Physiology (Definition) : is the science of the mechanical, physical, and biochemical functions of normal humans or human tissues or organs. The principal level of focus of physiology is at the level of organs and systems. Most aspects of human physiology are closely homologous to corresponding aspects of animal physiology, and animal experimentation has provided much of the foundation of physiological knowledge. Human physiology is one of the basic sciences of medical study, and as such is most often applied as medical care.It is the integration function of all levels.
Many physiologic variables (such as blood glucose (sugar) level, body temperature, blood pH, and so on) must be maintained within narrow limits for proper health. An overriding theme in physiology is that of homeostasis, maintaining a stable internal environment despite external fluctuations. Indeed, the primary functions of many organ systems are to maintain homeostasis. For instance, the urinary system helps to control water levels as well as that of blood pH and various waste products, and the circulatory system ensures a constant supply of oxygen and nutrients to tissues and the removal of waste products.
Human anatomy or anthropotomy is a special field within anatomy. It studies gross structures and systems of the human body, leaving the study of tissues to histology and cells to cytology. The human body, like the bodies of all animals, consists of systems, that consist of organs, that consist of tissues, that consist of cells.
Hippocrates of Cos (c. 460 BC–c. 380 BC) was an ancient Greek physician. He has been called "the father of medicine", and is commonly regarded as one of the most outstanding figures in medicine of all time.
Aristotle is known for being one of the few figures in history who studied almost every subject possible at the time. In science, Aristotle studied anatomy, astronomy, economics, embryology, geography, geology, meteorology, physics, and zoology. In philosophy, Aristotle wrote on aesthetics, ethics, government, metaphysics, politics, psychology, rhetoric and theology. He also dealt with education, foreign customs, literature and poetry. His combined works practically constitute an encyclopedia of Greek knowledge.
In 1901, Emil von Behring was awarded the first Nobel Prize in Physiology or Medicine for his work on serum therapy, which opened a new road in medical science and helped save hundreds of thousands of lives. The Prize has subsequently been awarded to a broad field including immunology, genetics, neurobiology, diagnostics and drug development, as mankind continues to struggle against disease and death.
The cell is the structural and functional unit of all living organisms, and is sometimes called the "building block of life." Cells are collections of molecules separated from the external environment by a cell membrane. Some organisms, such as bacteria, are unicellular, consisting of a single cell. Other organisms, such as humans, are multicellular, (humans have an estimated 100,000 billion or 1014 cells). The cell theory, first developed in 1839 by Schleiden and Schwann, states that all organisms are composed of one or more cells; all cells come from preexisting cells; all vital functions of an organism occur within cells, and cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells.
Biological tissue is any substance made up of cells that perform a similar function within an organism.
Organs: tissues form structural and functional units known as organs.
Organ system: groups of organs integrate their functions to create organ systems. The human body has 10 physiological organ systems.
Circulatory system: (heart, blood vessels, blood, lymph) transport of materials and lymphatics between all cells of the body.
Digestive system: (stomach, intestines, liver, pancreas) Conversion of food into particels that can be transported into the body; elimination of some wastes.
Endocrine : (throid gland, adrenal gland ) Coordination of body function through synthesis and release of regulatory molecules.
Immune system: (thymus, spleen, plymoh nodes) Defenses against foreign invaders.
Integumentary: (skin) Protection from external enviorment.
Musculoskeletal: (skeletal muscles, bones) Support and movement
Nervous system: (brain, spinal cord) coordination of body function through electrical signals and release of regulatory molecules.
Reproductive system: (ovaries and uterus, testes) Perpetuation of the specis ( not homeostasis)
Respiratory: ( lungs, airways) exchange of oxygen and carbon dioxide between the internal and external environments.
Urinary: (kidneys, bladder) Maintenance of water and solutes in the internal environment, waste removel.
Four systems exchange material between the internal and external environment:
1. respiratory system( gas) 2, digestive system ( nurients and water, and waste) 3, urinary system (water and solutes) 4, reproductive system (produce eggs and sperm) and the major organs of thoes four systems are hollow(lumens)
Lumen: is the small interior spaces, they are essentially extensions of the external environment. material that enters the lumens of these organs is not truly part of the internal environment until it crosses the tissue wall of the organ.
