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A2 Biology > Homeostasis > Flashcards

Homeostasis Flashcards

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1
Q

What is homeostasis?

A

Maintenance of a constant internal environment in organisms and ensures the cells of the body are in an environment that meets their needs and allows them to function normally

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2
Q

What sort of things does homeostasis control?

A
  • Temperature
  • pH
  • Water levels
  • 02 levels
  • Composition of blood
  • Tissue fluid
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3
Q

What ability does homeostasis give to the body?

A

Allows it to return to the set point and so maintain organisms in a balanced equilibrium

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4
Q

Why is homeostasis important?

A
  • Enzymes are sensitive to changes in pH and temperature , if they are away from their optimum the enzymes will denature
  • Changes to water potential of blood and tissue fluid may cause cells to shrink/burst
  • Maintaining a constant blood glucose concentration also ensures a constant water potential, blood glucose is vital as a reliable source of glucose for respiration
  • Organisms with the ability to maintain a constant internal environment are more independent of the external environment
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5
Q

What are the control mechanisms of homeostasis?

A
  1. The set point - Desired level at which system operates, changes to this are detected by receptors
  2. Receptor - Detects any changes from set point and informs controller
  3. Controller - Coordinates information and sends info to effectors
  4. Effector - Brings about changes needed to return system to it’s set point
  5. Feedback loop - Informs receptor of changes to system from the effector
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6
Q

What is thermoregulation?

A

The process of regulating an organism’s body temperature

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7
Q

What are some of the methods that an organism can use to gain heat?

A
  • Production of heat via metabolism of food during respiration
  • Gaining heat from environment by conduction, convection and radiation
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8
Q

What are some of the methods that an organism can use to lose heat?

A
  • Evaporation of water e.g. sweating

- Loss of heat to the environment by conduction, convection or radiation

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9
Q

What is meant by conduction?

A

Occurs mainly in solids and is the transfer of energy through particles. Heat causes the particles to vibrate and gain kinetic energy.

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10
Q

What is meant by convection?

A

Occurs in gases and liquids and is the transfer of heat as a result of the movement of the warmed matter itself. Heat rises and cool air falls

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11
Q

What is meant by radiation?

A

Energy transferred by electromagnetic waves, when these waves hit an object they normally heat it up

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12
Q

What are endotherms?

A

Animals that derive most of their heat from metabolic activities inside their bodies (“inside heat”)

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13
Q

What are ectotherms?

A

Animals that uses the environment to regulate it’s body temperature/gain heat (“outside heat”)

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14
Q

How is body temperature regulated in ectotherms?

A
  • Exposure to sun
  • Taking shelter
  • Gaining warmth from ground
  • Generating metabolic heat
  • Colour variations i.e. darker colours absorb more heat whereas lighter colours reflect it
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15
Q

What range is the core body temperature for endotherms?

A

35-40 degrees

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16
Q

What are the methods of gaining heat in endotherms?

A
  • Vasoconstriction: narrowing of the blood vessels and constriction of arteries, shunt vessels dilate
  • Shivering
  • Raising of body hair
  • Increased metabolic rate
  • Decreased sweating
  • Behavioural mechanisms e.g. sheltering from wind
  • Hormonal changes e.g. long term exposure to low temps causes the release of thyroxine by thyroid gland causing a sustained increased in metabolism
  • Small surface area: volume
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17
Q

What are the methods of losing heat in endotherms?

A
  • Vasodilation: dilation of blood vessels, arteries dilate and shunt vessels constrict so heat is lost via radiation
  • Sweating
  • Lowering of body hair
  • Behavioural mechanisms e.g. seeking shade
  • Panting
  • Decreased movement
  • Increased surface area: volume
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18
Q

What is hypothermia?

A

When core body temperature falls below 35.5 degrees for a sustained period of time

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19
Q

What is hyperthermia?

A

Sustained increase in body temperature above normal range (35-44 degrees)

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20
Q

What is the hypothalamus?

