Glands: Exocrine and Endocrine Glands, Practice Problems and FAQs

In a hot summer, we will be sweating too much. In the same way while playing we sweat a lot. We feel more thirsty and drink more water during this time. But no matter how much water you drink, more water will be lost from your body in the form of sweat. Right? 

                                                        Fig: Playing

What happens if you get emotional, be it happy or sad. You will get tears in your eyes. Can you tell me where these liquids are coming from or where are they stored in our body? Yes they are coming from sweat glands and tear glands or lacrimal glands respectively. 

So what do you think about the secretions of our body which regulates the physiological functions like growth, sexual development, blood pressure etc? Are they similar to those secretions from the skin and eyes? You might have heard that when we get anxious or frightened some chemicals are secreted inside the body. But all these secretions in our body are not produced from a single site. All the secretions have different compositions and different functions too. Let’s try to find out the answers to all these questions in this article by understanding different types of glands in depth. 

Table of contents

• Glands 
• Exocrine glands
• Endocrine glands
• Practice Problems
• FAQs

Glands

Glands are organs which produce and release chemical substances that perform a specific function in the body. They are of different types.

Types of glands

There are two types of glands present in the body. They are the exocrine glands and endocrine glands.

                                                             Fig: Types of glands

Exocrine glands

These glands secrete their products into specific ducts that carry the secretions into body cavities, lumen of an organ and the outer surface of the body. Exocrine glands are found in a variety of organs and they have a variety of roles in our body. Exocrine glands include sudoriferous (sweat) glands, sebaceous (oil) glands, mucous glands and digestive glands. Generally the skin, the gastrointestinal tract, or respiratory tract are also called exocrine glands.

                                       Fig: Exocrine glands 

Structure of the exocrine glands

The exocrine glands have two components in their structure. They are the glandular region and ductal region.

                           Fig: Structure of exocrine glands

Ductal region

This region is shaped like a tube. It is a single, thick, cuboidal cell wall that aids in secretory movement. The duct may be branched or unbranched. It is normally present in a simple coiled form.

Glandular region

The glandular region is responsible for the production of chemical substances that are secreted. This cell cluster might be circular or elongated. The cells present in this region are dependent on the substances released. Serous cells, for example, release proteins, while mucous cells exude fluids.

Functions of exocrine glands

The major functions of the exocrine glands are the regulation of body temperature, lubrication, lactation etc. They also help in the process of digestion and reproduction.

Types of exocrine glands

Exocrine glands help several organs in our body to function properly. Exocrine glands are classified as follows:

• Sweat glands
• Sebaceous glands
• Tear glands
• Ceruminous glands
• Mammary glands
• Digestive glands

Sweat glands

Sweat is produced and secreted by sweat glands. These sweat glands produce a clean, non-oily sweat that aids in body temperature regulation. It is of two types as follows:

Eccrine glands

These glands cover nearly the entire body surface. They directly open on the surface of the skin. 

Apocrine glands

These glands open into the hair follicle that leads to the surface of the skin.

Apoeccrine glands

They secrete more sweat compared to both eccrine and apocrine sweat glands. They play an important role in sweating. They are mostly sensitive to cholinergic activity. They can also be activated by adrenergic stimulation too. They commonly secrete a thin and watery sweat.

Sebaceous glands

Skin also possess sebaceous glands which open into hair follicles. Sebum is produced by sebaceous glands. Sebum is an oily fluid that preserves and lubricates the hair and skin.

                                  Fig: Sweat glands and sebaceous glands

Tear glands

Tear glands are also called lacrimal glands. They are found just above the upper eyelids. Every time we blink, they produce and exude a small amount of fluid that enters our eyes. This fluid aids in the moisturisation of the eyes.

                                                  Fig: Structure of tear glands

Ceruminous glands

They are glands found in the ears. They aid in the production of earwax or cerumen. Ear wax protects ears from infection and physical injury. Cerumen helps in trapping dust particles and repels water away from the tympanic membrane.

