Homeostasis

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  • Created by: r98
  • Created on: 01-04-16 21:15
What's homeostasis?
The maintenance of a constant internal environment in organisms.
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What bathes each cell and makes up the internal environment? What does it do?
Tissue fluid, it supplies nutrients and removes wastes.
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Why is it important to maintain the features of the tissue fluid at the optimum levels?
It protects the cells from changes in the external environment.
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What do variations in internal and external conditions bring about?
Continuous fluctuations.
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What is one reason that homeostasis is important?
The enzymes that control the biochemical reactions within cells are sensitive to changes in pH and temperature. Any changes to these factors reduces the efficiency of enzymes. A constant tempreature means reactions happen at constant rates.
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What is another reason that homeostasis is important?
The maintenance of a constant blood glucose concentration is essential in ensuring a constant water potential and a reliable source of glucose for respiration.
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Why is it important to maintain a constant water potential?
Changes of the water potential of blood and tissue fluids may cause cells to shrink and expand, so cells can't operate normally.
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What's another reason that homeostasis is important?
The organisms are more independent of the external environment. They have a wider geographical range and therefore have a greater chance of finding food, shelter, etc.
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What are the features of a self-regulating system?
The set point, receptor, controller, effector and feedback loop.
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What's the role of the receptor?
To detect any deviation from the set point and inform the controller.
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What's the role of the coordinator?
Coordinates information from various receptors and sends instructions to an appropriate effector.
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What's the role of the effector?
Brings about changes needed to return the system to the set point, this creates a feedback loop.
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What's the role of the feedback loop?
Informs the receptor of the changes to the system brought about by the effector.
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How does the brain decide the best course of action?
By analysing the information from all the detectors.
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What are 2 methods of gaining heat?
Production of heat (metabolism of food during respiration) & gaining heat from the environment (by conduction, convection and radiation).
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What are methods of losing heat?
Evaporation of water (sweating) & loss of heat to the environment (by conduction, convection and radiation).
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What are endotherms?
Animals that derive most of their heat from the metabolic activities that take place inside their bodies.
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What are ectotherms?
Animals that obtain a large proportion of their heat from sources outside their bodies (environment).
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Does the body temperature of an ectotherm fluctuate with that of the environment? Why?
Yes, because they gain most of their from the environment.
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How do ectotherms control their body temperature?
By exposing themselves to the Sun, taking shelter, gaining warmth from the ground, generating metabolic heat & colour variations.
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Why do lizards retreat into burrows at night?
To reduce heat loss when the external temperature is low.
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Why are lizards in colder environments generally darker in colour?
Darker colours absorb more heat.
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Does the body temperature of an endotherm fluctuate with that of the environment?
No, their body temperature remains relatively constant despite fluctuations in the external temperature.
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Why do mammals and birds living in cold climates have bodies with small surface area to volume ratios?
It's from within the 'volume' that heat is produced and from the 'surface area' that heat is lost. So the smaller this ratio, the easier it is to maintain a high body temperature.
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What are some features of animals in colder climates?
They have smaller extremities (e.g. ears) and thick fur, feathers or fat layers to insulate the body.
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What are the rapid chages in endotherms to conserve or gain heat?
Vasocontriction, shivering, raising of hair, increased metabolic rate, decrease in sweating, and behavioural mechanisms.
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How do the hair erector muscles in the skin being contracted conserve heat in endotherms?
The hairs on the body are raised, enabling a thicker layer of still air (good insulator) to be trapped next to the skin. This improves insulation and conserves heat.
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What behavioural mechanisms can be observed in endotherms that are trying to conserve or gain heat?
Sheltering from the wind, basking in the sun and huddling together.
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What are the rapid responses that enable heat to be lost from endotherms when the environmental temperature is high?
Vasodilation, increased sweating, lowering of body hair, and behavioural mechanisms.
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What happens during vasodilation?
The diameter of the arterioles near the surface of the skin becomes larger, allowing warm blood to pass close to the skin surface through the capillaries. The heat from this blood is then radiated away from the body.
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What is required to evaporate water from the skin surface?
Energy in the form of heat is required.
