris from our lungs and trachea) in our respiratory tracts; the inflammatory response which is the dilation of blood vessels and accumulation of WBCs at the site of an injury (the signs of which are that the area is red, hot, and swollen); and fever, a raised body temperature to inhibit the growth of pathogens. • Note that a fever is caused by your body to inhibit the growth of bacteria, etc., not by the “germs” themselves, per se. There are four main strategies of non-specific defence mechanism: 1. Mechanical defence • Nasal hairs filter the air that is drawn into the upper airways. • Cilia which line the airways, sweep bacteria and other particles away from the lungs. 2. Physical defence • The skin made up of squamous epithelium forms a tough impermeable barrier which normally keeps out bacteria and viruses. • Normally keeps out bacteria and viruses. • The mucous membranes that line the entry points of the body such as nose, eyes, mouth opening, airways, genital openings and anus produce fluids and/or sticky mucus. This traps microorganisms and stops them attacking the cells underneath. 3. Chemical defence • Fluids such as sweat, saliva and tears contain chemicals that create harsh environments for microorganisms. Sweat contains lactic acid and the enzyme lysosome, both of which slow down bacterial growth. • Stomach acid kills many microorganisms that manage to get this far. • When we are injured, blood clots at the injury site, sealing the breach to prevent entry of bacteria. 4. Biological defence • Normally a vast number of non-pathogenic bacteria live on skins and mucous membranes, also called as normal microflora. • These organisms do not harm the body but rather crowd out harmful bacteria preventing them from gaining a foot hold from launching a full- scale infection. SPECIFIC DEFENSE MECHANISMS • In cases where microorganisms get through the primary deterrents, there is a back-up system: the specific defense mechanisms. • This reaction is also referred to as the inflammatory response. Its purpose is to comprise a specific defense measure against a pathogen. • The specific defense system is not made up of actual organ structures, but it is made up of billions of cells. Thus, the specific defense system is known as a functional system, as opposed to an organ system. • When microorganisms penetrate the skin or the epithelium lining the respiratory, digestive, or urinary tracts, it results in inflammation. • Damaged cells release chemical signals such as histamine that increase capillary blood flow into the affected area (causing the areas to become heated and reddened). • The heat makes the environment unfavorable for microbes and raises the mobility of white blood cells. It also increases the metabolic rate of nearby cells. • Capillaries pass fluid into interstitial areas, causing the infected/injured area to swell. Platelets move out of the capillary to seal the wounded area. INFLAMMATORY RESPONSE & IMMUNE RESPONSE • When microorganisms penetrate the skin or the epithelium lining the respiratory, digestive, or urinary tracts, it results in inflammation. This reaction is called the inflammation response. • Damaged cells release chemical signals such as histamine that increase capillary blood flow into the affected area (causing areas to become heated and reddened.) The heat makes the environment unfavorable for microbes and raises the mobility of white blood cells. • It also increases the metabolic rate of nearby cells. Capillaries pass fluid into interstitial areas, causing the infected/ injured area to swell. Platelets move out of the capillary to seal the wounded area. The main symptoms of the inflammatory response are as follows: • The tissues in the area are red and warm, as a result of the large amount of blood reaching the site. • The tissues in the area are swollen, again due to the increased amount of blood and proteins that are present. • The area is painful, due the expansion of tissues, causing mechanical pressure on nerve cells, and also due to the presence of pain mediators. HOW DOES THE INFLAMMATORY RESPONSE END? • Obviously, the inflammatory response should only last for as long as the infection exists. Once the threat of infection has passed, the area should return to normal existence. • The actual process by which the inflammatory response ends is now only beginning to be understood. The key element is a phenomenon known as "Apoptosis". THE IMMUNE RESPONSE • The immune system also generates specific responses to specific invaders, such as bacteria, viruses, and substances that appear foreign and harmful to the body. A specific defense mechanism builds up resistance against a specific pathogen or antigen. • This system is more effective than the nonspecific methods as it has a memory component that improves response time when an invader of the same type (or species) is again encountered. Specific defenses are tailored to an individual threat. Two types of specific defenses are antibodymediated and cell-mediated responses. CELL-MEDIATED IMMUNITY • Cell-mediated Immunity requires direct physical contact with antigens. • It is provided by T cells and does not involve the secretion of antibodies. • T cells are involved in the attacking of certain bacteria, viruses, fungi and immunity to cancer cells. 