Question

21. Diagram or describe in words the negative feedback loop for blood sugar. Make sure to include BOTH what happens when blood sugar rises too high and what happens when blood sugar falls too low. Include the roles of the 2 main hormones involved, the organs that secrete those hormones, and the organs those hormones act on

Answer 1

Glucagon and insulin are the two hormones that involve in negative feedback loop of blood sugar. They maintain the blood sugar level at optimum standard. The endocrine part of pancreas consists of tissues called Islets of Langerhans. It is made up of α-cells and β-cells. The glucagon is secreted by α-cells and the β-cells secrete insulin. Both are peptide hormones.

Glucagon is a hyperglycaemic hormone. Maintaining the normal blood glucose levels is the main function of the hormone when blood sugar concentration goes high. Glucagon acts mainly on the liver cells (hepatocytes) and stimulates glycogen to be broken down into glucose (glycogenolysis) resulting in an increased blood sugar concentration in blood (hyperglycaemia). In addition, this hormone stimulates the process of gluconeogenesis which also contributes to hyperglycaemia. Gluconeogenesis is the process of synthesizing glucose or glycogen from substrates like glucogenic amino acids. Glucagon reduces the cellular glucose uptake and utilisation and maintain the glucose in the blood thus increase the blood sugar concentration.

Insulin does the opposite. Insulin acts mainly on cells of adipose tissue (hepatocytes, and adipocytes) when blood sugar concentration goes low, Insulin decreases the concentration of glucose in the blood. Insulin   helps in cellular glucose uptake and utilisation. It helps in decreased blood glucose levels (hypoglycaemia). Insulin also convert glucose into glycogen (glycogenesis) in the target cells. These actions together contributes to lower the blood sugar concentration.