Group 4
Members: Tony, Loc Bui, Jodie, Thomas
e-Facilitator: Cathy

The Exocrine & Endocrine System

Clinical Scenario
You have seen two patients this morning for an initial exam. The first one has complained of a severe dry mouth and after follow up salivary tests and clinical data you have confirmed that the patient has a severely compromised salivary flow. Your second patient disclosed in their medical history that they have an overactive thyroid gland, and at times suffers from anxiety attacks when subjected to high levels of stress.

Learning objectives:
  • define, compare and contrast the structure, location and function of endocrine and exocrine glands
  • discuss the physiology of both types of gland in the context of the above scenario
  • prepare and present an academic poster of your findings


· Introduction to Glands:

Endocrine Glands

Exocrine Glands


Salivary Glands:
- Histology of salivary glands:
- Structure:
- Parotid Gland:
- Submandibular Gland:
- Sublingual Gland:
- Minor Salivary Glands:

- Xerostomia & Clinical Relevance

The Thyroid Gland:

- Location and Structure:
- Normal Thyroid function:
- Abnormal function:
- Hyperthyroidism
- Graves Disease:
- Hypothyroidism:
- Hyperparathyroidism

Effects of Thyroid Disfunction on Oral Health
- Clinical Scenario

Introduction to Glands:

Glands arise during fetal life, from covering epithelia; epithelia where the cells are organised in layers that cover the external surface or line the cavities of the body, by means of proliferation and incursion of the epithelial cells into the subjacent connective tissue which is the followed by further cell differentiation.

Exocrine glands retain their connection with the surface epithelium from which they originated. This connection is transformed into tubular ducts lined with epithelial cells through which the glandular secretions go through to reach the surface. Endocrine glands are glands whose connections with the surface are lost during development. These glands are therefore ductless, and their secretions are picked up and transported to their site of action, by the bloodstream rather than by a duct system.

Exocrine Glands:

Exocrine glands are glands that produce secretions destined for the surface of an organ; numerous exocrine glands can be found inside the body, facilitating such processes as digestion. These glands can be separated into the secretory portion which contains the cells responsible for the secretory process, and the ducts, which transport the secretions. The duct system can be further divided into branched (compound gland) or unbranched (simple gland). The secretory portion of a compound or simple gland may be one of three structures;

(1) Tubular - secretory cells take on a tube-like shape

(2) Acinar - secretory cells take on a small, flask-like sac shape

(3) Tubuloacinar - both types of secretory cells present

Almost any combination of duct and secretory unit may occur. Exocrine glands can then be categorised by the mode by which they secrete:

(1) Apocrine Secretion - involves the discharge of membrane-bound, free, unbroken vesicles containing secretory products into the lumen. Examples include; goblet cells, some sweat glands, and the lipid component in the lactating mammary gland.

(2) Holocrine Secretion - involves the discharge of complete secretory cells with ensuing disintegration of the cells to release the secretory product into the lumen. Examples include; sebaceous glands of the skin and the meibomian glands on the eyelid, both of which, secrete their products along with the remnants of dead cells.

(3) Merocrine Secretion - cells that secrete via exocytosis from secretory vesicles opening into a gland's acinus and passing through an epithelial-walled duct or ducts and then onto a bodily surface or into the lumen, examples include sweat and salivary glands.

Image: Types of Multicellular Exocrine Glands

Marieb, N E & Hoehn, K (2007) Human Anatomy & Physiology, Seventh edition, Pearson Benjamin Cummings, p. 129 viewed October 8th 2009
external image Glands.jpg
Finally, exocrine glands can be classified by the products they secrete:

(1) Serous - glands that secrete proteins and enzymes, examples include chief cells and paneth cells
(2) Mucous - glands that secrete mucus, examples include oesophageal glands and pyloric glands
(3) Mixed - glands that secrete both proteins and mucus, examples include salivary glands

In general, all glands have a constant basal rate of secretion which is adapted by nervous and hormonal influences. The secretory portions of some exocrine glands are surrounded by contractile cells that are positioned between the secretory cells and the basement membrane. Similar to the mechanism of a muscle cell, these contractile cells have given rise to the labeling of myoepithelial cells; as these cells have common characteristics of both epithelial and muscle cells.

