Immune System

When you are asked to picture a human, what do you imagine? Someone young, strong, and healthy. When you imagine a human, you typically don't picture someone weak, frail and sick. That's courtesy of the immune system, whose function is to protect your body from the four categories of pathogens: bacteria, parasites, fungi and viruses. The immune system cells, leukocytes, can be classified into two separate categories: phagocytes and lymphocytes. Phagocytes consume invading organisms, and there are five different classes of phagocytes: basophils, neutrophils, eosinophils, monocytes and macrophages. Lymphocytes are capable of recognizing various pathogens, remembering them, and then destroying them whenever they invade. Lymphocytes can be classified into four primary groups: memory cells, killer cells, B lymphocytes and T lymphocytes. T lymphocytes can be further categorized as helper T cells and cytotoxic T cells. It is courtesy of lymphocytes that vaccines work: by injecting a weakened or dead form of a microorganism, the lymphocytes will recognize the pathogen when it attacks the body in full force, and the lymphocytes will then be able to fight them.

Types of pathogens

Types of leukocytes

Leukocytes and their functions

Key Immune System Terms:

Macrophage - A phagocyte that ingests invading organisms through phagocytosis, and destroys it by engulfing it into a lysosome.
Antigen - A foreign substance which invades the body and induces an immune response.
Helper T cell - A type of lymphocyte stored in the thymus that helps B cells destroy tagged antigens and signals phagocytes to perform their respective functions.
B cell - A type of lymphocyte stored in the bone marrow that tags invaders with antibodies to be destoryed by helper T cells.
Antibody - A type of protein manufactured by B cells and attached to antigens so that helper T cells can recognize and destroy the invading substance.
Killer cell - As their name suggests, killer cells are lymphocytes that consume invading organisms and either devour them or release chemicals which will destroy them.
Cytotoxic T cell - A type of lymphocyte that releases chemicals into a cell's plasma membrane, resulting in cytolysis. Cytotoxic T cells perform this function typically in cells infected by a virus before the viral DNA is replicated.
Memory cell - A type of lymphocyte that aids the function of antigen recognition.

Immune system cells

Immune system cells

Immune system cells

There are three primary types of immunity. The first, innate immunity, the immunity that we are born with. Some viruses or germs we are just naturally immune to, whereas other species would feel their effects. Our innate immunity also includes special immune cells, our mucus membranes and skin, which are our "first line of defense" when attacked by invading organisms. The second type of immunity is adaptive immunity, which develops as we grow, and includes lymphocytes which recognize invading organisms that we have been previously exposed to. The third type of immunity is passive immunity, is short-term immunity provided by another source. An example of passive immunity would be the antibodies passed from a mother's breast milk to her child.

Types of immunity

Two well-known immune system disorders are lupus and allergies. Lupus, made famous by the television show, House, is an autoimmune disorder. As in all autoimmune disorders, the immune system mistakes bodily tissues as foreign invaders and attacks them. Lupus is characterized by muscle soreness, joint pain and inflammation, and in some cases, attacks on the kidneys and other organs. Allergies are another abnormal immune system response, although this one is more common. Allergies occur when the immune system attacks antigens from our environment, and attack them as if they were pathogens. Allergic reactions can be characterized by a variety of responses, such as watery eyes, sneezing, itchiness, hives, swelling and anaphylaxis.

Sleep

It is what infants do all the time, and what teenagers cannot get enough of. Sleep. Approximately a third of one's life is spent sleeping, and these hours during which the body rests and the brain "recharges" is a surprisingly complex process. This process is regulated by chemical signals in the brain. These chemicals are called neurotransmitters, because they pass signals between neurons of the brain. Two primary neurotransmitters involved in sleep include serotonin and gamma-aminobutyric acid (GABA), which work as a "union of opposites," where serotinin is involved in keeping the body awake and alert, while GABA inhibits serotinin and other neurotransmitters involved in keeping one awake, promoting sleep. These neurotransmitters are signaled to be produced or inhibited by the production or lack thereof of melatonin, a hormone secreted by the pineal gland. The production of melatonin is regulated by the sleep-wake cycle, known as the circadian clock. When one is awake, light strikes the retina, which signals the suprachiasmatic nucleus to suppress the pineal gland's production of melatonin, which in turn results in the suppression of GABA production. However, at night, when less light strikes the retina, the suprachiasmatic nucleus stops suppressing the pineal gland's production of melatonin, which in turn allows for the production of GABA, thus promoting sleep.