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What are the behavioural mechanisms of endotherms that are trying to lose heat?
Avoiding the heat of the day by sheltering in burrows and seeking out shade.
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What are the stages in the regulation of core body temperature in endotherms?
The stimulus (change in body temp) is detected by receptors (thermoreceptors), which pass the information to a coordinator (the hypothalamus) in the brain, which then causes an effector (skin) to produce appropriate response.
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What two parts does the thermoregulatory centre in the hypothalamus consist of?
A heat gain centre & a heat loss centre.
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What activates the heat gain centre?
A fall in blood temperature.
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What does the heat gain centre control?
The mechanisms that increase body temperature.
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What activates the heat loss centre?
A rise in blood temperature.
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What does the heat loss centre control?
The mechanisms that decrease body temperature.
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What's the role of the hypothalamus?
It monitors the temperature of the blood passing through it.
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Where are thermoreceptors found?
In the skin and in the hypothalamus.
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How do thermoreceptors send impulses to the hypothalamus?
Along the autonomic nervous system.
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What information do thermoreceptors provide?
Information on the environmental temperature.
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What characteristics do all hormones have in common?
Hormones are: produced by glands, carried in the blood plasma, and are effective in small quantities.
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What doe target cells have on their cell-surface membrane?
Receptors that are complementary to the hormone.
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Which two hormones use the second messenger model mechanism?
Adrenaline and glucagon, 2 hormones imvolved in the regulation of blood glucose.
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What's the role of the hormone in the second messenger model of hormone action?
The hormone is the first messenger. It forms a hormone-receptor complex by binding to specific receptors on the cell-surface membrane of target cells.
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What does the hormone-receptor complex activate? What does this result in?
It activates an enzyme inside the cell that results in the production of a chemical (that acts as a second messenger).
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What does the second messenger cause?
A series of chemical changes that produce the required response.
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In the case of adrenaline, what's the response?
The conversion of glycogen to glucose.
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What is the pancreas and where is it situated?
It's a large, pale-coloured gland situated in the upper abdomen, behind the stomach.
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What does the pancreas do?
Secrete enzymes (protease, amylase and lipase) for digestion and hormones (insulin and glucagon) for regulating blood glucose.
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What are the groups of hormone-producing cells known as?
Islets of Langerhans.
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What are the two types of islets of Langerhans?
'a' cells (alpha) and 'B' cells (beta).
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Which type of islets of Langerhans is larger?
'a' cells.
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What do 'a' cells do?
Produce glucagon (hormone).
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What do 'B' cells do?
Produce insulin (hormone).
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What happens if blood glucose levels rise too high?
It lowers the water potential of the blood and creates osmotic problems that can cause dehydration.
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What is the normal level of blood glucose?
90 mg in each 100 cm3 of blood.
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What are the 3 sources from which blood glucose comes from?
Directly from the diet, glycogenolysis, and from gluconeogenesis.
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What is glycogenolysis?
The breakdown of glycogen.
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Where is glycogen stored?
In the liver and muscle cells.
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What is gluconeogenesis?
The production of new glucose (glucose from sources other than carbohydrates).
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What can the liver use to make new glucose?
Glycerol and amino acids.
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How do the 'B' cells respond to a rise in blood glucose level?
By secreting insulin directly into the blood plasma.
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What type of receptors do almost all body cells (not RBC) have on their cell-surface membranes? What binds to these receptors?
Glycoprotein receptors, that bind to insulin.
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What are the affects on insulin when it's combined with the receptors?
A change in the tertiary structure of the glucose transport protein channels, an increase in thr numver of carrier molecules in the cell-surface membrane, and activation of the enzymes that convert glucose to glycogen and fat.
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How does insulin, when combined to receptors, affect the glucose transport protein channels?
Changes their tertiary structure, causing them to change shape and open, allowing more glucose into the cells.
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How do the effects of insulin lower the blood glucose level?
By increasing the rate of: absorption of glucose into cells, respiratory rate of the cells, conversion of glucose into glycogen (glycogenesis) in cells of liver and muscle, and conversion of glucose to fat.
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How is lowering of the blood glucose level an example of negative feedback?
