Health Psychology Ch. 2

The Endocrine System

* 1. Complements the nervous system by acting more slowly 2. Is regulated by the hypothalamus and the pituitary gland. * Consists of a set of glands that work closely with the autonomic nervous system. It communicates with hormones which are secreted into the bloodstream. Certain chemicals are produced by glands and the nervous system and function as hormones and neurotransmitters. The nervous system is linked to the endocrine system by connections between the hypothalmus and the pituitary gland. Chemical messages from the hypothalamus to the pituitary gland cause the release of pituitary hormones into the blood. Most of these hormones stimulate other glands to secrete chemicals. The pituitary gland is called the master gland and secretes up to 8 hormones. There are dozens of different hormones. Some like estrogen - produced mainly in the ovaries - and testosterone - produced mainly in the testes are important in the reproductive systems. Other hormones affect blood pressure and the balance of various chemicals. There is a process called the hypothalmus- pituitary-adrenal axis which reacts to emergencies. In an emergency the hypothalamus sends a hormone called corticotropin-releasing factor to the pituitary gland. This releases adrenocorticotropic hormone (ACTH) into the blood. It travels throughout the body to cause the release of a variety of hormones, especially those in the adrenal glands. The adrenal glands are located on top of the kidneys and release several hormones in response to emergencies. One is cortisol which helps control swelling. Frequent secretions of cortisol can lead to ulcers and high blood pressure. Two other adrenal hormones are epinephrine and norepinephrine also called adrenalin and noradrenalin. They work with the sympathetic nervous system to produce such bodily reactions as speeding up heart and respiration rates and increasing the liver's sugar output to increase quick energy. After the emergency the hormones may stay in the blood system for a while. The impact of the nervous and endocrine systems in an emergency differ. The nervous system uses the above hormones as neurotransmitters and relaying quick commands that move instantly and have an immediate but brief effect. The hormones act more slowly but have a more enduring effect. The thymus gland is located in the chest, is large in infancy and childhood but diminishes in size after puberty. It is important in producing antibodies and immunities early in life. The thyroid gland is in the neck and produces thyroxine that regulates the body's growth and general activity level. There are two main disorders associated with the thyroid, hypothyroidism when the thyroid produces too little hormones and hyperthyroidism where the thyroid produces too much. Hypothyroidism can produce weight gain due to lower activity levels, sometimes dwarfism and mental retardation result. Hyperthyroidism leads to high activity levels, short attention spans, tremors, insomnia and weight loss. The pancreas is below the stomach and regulates blood sugar or glucose. It does this by producing glucagon and insulin. Glucagon raises the concentration of glucose in the blood and insulin lowers it. When the pancreas cannot produce enough insulin to counteract the effect of the glucagon hyperglycemia results. If it persists coma and death may result. And a special note about physiology: there are major structural variations in most major organs. What we think of as the usual structure occurs in only about two thirds of cases. *There is a temporary endocrine gland: the placenta, which is dislodged and expelled during birth, produces hormones that affect the mother and the fetus and provides nutrition and handles waste.* *Hormones that stimulate the production of other hormones end in 'tropic.'*

BP and Life Factors

A number of factors including a) temperature, heat causes vessels in the skin to enlarge, cardiac output and diastolic pressure fall, we often feel drowsy when this happens b) activity during and for a while after exercise increases BP c) emotional experiences like stress, anger, anxiety activate the sympathetic nervous system increasing systolic and diastolic pressure

Defending the Body With an Immune Response

A series of defenders is involved in protecting against invaders. A) First is the skin and the mucous membrane that lines the respiratory and digestive tracts. The skin acts like a wall and the mucous contains antibodies and antimicrobial substances. Many antigens breach this barrier - often through wounds - and the next line includes specific innate and non-specific immune processes. B) Phagocytes in your blood and tissues attack and consume invading substances and identify the antigen for T and B cells. B cells produce plasma cells which produce antibodies. Phagocytes are important with new invaders that have never produced memory B cells. Antibodies attach to the antigens making them easier to kill. C) Barrier three is the killer T cells which destroy the invaded cells. This is often begun by phagocytes presenting the cells to the T cells. This is especially important if there are no memory T cells of the antigen. As the invasion subsides suppressor cells slow down the attacks.