Serotonin molecule

Gamma-aminobutyric acid molecule

Circadian Rhythm

There are five stages of sleep; Stage 1, Stage 2, Stage 3 and Stage 4 sleep are all non-Rapid Eye Movement (nREM) periods, and the fifth stage is Rapid Eye Movement (REM) sleep. The complete cycle lasts approximately 90 minutes, and the average adult experiences 4-6 sleep cycles per night. In the nREM periods, the first stage of sleep is characterized by drowsiness. The body begins to relax, although sometimes one experiences hypnic jerks, sudden muscle spasms, associated with the feeling of falling. The second stage is characterized by light sleep. In this stage, one's body temperature lowers and heart rate slows, and on an electroencephalogram (EEG), a scientist would view slowing alpha waves with occasional spindles: sudden bursts of activity.The third stage is characterized by deep sleep. During this stage, one brain waves slow to delta waves, unlike the alpha waves that appear on an EEG during awakeness and stages 1-2. Stage 4 is the deepest stage of sleep, and it is believed to be the stage during which most brain recovery occurs. Finally, there are the REM periods. During these periods, brain waves appear to be similar to those seen when one is awake. Furthermore, one's blood pressure rises, breathing becomes erratic, and the brain is very active, yet one's muscles are paralyzed (with the exception of the cardiac and respiratory muscles). It is during REM sleep when one dreams. It is believed that REM sleep is essential for learning and memory retention. When one is sleep deprived for a long time, once they go through a full REM cycle, they experience REM-rebound, which is characterized by very intense dreams or nightmares. 

Sleep Cycle

Brain waves associated with each sleep stage

Sleep deprivation not only results in REM-rebound, it also causes difficulty in concentration and feelings of drowsiness, which can be very dangerous for it can result in car accidents or accidents at work (especially when working with heavy machinery). Furthermore, sleep deprivation weakens the immune system and can hinder many brain functions. Below is a table that illustrates how many hours of sleep one needs to maintain higher brain functioning.

Sleep deprivation

Necessary amounts of sleep

However, like in any physiological process in the human body, there are many disorders associated with sleep, including insomnia, sleep apnea, narcolepsy, and restless leg syndrome. Insomnia is characterized as recurring problems in falling or staying asleep. While there are medications to treat insomnia, most doctors encourage healthier habits before going to sleep, such as abstaining from technology, alcohol and caffeine. Sleep apnea is an incredibly dangerous sleep disorder characterized by periods during which one stops breathing during sleep and suddenly awakens. This disorder typically affects overweight people, particularly men, because of the pressure of excess adipose tissue compressing the pharynx. While the disorder is difficult to diagnose because the primary symptom is snoring, once diagnosed, there are multiple routes of treatment. In mild cases, lifestyle changes such as losing weight and quitting smoking could end the problem. In severe instances, there are multiple surgeries or therapies to treat the disorder. Another major sleep disorder is narcolepsy, which continues to puzzle doctors for there is no known singular cause. Narcolepsy is characterized by uncontrollable sleep attacks. In some cases, a narcoleptic may fall directly into REM sleep. It can be managed with stimulants in an attempt to keep the brain active. An additional, common sleep disorder is restless leg syndrome, a condition in which, when trying to fall asleep, one feels intense discomfort in their legs and the necessity to move them. Patients with restless leg syndrome often experience twitching in their legs when trying to fall asleep, which can be treated with medication. In order to learn more about treatments for sleep disorders, visit the Mayo Clinic's website, which takes a comprehensive look at disorders, symptoms, causes and treatments.