Thyroid Gland and Hormones

in this video we're going to have a look at the thyroid gland and the hormones that the thyroid gland produces we're going to take a look at how those thyroid hormones are produced where they act in the body and what they do and also what stimulates their production and their release now the first thing we need to talk about is the thyroid gland itself now there's going to be another video on the anatomy of the thyroid gland but we need to be able to identify where it is first thing is that if you take your windpipe or your trachea and you were to get your finger in you run your finger down the anterior aspect of your windpipe you would feel your Adam's apple now this is known as your laryngeal prominence and it's made up of laryngeal cartilage now remember both males and females have an Adam's apple why well it's just the laryngeal prominence it's more prominent in males because it's a secondary sexual characteristics and testosterone makes it more pronounced in its size so if you were to feel your Adam's apple and then you were to continue down and feel what's called your suprasternal notch which is this part right here between your Adam's apple and your suprasternal notch is where your thyroid is located and your thyroid wraps around your trachea and think about it as though it looks like a butterfly with the two wings those two wings are the two lobes of the thyroid gland hugging the anterior aspect of the trachea anterior and lateral now I want to talk about if we were to go into that thyroid gland and have a look at the cells and the tissue of the thyroid gland so you need to be aware that if you look histologically into the thyroid you'll find that there are these little pools like this in which you've got a single layer of epithelial cells surrounding this hollow lumen so this is the lumen and this is the single layer of cells and you've got many many many of these within the thyroid these are the functional units of the thyroid and what you'll find is that these cells this single layer of cells are called follicular cells follicular cells also known as thorough sites Thyra science alright in this lumen right here there is actually a fluid this fluid is called colloid and it's within this colloid that we produce thyroid hormone but we need a couple of things to come together here in the colloid to produce thyroid hormone now it's two major things that need to come together for this to happen the first thing you need is iodine the second thing you need is thorough globulin so you need I dine and thyroglobulin to come together in this colloid to produce thyroid hormone how does this work well let's first start with the iodine iodine is the fifty-third so let's write it over here iodine is the fifty-third atom in the periodic table which means it's quite heavy it's one of the heaviest atoms that we would ingest and utilize metabolically for the human body fifty-third atom on the periodic table it is found within many different types of foodstuffs so in high quantities you'll find it in eggs you'll find it in dairy you'll find it in seafood and you'll find it in various plants and vegetables how did I get it well the animals need to ingest it themselves and ultimately comes from the soil so what you'll find is that certain areas of the world that have high quantities of iodine in the soil means that the foodstuffs will also have high quantities of iodine in it but there are many places around the world where iodine is not rich in the soil and therefore not rich in the foods which means that some individuals may be limited to the amount of iodine they ingest how much iodine do we need per day well if you're around about a 70 kilogram adult in a 24-hour period you need 150 micrograms of iodine 150 micrograms per day is the quantity of iodine that you need to remain or to maintain healthy function of the thyroid gland to produce thyroid hormone 150 micrograms a day what's that it's around about a sixth of a gram but luckily for us our thyroid maintains a pool of iodine and there's actually around about eight thousand micrograms of iodine in the form of iodide stored within the thyroid which is what I ran about fifty days worth of storage so I've got around about fifty days of backup iodine available which is great just in case all right so we've got our iodine we've ingested it through our foodstuffs the body turns it into iodide and iodine is a charged form so iodine is the non charged form that you'll see on the periodic table which you'll see is just i it turns into iodide within the body which is im- now you know you already know that when you ingest sodium when you ingest calcium all these types of things often you'll ingest them in a way in which they don't possess their charge but once it's entered physiological fluids it will change its particular charge and so for example sodium becomes an na plus chloride becomes sale- I've already recorded a video discussing how this occurs so when we ingest iodine turns into iodide I negative and what happens is this is readily absorbed through our gastrointestinal tract and it tends to accumulate and concentrate in the thyroid gland so the thyroid glands the only part of the body that's actually going to use iodide now it absorbs it so there's going to be blood vessels all around here right so you're going to have blood vessels all around here and so the iodide which is absorbed through the gastrointestinal tract will float through the blood stream it'll come out of the blood stream into the extracellular fluid and it will be taken up by these follicular cells on