Insulin and Glucagon

Insulin and Glucagon

 

The bulk of the pancreas is an exocrine gland secreting pancreatic fluid into the duodenum after a meal.

However, scattered through the pancreas are several hundred thousand clusters of cells called islets of Langerhans.  The islets are endocrine tissue containing four types of cells. In order of abundance, they are the:

  •     beta cells, which secrete insulin
  •     alpha cells, which secrete glucagon
  •     delta cells, which secrete somatostatin
  •     gamma cells, which secrete a polypeptide of unknown function

 

1) Insulin

InsulinMonomer

 

Insulin 胰島素 is a hormone made by the pancreas allowing human body to use sugar (glucose) from carbohydrates in the food.  Insulin helps regulating blood sugar level from getting too high (hyperglycemia) or too low (hypoglycemia).

Human cells need sugar for energy.  But the latter is unable going into the former directly.  After eating food the blood sugar level increases, the cells in pancreas (beta cells β細胞) are triggered releasing insulin into bloodstream.  Then insulin triggers the cells to absorb sugar from bloodstream.

If accumulating more sugar than needed, insulin helps storing the sugar in liver and releaseing it later when the blood sugar level is low.  Or if more sugar is needed, such as in between meals or during physical activity.  Therefore, insulin helps balancing blood sugar levels and keeping them in a normal range.  When blood sugar levels increase, the pancreas secretes more insulin.

If the body unables producing enough insulin or the body cells are resistant to its effects hyperglycemia 高血糖 (high blood sugar) will be developped.  The latter can cause long-term complications if blood sugar levels stay elevated for long periods of time.

For more detail including insulin treatement please refers to following documentation;

1) Insulin    clickhere_red25
2) Living with Diabetes: Insulin Basics. June 7, 2013 issued by American Diabetes Association   clickhere_orange25
3) What is Insulin Resistance? issued by Joslin Diabetes Center      clickhere_green25
4) Insulin A to Z: A Guide on Different Types of Insulin.    clickhere_blue25

 

How does insulin work in the body?

 

Insulin, Glucose and You

 

Insulin and Glucagon Overview

 

2) Glucagon

Glucagon

 

Glucagon  胰高血糖素, a hormone, is produced by alpha cells in a part of the pancreas (islets of Langerhans 胰島).  The effects of glucagon are the opposite of that induced by insulin. The two hormones need to work side-by-side balancing blood glucose levels.

The role of glucagon in human body
Glucagon regulates the utilisation of glucose and fats.  It is released responding to low blood glucose levels whereby human body needs additional glucose, such as in vigorous exercise.

When glucagon is released it performs following works:

  •     Stimulating the liver to break down glycogen 肝醣 to be released into the blood as glucose
  •     Activating gluconeogenesis 糖原異生, to convert amino acids into glucose
  •     Breaking down stored fat (triglycerides 甘油三酯) into fatty acids for use as fuel by human cells

Glucagon and blood glucose levels
Glucagon keeps blood glucose levels high enough for human body to function properly.  When blood glucose levels are low, glucagon is released to trigger liver to release glucose into the blood.

Glucagon secretion varies depending on the foods consumed;

  •     In response to carbohydrate based meal, glucagon levels in the blood fall preventing blood glucose rising too high.
  •     In response to a high protein meal, glucagon levels in the blood increase.

Glucagon in diabetes
People suffering diabetes, glucagon’s presence can increase blood glucose levels too high.  The reason is either because insufficient insulin present or, as is the case in type 2 diabetes, the body is less able responding to insulin.

In type 1 diabetes, high levels of circulating insulin can inhibit the release of glucagon in response to hypoglycemia 低血糖.

 

Notes

Beta cells β細胞     clickhere_orange25
Glucagon 胰高血糖素    clickhere_red25
Gluconeogenesis     clickhere_green25
Glycogen 肝醣     clickhere_blue25
Hyperglycemia  高血糖     clickhere_red25
Hypoglycemia 低血糖    clickhere_orange25
Islets of Langerhans 胰島 clickhere_blue25
Somatostatin 生長抑素   clickhere_green25
Triglycerides  甘油三酯      clickhere_red25

 

Insulin 2: What is glucagon?

 

Insulin and Glucagon

 

3) Somatostatin

langerhans_islets_of_cells

 

The delta cells secrete somatostatin.  This consists of two polypeptides, one of 14 amino acids (the most active) and one of 28.  Somatostatin has a variety of functions.  They work to reduce the rate at which food is absorbed from the contents of the intestine.  Somatostatin is also secreted by the hypothalamus and by the stomach.

Hypothalamus     clickhere_orange25

Somatostatin is a mixture of two peptides, one of 14 amino acids, the other of 28.

Somatostatin acts on the anterior lobe of the pituitary to

  •     inhibit the release of growth hormone (GH)
  •     inhibit the release of thyroid-stimulating hormone (TSH)

 

 

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