Glands are specialized groups of cells or organs that secrete chemical substances.
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:
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.
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.
Let’s put the differences between endocrine glands and exocrine glands in a tabular form to understand it in a better way as follows:
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 pancreas behaving as an exocrine gland. Certain groups of cells embedded within the pancreas have different functions and produce hormone- insulin, the cells are known as islets of langerhans. Their secretions are absorbed into the capillaries surrounding the cells instead of secretions getting carried away by the ducts. So, pancreas acts as endocrine glands in this case. Thus, it is known as mixed glands.
The system comprising endocrine glands is called a ductless system as they do not have ducts and transport hormones directly to the blood. Some of the examples of ductless glands include hypothalamus, pituitary gland (anterior or posterior), thyroid, adrenal gland, etc.
Hormones are chemical substances secreted by endocrine glands in our body. These hormones are secreted directly into the blood by endocrine glands with no ducts in between.
Glands which act as endocrine as well as exocrine glands are called mixed glands. Pancreas is an example of mixed glands.
Some of the major glands of the endocrine system are pineal gland, hypothalamus, pituitary gland, thyroid gland, adrenal gland, thymus, testes and ovaries. Pineal gland secretes melatonin that regulates our sleeping pattern. Hypothalamus is situated at our forebrain and secretes neurohormone. Hypothalamus controls our body temperature, hunger and thirst and also connects the endocrine gland to the brain. Pituitary gland is situated at the base of the brain and it secretes growth hormone (STH); hypersecretion of STH leads to gigantism and hypo secretion leads to dwarfism. Pituitary gland is the smallest gland in the endocrine system, also known as master gland. Thyroid gland secretes thyroxine and it regulates mental, physical and sexual development.
Thyroid gland is the largest endocrine gland present in the neck between pharynx and larynx which secretes thyroxine. Iodine is required for the proper functioning of thyroid gland. Goitre is caused due to improper secretion of thyroxine or deficiency of iodine.
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Endocrine Glands (Glands without ducts)
Exocrine Glands (Glands with Ducts)
Glands which do not possess any ducts are called endocrine glands; their secretions called hormones, are transported by the blood.
Glands possessing ducts to help to transport their secretions in the place of their action are called exocrine glands.
Examples of Endocrine and Exocrine glands
Thyroid, pituitary, hypothalamus and adrenal glands
Esophageal glands, Liver, sebaceous glands, lacrimal (tear producing) glands, mammary glands and salivary glands.
These secrete hormones which are chemical substances in the body.
These secrete digestive juices and other excretory products like sweat.