Some organs, like the liver, have both endocrine and exocrine functions, and one cell type may function both ways. In the liver, cells that secrete bile into the duct system also secrete some of their products into the bloodstream. In other organs, some cells are specialised in exocrine secretion and others are specialised in endocrine secretion. For example, in the pancreas, the acinar cells secrete digestive enzymes into the intestinal lumen, whereas the islet cells secrete insulin and glucagon into the bloodstream.

Major Glands:

Junqueira, L C & Carneiro, J (2005) Basic Histology: Text & Atlas, Eleventh Edition, McGraw Hill Medical, p. 79 – 80, viewed 22 August 2009
Young, W & Wheater, P R (2006) Wheater's Functional Histology: A Text and Colour Atlas,
Fifth Edition, Elsevier Health Sciences, p. 95, viewed 10 October 2009


o ensure that the human body maintains homeostatic balance, two main systems are involved in detecting and responding to changes in both the internal and external environment. The Endocrine system, which regulates changes in the internal environment, is comprised of endocrine glands which act by releasing chemical messages, also known as hormones, directly into the blood stream where they travel and work on specific target cells (Tortora & Grabowski, 2000) Its mode of action is generally involved with bodily changes which require extended durations and generally take longer to activate (Tortora & Grabowski, 2000)


The glands of the endocrine system are essentially formed from clusters of epithelial cells, embedded in a layer connective tissue which is surrounded by a rich blood supply (Sherwood, 2009). They may present as individual organs; the thyroid or adrenal gland, or they may occur as bundles of cells embedded in the of another organ; the pancreatic islets and the interstitial cells of the testis (Sherwood, 2009).
Differences can be seen between the endocrine glands and the exocrine glands, in that the endocrine glands do not possess excretory ducts, and thus their secretions are generally released directly to the interstitial tissues (Sherwood, 2009). The secretions may then be picked up by blood and lymph capillaries and transported around the body, where they affect specific target cells, which may be situated a fair distance from the initial gland (Tortora & Grabowski, 2000).
The hormones produced by the endocrine glands may be
- Held inside glandular cells, such as in the pituitary gland
- Stored extracellularly, such as in the thyroid
- Or be released directly into the blood stream immediately after production, such as in the adrenal cortex. (Sherwood, 2009)

These may be seen in particular cells as granules and droplets which can be enhanced and seen easier using chemical staining techniques (Sherwood, 2009).
Hormones only affect the target cells which they are specific to, as only the target cells contain complementary plasma membrane protein receptors which are able available for binding(Sherwood, 2009). The union of the hormone and its specific receptor site, results in a series of processes which brings about a bodily response. While some hormones only target a particular cell type, others exist which target a wide range of different cells (Sherwood, 2009).

Complete Endocrine function
o Pituitary
o Parathyroid
o Thyroid
o Adrenal Gland

varied Function
o Hypothalamus
o Thymus
o Heart
o Stomach
o Pancreas
o Duodenum
o Kidney
o Skin
o Testes (male)
o Ovaries (female)
o Placenta (in pregnant female)

Complete Function uncertain
o Pineal
Table Adapted from: Sherwood, L (2001) Human Phsiology From Cells to Systems, Fourth edition, Brooks/Cole p. 634-636, viewed September 29th 2009


Sherwood, L (2001) Human Phsiology From Cells to Systems, Fourth edition, Brooks/Cole p. 634-636, viewed September 29th 2009

The Function of the endocrine system, primarily involves activities which include:
o Maintaining a constant internal environment by regulating metabolism, water and electrolyte balance.
o Allowing the body to adapt to changes as a result of stress
o Encouraging developmental growth which is smooth and sequential
o Controlling of reproductive mechanisms.
o Regulating the rate of production of red blood cells.
o Manageing and combining circulation, digestion and the absorption of food with the help of the autonomic nervous system, (Sherwood, 2001)

Salivary Glands -

Histology of Salivary Glands:

Salivary glands are responsible for the production of saliva in the oral cavity. The production of saliva has many roles in aiding the oral cavity. Such roles involve lubrication for the oral cavity, mechanical digestion, immune response and buffering capacity to protect the oral mucosa from acids and bacteria (Fehrenbach & Balogh, 2006).

