Glands are a group of cells or organs of the human or animal body which play an important role to secrete particular chemical substances for various body functions. Generally, a gland consists of cuboidal or columnar epithelial cells which are located on a basement membrane. They are enveloped by a plexus or meshwork of blood vessels. Glands in the body are classified into the following two categories: 1. Exocrine glands and 2. Endocrine glands.
Exocrine Glands
There are several glands which are responsible to secrete substances for making the body lubricated or protect the body. These types of glands collectively make up the exocrine system. They work independently and sometimes can cause disorders when they cannot function properly.
Some important exocrine glands:
- Sebaceous gland
- Sweat gland
- Brunner’s glands
- Salivary gland
- Mammary gland
- Mucous gland
- Prostate gland
- Gastric gland
- Lacrimal gland
- Ceruminous gland, etc.
Image showing some exocrine glands (sebaceous and sweat glands)
Exocrine glands consist of duct portion and a glandular portion where the glandular portion is branched. The glandular portion consists of either a round or elongated cluster of cells. These cells are different types and produce various substances. The most common cells include serous cells which excrete protein and mucous cells which produce mucus. They also secrete saliva, oil, earwax, milk, digestive enzymes, etc. The tubular or duct portion consists of a single, cuboidal cell that has a thick wall which helps in movement of the secretion. They are simple in structure and also have a simple coiled structure.
Types of Exocrine Glands
There are two types of exocrine glands on the basis the complexity of glands:
- Unicellular exocrine glands and
- Multicellular exocrine glands.
Exocrine glands are also grouped into three categories in terms of how substances are excreted:
Holocrine glands: They produce oily substances which make the skin soft, cover the hair, and provide a glossy hair coat. It also promotes the retention of moisture and helps to maintain hydration. Examples: sebaceous glands.
Merocrine glands: They are also known as eccrine glands. They produce secretory products especially proteins via exocytosis. Generally, they release substances through pores or cellular channels. Examples: salivary gland, sweat gland, tears gland, goblet cells, and intestinal glands, etc.
Apocrine glands: Apocrine glands are found in the axillae, areolae, periumbilical region, anogenital region, eyelids, and external auditory canals. They release their secretory products which contain within membrane-bound vesicles. Examples: mammary gland, sweat gland, lips, skin around anus, pubic region, and nipples.
Characteristics of Exocrine Glands:
- Substances secreted from the exocrine glands respond very quickly and they are conveyed through ducts and released accurately at the target area for specific functions.
- Their secretions do not pass through the kidney and no re-absorption occurs.
- The effects of exocrine secretion do not last a long time.
Functions of Exocrine Glands:
Secretions from exocrine glands play a vital role and aid in regulating a number of essential body functions:
- The lacrimal glands which are located in the eyes that help to make sure the eyes do not dry out.
- Secretion from sweat glands helps to regulate body temperature.
- They help to lubricate the skin.
- They help in food digestion.
- They enhance to produce milk and aid in nurture newborns through lactation.
- They help to aid in reproduction.
- It maintains the body`s balance.
Endocrine Glands
The different types of glands of the body collectively make up the endocrine system which produces hormones and performs various functions of the body. They regulate the metabolism, growth and tissue functions. They also control sexual functions, reproduction, and many other activities.
The word endocrine is derived from the Greek words ‘endo’ meaning within, and ‘crinis’ meaning to secrete. Endocrine glands secrete chemical substances into the blood which are known as hormones. Hormones maintain homeostasis and regulate the various physiological functions of the body. Some notable physiological functions include metabolism, growth, development, reproductions, mood and sleep with many other functions. Hormones also perform functions like a messenger responsible for instructing the body to do or prevent doing something.
The term hormone is derived from Greek word, hormao meaning to excite or to stimulate. British Scientist Starling and Bayliss (1904) first of all used the term hormone. They defined the hormone as any substrate normally produced in the cells in some part of the body and carried by the blood or lymph stream to distant parts which it affects for the good of the body as a whole.
The hormone can reach long distances through the bloodstream and can act over target organ to co-ordinate activity. This activity is also known as neuroendocrine. In the digestive system, some short-range endocrine activity also occurs which is also known as a paracrine activity.
Image showing endocrine glands
The endocrine glands are classified into:
- 1Discrete Endocrine Glands: They include- the pituitary gland (hypophysis), thyroid, parathyroid, adrenal and pineal glands.
- 2Endocrine component of glands with both an Endocrine and an Exocrine Function: They include- the kidney, pancreas, and gonads (testes and ovaries) and
- 3Diffuse Neuroendocrine system: It includes APUD cells.
Functions of Endocrine Gland
- It produces chemical substances, hormones which keep the body going.
- It maintains the metabolism of the body.
- It is responsible for the development of the body.
- It is also responsible for tissue features, sexual activities.
- It helps to make the body muscle and regulate the growth of bones.
Difference between Endocrine and Exocrine Glands
| Endocrine Glands | Exocrine Glands |
|---|---|
| They are ductless glands. | They are also known as duct glands. |
|
They release chemical substances into the bloodstream which are also known as hormones. |
They release substances through various ducts which are also known as enzymes. |
|
They are responsible for regulating growth, breast milk production, reproductive functions, etc. |
They are responsible for regulating temperature of the body, digestion, and keeping the eyes from drying out, etc. |
|
They are located near the target site and perform various functions at the target region. |
They are located far away from the target site and perform various functions at the target region. |
|
They secrete substances into the blood stream. |
They secrete substances and pour it directly at the site of action. |
|
They do not show rapid response because their secretions are conveyed through the blood stream to the target organ to complete their action. |
They exhibit a rapid response because they secrete the substances directly to the target organ to complete the action. |
|
The substances secreted from endocrine glands mainly regulate the long term activities of the target organs of our body. |
The substances secreted from the endocrine glands mainly regulate the short term activities of the target organs of our body. |
|
Examples: pituitary gland, thyroid gland, adrenal glands, parathyroid glands, pineal glands, testes, ovaries, etc. |
Examples: sweat glands, salivary glands, gastric glands, sebaceous glands, mammary glands, etc. |
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Concluding Remarks
Many physiological processes occur in the body of all living organisms. Among them, the basic physiological processes are metabolism, growth, responsiveness, reproduction, movements, respiration, digestion and excretion. To maintain life, these physiological processes should occur properly. In this case, secretions of endocrine and exocrine glands control the physiological processes of the body. The hormones secreted from endocrine gland serve as chemical messengers and regulate the physiology and behavior of the body while many enzymes secreted from the exocrine glands act as biological catalysts and speed up chemical reactions to perform many functions of the body.