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Due to popular demand you have the opportunity to create a glossary together.It really is important that you use your own words and please add your own definition to one that has been done. There is no one answer to any particular term.

Homeostasis –
is the maintenance of a relatively constant internal environment despite changing conditions in the internal and external environment.
Negative Feedback System – is a system in which the body reacts to a stimulus by completing a response that decreases the severity/magnitude of the stimulus.
Interstitial fluid – this is the fluid is found between cells. It is their immediate surroundings/environment. This fluid is also (and in my opinion more commonly) referred to extra cellular fluid.
Positive Feedback – this is when the response to the stimulus actually enhances or increases the magnitude of the stimulus. For example breast feeding.

Nervous System
the CNS is the central nervous system. It is composed of the brain and the spinal cord. Operating neurons in this system are inter neurons.
PNS – the PNS is the peripheral nervous system. It is involved in receiving signals from the external environment and transporting messages to effectors to carry out a response. Operating neurons in this system are sensory and motor neurons.

Neuron -
the functional unit of the nervous system (a nerve cell). The three main parts are the dendrites, cell body and axon.
Dendrite - a dendrite is the receiving end part of the neuron. It contains protein channels that the neurotransmitters bind to when they are released from the synaptic knob of another nerve cell.
Cell Body - the cell body is the part of the neuron that contains the nucleus and other membrane bound organelles.
Axon – the axon is the tail-like section of the neuron. The electrical impulse runs along the axon to the axon terminal/synaptic knob.
Myelin sheath – the myelin sheath is a cell that surrounds the axon. It provides the axon with insulation and allows the electrical impulse to travel faster. It is made up of schwann cells that wrap themselves around the axon.
Sensory neurons – carry information from a receptor to the CNS (also referred to as afferent). They are part of the PNS.
Motor neurons – carry information from the CNS to the effectors. (Also referred to as efferent). They are also part of the PNS.
Inter neurons – carry information within the CNS. They have different names including connecting neurons.
Action potential - the transference of an electrical impulse along an axon. When a receptor interacts with a signaling molecule, the inside of the neuron becomes a bit negative. If it becomes negative enough, ion channels will open and potassium ion will rush into the cell and sodium ions will rush out. This impulse causes vesicles with neurotransmitters to migrate to the pre-synaptic membrane.

Excitatory neurons - neurons that trigger an action potential
Inhibitory neurons - neurons that will inhibit an action potential and stop it from occuring in the next nerve cell. If there is one inhibitory and one excitatory neuron then there will be no action potential. If it is two excitatory and one inhibitory, action potential will occur.

Good start to the glossary, keep it going, I expect to see a whole lot of terms relating to the endocrine system, as well as stimulus-response model. VM

Stimulus Response Model
Stimulus Response Model
- this is like a flow chart that describes what happens when there is a change in the internal or external environment. The general chart includes the stimulus, receptor, relay, effecter and response.
Stimulus - a stimulus is change in any factor that demands a response because of the nature of the change.
Receptor - a receptor is a cell that detects change in the internal or external environment. Receptors have the capacity to trigger a response that will be appropriate to the change.
Relay - in this part, hormones and/or nerve cells work with the brain to cause the right response. For different stimuli, different hormones will be released and different nervous pathways will be activated.
Effector - this is the cell that effects the response. It is the cell that makes a change that will eliminate the stimulus or at least decrease its magnitude.
Response - the response is the change that is made by the body. The action taken to eliminate the stimulus.
Misalignment Detectors - these are detectors that sense change in the internal environment. Change that exceeds the normal range. Therefore it is a more serious detector because it is only activated when fluctuations are greater than usual.

Endocrine system
- hormones are chemical messengers that are released from glands, travel in the bloodstream and cause a response at a target cell.
Endocrine gland - tissues, organs (I think) that produces hormones and release them into the bloodstream when necessary.
Exocrine gland - glands that release substances out of the body. This could be water when sweating or pheromones when communication is necessary.
Autocrine hormones - are hormones that act on the cell they are released from
Endocrine hormones - these are hormones that enter the blood stream and act on far away cells.
Paracrine hormones - are hormones that act on nearby cells, in a localised area
Steroidal hormones - these hormones are of a lipid base and travel in the bloodstream and require protein carriers because they are water insoluble and water travels in bloodstream.
Non steroidal hormones - hormones not of a lipid base. Most are peptides. These do not require protein carriers because they are water soluble.
Protein carriers - these transporters carry steroidal hormones in the bloodstream because the steroidal hormones (being of a lipid base) can't interface with the water that is already in the bloodstream.

