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3. What is the topography of islet cells in the pancreas?

The word islet means small island, which originated from the French word

islette and refers to clusters of cells. A healthy adult human pancreas weighs

approximately 68 g (range 45–120 g) and consists of approximately one mil-

lion islets, and each islet contains about 3,000–4,000 cells. The endocrine pan-

creas constitutes approximately 1–2 % of the total weight of the pancreas, while

the rest (98 %) is contributed by the exocrine pancreas. The details about islet

cells in the pancreas are summarized in the table given below.

Islet cells Cell proportion (%) Cell distribution Hormone secreted

α-cells 40 Neck, body, and tail of the

pancreas

Glucagon

β-cells 50 Neck, body, and tail of the

pancreas

Insulin, amylin

δ-cells 8–10 – Somatostatin

PP-cells <1 Head of the pancreas Pancreatic polypeptide

ε-cells <1 – Ghrelin

4. How was the word “insulin” derived?

The word “insulin” was derived from a Latin word insula which means island.

The island in this context refers to the cluster of cells in the pancreas (“Insula”),

and the product of insula was termed as “insulin.” Both insula and islette refers

to island which means cluster of cells and are of Latin and French in origin,

respectively.

5. What is the insulin secretory profile in a normal individual?

Insulin is secreted in a pulsatile pattern in a healthy adult. This consists of rapid

burst at a frequency of every 4 min and ultradian oscillations every 15–20 min.

During the prandial phase, the oscillations are exacerbated in amplitude and

frequency and are appreciated as first and second phase of insulin secretion.

The pulsatile insulin secretion in postabsorptive period (basal) contributes

approximately 50 % of total daily insulin secretion and regulates hepatic glu-

cose output and suppresses lipolysis during inter-prandial and fasting state. The

meal-related insulin secretion during first phase initiates just prior to ingestion

of food and lasts for 5–15 min, while the second phase of insulin secretion

starts thereafter and continues for 120 min. The first-phase insulin secretion

occurs due to release of preformed granules, whereas the second phase is due

to neogenesis of insulin granules. The first-phase insulin secretion suppresses

the hepatic glucose output in immediate postprandial period, whereas the sec-

ond phase of insulin secretion promotes peripheral glucose uptake in skeletal

muscle and adipocytes.

12 Diabetes in the Young