6C - Control of blood glucose concentration Flashcards
1
Q
What is the regulation of blood glucose an example of?
A
The interactions between different hormones in achieving homeostasis.
2
Q
What are the 2 types of glands?
A
Exocrine and endocrine.
3
Q
What do exocrine glands do?
A
Secrete chemicals outside the body.
4
Q
What do endocrine glands do?
A
Communicate using hormones, carried in circulatory system, stimulate target cells with specific receptors.
5
Q
What type of response do endocrine glands produce?
A
A slow, long-lasting and widespread response.
6
Q
What is the endocrine system made of?
A
- Pituitary gland
- Thyroid and parathyroid gland
- Adrenal glands
- Pancreas
- Ovaries/uterus
- Prostate/testes
7
Q
What do the thyroid and parathyroid glands release?
A
Thyroxine
8
Q
What do the adrenal glands release?
A
Adrenaline
9
Q
What do the ovaries/uterus release?
A
Oestrogen/progesterone
10
Q
What do the prostate/testes release?
A
Testosterone
11
Q
What 3 main effects do hormones have in their target cells?
A
- Affect the permeability of the cell membrane.
- Cause the release of a ‘second messenger’ inside the cell.
- Diffuse into the cell and promote or inhibit transcription.
12
Q
Why do we need to control blood glucose?
A
- Hypoglycemia and hyperglycemia can kill cells due to the effect on water potential of the blood and tissue fluid.
- Required for cellular respiration.
- Required for the manufacture of many other cellular products.
13
Q
What can change the concentration of glucose in your blood?
A
Exercise and eating.
14
Q
What is the normal concentration of glucose in the blood?
A
Around 90 mg per 100cm^3 of blood.
5 mmol dm^-3
15
Q
What is blood glucose concentration monitored by?
A
Cells in the pancreas.
16
Q
When does blood concentration glucose rise?
A
After eating food containing carbohydrate.
17
Q
When does blood glucose concentration fall?
A
After exercise, as more glucose is used in respiration to release energy.
18
Q
What 2 hormones control blood glucose concentration?
A
Insulin and glucagon.
19
Q
What are insulin and glucagon secreted by?
A
Clusters of cells in the pancreas called islets of Langerhans.
20
Q
What makes up the islets of Langerhans?
A
Alpha and beta cells.
21
Q
What are the islets of Langerhans?
A
Group of hormone producing cells, scattered throughout the cells that make digestive enzymes.
22
Q
What do alpha cells do?
A
Detect low glucose concentration and secrete glucagon.
23
Q
What do alpha cells detect?
A
Low glucose concentration
24
Q
What do alpha cells secrete?
A
Glucagon
25
What is the size of alpha cells like compared to beta cells?
Larger
26
What do beta cells do?
Detect high glucose concentration and secrete insulin.
27
What do beta cells detect?
High glucose concentration
28
What do beta cells secrete?
Insulin
29
What is the size of beta cells like compared to alpha cells?
Smaller
30
Which is bigger, alpha or beta cells?
Alpha cells are larger.
31
What type of cell secretes glucagon?
Alpha cells
32
What type of cell secretes insulin?
Beta cells
33
What type of cell detects low glucose concentration?
Alpha cells
34
What type of cell detects high glucose concentration?
Beta cells
35
If low glucose concentration is detected, what hormone is secreted?
Glucagon
36
If high glucose concentration is detected, what hormone is secreted?
Insulin
37
From what 3 sources does blood glucose come from?
- Directly from the diet.
- Glycogen converted into glucose in the liver (glycogenolysis).
- From gluconeogenesis.
38
What do changes in supply and demand of glucose allow insulin, glucagon and adrenaline to do?
Operate to maintain a constant blood glucose concentration.
39
What do insulin and glucagon act on?
Effectors, which respond to restore the blood glucose concentration to the normal level.
40
What is glycogenesis?
Synthesis of glycogen from glucose.
41
What is glycogenolysis?
Breakdown of glycogen into glucose.
42
What is gluconeogenesis?
