8.8: Meet the Pancreas — Dual Roles in Digestion and Hormone Control

The endocrine pancreas consists of clusters of islet cells that secrete the hormones insulin and glucagon, which work together to regulate and maintain stable blood glucose levels throughout the body.

Master this section and you'll be able to

• Describe the location and structure of the pancreas, and the morphology and function of the pancreatic islets.
• Compare and contrast the functions of insulin and glucagon.
• Differentiate between Type 1 and Type 2 diabetes mellitus.

Location and Structure

The pancreas is a long, slender organ located behind the lower half of the stomach in the retroperitoneal space (Figure \PageIndex1\PageIndex{1}\PageIndex1). It stretches from the duodenum on its right side to the spleen on its left. Because it sits behind the peritoneum, it is considered a retroperitoneal organ.

Figure \(\PageIndex{1}\): Location of the Pancreas as Part of the Upper Abdominal Cavity. The pancreas is situated posterior to the bottom half of the stomach. 

 

Exocrine Function

Most of the pancreas functions as an exocrine gland. It is composed of acinar cells, which produce digestive enzymes that form pancreatic juice. These cells are arranged in small, pouch-like clusters that connect to the pancreatic duct, a central passageway that carries the digestive secretions into the duodenum, where they help break down food.

Endocrine Function

Scattered among the acinar tissue are about a million small clusters of endocrine cells known as pancreatic islets (islets of Langerhans). These islets function as tiny hormone factories, secreting several vital hormones, most notably:

• Insulin, which lowers blood glucose

• Glucagon, which raises blood glucose

Together, these hormones maintain blood glucose homeostasis and ensure the body has a stable energy supply.

Cells and Secretions of the Pancreatic Islets

For this course, we will focus on the alpha and beta cells of the pancreatic islets (Figure \PageIndex1\PageIndex{1}\PageIndex1 and Figure \PageIndex2\PageIndex{2}\PageIndex2). In addition, there are two other cell types whose secretions are distinct hormones that also enter the bloodstream and act on their specific target cells.

• The alpha cell produces the hormone glucagon and makes up approximately 20 percent of each islet. Glucagon plays an important role in blood glucose regulation; low blood glucose levels stimulate its release.
   
• The beta cell produces the hormone insulin and makes up approximately 75 percent of each islet. Elevated blood glucose levels stimulate the release of insulin.

Figure \(\PageIndex{2}\): The Pancreas. The endocrine portion of the pancreas is small clusters of cells called pancreatic islets.  Multiple hormones are secreted by the islets, with the two regulating blood glucose levels coming from the beta cells (insulin) and alpha cells (glucagon). (Image credit: "Endocrine Pancreas" by Jennifer Lange is licensed under CC BY-NC-SA 4.0, derivatives of original works "Leiden - Drawing pancreas and neighbouring organs - no labels" by Ron Slagter and "Endocrine Pancreas" by Cenveo.)

 

Figure \(\PageIndex{3}\): Histology of the Pancreas. On slides the pancreatic islets are seen as clusters of smaller, lighter staining cells that the surrounding blocks of acini (acinar cells).  (Image credit: "Histology of the Pancreas" by Jennifer Lange is licensed under CC BY-NC-SA 4.0, slide provided by the Regents of the University of Michigan Medical School © 2022.)

 

Regulation of Blood Glucose Levels by Insulin and Glucagon

Glucose is the body’s main energy source and the fuel most cells rely on for cellular respiration, the process that produces ATP. The body obtains glucose by digesting carbohydrate-rich foods and beverages, breaking down complex carbohydrates into simple sugars that are absorbed into the bloodstream. After eating, when blood glucose levels rise, cells can immediately use glucose for energy. Any extra glucose is stored in the liver and skeletal muscles as glycogen for short-term energy needs, or converted into triglycerides and stored in adipose tissue for long-term use.

The body keeps glucose levels within a narrow, healthy range through precise hormonal regulation. Specialized receptors in the pancreas constantly monitor blood glucose concentrations. When levels are high, the pancreatic islets release insulin, which promotes glucose uptake into cells and glycogen storage. When levels drop, the alpha cells  of the pancreatic islets release glucagon, which triggers glycogen breakdown and glucose release into the blood. This ongoing balance ensures homeostasis, specifically a steady supply of energy for all the body’s cells.