                                Fig: Location of ceruminous glands

Mammary glands

These are the modified sweat glands located in the chest region in mammals. They remain underdeveloped till puberty. Milk is produced by mammary glands in females during pregnancy. Milk is a nutrient rich secretion which gives nourishment to the baby. The first milk called colostrum contains the secretory antibody called IgA1 which protects the baby from infections. 

                     Fig: Structure of mammary gland

Digestive glands

In addition to the above glands, digestive glands are also present in the body. This mainly helps in the digestion process in the alimentary canal. They are as follows:

• Salivary glands
• Gastric glands
• Intestinal glands
• Liver 
• Pancreas

Salivary glands

They are glands that produce and secrete saliva. It aids in chewing, swallowing, and digestion of different food items. It also lubricates and protects tissues present in the inner lining. They are of three types normally as follows:

• Parotid gland
• Sublingual gland
• Submandibular gland or submaxillary gland

                                Fig: Location of salivary glands

Gastric glands

Glands in the stomach are called gastric glands. They release gastric juice which possess enzymes that aid in the digestion of food materials. 

                                               Fig: Structure of gastric glands

Intestinal glands 

They are present in the small intestine. They are of two types as follows: 

• Brunner’s glands
• Crypts of Lieberkuhn

Brunner’s glands

They are located in the first part of the small intestine known as the duodenum. Mucus produced by the Brunner’s glands protects duodenum from stomach acid (HCl). They also help in the digestion and absorption of nutrients.

Crypts of Lieberkuhn

Glandular cells which are present in the pits of the villi in the gastrointestinal tract are called crypts of Lieberkuhn. They are composed of specialised secretary cells which secrete intestinal juice. 

                      Fig: Brunner’s gland and crypts of Lieberkuhn 

Liver

Liver is the largest digestive gland. It secretes bile into the duodenum part of the small intestine via the hepatopancreatic ducts. Bile from the liver helps normally in the emulsification of fats.

                                                  Fig: Liver

Pancreas

The pancreas is the second largest digestive gland which secretes pancreatic juice into the duodenum via the hepatopancreatic duct. It is a heterocrine gland and shows both endocrine and exocrine activities. Islets of Langerhans are the endocrine part that produce hormones whereas pancreatic acini are the exocrine part that produces enzymes. 

                                    Fig: Pancreas

Mechanisms of secretion of exocrine glands

Merocrine, apocrine, and holocrine are the three processes by which exocrine glands discharge their secretions.

Merocrine glands

The most prevalent subtype of exocrine glands are merocrine glands. Exocytosis is considered as the process by which merocrine gland secretions normally leave the cell. There is no cell destruction in this form of secretion. The eccrine sweat gland is an example of merocrine secretion.

Apocrine glands

Apocrine glands, on the other hand, develop membrane buds that break off into the duct. It results in the loss of a portion of the cellular membrane. The mammary gland, which produces breast milk, is considered as one of the well-known apocrine glands.

Holocrine secretion

It occurs when the cellular membrane ruptures and the product is released into the duct. Holocrine secretion is shown by sebaceous glands.

Disorders of exocrine glands

Exocrine glands are spread throughout the body and they might be affected by a variety of conditions and disorders. These are as follows:

Hyperhidrosis

It is the medical term used for excessive sweating. It happens when sweat glands create more sweat than the body requires.

Bromhidrosis

Excessive body odour is called bromhidrosis. When bacteria on the skin begins to break down dried sweat, it causes bromhidrosis.

Acne vulgaris

It occurs when the sebaceous glands become clogged with sebum. This causes pimples by releasing free fatty acids, which cause an inflammatory response.

                             Fig: Acne vulgaris

Sjögren's syndrome

It is an autoimmune disorder. It lowers the quantity of moisture produced by salivary and lacrimal glands. This results in a dry mouth and eyes normally.

              Fig: Common symptoms of Sjögren's syndrome

Mammary duct ectasia

The swelling and thickening of milk ducts is known as mammary duct ectasia. Milk ducts may get blocked as a result of this condition.