Differences between the internal and external environment:
This involes the bacterium E. coli. This organism normally lives and reproduces in the lumens of the large intestine, an interior space that is continuous with the external enviorment. In this location, the organism does not harm the hot. However, if the interstinal wall is punctured by disease or accident and E. coli enters the internal environment of the body. a serious infection can result.
Why the nervous and endocrine systems coordinate body function?
Because this is the integrative nature of physiological function, the lines between organ systems blur sometimes.
What is the difference between function and process?
The function of a physiological system or event is the "why" of the system or event. why does the system exsit? This is way of thinking about a subject is called the telelogical approach.
Eg. of telelogical approach: the answer to the question of why red blood cells transport oxgen is "because red blood cells bring oxygen to the cells that nee it." This explains the reason red blood cells transport oxygen but says nothing about how the cells transport oxygen.
The processes are the "how" of a system. It is a way of mechanistic approach. Eg. the mechanistic answer to the question of why red blood cells transport oxygen is "because there are hemoglobin molecules that combine reversily with the oxygen molecules."this explains how oxygen transport occurs but says nothing about the signigicance of oxygen transport to the intact animal.
Extracellular fluid and intracellular fluid
the extracellular fluid is the body fluid that surrounds the cells and makes up 1/3 of total body water volume, the other 2/3 being intracellular fluid. The ECF is the body's internal environment and serves as the interfce between the external environment and the cells. It
can be divided into 2 major subcompartments, interstitial fluid and blood plasma. The extracellular fluid can be further divided into 2 minor subcompartments, transcellular fluid and lymph.In humans, the normal glucose concentration of extracellular fluid that is regulated by homeostasis is approximately 5 mM.The pH of extracellular fluid is tightly regulated by buffers around 7.4.
the intracellular fluid is the cytosol (cf. cytoplasm, which also includes the organelles) is the internal fluid of the cell, and a portion of cell metabolism occurs here. Proteins within the cytosol play an important role in signal transduction pathways and glycolysis. They also act as intracellular receptors and form part of the ribosomes, enabling protein synthesis.In prokaryotes, all chemical reactions take place in the cytosol. In eukaryotes, the cytosol contains the cell organelles; this is collectively called cytoplasm.The cytosol is not a "soup" with free-floating particles, but is highly organized on the molecular level. As the concentration of soluble molecules increases within the cytosol, an osmotic gradient builds up toward the outside of the cell. Water flows into the cell, making the cell larger. To prevent the cell from bursting apart, molecular pumps in the plasma membrane, the cytoskeleton, the tonoplast or the cell wall (if present), are used to counteract the osmotic pressure.
Why is homeostasis important?
When conditions outside the body change, the changes are relfected in the composition of the ECF, which in turn affects the cells. (cells are not very tolerant of changes) As a results, a variety of mechanisms have evolved that maintain the composition of the EXF within a narrow range of values. The body's ability to maintain internal stability is known as homeostasis. This and the regulation of the internal enviornments are centeral precepts of physiology. All sorts of factors affect the suitability of the human body fluids to sustain life; these include properties like temperature, salinity, and acidity, and the concentrations of nutrients such as glucose, various ions, oxygen, and wastes, such as carbon dioxide and urea. Since these properties affect the chemical reactions that keep bodies alive, there are built-in physiological mechanisms to maintain them at desirable levels.
Eg.
- Thermoregulation
- The skeletal muscles can shiver to produce heat if the body temperature is too low.
- Non-shivering thermogenesis involves the decomposition of fat to produce heat.
- Sweating cools the body with the use of evaporation.
- Chemical regulation
Most of these organs are controlled by hormones secreted from the pituitary gland, which in turn is directed by the hypothalamus.
What is pathological condition?
Failure to maintain homeostasis disrupts normal function and resulits in a disease state or phathological condition. Ths study of body function in a dieases state is known as pathophysiology.
Dieases generally can be divided into 2 groups according to their origin.
1, those in which the problem arises from internal failure of some normal physiological process.
2, those that originate from outside source.
Internal dieases include : 1, abnormal growth of cells which may cause cancer or tumors. 2, production of antibodies by the body against its own tissues (autoimmune disease). 3, the premature death of cells or the the failure of cell processes. 4, inherited disorders are also considered to have internal causes.
External disease include : 1, toxic chemicals 2, physical trauma 3, foreign invaders such as viruses and bacteria.
