Nutrition Science and Everyday Application - beta v 0.1

Glucose Regulation and Utilization in the
Body
On the last page, we traced the process of digesting the carbohydrates in a slice of pizza
through the gastrointestinal tract, ending up with the absorption of monosaccharides across
the cells of the small intestine and into the bloodstream. From there, they travel to the liver,
where fructose and galactose are converted to glucose.
After any meal containing carbohydrates, you experience a rise in blood glucose that can
serve as fuel for cells around the body. But during the periods between meals, including
while you’re sleeping and exercising, your body needs fuel, too. To ensure that you have
enough glucose in your blood at any given time, your body has a finely-tuned system to
regulate your blood glucose concentration. This system allows you to store glucose when
you have excess available (when your blood glucose is high) and to pull glucose out from
your stores when needed (when your blood supply gets low).
Your body’s ability to maintain equilibrium or a steady state in your blood glucose
concentration is called homeostasis. It’s a critical part of normal physiology, because if your
blood glucose gets too low (called hypoglycemia), cellular function starts to fail, especially in
the brain. If blood glucose gets too high (called hyperglycemia), it can cause damage to cells.
HORMONES INVOLVED IN BLOOD GLUCOSE REGULATION
Central to maintaining blood glucose homeostasis are two hormones, insulin and glucagon,
both produced by the pancreas and released into the bloodstream in response to changes
in blood glucose.
• Insulin is made by the beta-cells of the pancreas and released when blood
glucose is high. It causes cells around the body to take up glucose from the blood,
resulting in lowering blood glucose concentrations.
• Glucagon is made by the alpha-cells of the pancreas and released when blood
glucose is low. It causes glycogen in the liver to break down, releasing glucose into
the blood, resulting in raising blood glucose concentrations. (Remember that
glycogen is the storage form of glucose in animals.)
The image below depicts a mouse islet of Langerhans, a cluster of endocrine cells in the
pancreas. The beta-cells of the islet produce insulin, and the alpha-cells produce glucagon.
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