Biology

The secretion of enzymes and hormones

Secretion of enzymes

The majority of cells in the pancreas manufacture and release digestive enzymes - Exocrine Function

Cells are found in small groups surrounding tiny tubules into which they secrete digestive enzymes. The tubules join to make up the Pancreatic Duct - this carries the fluid containing the enzymes into the first part of the small intestine.

Fluid contains the following enzymes
- Amylase-
-Trypsinogen
- Lipase

Secretion of hormones

Certain areas of the pancreas called the Islets Of Langerhans contain different types of cells.
Alpha Cells- manufacture and secrete the hormone Glucagon
Beta cells- Manufacture and secrete the hormone Insulin.

The Islets are well supplied with blood capilaries and these hormones are secreted directly into the blood. This is the endocrine function of the pancreas.

The control of blood glucose

The concentration of blood glucose is carefully regulated. The cells in the Islets of Langerhans monitor the concentration of glucose in the blood.
The normal blood concentration of glucose is 90mg 100cm-3.
If the concentration rises or falls away from the acceptable concentration then the alpha and beta cells in the Islets of Langerhans detect the change and respond by releasing a hormone.

If blood glucose rises too high

A high blood glucose concentration is detected by the Beta cells. In response the beta cells secrete insulin into the blood. The Target cells are the liver cells or Hepatocytes, muscles cells and some other body cells including those in the brain.
These possess the specific membrane-bound receptors for insulin. When the blood passes these cells the insulin binds to the receptors. This activates the adenyl cyclase inside each cells which converts ATP to cAMP (cyclic AMP). This cAMP activates a series of enzyme-controlled reactions in the cells:
Insulin has several effects on the cells
- More glucose channels are placed into the cells surface membrane
- More glucose enters the cells
- Glucose in the cells is converted to glycogen for storage
- More glucose is converted to fats
- More glucose is used in respiration
The increased entry of glucose, through the specific channels, reduces the blood glucose concentration.

If blood glucose drops too low

A low blood glucose concentraion is detected by the Alpa cells. In response the Alpha cells secrete the hormone glucagon. Its target cells are the Hepatocytes (liver cells) which possess the specific receptor for glucagon. The effects of glucagon include:
- Conversion of glycogen to glucose
- Use of more fatty acids in respiration
- The production of glucose by conversion from amino acids and fats.

The overall effect of these changes is to increase the blood glucose concentration.