In both internal and external dieases, when homeostasis is disturbed, the body attempts to compensate. If the compensation is successful, homeostasis is restored.
What is diabetes mellitus?
A metabolic disorder characterized by abnormally high blood glucose concentrations. it is a whole family of dieases with varying causes and manifestations.
Integration of body systems: The ability of the different organ systems to coordinate with each other, work together to maintain homeostasis, and carry out the functions of the body.
Cell-to-cell communication and coordination: Integration and homeostasis both require that the cells of the body communicate with one another rapidly and efficiently. A variety of sensing mechanisms monitor changes in the internal and external environments. most cell-to-cell communication uses chemical signals, although the nervous system adds speed by means of electrical signals. Information is sent between distant cells through the movement of blood in the circulatory system or along the specialized cells of the nervous system.
Movement of substances and information across cell membranes: Communication between the internal environment of the cells and the extracellular fluid requires information transfer across the cells membrane.
Compartmentation of the body and cell: cell membranes separate cells from each other and from the ECF. Similarily, within a cell, membrances divide the cell into discrete units or organelles. This compartmentation, allows different areas to specialize their functions.
Energy flow: living processes require the continuous input of energy. Energy is used to do work. In the body, energy is used to synthesis and breakdown of molecules, to transport moleculies across cell membrances, and to creat movement.
The principles of mass balance and mass flow: This las says that if the amount of a substance in the body remains constant, any gain must be offset by an equal loss. Eg. in order to maintain constant body temperature, heat gain from the external environment and from the metabolism must be offset by heat loss back to the enternal. Most substances enter the body from the outside, although some, like heat, can be produced internally. The major routes for loss from the body are the urinary and digestive systems (in the urine and feces), the repiratory system, and integumentary system (skin). Some aspects of mass balance are monitored by sensors (receptor) that detect changes in the internal and external environments.
Total amount of substance X in the body = intale + production - output.
Mass flow (amount/min) = concentration (amount/vol) x volume flow (vol/min)
Dehydration is the removal of water (hydor in ancient Greek) from an object. Medically, dehydration is a serious and potentially life-threatening condition in which the body contains an insufficient volume of water for normal functioning.
Desiccation is the state of extreme dryness, or the process of extreme drying. It is an extreme form of dehydration (though dessication is not a medical condition).
Sicentific inquiry: Observation and experimentation are the key elements of scientific inquiry.
Hypothesis : A logical guess, or an event or phenomenon observed by an investigator using prior knowledge.
What is independent variable and dependent variable?
An independent variable is that variable presumed to affect or determine a dependent variable. It can be changed as required, and its values do not represent a problem requiring explanation in an analysis, but are taken simply as given.
More generally, the independent variable is the thing that someone actively controls/changes; while the dependent variable is the thing that changes as a result. Thus independent variables act as catalysts for dependent variables. In other words, the independent variable is the "presumed cause", while dependent variable is the "presumed effect" of the independent variable.
Experiment (Latin: ex-+-periri, "of (or from) trying"), is a set of actions and observations, performed in the context of solving a particular problem or question, to support or falsify a hypothesis or research concerning phenomena. The experiment is a cornerstone in the empirical approach to acquiring deeper knowledge about the physical world.
Control Group : a duplicate of experimental group in every respect except that the manipulated variable is not changed from its normal value. The purpose of the control group is to ensure that any observed changes are due to the experimental manipulation and not to an outside factor.Data: During an experiment, the investigator caregully collect facts that the manipulated variable has on the observed variable.
Graph : A common format for presenting data.
Replication :If one experiement supports a hypothesis, then experiment should be repeated to ensure that the results were not an unusual one-time event. this step is called replication.
Scientific theory: When data support a hypothesis in multiple experiments, the hypothesis may become a scientific theory.
Scientific model : A model (or conceptual model) is a theoretical construct that represents physical, biological or social processes, with a set of variables and a set of logical and quantitative relationships between them. Models in this sense are constructed to enable reasoning within an idealized logical framework about these processes and are an important component of scientific theories. Idealized here means that the model may make explicit assumptions that are known to be false in some detail. Such assumptions may be justified on the grounds that they simplify the model while, at the same time, allowing the production of acceptably accurate solutions.