Cystic fibrosis

It is a disease that causes sticky, thick mucus to accumulate in organs such as the lungs and pancreas. It is caused by the mutation in a protein required for the production of mucus.

                      Fig: Common symptoms of cystic fibrosis

Brunner's gland hyperplasia

Brunner's gland hyperplasia is a benign (noncancerous) tumour of the duodenum.

Pancreatitis

Pancreas may cease generating digestive enzymes as a result of pancreatitis. Enzymes are required for food digestion in the small intestine and hence it will affect the various digestive processes.

                                 Fig: Common symptoms of pancreatitis

Endocrine system

Endocrine system is a system of glands that secrete hormones to control and coordinate various physiological processes. 

Endocrine glands

They are the ductless glands. They are able to release their secretions called hormones directly into the bloodstream. Substances secreted by endocrine glands act as chemical messengers. The various endocrine glands present in the human body are as follows: 

• Pituitary gland
• Pineal gland
• Thyroid gland 
• Adrenal gland 
• Pancreas
• Parathyroid gland
• Thymus gland
• Gonads (testis in males and ovary in females)

Apart from these glands there are some other organs which can produce hormones, especially the local hormones. They are the gastrointestinal tract and kidneys. 

Hormones

Hormones are chemical messengers produced in response to a specific stimulus. They are the non-nutrient chemical messengers that are transported to target cells. They are produced in trace amounts.

                          Fig: Endocrine glands in the human endocrine system

Major endocrine glands

Hormones are produced by the following types of endocrine glands:

Hypothalamus

It is a gland in the fore brain that regulates the endocrine system. It uses information from the neural system to determine when to notify other glands to create hormones, including the pituitary gland. The hypothalamus is in charge of several bodily functions, including mood, hunger, thirst, sleep patterns, and sexual function. It can control the production of hormones from the pituitary gland.

                                                Fig: Location of hypothalamus

Hormones secreted by hypothalamus

The hormones secreted by hypothalamus are as follows:

• Thyrotropin releasing hormone (TRH)
• Growth hormone releasing hormone or somatotropin releasing hormone (GHRH OR SRH)
• Growth hormone inhibiting hormone (GHIH)
• Prolactin releasing hormone (PRH)
• Corticotropin releasing hormone (CRH)
• Melanocyte releasing hormone (MRH)
• Melanocyte inhibiting hormone (MIH)
• Oxytocin 
• Vasopressin or ADH (Antidiuretic hormone)

Pituitary gland

This tiny gland is approximately the size of a pea, but it performs a critical function. It produces hormones that regulate the thyroid gland, pineal gland, thymus gland, adrenal glands, ovaries, and testicles. Hence it is called the master gland. The pituitary gland controls a variety of processes including growth. It is located at the very bottom of our brain. 

                                              Fig: Structure of pituitary gland

Hormones released by anterior pituitary

The hormones released by anterior pituitary are: 

• Growth hormone (GH) or somatotropic hormone (STH) or somatotropin 
• Thyroid stimulating hormone (TSH)
• Adrenocorticotropic hormone (ATH)
• Prolactin (PRL) or luteotropic hormone (LTH)
• Gonad stimulating hormones (GSH) or gonadotropins
  • Follicle stimulating hormone (FSH)
  • Luteinizing hormone (LH)

Hormones released by the intermediate lobe of pituitary

Only one hormone is released by the intermediate lobe and it is the melanocyte stimulating hormone (MSH).

Hormones released by the posterior pituitary

The hormones stored and secreted by the posterior pituitary are as follows:

• Oxytocin 
• Vasopressin or Antidiuretic hormone (ADH)
   

Pineal gland

This gland regulates the sleep wake cycle by secreting melatonin. It controls the circadian rhythm or the 24 hour diurnal rhythm of the body. 

                                                       Fig: Location of pineal gland

Hormones of the pineal gland

The hormones released by the pineal gland are as follows:

• Melatonin
• Serotonin 

Thyroid gland

It is a butterfly-shaped gland located in front of the trachea. It is in charge of metabolism.

