Term
| Who first recognised the importance of the internal environment? |
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Definition
| Claude Bernard who is quoted to have said “the fixity of the interior environment is the condition for free life”. |
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Term
| Who first coined the term Homeostasis and what does it refer to? |
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Definition
| Walter Cannon and it refers to the ability of multicellular organisms to maintain the extracellular fluid within the limits required for survival in the face of varying external environments. |
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Term
| When is homeostasis in play? |
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Definition
| The body is in homeostasis when the controlled variable is either at equilibrium or in a steady state. |
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Term
| What does it mean if the variable is at equilibrium? |
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Definition
| If the variable is at equilibrium then it remains at the set point and no extra energy is required to keep it there with an example of core body temperature when in a room of normal temperature. |
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Term
| What does it mean if the variable is in a steady state? |
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Definition
| If the variable is in a steady state then the variable remains at the set point but energy expenditure is required to keep it there for example when sitting in a colder room. |
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Term
| What are some examples of homeostatic variables? |
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Definition
| Composition of body fluids, pH, core body temperature, oxygen, glucose, ions, minerals, and waste removal etc. |
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Term
| How is homeostasis maintained? |
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Definition
| By ensuring that the cells are in an environment that meets their needs and allows them to perform normally under changing external environments. |
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Term
| How are the variables maintained within narrow limits and what happens in the case of failure? |
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Definition
| Through homeostatic control systems and the ability of the body to self-regulate. Failure to do so usually results in illness (pathophysiology). The role of health professionals is to restore homeostasis. |
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Term
| What is meant by the external environment for unicellular organisms? |
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Definition
| In unicellular organisms the external environment is the outside world and the organism thus has limited capacity to deal with the changing environment. This means work must be done to compensate. |
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Term
| What is meant by the external environment for multicellular organisms? |
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Definition
| The problems encountered by unicellular organisms are solved by having ECF bathing the cells which uses homeostatic mechanisms to maintain the components at set point values for survival. |
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Term
| What is the role of the respiratory system? |
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Definition
| Exchange of carbon dioxide and aiding in the maintenance of pH. |
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Term
| What is the role of the cardiovascular (circulatory) system? |
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Definition
| Circulating blood around the cells which carries nutrients, wastes, and helps with heat loss. |
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Term
| What is the role of the gastrointestinal system? |
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Definition
| This transfers nutrients and water to the blood. |
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Term
| What is the role of the kidney (urinary) system? |
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Definition
| This removes waste as well as regulates water volume, salts, and pH levels. |
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Term
| What is the role of the nervous system? |
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Definition
| Regulation of the other systems and control of movement. |
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Term
| What is the role of the musculoskeletal system? |
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Definition
| It controls movement of the lungs and powers and directs skeletal movement. |
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Term
| What is the role of the immune system? |
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Definition
| To protect other systems from damage by pathogenic organisms. |
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Term
| What is the role of the endocrine system? |
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Definition
| This has a variety of specific, direct, and regulatory roles as well as playing an important part in maintaining homeostasis. |
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Term
| What is the role of the skin? |
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Definition
| Protection and allowing heat gain or loss. |
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Term
| How does a feedback control system work? |
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Definition
| Changes in the controlled variable are detected by the sensor and this information is sent to the integration centre which compares the detected value to the set point and activates the effectors. |
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Term
| What is the difference between positive and negative feedback? |
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Definition
| Negative feedback (core body temperature) aims to reduce the deviation from set point while positive feedback aims to increase the deviation from set point (child birth and blood coagulation). |
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Term
| How is the child birth positive feedback cycle initiated? |
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Definition
| Birthing is initiated by the release of oxytocin from the posterior pituitary gland which stimulates uterine contraction. |
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Term
| How does the birthing cycle continue? |
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Definition
| Uterine contraction releases prostaglandins which trigger further contractions. These push the baby’s head down causing cervical stretch which stimulates contraction and oxytocin release. |
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Term
| How do positive feedback cycles complete? |
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Definition
| Positive feedback cycles complete once the trigger (ie baby) is removed. |
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Term
| How is core body temperature maintained? |
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Definition
| Variation is detected by central thermoreceptors in the hypothalamus and here the actual value is also compared to the set point. This information is then transmitted to the effectors. |
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Term
| What are the effectors when aiming to increase core temperature to the set point value? |
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Definition
| The effectors increase cell metabolism. Skeletal muscles shiver, skin and blood vessels constrict, and piloerector muscles cause goose bumps. |
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Term
| What is a feedforward cycle? |
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Definition
| Feedforward systems act in anticipation of a change to prevent an alteration of the set point value for the controlled value to reduce the likelihood of deviation. |
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Term
| How does the feedforward cycle work? |
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Definition
| Feedforward has a similar mechanism to the feedback cycle but the sensor works based on sensory information and memory in regards to a particular event in the external environment. |
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Term
| What is physiological feedforward and what are some examples? |
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Definition
| Physiological feedforward refers to anticipatory physiological adjustments and biological rhythms such as |
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Term
| How does failure of homeostasis occur? |
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Definition
| Caused be extreme external environments or organ failure, although organ failure can result from failure of homeostasis. This can also cause chronic illnesses. |
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Term
| What can cause organ failure? |
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Definition
| Genetic reasons, degeneration, toxins, trauma, allergy/inflammation, autoimmune, infection, and cancer. |
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Term
| What is the role of a health professional? |
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Definition
| To research the causes and find ways to prevent them, find new and better treatments, and provide support for those in need. |
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Term