- these are receptors that are sensitive to chemical stimuli. These stimuli could be hormones, pH levels, oxygen.
Mechanoreceptors - these are sensitive to physical stimuli for instance gravity.
Photoreceptors - these receptors are sensitive to light.
Thermoreceptors - are sensitive to temperature fluctuations.

Signaling molecules and stuff
- a type of signaling molecule that is released from the body and has an external effect, i.e., it operates outside of the body. Used mainly by animals as a means of communication.
Neurotransmitter - a signaling molecule that is released from the pre synaptic membrane of neurons. They cross the synaptic cleft and trigger an action potential in the next neuron when they bind to a receptor on the post synaptic membrane.
Neurohormone - hormone released from a neurosecretory vesicle in a nerve cell that stimulates another gland to release a hormone. The hypothalamus sends a lot of these to the pituitary gland.
Hormone - a hormone is another signaling molecule that is released from glands and travels in the bloodstream to target cells where they cause an effect.
Signal transduction - this is a process where once a signaling molecule has attached to a receptor on or inside a cell, a biological pathway is triggered in the cell. This pathway will produce an appropriate response to the stimulus whether it be positive or negative feedback. For example, when insulin attaches to a receptor on a muscle cell, a biological pathway will be activated where glucose is taken in then converted to glycogen. This process may involve many different enzymes and substances.

Infectious disease
- a disease that is passed on from one organism to another e.g. influenza
Non-infectious disease - a disease that isn't passed on from one organism to another. It can be hereditary, a result of poor nutrition e.g. diabetes.
Contagious disease - a disease that can be 'caught' by another individual through being in close proximity with another, exchanging body fluids or touching another individual with the disease.
Non-contagious disease - a disease that can't be passed on by methods of transport listed above in 'contagious disease'
Infectious diseases: sporadic - an occasional occurrence of the disease
endemic - the disease occurs regularly but can be controlled
epidemic - there is an outburst of the disease
pandemic - an outburst of the disease affecting multiple countries

- a disease causing agent. It is not the disease itself, but rather the organism or non living agent that causes the disease
Viruses - viruses are a non-cellular pathogen. They reproduce by injecting their genetic material into a cell and causing more of itself to be produced
Retroviruses - these guys start with RNA and turn it into DNA with the use of an enzyme called reverse transcriptase. This is the opposite of most other viruses that start with DNA and turn it into RNA.
Prions - prions are also non cellular pathogens. They are mere abnormal proteins that are able to produce more of themselves by transforming other normal proteins into copies of themselves.
Viroid - the last type of non-cellular pathogen. They are pieces of RNA known to cause disease but they only affect plants. They are smaller than prions.
Bacteria - bacteria are prokaryotic cells that are found and classified according to their different shapes. Some are photosynthetic, others chemosynthetic.
Types of anaerobic bacteria: Facultative - they are able to survive in the presence of oxygen as well as without the presence of oxygen
Obligate - they can only survive in areas without oxygen e.g. deep down in the soil
Fungi - Fungi are a eukaryotic pathogen. They spread through spores that land on surfaces where they can grow.
Protozoa (protista) - single celled eukaryotes that have a complex life cycle. E.g. plasmodium sp that causes malaria
Multi-cellular animals - These comprise of two types of parasites:
Ectoparasites - these infect the host externally. E.g. mosquitoes. They can also be vectors for other pathogens. They have multi-stage lifecycles (primary host, secondary host)
Endoparasites - infect the host internally, they grow inside the host eg. Flukes.
Bacteriophages - they infect bacteria and use a similar method to viruses when they infect their host cells.
Nematodes - small unfragmented worm-like animals including roundworms.