What are Antibodies?

Antibodies are protein molecules called immunoglobulins. They attach to the surface of antigens and a) slow down the invader making it a more attractive target for phagocytes b) they recruit protein substances that puncture the membrane of the invading organism c) they find new invaders and form memory B cells

Antigens

Any substance that can trigger an immune system response is called an antigen. Bacteria, fungi, protozoa and viruses are all antigens. Bacteria and viruses are recognizable by their protein coats and DNA. Bacteria are microorganisms. They are essential to life because they help break down organic matter. They cause TB, scarlet fever, food poisoning. They multiply quickly and compete with our cells for nutrients, they also excrete harmful/toxic material. They can be treated with antibiotics but resistant strains are appearing because of overuse of antibiotics. Viruses are particles of protein and nucleic acid that are smaller than cells and strictly speaking not alive. They are just genetic information. This allows them to reproduce. They function by invading a cell and taking over its metabolism to regenerate itself and not the cell itself. When they have reproduced enough they rupture the cell and invade their neighbors They are the smallest antigens and flu, measles, polio and herpes are spread by viruses. The immune system often recognizes transplanted organs as antigens. When you hear a transplant has been rejected it is this phenomena you are hearing about. The closer the genetic relationship between donor and recipient the less likely this is too happen. Drugs can suppress the immune system reaction but at the cost of lowering its response to other/genuine antigens. In some people the immune system attacks substances that are not dangerous like pollen, tree molds, animal dander. These are allergens and they trigger sneezing and skin rashes which are known as allergic reactions. Being allergic is partly determined by heredity. Injections of small doses of allergen can reduce the symptions.

Blood Pressure

Arteries are elastic and expand when pressure is applies. The force on the artery walls when the heart is at rest is called diastolic pressure. When the heart pumps the maximum force is called systolic pressure. BP is represented by two numbers, the larger for systolic and lower for diastolic pressure and represents the height in mm that a column of mercury can be raised. Blood pressure varies from person to person and in different body parts.

Blood Composition

Because blood has cells suspended in liquid it is sometimes thought of as liquid tissue. A human body has about 10 pints and it is quickly replaced which is why we can donate blood with little negative effect. Blood has two components plasma and formed elements.

Hypertension

High BP strains and damages the heart and arteries. If you have BP above 140/90 - in some countries this is referred to as 14/9 - for a period of several weeks or more you have hypertension. 120/80 is prehypertension. If it exceeds 200 there is a danger of rapturing a vessel - often in the brain causing a stroke. There are many causes of hypertension including being overweight and age though part of this that older people are more likely to be overweight. In primitive societies where people are generally not obese in late adulthood, hypertension is not seen. Other factors are race, gender and family history. In the past men were more prone to hypertension, now for people above 50, there is higher prevalence among women. *Risk factors for hypertension: there are two kinds, controllable and uncontrollable. Uncontrollable include age, ethnicity, family history, African Americans have higher than average BP. Controllable: 1. being overweight: the more you weigh the harder your heart has to work to supply blood to your body 2. sedantary 3. smoking: increases BP in the short and long term 4. too much sodium in diet, too little potassium: the balance is what matters 5. too little vitamin D: this is new research and still not verified 6. too much alcohol 7. stress 8. certain chronic conditions: kidney disease, diabetes, sleep apnia*

What is Immuno-competence?

It is the extent to which your immune system functions properly to ward off infection. There are inter-individual differences in immuno-competence across phases and context of development. .

What does the nervous system do?

It receives information about changes in the environment from sensory organs and send instructions to our muscles and other internal organs on what to do

Pyschoneuroimmunology (PNI) What is it?