Anatomy of the salivary glands. (Edgar & Dawes, 2005 p.5)

There are three main salivary glands in the oral cavity consisting of the parotid glands, submandibular glands and sublingual glands. These are considered to be the major salivary glands. There are also minor mucous salivary glands. The histology of the gland differs according to the gland type (Edgar & Dawes, 2004). The parotid glands are a serous type gland whereas the sublingual and submandibular glands are a mix of both serous and mucous, as well as the minor glands being of mucous type. Developments of all salivary glands occur between four and twelve weeks of embryonic life. Edgar states that the parotid gland is the first to develop, followed by the sublingual, submandibular and minor salivary glands.

The development of the salivary glands occurs in a similar manner. The process begins with an in growth of epithelium that extends from the stomatodeum into the ectomesenchyme and ultimately branches freely to form all the functional components of the gland. The process then continues on to differentiate surrounding ectomesenchyme to produce connective tissue aspects of the gland (Sreeny, 1988). The connective tissue of the gland is divided into the capsule, and thus surrounds the outer area of the gland and septa. Septa aids in dividing the inner part of the gland into larger lobes and smaller lobules. The capsule and septa are responsible for the vital nerves and blood vessels that serve the gland (Fehrenbach & Balogh, 2006).

The function of salivary glands is to produce saliva which contains minerals, electrolytes, buffers, enzymes, immunoglobulins, and metabolic wastes. The process in which saliva is secreted is controlled by the autonomic nervous system (Fehrenbach & Balogh, 2006).

Structure of the salivary gland. (Edgar & Dawes, 2005 p. 7)

Structure of salivary glands according to (Edgar & Dawes, 2004) consists of acini which are secretory end pieces of the glandular tissue and the branched ductal system. The parotid glands which are a serous gland are specific in structure as the end piece cells are arranged in spherical form (Edgar & Dawes, 2004). In mucous glands however, the arrangement is of a tubular nature resulting in large central lumen. There are three types of ducts present in all salivary glands(Edgar & Dawes, 2004). The intercalated ducts are the first point of passage for fluid. These ducts have low cubodial epithelium and narrow lumen (Sreeny, 1988). Secretions then follow passage into the striated ducts which lined with cells that contain many mitochondria. Lastly, saliva flows through excretory ducts which are lined with stratified squamous epithelium at the terminal end (Edgar & Dawes, 2004).

Parotid Gland:

Image of a parotid gland. Accessed at on the 4/10/09.
Image of a parotid gland. Accessed at on the 4/10/09.

The parotid glands are larger in size in comparison to the sublingual and submandibular glands. Their shape structure reflects a wedge shape. The percentage of saliva volume provided by this gland is only 25 percent of the total volume (Fehrenbach & Balogh, 2006). The parotid glands are located behind the ramus and towards the front of the ear (Edgar & Dawes, 2004). The peripheral branches of the facial nerve (VII) are related closely with the parotid gland. The walls of the parotid duct are thick due to the unification of the ductules which is also responsible for the drainage of lubules of the gland (Edgar & Dawes, 2004). The duct is situated anterior to the border of the gland and on the surface of the masseter muscle. The duct then curves over the anterior border of the masseter muscle and opens within the oral cavity in papilla adjacent to second upper molars. Parotid secretions are serous.

Submandibular Gland:

Image of a submandibular gland. Accessed at on 4/10/09.
Image of a submandibular gland. Accessed at on 4/10/09.

The submandibular gland is half the size of parotid glands. It is responsible for 65 percent of salivary volume and is situated beneath the mandible in the submandibular fossa, posterior to the sublingual salivary gland (Fehrenbach & Balogh, 2006). It is also wedged between the body of the mandible and mylohyoid muscle (floor of mouth) (Sreeny, 1988). The ducts are thin walled in this gland as they open into the floor of the mouth underneath the anterior part of the tongue via the sublingual papilla. The secretion is a product of both mucous and serous fluid (Edgar & Dawes, 2004).

Sublingual Gland:

Image of a sublingual gland accessed at on 4/10/09.
Image of a sublingual gland accessed at on 4/10/09.