Synthesis of glucose from lipids, amino acids or nucleic acids.
43
What is the synthesis of glycogen from glucose called?
Glycogenesis
44
What is the breakdown of glycogen into glucose called?
Glycogenolysis
45
What is the synthesis of glucose from lipids, amino acids or nucleic acids called?
Gluconeogenesis
46
What is glycogenesis activated by?
Insulin
47
What is glycogenolysis activated by?
Glucagon
48
What is gluconeogenesis activated by?
Glucagon
49
What is another name for liver cells?
Hepatocytes.
50
What does insulin do?
Lowers blood glucose concentration when it's too high.
51
What does glucagon do?
Raises blood glucose concentration when it's too low.
52
Explain how blood glucose concentration is regulated when it is too high
1) Beta cells in the islets of Langerhans detect it is too high and secrete insulin into the bloodstream.
2) Insulin binds to specific receptors on the cell surface membranes of liver and muscle cells.
3) It increases the permeability of muscle-cell membranes to glucose, so the cells take up more glucose. This involves increasing the number of channel proteins in the cell membrane.
4) Insulin also activates enzymes in the liver and muscle cells that convert glucose into glycogen (glycogenesis).
5) The cells are able to store glycogen in their cytoplasm, as an energy source.
6) Insulin also increases the rate of respiration of glucose, especially in muscle cells.
7) Excess glucose may also undergo conversion to fat.
53
Where does insulin bind to lower blood glucose concentration?
Cell membrane of liver and muscle cells.
54
What does insulin do once it has bound to the cell membrane of muscle cells?
It increases the permeability of muscle-cell membranes to glucose, so the cells take up more glucose. This involves increasing the number of channel proteins in the cell membrane.
Insulin also activates enzymes in the liver and muscle cells that convert glucose into glycogen (glycogenesis).
55
What does insulin do once it has bound to the cell membrane of liver cells?
Insulin activates enzymes in the liver and muscle cells that convert glucose into glycogen (glycogenesis).
56
What does insulin do to the rate of respiration of glucose?
Increases the rate of respiration of glucose, especially in muscle cells.
57
What might happen to excess glucose when insulin tries to reduce blood glucose concentration?
It may undergo conversion to fat.
58
Explain how blood glucose concentration is regulated when it is too low
1) Alpha cells in the islets of Langerhans detect it's low and secrete glucagon into the bloodstream.
2) Glucagon binds to specific receptors on the cell membranes of liver cells.
3) Glucagon activates enzymes in the liver cells that break down glycogen into glucose (glycogenolysis).
4) Glucagon also activates enzymes that are involved in the formation of glucose from glycerol and amino acids (gluconeogenesis).
5) Glucagon decreases the rate of respiration of glucose in cells.
59
Where does glucagon bind to raise blood glucose concentration?
Cell membranes of liver cells.
60
What does glucagon do once it has bound to the cell membrane of liver cells?
- Activates enzymes in the liver cells that break down glycogen into glucose (glycogenolysis).
- Activates enzymes that are involved in the formation of glucose from glycerol and amino acids (gluconeogenesis).
61
What does glucagon do to the rate of respiration of glucose?
Decreases the rate of respiration of glucose in cells.
62
What feedback mechanism keeps blood glucose concentration normal?
Negative feedback mechanism.
63
What is the response of hormone like compared to the response produced by nervous impulses and why?
Because hormones travel in the blood to their target cells, the response produced are slower but longer lasting (as hormones aren't broken down as quickly as neurotransmitters).
64
Explain how the negative feedback mechanism is involved when blood glucose becomes too high?
- Pancreas detects blood glucose concentration is too high.
- Beta cells secrete insulin and alpha cells stop secreting glucagon.
- Insulin binds to receptors on liver and muscle cells.
- Cells take up more glucose, glycogenesis is activated and cells respire more glucose.
- Less glucose in the blood.
65
Explain how the negative feedback mechanism is involved when blood glucose becomes too low?
- Pancreas detects blood glucose concentration is too low.