this basal side so the iodide is taken up let's draw it over here iodide is taken up on the basal side of these cells taken in through a sodium iodide symporter what that means is if that's the cell right you're gonna have sodium iodide and they're both taken in together through a sodium iodide symporter okay iya da sodium is going down its concentration gradient taking iodide with it now it's inside the follicular cells and then from there I died can diffuse via the apical membrane into that colloid so now we have iodide here within the colloid now the iodide needs to become oxidized what does that mean oxidized means it loses electrons have you ever heard of Leo L a loss of electrons is oxidation loss of electrons is oxidation and iodide is oxidized by hydrogen peroxide h2o2 right iodide is oxidized by hydrogen peroxide and you may think isn't that poisonous to us isn't that dangerous well remember that even though our body produces what we call these free radicals or oxidative species that yes in abundance they can be damaging and that's called oxidative stress but we do require these oxidative species to maintain health to certain degree so it actually promotes immune function and in this case hydrogen peroxide is used to oxidize iodide and then once it's oxidized iodide is available and ready for use now what does the iodide do once it's been oxidized in this colloid well it binds to thyroid globulin so the thyroid globulin is produced and is stored here in this colloid and we'll right thyroglobulin as T G so we've got iodide and thyroid globulin here in the colloid they need to come together and this coming together is supported through an enzyme peroxidase so peroxidase comes along helps them come together and what you'll find is this so when iodide comes together with thyroid globulin you produce a couple of molecules so I want to highlight what these molecules are so if iodide come together with thyroid globulin they can produce so remember with with the help of an enzyme which is approximate one Ayad Oh tyrosine mono I dote I Rosine mono means one I do is the iodine tyrosine is referring to the tyrosine subunit within the thyroid globulin thyroid globulin is a very big protein it's around about I think it's about 660 kilo daltons in size quite a big protein and it has numerous tyrosine residues which is an amino acid within that protein so proteins are just accumulations of amino acids there's multiple I think they can be up to 160 tyrosine amino acids within a single thyroid globulin but if you've only got one iodine attached to this thyroid globulin it's called mono audio tyrosine and that sometimes written as MIT if you have to iodine binding to the tyrosine to iodine and so binding to the thyroid globulin what you get then is dye I addo tyrosine which is written as d I T right so you can produce if you've got to iodine binding to a thyroid globulin - that's diono tyrosine if you've got one binding that's mono I don't tyrosine they're actually inert these two things they're here now they've accumulated in this colloid we've got MIT and di T but they're inert they don't do anything so they need to be turned into something else well what do they turn into well if you take to die I don't tyrosine if you take a di T and bind it with the di T you got to I'd open to I know it gives you four I though that gives you something called tetra Ayad oh no it's not tyrosine its thyromine Cyro named tetra meaning for i do' thyromine but it's not called that it's a ridiculous name we just caught thyroxine thyroxine and we write thyroxine as T for this t4 or thyroxine is one of the thyroid hormones t4 thyroxine one of the thyroid hormones we actually produce or we probably have it stored within our thyroid gland around about five thousand micrograms of that which is about 5 grams we've about 5 grams of thyroxine stored now our thyroid itself is only about 20 grams okay so got a huge amount of backup thyroxine available and again if you think about that I said iodine we've got about 50 days backup if we think about this well that's around about 50 days as well we only use about 1% every day of our fire rock scene that we've got stored in our thyroid gland so we've got all this backup available ok so that's the first third hormone that's produced the second thyroid hormone that's produced is if we take a mono i do't i Rosine and bind it with a dye i do-- tyrosine and that's one plus two gives us three that then gives us a try Ayano siren een try I do need and the triad Oh thorough Nene is known as t3 because there's three and that is the other thyroid hormone now in actual fact these are the two for hormones that we need to look at now there's another thyroid hormone that's produced called calcitonin but we're not going to talk about Kelsey tonin today so the two thurid hormones that are produced are T 3 and T 4 T 4 so of all the thyroid hormones produced 80 percent of it is t4 and obviously 20% of it is t3 so the majority is t4 however so that means that now in here we've got t4 t3 and what happens is because the thyroid gland is a gland it's part of the endocrine system endocrine means that it's going to release chemicals called hormones into the bloodstream and these hormones will travel all throughout the body to have their effect so when we release t4 and t3 into the bloodstream the majority is t4 but t4 doesn't necessarily do anything t4 actually needs to be turned into t3 in order for it to have an effect so t4 needs to be turned into t3 and then the t3 has effect okay how does the t4 turn into t3 through something called a D ayudarnos