1. macrogphages engulf invaders 2. antigens appear on macrophage surface 3. Helper T-cells bind to macrophage surface sending out chemical messages 4. T-cells multiply and get specific Killer T-cells to come help 5. T-cells attaches to infected cell and kills them with chemicals 6. Killer T-cells move them on to additional targets ANTIBODY-MEDIATED (HUMORAL) IMMUNITY • Antibody-Mediated (Humoral) Immunity results from the production of antibodies specific to a given antigen (antibody-generators, located on the surface of an invader). • Antibodies bind to the antigens on invaders and kill or inactivate them in several ways. Most antibodies are themselves proteins or are a mix of protein and polysaccharides. • Antigens can be any molecule that causes antibody production. • Antibody-mediated immunity is provided by the B cells (a specific type of white blood cell called macrophages). Within a few days after an infection, an antigen causes the production of large amounts of the antibody capable of interacting with it. • Stages in this process are: 1. antigen detection 2. pathogen activates specific B cells 3. macrophages activate helper T cells 4. B cells and T cells meet and B cells produce antibodies or memory cells 5. antibody's "tag" invaders for further elimination • Each stage is directed by a specific cell type. Killer T-Cells • Defends the body by destroying foreign, infected, and cancerous cells. • A cell infected with a virus will display viral antigens on its membrane. • Killer T-cells recognize the viral antigens and attach to that cell's plasma membrane. • The T-cells secrete proteins that punch holes in the infected cell's plasma membrane. • The infected cell dies. Helper T-Cells • Regulate immune responses • Enabling the other T-cells and B-cells to perform their functions by secreting messenger proteins or by direct contact with other cells. • It is this cell that is destroyed by the HIV virus in patients with Acquired Immune Deficiency Syndrome (AIDS) Memory Cells • Remain in the body awaiting reintroduction of the antigen. VACCINATION • Vaccination is a term derived from the Latin vacca (cow, after the cowpox material). A vaccine stimulates the antibody production and formation of memory cells without causing the disease. • Vaccines are made from killed pathogens or weakened strains that cause antibody production but not the disease. Vaccines exist for all sorts of diseases, both viral and bacterial: measles, mumps, whooping cough, tuberculosis, smallpox, polio, typhoid, etc. Vaccination Schedule 2, 4, 6 months 12 months 18 months 4-6 years Grade 5 Grade 9 Yearly Every 10 years Diphtheria, whooping cough, lockjaw, polio, influenza type B, pneumococcal infections Measles, mumps, German measles, chickenpox, meningitis Two booster needles to continue protection Diphtheria, tetanus, whooping cough, polio, measles, mumps, rubella Hepatitis B, Human Papillomavirus (girls only), meningitis Diphtheria, tetanus, whooping cough, HPV (girls only), meningococcal conjugate Influenza (high risk groups) Booster dose: tetanus, diphtheria TYPES OF IMMUNITY Active Immunity • Active Immunity develops after an illness or vaccine. Vaccines are weakened (or killed) viruses or bacteria that prompt the development of antibodies. Passive Immunity • Passive Immunity is the type of immunity that is short-lived, usually only lasting a few weeks. It is given to combat a specific disease. Examples include: • A mother's breast milk contains antibodies received by the baby. These only last several weeks • Gamma Globin shot is purely an injection of antibodies to provide temporary immunity. You might receive a Gamma Globin shot if you travel outside the country. ALLERGIES • An allergy is an abnormal high sensitivity reaction to an ordinarily harmless substance. The immune system of an allergic person reacts when an allergen (antigen that triggers the allergic reaction) is absorbed into the body, treating the substance as a harmful invader, causing the white blood cells to being producing antibodies. The most common allergies include: • pollens • molds • insect stings • household dust mites • animal dander • foods • medication • insect droppings • An extreme, life-threatening allergic reaction usually to food, medication or insect bites is called an anaphylactic reaction. • It can result in breathing problems, dizziness, hives, a sudden drop in blood pressure, an asthma attack, or unconsciousness. It can be fatal. • It must be treated promptly. An emergency kit containing