Immune system
Specific immune system
- specific immunity reacts in a specific manner to each infection. It is part of the third line of defense. Cells belonging to this system attach to, disarm, destroy and remove foreign substances. It is able to distinguish between self and non-self cells. It has a memory that allows it to recognise foreign substances if they return. The level of response is greater for the secondary infection by the same organism.
Non-specific immunity - a general response is produced and it acts the same way irrespective of the invading pathogen. It has no memory of previous infection and the level of response is always the same. Involves physical, chemical and cellular defenses. This is the first (external) and second (internal) line of defense.
1st line of defense - this is the external barriers like skin and hair. Tears (antibacterial), sweat (acidic) and enzymes in the mucus are also 1st liners.
2nd line of defense - this is the internal mechanisms. Includes interferons, phagocytes, natural killer cells, inflammation and histamines.
3rd line of defense - the specific stuff. Lymphocytes are the key white blood cells involved. They can be classified as humoral or cell-mediated responses.
Lymphatic system - the lymphatic system is a network separate to the bloodstream. It is responsible for filtering the interstitial fluid.
Lymph nodes - these are the 'stations' where many of the macrophages and other digestive and killer cells are found. The interstitial fluid passes through these nodes (situated all around the body) and is cleansed there.

Non-specific immunity
- (a type of cytokine) these are chemicals that are produced and released by a viral infected cell as soon as it is infected. It travels to nearby cells to warn them to put up a defense against the virus before it infects them.
Histamines - histamines are chemicals released from mast cells that attract phagocytes e.g. macrophages.
Natural killer cells - these cells destroy viral infected cells that are displaying the antigens of the virus. The kill these cells so that the virus can't spread.
Mast cells - simply release histamines so that more phagocytes are brought to the area of infection.
Cytokines - cytokines are small proteins released from cells as a means of communication. They are signaling molecules that tell other cells there is a dangerous invader. They can trigger a variety of responses both specific and non-specific.
Macrophages - these are large white blood cells that engulf foreign substances and destroy them
Pyrogens - pyrogens are signaling molecules that are sent to the hypothalamus and cause it to raise the temperature - resulting in fever.
Fever - a non specific immune response whereby the temperature of the body is raised so that bacteria don't flourish as well. Fever reduces their growth rate and allows our immune response more time to come up with an appropriate response. It also speeds up our own immune response.
Inflammation - involves increased blood flow to the affected area, increased permeability of blood vessels causing swelling and increased movement of phagocytes and other white blood cells out of blood vessels and into the surrounding tissue.

Specific immunity
Humoral response
- this is an immune response to pathogens in body fluid. It involves B lymphocytes which create an antibody response.
Cell mediated immunity - this is an immune response to pathogens in cells. It involves T lymphocytes.
Lymphocytes - are specific white blood cells that evolve into either T-lymphocytes or B-lymphocytes to be used in the cell-mediated and humoral response systems.
Clonal selection theory - this theory states that we are born with hundreds of millions of different kinds of B cells that each have specific antigen binding sites for a specific antigen that could exist. The binding site only changes a tiny bit for each B cell so not many genes are needed.

Humoral response
- these cells are produced in the bone marrow and have glycoproteins that attach to specific antigens of pathogens. When the antigen attaches, the B-lymphocyte starts to produces and secrete antibodies.
Antibodies - antibodies are Y-shaped glycoproteins that are secreted from B-cells and neutralise (not kill) pathogens. They work in a number of different ways:
1. Neutralisation - the antibody attaches to the receptors of a virus so that it can't invade a cell (because its receptors are being blocked)
2. Agglutination - the antibodies work to form a bunch of the pathogen so that it can then be destroyed by a macrophage.
3. Precipitation - like agglutination
4. Complement - the antibodies will cause compliment molecules to lodge themselves in the membrane of a pathogen causing to 'pop' or leak, thus destroying it.
Thymus - the place where T-lymphocytes are created.
Antigen receptors - these are the glycoproteins (Y-shaped) on the plasma membranes of B-cells. As the name suggests, they their purpose is to bind to antigens.
Antigen-antibody complex - the site where the antibody binds to an antigen.
Immunoglobulins - another name for antibodies.
Plasma - a B-cell that is devoted to making thousands of the same antibody. It only comes into effect once an immune response for that particular antibody and antigen has been activated.
Memory - these are B-cells that remain in the lymphatic tissue after the pathogen has been destroyed. They detect for further 'revisits' by the same pathogen.
Primary response - the first response to the invading pathogen. This is the production of memory and plasma cells.
Secondary response - this is the response to a pathogen who returns. This response is much greater and faster.