A

Small part of brain that acts as a coordinator during changes in body temperature

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21
Q

What two centres does the hypothalamus consist of?

A

Heat loss and heat gain centre

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22
Q

What is the pathway of producing a response to a change in body temperature?

A

Stimulus - Change in body temperature
Receptors - Thermo receptors
Coordinator - Hypothalamus
Effector - Skin

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23
Q

Which part of the nervous system do the thermo receptors send their signals to the brain?

A

Via the autonomic nervous system

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24
Q

What activates the heat gain centre in the hypothalamus?

A

A fall in blood temperature

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25
Q

What activates the heat loss centre in the hypothalamus?

A

A increase in blood temperature

26
Q

What is the normal concentration of glucose in the blood?

A

90 mg per 100 cm 3

27
Q

What things cause changes to blood glucose concentration?

A

Eating, causes it to rise after eating foods that contain carbohydrates and exercise, causes it to fall as more glucose is used up for respiration

28
Q

What are hormones?

A

Chemicals secreted by glands that are carried in the blood plasma and act on target cells. They are effective in small quantities and have a wide spread and long lasting effect.

29
Q

What are the steps of the second messenger model in hormone function?

A
  1. The hormone is the first messenger
  2. Binds to receptor on target cell
  3. Forms hormone-receptor complex
  4. This complex activates enzyme inside target cell
  5. Enzyme produces either a chemical or another hormone that acts as the second messenger
  6. Second messenger causes a series of chemical changes that lead to the required response
30
Q

Which two hormones are involved in the second messenger model in the regulation of blood glucose?

A

Adrenaline and glucagon

31
Q

What does the pancreas produce/secrete?

A
  • Digestive enzyme: protease, amylase and lipase

- Blood glucose regulation hormones: insulin and glucagon

32
Q

What is the role of the pancreas in regulating blood glucose?

A

Produces insulin and glucagon. Also contains islets of Langerhans which produce a cells and b cells

33
Q

What are islets of Langerhans?

A

Hormone-producing cells found in the pancreas that produce a cells and b cells

34
Q

What are the a cells responsible for?

A

Producing the hormone glucagon

35
Q

What are the b cells responsible for?

A

Producing the hormone insulin

36
Q

Why must glucose levels in mammals remain fairly constant?

A

Required for respiration to release energy for cells

37
Q

What happens if glucose levels are too high?

A
  • Water potential of blood is lowered, which may lead to dehydration and causes osmotic problems for cells
  • Muscles break down
  • Weight loss
  • Tiredness
  • Hyperglycaemia
38
Q

What happens if glucose levels are too low?

A
  • Cells deprived of energy and die, brain cells are particularly vulnerable to this
  • Sweating
  • Hunger
  • Irritability
  • Double vision
  • Hypoglycaemia
39
Q

Where does glucose come from?

A
  1. Diet - Carbohydrate breakdown
  2. Breakdown of glycogen (glycogenolysis) - stored in liver and muscle cells, formed by converting excess glucose from the diet during glycogenolysis
  3. Gluconeogenesis - Production of new glucose which is not from diet, liver makes glucose from glycerol and amino acids

2 and 3 are methods of homeostasis!

40
Q

What can cause glucose levels to fluctuate?

A
  • Diet varies
  • Animals do not eat constantly , i.e. during sleep
  • Used at different rates depending on activity/stress
41
Q

What hormones must work together in order to counteract glucose fluctuations?

A

Glucagon, insulin and adrenaline

42
Q

What are b cells and insulin responsible for in the regulation of blood glucose?

A

B cells detect a rise in blood glucose and secrete insulin into the blood plasma, which then insulin binds to glycoprotein receptors on the CSM of body cells

43
Q

What happens when insulin binds to glycoprotein receptors on the CSM of body cells?

