Thyroid gland #Part2 Hormones Physiology & Hyperthyroidism

Thyroid gland

Part 2

Physiology and Grave's disease (hyperthyroidism) 

How does the thyroid gland synthesizes the thyroid hormones?

The hypothalamic pituitary thyroid axis

  First of all, the thyroid gland hormones are T3 (Triiodothyronine), T4 (Thyroxine), and Calcitonin, iodine is an essential element for the synthesis of these hormones, the thyroid gland is situated in front of the trachea below the hyoid bone ( the only floating bone), Moreover, the thyroid gland is very crucial to our body's metabolism at which it tends to make sure that the cells in your body are working properly by instructing every cell in the body when to consume oxygen and nutrients making it responsible for our growth and providence of better health, Furthermore, the calcitonin secreted by the thyroid gland, is an essential hormone that reduces your body's calcium level in the blood when it goes haywire, Ultimately, the thyroid gland allows our cells to use energy, grow and reproduce.

  It begins when a part of the brain called hypothalamus secretes TRH (thyrotropin-releasing hormone) stimulates the pituitary gland to release TSH (thyroid stimulating hormone) which induces the thyroid gland to release its hormones, usually there is a negative feedback when the thyroid hormones are too much in the blood that should eventually inhibit the release of TRH from hypothalamus.

  Now, the thyroid gland consists of lobules that each containing smaller cells called follicles ( follicular cells ) the lumen of these surrounded follicular cells are called colloid. Deep into a cellular level We have the cell membrane of the follicular cells which is surrounded by blood vessels that feed it with oxygen and the needed nutrients, the TSH molecules coming from the pituitary gland through the bloodstream binds to G-protein coupled receptors (GPCRs) present on the cells' membranes which then exchanges GTP to GDP thereby increases the cellular cyclicAMP (adenosine monophosphate) levels essentially increases the production of thyroid hormones ( T3 & T4) that eventually maintains the body's metabolism.

 GPCRs are family of receptors that are found almost in every eukaryotic cell and has various bodily functions in our physiology. ***There will be a specific topic about GPCRs since they have a very important bodily function also it is a heavily researched topic***
But for now, you can understand their mechanism through here --> https://www.youtube.com/watch?v=ZBSo_GFN3qI&t=183s 

How does that happen? The Physiology of Thyroid's hormones

 A quick recap of the previous paragraphs, On a cellular level We have the thyroid gland's follicular cells forming the colloid surrounded by blood vessels which contain all the nutrients and essential elements required for the synthesis of the thyroid's hormones, it contains various cations and anions such as Na⁺, K⁺, Ca⁺², Cl^-, (HCO3)^- and I^- among other things.

 Inside the follicular cells, the endoplasmic reticulum through which proteins are synthesized, Special proteins are synthesized inside which makes up most of the thyroid gland's proteins '' Thyroglobulin'' dimeric protein, It then travels to the Golgi apparatus to be packaged, After that it is transported to the colloid.

 The follicular cells contain the following NIS '' Sodium and Iodine symporter'' (transporter), sodium and potassium pump and transporter called ''Pendrin''.

The NIS '' Sodium and Iodine symporter'', it allows iodine and sodium ions to go inside the follicular cells from the blood vessels at the same time, simultaneously the sodium can go out when the potassium ions come in; because the thyroid hormones synthesis occurs in the colloid and not in the follicular cells so the Iodide ions need to be transported to the colloid.

Pendrin ''transporter'' it transports the iodide ions to the colloid from the cells which is exchanged by chloride ions at the same time. Moreover, there are Peroxidases that oxidizes the iodide ions to iodine which is, later on, attaches to the Thyroglobulin ( several chains of Tyrosine molecules)

When one iodine molecule attach to thyroglobulin, We have MonoIodoTyrosine   

            Two iodine molecule attach to thyroglobulin, We have DiIodoTyrosine

 If MonoIodoTyrosine (MIT) binds with DiIodoTyrosine (DIT) by ester bonds, we have triiodothyronine. But, If DiIodoTyrosine (DIT) binds with DiIodoTyrosine (DIT), we have Thyroxine, Yet the hormones aren't ready yet since the complex is still a part of the thyroglobulin.

The synthesized complex before will move back to the follicular cells in vesicles via pinocytosis, in which it will be attached to the lysosomes found in the follicular cells, they will bind to the endosome and break down the 2 hormones from the thyroglobulin to be released in the blood.

