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Biology > 16. Homeostasis > Flashcards

16. Homeostasis Flashcards

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1
Q

Define homeostasis

A

The maintenance of a constant internal environment

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2
Q

Name 4 things that must be controlled in an organism via homeostasis

A
  • temperature
  • pH
  • water potential of blood and fluids
  • blood glucose and concentration
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3
Q

Why must pH and temperature be controlled in an organism via homeostasis

A
  • enzymes and proteins (eg. protein channels) in the body are sensitive to changes in pH and temperature
  • that can cause them to denature
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4
Q

Why must water potential be controlled in an organism via homeostasis

A
  • changes to water potential of blood and tissue may cause cells to shrink or burst (via osmosis)
  • cells would not be able to function
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5
Q

What other factor must be maintained to ensure a constant water potential

A

Blood glucose concentration

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6
Q

What does the ability to maintain a constant internal environment mean

A
  • organisms have a wider geographical range
  • which increases the chance of finding food, shelter etc.
  • as they are more independent of changes in the external environment
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7
Q

Name the stages in a self-regulating system

A
  • optimum point
  • receptor
  • coordinator
  • effector
  • feedback mechanism
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8
Q

What is the optimum point in a self-regulating system

A
  • the point at which the system operates best

- it is monitored by a receptor

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9
Q

What is a receptor in a self-regulating system

A
  • detects any deviation from the optimum point

- informs the coordinator

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10
Q

What is a coordinator in a self-regulating system

A
  • coordinates information from receptors

- sends instructions to an appropriate effector

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11
Q

What is an effector in a self-regulating system

A
  • often a muscle or a gland

- brings about the changes needed to return the system to the optimum point

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12
Q

What is a feedback mechanism in a self-regulating system

A

-by which a receptor responds to a stimulus created by a change to the system brought about by the effector

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13
Q

What is negative feedback

A

A series of changes, important in homeostasis that, result in a substance being restored to its normal level

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14
Q

What is positive feedback

A

Process which results in a substance that departs from its normal level becoming further from its norm.

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15
Q

Give an example of negative feedback

A

Regulation of blood glucose

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16
Q

Give an example of positive feedback

A
  • in neurones where a stimulus leads to a small influx of sodium ions
  • this influx increases the permeability of the neurone membrane to sodium ions, more ions enter, causing further increase in permeability
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17
Q

Describe the one side of the feedback loop with glucagon (control of blood glucose)

A
  • if there is a fall in the conc. of glucose
  • this stimulus is detected by receptors on the cell-surface membrane of the alpha cells (coordinator) in the pancreas
  • these alpha cells secrete the hormone glucagon
  • glucagon causes liver cells (effectors) to convert glycogen into glucose
  • which is released into the blood, raising the glucose concentration
  • as this blood with a raised glucose concentration circulates back to the pancreas there is reduced stimulation of alpha cells
  • which therefore secrete less glucagon
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18
Q

The secretion of glucagon leads to…

A

A reduction in its own secretion

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19
Q

Describe one side of the feedback loop with insulin

A
  • if there is a rise in the conc. of glucose
  • this stimulus is detected by receptors on the cell-surface membrane of the beta cells (coordinator) in the pancreas
  • these beta cells secrete the hormone insulin
  • insulin increases the uptake of glucose by cells
  • its conversion to glycogen and fat
  • decreasing the glucose concentration
  • as this blood with a lowered glucose concentration circulates back to the pancreas there is reduced stimulation of beta cells
  • which therefore secrete less insulin
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20
Q

Where are hormones produced and secreted

A
  • produced in gland

- secreted directly into the blood

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21
Q

What are hormones effective at and what kind of effect do they have

A
  • low concentrations

- widespread and long lasting effect

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22
Q

What is the mechanism of hormone action

A

Second messenger model

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23
Q

Name two hormones use the second messenger model mechanism

A

Adrenaline and glucagon

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24
Q

Describe the steps in the second messenger model mechanism involving adrenaline

A
  • adrenaline binds to a transmembrane protein receptor with the cell-surface membrane of a liver cell
  • the binding of adrenaline causes the protein to change shape on the inside of the membrane
  • this change of protein shape leads to the activation of an enzyme called adenyl cyclase
  • the activated adenyl cyclase converts ATP to cAMP
  • the cAMP acts as a second messenger that binds to the protein kinase enzyme, changing its shape therefore activating it
  • the active protein kinase enzyme catalyses the conversion of glycogen to glucose
  • which moves out of the liver cell by facilitated diffusion and into the blood through protein channels
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25
Q

What does adrenaline bind to in the second messenger model mechanism involving adrenaline

A

-adrenaline binds to a transmembrane protein receptor within the cell-surface membrane of a liver cell

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26
Q

What effect does adrenaline binding to a transmembrane protein have, in the second messenger model mechanism involving adrenaline

A

-the binding of adrenaline causes the protein to change shape on the inside of the membrane

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27
Q

What does the change in the shape of the transmembrane protein lead to

A

-the activation of an enzyme called adenyl cyclase

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28
Q

Name two enzymes involved in the second messenger model mechanism

A
  • adenyl cyclase

- protein kinase

29
Q

What does adenyl cyclase do

A

-converts ATP to cAMP

30
Q

What does cAMP act as

A

-a second messenger

31
Q

What does cAMP bind to and what effect does it have

A

-binds to the protein kinase enzyme, changing its shape therefore activating it

32
Q

What does protein kinase do

A

-the active protein kinase enzyme catalyses the conversion of glycogen to glucose

33
Q

What happens to the glucose produced using the second messenger model involving protein