epinephrine (adrenaline) is usually used by patients prone to these attacks. • It counters the fatal effects by working directly on the cardiovascular and respiratory systems. It also rapidly constricts blood vessels, relaxes muscles in the lungs to improve breathing, reverses swelling, and stimulates the heartbeat. THE LYMPHATIC SYSTEM • The lymphatic system can be thought of as a secondary circulatory system. • The lymph vessels contain a clear, colorless fluid called lymph, which is derived from a network of capillaries which collect this clear fluid as it filters through the capillaries of the blood. • The lymphatic system provides our immune defenses, filters foreign substances and cell debris from the blood and destroys them; and produces a type of white blood cells known as lymphocytes, which circulate in the blood and lymph vessels. • Lymph passes from tiny capillaries to lymph vessels and flows through lymph nodes that are located along the course of these vessels. • Cells of the lymph nodes phagocytize, or ingest bacteria, old red blood cells, and toxic and cellular waste. • Finally, the lymph flows into either the thoracic duct, a large vessel that runs parallel to the spinal column, or into the right lymphatic duct, both of which transport the lymph back into veins of the shoulder areas where is re-enters the general circulation. • All lymph vessels contain one-way valves, like the veins, to prevent backflow. • In an infection, the lymph nodes occasionally become enlarged with lymph and white blood cells and become palpable (can be felt by an examiner). These can be felt most easily at the neck, in infections of the neck and head; in the axillary region (the armpit), in infections of the breast or arm; and in the inguinal region (the groin), in infections of the pelvis or lower extremities. • The tissues of the lymphatic system include the spleen, thymus, bone marrow, and aggregates of lymphatic tissue located in the tonsils and intestines. • The spleen, thymus, and bone marrow manufacture lymphocytes, which are the major cell type of the system. • Lymphocytes arise from by mitosis of stem cells in the bone marrow. • Stem cells differentiate into the major players in the immune system (granulocytes, monocytes, and lymphocytes). • The spleen is also involved in the destruction of old cells and other substances by phagocytosis and plays a role in immune responses. • The thymus is considered the central organ that controls lymphocyte production and antibody formation. • Lymphocytes can be classified as T cells (thymus-derived) or B cells (bone-marrow-derived). Other cells of the lymphatic system include monocytes, which function to ingest foreign substances. Monocytes are believed to originate from lymphocytes. BLACK GREEN YELLOW BROWN PINK WHITE RED BLUE PURPLE ORANGE BLACK GREEN YELLOW BROWN PINK WHITE RED BLUE PURPLE ORANGE You probably noticed that it is rather tough to say the names of the colors very fast, since your brain is also reading the text, which is almost unavoidable...The right half of your brain is trying to say the colors, the left half is trying to say the word itself. THE NERVOUS SYSTEM • Your nervous system coordinates and controls the essential functions in your body. It receives and relays information about activities within your body and monitors and responds to internal and external changes. • You can think of your nervous system as a communication system by with the various cells and parts of your body interacting with the outside world. • Without your nervous system you would be incapable of responding to changes inside and outside your body. In other words, you would be unable to maintain homeostasis CNS • The Central Nervous System consists of the Brain and Spinal Cord. It contains millions of neurons (nerve cells). • If you slice through some fresh brain or spinal cord you will find some areas appear grey whilst other areas appear rather white. The white matter consists of axons, it appears white because it contains a lot of fatty material called myelin. • The myelin sheath insulates an axon from its neighbours. This means that nerve cells can conduct electrical messages without interfering with one another. • The grey matter consists of cell bodies and the branched dendrites which effectively connect them together. • Different areas of the brain are concerned with different functions. For example, you "see stars" when you bang your head and stir up the visual centre which is at the back of your brain. • There are areas of the brain which deal with speech, hearing, smell, sight, movements, salivating, and so on. • Some of these centres are concerned with the information coming into the brain (sensory areas) and others are concerned with making something happen (motor centres). • What do you do when you bite into a ripe apple? Do you wiggle your toes or salivate? • Some responses are very