- Alpha cells secrete glucagon and beta cells stop secreting insulin.
- Glucagon binds to receptors on liver cells.
- Glycogenolysis is activated, gluconeogenesis is activated and cells respire less glucose.
- Cells release glucose into the blood.
66
What is GLUT4?
A glucose transporter.
67
What does insulin do to glucose transporters?
Makes them available for facilitated diffusion.
68
What do skeletal and cardiac muscle cells contain which help facilitated diffusion?
A channel protein called GLUT4 which is a glucose transporter.
69
What happens to GLUT4 when insulin levels are low?
GLUT4 is stored in vesicles in the cytoplasm of cells.
70
What happens to GLUT4 when insulin binds to receptors on the cell-surface membrane?
It triggers the movement of GLUT4 to the membrane.
71
What can happen to glucose by the GLUT4 protein?
Glucose can be transported into the cell through the GLUT4 protein, by facilitated diffusion.
72
What hormone is adrenaline like?
Glucagon
73
What does adrenaline do to blood glucose concentration?
Increases it.
74
Where are the adrenal glands found?
Just above your kidneys.
75
When is adrenaline secreted?
When there's a low concentration of glucose in your blood, when you're stressed and when you're exercising.
76
Explain the interaction between insulin and glucagon in the regulation of blood glucose
- Act in opposite directions (antagonistically).
- System is self-regulating through feedback, concentration of glucose in blood that determines the quantity of hormone produced.
- The concentration of blood glucose isn't constant, process of negative feedback work, only when concentrations fall or increase beyond the set point.
77
How does adrenaline regulate blood glucose concentration?
- Increases blood glucose concentration.
- Adrenaline binds to receptors in the cell membrane of liver cells.
- This activates glycogenolysis and inhibits glycogenesis.
- Also activates glucagon secretion and inhibits insulin secretion, which increases glucose concentration.
- Adrenaline gets the body ready for action by making more glucose available for muscles to respire.
78
What does adrenaline activate when regulating blood glucose concentration?
Glycogenolysis and glucagon secretion .
79
What does adrenaline inhibit when regulating blood glucose concentration?
Glycogenesis and insulin secretion.
80
Explain the second messenger model
1) Adrenaline and glucagon bind to their receptors and activate an enzyme called adenylate (adenylyl) cyclase.
2) This binding causes the protein inside the cell to change shape.
3) This activates the enzyme adenylyl cyclase to convert ATP into cyclic AMP, a second messenger.
4) cAMP binds to protein kinase A, activating it by changing its shape.
5) Protein kinase A activates a cascade (a chain of reactions) that breaks down glycogen into glucose (glycogenolysis), which then moves out of the liver cell and into the blood by facilitated diffusion using channel proteins.
81
What can both adrenaline and glucagon activate?
Glycogenolysis inside a cell even though they bind to receptors on the outside of the cell.
82
What do the receptors for adrenaline and glucagon have?
Specific tertiary structures that make them complementary in shape to their respective hormones.
83
What enzyme do adrenaline and glucagon activate when they bind to their receptors?
Adenylate cyclase (adenylyl cyclase).
84
What is adenylate cyclase (adenylyl cyclase)?
An enzyme.
85
What does activated adenylate cyclase (adenylyl cyclase) do?
Converts ATP into a chemical signal called a 'second messenger' - cyclic AMP (cAMP).
86
What is ATP converted into in the second messenger model?
A chemical signal called a 'second messenger' - cyclic AMP (cAMP).
87
What is the second messenger in the second messenger model?
Cyclic AMP (cAMP).
88
What does cyclic AMP (cAMP) do?
Activates protein kinase A.
89
What is protein kinase A?
An enzyme.
90
What is protein kinase A activated by?
Cyclic AMP (cAMP).
91
What does protein kinase A do?
Activates a cascade (a chain of reactions) that breaks down glycogen into glucose (glycogenolysis), which then moves out of the liver cell and into the blood by facilitated diffusion using channel proteins.
92
What is the first messenger in the second messenger model?
