Difference Between Endocrine and Exocrine Glands

Let’s first understand what glands are before knowing the meaning and difference between endocrine and exocrine glands. Glands are specialized groups of cells or organs that secrete chemical substances. The two classifications of glands are:

1. Endocrine Glands

These are the glands that secrete chemical substances into the bloodstream or tissues of the body. Endocrine glands are ductless i.e. they do not go to any duct before releasing chemical substances also known as hormones in the bloodstream. Hormones are messengers that are responsible for telling some part of the body to do something or to cease doing something.

Examples of Endocrine Glands

• Pineal gland located in the brain secretes melatonin in response to the dark conditions in the environment and induces sleep. It also regulates the female reproductive cycle and starts puberty. Estrogen, progesterone, and testosterone are the hormones that cause puberty to look hard. 

• Ovaries are glands that release estrogen and progesterone to give female characteristics. 

• Testes are the glands that release testosterone to promote male characteristics. 

2. Exocrine Glands

These are the glands that secrete chemical substances into ducts that help in releasing the secretions. Most of these glands release the secretions to the outside of the body whereas others release the secretions to the outside of the gland onto a surface still within the body. It can also be said that these glands synthesize and secrete their products onto a surface directly or via a tube/duct. Some ducts are also known to modify the secretions.

Examples of Exocrine Glands

• Pancreatic acinar cell: Its secretions are stored in vesicles and transported to the apical surface and then released (exocytosis) and it is called merocrine secretion.

• Lactating mammary gland secretion is released with some cytoplasm surrounded by plasma membrane; this kind is called apocrine secretion.

• Sebaceous gland involves programmed cell death where secretions and cell debris are released. It is called holocrine secretion.

Distinguish Between Endocrine and Exocrine Glands

Let’s put the differences between endocrine glands and exocrine glands in a tabular form to understand it in a better way as follows:

Important Facts about Endocrine System You Should Know

The endocrine system acts and works like one signal system and sends instructions through chemical messengers called hormones. The endocrine system mainly has glands that produce hormones to regulate some important functions in the human body like metabolism, reproduction, growth, and sleep. Each and every hormone has its own unique functions and is responsible for the growth of different organs in the human body. Furthermore, there are some surprising facts about the endocrine system, hormones, and glands which are mostly unknown to everyone. Let's move further and have a look at the list of these important facts.

1. Endocrinology Exists more than 2,000 Years Ago – According to the facts available in the book of Author Robert K. G. Temple, "The Genius of China: 3,000 Years of Science, Discovery, and Invention" (Prion, 1998)", Endocrinology is used by ancient Chinese people to extract sex and pituitary hormones from human urine. They used sulfate mineral gypsum and the chemical compound saponin to extract these hormones. They used it for different medicinal purposes and to cure different diseases related to sexual organs in humans.

2. Endocrine System Doesn't Produce all Types of Hormones – The endocrine system generally has glands that produce hormones like the adrenal gland, pancreas, parathyroid gland, reproductive glands, pineal gland, hypothalamus, pituitary gland, and thyroid gland. Apart from that, there are other organs available in the human body which also produce hormones but they are not a part of the endocrine system. For example, estrogen and progesterone are hormones produced by the placenta of a pregnant woman, ghrelin and gastrin are produced by the stomach which strikes hunger in humans and are not parts of the endocrine system.

3. Urine can be used to Diagnose Diabetes – When the pancreas stops producing insulin in the human body which is necessary to control blood sugar levels that disorder is called diabetes which is one of the most common diseases in the world right now. Nowadays, to check blood sugar levels, physicians use blood, but in older times, human urine was also used to diagnose diabetes disease in humans. Diabetes was first diagnosed by the ancient Greek physician Hippocrates (c. 460-377 B.C.), the "Father of Medicine," he used human urine to check the distinct sweetness.

4. Pancreas has Two Different Functions – We all know that generally there are two glands in the human body: endocrine and exocrine glands. The salivary glands, sweat glands, and mammary glands come under exocrine glands which secretes their products through ducts. But endocrine glands use hormones without ducts to release their products directly into the blood. Only the pancreas is the organ in the human body that has both types of glands as insulin and glucagon come under the endocrine system. On the other hand, the pancreas also produces pancreatic juice with digestive enzymes via ducts which come under the exocrine system.

5. Alcohol can Harm the Endocrine System – From increasing the risk of heart disease to damaging the liver permanently, there are different ways alcohol can harm human organs. Just like other organs, alcohol can immensely affect the endocrine system as well from irregulation in blood sugar to reducing testosterone levels in humans, alcohol can damage the endocrine system in a number of ways. Consumption of alcohol also increases the risk of osteoporosis by damaging a calcium-regulating hormone called parathyroid hormone.

6. Stress Adversely Affects the Endocrine System – We all know that stress is harmful to human health but the majority of stress-taking people don't know what stress can do with the endocrine system. During stress, the human body secretes hormones quickly at a higher pace, a much higher pace than normal, which automatically generates more energy which in turn is not adopted by the human body. During frequent stressful events, the blood volume increases which flows directly towards skeletal muscles and adrenaline is released by the pituitary–adrenal axis which is responsible for increasing the blood volume and flow rate which causes high blood pressure. During this process, metabolic activity also enhanced through the secretion of growth hormones produced in the pituitary gland.

7. Dogs Played an Important Part in Endocrine Research – Apart from mice and guinea, pigs researchers used dogs to study the endocrine system in the late 19th and 20th centuries. "English physiologist Sir Edward Albert Sharpey-Schafer and English physician George Oliver" injected extracts of adrenal glands from one dog to other dogs which ultimately increased hypertension and rapid heartbeat in dogs due to availability of adrenaline in the injected substances.

Why is Pancreas Known as Mixed Glands?

It is because pancreas acts as endocrine as well as exocrine glands. It secretes pancreatic juice which is emptied into the duodenum by the pancreatic duct. It is the pancreas behaving as an exocrine gland. Certain groups of cells embedded within the pancreas have different functions and produce hormone- insulin, these cells are known as islets of Llangerhans. Their secretions are absorbed into the capillaries surrounding the cells instead of secretions getting carried away by the ducts. So, the pancreas acts as endocrine glands in this case. Thus, it is known as mixed glands.