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What's the difference between the neuroendocrine system vs endocrine system?

What's the difference between the neuroendocrine system vs endocrine system?



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This is what I have understood so far:

Neuroendocrine system involved neuroendocrine cells (also known as neurosecretory cells) that receive nerve impulses by a sensory neuron to release neurohormones into the blood stream. The endocrine system releases hormones by endocrine cells into the blood stream when a receptor protein senses a stimulus.

Here are my questions:

  1. When it comes to the brain, are the neurosecretory cells located in the hypothalamus or the posterior pituitary gland or both?

  2. Is the hypothalamus and the posterior pituitary gland classified as neuroendocrine glands and is the anterior pituitary classified as an endocrine gland?

  3. If the posterior pituitary gland is indeed a neuroendocrine gland, is ADH and Oxytocin, which are both released by the posterior pituitary gland, classified as "neurohormones", not just the classic hormones?


Neuroendocrine systems can be defined as the sets of neurons, glands and non-endocrine tissues, and the neurochemicals, hormones, and humoral signals they produce and receive, that function in an integrated manner to collectively regulate a physiological or behavioral state.

The neuroendocrine system is the mechanism by which the hypothalamus maintains homeostasis, regulating reproduction, metabolism, eating and drinking behaviour, energy utilization, osmolarity and blood pressure. (Source)

The central neuroendocrine systems serve as an interface between the brain and many of the peripheral endocrine systems. This chapter discusses the hypothalamic control of anterior pituitary systems regulating stress, basal metabolism, growth, reproduction, and lactation. Each of these systems involves one or more hypothalamic releasing or inhibiting hormones, released from hypothalamic neurons that terminate in the portal capillary vasculature that projects from the median eminence at the base of the hypothalamus to the anterior pituitary gland. There, the hypothalamic hormones act upon subsets of anterior pituitary cells to regulate pituitary hormone release and downstream physiological functions. Other hypothalamic neuroendocrine cells control water/salt balance, and lactation/parturition, through the release of vasopressin and oxytocin from nerve terminals that arise in hypothalamus and project to the posterior pituitary gland. Together, these hypothalamic neuroendocrine functions enable the central nervous system to respond rapidly to internal or external environmental change, and to maintain a response through endocrine hormonal transducers. (Gore, 2013).

The endocrine system is a group of glands and other structures that release internal secretions called hormones into the circulatory system.

Endocrine organs are richly vascularized ductless organs that produce hormones. The epithelial cells of the organ secrete their hormone product directly into the bloodstream where, upon binding with specific receptors in target organs, cellular functions are affected. The endocrine systemincludes not only the endocrine glands (pineal, pituitary, thyroid, parathyroid, and adrenal) but also single cells and small clusters of cells in the thorax and abdomen known as paraganglia. This chapter addresses the thyroid, parathyroid, adrenal, pituitary and pineal glands, and paraganglia. In addition to size differences, several features of endocrine tissues differ between rodents and humans, and often between rodents. (La Perle & Dintzis, 2018).

Question 1

When it comes to the brain, are the neurosecretory cells located in the hypothalamus or the posterior pituitary gland or both?

Neurosecretory cells are found in the hypothalamus. (Source)

There are two types of neurosecretory cells: magnocellular cells and parvocellular cells. Magnocellular cellsare large cells, having long axons that terminate in the neurohypophysis (also known as the posterior pituitary). Magnocellular cells release the hormones vasopressin and oxytocin to the general circulation; we will talk about the physiology of these hormones in Conjoint 403. The parvocellular cells are small cells, with shorter axons that terminate at a capillary-rich bulge at the base of the hypothalamus known as the median eminence.

Question 2

Is the hypothalamus and the posterior pituitary gland classified as neuroendocrine glands…

No

… and is the anterior pituitary classified as an endocrine gland?

Yes.

The following is from: https://courses.lumenlearning.com/boundless-ap/chapter/the-pituitary-gland

(emphasis mine)

The posterior pituitary (or neurohypophysis) comprises the posterior lobe of the pituitary gland and is part of the endocrine system. Despite its name, the posterior pituitary gland is not a true gland; rather, it is largely a collection of axonal projections from the hypothalamus that terminate behind the anterior pituitary gland.

The pituitary gland is an endocrine gland, about the size of a pea, that sits in a small, bony cavity at the base of the brain whose secretions control the other endocrine glands and influence growth, metabolism, and maturation.