| What is the total body water distribution? |
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Definition
| In males 60% is water weight and in females 55%. ECF makes up 1/3 of the water weight with ICF making up the other 2/3. Of the ECF 4/5 is interstitial fluid and 1/5 is plasma. |
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Term
| How compartmentalisation achieved and what is its purpose? |
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Definition
| It is achieved by having barriers to separate the compartments. The barriers have selective permeability to control the entry and exit of substances allowing different conditions within compartments. |
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Term
| What is the intracellular concentration of sodium, potassium, calcium, chloride, and bicarbonate? |
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Definition
Sodium – 145mmol/L
Potassium – 5mmol/L
Calcium – 1mmol/L
Chloride – 100mmol/L
Bicarbonate – 24mmol/L |
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Term
| What is the extracellular concentration of sodium, potassium, calcium, chloride, and bicarbonate? |
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Definition
Sodium – 15mmol/L
Potassium – 150mmol/L
Calcium – 10-4mmol/L
Chloride – 7mmol/L
Bicarbonate – 10mmol/L |
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Term
| What is the pH and osmolarity in the ICF and ECF? |
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Definition
| In the Extracellular fluid the pH is 7.4 while it is 7.1 in the Intracellular fluid. The osmolarity is 275-295mosmol/L in both compartments. |
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Term
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Definition
| Hyponatremia is an abnormally low salt (sodium) concentration in the blood which occurs when a person loses too much salt through excessive dilute urination or dilutes the ECF through excess water consumption. |
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Term
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Definition
| Hypertension is often associated with high blood pressure and is correlated with elevated sodium in the extracellular fluid. |
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Term
| Why is hyponatremia life threatening? |
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Definition
| Normally the kidneys can excrete excess water but if excessive then the ECF and ICF will increase in volume leading to cell swelling which compromises body function particularly in the brain where swelling may block blood. |
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Term
| How is the stability of an internal environmental variable achieved? |
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Definition
| Through the balance of inputs and outputs where the magnitude doesn’t matter but rather the balance between them. |
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Term
| What happens in negative feedback systems? |
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Definition
| A change in the variable being regulated brings about responses that move the variable back towards its set point value. |
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Term
| Can homeostatic systems maintain complete constancy of any given feature in the internal environment? |
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Definition
| No and therefore regulated variables will have a more or less narrow range of normal values according to the external environmental conditions. |
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Term
| Can the set point for a variable change? |
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Definition
| The set point of some variables can be reset – that is be physiologically raised or lowered. |
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Term
| What happens if one variable must deviate from set point to help return another variable to the normal range? |
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Definition
| There is a hierarchy of importance so that the constancy of certain variables may be altered markedly to maintain others within their normal range. |
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Term
| What are the main functions of the plasma membrane? |
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Definition
| Enclose the cell’s organelles, solutes, substrates, enzymes, and genetic material etc, regulate movement of substances into/out of the cell, provide a site of anchorage, and provide signalling molecule detection sites. |
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Term
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Definition
| Random thermal motion whereby substances have a tendency to move from a high concentration to a low concentration until they become uniformly and evenly distributed through the available volume. |
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Term
| What is the rate of diffusion? |
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Definition
| The rate of diffusion increases in proportion to the square of the distance over which the molecules must diffuse. This means it is rapid over short distances and very slow over long distances. |
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Term
| What is the main thing that affects cell size? |
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Definition
| The rate of diffusion. It is important that diffusion occurs relatively quickly to provide the nutrients for cell activity. The bigger the cell the longer it takes. This is why multicellular organisms need a circulatory system. |
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Term
| What is flux and how can it be calculated? |
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Definition
| Flux is net movement of particles between compartments. The unit is mol.sec.cm-1. It is shown using J and J=PAΔC where P is the permeability constant at a temperature, A is area, and C is concentration difference. |
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Term
| What is an integral membrane protein? |
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Definition
| These are imbedded in the membrane and generally span the width. These may form selective pores through which water soluble substances can pass to enter or exit the cell. |
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Term
| What is a peripheral membrane protein? |
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Definition
| These may project on only one side of the plasma membrane and often have an important job in anchoring the membrane to the cytoskeleton and extracellular environment. |
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Term
| What are some examples of integral membrane proteins? |
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Definition
| Aquaporins, Urea transporters, ion channels, solute carriers, and ATPases. |
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Term
| What is the plasma membrane composed of? |
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Definition
| A phospholipid mosaic membrane with non-polar tails poking in and polar heads poking out, carbohydrate chains, channels or pores, integral membrane proteins, peripheral proteins, and transmembrane proteins. |
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Term
| What is an integral membrane receptor? |
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Definition
| A receptor that binds to chemical messengers such as hormones sent from other cells. |
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Term
| What is an integral membrane enzyme? |
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Definition
| An enzyme breaks down a chemical messenger and terminates the effect on the target cell. |
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Term
| What is a channel protein? |
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Definition
| A channel protein is constantly open and allows solutes to pass into and out of the cell. |
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Term
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Definition
| A gated channel opens and closes to allow solutes through only at certain times. |
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Term
| What is a cell identity marker? |
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Definition
| A cell identity marker is a glycoprotein that distinguishes the body’s own cells from foreign cells. |
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Term
| What is a cell adhesion molecule? |
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Definition
| A cell adhesion molecule binds one cell to another. |
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Term
| What is required in order for a substance to dissolve across a membrane? |
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Definition
| The substance must either be non-polar or have a specific transmembrane pathway. |
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Term
| What are the two types of mediated transport? |
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Definition
| Facilitated diffusion is where proteins provide a specific pathway for solute diffusion. Active transport is when energy is required to move substances against the concentration gradient. |
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Term
| What is the driving force of diffusion and how is it established? |
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Definition
| The driving force of diffusion is the electromotive force which is set up by both the concentration difference across the cells and the electrical difference due to the ionic charges. |
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