A

-it moves out of the liver cell by facilitated diffusion and into the blood through protein channels

34
Q

Where are the hormones insulin and glucagon produced

A

Pancreas

35
Q

What are the hormone producing cells called in the pancreas

A

Islets of Langerhans

36
Q

What are the two types of Islets of Langerhans

A
  • alpha cells

- beta cells

37
Q

What are alpha cells

A
  • a type of Islets of Langerhans
  • produces glucagon
  • slightly larger
38
Q

What are beta cells

A
  • a type of Islets of Langerhans
  • produces insulin
  • slightly smaller
39
Q

Where do the hormones insulin and glucagon take effect

A

The liver

40
Q

Define glycogenesis

A

The conversion of glucose into glycogen

41
Q

Define glycogenolysis

A

The breakdown of glycogen to glucose

42
Q

Define gluconeogenisis

A

The production of glucose from sources other than carbohydrate

43
Q

Define two substances that can act as a source of glucose other than a carbohydrate

A
  • glycerol

- amino acid

44
Q

Why must blood glucose concentration remain constant

A
  • if too low cells are deprived of energy and die

- if too high it lowers the water potential of the blood, causing cells to shrink

45
Q

Name and describe 3 factors that influence blood glucose concentration

A
  • diet, glucose is absorbed by the hydrolysis of carbohydrates e.g, starch, maltose, lactose and sucrose
  • glycolysis (from the hydrolysis of glycogen in the SI), stored in the liver and muscle cells
  • from gluconeogeneisis
  • glucogenisis
46
Q

Name 3 hormones that maintain a constant blood glucose

A
  • insulin
  • glucagon
  • adrenaline
47
Q

What do insulin molecules bind to

A

Specific glycoprotein receptors on cell-surface membranes

48
Q

Describe 4 ways blood glucose concentration is lowered when insulin binds with receptors

A
  • glucose transport carrier proteins allow more glucose through
  • number of glucose transport channels is increased
  • glycogenesis and fat production (from glucose)
  • increasing the respiratory rate of cells so more glucose is used up (increasing the uptake of glucose)
49
Q

Describe how glucose transport carrier proteins allow more glucose through when insulin binds with receptors, thereby decreasing glucose concentration

A
  • insulin binds with receptors on cell surface membranes
  • glucose transport carrier proteins tertiary structure changes
  • changes shape to be more open allowing more glucose to move into the cells via facilitated diffusion
50
Q

Describe how the number of glucose transport channels is increased by the binding of insulin to receptors on the cell surface membrane, thereby decreasing glucose concentration

A
  • at low concentrations of insulin the protein from which the glucose transport channels are made of is contained in vesicles
  • a rise in insulin concentration causes vesicles to fuse with the cell-surface membrane when insulin binds to the receptors
  • this increases the number of glucose transport channels
51
Q

Why is the secretion of insulin a negative feedback loop

A
  • the effect of B cells cause the decrease in glucose concentration
  • this causes the B cells to reduce their secretion of insulin
52
Q

Describe 3 ways blood glucose concentration is increased when glucagon binds with receptors

A
  • activating enzymes that convert glycogen into glucose (glycolysis)
  • activating enzymes involved in the conversion of amino acids and glycerol into glucose (gluconeogenesis)
53
Q

How does insulin cause glycogenesis and fat production (from glucose), thereby decreasing glucose concentration

A

by activating the enzymes that cause glycogenesis and fat production (from glucose)

54
Q

Why is the secretion of glucagon a negative feedback loop

A
  • the effect of A cells cause the increase in glucose concentration
  • this causes the A cells to reduce their secretion of glucagon
55
Q

How does adrenaline raise blood glucose concentration

A
  • attaching to protein receptors on cell-surface membrane of target cells
  • activating enzymes that causes the breakdown of glycogen to glucose in the liver
56
Q

How are the hormones insulin and glucagon said to work

A

Antagonistically

57
Q

What is diabetes

A

A metabolic disorder caused by the inability to control blood glucose concentration due to to a lack of the hormone insulin or a loss of responsiveness to insulin

58
Q

Type 1 diabetes is

A

Insulin dependent

59
Q

Type 2 diabetes is

A

Insulin independent

60
Q

What is type 1 diabetes caused by

A
  • due to the body being unable to produce insulin.
  • may be the result of an autoimmune response
  • where the body’s immune system attacks its own cells, in this case the B cells of islets of Langerhans.
61
Q

When does type 1 diabetes usually develop

A

In childhood

62
Q

What is type 2 diabetes caused by

A
  • glycoprotein receptors on body cells become lost or lose their responsiveness
  • may also be due to an inadequate supply of insulin.
63
Q

When does type 2 diabetes usually develop

A

People over the age of 40

64
Q

In what way does type 1 diabetes develop

A
  • quickly over a few weeks

- signs and symptoms are obvious

65
Q

In what way does type 2 diabetes develop

A
  • slowly

- symptoms are less severe and may go unnoticed

66
Q

How is type 1 diabetes controlled

A

By injections of insulin

67
Q

Why cannot insulin be taken by the mouth

A
  • insulin is a protein

- would be digested

68
Q

How is insulin dose decided and why

A
  • must be matched exactly to glucose intake
  • if too much insulin was taken she will experience a low blood glucose concentration that could result in unconsciousness
  • correct dose is insured by monitoring blood glucose concentration using biosensors
69
Q

How is type 2 diabetes controlled

A
  • regulating the intake of carbohydrate in the diet and exercise
  • sometimes supplementary injections or drugs that stimulate insulin production

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