It takes an interdisciplinary approach and is the study of the relationship between psychological states and the function of the immune system. It has three components: 1. Pyscho (psychology) 2. Neuro (nervous system) 3. Immunology (immunity to disease) Robert Ader is the father of this the study of the connection between the brain and the immune system. PNI has uncovered direct links between psychological states and biological processes. PNI data are in a form that makes sense to scientists whose training is more biomedical by nature. Key questions: 1. What is the relationship between our psychological states and our health. 2. What are the biological mechanisms linking psychological states (affects and cognitions) or mental disease to our immune system. How does this affect health and disease? 3. Why is PNI important to health professionals? 4. How does the immune system work to fight infection?

Make a PNI Study

One variable, most likely the dependent variable, will be white blood cell count. In my study the independent variable will be hours spent practicing the piano.

PNI From Chapter 4 of the Textbook

Psychoneuroimmunology This field focuses on the relationship between psychosocial processes and atcivities of the immune, nervous and endocrine systems. These systems form a feedback loop as the nervous and endocrine systems send chemical messages in the form of neurotransmitters and hormones that increase and decrease immune function while the immune system produces ACTH and ctyokines that feed information to the brain. The brain appears to regulate immune system function because too much activity causes autoimmune system diseases and too little leads to illness. Emotions and Immune Function Emotions, both positive and negative, play an important roles in immune function. Pessimism and depression impair immune function. Positive emotions give the immune system a boost, positive events increase antibody counts for two days after the event. People who lose their jobs show impaired immune function until they find new jobs when the immune system bounces back to normal levels. Stress can evoke increases in inflammatory substances in the blood which can lead to rheumatoid arthritis atherosclerosis and other chronic conditions. In conditions of chronic stress the immune system is less sensitive to the normal anti-inflammatory effects of cortisol. Psychological Modifiers of Immune System Reactivity People with strong social support have stronger immune systems. Related to this is disclosure - the describing of one's feelings about stressful events - which has been shown to enhance immune system function, especially in cynically hostile people. Optimism is associated with lower levels of inflammation and better immune function but can backfire because optimists are more likely to persist in taxing efforts to control stressful situations. Lifestyles and Immune Function Do all the good things, diet, sleep, exercise predicts better immune function. Smoking and poor sleep does the reverse. Conditioning Immune Function Immune suppression can be conditioned. In an experiment with rats they were given a stimulus followed by a nausea inducing drug. The drug suppressed immune function. The rats were presented with the stimulus for several weeks with the drug and several died because the drug had been predictive of the immune suppressing drug.

Cardiovascular Disorders

The accumulation of fatty plaque on artery walls is called atherosclerosis - not a disorder but could lead to one. The plaque tends to harden reducing the diameter and elasticity of the arteries producing arteriosclerosis and results in higher blood pressure. This can begin at 15. A heart attack or myocardial infarction. An infarction refers to death of heart muscle tissue caused by a blockage of in an artery that causes the flow of blood to be stopped. The usual cause is a clot in an artery with atherosclerosis. Congestive heart failure is another form of heart disease and results from severe atherosclerosis and results in reduced pumping capacity. It is common in old age but tends to ne disabling rather than immediately fatal. Angina pectoris is caused by a temporary obstruction in an artery and causes chest tightness and strong pain but little damage occurs. Can be brought on by strong exertion. Aneurysms are bulges, often caused by hypertension induced weaknesses, in a major blood vessel. If the bulge ruptures the person may die. Strokes/ischemic stroke occur when blood flow to the brain is interrupted by an event in a cerebral vessel. This can be a rupture or a thrombosis which is a blockage from a blood clot. It may cause paralysis and sensory impairment depending on where it occurs.

Central Nervous System

The brain and spinal cord develop quickly after birth. By two years of age it has 75 % of its adult weight and 90 % by age five. We divide the brain into three parts, forebrain, cerebellum and brainstem. Of course, each has special functions.

