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14.1.714-15 · Homeostasis and Control

The Control of Blood Glucose — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 9 parts Lesson 8 of 31 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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14.1.7 The Control of Blood Glucose — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Explain how insulin and glucagon control blood glucose by negative feedback.Too low — cells may lack glucose for respiration and fail to function.Too high — disrupts normal cell func…

  • Amplification
  • Only liver cells
  • GLUT proteins
  • Glucokinase
  • Glycogen synthase
  • Reabsorption

Part 1 of 7Why blood glucose is controlled

Too low
  • Too low cells may lack glucose for respiration and fail to function.
Too high
  • Too high disrupts normal cell function.
Hormones
  • Hormones insulin and glucagon from the islets of Langerhans in the pancreas.
Cells
  • α cells secrete glucagon and β cells secrete insulin; both act as receptors.

Part 2 of 7Response to a fall in blood glucose

Detection
  • α and β cells in the pancreas detect the decrease.
α cells
  • α cells secrete glucagon.
β cells
  • β cells stop secreting insulin, reducing glucose use by liver and muscle cells.

Part 3 of 7Glucagon and the second messenger cascade

1
Glucagon binds receptors on the surface membrane of liver cells.
2
The receptor changes shape, activating a G protein.
3
The G protein activates adenylyl cyclase.
4
Adenylyl cyclase converts ATP to cyclic AMP (cAMP), the second messenger.
5
cAMP activates protein kinase A.
6
Protein kinase A activates phosphorylase kinase by adding phosphate groups.
7
Glycogen phosphorylase breaks down glycogen to glucose (glycogenolysis).
Amplification
  • Amplification the cascade amplifies the signal.
Only liver cells
  • Only liver cells muscle cells have no glucagon receptors.

Part 4 of 7Response to a rise in blood glucose

1
Glucose enters β cells by facilitated diffusion.
2
The β cells respire glucose, making ATP.
3
High ATP closes potassium channels, changing the membrane potential.
4
Voltage-gated calcium channels open.
5
Calcium ions enter and the β cells secrete insulin by exocytosis.

Part 5 of 7Action of insulin

Targets
  • Targets muscle cells, fat cells, adipose tissue and liver cells, which have insulin receptors.
GLUT proteins
  • GLUT proteins insulin causes vesicles containing GLUT proteins to fuse with the surface membrane.
Uptake
  • Uptake facilitated diffusion of glucose into cells increases.
Glucokinase
  • Glucokinase phosphorylates glucose, trapping it in cells.
Glycogen synthase
  • Glycogen synthase converts glucose to glycogen (glycogenesis).

Part 6 of 7Negative feedback control

Receptors
  • α and β cells in the pancreas.
Effectors
  • Effectors liver cells for glucagon; liver, muscle and fat cells for insulin.
Principle
  • Principle each hormone's effect brings the glucose level back to normal.

Part 7 of 7More from the specification

1Ultrafiltration in Bowman's capsule
  • High hydrostatic pressure in glomerulus capillaries forces water, glucose, urea,
  • and mineral ions across the basement membrane into Bowman's capsule to form glomerular filtrate.
2Selective reabsorption in the proximal convoluted tubule
  • All filtered glucose and amino acids are actively reabsorbed back into peritubular capillaries from the nephron filtrate via sodium-dependent co-transport.
3Osmoregulation and collecting duct permeability
  • Antidiuretic hormone (ADH) increases aquaporin insertion in collecting duct membranes, facilitating water reabsorption down an osmotic gradient to concentrate urine.
4Ultrafiltration in Bowman's capsule
  • High hydrostatic pressure in glomerulus capillaries forces water, glucose, urea,
  • and mineral ions across the basement membrane into Bowman's capsule to form glomerular filtrate.
5Selective reabsorption in the proximal convoluted tubule
  • All filtered glucose and amino acids are actively reabsorbed back into peritubular capillaries from the nephron filtrate via sodium-dependent co-transport.
6Osmoregulation and collecting duct permeability
  • Antidiuretic hormone (ADH) increases aquaporin insertion in collecting duct membranes, facilitating water reabsorption down an osmotic gradient to concentrate urine.
7Luminal membrane
  • Cell surface membrane facing the lumen.
8Glucose oxidase
  • Enzyme oxidising glucose to gluconic acid and hydrogen peroxide.
9Basement membrane
  • Collagen and glycoprotein filter layer.
10Plasma
  • The liquid part of blood.
11Glomerulus
  • A knot of capillaries inside the Bowman's capsule.
12Gradient
  • A difference in concentration.
13Water potential
  • A measure of the tendency of water to move; pure water has the highest.
14Epithelial cell
  • A cell forming a covering or lining layer of tissue.
15Amino acid
  • The unit from which proteins are made; the sequence decides the protein's shape and function.
16Selective reabsorption
  • Return of useful substances from the filtrate to the blood.
17Glomerular filtrate
  • Fluid that enters Bowman's capsule.
18Filtrate
  • The liquid collected in the Bowman's capsule.
19Capsule
  • Protective outer layer on some bacteria.
20Capillary
  • Vessel one cell thick where exchange takes place.
21Reabsorption
  • Return of useful substances from the filtrate to the blood.
22Nephron
  • Kidney tubule that filters blood and forms urine.
23Homeostasis
  • The maintenance of a constant internal environment.
24Kidney
  • An organ that filters the blood and produces urine.

Key terms

TermMeaning
InsulinHormone lowering blood glucose.
GlucagonHormone raising blood glucose.
GlycogenolysisBreakdown of glycogen to glucose.
GlycogenesisConversion of glucose to glycogen.
Second messengerMolecule such as cAMP that spreads a signal inside a cell.
GLUT proteinGlucose transporter inserted into the membrane by insulin.
Islets of LangerhansPancreatic endocrine tissue.

Avoid these mistakes

1
Saying muscle cells respond to glucagon — only liver cells do.
2
Mixing up the cells — α cells make glucagon and β cells make insulin.
3
Saying insulin makes glucose leave cells — it increases uptake and storage.
4
Forgetting the second messenger — cAMP is produced inside the liver cell.

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