Regulation of Blood Glucose

Question 1

Glucose

Answer 1

• Glucose is the principal fuel used by the body in cellular respiration. It is the result of carbohydrate digestion from the food we eat.
• As a result the concentration of glucose present in blood will be higher after a meal full of carbohydrates and low after fasting.
• Glucose concentration is controlled by the Liver and the secretions of the Pancreas and the Adrenal Glands
• Glucose can be stored in the liver and muscles as glycogen

Question 2

Role of the Liver 1

Answer 2

• Digestion of products, including glucose, reaches the liver via the hepatic portal vein after a meal
• So the liver has the first chance to absorb glucose from digested food

Question 3

Role of the Liver 2

Answer 3

The liver controls high glucose concentraition by:

1. Removing some glucose for energy for liver functions
2. Converting glucose into glycogen (Glycogenesis) for short-term storage in the liver or muscle cells (stimulated by insulin)
3. Continue circulating glucose in blood to be used by other cells for energy
4. Converts excess glucose into fat in adipose tissue for long-term storage

The liver controls low glucose concentrations by:

1. Converting glycogen into glucose (Glycogenolysis), stimulated by glucagon

Question 4

Glycogenesis

Answer 4

• Formation of glycogen from other carbohydrates, especially glucose.
• Hormones: insulin
• Decrease blood glucose level
• Excess glucose in the blood is converted to glycogen. Insulin stimulates glycogenesis in response to high blood glucose. Glycogen is stored in the liver and muscle tissue.

Question 5

Glycogenolysis

Answer 5

• Breakdown of glycogen to glucose
• Hormones: glucagon, adrenaline, noradrenaline, cortisol
• Increases blood glucose level
• Conversion of stored glycogen to glucose (glycogen breakdown). The free gluose is released into the blood.
• Adrenaline/Noradrenaline only involved if it is a fight/flight response, not if it is a response to low blood glucose levels in response to fasting

Question 6

Gluconeogenesis

Answer 6

• Conversion of fats (fatty acids, glycerol) or proteins (amino acids) into glucose
• Hormones: glucagon, glucocorticoids, cortisol
• Increases blood glucose level
• Production of glucose from non-carbohydrate sources (e.g. glycerol, pyruvate, lactate and amino acids). In response to fasting, starvation or prolonged periods of exercise when glycogen stores are exhausted. It is also part of the general adaptation syndrome in response to stress.

Question 7

Role of the Pancres

Answer 7

The hormone-secretory cells are located in the Islets of Langerhans. There are 2 types of cells: alpha and beta cells

- the regulation of blood glucose levels by insulin and glucagon involves a steady state (negative feedback) system

Question 8

Role of the Pancres - Alpha Cells

Answer 8

• Chemoreceptors in alpha cells detect low glucose concentration
• Hormone: Glucagon
• Incerases blood glucose concentration:
  1. Stimulates glycogenolysis (glycogen to glucose) in the liver
  2. Stimulates gluconeogenesis in the liver which produces glucsose from animo acids and fats

Question 9

Role of the Pancrease - Beta Cells

Answer 9

• Chemoreceptors in beta cells detect high glucose concentration
• Hormone: Insulin
• Decreases blood glucose concentration in 2 main ways:
  1. Stimulates glycogenesis (glucose to glycogen) in the liver (100g) and muscles (400g)
  2. Accelerates uptake of glucose into cells
• In addition insulin can also: stimulate conversion of glucose into fats in adipose tissue, increase protein synthesis in some cells

Question 10

Role of the Adrenal Glands

Answer 10

• Produce 2 types of hormones that help increase blood glucose concentration and so have a similar effect to glucagon:
  1. Glucocorticoids from the adrenal cortex e.g. Cortisol. The adrenal cortex is regulated by Adrenocorticotrophic Hormone (ACTH) from the anterior pituitary gland
  2. Adrenaline/Noradrenaline from the adrenal medulla following stimulation by the sympathetic nervous system

Question 11

Role of the Adrenal Glands - Glucocorticoid e.g. Cortisonl

Answer 11

• produced from Adrenal Cortex
• increased blood glucose levels
• regulates carbohydrate metabolism by ensuring enough energy is provided to cells:
  1. Glycogenolysis (glycogen to glucose) in the liver
  2. Gluconeogenesis - protein breakdown in muscles to remove amino acids and trasport them to liver, amino acid then converted to glucose
• Fatty acids mobilised from fatty tissue to be used by muscle for energy

Question 12

Role of the Adrenal Glands - Adrenaline/Noradrenaline

Answer 12

• produced from Adrenal Medulla
• increases blood glucose levels
  1. mimics sympathetic stimulation to increase blood glucose and counteracts insulin:
• stimulates production of lactic acid from glycogen stored in skeletal muscle cells
• lactic acid used by liver to make glucose