The smallest of all glands, the sublingual gland is not capsulated and is only responsible for 10 percent of salivary volume. (Fehrenbach & Balogh, 2006) The sublingual gland is situated in the floor of the mouth beneath the sublingual folds of mucous membrane. It consists of numerous small ducts ranging from around 8 to 20 that open into the mouth on the peak of the sublingual folds. (Edgar & Dawes, 2004) Although the sublingual glands have a mix of both serous and mucous cells, the secretory product is mainly of mucous fluid. The sublingual duct empties into the oral cavity via the same opening as the submandibular duct, which is known as the sublingual caruncle. (Sreeny, 1988)

Minor Gland:

Image of minor gland accessed from on 4/10/09
Image of minor gland accessed from on 4/10/09

The minor glands are the smallest glands in the mouth in comparison to the major glands, the difference being that they are more numerous and have shorter ducts that open directly onto the mucosa surface (Fehrenbach & Balogh, 2006).These glands are found in tissues in various areas of oral cavity. Most of the minor salivary glands secrete a mucous product with a serous component. Although there is a gland known as the von Ebner’s gland which only contains serous cells thus resulting in a secretion of only serous product (Fehrenbach & Balogh, 2006).

Xerostomia & Clinical relevance:
Image of a patient with dry mouth accessed at on 4/10/09
Image of a patient with dry mouth accessed at on 4/10/09

Xerostomia can be described as a feeling of dryness to the oral cavity. This is the resulting sensation of hyposalivation which is a measurable decrease in function of one or more salivary glands which compromises saliva flow. Hyposalivation & Xerostomia are often caused by the use of pharmaceutical drugs that have side effects (Van der waal, 1997)

Sjorgens syndrome has also been identified as causer of xerostomia as it is a chronic inflammatory disorder of salivary glands. It directly affects exocrine glands of the body (Graamans, 1991).
Another possible cause for xerostomia is the procedures used in head and neck radiotherapy for treatment of cancer (Edgar & Dawes, 2004)

“Prevalence of xerostomia increases with age and affects 30% of the population aged 65 years and older” (Edgar & Dawes, 2005) . Several habbits such as smoking, consumption of caffeine have been shown to increase risk of xerostomia (Van der waal, 1997).
associated with xerostomia and hyposalivation in the oral cavity.
- Dryness of lips
- Dryness of buccal mucsoa
- Absence of saliva produced by gland palpation
- High total decayed/missing filled teeth (DMFT) score.
- Often thirsty
- Difficulty swallowing/speaking
- Difficulty with dry foods

(Edgar & Dawes, 2004)

Non- oral symptoms: associated with xerostomia and hyposalivation in oral cavity.
- Dry throat
- Blurred vision
- Dry skin
- Constipation
- Nasal dryness
- Vaginal dryness
- Itching or burning sensations

(Van der Waal, 1997)

Clinical implications of xerostomia:

- Recurrent dental cairies due to the inability to restore pH levels to neutrality and inhibit bacteria after food consumption
- Gingivitis fungal infections
- Possible root cairies
- Enhances the risk of erosion on teeth
- Cervical regions of teeth receive greater abrasion from toothbrushes – sensitive to erosion. Occlusal and incisal surfaces are exposed to attrition due to insufficient saliva to permit remineralisation.

(Van der Waal, 1997)


- Establishment of diagnosis
- Thorough head, neck and oral examination,
- Collection of saliva for testing
- Communication is critical between other health practitioners
- Management and monitoring of pharmaceutical use
- Scheduling of frequent dental evaluations due to high prevalence
- Maintain proper oral hygiene and keep hydration levels up
Diet planning to reduce risk activities such as smoking caffeine etc.
Dry surfaces often managed with oral moisturisers, lubricants
- Medications also an option
(Edgar & Dawes, 2004)


The Thyroid Gland

Location and Structure:

The Thyroid gland is a large, bowtie shaped, Endocrine Gland found in the neck, lying to the front and side of the larynx and trachea. The thyroid has two conical shaped lobes (left and right) that are connected anteriorly by a band of tissue called an ‘isthmus’. The entire gland is surrounded by a thin connective tissue capsule called a ‘fascia’ that is firmly attached to the upper part of the trachea (Abrahams, 2007). This attachment allows the thyroid gland to move along with the larynx when a person swallows (Fehrenbach and Herring, 2007).

There is often a small, third lobe which extends upwards from near the isthmus called the pyramidal lobe. Four additional pea-sized endocrine glands, parathyroid glands, are embedded within the rear tissue of the main thyroid gland (Etherington, 2005).