The Cardiovascular System

The cardiovascular system is intended to service the cells of the body. Blood circulates through arteries, veins and capillaries without ever touching the cells it nourishes. All transfers are through of waste products, oxygen and nutrients go through membranes and fluid filled space. The heart drives the CVS *which is also called the circulatory system* It is a pump about the size of your fist - 250- 300 grams - which beats 100,000ish times a day. The muscle portion is called the myocardium. It has four chambers, the upper two are atriums and the lower two are ventricles. Divided in two halves by the septum, Coronary arteries service the myocardium bringing oxygen and nutrients while taking CO2 away. Blood enters the right atrium of the heart via the superior vena cava carrying waste CO2 form the cells and is deficient in oxygen. When the atrium is filled, blood passes to the right ventricle. Valves prevent backflow into the atrium. The blood is pumped from the ventricles and the blood in the right ventricle goes to the lungs. Here it becomes oxygenated and reassumes its red color. The newly oxygenated blood flows to the left atrium and passes over to the left ventricle where it gets pumped into the aorta on its way to general circulation in the body before returning to the heart again. This cycle takes about a minute in a resting person. Portions of each quantity of blood pumped by the heart travel through the kidneys where waste is removed and eliminated in urine and to the liver where harmful debris like bacteria are cleansed away. Nutrients are also stored in the liver until needed.

The Immune System

The immune system is made up of organs and cells. It was not studied by scientists until after the 1970s. It is now a hot area of study and we know the immune system is highly sensitive to foreign matter and it is able to distinguish between self and non-self. It communicates with the endocrine system and other systems.

Why Do We Get Sick?

The immune system is pretty sophisticated, why is it that we get sick? 1. Developmental Changes in the Immune System Newborns arrive with little in the way of immune system and only have one antibody. If they are breast fed they receive another through the mother's milk. In industrialized societies most infants are vaccinated which produces memory lymphocytes. The immune system develops rapidly in childhood, which is why children get less sick as they age. The effectiveness of the immune system declines in old age. The number of T and B cells and antibodies does not decrease significantly but their effectiveness does and the elderly have trouble generating enough lymphocytes and antibodies to fight an invasion. 2. What Effects do Lifestyle, Stress and Immune Function Have? All the usual suspects affect the immune system: smoking, poor diet sedentary lifestyles. Killer T cell levels are lower in people with high stress and loneliness. Weaker immune function was found in unhappily married women than those pleased with their marriages. 3. Autoimmune Diseases Sometimes the immune system mis-functions and directs itself at the body. The diseases created by this are called auto-immune diseases and include rheumatoid arthritis which attacks bones and tissues and rheumatic fever which attacks heart muscles. MS results from immune system attacks on the myelin sheath. Systemic lupus erythematosus effects the skin and the heart. Factors that contribute to autoimmune diseases include heredity and responses to previous diseases. Tolerance is the ability of immune system cells to remember and respond to a remembered antigen (while not responding to the body's own cells)

How the nervous system works

The nervous system constantly sends commands to muscle tissue and organs through a network of billions of cells called neurons. Neurons generally have a cell body and branches called dentrites which generally receive messages from neighbouring cells. These messages come from another branchy part of cells the axons which are coated by the myelin sheath and split like a river delta at their end. The gaps between these axon terminals or synaptic terminals are called synapses. Electrochemical messages cross these these fluid filled gaps. If chemical activity in the dendrite reaches a high enough level, that is enough ions are accumulated, an electrical impulse an action potential is triggered. When these firings occur at abnormal rates they manifest as epilepsy. There are dozens of neurotransmitters and some excite neighbouring cells increasing the likelihood they will fire while others inhibit the cells making firing less likely. At birth the brain weighs one quarter of its peak weight, but the basic structure has been formed for all the neurons the person will have. Most of the growth in brain size results from the growth of glial cells and the addition of myelin. The myelin sheath prevents unintended stimulation from adjacent cells. Multiple sclerosis results when the sheath degenerates. The network of dentrites and synaptic knobs expands as the infant grows. During the first years of life the myelin grows down from the head to the shoulders, to the arms and hands and chest abdomen and legs. We see this in the infant gaining control of their upper body before the lower reaches of their body. Lack of nutrition can retard myelin, glial cell and dentrite development with lasting negative effects on motor control and intellectual performance. The brain forms few new neurons after birth and the new cells are limited to certain areas. Starting in early adulthood the brain begins to lose weight. Though the number of cells does not change much the synapses do. Declines in physical and mental ability begin to be seen in a person's 50s and 60s. The nervous system is complex and has two major divisions: the central nervous system, the peripheral nervous system. Each connects with lower order structures.