Cell-mediated response
T lymphocytes
- these are the specific white blood cells to the cell-mediated response system. The main ones are Helper and Cytotoxic T lymphocytes but there is also T memory and suppressor cells.
T Helper cells - these cells are like the alarm for the body. They bind to antigens presented by APCs and signal a response by bringing cytotoxic T cells to the area and causing B lymphocytes to divide and differentiate. They release cytokines called interleukin which communicate with B cells and Cytotoxic T cells.
Cytotoxic T cells - these cells are the cells that destroy the APC. They release a chemical called perforin causing lysis of the cell and consequential death.
APC - APCs are antigen presenting cells (usually macrophages) They engulf the pathogen and display its antigens on its surface so that a T Helper cell can come along, bind and trigger an immune response.
Perforin - perforin is a chemical that pops holes in a cell causing it to lyse. It is used by T Cytotoxic cells.
Interleukin - a signaling molecule released by a macrophage when a T helper cell binds to the self non-self site. It stimulates the T helper cells to raise the alarm. The T helper cell then releases interleukin 2 which activates other T cells and B cells.

Defense mechanisms
Major histocompatibility complex (MHC)
- these are genes that program the functioning of proteins and glycoproteins on the plasma membrane. These proteins are called markers.
Markers - membrane proteins synthesised by the MHC. They are useful because our immune system recognises these markers as our own cells and knows therefore not to attack us.
Antigens - these are markers on foreign cells that get recognised and targeted by our immune system.
Encapsulation - A plant immune response whereby a capsule of connective tissue is produced it surrounds the pathogen - cutting it off. Within the capsule, phagocyte cells can ingest the invader.
Antigen mimicry - this is a defense mechanism of an antigen. It can take up host molecules and insert them onto its own surface so that the immune system doesn't recognise it as non-self.
Antigenic variation - this is another defense mechanism of a pathogen. Some pathogens have the ability to change their surface makers - change their antigens. Once the non-self cell has had its antigens recognised, the B cells go about producing antibodies but by the time the antibodies have come to nullify the antigens, they have changed and the antibodies no longer fit. This means that each time the body undergoes a primary response which is far inferior and much less effective than a secondary response if the pathogen wants to return.

White blood cells
- this is the general term for white blood cells
Monocytes - Part of the non-specific immune system. They turn into macrophages and engulf invaders and debris by endocytosis. They leave the bloodstream.
Neutrophils - These do the same thing as monocytes (turn into macrophages) but they stay in the bloodstream. They are mostly non-specific but can be specific if directed by antibodies.
Bosophils - These white blood cells release histamines and are involved in inflammatory and allergic reactions.
Eosinophils - Part of the non-specific immune system. They chemically attack parasitic invaders.
Lymphocytes - These turn into T-cells and B-cells. They are part of the specific immune system.

OK the neurohormone has been left blank. Perhaps someone else can attempt to write a description for this type of signalling molecule. Also, signal transduction doesn't actually include the interaction of signalling molecule with receptor. So try and reword this. VM
*i've reworded this to leave out the initial interaction. is it accurate now?
Yes the first bit is better but I think it still needs to be clear that the pathway doens't actually counteract the stimulus but rather converts the stimulus into an appropriate cellular response. I say this because the response may be part of a negative or positive feedback system or it could just be response in general. VM

*i've tried again - hopefully this time its ok. Can you also check my definition for neurohormone because i think its correct but im not sure. Does it travel in the bloodstream?
Yep the description of signal transduction is good. The neurohormone is also ok, I think the key is to know how they differ from both neurotransmitters and other hormones, ie they are released from neuroscretory cells (usually in brain) and can act on a "distant" target travelling via the bloodstream. VM