Crossover study: it is a way to reduce variability within a test population, whether human or animal, is to do a crossover study. In a crossover study, each animal acts both as experimental animal and control. Thus, the individual's response to the treatment can be compared with the individual's own control value. This method is particularly effective when there is wide variability within a population.
Blind study : In setting up an experiment with human subjects, we must try to control the placebo effect. The simplest way to do this is with a blind study, in which the subject does not know whether he or she is receiving the drug or the placebo.
Double-blind study: To avoid the researcher's expectations of what the treatment will or will not do may color their measurements or interpretations, researchers often use double-blind study, in which a third party, not involved in the experiment, is the only one who knows which group is receiving the experimental treatment and which group is receiving the control treatment.
Double-blind crossover study: To minimizing psychological effects, we use double-blind crossover study, in which the control group in the first half of the experiemtn becomes the experimental groupd in the second half.
Placebo effect: A significant variable in human studies is the psychological aspect of administering a treatment. If you give someone a pill and tell the person that it will have a certain effect, there is a strong possibility that it will have the effect, even if the pill contains only sugar or an inert substance. It shows the ability of our minds to regulate the physiological functioning of our bodies.
Cell to Cell communication
Diffusion: is only adequate for information exchange between neighboring cells, because diffusion is ineffective over long distances. Multicellular organisms requrie additional methods for moving signals from one part of the body to another.
What mechanisms are involved in the coordination of body functions?
1, Blood flowing through our efficient circulatory system makes a complete circuit about once a minute, moving material from one part of the body to another.
2, nervous system takes care of more rapid communication, with electrical signals traveling as fast as 120m/sec.
3, the combination of simple diffusion across the small distances, widespread distribution of materials through the circulatory system, and rapid, specific delivery of messages by the nervous system enables each cell in the body to communicate with most other cells.
Homeostasis: the process by which the body maintains a relatively stable internal environment in the face of either an external or an internal disturbance.
How many cells estimated in the human body?
75 trillion cells. All thoes cells face a task --- to communicate with each other in a manner that is rapid yet also conveys a tremendous amount of information.
What are the two types of physiological signals?
1, Electrical signals and 2, chemical signals.
What is signal?
a signal is the sequence of states of a communications channel that encodes a message.In a communications system, a transmitter encodes a message into a signal, which is carried to a receiver by the communications channel.
Biological membrane potentials. The value of the signal is a straightforward electric potential ("voltage"). The domain is more difficult to establish. Some cells or organelles have the same membrane potential throughout; neurons generally have different potentials at different points. These signals have very low energies, but they can be measured in aggregate by the techniques of electrophysiology.
a signal or biopotential is an electric quantity (voltage or current or field strength), caused by chemical reactions of charged ions. Another use of the term lies in describing the transfer of information between and within cells, as in signal transduction. Biological signals can also be seen as an example of signal (information theory).
What is electrical signal and chemical signal?
electrical signals are changes in a cell's membrane potential.
chemical signals are molecules secreted into the ECF by cells, and they are responsible for most communication within the body.
What is target cell?
The cells that receive electrical or chemical signals are called target cells, or taret.
Four basic methods of cell-tocell communication?
1, gap junctions: allow direct sytoplasmic transfer of electrical and chemical signals between adjacent cells;
2, contact-dependent signals that occur when surface molecules on one cell bind to surface molecules on another cell;
3, local communication by chemicals that diffuse through the ECF
4, long-distance communication through a combination of electrical signals carried by nerve cells and chemical signals transported in the blood.
What is gap junctions communication?
Gap junctions transfer chemical and electrical signals directly between cells. Potein channels that create cytoplasmic bridges between adjacent cells. A gap junction forms from the union of membrane-spanning protein called connexins. on two adjacent cells. The united connexins create a protein channel connexon that can open and close. When the channel is open, the connected cells function like a signle cell with multiple nuclei( a syncytium).
When gap junctions are open, ions and small molecules diffuse from the cytoplasm of one cell to the cytoplasm of the next. Larger molecules are excluded.
Jap junctions are the only means by which electrical signals can pass directly from cell to cell.
Are all the gap junction alike? What is isoforms? What is the function of isoform?