Plasma

The remaining 55% of blood is plasma and 90 % of this is water. The remainder consists of proteins and other organic and inorganic material. Plasma proteins increase blood thickness and are very important as they include hormones, enzymes and waste products as well as nutrients from digestion, vitamins, minerals, simple sugars, amino acids and fatty materials. The fatty materials are lipids and include triglycerides and cholesterol. *Saturated and trans fats are the most dangerous for health. Cholesterol can be produced by the body or come from the diet, it is highly saturated and can build up plaque on the artery walls causing them to harden and narrow.*

What Types of Tests are Used?

There are a few. 1. Enumerative Assay A lab test done to count cells (typically white blood cells) as they exist in the blood stream. PNI researchers look for: a) a minimum number of cells for adequate immune function. b) a balance between cell types 2. Functional Tests of Immuno-competence This is measuring the cells in action. There are two types: a) in vitro: tests performed outside the body, these tests begin with a blood sample and a mitogen - a relatively harmless substance that stimulates immune system cell activity as though the immune system was acting against the invading cell or antigen b) in vivo: tests that are performed inside the body of a living person

BP and the Law of Fluid Dynamics

There are five aspects to consider. A) cardiac output, the more the heart pumps the higher the pressure will be B) blood volume, the total amount of blood in the system, the more there is the higher the pressure C) peripheral resistance, resistance is generally greater in narrower arteries D) elasticity, the more easily the vessels expand the lower the pressure, especially the systolic pressure E) viscosity, how thick is the blood? the more red blood cells the greater the viscosity and the harder it is to push around

What Makes PNI Measurement Expensive?

There are methodological challenges: 1. There are only several places in the body where immune cells are located. 2. There are a variety of forms cellular activity can take and these forms may act independently of each other.

What Influences Blood Pressure

There are two perspectives on what determines blood pressure. One involves the law of fluid dynamics and the other involves factors in people's lives that affect these dynamics.

The Soldiers of the Immune System

There are two types of white blood cells: lymphocytes and phagocytes. Phagocytes are scavengers that patrol the body. They engulf and ingest anything suspicious they find even particles of dust. They give non-specific immunity - that is they respond to any antigen. Lymphocytes are more discriminating and are tailored to attack specific antigens. There are two kinds of specific immunity.

Formed Elements in Blood

These make up about 45 % of blood volume. There are three types of formed elements a) red blood cells are the most numerous, there are about 5 million in a cubic mm of blood, they survive for three months on average and are made in the bone marrow, oxygen attaches to the protein hemoglobin in the cells, anemia results if the level of red blood cells or hemoglobin content goes below normal levels b) leukocytes are white blood cells, they are produced in bone marrow and various organs, they engulf and destroy bacteria, normally there are several thousand in a cubic mm of blood, leukemia is a disease where abnormal blood cells are produced in large quantities and force out the normal leukocytes c) platelets are produced in the bone marrow that enable the body to prevent blood loss, they are granular fragments which plug tiny wounds helping blood clot, hemophilia will result if a critical protein in missing and platelets lose their power to limit bleeding