While the pituitary gland is known as the master endocrine gland, both of its lobes are under the control of the hypothalamus: the anterior pituitary receives its signals from the parvocellular neurons, and the posterior pituitary receives its signals from the magnocellular neurons.

The anterior pituitary, also called the adenohypophysis, is a major organ of the endocrine system, and is the glandular, anterior lobe of the pituitary gland.

The anterior pituitary gland secretes 7 hormones: follicle stimulating hormone, luteinizing horomone, adrenocorticotropic horomone, thyroid stimulating horomone, prolactin, endorphins, and growth hormone.

The posterior pituitary gland does not synthesize any hormones. Hormones known as posterior pituitary hormones are synthesized by the hypothalamus, and include oxytocin and antidiuretic hormone (ADH), also called arginine vasopressin or vasopressin (Liu, 2007). The hormones are then stored in neurosecretory vesicles (Herring bodies) before being secreted by the posterior pituitary into the bloodstream.

With regard to neurohormones mentioned in question 3, neurohormones are hormones that are produced by neurosecretory cells and released by nerve impulses (e.g., norepinephrine, oxytocin, vasopressin).

This is the part which can be confusing. Whilst ADH and oxytocin are released from the posterior pituitary gland, which is an endocrine gland, the hormones are produced by neurosecretory cells within the hypothalamus and they are stored in and released from neurosecretory vesicles within the posterior pituitary gland. Therefore they are classed as neurohormones.

References

Gore, A. C. (2013). Neuroendocrine systems. In Fundamental Neuroscience (Fourth Edition) (pp. 799-817). doi: 10.1016/B978-0-12-385870-2.00038-X

La Perle, K. M. D., & Dintzis, S. M. (2018). Endocrine system. In Comparative Anatomy and Histology (pp. 251-273). Academic Press. doi: 10.1016/B978-0-12-415759-0.00058-3

Liu, K. D. (2007). Hyponatremia and Hypernatremia. In Critical Care Secrets (Fourth Edition) (pp. 285-290). doi: 10.1016/B978-1-4160-3206-9.10044-8


Not all hormones enter the blood - just as a quick addendum to the thorough reply above, and as per a comment above stating not all hormones from neuroendocrine cells go into circulation - seems to be true: many of the neuroendocrine cells release hormones directly into the organ where those cells appear - as per the gut, heart, lungs - here's a nice visual overview

https://byjus.com/biology/hormones-heart-kidney-git/


Similarities and differences among neuroendocrine, exocrine, and endocytic vesicles

Secretory and endocytic vesicles have analogous functions as cyclic carriers between specific cellular compartments. The centrifugally functioning secretory system operates from the Golgi complex, whereas the centripetally functioning endocytic system operates from the cell surface. Further, within polarized epithelial cells the export traffic can be directed to a distinct plasmalemmal domain which distinguishes exocrine from endocrine secretion and import traffic can be directed transcellularly. These shuttle operations involve a special class of lipid-rich, protein-poor membranes that appear to use an inwardly directed H+-translocase activity to varying extents for pH-dependent sorting and for accumulation and concentration of transported molecules. Comparative analyses of purified membrane preparations from exocrine and endocrine sources identify compositional overlap between different types of shuttle membrane. However, the structural elements that specify a particular origin or destination for a given carrier or determine function in storage and stimulus-dependent shuttling remain unknown.


The endocrine pancreas consists of endocrine cells that are arranged in “islets” and release hormones into the bloodstream. Neuroendocrine tumors arise from endocrine cells in the pancreas, which cluster together like an island and are called islet cells. These cells play an important role in regulating the body’s blood sugar.

One type of pancreatic neuroendocrine tumor, ιnsulιnoma, may lead to too much ιnsulιn and cause blurred vision, headache, fast heartbeat, and feeling lightheaded, tired, weak, shaky, nervous, irritable, sweaty, confused, or hungry.

Another type, called glucagonoma, can cause high blood sugar and cause headaches, frequent urination, dry skin, and mouth, or feeling hungry, thirsty, tired, or weak.

What is a neuroendocrine tumor?

Neuroendocrine tumors (NETs) are an uncommon cancer of the neuroendocrine cells, which receive messages from the nervous system and then release hormones into the bloodstream. When a neuroendocrine cell becomes cancerous, it divides uncontrollably, without stopping, forming tumors.