(Note: They also can be de-ionized into Iodide molecules and Tyrosine)

 Inside the bloodstream, there are thyroid-binding proteins which act as emulsifiers to bind the thyroid hormones ( which are lipid-structures ) that are water-insoluble will bind with the thyroid-binding proteins to be delivered to the certain cells for metabolism regulation.

 Let's take skeletal muscle cells as an example. The cells' membranes composition is lipid-bi-layered so the thyroid hormones goes easily through it, they enter the nucleus and bind to thyroid hormone receptors and retinoid X receptors, this will initiate gene transcription for specific mRNAs that will promote the thyroid hormone response resulting in the release of mRNA to the cytoplasm to be translate as a promotion for the thyroid hormone response ( this is like the feedback of the reception of thyroid hormones to the cells) and Ultimately, increasing the metabolic rate depending on which the area these hormones were attached to.

(Note: T3 is more active than T4, therefore when these hormones reach their destined cells, T4 is converted to T3)

 The thyroid gland has a great impact on us regulating and maintaining our metabolism every bit of second, it promotes the growth of tissues, regulate your heart pumps, maintaining blood pressure, body temperature, triggers the production of digestive juices, and basically the thyroid gland's hormones are mainly concerned with the main thing that a human body cannot do without it which is our Homeostasis. 

 So what would happen if a defect occurred within the thyroid gland that made it secrete its hormones continuously with no inhibition of secretion....

 A condition known as Hyperthyroidism is achieved (Note, Hyper=over) it is an over secretion of the thyroid's hormones T3 & T4, and there are a lot of causing agents that lead to Hyperthyroidism, certain medicine, auto-immune (Graves) disease, pituitary adenoma (Tumors), multinodular goitre, and thyroid adenomas especially the toxic ones ( and by toxic ones I mean the over secretion)

So let's pick up Graves disease as a causing agent for Hyperthyroidism...
 Basically, Graves disease is an auto-immune disease, and auto-immune disease is due to the attack of the body's own antibodies to specific tissue in the body counting it as a foreign invader, and in Graves disease, there are auto-antibodies that attack the Thyroid's TSH receptors mimicking the function of TSH molecules (common one) by binding to the thyroid's TSH receptors, so whenever too much secretion of thyroid hormones, a negative feedback will happen in order to inhibit the secretion of TRH & TSH to stop the secretion of T3 & T4 but since these auto-antibodies already bound to the TSH receptors of the thyroid gland follicular cells, a non-stop secretion of the thyroid's hormones will be flowing causing an overactivity in the body ''Hyperthyroidism''

(There are Thyroglobulin antibodies & Thyroid peroxidase antibodies. But these are less common)

From where do these antibodies come from?

 To begin with..., antigen-presenting cells like Dendritic cells during infections, they might present antigens of the thyroid's follicular cells marking them as an enemy to naive T-lymphocytes which when activated they activate a specific type of cells called B-lymphocytes which are transformed to Plasma cells ( a type of immune system cells that secrete antibodies) which will then secrete these auto-antibodies that will attack the Thyroid's TSH receptors mimicking the function of TSH molecules.

 A microscopical view of the thyroid gland can show us packed follicular cells with a tightened colloid, and also traces of scattered T-lymphocytes.

Symptoms of Graves disease

• Goitre, an enlargement of the thyroid gland, this can be noticed on the neck as a belly like protrusion.
  

• Increased metabolic rate, therefore hyperactivity and irritability.
• Difficulty in sleeping (Insomnia) 
• Sweating
• Heat intolerance
• Graves ophthalmopathy, since the TSH receptors can be found all over our body cells, sometimes the auto-antibodies manage to bind to the TSH receptors on the tissues surrounding the eye. 
  
• Weight loss
• Graves dermopathy
  
   

• Faster heartbeat (Tachycardia) which can lead to congestive heart failure (CHF)
• Anxiety
• Hyperreflexia - briefly is the overreaction of the involuntary nervous system to any external stimuli.
• Hand tremors, an uncontrolled rhythm movement of the hand due to abnormal signals in the brain that miscommunicates with the hands and muscles - hand tremors can also happen due to neurological disorders such as dopamine deficiency like in Parkinson's disease ( you can check out this video ( I do not own it) about Tremor disorders: https://www.youtube.com/watch?v=-Y3kex_8UoY)

References

• https://www.youtube.com/user/armandohasudungan
• https://www.youtube.com/user/aimmds
• https://www.youtube.com/watch?v=SCV_m91mN-Q
• http://www.yourhormones.info/glands/thyroid-gland/

Next will be - the effect of anabolic steroids on the thyroid hormones and ultimately the metabolism.