Lowering of blood glucose level causes 'B' cells to reduce their secretion of insulin (= negative feedback).
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What do the 'a' cells of the islets of Langerhans detect and how do they respond?
They detect a fall in blood glucose and respond by secreting glucagon (hormone) directly into the blood plasma.
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Why do only liver cells respond to glucagon?
Only liver cells have receptors that bind to glucagon.
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What is the response of liver cells once glucagon has binded to its receptors?
They activate an enzyme that converts glycogen to glucose, and increase the conversion of amino acids and glycerol into glucose.
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What is the name given to the process of converting amino acids and glycerol into glucose?
Gluconeogenesis.
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What is the overall effect of the response of liver cells?
Increase in the amount of glucose in the blood, returning it to its normal level.
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How is the raising of the blood glucose level an example of negative feedback?
The raising of the blood glucose level causes the 'a' cells to reduce the secretion of glucagon (= negative feedback).
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What other hormone, apart from glucagon, can increase blood glucose level?
Adrenaline.
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What produces adrenaline? Where is this structure found?
The adrenal glands, that lie above the kidneys.
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How does adrenaline raise the blood glucose level?
By activating an enzyme that causes the breakdown of glycogen to glucose in the liver, & by inactivating an enzyme that synthesises glycogen from glucose.
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Why are the two hormones, insulin and glucagon, said to act antagonistically?
Becuase they act in opposite directions. Insulin lowers the blood glucose level, whereas glucagon increases it.
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What determines the quantity of insulin and glucagon produced?
The level of glucose in the blood.
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Is the level of glucose constant? Why?
No, it fluctuates around a set point. This is because of the way negative feedback mechanisms work.
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What is diabetes?
A chronic disease in which a person is unable to metabolise carbohydrate, especially glucose, properly.
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What is diabetes caused by?
An inability to control blood glucose levels due to a lack of the hormone insulin or a loss of responsiveness to insulin.
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What are the two forms of diabetes?
Type I (insulin dependent) & Type II (insulin independent).
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What is Type I diabetes due to?
It's due to the body being unable to produce insulin. It may be the result of an autoimmune response whereby the body's immune system attacks the 'B' cells of the islets of Langerhans.
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Who usually develops Type I diabetes and how long does it take to develop?
It normally begins in childhood. It develops quickly, usually over a few weeks, and has obvious symptoms.
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What is Type II diabetes due to?
It's normally due to glycoproteins receptors losing their responsiveness to insulin. However, it may a;so be due to an inadequate supply of insulin from the pancreas.
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Who usually develops Type II diabetes and how long does it take to develop?
People over the age of 40 years. People who are overweight are particularly likely to develop Type II diabetes. It develops slowly, and symptoms are usually less severe.
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What are the symptoms of diabetes?
High blood glucose level, presence of glucose in urine, increased thirst and hunger, need to urinate excessively, genital itching or regular episodes of thrush, tiredness, weight loss, blurred vision.
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How can Type I diabetes be controlled?
By injections of insulin.
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Why can't the insulin be taken by mouth?
Because it's a protein, so it would be digested in the alimentary canal.
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Why must the dose of insulin injected have to match exactly the glucose intake?
Because if too much insulin is injected, the diabetic will experoence a low blood glucose level, that could result in unconsciousness.
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Why and how are blood glucose levels monitored?
To ensure the correct dose of insulin. Using biosensors.
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How can Type I diabetics lead normal lives?
By injecting insulin and managing their carbohydrate intake and exercise carefully.
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How is Type II diabetes controlled?
By regulating the intake of carbohydrate in the diet and matching this to the amount of exercise taken.
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In some cases, what other measures can be taken to control Type II diabetes?
Injections of insulin or the use of drugs that stimulate insulin production. Other drugs slow down the rate at which the body absorbs glucose from the intestine.
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Other cards in this set

Card 2

Front

What bathes each cell and makes up the internal environment? What does it do?

Back

Tissue fluid, it supplies nutrients and removes wastes.

Card 3

Front

Why is it important to maintain the features of the tissue fluid at the optimum levels?

Back

Preview of the front of card 3

Card 4

Front

What do variations in internal and external conditions bring about?

Back

Preview of the front of card 4

Card 5

Front

What is one reason that homeostasis is important?

Back

Preview of the front of card 5
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Comments

Proffessor

By far my favourite flashcards to read on a Friday night with a glass of wine and the telly on. really relaxing stuff. Thank you 'r98' for making my evening. After my husband left I've been lonely.

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