we need to take away one iodine right so four to three that's four iodine that's three need to take away a single I don't know - residue through an enzyme called a die a D i Deniz d ir denies now there's two types right you've got type 1 and type 2 so type 1 you're going to find in the kidney and liver and so forth so kidney liver type 2 you'll find at the brain pituitary for example other areas so type one kidney liver whoops type 2 brain and pituitary what it does is it takes away nylon residue turns t4 to t3 why am I telling you this because at the centre of a DI denies the enzyme is another atom that we need called selenium so I said one atom that we need to produce thyroid hormone is iodine now another one which allows us to turn t4 into the active t3 is selenium and selenium I think is the 34th atom on the periodic table again quite heavy but also means that our diet must contain selenium in order for us to have an abundant or an adequate level of t3 floating through our bloodstream now another thing we've got t4 t3 floating around 80% of it is t4 needs to be turned into t3 due to these I Denise's if it's a liver or kidney or other periphery it's type 1 if it's going to be happening at the brain pituitary it's time to then its turn to type t3 but what you're gonna find is that thyroid hormones don't usually float around freely they need to be bound to a protein so there are two well there's actually three proteins but I'm only going to talk about the two major binding proteins for thyroid hormone the most abundant protein is not albumin but it's something called t b p t BP is thyroxine binding protein thyroxine binding protein so 80% of thyroid hormone is bound by t BG t BP and the remaining 20 odd percent is through albumin okay now that if you do the calculations 80 plus 20 equals 100% that means there's no free floating or free thyroid hormone that's not true there is around about 1% ish of thyroid hormone is free floating oops about 1% is free hormone it's the free hormone that has the effects are only free hormone can do what it needs to do okay go to the tissues have its particular thyroid hormone based effect which means again you've got 80% of the hormone is t4 but it doesn't do anything needs to be turned to t3 it does this through a DI a-- denies which requires selenium once it's t3 it can't be bound but nearly a hundred percent of thyroid hormone is bound both t4 t3 through both TB p and albumin and it needs to be freed in order for it to have its effect okay what all this means is that if you measure thyroid hormone in a laboratory test there's a couple of things you need to measure free hormone is important right so you need to measure free hormone but you also need you also could measure tbp as well okay so once you've got your free so once this protein has released the thyroid hormone the thyroid hormone needs to have its effect so how does it have its effect on what does it do well once it's let go thyroid hormone will go to the tissues of certain organs or structures of the body goes for the cells and let's just say we're going to sell here and remember you got a bilayer you've got t3 coming in in a Cell you've got a nucleus and that nucleus has the DNA t3 does not have its effect on surface receptors t3 has its effect inside the cell on the DNA itself so thyroid hormone works on the DNA and alters transcription transcription is whether we are going to read that DNA molecule and make more copies turn the gene into a protein and then have its effect or not read it transcription okay so transcription then translation so thyroid hormone goes into the cell and actually has its effect on receptors at the DNA itself altering transcription now what type of transcription is it going to do okay well it depends on where it goes so for example if it goes to the liver if thyroid hormone goes to the liver it tells the liver to increase its ability to clear cholesterol so the liver increases cholesterol clearance that means if you don't have enough thyroid hormone it may lead to cholesterol abundance or accumulation and this could lead potentially into after a sclerosis so that means thyroid dysfunction has been associated with atherosclerosis if tyroid hormone goes to the heart well it can tell it to increase contractility so its ability to contract hard and its heart rate that means that thyroid hormone issues can also result potentially in something called atrial fibrillation increased heart rate right now if thyroid hormone goes to other tissues goes to the bone it alters bone remodeling so growth bone buildup a breakdown it alters our basal metabolic rate the basal metabolic rate is how quickly we build things up and break things down it can alter mental alertness alter respiration it can alter many many different things basically and has global systemic effects throughout the body and has its primary role in growth and development and metabolism all right now thyroid hormone is so important for the developing fetus that if a mother does not have enough iodine she's not going to create enough thyroid hormone and that child will have developmental issues for the fetus thyroid hormone is required for appropriate nervous system development which means without thyroid hormone the fetus does not divide an adequate nervous system and can result in mental retardation and this is known as ISM ISM is not enough thyroid hormone for the fetus having problem with the nervous system development all right so that's that we now need to talk about what stimulates this whole process of thyroid hormone production right so we don't just eat