14.4.2
Controlling Blood Glucose
Insulin
Insulin
When blood glucose concentration increases above the optimum concentration (90mg 100cm−3), insulin returns the level to normal through negative feedback. The steps involved are:


1) Detection by beta cells
1) Detection by beta cells
- High blood glucose concentration is detected by the beta (β) cells in the pancreas.
- Beta cells are located in the islets of Langerhans.
- When glucose diffuses from a high concentration outside the cell to a lower concentration inside the beta cell, the glucose is metabolised, producing ATP.
- When ATP concentration increases, potassium ion channels close. This lowers the negativity inside the cell, changing the potential over the membrane.
- The potential change triggers the opening of voltage-gated calcium ion channels.
- Calcium in the beta cell triggers the vesicles containing insulin to move to the cell surface membrane to be secreted by exocytosis.


2) Secretion of insulin
2) Secretion of insulin
- Beta cells respond to high blood glucose concentration by secreting a hormone called insulin into the blood.
- Insulin travels in the blood to the liver and muscle cells.


3) Binding to muscle cells
3) Binding to muscle cells
- Insulin binds to receptors on the muscle cell membranes.
- The muscle cells insert more glucose channel proteins in the cell membrane. This causes:
- The rate of uptake of glucose by muscle cells to increase.
- The rate of respiration in the muscle cells to increase.


4) Glycogenesis
4) Glycogenesis
- Insulin binds to receptors on the liver cell membranes.
- The liver cells produce enzymes that convert glucose to glycogen.
- Glycogen is stored in the liver cells' cytoplasm.
- This process is called glycogenesis.


Importance of insulin
Importance of insulin
- The role of insulin in lowering blood glucose concentration is important for maintaining an optimum blood water potential.
- If blood glucose levels were not reduced by insulin, the blood water potential would decrease.
- Water in the cells in the body would diffuse out, causing the cells to shrink and die.
Glucagon
Glucagon
When blood glucose concentration decreases below the optimum concentration (90mg 100cm−3), glucagon, like insulin, returns the level to normal through negative feedback. The steps involved are:


1) Detection by alpha cells
1) Detection by alpha cells
- Low blood glucose concentration is detected by the alpha (α) cells in the pancreas.
- Alpha cells are located in the islets of Langerhans.


2) Secretion of glucagon
2) Secretion of glucagon
- Alpha cells respond to low blood glucose concentration by secreting a hormone called glucagon into the blood.
- Glucagon travels in the blood to the liver cells.


3) Glycogenolysis
3) Glycogenolysis
- Glucagon binds to receptors on the liver cell membranes.
- The liver cells produce enzymes that convert glycogen to glucose.
- This process is called glycogenolysis.


4) Gluconeogenesis
4) Gluconeogenesis
- Binding of glucagon to liver cell membranes also causes the release of enzymes that form glucose from glycerol and amino acids.
- This process is called gluconeogenesis.


5) Rate of respiration
5) Rate of respiration
- Glucagon also slows the respiration rate in cells.
- Slowing respiration slows the rate at which glucose is used up.


Importance of glucagon
Importance of glucagon
- The role of glucagon in increasing blood glucose concentration is important for survival.
- If blood glucose levels were not increased by glucagon, there would not be enough glucose available for respiration.
- If there is not enough glucose for respiration, there will be no energy available for survival.
Adrenaline
Adrenaline
Adrenaline is a hormone that is secreted in response to low blood glucose concentration. It is also released during exercise and in times of stress. The steps of the adrenaline response are:


1) Secretion of adrenaline
1) Secretion of adrenaline
- Adrenaline is secreted from the adrenal gland in response to low blood glucose concentration, exercise and stress.


2) Binding to liver cells
2) Binding to liver cells
- Adrenaline binds to receptors on the liver cell membrane.
- Adrenaline induces two reactions in the liver cells:
- Activation of glycogenolysis (glycogen → glucose).
- Inhibition of glycogenesis (glucose → glycogen).
- Adrenaline also promotes secretion of glucagon from the pancreas and inhibits secretion of insulin.
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
Jump to other topics
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
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