Organs of the Immune System

These organs are generally referred to as lymphatic or lymphoid organs because they have a primary role in development and deployment of lymphocytes. The main organs are the spleen, thymus, bone marrow, lymph nodes and vessels. The bone marrow, the soft tissue in all bones, produces lymphocytes. Some of these cells travel to one of two organs: a) The thymus which is an endocrine gland located in the chest b) another organ that the textbook says is unknown but believed to mimic the function of the bursa organ found in birds. Most of this processing occurs before birth and in infancy. The spleen acts as a filter that removes antigens, you can live without it but will be at greater risk of infection. Lymph nodes are bean shaped masses of spongy tissue that are distributed throughout the body. Large clusters are found in the neck, armpits, abdomen, and groin. Each node contains filters that capture antigens and compartments that contains lymphocytes. The filter and compartments are connected by lymph vessels which contain a clear liquid called lymph. These vessels empty into the bloodstream. If infected with cancer this network will cause it to spread. Lymphocytes and antigens that enter the blood travel to the spleen an organ in the upper left side of the abdomen. It acts like a giant lymph node that is traversed by blood rather than lymph. It filters out antigens and is a home base for white blood cells. It also removes worn-out red blood cells. Cytokines and interleukins are like neurotransmitters for the immune system. They are small proteins secreted by some white blood cells and act as chemical messages of the immune system.

Antibody-mediated Immunity

This attacks fungi, bacteria, protozoa and viruses while they are still in body fluids and before they have invaded cells. The soldiers in this approach are B cells and they act directly on the antigen as opposed to the T cells which attack infected cells in the body. B cells give rise to plasma cells that produce antibodies. This process is often induced by helper T cells or inhibited by suppressor T cells. Memory B cells develop a memory for a specific antigen after being exposed to it and act only on that antigen. These memory B cells are also called immunoglobin or Ig. (B cells - when reencountering a specific pathogen produce an antibody designed to eliminate the pathogen, the process takes time)