                      Fig: Location of thyroid gland

Hormones released by the thyroid gland

The hormones released by the thyroid gland are as follows:

• Thyroxine or tetraiodothyronine or T4
• Triiodothyronine or T3
• Thyrocalcitonin 

Parathyroid glands

These are four small glands of about the size of a grain of rice. They are located on the posterior surface of the thyroid gland. They regulate the calcium levels in the body. Calcium is required for the proper functioning of the heart, kidneys, bones, and nervous system. 

                          Fig: Location of parathyroid gland

Hormones of parathyroid gland

Parathyroid glands secrete only one hormone and it is the parathyroid hormone (PTH) or parathormone. 

Thymus

The thymus is an endocrine gland that also plays a critical role in the immune system. Thymosins are tiny protein hormones secreted by the thymus. As a person grows older, the thymus shrinks in size. In the aged people, this inevitably leads to a weakened immune system.

                  Fig: Location of thymus gland

Hormone of the thymus gland

Thymus secretes only one hormone, which is thymosin.

Adrenal glands

Body possesses two adrenal glands. They are located on top of the kidneys. The various body activities like metabolism, blood pressure, sexual development, and stress response are controlled by them. It consists of the adrenal cortex and adrenal medulla.

                                                Fig: Location of adrenal gland

Hormones secreted by the adrenal gland

Hormones secreted by the adrenal cortex are considered as corticoids. They are as follows:

• Mineralocorticoids
• Glucocorticoids
• Gonadocorticoids 

Hormones secreted by the adrenal medulla are considered as catecholamines. They are as follows: 

• Adrenaline or epinephrine 
• Noradrenaline or norepinephrine

Pancreas

It is a part of our endocrine system and also plays an important role in digestion by producing enzymes. 

                      Fig: Location of pancreas

Hormones secreted by pancreas

Islets of Langerhans of pancreas consist of three types of cells that can secrete hormones. They are alpha cells, beta cells, and delta cells. The hormones secreted by these cells are as follows:

• Alpha cells - Glucagon
• Beta cells - Insulin
• Delta cells - Somatostatin

Ovaries

The ovaries in women produce the sex hormones oestrogen, progesterone, and testosterone. In the lower abdomen, women have two ovaries, one on either side of the uterus.

                     Fig: Location of ovaries

Hormones secreted by the ovaries

The various hormones secreted by the ovaries are as follows:

• Oestrogen 
• Progetstrone 
• Relaxin
• Inhibin 

Testes

They are also called testicles. In men they produce sperm and release the hormone called androgens. The male secondary sexual characters are under the influence of this hormone. Sperm production, physical strength, and sex drive are affected by this hormone.

             Fig: Location of testes

Hormones secreted by the testes 

The hormones secreted by the testes are as follows:

• Testosterone 
• Inhibin 

Development of endocrine system

All three embryonic germ layers in the embryo give rise to the endocrine system. The mesoderm gives rise to the endocrine glands that make steroid hormones, such as the gonads and adrenal cortex. The amine, peptide, and protein hormones are produced by endocrine glands that develop from the endoderm and ectoderm.

Difference between exocrine and endocrine glands

The major differences between the exocrine and endocrine glands are as follows: 

Practice Problems

Q 1. Which of the following statements are correct about exocrine glands?

1. Exocrine glands are ductless glands
2. Generally the skin, the gastrointestinal tract, or respiratory tract are called exocrine glands
3. The exocrine glands have two components to their structure. They are the glandular region and ductal region
4. The major functions of the exocrine glands are the regulation of body temperature, lubrication, lactation etc. 

a. A, B, C, D

b. A, B, C
c. B, C, D
d. All of the above

Answer: Exocrine glands secrete their products into ducts that carry the secretions into body cavities, lumen of an organ and the outer surface of the body. Exocrine glands are found in a variety of organs and perform a variety of roles in the body. They include sudoriferous (sweat) glands, sebaceous (oil) glands, mucous glands and digestive glands. Generally the skin, the gastrointestinal tract, or respiratory tract are called exocrine glands. Hence the correct option is c.