Adrenaline.
93
When does diabetes occur?
When blood glucose concentration is not controlled properly.
94
What is diabetes full name?
Diabetes mellitus.
95
What is diabetes?
A condition where blood glucose concentration can't be controlled properly.
The person is unable to metabolise carbohydrates properly, especially glucose.
96
What is hyperglycemia?
Too high blood glucose.
97
What is hypoglycemia?
Too low blood glucose.
98
Where is the pancreas?
Upper abdomen, behind the stomach.
99
What does the pancreas do?
- Produces enzymes (protease, amylase, lipase) for digestion.
- Produces hormone (insulin, glucagon) for regulating blood glucose concentration.
100
Where is the liver?
Immediately below the diaphragm.
101
What cells make up the liver?
Hepatocytes.
102
What does the liver do?
Filters blood from the digestive tract. detoxifies chemicals and regulates blood glucose concentration through the use of hormones.
103
What 3 important processes take place in the liver?
Glycogenesis, glycogenolysis, gluconeogenesis.
104
Which type of diabetes is the most common?
Type II.
105
What are the 2 types of diabetes?
Type I and type II.
106
What is type I diabetes described as?
Insulin dependent.
107
What happens in type I diabetes?
The immune system attacks the beta cells in the islets of Langerhans so they can't produce any insulin.
(Autoimmune response.)
108
What might type I diabetes be caused by?
Not known exactly - might be a genetic predisposition or triggered by a viral infection.
109
When does type I diabetes usually begin?
In childhood.
110
What is the onset of symptoms like in type I diabetes?
Rapid onset.
111
What are the signs of type I diabetes?
Frequent urination, glucose in the urine, genital itching, weight loss, tiredness.
112
What happens after eating in type I diabetes?
The blood glucose level rises and stays high - hyperglycemia. This can result in death if left untreated.
113
What can hyperglycemia result in if left untreated?
Death
114
Where does the glucose go in type I diabetes and why?
The kidneys can't reabsorb all of the glucose so some of it is excreted in the urine.
115
Roughly how many people have diabetes?
>415 million people.
116
What percentage of cases of diabetes does type Ii diabetes make up?
90%.
117
How is type I diabetes treated?
Insulin therapy - regular insulin injections 2-4 times a day or the use of an insulin pump to deliver insulin continuously.
118
Why does insulin therapy have to be carefully controlled?
Because too much insulin can produce a dangerous drop in blood glucose levels - hypoglycemia.
119
What 2 ways can insulin therapy be delivered?
Regular insulin injections or the use of an insulin pump.
120
What can't insulin be taken by mouth?
Because it would be digested.
121
What must the dose of insulin given in insulin therapy match?
The glucose intake.
122
What can blood glucose be monitored by?
Biosensors.
123
What has shown promise in potentially leading to a cure for type I diabetes?
Recent trials in transplanting insulin-producing cells have shown promise.
124
What helps to avoid a sudden rise in glucose?
Eating regularly and controlling simple carbohydrate intake (intake of sugars).
125
When does type II diabetes usually begin?
Later in life (over age 40).
126
What is type II diabetes often linked with?
Obesity.
127
When in type II diabetes more likely?
In people with a family history of the condition.
128
Besides obesity, what are risk factors for type II diabetes?
Lack of exercise, age and poor diet.
129
When does type II diabetes occur?
When the beta cells in the islets of Langerhans don't produce enough insulin or when the body's cells don't respond properly to insulin.
130
Why don't the beta cells respond properly to insulin in type 2 diabetes?
Because the insulin (glycoprotein) receptors on their membranes don't work properly (they are lost or lose responsiveness and so don't take up enough glucose.
This means the blood glucose concentration is higher than normal.
131
What is the onset of symptoms like in type II diabetes?
Develops slowly with symptoms not severe.
132
How can type 2 diabetes be treated?
By eating a healthy, balanced diet, losing weight (if necessary) and regular exercise - regulating intake of carbohydrates in the diet.
Glucose-lowering medication (drugs that stimulate insulin production) can be taken if diet and exercise can't control it.