Primary sites for neuroendocrine tumors

NETs can occur throughout the body, but most commonly form in the:

Since they arise in hormone-producing cells, a neuroendocrine tumor can overproduce hormones and release them into the bloodstream, causing a range of symptoms. These symptoms are commonly mistaken for other conditions such as irritable bowel syndrome, colitis, asthma, or menopause. One in two neuroendocrine tumor patients is misdiagnosed. On average, people have symptoms for five years before learning they have a neuroendocrine tumor. When it takes that long to obtain an accurate diagnosis, cancer can spread to other organs. More than half of NETs spread beyond the primary site before they are diagnosed.


Contents

Intestinal enteroendocrine cells are not clustered together but spread as single cells throughout the intestinal tract. [7]

Hormones secreted include somatostatin, motilin, cholecystokinin, neurotensin, vasoactive intestinal peptide, and enteroglucagon. [9] The enteroendocrine cells sense the metabolites from intestinal commensal microbiota and, in turn, coordinate antibacterial, mechanical, and metabolic branches of the host intestinal innate immune response to the commensal microbiota. [10]

K cell Edit

K cells secrete gastric inhibitory peptide, an incretin, which also promotes triglyceride storage. [11]

L cell Edit

L cells secrete glucagon-like peptide-1, an incretin, peptide YY3-36, oxyntomodulin and glucagon-like peptide-2. L cells are primarily found in the ileum and large intestine (colon), but some are also found in the duodenum and jejunum. [12]

I cell Edit

I cells secrete cholecystokinin (CCK), and are located in the duodenum and jejunum. They modulate bile secretion, exocrine pancreas secretion, and satiety. [13]

G cell Edit

Stomach enteroendocrine cells, which release gastrin, and stimulate gastric acid secretion. [14]

Enterochromaffin cell Edit

Enterochromaffin cells are enteroendocrine and neuroendocrine cells with a close similarity to adrenomedullary chromaffin cells secreting serotonin. [15]

Enterochromaffin-like cell Edit

Enterochromaffin-like cells or ECL cells are a type of neuroendocrine cell secreting histamine.

N cell Edit

Located in the jejunum, N cells release neurotensin, and control smooth muscle contraction. [16]

S cell Edit

S cells secrete secretin from the duodenum and jejunum, and stimulate exocrine pancreatic secretion. [13]

D cell Edit

Also called Delta cells, D cells secrete somatostatin.

Mo cell (or M cell) Edit

Gastric enteroendocrine cells are found in the gastric glands, mostly at their base. The G cells secrete gastrin, post-ganglionic fibers of the vagus nerve can release gastrin-releasing peptide during parasympathetic stimulation to stimulate secretion. Enterochromaffin-like cells are enteroendocrine and neuroendocrine cells also known for their similarity to chromaffin cells secreting histamine, which stimulates G cells to secrete gastrin.

Pancreatic enteroendocrine cells are located in the islets of Langerhans and produce most importantly the hormones insulin and glucagon. The autonomous nervous system strongly regulates their secretion, with parasympathetic stimulation stimulating insulin secretion and inhibiting glucagon secretion and sympathetic stimulation having opposite effect. [20]

Rare and slow growing carcinoid and non-carcinoid tumors develop from these cells. When a tumor arises it has the capacity to secrete large volumes of hormones. [2] [21]

The very discovery of hormones occurred during studies of how the digestive system regulates its activities, as explained at Secretin § Discovery.


The endocrine system relies on hormones to elicit responses from target cells. These hormones are synthesized in specialized glands at a distance from their target, and travel through the bloodstream or inter-cellular fluid. Upon reaching their target, hormones can induce cellular responses at a protein or genetic level.

This process takes significantly longer than that of the nervous system, as endocrine hormones must first be synthesized, transported to their target cell, and enter or signal the cell. However, although hormones act more slowly than a nervous impulse, their effects are typically longer lasting.

Additionally, the target cells can respond to minute quantities of hormones and are sensitive to subtle changes in hormone concentration. For example, the growth hormones secreted by the pituitary gland are responsible for sustained growth during childhood.


The Peripheral Nervous System

The peripheral system (PNS) is composed of nerves that extend outside of the central nervous system. The nerves and nerve networks that make up the PNS are actually bundles of axons from neuron cells. The nerve bundles can be relatively small or large enough to be easily seen by the human eye.

The PNS is further divided into two different systems: the somatic nervous system and the autonomic nervous system.

Somatic Nervous System

The somatic nervous system transmits sensory communications. It is responsible for voluntary movement and action. It is composed of sensory (afferent) neurons and motor (efferent) neurons.