The lobes of the thyroid gland are made up of many spherical follicles, created by cuboidal or squamous epithelial cells arranged around a central cavity. The epithelial cells produce a glycoprotein, called thyroglobulin, which combines with iodine in the central cavity of each follicle to create a substance called ‘colloid’ (Marieb and Hoehn, 2007). The two thyroid hormones, thyroxine and triiodothyronine, are derived from this colloid and then secreted into the bloodstream (Abrahams, 2007).

The parafollicular cells of the parathyroid glands, found between the follicles of the thyroid gland, are responsible for the production and secretion of an additional hormone called Calcitonin (Etherington, 2005).

The parathyroid glands, embedded within the thyroid gland, produce their own independent hormone called the parathyroid hormone that is also secreted directly into the blood (Marieb and Hoehn, 2007).

(Encyclopedia Britannica Online, 2008)

Normal Thyroid Function:

In normal function, the production of the thyroid hormones is under the control of thyroid stimulating hormone (THS) released by the pituitary gland, found in the brain (Abrahams, 2007). When thyroid hormone levels are high in the blood stream, the production of thyroid stimulating hormone is suppressed, which causes the thyroid gland to stop the production of hormone. When the levels of thyroid hormone in the blood become too low, the production of TSH is restimulated, causing the thyroid to restart hormone production; this is an example of a negative feed back loop and helps to maintain normal thyroid hormone levels in the bloodstream (Etherington, 2007).

The two Thyroid Hormones, mostly thyroxine, are secreted directly into the bloodstream and have an effect on most cells in the human body (Etherington, 2007).

“Except for the adult brain, spleen, testes, uterus and the thyroid gland itself, thyroid hormone affects virtually every cell in the body”.

(Marieb and Hoehn, 2007, pg 621)

Thyroxine stimulates the enzymes concerned with cellular respiration and increases the metabolic rate of each cell. In normal amounts, the hormones also increase body heat production and influence the following physiological functions;

· Normal development of the nervous system in babies and children

· Function of the nervous system in adults

· Functioning of the heart

· Muscular development and function

· Growth and maturation of the skeleton

· Gastrointestinal motility

· Secretion of digestive juices

· Female reproductive ability

· Lactation

· Hydration and secretion of the skin

Abnormal Thyroid Function:

The thyroid gland is susceptible to various problems and many subsequent problems can arise from the abnormal function of this major gland (Abrahams, 2007). Because the hormones produced by the thyroid gland have such a widespread effect on the cells and organ in the body, any abnormalities in thyroid hormone level (either too much or too little) can have wide-ranging effects.


In hyperthyroidism, there is an abnormally high amount of thyroid hormone circulating in the blood. The excess hormone is caused by overactive thyroid tissue, the result of either an isolated, overactive nodule, or the ill function of the entire gland (Etherington, 2005). The overactivity can also result from abnormal stimulation by THS, as is seen in Graves disease.
Primary Hyperthyroidism is caused by illnesses and problems that affect the thyroid gland itself. These include thyroid digenesis, inherited metabolic defects, environmental damage and environmental factors such as medications. Secondary hyperthyroidism occurs when problems occur with the Thyroid Stimulating Hormone, or when other substances imitate the effects and falsely stimulate the production of additional thyroid hormone (Merieb and Hoehn 2007).


Depending on the excess amount of thyroid hormone circulating the blood stream, a person might suffer one or all of the following symptoms:

· Increased nervousness
· Increased appetite
· Weight loss
· Poor tolerance of hot weather
· Increased sweating
· Palpitations
· Increased frequency of bowl movements
· Menstrual problems
· Infertility
· Muscular weakness
· Increased heart rate

The thyroid gland may also swell and become enlarged causing what is known as a goiter. Anxiety is one of the most common symptoms of hyperthyroidism, closely followed by nervousness, feelings of stress and irritability.

(, viewed 10/10/09)

Depending on the characteristics of the patient, hyperthyroidism can be treated with anti-thyroid drugs (to interfere with hormone production), radioactive iodine (to destroy thyroid tissue) or surgical removal of the overactive tissue.
If severe and left untreated, hyperthyroidism can lead to heart attacks, arrhythmias, heart failure, progressive weight loss and eventually death.