simple and everyone makes the same response: e.g. we all sneeze when our noses are tickled. • Other stumuli are much more complicated and we do not all react or respond in the same way. PNS • The Peripheral Nervous System consists of all the sensory nerves (these feed information into the spinal cord and brain) and the motor nerves (these carry messages to other parts of the body from the brain and spinal cord). • Sensory nerves contain sensory neurones. Motor nerves contain motor neurones. Mixed nerves contain both sensory and motor neurones. • Sensory neurones are usually connected to motor neurones by intermediate neurones (sometimes called inter neurones). • Sensory, intermediate and motor nerves have gaps between them called synapses. • The Central Nervous System is divided into the somatic nervous system and the autonomic nervous system. • The somatic nervous system controls skeletal muscle as well as external sensory organs such as the skin. This system is said to be voluntary because the responses CAN be controlled consciously. • Reflex reactions of skeletal muscle however are an exception. These are involuntary reactions to external stimuli. • The autonomic nervous system controls involuntary muscles, such as smooth and cardiac muscle. • This system is also called the involuntary nervous system. • The autonomic nervous system can further be divided into the parasympathetic and sympathetic divisions. • The parasympathetic division controls various functions which include inhibiting heart rate, constricting pupils, and contracting the bladder. • The nerves of the sympathetic division often have an opposite effect when they are located within the same organs as parasympathetic nerves. • Nerves of the sympathetic division speed up heart rate, dilate pupils, and relax the bladder. • The sympathetic system is also involved in the flight or fight response. • This is a response to potential danger that results in accelerated heart rate and an increase in metabolic rate. THE BRAIN The Cerebrum • The cerebrum or cortex is the largest part of the human brain, associated with higher brain function such as thought and action. The Cerebellum • The cerebellum, or "little brain", is similar to the cerebrum in that it has two hemispheres and has a highly folded surface or cortex. This structure is associated with regulation and coordination of movement, posture, and balance. Medulla Oblongata • This structure is the "tail" part of the brain stem, between the pons and spinal cord. It is responsible for maintaining vital body functions, such as breathing and heart rate. Pons • Part of the hindbrain. It is involved in motor control and sensory analysis. It has parts that are important for the level of consciousness and for sleep. Corpus Callosum • Is a bundle of axons which connects the two hemispheres. Frontal Lobe- associated with reasoning, planning, parts of speech, movement, emotions, and problem solving Parietal Lobe- associated with movement, orientation, recognition, perception of stimuli Occipital Lobe- associated with visual processing • Temporal Lobe- associated with perception and recognition of auditory stimuli, memory, and speech RIGHT-BRAINED & LEFT-BRAINED • The term was coined by psychologist Julian Jaynes, who presented the idea in his 1976 book The Origin of Consciousness in the Breakdown of the Bicameral Mind. • The right hand and eye could name an object, such as a pencil, but the patient could not explain what it was used for. • When shown to the left hand and eye, the patient could explain and demonstrate its use, but could not name it. • Further studies showed that various functions of thought are physically separated and localized to a specific area on either the left or right side of the human brain. This functional map is consistent for an estimated 70 to 95 percent of us. NERVE IMPULSES • One of the basic life functions of all living things is the ability to respond to a stimulus. There are many stimuli to which an organism must respond: a change in air temperature, a change in carbon dioxide level in the blood, contact with a hot or sharp object, the itch at the end of your nose, the hardness of your chair, the cramp in your leg, a feeling of hunger, and many more that have not been mentioned. • There are three main types of structures related to stimuli and responses. Each has a specific function in relation to the others. • The three structures are receptors, neurons, and effectors. • A receptor is a kind of sensor that picks up information about an organism's internal or external environment. • Receptors may be neurons themselves, or they may be organs that are specialized for detecting stimuli. • A receptor picks up a certain kind of stimulus. For example, the eye is a receptor that is sensitive to light, but not to odour. • A neuron is a specialized cell that transmits electrochemical messages, or nerve impulses, from