Pituitary gland

Pituitary gland

Pituitary gland

Pituitary gland is considered as the master gland as it controls the functions and secretion of most of the endocrine glands. The gland is located beneath the brain and in connection with the hypothalamus, The gland consists of 2 parts:

• Adenohypophysis: It consists of the anterior and middle lobe - developed embryonically from the roof of the mouth.
• Neurohypophysis: It consists of the posterior lobe and a part of the brain called the infundibulum ( a stalk connecting the gland to the brain) - developed from the back of the forebrain.

****Note: Hypophysis means Pituitary,..Plural: hypophyses

Hormones of the Adenohypophysis ( anterior lobe of the pituitary gland):

1. Growth hormone (G.H.)

It controls metabolism especially protein synthesis, accordingly it controls the physical growth of the body.

Hypo-secretion ( Hypo=less or weak) of this hormone during childhood causes Dwarfism and its hyper-secretion ( hyper=over) during the same period causes Gigantism.

Hyper-secretion of G.H. in adults causes Acromegaly which is characterized by increased bone growth at the extremities and characterized by enlarged hands, feet, fingers and bones of the face.

      2. Pituitary Trophins:

A group of hormones that affect the activity and secretion of other glands and includes:

1. Thyrotrophin (thyroid stimulating hormones) (TSH) ---> check out this brief topic about thyroid gland at - http://allaboutbiologyworld.blogspot.com/2016/05/thyroid-gland-brief-notes.html
2. Adrenocorticotrophic hormone (ACTH) which affects the function of the adrenal (Suprarenal) cortex.
3. Gonadotrophic hormones - Affect the function of gonads ( ovaries in females and testes in males).

This group includes:

1. Follicle stimulating hormone (FSH) which affects the growth of the ovarian follicles and formation of Graafian follicles in females and formation of seminiferous tubules, spermatozoa in male.
2. Lutinizing hormone (LH) which stimulates the formation of corpus luteum in females and the formation and secretion of interstitial cells in the testes of males.

These two hormones are important for sexual maturity as they are responsible for secretion of male and female sex hormones

.

         3. Prolactin: stimulates milk formation and secretion from mammary glands ( breasts).

Hormones of the neurohypophysis ''Posterior lobe of the pituitary gland'':

Two hormones are secreted from the nerve cells in the hypothalamus and called the secretary neurons, and reach the neurohypophysis ( posterior lobe of pituitary) through the infundibulum after which they are released to the blood stream.

The two hormones are:

1. Antiduretic hormone (ADH) (Vasopression):

This hormone increases the re-absorption of water from the kidney tubules and decreasing the volume of urine excreted. In addition it increases blood pressure.

        2. Oxytocin:

This hormone affects the uterine contraction and increases it during delivery ( labour). Gynecologists use this hormone to accelerate the birth of a baby by stimulating strong contractions of uterine muscles ( synthetic type '' Pitocin'' of Oxytocin) 

In addition oxytocin stimulates the release of milk from mammary glands with the beginning of lactation ( milk letting hormone).

References used:

https://www.accessdata.fda.gov/drugsatfda_docs/label/2014/018261s031lbl.pdf

https://www.khanacademy.org/science/health-and-medicine/advanced-endocrine-system/endocrine-system-introduction/v/hypothalamus-and-pituitary-gland

http://www.audioenglish.org/dictionary/hypophysis.htm

+My highschool Biology book which provided a lot of content.

I hope you ladies and gentlemen like the topic, please if you find it informative like, share and perhaps follow my blog so as to be tuned whenever a new post comes
Thanks a lot 
#Biology 
#WeliveWelearn
allaboutbiologyworld.blogspot.com

Pancreas- brief notes

The Pancreas 

Pancreas is considered to be a mixed gland. this organ controls our body's sugar level and produces a special juice called pancreatic juice that literally releases the nutrients present in any meal you have eaten so it has a role in our Metabolism, the pancreas is situated behind our stomach see Fig.1 which means that one of its main functions is to assist in breaking down food through a mixture made of water, sodium bicarbonate and digestive enzymes.