No, they are not all alike. There are 20 different variations of connexins that may mix or match to form gap junctions. When a protein such as connexin has several similar forms, the variants are knows as subtypes or isoforms. The existence of connexin isoforms allow gap junction selectivity to vary from tissues to tissues.
What is contact-dependent signals?
Contact-dependent signals require cell-to-cell contact. Some cell-to-cell communication require that surface molecules on one cell bind to a surface moledule of another cell. This type of direct contact signaling occurs in the immune system and during growth and development, such as when nerve cells send out long extensions that must grow from the central axis of the body to the distal ends fo the limbs. CAMs, adhere one cell to another cell but not participate in cell-cell signaling.
What is local communication by chemicals?
Local communication is accomplished by paracrines and autocrines.
What is paracrine? what is Paracrine signalling ?
is a chemical that is secreted by a cell to act on cells in its immediate vicinity.Paracrine signalling is a form of signalling in which the target cell is close to the signal releasing cell, and the signal chemical is broken down too quickly to be carried to other parts of the body. The signal chemical is called the paracrine agent. Examples of paracrine signalling include growth factor signalling and clotting factors. Growth factor signalling plays an important role in many aspects of development. In mature organisms paracrine signalling functions include responses to allergens, repairs to damaged tissue, formation of scar tissue, and clotting. Overproduction of some paracrine growth factors has been linked to the development of cancer.
What is autocrine?What is autocrine signaling?
If the signal moleule acts on the cell that secreted it, the chemical is called an autocrine.Autocrine signaling is a form of signalling in which a cell secretes a chemical messenger (called the autocrine agent) that signals the same cell.
How does Local communication by chemicals happen?(diffusion)
Local communication is accomplished by paracrins and autocrines. They reach their target cells by diffusing throught the intersititial fluid. Because distance is a limiting factor for diffuction, the effective range of the chemical signal is restricted to adjacent cells.
A good example of a paracrine is histamine, a chemical released from damaged cells. When you scratch yourself with a pin, the red, reaised wheal that results is due in the part to the local release of histamine from the injured tissue. The histamine acts as a paracrine, diffuing over to the capillaries in the immediate area of the the injury and making them more permeable to whie blood cells and antibodies in the plasma.
Cytokines are regulatory peptides that usually act close to the site where they are secreted.
Eicosanoids are lipid-derived paracrinesand autocrines.
How does long-distance communication take place?
Electrical signals, hormones and neurohormones carry out long-distance communication.
All cells in the body can release paracrines, but most long distance communication between cells is the responsibility of the nervous and endocrin systems. The endocrine system communicates using hormones, chamicalsignals that are secreted into the blood and distributed all over the body by the circulation. Hormones comes in contact with most cells of the body but only those cells with receptors for the hormones are target cells.
1, Hormones are secreted by endocrine glands or cells into the blood. Only target cells with receptors for the hormones will respong to the signals.
How does nervous system communicate?Why nervous system and endocrine system work integrately?
The nervous system used a combination of chemical signals and electrical signals to communicate.
1, An electrical signals travels along a nerve cell (neuron) until it reaches the very end of the cell, where it is translated into a chemical signal secreted by the neuron.
2, If the chemical signal diffused from the neuron across a narrow ECF space to a target cell and has a rapid effect, it is called a neurotransmitter.
3, If a neurocrine acts more slowly as an autocrine or paracrin, it is called a neuromodulatory. If the the neurocine released by the neuron diffuses into the blood for distribution, it is called a neurohormone.
The similarities between neurohormones and hormones secreted by the endocrine system blur the distrinction between the nervous and endocrine systems, making them a continuum rather than two distinct systems.
What are four Cannon's postulates?
Cannon proposed a list of parameters that are under homeostatic control based on observations made by numerous physiologists and physicians. We now know that his list of regulated variables was both accurate and complete. Cannon divided his parameters into what he called environmental factors that affect cells (osmolarity, temperature, and pH) and "materials for cell needs"--nutrients, water, sodium, calcium and others" Cannon's internal secretions are the hormones and other chemicals that our cells use to communicated with each other.
Cannon also postulated a number of properties of hoeostatic control systems that were validated in the succedding years.
1, The role of the nervous system in preserving the "fitness" of the internal environment.
Fitness means conditions that are compatible with normal function. The nervous system coordinates and integrates blood volume, osmolarity, blood pressure and body temperature, among other parameters.