the receptors to the effectors. • An effector is a structure that responds when it is stimulated by nerve impulses. • The principal effectors are muscles and glands. Muscles respond by contracting; glands respond by secreting. • The human nervous system is made up of 10 to 12 billion nerve cells called neurons. • Some neurons, such as those in the brain, are a fraction of a centimeter in length. Others, such as those that run through the legs, are as long as a meter, going from the toes to the spinal cord. • A neuron has several distinct parts, as shown below. • The cell body of the neuron contains the nucleus and most of the cytoplasm known as soma. Soma flows into the extensions. The shape of the cell body varies. Some are round, while others resemble a diamond or are irregular in shape. • Nerve fibers extend from the cell body. These fibers contain one long fiber, the axon, and one or more short fibers, the dendrites. A neuron can have as many as 200 dendrites. While the dendrites are shorter than the axon, they branch extensively because their function is to pick up impulses, either from receptors or other neurons in the vicinity, and conduct them toward the cell body. • The axon carries the impulses away from the cell body, passing it on to other neurons or cells. • The axons of many neurons are covered with a white, fatty protein known as myelin sheath. • The main function of this sheath is to insulate the axon, preventing the loss of chemical ions that are present in the nerve fiber. Since these ions are necessary for the transmission of impulses along a nerve cell, the presence of a myelin sheath increases the speed of transmission. • The myelin sheath is formed of flat Schwann cells, which are wrapped around the axon like a jellyroll. In myelinated axons, gaps that are not covered with the myelin sheath are called nodes of Ranvier. • Nerve impulses jump from node to node, resulting in transmission up to 20 times faster than in nonmyelinated axons. • Biologists classify neurons according to their function. There are sensory neurons, associative neurons, and motor neurons. • Sensory neurons transmit impulses from receptors to the brain or spinal cord. These pick up the stimuli of sight, smell, sound, taste, and touch. Sensory neurons are important in carrying messages about a person's internal or external environment. • Associative neurons, (also called interneurons or association neurons) found only in the brain, ganglia, or spinal cord, are responsible for coordinating nervous activity (they “decide” what to do) and relaying the messages from the sensory neurons to the proper motor neurons to effect an appropriate action by the effectors (muscles and glands). • Motor neurons receive messages from the associative neurons in the brain and spinal cord and activate the muscles and glands (the effectors). • A nerve is a bundle of nerve fibers (axons) bound together by a sheet of connective tissue. • Nerves consist primarily of axons of neurons. • The cell bodies of those neurons are gathered together into groups. • A group of cell bodies that is located outside the brain or spinal cord makes up a ganglion. • A group of cell bodies that is inside the brain or the spinal cord is referred to as a nerve center. • Within the brain and spinal cord, the myelinated fibers form areas referred to as white matter. The cell bodies of the neurons and unmyelinated fibers make up the gray matter of the brain and spinal cord. The Synapse • Because one neuron does not touch another, there is no contact between them, and the electrochemical impulse cannot pass directly from one nerve cell to another. The microscopic space that exists between the axon of one neuron and the dendrite of another is called a synapse. • An axon ends in many small fibers. The endings of axons (synaptic knobs) have cytoplasmic vesicles called synaptic vesicles inside them. • These tiny sacs are filled with compounds called transmitter substances (also known as neurotransmitters). • Neurotransmitters include the following compounds: acetylcholine, noradrenalin, dopamine and serotonin. • When an impulse reaches the end of an axon, it stimulates the synaptic vesicles to release their transmitter substance into the synapse. • The substance, acetylcholine, for example, diffuses across the synapse to the dendrite of the adjacent neuron. • The acetylcholine combines with the receptor molecules in the cell membrane of the dendrite or cell body of the next neuron, increasing the permeability of the membrane at that point on the second neuron to sodium ions, and reversing the polarization of the membrane. • The electrochemical impulse starts on its way along that neuron. • Transmission of acetylcholine from a motor neuron axon to a muscle cell (across a neuromuscular junction) stimulates the muscle cell to contract. • Enzymes destroy the transmitters shortly after they are