Group 7 Endocrine System: Adrenal Glands
E-Facilitator: Cathy
Learning Outcomes
  • Locate the Adrenal Glands and differentiate between the Adrenal Medulla and the Adrenal Cortex
  • Describe the relationship between the Adrenal Glands and the Nervous System
  • List and discuss the hormones that the Adrenal Glands produce and their effects on the body
  • Explain why synthetic Adrenaline is often added to local anaesthetics used in dentistry




Location of the Adrenal Glands and differences between the Adrenal Medulla and the Adrenal Cortex


The adrenal glands are a pair of glands located near the superior portion of each kidney(3). This is why they are also known as suprarenal glands (2).
They are approximately
  • 3-5 cm in height
  • 2-3 cm in width
  • less than 1 cm thick
  • and weigh from 31/2 to 5 grams (3)

There are 2 structural and functional regions of the adrenal gland;

1) the outer region is called the adrenal cortex (1)
2) the inner region is called the adrenal medulla (1)

In general, the function of the adrenal glands is to produce a number of different hormones that are essential to the needs of the human body. Both parts of the adrenal glands perform very separate functions as they produce different hormones (1) (3). *This will be discussed in greater depth later on*
.

external image illu_adrenal_gland.jpg

Diagram from http://training.seer.cancer.gov/module_anatomy/unit6_3_endo_glnds3_adrenal.html (2)


The relationship between the Adrenal Glands and the Nervous System


The adrenal glands are an endocrine gland that help regulate the bodies internal organs. They are part of the bodies autonomic nervous system meaning they are not under conscious control in the body. They respond to hormones that are released involuntarily by the pituitary gland under command from the hypothalamus. The hypothalamus detects any imbalance by positive or negative feedback and releases hormones to stimulate other endocrine glands which either help with stimulate the sympathetic or parasympathetic nervous system (5). The adrenal glands are part of the sympathetic nervous system which help prepare the body for physical activity. Stimulation of the sympathetic nervous system results in a number of responses including constriction of blood vessels supplying the skin, dilation of blood vessels supplying the heart and skeletal muscles, dilation of the bronchioles to facilitate increased ventilation, and release of glucose from the liver. The nerve endings use adrenaline and noradrenalin as a neurotransmitter (6).


The actions of the autonomic nervous system are largely involuntary (in contrast to those of the sensory-somatic system). It also differs from the sensory-somatic system is using two groups of motor neurons to stimulate the effectors instead of one.(9)

  • The first, the preganglionic neurons, arise in the CNS and run to a ganglion in the body. Here they synapse with
  • postganglionic neurons, which run to the effector organ (cardiac muscle, smooth muscle, or a gland).
The autonomic nervous system has two subdivisions, the
  • sympathetic nervous system and the
  • parasympathetic nervous system.(9)


The preganglionic motor neurons of the sympathetic system arise in the spinal cord. They pass into sympathetic ganglia which are organized into two chains that run parallel to and on either side of the spinal cord.

The preganglionic neuron may do one of three things in the sympathetic ganglion:
  • synapse with postganglionic neurons which then reenter the spinal nerve and ultimately pass out to the sweat glands and the walls of blood vessels near the surface of the body.
  • pass up or down the sympathetic chain and finally synapse with postganglionic neurons in a higher or lower ganglion
  • leave the ganglion by way of a cord leading to special ganglia (e.g. the solar plexus) in the viscera. Here it may synapse with postganglionic sympathetic neurons running to the smooth muscular walls of the viscera. However, some of these preganglionic neurons pass right on through this second ganglion and into the adrenal medulla. Here they synapse with the highly-modified postganglionic cells that make up the secretory portion of the adrenal medulla.(9)
The neurotransmitter of the preganglionic sympathetic neurons is acetylcholine (ACh). It stimulates action potentials in the postganglionic neurons.
The neurotransmitter released by the postganglionic neurons is noradrenaline (also called norepinephrine).
The action of noradrenaline on a particular gland or muscle is excitatory is some cases, inhibitory in others. (At excitatory terminals, ATP may be released along with noradrenaline.)

