[Music] hello it's us again I'm sure I'm sure we talked about a thyroid in the past we probably like pointed at it in stuff but apparently we haven't talked about the anatomy of the five-week gland before well that's easily remedied oh is it because I'm probably enough to get a microscope oh all right 500 weed gland where is it what does it do you know really vaguely blood supply only does it get any innovation and if we're going to talk about the thyroid gland we need to talk about the parathyroid glands at the same time because they're right there and they're going to be sharing the lab let's apply innovation and we should talk about structures nearby because there are a few important points there right well here it is so that's the easy bit three-three us a greek word three offs and i dose meaning shapes are three offs refers to a shield this is the thyroid college here this is that prominent bit of college you can feel they're forming the laryngeal prominence for the Adam's apple so shield-shaped describes the thyroid cartilage nearby is this gland so this plan gets called the thyroid gland the two are separate they don't they're not really functionally related the thyroid college is part of the larynx is part of the airway the thyroid gland is involved in metabolism if you were to use one word and we can see that in fact here the thyroid gland is a little inferior to the thyroid cartilage and it's in fact most of that the gland you can see it's got two lobes so most of the gland is actually spread laterally and if you imagine they're deep to the final exam here we go the trachea and then this lump here is the cricoid cartilage you know the firework okay cricoid cartilage thyroid college so in fact the two lobes of the thyroid gland in most people are a little lateral to the airway to the trachea and the cricoid cartilage and then we have this central isthmus this joining bit linking the two lobes together which overlaps the two trickier those correlational swings at your key which is why yeah you can palpate all this right you can I'll pay all these collagenous bits but the thyroid gland actually start off in the tongue so in the early embryo the thyroid gland begins to form here and there leaves this little depression in the posterior part of the tongue called the foramen cecum and it descends in the developing embryo to its final location this is interesting because it means that some people might have bits of thyroid tissue in unexpected places so ectopic thyroid tissue and then it's often something that gets called a pyramidal lobe here like a stickier pointy bit of thyroid tissue and it's not you know it's uncommon but I think it's maybe ten percent the population something like that I have it so it's you know it's uncommon but it's not super rare so you might find some final tissue extending up here and what that's doing is is is showing you how the thyroid tissue descended - it's a dolt location some of it didn't get all of the way the other thing that happens is that the thyroid gland as it descends it trails are duct a tube between the posterior tongue and the descending thyroid tissue now normally that thyroglossal duct gets obliterated destroyed it closes up and disappears then some people bits of the final gloss or duct might persist and they might go fill with fluid so if you find a midline mobile cyst maybe it's a fiberglass or cyst maybe it's a remnant of the fiberglass or duct which is just filled with fluid important this so the larynx describes a bunch of structures adjacent to the thyroid and the trick here the one thing on here which I can't show you I'm not really not that fussed about showing you other strap muscles of the neck so there are a load of strap muscles thin flat muscles covering all these things and what we've had to do here is remove sternohyoid and sternothyroid to strap muscles on either side as they're going from the sternum to the hyoid which is up here remove those two see the thyroid gland so the thyroid gland is deep - a couple of strap muscles and the other bits of structure to it is it's got a thin capsule and it's within the visceral component of the fashion of the neck so it's in this pre to akhil region that we talked about and we look to the fashion of the neck blood supply and the blood supply is interesting because what we've got here is we've got you know a relatively dizzy little gland but it's got a big blood supply and in fact on here we can only see parts of it PZ - remember what we've got cuz we've got the superior thyroid artery and the inferior thyroid artery we can see that the superior thyroid artery is dropping down here it's a branch of can see where we are the external carotid artery so common carotid artery is dividing here into external and internal carotid artery so the superior thyroid artery is one of the first branches of the external carotid artery now what we can't see because it would be tricky to show in a model is that the inferior thyroid artery is coming up from inferior lis now over here we've got the subclavian artery going out that way oh yeah we can see that one going that way the subclavian artery has a thigh Rosoff I call trunk popping off it around here in the neck Bhairo cervical so that's going to give branches off to the thyroid gland namely that inferior thyroid artery and branches to the neck that's the service there is another artery that gets this point is called the the thyroid EMA artery Mima today is ever an artery I've discussed with anybody but um this artery is again uncommon tends to branch from the brachiocephalic trunk sometimes you come from other places like the artery aorta and it runs up the choke you in the midline to run to thee to the five hundred glance there's another thing that gets mentioned and that's it now why has the thyroid gland got such a rich blood supply well it's because it's it's it's hormonal so most of the cells in the thyroid gland and making hormones they're making will get referred to as t3 and t4 so triiodothyronine and tired of thyromine which tends to get called thyroxine I think that's right there's a huge amount of physiology here and the production is driven by hormones produced in the pituitary gland namely thyroid stimulating hormone so there are hormonal feedback loops controlling all this now the hormones made by the thyroid gland and revolting regulating metabolism regulating energy use by pretty much all the cells in the body they're really important in growth and development in the fetus and in children they're they affect carbohydrate uptake in the gut they affect heat production and and that sort of thing right so that that's the role of the thyroid gland is to check out hormones that affect a huge number of cells in the body to do all of those things that's why they're so vascular so those cells making the t3 and t4 hormones are the follicular cells so there are follicles if you ever look under the microscope we can see a little bit of this but your imagine here cause you've got sections cut through that you've got blogs write blobs of Cola weed stored stuff within the thyroid glands and those surrounded by follicular cells were making follicles so there are balls in there so the follicular cells are making the 500-word hormones and they're making those hormones from