2, The concept of tonic level of activity.
This is like the volume control on a radio, which enables you to make the sound level louder to softer by turning a single knob. A physiological example of a tonically active control system is the nervous regulation of diameter in certain blood vessels, where increaed input from the nervous system decrease diameter, while decreased input from the the nervous system causes the diameter to increase.
3, The concept of antagonistic controls.
Systems that are not under tonic control are usually under antagonistic control, eight by hormones or the nervous systems. Eg. insulin and glucagon are antagonistic hormones. Insulin decreases the concentration of glucose in the blood, while glucagon increase it. In pathways controlled by the nervous system, the sympathetic and parasympathetic divisions oftern have opposing effects. Eg. chemical signals from a sympathetic neuron increase heart rate, while chemical from a parasympathetic neuron decrease it.
4, The concept that chemical signals can have different effects in differnt tissues of the body
Homeostatic agents, antagonistic in one region of the body, may be cooperative in another region. A single chemical signal can have different effects depending on the receptor at the target cell. Eg. epinephrin constricts or dilates blood vessels, depending on whether the vessel has alpha or beta adrenergic receptors. if it bind to alpha receptors, the vessel constricts; if it binds to beta receptor, the vessel dilates.
Control pathways of homeostasis
Homeostasis is a continuous process that involves monitoring multiple parameters, then coordinating appropriate responses to minimize any disturbance. Its responses may take place in small, localized regions of the body or they may be bodywide, or systemic, responses. In either case, the process always has three components:
1, a stimulus or change in a regulated variable
2, a cell or tissue that evaluates the stimulus and initiates a response
3, the cells or tissues that carry out the response.
What is local control?
The simplest control takes place strictly at the tissue or cell involved. In local control, a relatively isolated change occurs in the vicinity of a cell or tissue and evokes a paracrine or autocrine respons.
Paracrines and autocrines are responsible for the simplest control system. In local control, a cell or tissue senses a change in its immediate vicinity and responds. The response is restricted to the region where the change took place.
Eg. oxygen concentration in a tissue decreases. The cells lining the small blood vessels bringing blood to that area sense the fall in oxygen concentration and respond by secreting a paracrin. The paracrin relaxes muscles in the blood vessel wall, dilating the blood vessels and bring more blood and oxygen to the area. Paracrines that are involved in this response include carbon dioxide and metabolic products such as lactic acid.
What is reflex control?
In a reflex pathway, control of the reaction lies outside the organ that carries out the response. Reflex--mean any long-distance pathway that used the nervous system, endocrine system, or both to receive input about a change, integrate the information, and react appropriately.
Replext pathway can be broken down into two parts:
1, a response loop and 2, a feedback loop.
The response loop begins with a stimulus and ends with the response of the target cell. A repsonse lopp has three primary components: 1, an input signal 2, integration of the signal 3, an output signal.
The sequences of a response loop:
stimulus----receptor----afferent pathway( incoming signal)----integrating center(control center evaluate signal and compares it with the setpoint and decides on an response)-----efferent pathway (outgoing signal)----effector(target cell or tissue)----response(bring the situation back to limits).
What is sensory receptors?
sensory receptor is a structure that recognizes a stimulus in the internal or external environment of an organism. In response to stimuli the sensory receptor initiates sensory transduction by creating graded potentials or action potentials in the same cell or in an adjacent one.The sensory receptor may be a specialized portion of the plasma membrane, or a separate cell associated with a neuron ending.
Afferent pathway: in a nervous reflect, the afferent pathway is the electrical and chemical signal carried by a nerve cell. In endocrine reflexes, there is no afferent path because the stimulus comes directly into the endocrine cell, which serves as both sensor and integrating center.
Integrating center: In endocrin reflex, the integrateing center is the endocrine cell. In nervous reflexes, the integrating center lies within the central nervous system, which is composed od the brain the the spinal cord.
Efferent pathway: In nervous system, the efferent path is always the electrial and chemical signal transmitted by an efferent neuron. Because electrical signals traveling through the nervous system are idential, the distinguishing characteristic of the the anatomical route taken by the nerve cell through which the signal goes.
Effectors:are the cells or tissues that carry out the response. The targets of nervous reflexes are muscles, glands, and some adipose tissue. The target of endocrine pathways are any cells that have the proper receptor for the hormone.
