GLUCOSE HOMEOSTASIS
PREPARED BY MR. ABHIJIT DAS
Glucose homeostasis is the body's ability to regulate and maintain stable blood
sugar levels. It involves a complex interplay between organs, hormones,
and enzymes to ensure that glucose levels stay within a narrow range to support
proper bodily functions.
The normal
range for blood glucose levels in adults is typically between 70-100 mg/dL when fasting
(not having had anything to eat or drink, except for water, for at least
8 hours) and less than 140 mg/dL two hours after a meal.
SOURCES OF GLUCOSE
1.
Carbohydrates:
Carbohydrates are the primary source of glucose in the body. They are found in
foods such as bread, rice, fruits, and vegetables.
When carbohydrates are broken down in the body, they are converted into
glucose, which can be used for energy.
2.
Glycogen:
Glycogen is a complex carbohydrate that is stored
in the liver and muscles. When the body
needs glucose, glycogen is broken down into glucose and released into the
bloodstream.
3.
Gluconeogenesis:
This is a process in which the body creates glucose
from non-carbohydrate sources, such as proteins,
and fats. This process is particularly
important during fasting or prolonged exercise when the body needs to maintain
glucose levels.
REGULATION OF BLOOD GLUCOSE LEVEL
Blood glucose levels are tightly regulated
by a complex interplay of hormones, including incretins,
amylin, insulin, glucagon, epinephrine, and cortisol.
INCRETINS
Incretins, such as GLP-1 (glucagon-like peptide-1) and GIP
(gastric inhibitory polypeptide), are hormones released
from the gut in response to food intake.
They stimulate insulin release from the pancreas, inhibit
glucagon release, and slow down the rate at
which the stomach empties its contents into the small intestine.
Incretins also activate the satiety center
in the hypothalamus to decrease appetite and
food intake.
AMYLIN
Amylin is a hormone co-secreted with insulin by beta cells in the pancreas.
It slows down the rate at which food empties from
the stomach, which helps to regulate blood glucose levels by reducing
the amount of glucose entering the bloodstream after a meal. Amylin also promotes satiety and reduces food intake.
Additionally, it helps to regulate blood glucose levels by inhibiting the secretion of glucagon from the
pancreas and promoting insulin release.
INSULIN
In the liver,
Insulin stimulates the conversion of glucose into
glycogen, a process called glycogenesis,
thereby promoting the storage of glucose in the liver.
In muscle
cells, insulin promotes the uptake of
glucose through the GLUT4 transporter,
a protein that facilitates the transport of glucose across the cell membrane.
Insulin triggers the translocation of GLUT4 from intracellular compartments to the plasma membrane,
allowing glucose to enter the cell and be used for energy or stored as glycogen.
GLUCAGON
Glucagon is a hormone secreted by the alpha cells of the pancreas,
and it plays a crucial role in raising blood glucose levels in the body. It
acts in opposition to insulin, which lowers blood glucose levels.
When blood glucose levels are low,
glucagon is released to stimulate the liver to convert stored glycogen into glucose and release it into the
bloodstream, a process known as glycogenolysis.
Glucagon also promotes the production of glucose from non-carbohydrate sources,
such as amino acids and fatty acids, a process called gluconeogenesis.
EPINEPHRIN
Epinephrine, also
known as adrenaline, is a hormone produced by the adrenal glands.
In the liver,
epinephrine stimulates the breakdown of glycogen
into glucose, a process known as glycogenolysis.
This glucose is then released into the bloodstream, raising blood glucose
levels. Epinephrine also stimulates the production
of glucose from non-carbohydrate sources, such as amino acids and fatty
acids, a process known as gluconeogenesis.
In muscle
tissue, epinephrine promotes the breakdown of glycogen
into glucose, which is then used by the muscles for energy.
At the same time, epinephrine reduces glucose uptake by peripheral
tissues such as adipose tissue, helping to ensure that glucose is
available to the muscles where it is needed most.
CORTISOL
Cortisol is a hormone produced by the adrenal
glands in response to stress. One of
its primary functions is to increase blood glucose levels in the body,
particularly during periods of stress or fasting.
In the liver,
cortisol stimulates the breakdown of glycogen into
glucose, a process known as glycogenolysis. This glucose is then
released into the bloodstream, raising blood glucose levels. Cortisol also
stimulates the production of glucose from
non-carbohydrate sources, such as amino acids and fatty acids, a process
known as gluconeogenesis.
Cortisol also reduces
glucose uptake by peripheral tissues such
as muscle and adipose tissue, which allows glucose to be available for other
vital organs such as the brain, heart, and liver.
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