Sodium bicarbonate's role is to neutralizes the stomach's acidity so as to let the digestive enzymes perform their functions, enzymes such as Lipase, Protease, and Amylase. (exocrine function) these digestive enzymes are secreted from cells called Acinar cells see Fig.2

Lipase breaks down the fatty substances

Protease help in splitting up proteins

Amylase divides carbohydrates into energy-rich sugars

So these past three enzymes have a great role in our metabolism, another function of the pancreas which is considered to be crucial is controlling the amount of sugar in the human's blood through two hormones:

Insulin and glucagon which are produced from special small glandular cells in the pancreas called the Islets of Langerhans (endocrine function) see Fig.3 the islets of langerhans has two types of cells (alpha & beta cells) see Fig.4

The alpha cells are usually small in number and secretes glucagon hormone, this hormone is secreted only when the blood sugar level is falling down or too low, by telling the cells and livers to release sugar in the bloodstream, converting the stored glycogen for example in the liver to glucose.

The beta cells represents the majority of cells and secretes a hormone called insulin which antagonizes the action of glucagon. Mainly it makes the excess sugar moves back to the cells, it stimulates the oxidation and utilization of glucose by the cells as it is important for transport of all monosaccharides (except fructose) across the cell membrane also stimulates the conversion of glucose to glycogen ( to be stored in the liver or muscles) or to lipids.

We can say that the balance between insulin and glucagon is what keeps our body's health maintained but any failure in either the secretion of insulin or glucagon can lead to a condition called Diabetes Mellitus, the increase in glucose level in the blood is associated with abnormal appearance, excretion of glucose in urine with the excretion of large volume of water which explains the symptoms of continuous thirst sensation and excessive micturition, blood vessels becomes hardened, heart attacks, kidney failure and strokes.

Also from what we learn from this video is that people who have diabetes their body tends to have high glucagon level which increases the sugar level making it worse.

The pancreas is more like an instructor that guides our body to maintain a good health.

Like and share it please incase you find it informative to let everyone knows about this important topic.

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Thanks to #TedEd for developing this video which is full important and helpful notes

Fig.1

Fig.2

Fig.3

Fig.4

Thyroid gland-brief notes

Thyroid gland

In contact with the trachea, lies a powerful gland named as Thyroid gland, a gland that has an enormous power over our body.Structure: consists of two lobes, each one has lobules, these lobules contain cells named follicles, functioning as a store to the hormones the thyroid gland se

nds, they are Thyroxine& Triiodothyronine or T3 and T4 respectively so Iodine is an essential element that mainly build up these hormones.

The thyroid gland has various functions and effects over the human body, it's role is to ensure the proper work of the body's cells by delivering these hormones to every single cell, it instruct every cell when to consume oxygen for aerobic respiration and nutrients for maintaining the body's metabolism that means it has a major function in our physical and mental growth, it makes sure that our heart pumps blood properly.
The thyroid gland is controlled by the human body's MASTERMIND gland which is the ''Pituitary gland'', this gland can be found deep below brain, it makes sure when the thyroid gland secrets it's hormones, the pituitary's role is to sense if the hormonal levels are too low or too high by secreting a hormone named ''TSH'' thyroid stimulating hormones which induce/stimulates the thyroid gland.

Everything has disorders, 1st:Hyperthyroidism where the thyroid gland sends a lot of hormones that means the cells are overloaded with instructions making the individual overactive experiencing a high metabolism signaled by:1)faster heart beat 2) constant hunger 3)high weight loss 4) sleep difficulty and much more
On the other hand, 2nd disorder: Hypothyroidism where the thyroid gland sends a few hormones that means cells doesn't have many messengers to guide them, therefore, metabolism diminishes to a low level. signaled by:1) high weight gain 2) sluggishness( delay) ( lag) 3)sensitivity to cold 4) swelling joints 5)depression and much more
Well I really have to admit that the study of hormones is amazing, we can literally say it is what our metabolism based on, it is the key the ignites our metabolism.










Thanks to ‪#‎TedEd‬ for developing this informative video.
If you understood it well, go ahead and try answering these six easy questions on http://www.sporcle.com/games/ahmedmaxi93/about-thyroid-gland

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A picture showing the position of thyroid gland

Here is another picture expressing thyroid gland's dysfunctions










Thyroid gland in a nutshell