released into the synapses and neuromuscular junctions. • Acetylcholinesterase, for example, digests acetylcholine to acetic acid and choline. These compounds diffuse back into the axon where they are used again in the synthesis of acetylcholine. • If the excess transmitter substances were not broken down by enzymes, they would continue to initiate impulses in dendrites indefinitely and cause muscles to contract continuously. • When an effector responds to an impulse as described previously, the response is called a reflex act. • A reflex act is an automatic or involuntary action, which is always the same when a particular stimulus is involved. • The closing of the pupil of the eye in response to bright light or the rapid withdrawal of the hand after touching something hot, are both examples of the reflex act. • Reflex activity is predictable; it provides a rapid reaction protecting the body from harm. Reflex acts occur in a fraction of a second, before a person has time to think consciously about what appropriate action is required. • A reflex arc is initiated by stepping upon a sharp stone. Impulses, started by receptors in the toe, travel along sensory neurons to the spinal chord, where associative neurons are stimulated. • The impulses are "switched" to other neurons—among them motor neurons that stimulate leg muscles to contract and move the foot away from the rock. • Impulses going from the injured toe to the spinal cord result in reflex movement, but also travel up nerve pathways to the brain. • Associative neurons in the brain are activated. Impulses may pass from the brain to many parts of the body, leading to voluntary movement. • The reflex arc consists of five parts, which usually involve three neurons (two or more than three are quite common). The reflex arc requires: • Receptor. The receptor recognizes some change in the environment, whether heat, light, sound, or some other factor. The receptor is stimulated to initiate a nervous impulse. • Sensory neuron. The sensory neuron conducts the impulse from the receptor to the spinal cord. • Associative neuron. The associative neuron directs the impulse from the sensory neuron to the motor neuron. It allows the impulse to be routed into a number of possible pathways. • Motor neuron. The motor neuron carries the impulse to the appropriate organ (usually a muscle) to produce the response. • Effectors. The effector is the muscle or organ that will contract or otherwise respond appropriately to the stimulus. • When a doctor wants to check your reflexes, he sometimes strikes the tendon just below the knee cap with his little rubber hammer. He watches to see if your lower leg moves forward immediately. If it does, all is well. • This forward movement of the lower leg is a reflex act and happens involuntarily. • The rubber hammer strikes the tendon, pulling it down, and stretches the muscles in the upper thigh. • The stretch receptors, being embedded in the thigh muscles, pick up the stimuli. Let us follow the path of an impulse generated by only one receptor through the reflex arc to one effector. • Provided the stimulus has exceeded the receptor's threshold, an impulse will be initiated there and propagated along a sensory neuron. The impulse travels to the spinal cord. At this point, the synaptic knobs on the axon's end fibers stimulate their synaptic vesicles to release acetylcholine into the synapse between them and the dendrites of associative neurons (sometimes called interneurons). One associative neuron takes the impulse to the brain; a second, using the same method of impulse transfer as related above, takes the impulse directly to a motor neuron's dendrites. The impulse propagates itself along the axon of the motor neuron. When the impulse reaches the motor end plates at the end of the neuron, they are stimulated and cause contraction of the upper thigh muscle (the effector), which moves the lower leg forward. Because of this quick responding reflex act, your leg responds to the tap of the hammer even before you are aware of the pain. THE ENDOCRINE SYSTEM • As we have learned, the nervous system communicates information about activities within your body and monitors and responds to internal and external changes. The endocrine system is the system of the body that deals with chemical communication by means of hormones, the ductless glands that secrete the hormones, and those target cells that respond to hormones. The foundations of the endocrine system are the hormones and glands. • The endocrine system functions in maintaining the basic functions of the body ranging from metabolism to growth. • Both systems are essential in the maintenance of homeostasis. • The nervous system acts very quickly, but its effects are short-lived. • The endocrine system reacts more slowly to a change in the body, but its effects last longer. Hormones • Hormones are chemical messengers released by