iodine and then the iodine comes in and then it bonds with the thyroid globulin the thyroid globulin bound to the iodine turns into MIT and ER teen and they come together from t4 and t3 and then they get released it doesn't just happen it needs a trigger to tell to do so and also need something to tell it to stop so let's talk about that now as you should know the endocrine system has a master regulator and that master regulator is the hypothalamus so the hypothalamus you know is in the brain you're gonna have the hypothalamus which is around about there it's gonna have so let's just draw the hypothalamus here you've got the pituitary glands with the anterior and posterior pituitary glands and what we want to look at here is the anterior pituitary gland right this is the anterior pituitary gland and the anterior pituitary gland has a number of hormones but the only hormone we want to talk about today is a hormone called thyroid stimulating hormone known as TSH that's the hormone produced and released by the anterior pituitary gland but the thyroid the hypothalamus itself it needs to release a hormone to tell the anterior pituitary gland to release TSH and this is called thyrotropin-releasing hormone what a wonderful name thyrotropin-releasing hormone ira tropen releasing hormone also known as TR H how do you remember these two because they sound similar thyrotropin-releasing hormone and thyroid stimulating hormone okay the thyroid stimulating hormone stimulates the thyroid this is the hormone released from the anterior pituitary gland travel through the bloodstream go to the thyroid and it stimulates this whole thing to occur in actual fact TSH controls every level of this process it stimulates iodine concentration in the colloid it stimulates the binding of iodine with thyroid globulin stimulates t4 t3 production and t4 t3 release into the bloodstream TSH controls all of that but it will only be released if the hypothalamus tells it to be released when the hypothalamus releases thyrotropin-releasing hormone thyrotropin if a hormone has tropen on the end it's telling you that it's going to tell another gland to release another hormone so it's a hormone that ultimately tells another gland to release another hormone so that's why it's called thyrotropin because it's traveling to another gland the anterior pituitary to release its hormone which is TSH so that is released by the hypothalamus goes to the anterior pituitary gland which will release TSH that will travel to the thyroid gland to release its hormone which is thyroid hormone t4 t3 which would travel around the body and control growth development metabolism with a couple of other things all right this whole process is regulated by negative feedback all right now remember I told you that you're going to have t4 and t3 floating around the body with the majority of it 99% of it right bound to proteins which are tbp and albumin with around about one percent free okay if the levels of these increase if t4 t3 predominately t4 but if t4 t3 levels go too high they because they're floating through the bloodstream will ultimately get here to the anterior pituitary gland and it will negatively regulate the release of TSH so if t4 t3 levels get too high it tells TSH hey don't be released which means this process slows down and then there's less t4 t3 okay now in actual fact what can happen it's basically the free levels that stimulate this process okay the three levels if the free levels get too high this is important because you could have increased t4 t3 right increased levels but if you remain at one percent free right so let's just say we normally we have 50 units we have we okay let's say a hundred units we have a hundred units of t4 t3 floating around the body bound to t BP in albumin and we have one unit that's free all right it's this one unit that will go back and feed and say hey it's okay if that one unit increases to five units but we still have a hundred units bound here that is going to tell it to inhibit stop we've got too much floating around but what's going to happen is if the ratio increases and that goes to 500 units and that goes to five units the ratio has remained the same right and it's you're gonna have what's called a youth thyroid effect the thyroid basically maintains its current function okay so it's all about that ratio alright last thing I want to talk about is hyper and hypo thyroidism so let's have a look first at hyper hyper thyroidism okay the hyper means more than and so it's basically hyperthyroidism is the increased production of t4 t3 increased production of t4 t3 and this is usually due to increased stimulation of thyroid gland now what stimulates the thyroid gland TSH so usually this is due to increased TSH what increases TSH the anterior pituitary and often it's due to certain cancers so adenoma Zoar growths so cancers growth of pituitary gland and the reason why this is the case is because if TSH increases and increases t4 t3 there should be a negative feedback so that should come back and say hey stop being released but if it's a cancer or some sort of tumor adenoma for example it doesn't listen to those those signals that's actually one of the cardinal signs of cancers is that it doesn't listen to signals coming from the body telling it to be regulated so can't say the pituitary can increase TSH which stimulates the thyroid gland increase in production t4 t3 and this is called hyper thyroidism alright but the but this isn't the most common cause of hyperthyroidism okay the most common cause of hyperthyroidism is something called Graves disease most