Eventually, insulin injections may be needed.
133
Can type I diabetes be cured?
No
134
Can type II diabetes be cured?
Yes
135
What has the increasingly common problem of type II diabetes been linked to in the UK?
Increasing levels of obesity, a move towards more unhealthy diets and low levels of physical activity.
136
What can type II diabetes cause?
Additional health problems, including visual impairment and kidney failure.
137
Is type I diabetes associated with high or low blood glucose?
High
138
Is type II diabetes associated with high or low blood glucose?
High
139
What are the signs of type II diabetes?
Similar to type I - frequent urination, glucose in the urine, genital itching, weight loss, tiredness.
140
What do health advisors recommend that people do to reduce the risk of developing type II diabetes?
- Eat a diet that's low in fat, sugar and salt, with plenty of whole grains, fruit and vegetables.
- Take regular exercise.
- Lose weight if necessary.
141
What aims to educate people in order to reduce their risk of developing conditions like type II diabetes and how?
Campaigns like the NHS's Change4Life - educates people on how to have a healthier diet and lifestyle.
142
What have health advisors challenged in order to combat type II diabetes and how?
Challenged the food industry to reduce the advertising of junk food (particularly to children), to improve the nutritional value of their products, and to use clearer labelling in products - allowing consumers to make healthier choices about what to buy.
143
What have some food companies done in response to criticism and how (in terms of lowering the risk of type II diabetes)?
Some food companies have attempted to make their products more healthy, e.g.
- Using sugar alternatives to sweeten food/drinks.
- Reducing the sugar, fat and salt content of products.
144
What practical technique is used to determine the concentration of a glucose solution?
Colorimetry
145
What is the normal concentration of glucose in the urine?
Very low - between 0 and 0.8mM.
146
What might a higher glucose concentration of 0-0.8 in the urine indicate?
Diabetes
147
How do you determine the concentration of glucose in a 'urine' sample using colorimetry?
1) Make up several glucose solutions of different known concentrations.
2) Do a quantitative Benedict's test (add quantitative Benedict's reagent to sample and heat in a water bath that's been brought to the boil) on each solution (plus a negative control of pure water). Use the same amount of Benedict's solution in each case.
3) Use a colorimeter (with a red filter) to measure the absorbance of the Benedict's solution remaining in each tube.
4) Use the results to make the calibration curve, showing absorbance against glucose concentration.
5) Then you can test the unknown solution, i.e. the 'urine' sample, in the same way as the known concentrations, and use the calibration curve to find the concentration of glucose in the sample.
148
What is quantitative Benedict's reagent/how is is different to normal Benedict's reagent?
When heated with glucose, the initial blue colour is lost, but a brick-red precipitate is not produced.
149
What does a colorimeter do when used to determine glucose concentration?
Measures the light absorbance of the solution after the quantitative Benedict's test has been carried out.
150
What would the result of the quantitative Benedict's test and colorimetry be the higher the glucose concentration?
The higher the concentration of glucose, the more blue colour will be lost (i.e. the paler the solution will become), decreasing the absorbance of the solution.
151
How would you make 5 serial dilutions with a dilution factor of 2 starting with an initial glucose concentration of 4mM?
1) Line up 5 test tubes in a rack.
2) Add 10cm^3 of the initial 4mM glucose solution to the first test tube and 5cm^3 of distilled water to the other 4 test tubes.
3) Then, using a pipette, draw 5cm^3 of the solution form the first test tube, add it to the distilled water in the second test tube and mix the solution thoroughly. You now have 10cm^3 of the solution that's half as concentrated as the solution in the first test tube (it's 2mM).
4) Repeat this process 3 more times to create solutions of 1mM, 0.5mM and 0.25mM.
152
How do you do a quantitative Benedict's test?
Ad quantitative Benedict's reagent to a sample and heat it in a water bath that's been brought to the boil.
153
What are the axis on the calibration curve for glucose concentration?
```
x = concentration of glucose
y = absorbance value
```