specialized endocrine cells or specialized nerve cells. • They transfer information and instructions from one set of cells to another. Although many different hormones circulate throughout the bloodstream, each one affects only the cells that are genetically programmed to receive and respond to its message. • Hormone levels can be influenced by factors such as stress, infection, and changes in the balance of fluid and minerals in blood. • A gland is a group of cells that produces and secretes, or gives off, chemicals. • A gland selects and removes materials from the blood, processes them, and secretes the finished chemical product for use somewhere in the body. • Some types of glands release their secretions in specific areas. For instance, exocrine glands, such as the sweat and salivary glands, release secretions in the skin or inside of the mouth. • Endocrine glands, on the other hand, release more than 20 major hormones directly into the bloodstream where they can be transported to cells in other parts of the body. The Neuroendocrine System • The endocrine system and the nervous system are so closely associated, that they are collectively called the neuroendocrine system. • Neural control centres in the brain control endocrine glands. The main neural control centre in the brain is the hypothalamus. • Suspended from the hypothalamus by a thin stalk is the pituitary gland. • The hypothalamus sends messages to the pituitary gland, which then releases hormones that regulate body functions. Pituitary Gland • The pituitary gland is found on a small stalk at the base of the brain. It controls the action of all other endocrine glands and is therefore often referred to as the “master gland”. • It is composed of two separate halves: the posterior lobe which is derived from brain tissue and the anterior lobe which is derived from epithelial tissue of the roof of the mouth. • The posterior lobe of the pituitary gland secretes two hormones which are manufactured by specialized neurons of the hypothalamus and stored in the posterior lobe. • These hormones are oxytocin and antidiuretic hormone (ADH), also known as vasopressin. • Oxytocin causes contractions of the smooth muscle in the uterus during childbirth. It is also important in the transport of milk from the glands to the nipple. In males, it is needed to stimulate muscles of the sperm duct to propel the sperm out of the body. • Antidiuretic hormone (ADH) controls the elimination of water from the kidneys. If water concentration in the body decreases, the amount of ADH released into the bloodstream increases. • More water is reabsorbed by the kidneys and retained in the body. If the hypothalamus does not produce ADH in sufficient quantities, a condition called diabetes insipidus results as the body eliminates too much water. ADH also influences blood pressure by causing the small arteries to contract. Nervous System Endocrine System How It Communicates Impulse across synapses Hormones in blood Response Speed Responds very rapidly Responds slowly How Long It Lasts (Duration) Short-term and reversible effects Longer lasting effects Where Does It Go? Signal runs through nerves to specific cells Hormones broadcast to target cells everywhere What Does It Do? Causes glands to secrete or muscles to contract Causes changes in metabolic activity Protecting Your Head! • Sports injuries that affect the central and peripheral nervous system are responsible for thousands of deaths or permanent peripheral damage in Canadian youth. • A concussion is caused by the brain being subjected to a trauma where it twisted. Often both brain cells and blood vessels that feed the brain are affected. Blood flow to the brain is restricted by the increase in pressure due to swelling. This results in an "energy crisis" in the brain that can last for weeks. • The brain floats in cerebrospinal fluid and is encased in the skull. These protections allow it to withstand many of the minor injuries that occur in day to day life. • However, if there is sufficient force to cause the brain to bounce against the rigid bones of the skull, then there is potential for injury. • It is the acceleration and deceleration of the brain against the inside of the skull that can cause the brain to be irritated and interrupt its function. The acceleration can come from a direct blow to the head or face, or from other body trauma that causes the head to shake • If a second concussion occurs before the brain recovers from the first one, the energy-starved cells in the brain are likely to die, and individuals may experience a life-threatening swelling of the brain, referred to as second impact syndrome (SIS). • Half of individuals with SIS die, and it is most common in male adolescents and young adults. The long term effects of concussions vary from negligible to cognitive and behavioural impairments, and may depend on the number of concussions.