Responses: there are two levels of response that can be given for any reflex.
1, the very specific cell or tissues response that results from combination of the signal ligand with the receptor: opening a channel, initiating protein synthesis, or modifying enzyme activity.
2, the more general systemic respone describes what those sepcific events mean to the tissue or the organism asa a whole. Eg. when the hormnone epinephrine combines with Blta adrenergic receptors on the walls of certain blood vessels, the cellular response is relaxation of the smooth muscle. The systemic response to relaxation of the blood vessel wall is increased blood flow through the vessel.
Setpoint:is the target value that an automatic control system. Hoever, it can vary from person to person, or even fro the same individual over a period of time.
Factors that influence an individual's setpoint: inheritance and the conditions to which the person has become accustomed.
Acclimatization (Acclimation): The physiological adaptation of an animal or plant to changes in climate or environment, such as light, temperature, or altitude.
Feedback loop: feedback is a process whereby some proportion or in general, function, of the output signal of a system is passed (fed back) to the input. Often this is done intentionally, in order to control the dynamic behaviour of the system.
In biological systems such as organisms, ecosystems, or the biosphere, most parameters must stay under control within a narrow range around a certain optimal level under certain environmental conditions. The deviation of the optimal value of the controlled parameter can result from the changes in internal and external environments. A change of some of the environmental conditions may also require change of that range to change for the system to function. The value of the parameter to maintain is recorded by a reception system and conveyed to a regulation module via an information channel.
Biological systems contain many types of regulatory circuits, among which positive and negative feedbacks. Positive and negative don't imply consequences of the feedback have positive or negative final effect. The negative feedback loop tends to slow down a process, while the positive feedback loop tends to accelerate it.
Feedback and regulation are self related. The negative feedback helps to maintain stability in a system in spite of external changes. It is related to homeostasis. Positive feedback amplifies possibilities of divergences (evolution, change of goals); it is the condition to change, evolution, growth; it gives the system the ability to access new points of equilibrium.
For example, in an organism, most positive feedbacks provide for fast autoexcitation of elements of endocrine and nervous systems (in particular, in stress responses conditions) and play a key role in regulation of morphogenesis, growth, and development of organs, all processes which are in essence a rapid escape from the initial state. Homeostasis is especially visible in the nervous and endocrine systems when considered at organism level.
Feedback is also central to the operations of genes and gene regulatory networks. repressor (see Lac repressor) and activator proteins are used to create genetic operons, which were identified by Francois Jacob and Jacques Monod in 1961 as feedback loops.
Negative feedback is the process of feeding back to the input a part of a system's output, so as to reverse the direction of change of the output. This tends to keep the output from changing, so it is stabilizing and attempts to maintain homeostasis. When a change of variable occurs within a stable range, the system will attempt to establish equilibrium. Negative feedback is also used in many types of amplification systems to stabilise and improve their amplification characteristics (see e.g. Operational amplifiers).
A simple and practical example is a thermostat. When the temperature in a heated room reaches a certain upper limit the room heating is switched off so that the temperature begins to fall. When the temperature drops to a lower limit, the heating is switched on again. Provided the limits are close to each other a steady room temperature is maintained. The same applies to a cooling system, such as an air conditioner, a refrigerator, or a freezer.
Positive feedback is a type of feedback. Open systems (ecological, biological, social) contain many types of regulatory systems, among which are systems that involve positive feedback and its relative negative feedback.
When a change of variable occurs in a system, the system responds. In the case of positive feedback the response of the system is to change that variable even more in the same direction. For a simple example, imagine an ecosystem with only one species and an unlimited amount of food. The population will grow at a rate proportional to the current population, which leads to positive feedback. This has a de-stabilizing effect, so left unchecked, does not result in homeostasis. In some cases (if not controlled by negative feedback), a positive feedback loop can run out of control, and can result in the collapse of the system. This is called vicious circle, or in Latin circulus vitiosus.
Positive and negative do not mean or imply desirability. The negative feedback loop tends to slow down a process, while the positive feedback loop tends to speed it up. Positive feedback is used in certain situations where rapid change is desirable.
One common example of positive feedback is the network effect, where more people are encouraged to join a network the larger that network becomes. The result is that the network grows more and more quickly over time.
posted by C-T @ 6:43 PM
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