Question

There are many types of cells in the human body with many different functions. Pick a particular type of cell (exocrine secretory cells, hormone secreting cells, etc) and discuss its function within the body. Talk about common locations for the type of cell and discuss the clinical significance of the cell.

Answer 1

Hormone secreting Endocrine cells:

There are three types of endocrine cells; alpha cells which secrete glucagon, beta cells which secrete insulin, and delta cells which inhibit the secretion on glucagon and insulin.

Alpha cells (A cells) secrete the hormone glucagon.

Beta cells (B cells) produce insulin and are the most abundant of the islet cells.

Delta cells (D cells) secrete the hormone somatostatin, which is also produced by a number of other endocrine cells in the body.

Location of Alpha cells:

Alpha cells (more commonly α-cells) are endocrine cells in the pancreatic islets of the pancreas. Alpha cells are located in the periphery of the islets. Alpha cells can be identified by their characteristic granules with a large dense core and a small white halo. They make up to 20% of the human islet cells synthesizing and secreting the peptide hormone glucagon.

Function of Alpha cells:

It is use to elevate glucose levels, glucagon binds to receptors on hepatocytes (liver cells) and some other cells (e.g. kidney cells). This activates an enzyme, glycogen phosphorylase, inside the Hepatocyte to Hydrolyse glycogen to glucose.

It works to raise the concentration of glucose and fatty acids in the bloodstream, and is considered to be the main catabolic hormone of the body.

Clinical significance of Alpha cells:

It is used as a medication to treat a number of health conditions. Its effect is opposite to that of insulin, which lowers extracellular glucose.

It is produced from proglucagon, encoded by the GCG gene.

The pancreas releases glucagon when the amount of glucose in the bloodstream is too low. Glucagon causes the liver to convert stored glycogen into glucose, which is released into the bloodstream

High blood-glucose levels, on the other hand, stimulate the release of insulin. Insulin allows glucose to be taken up and used by insulin-dependent tissues.

Thus, glucagon and insulin are part of a feedback system that keeps blood glucose levels stable.

Glucagon increases energy expenditure and is elevated under conditions of stress. Glucagon belongs to the secretin family of hormones.

Location of Beta cells:

Beta cells (β cells) are a type of cell found in pancreatic islets that synthesize and secrete insulin and amylin. Beta cells make up 50–70% of the cells in human islets.

Function of Beta cells:

Insulin synthesis

Beta cells are the only site of insulin synthesis in mammals. As glucose stimulates insulin secretion, it simultaneously increases proinsulin biosynthesis, mainly through translational control.

Insulin secretion

In beta cells, insulin release is stimulated primarily by glucose present in the blood. As circulating glucose levels rise such as after ingesting a meal, insulin is secreted in a dose-dependent fashion. This system of release is commonly referred to as glucose-stimulated insulin secretion (GSIS).

Clinical significance of Beta cells:

Type 1 diabetes

Type 1 diabetes mellitus, also known as insulin dependent diabetes, is believed to be caused by an auto-immune mediated destruction of the insulin producing beta cells in the body.

Type 2 diabetes

Type 2 diabetes mellitus, also known as non insulin dependent diabetes and as chronic hyperglycemia, is caused primarily by genetics and the development of metabolic syndrome. The beta cells can still secrete insulin but the body has developed a resistance and its response to insulin has declined.

Insulinoma

Insulinoma is a rare tumor derived from the neoplasia of beta cells. Insulinomas are usually benign, but may be medically significant and even life-threatening due to recurrent and prolonged attacks of hypoglycemia.

Location of Delta cell:Delta cells (δ-cells or D cells) are somatostatin-producing cells. They can be found in the stomach, intestine and the pancreatic islets.

Function of Delta cell: Delta cells make somatostatin, a hormone that inhibits the release of numerous hormones in the body.

Clinical significance of Delta cell:

A tumor of the delta cells is called a "somatostatinoma".

When a person is infected with H. pylori the lower region of the stomach, the antrum, is predominantly inflamed. This is where most of the D cells in the stomach are. The bacteria produce a cloud of ammonia around themselves using urease to protect them from the stomach acid; however, this reacts with the acid producing ammonium which is toxic to cells. This leads to many of the D cells dying and therefore a lower level of somatostatin being secreted. This results in higher levels of gastrin and stomach acid being secreted. This, combined with the damage from ammonium, leads to ulceration of the stomach wall.