The Endocrine System – Pancreas Anatomy and Physiology

The pancreas, which is located in the curve of the duodenum, is a flat organ measuring between 12.5cm-15cm. It is a composite gland – both an exocrine and an endocrine gland: Exocrine acini secrete digestive enzymes into the duodenum, while the Islets of Langerhans help with carbohydrate metabolism.

Pancreas Blood Supply

The Splenic Artery supplies the pancreas with blood, while venous return is completed through small veins within the Splenic Vein.

Pancreas Nerve Supply

The Autonomic Nervous System (ANS) innervates the pancreas. Parasympathetic Vagal Fibres stimulate exocrine secretion, while Sympathetic Vasoconstrictor Impulses travel through nerves derived from spinal cord segments T6-T10 which pass through blood vessels within the pancreas. This reflects why pancreatic pain frequently radiates these nerve pathways.

The Endocrine Portion

The Islets of Langerhans contain 4 types of cells:

1. Alpha Cells – make up 15% of the pancreatic islet cells; secrete Glucagon
2. Beta Cells – make up 80% of the pancreatic islet cells; secrete Insulin
3. Delta Cells – make up 5% of the pancreatic islet cells; secrete Somatostatin
4. F Cells – secrete Pancreatic Polypeptide

• Glucagon INCREASES blood glucose level
• Insulin DECREASES blood glucose level
• Somatostatin INHIBITS insulin and glucagon, acting as a regulator
• Pancreatic Polypeptide INHIBITS somatostatin secretion, gallbladder contraction, and digestive enzyme secretion (Pancreatic Polypeptide is secreted near the end of the digestive system)

Glucagon

The main function of glucagon is that of increasing blood glucose level. This is carried out through the following process:

1. Glucagon increases glycogen conversion into glucose within the liver (glycogenolysis) AND increases nutrient (amino acids, glycerol and lactic acid) conversion into glucose within the liver (gluconeogenesis)
2. Liver releases glucose into the blood, causing an increase in blood sugar level
3. Blood sugar level controls secretion of glucagon through a negative feedback mechanism

lysis = breaking down of glycogen

neo = new

genesis = production

Secretion of glucagon is STIMULATED by:

• decreased blood glucose level
• protein-based foods
• exercise

Secretion of glucagon is INHIBITED by:

• somatostatin
• insulin

Insulin

Islet beta cells produce insulin, which increases protein build-up within the cells. Insulin regulation is controlled by a negative feedback mechanism based on the blood sugar level.

Insulin decreases blood sugar level through the following process:

1. increases glucose transportation from the blood into the cells
2. increases glucose conversion into glycogen (glycogenesis)
3. decreases glycogenolysis and gluconeogenesis
4. stimulates glucose conversion to fatty acids
5. stimulates protein synthesis

Secretion of insulin is STIMULATED by:

• increased blood glucose level
• acetylcholine (released by parasympathetic vagus nerve fibres)
• amino acids (arginine and leucine)
• growth hormone (GH) (which causes increase in blood sugar level)
• ACTH (adrenocorticotropic hormone) (stimulates glucocorticoids secretion leading to hyperglycaemia, indirectly stimulating insulin release)

Secretion of insulin is INHIBITED by:

• somatostatin (GIF – growth hormone inhibiting factor)

Insulin production is also AFFECTED by:

• stomach and intestinal gastrin
• secretin
• cholecystokinin
• gastric inhibitory peptide (GIP)

Insulin vs Glucagon

Somatostatin

Somatostatin is secreted by delta cells in the Islets of Langerhans following an increase in blood glucose, fatty acids, and amino acids due to an ingested meal. Somatostatin travels in the blood, slowing down the absorption of nutrients from the GIT, acting as paracrine secretion, diffusing into tissue fluid targeting nearby cells, and inhibiting both insulin and glucagon release from nearby alpha and beta cells.

Somatostatin secretion is INHIBITED by pancreatic polypeptide.

Pancreatic Polypeptide

Pancreatic Polypeptide inhibits secretion of somatostatin, gallbladder contraction, and secretion of pancreatic digestive enzymes.

Secretion of pacreatic polypeptide is STIMULATED by:

• protein-containing meals
• fasting
• exercise
• hypoglycaemia

Secretion of pancreatic polypeptide is INHIBITED by:

• somatostatin
• hyperglycaemia

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Claire

Claire Galea is a mum of three currently in her final year following a Degree in Nursing at the Faculty of Health Sciences, University of Malta, as a mature student.

Claire is keen about public education on health-related subjects as well as holistic patient-centered care. She is also passionate about spreading awareness on the negative effects that domestic abuse leaves on its victims’ mental, emotional, social and physical wellbeing.

Claire aspires to continue studying following completion of her Nursing Degree, because she truly believes in lifelong education.

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Author: Claire

Claire Galea is a mum of three currently in her final year following a Degree in Nursing at the Faculty of Health Sciences, University of Malta, as a mature student. Claire is keen about public education on health-related subjects as well as holistic patient-centered care. She is also passionate about spreading awareness on the negative effects that domestic abuse leaves on its victims’ mental, emotional, social and physical wellbeing. Claire aspires to continue studying following completion of her Nursing Degree, because she truly believes in lifelong education. View all posts by Claire