common or at least the most common in Western countries Graves disease and it's autoimmune now what actually happens is that antibodies that sir autoimmune means your body is recognizing yourself as foreign and is attacking it so what actually happens is antibodies that your body's producing goes to those follicular cells right goes to particular receptors on them that TSH would bind to binds to those TSH receptors and mimic the role of TSH and keep telling it to produce more and produce more and produce more thyroid hormone that's Graves disease so what you need is some sort of competing antibodies that can bind to those receptors competitively and inhibit from stimulating it bats Graves what about hypothyroidism well in hypothyroidism that's obviously going to be and under production so let's change this hypothyroidism is a decreased production of t4 and t3 now you can have primary hypothyroidism or secondary hyperthyroidism so primary hypothyroidism primary hyperthyroidism is if you've got a decreased production t4 t3 and it's due to problems with the gland itself okay primary gland itself not producing t4 t3 secondary hypothyroidism is because something is inhibiting that gland from releasing it something else inhibiting gland this may be due to decreased TSH release which means if you can fix this so with these secondary issues it usually means that if you can fix the underlying cause the gland will start to produce normal amounts so this again can be due to certain cancers or disorders or tumors which negatively impact the release of TSH okay that's a secondary cause primary where the gland itself is not doing it well one of the most common causes of hypothyroidism is something called Hashimoto's thyroiditis how she Moto's thyroiditis and again most common cause of hypothyroidism and again it's an autoimmune disorder in which antibodies are coming along binding to those TSH receptors and other areas and actually destroying the thyroid tissue so instead of stimulating it like a dozen Graves disease it destroys the tissue and if the tissues destroyed then no t4 no t3 and that means the tissue can't produce anything okay so that's Hashim oh noes now what are the signs and symptoms well if you have hyperthyroidism that usually results in a goiter now our gota is this us over the volume so remember when I drew these follicular cells surrounding that colloid okay so because there's numerous ones of these if you start producing more and more and more and more t4 t3 then this colloid this fluid starts to get larger and larger in volume because there's more stuff in it if they get larger and larger that means parts of the gland nodules of the gland start to form and it starts to protrude and it usually protrudes anterior laterally and you get this side distension of the thyroid gland itself usually due to a hyperthyroidism however you can have a hypothyroid guider and this is caused due to not enough iodine so in your diet so if you don't have enough iodine in your diet remember what happens is you need iodine to come in and you need the production of thyroid globulin and then they come together and produce thyroid hormone but if you don't have enough iodine in your diet what happens is you produce thyroid globulin B not producing t4 so it sends a signal to your brain saying hey there's not enough thyroid hormone stimulate Tia trh release stimulate TSH will each release comes in and tries to promote more of this coming in but there's no iodine to come in but it still stimulates for a globulin production so you start getting this increased level of thyroid globulin in the colloid and the colloid starts to grow in volume even though you've got no iron in and because you're still not producing t4 it keeps going back to the central nervous system telling it keep producing keep producing and you've got this cyclical thing occurring in which you produce too much colloid and again and good is being produced so you can have a goiter for hyperthyroidism too much colloid produced because too much hormones produced or you can have it going to being produced because of not enough iodine now this was the most common cause of goiter but what you'll find is that now we have our food fortified with iodine and you may see on your table iodized salt that I died salt is to get enough iodine into your diet regardless of where you are on the planet whether you have enough in your diet or not nothing your diet alright there's other things that happen so if you have hyperthyroidism it stimulates metabolic function and so you get increased sweating you have increased body temperature increased weight loss for example and you can have these ocular protrusions because it alters the tissue at the back of your eyes thickens it starts to push it out as well for hypothyroidism because of the metabolic effects you tend to gain weight you tend to get cold for example the fat gets redistributed around your body you can get fat at the back of the neck called a Buffalo Hump you can get a larger cheeks due to fatty depositions and so forth ok so this is the thyroid gland and the thyroid hormones that are produced hopefully you enjoyed it let me know

Channel: Dr Matt & Dr Mike

Views: 155,333

Keywords: thyroid, thyroid homrone, t3, t4, triiodothyronine, thyroxine, tetraiodothyronine, monoiodotyrosine, diiodotyrosine, MIT, DIT, hypothalamus, pituitary, anterior pituitary, TSH, trh, thyroid stimulating hormone, endocrine, grave disease, hashimoto, hasimoto's thryoiditis, hyperthoidism, hypothyroidism

Id: FCngwKqLaT0

Length: 36min 25sec (2185 seconds)

Published: Thu Jun 07 2018