Q 2. Where are the hypothalamus, pituitary and pineal gland located?

a. Thoracic cavity 
b. Vertebral cavity 
c. Cranial cavity 
d. Abdominal cavity 

Answer: The cranial cavity or the intracranial space, is the space within the skull. This cavity encloses the brain. All the three glands, hypothalamus, pituitary gland and pineal gland are located in the forebrain. Hence the correct option is c.

Q 3. Identify ‘a’ , ‘b’ and ‘c’ in the figure given below.

a. A - Thyroid, B - Adrenal gland, C - Pancreas
b. A - Thymus, B - Pancreas, C - Adrenal gland
c. A - Parathyroid, B - Thymus, C - Pancreas
d. A - Thymus, B - Pancreas, C - Adrenal gland

Answer: Thymus gland, located in the thoracic region, is a site of maturation of T-lymphocytes. It degenerates with age. The adrenal gland is placed above the kidney in the body. The outer region of the adrenal gland is called cortex and inner is called medulla. The cortex region produces hormones called corticoids. Pancreas is a heterocrine gland. It has both endocrine and exocrine function. The endocrine part of the pancreas produces three hormones called somatostatin, insulin and glucagon. Hence the correct option is d.

Q 4. Explain the mechanism of secretion of exocrine glands?

Answer: Merocrine, apocrine, and holocrine are the three processes by which exocrine glands discharge their secretions. The most prevalent subtype is merocrine glands. Exocytosis is considered as the process by which merocrine gland secretions leave the cell normally. There is no cell destruction in this form of secretion. The eccrine sweat gland is an example of merocrine secretion. Apocrine glands, on the other hand, develop membrane buds which break off into the duct. It results in the loss of a portion of the cellular membrane. The mammary gland, which produces breast milk, is a well-known example of apocrine gland. Holocrine secretion occurs when the cellular membrane ruptures and the product is released into the duct. Holocrine secretion is shown by sebaceous glands.

FAQs

Q 1. Which are the animals that have sweat glands?
Answer: Other than humans, there are a variety of living species that can sweat. Horses, monkeys, apes, and hippos are the common examples. Dogs and cats do sweat a little through their paws. Horses and hippos produce some of the most peculiar sweat on the planet. Whales, dolphins, and porpoises are members of the Cetacea order of marine mammals. They don't have sweat glands because they spend so much time in water.

Q 2. Who is considered as the father of endocrinology?
Answer: The father of endocrinology is Charles Edward Brown-Sequard. He was a physician who made the first substantial contribution to the field of endocrinology in 1856. In a study presented to the Academy of Sciences in Paris, he stated that ‘removal of both adrenal glands from animals was lethal.’\

Q 3. When was the term hormones introduced?
Answer: Scientists began to believe that different organs in the body must communicate chemically in the years of the 1800s, and they realised later that extracts from endocrine tissues may be used to treat specific ailments. However, it wasn't until the early 1900s that the term ‘hormone’ was coined. In 1902, English physiologists William Bayliss and Ernest Starling came to the conclusion that molecules subsequently dubbed hormones were in charge of the secretion of the pancreas. This contradicted the widely held belief that the secretions were triggered by neural reflexes. Scientists eventually identified that pancreatic secretions were influenced by both hormonal and neurological mechanisms. In the early part of the twentieth century, the new word stimulated extensive research on the endocrine system, with scientists working feverishly to discover and comprehend it.

Q 4. What is the chemical composition of saliva?
Answer: Saliva is a complex physiological fluid made up of nearly all water, inorganic and organic compounds, and proteins such as enzymes, mucus, and glycoproteins. Saliva composition fluctuates during the day and between individuals. Sodium, potassium, calcium, bicarbonate, thiocyanate, and phosphate are among the ions found in saliva. Low molecular weight chemical compounds including uric acid and lactate, immunoglobulins, enzymes, and mucins, as well as some key hormones like cortisol, are all found in saliva.

YOUTUBE LINK: https://www.youtube.com/watch?v=AVRev-A5L4k

https://www.youtube.com/watch?v=8XI1_gISVME

Related Topics