Sensory neurons carry information from the nerves to the brain and spinal cord while motor neurons transmit information from the central nervous system to the muscle fibers.

Autonomic Nervous System

The autonomic nervous system is responsible for controlling involuntary functions such as heartbeat, respiration, digestion, and blood pressure. The system is also involved in human emotional responses such as sweating and crying.

The autonomic nervous system is subdivided into the sympathetic nervous system and parasympathetic nervous system.

  • Sympathetic nervous system: The sympathetic nervous system controls the body’s response to an emergency. When the system is aroused, your heart and breathing rates increase, digestion slows or stops, the pupils dilate and you begin to sweat. Also known as the fight-or-flight response, the system is preparing your body to either fight the danger or flee.
  • Parasympathetic nervous system: The parasympathetic nervous system counters the sympathetic system. After a crisis or danger has passed, the system helps to calm the body by slowing heart and breathing rates, resuming digestion, contracting the pupils, and stopping sweating.

Difference Between Nervous System and Endocrine System

The main difference between the Nervous System and the Endocrine System is that the Nervous System uses electrical signals or impulses and Endocrine System uses chemical messengers to send signals.

Nervous System vs. Endocrine System

The nervous system is composed of neurons, nerves, and glial cell while the Endocrine system is composed of endocrine glands. The nervous system transmits signals electrically and chemically, whereas Endocrine system transmits signals through chemicals. The nervous system involves the conduction of impulse while Endocrine system does not involve the conduction of impulses. The nervous system works through chemicals like serotonin, epinephrine, etc. while the Endocrine system works through chemicals called hormones. The nervous system shows response in milliseconds, on the other hand Endocrine system shows response depending upon the nature of hormone involved e.g. from seconds to days.

Comparison Chart

Nervous SystemEndocrine System
The Nervous system is the system that comprises of a complex network of nerves, neurons, and glial cells and acts as messenger controlling different functions of the body.The endocrine system is the system of various ductless glands that secrete hormones which maintain homeostasis and growth and development of the body.
Mode of Signaling
Electrical, ChemicalChemical
Chemical Messengers
Neurotransmitters e.g Serotonin, NorepinephrineHormones
Onset Time of Response of Target Cell
MillisecondRequires more time than neuronal signaling and time differs for different hormones.
The End Time of Response
Response ceases quickly after the end of neuronal signaling.The response shown by the Endocrine system stays longer.
Specificity
Neuronal signaling is specific in its action.Endocrine signaling is less specific in its action.
Response to Changes in the Environment
The nervous system shows quick response to rapid changes in the environment.The endocrine system shows late response to rapid changes in the environment.
Distance Traveled
Always shortLong or short
Targeted Environment
Internal or externalInternal

What is the Nervous System?

The Nervous system is a complex organ system. The Nervous system comprises of a complex network of nerves, neurons, and glial cells. The neurons are primary cells of the nervous system. The neurons are responsible for computation and communication associated with neurons. Glial cells play a supportive role. The function of Nervous system is that it carries messages in the form of impulses from the body to the brain and spinal cord, data in messages are integrated into the brain, and after processing of data in the brain, the impulses are conducted from brain and spinal cord to body for response. The nervous system has two further subdivisions — the central nervous system CNS and peripheral nervous system PMS. The CNS comprises of brain enclosed in the cranium and spinal cord enclosed in the vertebral column. The CNS has numerous centers which are subdivided to the brain and spinal cors and are necessary for the integration of data. The PNS comprises of spinal and cranial nerves which are linked to brain and spinal cors. The PNS is named so because its location is on the periphery, beyond the central position. The PNS is subdivided into the somatic nervous system and autonomic nervous system. The somatic nervous system controls functions of skin, bones, joints, and skeletal system voluntarily. The autonomic nervous system controls functions of internal organs, smooth and cardiac muscles, and blood vessels. The Nervous system is also associated with some disorders which affect its activity these disorders include Alzheimer’s disease, Bell’s palsy, cerebral palsy, epilepsy, motor neuron disease, multiple sclerosis, etc.

What is the Endocrine System?