A
  • The tertiary structure of glucose transport protein channels changes, causing them to open and allowing more glucose into the cell
  • There is an increase in carrier molecules in CSM
  • Activation of enzymes that convert glucose into glycogen and fat
44
Q

How do the changes created by the work of b cells and insulin cause blood glucose to decrease?

A
  • Increased rate of absorption of glucose into cells
  • Increased respiratory rate
  • Increased conversion of glucose to glycogen
  • Increased conversion of glucose to fat
45
Q

What does the lowering of blood glucose cause b cells to do?

A

Reduce their secretion of insulin = negative feedback

46
Q

What are a cells and glucagon responsible for in the regulation of blood glucose?

A

A cells detect a fall in blood glucose and secrete glucagon, which initiates the break down of glycogen to glucose. Glucagon also binds to the glucagon receptors on liver cells

47
Q

What happen when glucagon binds to the glucagon receptors on liver cells?

A
  • Glycogenolysis: activates an enzyme that converts glycogen to glucose
  • Gluconeogenesis: converting amino acids and glycerol into glucose
48
Q

What does the increase of blood glucose cause a cells to do?

A

Reduce their secretion of glucagon = negative feedback

49
Q

What is the role of adrenaline in regulation blood glucose and how does it work?

A

It acts as the first messenger in SMM and increases blood glucose by:

  • Activating an enzyme that causes breakdown of glycogen to glucose in the liver
  • Inactivating an enzyme that synthesises glycogen from glucose
50
Q

What happens when glucose levels fall below a set point(norm)?

A

Reduced insulin secretion and increase in blood glucose

= negative feedback

51
Q

What happens when glucose levels rise above a set point(norm)?

A

Reduced glucagon secretion and decrease in blood glucose = negative feedback

52
Q

What happens to get glucose back into the system?

A
  • conversion of glycogen to glucose
  • conversion of amino acids to glucose
  • Glucose entering from diet
53
Q

What happens to get glucose out of the system?

A
  • Increased cellular respiration
  • Conversion of glucose into glycogen
  • Conversion of glucose into fat
  • Absorption of glucose into cells
54
Q

What is diabetes?

A

A metabolic disorder in which the body is unable to regulate the level of blood glucose. Two types: Type I and Type II. It is a chronic disease

55
Q

What are the symptoms of diabetes?

A
  • Increased blood glucose levels
  • Glucose in urine
  • Increased thirst and hunger (especially in children)
  • Feeling very tired
  • Urinating frequently
  • Weight loss and loss of muscle bulk
  • Slow healing of cuts and grazes
56
Q

What is Type I diabetes?

A

Insulin dependent - Body unable to produce sufficient insulin. Normally begins in childhood and may be the result of an autoimmune response where immune system attacks b cells of the islets of Langerhans. It develops quickly

57
Q

What is Type II diabetes?

A

Insulin independent - Glycoprotein receptors on body cells lose their responsiveness to insulin, or causes by a reduced supply of insulin from pancreas. Usually develops in adults over the age of 40 and is slow developing. Obesity and poor diet can lead to teenage incidences.

58
Q

How is Type I diabetes controlled?

A
  • Injecting insulin 2-4 times a day
  • Matching insulin dose to blood glucose concentration exactly
  • Monitoring carbohydrate intake and exercise
  • Injecting insulin into muscle/fat in thighs so there is a slower release into blood stream?
59
Q

Why can’t insulin be taken orally?

A

Insulin is a protein and so would be digested by protease

60
Q

What happens if too little insulin is injected?

A

Blood glucose levels remain high (hyperglycaemic)

61
Q

What happens if too much insulin is injected?

A

Blood glucose levels fall too low (hypoglycaemic)

62
Q

How is Type II diabetes controlled?

A
  • Regulating carbohydrate intake and exercise
  • Occasionally injecting insulin or other drugs that stimulate insulin
  • Give drugs that slow down glucose absorption from the intestine

A2 Biology (12 decks)

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