Forebrain

This is the outer most part of the brain and has two subdividions: the telecephalon and the diencephalon which includes the thalamus and hypothalamus. The cerebrum is the largest portion of the brain and includes the cerebral cortex which is the outermost layer. It has two halves left hemisphere and right hemisphere. They look alike but control different processes. They control opposite sides of the body. In most people rge left side handles reasoning, spoken and written language, and numerical skills. The right processes visual imagery emotions and the perception of patterns. The front part of the cerebral cortex is the frontal lobe and the back part contains the parietal, occipital and temporal lobes. The frontal lobe contains the motor cortex which controls the skeletal muscles. During surgery if this part of the brain is stimulated some part of the body will move. It is also involved in the association of ideas, planning, self-awareness and emotion. Injuries to these areas can change personality. The temporal lobe is mainly involved in hearing but also does some vision and memory. Damage to this area can impair a person's comprehension of speech and the ability to pinpoint the origin of sound. The occipital lobe is home to the visual areas of the brain, damage to it can produce blindness and the inability to recognize an object by sight. The parietal lobe is involved mainly in body sensations such as pain cold heat touch and body movement. The second part of the telencephalon is the limbic system. It is in the innermost edge of the cerebrum. The limbic system is not well understood but contains areas important in the expression of emotions such as fear anger and excitement. The diencephalon includes two structures - the thalamus and the hypothalamus - that lie below and are partially encircled by the limbic system. The thalamus is the chief relay station in directing sensory messages, such as pain or visual images to the appropriate parts of the the cerebrum such as the occipital or parietal lobes. Commands from the motor cortex to muscles pass through the thalamus on their way to the cerebrum. The hypothalamus is smaller that the thalamus and plays an important role in people's emotions and motivations. It affects eating, drinking and sexual activity. It arouses the sensations of hunger and thirst. It is also responsible for homeostasis the state of balance in bodily function, like temperature and heart rate. When we are cold it makes us shiver. It plays a role in our reaction to stress. The cerebellum lies at the back of the brain, below the cerebrum, its main function is to coordinate movements and maintain balance. It has connections to the motor cortex and most sense organs. The cerebellum smooths out the jerkiness in our movements. Injuries to the cerebellum can result in ataxia where movements become uncoordinated and jerky. The brainstem is the lowest portion of the brain. t is the knob at the top of the spinal cord. The midbrain lies at the top of the brainstem. It connects to the thalamus and relays messages to parts of the forebrain. Parkinson's disease results from deterioration of areas in the midbrain. The reticular system is a network of neurons that extends from the bottom to the top of the brainstem and into the thalamus. It plays a role in sleep, arousal and attention. When this area is damaged comas often result. The pons is a large bulge at the fromt of teh brain stem and is involved in eye movements, facial expressions and chewing. The medulla contains vital centres that control breathing, heart rate and the diameter of blood vessels. Polio damages the areas that control breathing. The spinal cord extends down the spine from the brainstem. It transmits messages from the brain to various parts of the body. It contains neurons that carry impulses away from the brain to muscles - the efferent direction - and toward the brain from sense organs - the afferent direction. Damage to the cord results in impaired motor function or paralysis. Loss of the use of all limbs is called tetraplegia. The peripheral nervous system has two parts the somatic nervous system and the autonomic nervous system. The somatic nervous system is involved in both sensory and motor functions, serving mainly in the skin and skeletal muscles. The autonomic nervous system activated internal organs such as lungs and intestines and reports to the brain on these systems. In the somatic nervous system afferent nerves carry messages from the sense organs to the spinal cord. Efferent nerves carry messages to activate the striated skeletal muscles like those in the face, arms and legs that we can move voluntarily. The autonomic nervous system has neurons that carry messages between the spinal cord and the smooth muscles of internal organs and glands and blood vessels. It has two divisions, the sympathetic nervous system and the parasympathetic system. The sympathetic nervous system helps us mobilize and expend energy when responding to emergencies, expressing strong emotions and performing strenuous activity. It speeds up the heart, dilates certain arteries to increase flow to the heart and constricts others, increases perspiration and decreases salivation. It is called sympathetic because it acts in agreement with your emotions. The parasympathetic nervous system regulates quiet or calming processes, helping our individual organ systems conserve and store energy. After an emergency it restores the body to its normal state. This is done through 12 sets of cranial nerves most of which originate in the brainstem. The vagus nerve extends from there to the muscles of most major organs.

Cell-mediated Immunity

This operates at the level of the cell. The work here is done by T-cells, so called because they matured in the thymus. There are several kinds: a) killer T cells (also called CD8 cells or maybe natural killer cells) attack three kinds of targets, transplanted tissue, cancerous cells and cells that have already been invaded by antigens, b) memory T cells are imprinted with info that allows them to recognize previous antigens like mumps, they can circulate in the blood stream for decades to prevent a second infection c) delayed hypersensitivity T cells they produce lymphokines which stimulate other T cells to grow and are involved in delayed immune reactions like fighting poison ivy d) helper T cells they get reports form white blood cells in the bloodstream about invasions and go to the spleen and lymph nodes to stimulate lymphocytes to attach and reproduce, they are from both cell-mediated and antibody immunity e) suppressor T cells operate in slowing down or stopping cell mediated immunity processes as an infection is conquered

What About Cancer?

Why doesn't this work on cancer cells? Cancer cells have antigens on their surfaces some of which cannot be attacked. Some cancers release substances that suppress immune response and some cancer cells are not easy to recognize. Some researchers have tried to manufacture antibodies that can attack specific kinds of cancer cells.

pathogen

a bacterium, virus, or other microorganism that can cause disease.

Homeostatis

the dynamic physiological response on the part of the body to maintain a stable internal state in spite of the external environment Shared responsibility of all systems, involves regulating temperature * Good communications of all systems* Has a role in emotions* no clue what that role is