Graves Disease:

Graves disease occurs when the body’s immune system begins to produce an antibody that has the same effect as thyroid stimulating hormone, effectively the body’s own immune system attacking itself. Because the body believes it requires more thyroid hormone, it is produced in the thyroid gland is excessive amounts, causing the thyroid gland to swell and large goiters to develop (Abrahams, 2007). People suffering from graves disease experience all the symptoms of hyperthyroidism to the extreme. An additional condition called exophthalmos, in, which the eyeballs protrude, can also result (Etherington, 2005).
Graves disease is more common in women then men and is diagnoses with various blood tests to detect the THS mimicking antibody. In the past, Graves disease was treated with the use of harmful irradiation. This is an out dated procedure and when used in children can lead to thyroid cancers (discussed later) because of the quickly dividing cells of young, growing tissue.

(Ryan, 1997,, Viewed 10/10/09)


When the thyroid produces and inadequate amount of thyroid hormone, a condition called hypothyroidism is the result. The reasons the thyroid is producing too little hormone are similar to why it could be producing too much; sections of the gland that aren’t functioning correctly, an entire ill functioning gland or an imbalance of THS. Tumours and a disease called Hashimoto Disease are also common reasons the thyroid gland will have a reduced ability to produce thyroid hormone (Etherington, 2005).
If Iodine levels in a person diet are inadequate, the thyroid gland will continue to produce colloid, but will not be able to completely synthesize thyroid hormones. Additional colloid will be produced when low hormone levels are detected, and the thyroid will swell and become a goiter (marieb and Hohen, 2007).
Thyroid hormone is vital for the proper growth and development of growing children; therefore, the importance of a balanced amount of thyroid hormone is dependent on the age and stage of development of a person. Hypothyroidism in children is known as Cretinism and will result in the following:
· Mental retardation
· A short, disproportionately sized body
· Thick tongue
· Thick neck
Older people suffering from hypothyroidism will experience one or more of the following:

· A slowed metabolism
· Low body heat production
· Puffy thick skin below the eyes
· Thick skin on lips, fingers or legs
· Lethargy
· Mental sluggishness
· Weight gain
· Loss of hair


The small endocrine glands that are embedded within the large thyroid gland, called the parathyroid glands can also adversely effect the body if not functioning properly. The hormone produced by these glands, parathyroid hormone, is responsible for the action of bone resorption throughout the body.
An over production of this hormone, usually the result of a tumour, causes excess calcium to be removed from bones which can cause them to soften and become deformed.
High levels of parathyroid hormone can also interfere with the function of the nervous system (causing abnormal reflexes and weakening of the skeletal muscles) and can increase the likelihood of kidney stones.
Diagnosis of hyperparathyroidism is made by taking blood tests and finding increased levels of parathyroid hormone and calcium in the blood.

Effects of Thyroid Disorders on Oral Health:


Anxiety and increased irritability are two of the most common symptoms of hyperthyroidism. Increased anxiety and stress, wether the result of an underlying condition or not, can have some adverse effects on the health of a persons teeth and gums. When a person is stressed, the function of their salivary glands, among other things, is reduced to help the body cope and manage the stressor effectively. If the stress continues over a long period of time and the salivary flow continues to be decreased, a person can developed a condition known as Xeristomia, or dry mouth (discussed above).
In addition to affecting the salivary glands, high stress levels caused by hyperthyroidism can increase the intensity of a condition called Bruxism – a Para functional habit where a person persistently grinds and clenches their teeth. If high levels of stress continue over long periods of time, wear facets become present on occlusal surfaces of teeth, and more serious and painful craniomandibular disorders can result (Mouth and Hume, 2005).


The increased secretion of the hormone produced by the Parathyroid Glands, embedded within the thyroid gland, can also have obvious effects on the oral cavity. The hormone, Parathyroid Hormone, is responsible for the process of bone resorption throughout the body, and any increased levels in the blood stream cause the action of this to increase (Etherington, 2005).
The Alveolar bone, which surrounds the roots of teeth, is particularly sensitive to the increased levels of Parathyroid hormone in the blood. A study conducted by Frankenthal, et al in 2009 found that hyperparathyroidism patients were more likely to have reductions in the laminar durra surrounding the roots of teeth on dental radiographs. Increased levels of the hormone also correlated with a widening of the periodontal ligament space surrounding teeth as well as decreased overall alveolar bone density (Frankenthal, et al, 2009).

Reference List

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