iodine and tyrosine the amino acid so the follicular cells are doing most of the work now there are also occasional power of follicular cells which we're probably not going to spot under the microscope but these are K you know power of follicular cells we've got a completely different job they're making calcitonin and calcitonin reduces blood calcium levels calcium in the blood is crucial for all sorts of cellular activity so they're maintaining the Ryoma of calcium in your blood at all times is a good thing power of follicular cells in the thyroid gland make a calcitonin which encourages cells to take calcium out of the blood so that's what we see in the thyroid gland so the thyroid gland is an endocrine organ it's making hormones to put into the blood to affect cells around the body so blood goes into the thyroid glands through those two arteries now it comes out through three veins on either side we can see only one here but if we take this off we can see where they drain to now we have superior middle and inferior thyroid veins still very straightforward so I can't demonstrate all of the thyroid veins on here but it's not a big deal I'll show you why now you can see the big blood vessels here we've got the the internal jugular vein draining down here and we've got the two brachiocephalic veins here superior vena cava so the superior and middle thyroid veins drain to the internal jugular vein and the inferior thyroid veins which were kind of seeing here drain to the brachiocephalic vein veins being veins there is some variety he and what-have-you another note of alley arteries is that because the superior and inferior thyroid artery has come from two different arteries so they come from the external carotid artery and subclavian artery they unless the Mo's quite happily within the thyroid gland meaning there's a casual circulation here between the external carotid artery and the subclavian artery innovation well there is sympathetic innervation to the thyroid gland I've seen that described in a number of places there are cervical sympathetic ganglia up in the neck so the the sympathetic trunk of the sympathetic chain continues up into the neck sympathetic fibers jump onto the arteries and follow the arteries into the thyroid gland does it matter these sympathetic fibers are vasomotor not security motor so what I'm saying is is that these can affect the dilation of the artery so they can affect the blood flow to the fibroid gland but they're not gonna trigger the thyroid gland to make more stuff the secretion of hormones from the thyroid gland and the production of hormones is controlled by the pituitary glands so it's under hormone control not nervous control lymphatic drainage we're in the neck there are loads of lymph nodes nearby look we got the trachea here's we've got power to a Q lymph nodes and all sorts essentially lymph from the fibroid gland is gonna drain pretty much to any and every nearby lymph node I keep it simple firewood gland done I think right yeah they're BlueTEC from last week parathyroid glands now the parathyroid glands a worth talk about not just because they're here but because they share a lot of stuff we've been talking about ok these are probably a little bit right see this is from here got tongue and stuff fibroid gland here and the parathyroid glands are kind of on the that's a bit there's a bit big it's a bit of a generous though we're parathyroid gland that the parathyroid glands are on the kind of posterior surface of the thyroid gland and there is a superior one and yes a little bit big probably a superior one and an inferior one on either side in life they kind of brainley soft yeah not not dissimilar to that shape but they're kind of brown shaped and they're outside of that thin capsule of the thyroid gland but they're sat on top of it so the blood supply to the parathyroid glands and the innovation is the same as the thyroid gland the same things are getting there right so there are four parathyroid glands two on either side superior and inferior now the parathyroid glands the cells in their hair which get called chief cells something they make parathyroid hormone so parathyroid hormone this is the Colbert right parathyroid hormone raises the level of blood calcium so it works in opposition to the calcitonin in the thyroid gland and yeah the thyroid gland supposed to be doing this other job of regulating metabolism and stuff isn't that why don't we why why don't you just have anyway so parathyroid hormone works by then encouraging osteoclasts in the bone to release from the bone because that's where you store your calcium and put it back into the blood it encourages the kidney to reabsorb more calcium so you keep all of your calcium it encourages production of an active and active form of vitamin d3 that encourages the small intestine to absorb more calcium and that sort of thing parathyroid hormone parathyroid glands increase blood calcium levels calcitonin made by the para follicular cells in the thyroid gland caused a decrease in blood calcium and they work together to keep your blood calcium levels just right all yourselves really happy and they can they can do their thing isn't that neat the parathyroid glands can be a little bit of variable in their position they also descend in the developing neck in it but that's a story for another day right what we've covered are the pertinent parts of the anatomy of the thyroid and parathyroid glands location function within reason nearby structure all nearby structures I almost forgot one blood supply venous drainage innovation that's all thing right the big nearby structure so if we've got the thyroid gland here at the laryngeal cartilages and here's the trick here the big nearby structure is the recurrent laryngeal nerve and the recurrent laryngeal nerve is a branch of the vagus nerve the biggest nervous is running down the neck who's running with these guys and then it dives to try and get to the esophagus so we can get the GI tract and get down here and that sort of thing right he's off a number of branches as it goes one of those branches is the recurrent laryngeal nerve and again because of some really cool embryology which is a story for another day your current laryngeal nerve on the Left loops around the arch of the aorta and then goes back up so it ascends with the chuckya laterally and on the right it loops around the right subclavian artery and then loops and then passes back up it ascends to the larynx with the trachea the recurrent laryngeal nerve main job is to innervate all of the trinsic muscles of the larynx which I'm using to speak with and control my voice and that sort of thing right and it's running kind of posterior to the thyroid gland so any surgery on the thyroid gland any operation working in this area or the parathyroid glands I guess has a risk of damaging the recovering laryngeal nurse you must be aware of the path of a recovery laryngeal nerve so that you don't damage it if you're removing thyroid tissue or something like that they see you everyone's there right almost forgotten that and that would have been embarrassing right that's the anatomy of the thyroid gland parathyroid glands are nearby structures that are worth talking about today right yeah think so okay see you guys next week [Music]