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Glucagon

Receptors in the pancreas can sense the decline in blood glucose levels, such as during periods of fasting or during prolonged labor or exercise ( [link] ). In response, the alpha cells of the pancreas secrete the hormone glucagon    , which has several effects:

  • It stimulates the liver to convert its stores of glycogen back into glucose. This response is known as glycogenolysis. The glucose is then released into the circulation for use by body cells.
  • It stimulates the liver to take up amino acids from the blood and convert them into glucose. This response is known as gluconeogenesis.
  • It stimulates lipolysis, the breakdown of stored triglycerides into free fatty acids and glycerol. Some of the free glycerol released into the bloodstream travels to the liver, which converts it into glucose. This is also a form of gluconeogenesis.

Taken together, these actions increase blood glucose levels. The activity of glucagon is regulated through a negative feedback mechanism; rising blood glucose levels inhibit further glucagon production and secretion.

Homeostatic regulation of blood glucose levels

This diagram shows the homeostatic regulation of blood glucose levels. Blood glucose concentration is tightly maintained between 70 milligrams per deciliter and 110 milligrams per deciliter. If blood glucose concentration rises above this range (hyperglycemia), insulin is released from the pancreas. Insulin triggers body cells to take up glucose from the blood and utilize it in cellular respiration. Insulin also inhibits glycogenolysis, in that glucose is removed from the blood and stored as glycogen in the liver. Insulin also inhibits gluconeogenesis, in that amino acids and free glycerol are not converted to glucose in the ER. If blood glucose concentration drops below this range, glucagon is released, which stimulates body cells to release glucose into the blood. All of these actions cause blood glucose concentration to decrease. When blood glucose concentration is low (hypoglycemia), alpha cells of the pancreas release glucagon. Glucagon inhibits body cells from taking up glucose from the blood and utilizing it in cellular respiration. Glucagon also stimulates glycogenolysis, in that glycogen in the liver is broken down into glucose and released into the blood. Glucagon also stimulates glucogenogenesis, in that amino acids and free glycerol are converted to glucose in the ER and released into the blood. All of these actions cause blood glucose concentrations to increase.
Blood glucose concentration is tightly maintained between 70 mg/dL and 110 mg/dL. If blood glucose concentration rises above this range, insulin is released, which stimulates body cells to remove glucose from the blood. If blood glucose concentration drops below this range, glucagon is released, which stimulates body cells to release glucose into the blood.

Insulin

The primary function of insulin    is to facilitate the uptake of glucose into body cells. Red blood cells, as well as cells of the brain, liver, kidneys, and the lining of the small intestine, do not have insulin receptors on their cell membranes and do not require insulin for glucose uptake. Although all other body cells do require insulin if they are to take glucose from the bloodstream, skeletal muscle cells and adipose cells are the primary targets of insulin.

The presence of food in the intestine triggers the release of gastrointestinal tract hormones such as glucose-dependent insulinotropic peptide (previously known as gastric inhibitory peptide). This is in turn the initial trigger for insulin production and secretion by the beta cells of the pancreas. Once nutrient absorption occurs, the resulting surge in blood glucose levels further stimulates insulin secretion.

Precisely how insulin facilitates glucose uptake is not entirely clear. However, insulin appears to activate a tyrosine kinase receptor, triggering the phosphorylation of many substrates within the cell. These multiple biochemical reactions converge to support the movement of intracellular vesicles containing facilitative glucose transporters to the cell membrane. In the absence of insulin, these transport proteins are normally recycled slowly between the cell membrane and cell interior. Insulin triggers the rapid movement of a pool of glucose transporter vesicles to the cell membrane, where they fuse and expose the glucose transporters to the extracellular fluid. The transporters then move glucose by facilitated diffusion into the cell interior.

Questions & Answers

what are the characteristics of blood
yeboah Reply
they are red in colour
Tawoi
Me phone no petandi meku doubt vunte nenu phone chesi cheputhanu
Mohan Reply
What is respiratory disease
Rita Reply
What are the importance of homeostasis in human body?
Pablo Reply
homeostasis
Abena
it help to keep our salt and water balance
Husna
Homeostasis regulates and mentain internal equilibrium (ie temperature and pH) of the body.
Edmund
maintain temp and ph so our enzyme works properly
Husna
The inability of the body regulating and maintaining the temp. and pH results in disease affection.
Edmund
formation of the bone
Ali Reply
.
mohamed
عاوز ايه يعني من الفورمايشن
Doctor
notes on cell theory and discovery
Masika Reply
Cell theory are a set of rules for overall knowledge on cells. The most famous set of rules include: All cells arise from other cells. The cell is the functional unit of life. The structure (organelles) and morphology of the cell indicates it's main functions.
Carmelo
Antonie Van L. was the first to actually observe alive microorganisms (such as protist and bacteria) in a microscope in the 1600s.
Carmelo
electro phisiology meand
aparna Reply
rouleaux formation factors
Hridya Reply
can anyone suggest me how to learn forearm and hand topic of anatomy?
Anjali Reply
can anyone suggest me how to learn forearm and hand anatomy topic?
Anjali
can anyone suggest me how to learn forearm and hand topic of anatomy? pls pls tell
Anjali
check out youtube videos for trickss and while learning the boness part keep the bone wid u and learn ..... hope it helps u
Subuhi
ohk
Anjali
formation of the bone
Ali
what is the space between d dura mater and pia mater
Uwakwe Reply
Subdural space
Juveriya
Actually sub dural space is space between dura and arachnoid mater And sub arachnoid space is space between arachnoid and pia mater
Juveriya
the smallest bone in the body
Bahja Reply
stapes is the smallest bone in human Body
dipayan
Yeah
Ridwan
what is cell membrane
Hajara
cell membrane is like a protective cover of a cell and it's cytoplasm
dipayan
thanks
Hajara
list two adpitive mechanism that control homeostasis condition
Hajara
positive and negative feedback Mechanism
dipayan
@Dipayan, a cell membrane encloses and surrounds the cytoplasm of the cell. It's structure varies between species of life (eukaryotes, archaea, bacteria), but it is mostly composed of phospholipid, arachidonic acid, proteins, glycoproteins, glycolipids, and cholesterol.
Carmelo
and the glycoprotein and polysaccharides of the cell membrane forms the glycocalyx which has several functions especially in a bacteria.
Norom
can we stain sputum samples?
Apai Reply
Yes
Dorcas
wat do we use in staining them?
Apai
gram stain
Mawuli
Hello
bona
zeel Nelson stain
bona
why the ganglion cyst bumps?
dipayan Reply
i think fats gather under the skin
Matthew
but there were some tissue is present
dipayan
plz Matthew clearly present your answer
dipayan
appilied physiology of umn and lmn lesion
Ananthan Reply
what is umn and imn
dipayan
I don't know
bona
saaa
Patricia
Upper motor neurons (UMN) are responsible for conveying impulses for voluntary motor activity through descending motor pathways that make up the upper motor neurons. UMN send fibers to the LMN, and that exert direct or indirect supranuclear control over the LMN of the cranial and spinal nerves.
Amit
What is your doubt
Mohan
Anatomy of functions of the skeletal system
Tobokwa Reply

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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