The endocrine system is the system of various ductless glands that secrete hormones which are chemical messengers. Ductless glands of the endocrine system are called endocrine glands. Hormones circulate in the blood to affect specific organs. The endocrine system helps to maintain the homeostasis in the body. The endocrine system develops a connection between the hypothalamus and all parts of the body which are involved in different functions like growth and development, metabolism, and reproduction. The endocrine system releases two types of hormones, steroidal hormones, and protein-based hormones. The endocrine system regulates its hormones except in case of childbirth through the feedback mechanism. The immune system also helps the endocrine system in regulating the levels of the hormones. The Endocrine system works by main endocrine glands which include the pituitary gland, thyroid gland, parathyroid gland, adrenal gland, pancreas, and gonads. Hormones of these glands act non specifically, e.g. Oxytocin in the uterus causes uterine contractions while Hormones of the endocrine system target the cell depending upon the nature of the hormone. In case of the steroidal hormone, the hormone diffuse through the cell membrane of the target cells binds to receptor protein which activates DNA segment leading to activation of the particular gene ultimately leading to the production of enzymes for different physiological functions. The water-soluble hormones bind to a protein receptor on the surface of the cell membrane. The receptor protein stimulates the production of second messengers, which help in the production of different physiological actions. The endocrine system if do not work properly then different endocrine disorders occur, e.g. in case of thyroid gland disorders are Hypothyroidism, gigantism, dwarfism

Key Differences

  1. The nervous system is composed of neurons, nerves, and glial cell, while the Endocrine system is composed of endocrine glands.
  2. The nervous system works through chemicals and nerves, whereas the Endocrine system works through chemicals.
  3. The nervous system gives response quickly on the other hand, the Endocrine system delays in response as compared to the nervous system.
  4. The nervous system shows response to both internal and external environment change while the Endocrine system shows a response to change in the internal environment.

Conclusion

The main conclusion of the above discussion is that both the Nervous system and endocrine system are the body’s messenger systems and important for normal physiology of the body.

Janet White

Janet White is a writer and blogger for Difference Wiki since 2015. She has a master's degree in science and medical journalism from Boston University. Apart from work, she enjoys exercising, reading, and spending time with her friends and family. Connect with her on Twitter @Janet__White


Paracrine Signaling

Figure 2. The distance between the presynaptic cell and the postsynaptic cell—called the synaptic gap—is very small and allows for rapid diffusion of the neurotransmitter. Enzymes in the synaptic cleft degrade some types of neurotransmitters to terminate the signal.

Signals that act locally between cells that are close together are called paracrine signals. Paracrine signals move by diffusion through the extracellular matrix. These types of signals usually elicit quick responses that last only a short amount of time. In order to keep the response localized, paracrine ligand molecules are normally quickly degraded by enzymes or removed by neighboring cells. Removing the signals will reestablish the concentration gradient for the signal, allowing them to quickly diffuse through the intracellular space if released again.

One example of paracrine signaling is the transfer of signals across synapses between nerve cells. A nerve cell consists of a cell body, several short, branched extensions called dendrites that receive stimuli, and a long extension called an axon, which transmits signals to other nerve cells or muscle cells. The junction between nerve cells where signal transmission occurs is called a synapse. A synaptic signal is a chemical signal that travels between nerve cells. Signals within the nerve cells are propagated by fast-moving electrical impulses. When these impulses reach the end of the axon, the signal continues on to a dendrite of the next cell by the release of chemical ligands called neurotransmitters by the presynaptic cell (the cell emitting the signal). The neurotransmitters are transported across the very small distances between nerve cells, which are called chemical synapses (Figure 2). The small distance between nerve cells allows the signal to travel quickly this enables an immediate response, such as, Take your hand off the stove!

When the neurotransmitter binds the receptor on the surface of the postsynaptic cell, the electrochemical potential of the target cell changes, and the next electrical impulse is launched. The neurotransmitters that are released into the chemical synapse are degraded quickly or get reabsorbed by the presynaptic cell so that the recipient nerve cell can recover quickly and be prepared to respond rapidly to the next synaptic signal.


Basic Plan of the Nervous System

Motor Systems are Organized Hierarchically

There are three different motor systems: skeletal, autonomic, and neuroendocrine. The first controls striated muscles responsible for voluntary behavior the second controls smooth and cardiac muscle, and many glands and the third controls pituitary gland hormone secretion. The skeletal motor system is understood best and thus serves as a prototype for examining basic organizing principles presumably similar for all three.