The release of noradrenaline
  • stimulates heartbeat
  • raises blood pressure
  • dilates the pupils
  • dilates the trachea and bronchi
  • stimulates the conversion of liver glycogen into glucose
  • shunts blood away from the skin and viscera to the skeletal muscles, brain, and heart
  • inhibits peristalsis in the gastrointestinal (GI) tract
  • inhibits contraction of the bladder and rectum
In short, stimulation of the sympathetic branch of the autonomic nervous system prepares the body for emergencies: for "fight or flight".

Activation of the sympathetic system is quite general because
  • a single preganglionic neuron usually synapses with many postganglionic neurons;
  • the release of adrenaline from the adrenal medulla into the blood ensures that all the cells of the body will be exposed to sympathetic stimulation even if no postganglionic neurons reach them directly.(7)

The Medulla


The adrenal medulla consists of masses of neurons that are part of the sympathetic branch of the autonomic nervous system. Instead of releasing their neurotransmitters at a synapse, these neurons release them into the blood. Thus, although part of the nervous system, the adrenal medulla functions as an endocrine gland.
The adrenal medulla releases:
  • adrenaline (also called epinephrine) and
  • noradrenaline (also called norepinephrine)
Both are derived from the amino acid tyrosine.
Release of adrenaline and noradrenaline is triggered by nervous stimulation in response to physical or mental stress. The hormones bind to adrenergic receptorstransmembrane proteins in the plasma membrane of many cell types.
Some of the effects are:
  • increase in the rate and strength of the heartbeat resulting in increased blood pressure;
  • blood shunted from the skin and viscera to the skeletal muscles, coronary arteries, liver, and brain;
  • rise in blood sugar;
  • increased metabolic rate;
  • bronchi dilate;
  • pupils dilate;
  • hair stands on end ("gooseflesh" in humans);
  • clotting time of the blood is reduced;
  • increased ACTH secretion from the anterior lobe of the pituitary.
All of these effects prepare the body to take immediate and vigorous action.(9)

external image autonomic.gif http://images.google.com.au/images?qsympathetic+nervous+system&hl=en&rls=GGLR,GGLR:2006-7,GGLR:en&um=1&sa=X&oi=images&ct=title

(11)

9292.jpg Diagram from Endocrine system Information (5). moz-screenshot.jpgA4adregl.jpg Diagram from Answers.com (6) adrenals.jpg Diagram from Endocrine system information (5)


The hormones that the Adrenal Glands produce and their effects on the body

Adrenal gland hormone secretion
Adrenal gland hormone secretion


Diagram from Medline Plus (4)

There are 2 structural and functional regions of the adrenal gland;
1) the outer region is called the adrenal cortex (1)
2) the inner region is called the adrenal medulla (1)
Both parts of the adrenal glands perform very separate functions as they produce different hormones. However, both are essential to the healthy function of the body. (1) (3)


1) Adrenal Cortex

The adrenal cortex secretes hormones that have an effect on the body's metabolism, on chemicals in the blood, and on certain body characteristics. The adrenal cortex secretes corticosteroids and other hormones directly into the bloodstream. (2)
The adrenal cortex is subdivided into 3 zones according to the hormones that each zone secretes. (3)

  • the outer zone- zona glomerulosa
  • the middle zone- zona fasciculata
  • the inner zone- zona reticularis

  • Zona Glomerulosa

Its primary secretions are a group pf hormones called mineralocorticoids . They affect mineral homeostasis.(3)
This means that they play a role in conserving the electrolytes and water in the body, particularly the concentrations of sodium (Na+) and potassium ions (K+). (1)(3)


  • Zona Fasciculata
Secretes mainly glucocoticoids which affect glucose homeostasis.The principal glucocorticoid is cortisol, which increases blood glucose levels.(2)


  • Zona Reticularis

Synthesises small amounts of androgenic steroids or androgen steroids. Male hormones (androgens) and female hormones (oestrogens) are secreted in minimal amounts in both sexes by the adrenal cortex, but their effect is usually masked by the hormones from the testes and ovaries. (2)


2) Adrenal Medulla

The hormones secreted in the adrenal medulla, unlike those secreted by the adrenal cortex, are not essential to life. The hormones secreted assist a person in coping with physical and emotional stress.(2)(3)
The 2 main hormones synthesised by the adrenal medulla are epinephrine and norepinephrine.