Figure \(\PageIndex{4}\): Glucose Homeostasis. Blood glucose levels are regulated by two pancreatic hormones that act antagonistically. (Image credit: "Glucose Homeostasis" by Gabrielle Spurlock is licensed under CC BY-NC-SA 4.0.  Pancreas image by Ron Slagter; liver image by Ron Slagter.)

 

Hormones of the Pancreas

Associated hormone (and the cells that secretes it)	Effect
Insulin (beta cells)	Reduces blood glucose levels
Glucagon (alpha cells)	Increases blood glucose levels

 

 

Interactive Element

Watch this Kahn Academy video up to time-point 5:39.  (We are not covering the third hormone talked about).  

 

DISORDERS OF THE...

Endocrine System: Diabetes Mellitus

When the body’s finely tuned system for controlling blood glucose goes awry, the result can be a chronic disorder known as diabetes mellitus. This condition arises when the pancreas does not produce enough insulin, or when body cells stop responding properly to it. The outcome is the same either way — too much glucose stays in the bloodstream, and that creates serious health problems over time.

How Common Is It?

Diabetes mellitus is one of the most rapidly growing health concerns worldwide. In the United States alone, more than 18 million adults and over 200,000 children have been diagnosed, and an additional 7 million adults may have it without knowing. Another 79 million people are thought to have pre-diabetes, where blood glucose levels are elevated but not yet high enough to be classified as diabetes.
 

The Two Major Types

Type 1 Diabetes: When the Body Attacks Itself

Type 1 diabetes is an autoimmune disease — the immune system mistakenly targets and destroys the pancreas’s β (beta) cells, which normally produce insulin. Without insulin, cells cannot absorb glucose for energy. People with this form of diabetes must rely on synthetic insulin injections or pumps to survive.
Type 1 diabetes accounts for less than 5 percent of all cases and often begins in childhood or adolescence. Certain genetic factors are known to increase susceptibility.

Type 2 Diabetes: When Cells Stop Listening

Far more common, Type 2 diabetes makes up about 95 percent of all cases. Here, the pancreas still produces insulin, but body cells become resistant to its effects. In response, the pancreas works overtime to release even more insulin — until the β cells eventually burn out.
Lifestyle factors play a big role: poor diet, inactivity, and excess body weight all increase risk. In fact, 80–90 percent of people with type 2 diabetes are overweight or obese.
The good news? In many cases, type 2 diabetes can be reversed through moderate weight loss, regular physical activity, and a balanced diet. If these steps are not enough, medications — or eventually insulin — may be required to keep blood glucose within a healthy range.
 

Classic Signs and Symptoms

Two early warning signs are excessive urination (polyuria) and excessive thirst (polydipsia).
When glucose levels rise too high, the kidneys can no longer reabsorb all the sugar. Glucose spills into the urine, dragging water with it by osmosis. The result is a large volume of sweet-smelling urine, dehydration, and an almost unquenchable thirst. Because the body’s cells cannot use glucose properly, people with diabetes also often experience constant hunger (polyphagia) and fatigue.
 

Long-Term Complications

Uncontrolled high blood glucose (hyperglycemia) damages tissues throughout the body, particularly blood vessels and nerves. Over time, this can lead to:

• Atherosclerosis, increasing the risk of heart attack and stroke

• Kidney failure, from damage to the tiny filtration vessels

• Retinopathy and blindness, from injury to eye blood vessels

• Poor circulation and neuropathy, especially in the hands and feet
  These changes can result in ulcers, infections, and even amputations of toes, feet, or legs.

If the body cannot use glucose at all, it begins burning fat for energy instead. This process produces ketone bodies, which are acidic. When they accumulate, ketoacidosis develops—a dangerous condition that can lead to diabetic coma if untreated.
Altogether, diabetes remains one of the leading causes of death in the United States.
 

Diagnosis and Treatment

A diagnosis is made when blood tests show abnormally high glucose levels. Treatment depends on the type and severity of diabetes and the individual’s ability to make lifestyle changes.
For many people with type 2 diabetes, healthy eating, exercise, and modest weight loss can significantly lower blood glucose. If that is not enough, doctors may prescribe oral medications that improve the pancreas’s insulin response or increase insulin sensitivity. In advanced cases, insulin therapy becomes necessary.
Ongoing research continues to expand treatment options, offering hope that one day we can prevent or even cure this complex metabolic disease.