The skeletal motor system is arranged hierarchically ( Fig. 2.17 ), the lowest level consisting of brainstem-spinal cord α-motoneurons whose axons synapse directly on striated muscle fibers. The next higher level consists of motor pattern generators (MPGs), and the highest level has motor pattern initiators (MPIs) that “recognize” or alter their output in response to specific input patterns and project to unique sets of MPGs. Ethologists refer to MPIs as “innate releasing mechanisms.” One reason central neural circuitry is so complex is that each of the three input types (sensory, intrinsic, cognitive) may go directly to each general level of the motor system hierarchy.

Figure 2.17 . Hierarchical organization of the skeletal motor system. At the simplest level (1), motoneuron pools (MN) innervate individual muscles generating individual components of behavior. At the next higher level (2), additional interconnected interneuron pools, called motor pattern generators (MPG), innervate specific motoneuron pool sets. At the highest level (3), additional interconnected interneuron pools, called motor pattern initiators (MPI), innervate specific MPG sets. MPIs can activate complex, stereotyped behaviors when activated (or inhibited) by specific patterns of sensory, intrinsic, and/or cognitive inputs. Note that MPGs and MPIs themselves may be organized hierarchically (dashed lines) and that sensory, intrinsic, and cognitive inputs may go directly to any level of the motor system hierarchy.

The MPGs and MPIs themselves are hierarchically arranged. This organization is particularly easy to see conceptually for the MPGs subserving locomotor behavior. In the spinal cord, simple MPGs coordinate the reciprocal innervation of muscle pair antagonists across individual joints, more complex MPGs coordinate activity in the set of simpler MPGs for all the joints in a limb, and still more complex MPGs coordinate activity in MPGs for all four limbs. At the next higher level there is a brain hierarchy of MPIs for locomotion that is activated by specific input patterns and projects to the spinal locomotor pattern generator network.


Definition

Endocrine Glands: Endocrine glands are a type of glands that secrete substances (hormones) into the blood stream.

Exocrine Glands: Exocrine glands are a type of glands which release its secretion external to or at the surface of an organ with the help of a canal or duct.

Ducts

Endocrine Glands: Endocrine glands are a type of ductless glands.

Exocrine Glands: Exocrine glands may or may not have ducts.

Secretion

Endocrine Glands: Exocrine glands secrete into the blood.

Exocrine Glands: Endocrine glands pour their secretions directly at the site of action.

Type of Secretion

Endocrine Glands: Endocrine glands secrete hormones.

Exocrine Glands: Exocrine glands secrete enzymes.

Target

Endocrine Glands: The target of the endocrine glands is located away from the gland.

Exocrine Glands: The target of the exocrine glands is found very close to the gland.

Response Time

Endocrine Glands: The response of endocrine glands is delayed since the secretion should be transported through the blood to the target organ.

Exocrine Glands: Exocrine glands show a rapid response since the substances are secreted directly to the target organ.

Function

Endocrine Glands: The exocrine glands mainly control long term activities of the target organs.

Exocrine Glands: The secretions of the endocrine glands mainly control short term activities of the body.

Types

Endocrine Glands: Primary endocrine glands and the secondary endocrine glands are the two types of endocrine glands found in the body.

Exocrine Glands: Unicellular exocrine glands, multicellular exocrine glands, merocrine glands, apocrine glands, serous glands, mucous glands, and mixed glands are the types of exocrine glands found in the body.

Examples

Endocrine Glands: The thyroid gland, pituitary gland, and adrenal glands are the examples of endocrine glands.

Exocrine Glands: The gastric glands, salivary glands, and sweat glands are the examples of exocrine glands.

Conclusion

Endocrine glands and exocrine glands are the two types of glands which produce and secrete chemical substances to regulate the functions of the body. Endocrine glands mainly secrete hormones. Since endocrine glands lack ducts, the secretions of the gland are directly released to the blood. Exocrine glands secrete enzymes and mucus. Most exocrine glands are composed of ducts as well. The main difference between endocrine glands and exocrine glands is the structure and function of each gland.

Reference:

1. “Endocrine Glands.” Visible Body – Virtual Anatomy to See Inside the Human Body. N.p., n.d. Web. Available here. 24 July 2017.
2. Darling, David. “Exocrine glands.” The Worlds of David Darling. N.p., n.d. Web. Available here. 24 July 2017. .

Image Courtesy:

1. “Illu endocrine system” Public Domain) via Commons Wikimedia
2. “Centroacinar cells” By Mikael Häggström – Basic histology – Junqueira & Carneiro, ISBN 0-07-144091-7, McGraw-Hill Education 2005 (Public Domain) via Commons Wikimedia

About the Author: Lakna

Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things