  • epinephrine (also called adrenaline) increases the heart rate and force of heart contractions, facilitates blood flow to the muscles and brain, causes relaxation of smooth muscles, helps with conversion of glycogen to glucose in the liver, and other activities.(1)

  • norepinephrine (also called noradrenaline) has little effect on smooth muscle, metabolic processes, and cardiac output, but has strong vasoconstrictive effects, thus increasing blood pressure. (1)
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Why synthetic Adrenaline is often added to local anaesthetics used in dentistry

Epinephrine is the technical name used for synthetic adrenaline. Its chemical composition formula is C9H13NO3. It is often added to local anaesthetics used in dentistry because it constricts blood vessels at the site it is injected, keeping the anaesthetic in the area for a longer time. This constriction helps the anaesthetic to work more intensely for a longer time ensuring the patient operated on has a painless procedure. The epinephrine helps prepare the body for stressful situations the same way as natural adrenaline does in the ‘fight or flight’ theory. The epinephrine is intended for use in the surrounding tissues only, constricting a ’local’ area so that usually no side effects are noticed. If an anaesthetic with epinephrine is absorbed directly into the blood stream or a patient is especially sensitive to it they may feel some side effects. (8) These side effects include:
  • Dizziness
  • Palpitations - an irregular or unusually rapid beating of the heart
  • Racing heart
It is important to note that these symptoms sometimes follow soon after an injection with a patient suffering anxiety because the patient will release natural adrenaline.(8)

If it is known that a patient has a particularly strong reaction to epinephrine then an alternate anaesthetic should be used. There are a few including : Polocaine, Isocaine or Citanest. To be certain that an anaesthetic does not have epinephrine or epinephrine-like compounds added (for epinephrine sensitive patients) you must specify with the following word plain as in Polocaine-plain, Carbocaine-plain Citanest-plain etc. These anaesthetics do not effectively work for as long as the adrenaline based anaesthetics. It is common to use several injections when using non-adrenaline based local anaethetics particularly for the maxilla. In the lower jaw they are only slightly shorter -acting. (8)


Diseases Associated with the Adrenal Glands

Cushing’s Disease ·

Cushing's syndrome is caused by the adrenal gland's excessive secretion of cortisol (hydrocortisone). Increases the adrenal gland's secretion of glucocorticoid hormones will cause Cushing's syndrome, including adrenal tumours, enlargement of the outer layers of the adrenal gland, or overproduction of adrenocorticotropic hormone (ACTH). Excess ACTH may result from pituitary tumours (Cushing's disease), as in Cushing's first group of symptomatic patients, or from inappropriate production of the hormone by other tissues. Treatment with corticosteroid drugs may also induce Cushingoid symptoms.(7)


Symptoms of Cushing’s Disease

  • Persistent hyperglycaemia (steroid diabetes).
  • Dramatic losses in muscle.
  • Bone protein and water and salt retention leading to hypertension and edema.


Physical signs of cushing's Disease

  • Swollen ‘moon’ face.
  • Redistribution of fat to the abdomen and the posterior neck (a ‘buffalo hump’).
  • Tendency to bruise.
  • Poor wound healing.
  • Present infections may become overwhelmingly severe before producing recognizable symptoms.
  • Bones can spontaneously fracture.(7)

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Causes of Addison’s Disease

  • An autoimmune disease- the immune system attacks the adrenal glands.
  • Attributed to tuberculosis.
  • Addison disease also can be caused by fungal infections or cancer (7).

Symptoms of Addison’s Disease

  • Abnormal pigmentation of the skin & mucous membranes.
  • Bodily weakness.
  • Weight loss.
  • Low blood pressure.
  • Emotional instability.
  • Gastrointestinal upset.
  • Deficiencies in both glucocorticoids and mineralocorticoids.
  • Low sodium levels and high potassium levels (7).

Picture3.jpg

References