hello students today we will discuss about the anatomy of thyroid gland in today's lecture we will discuss the external features of the thyroid gland and its relation so what is the thyroid gland thyroid means that it is a shield shaped gland and thyroid gland is situated low down at the front of neck below and lateral to thyroid cartilage now this is the important thing which you have to understand that in exam so many times you have this question palpate your thyroid gland now when you have this question student generally do the palpation on this prominence which is known as laryngeal prominence or adam's apple but you have to understand that thyroid gland is not not related with this prominence and now in this diagram you can understand that this is your thyroid cartilage now this thyroid cartilage is having this midline prominence which you can feel in the midline of your neck and thyroid gland is situated lower you can see the thyroid gland is situated lower to this prominence in the lower part of the neck so if you want to palpate the thyroid gland you have to be little bit lower in the neck not at the thyroid cartilage so this is the first and most important thing when you are reading this gland that it lies in the lower part of the neck below and lateral to thyroid cartilage now what is the vertebral label of the thyroid cartilage thyroid gland what does it means that if you will have the vertebral column in the posterior side parallel to this gland it starts from the c5 and it end at t1 vertebra so this is the important thing for your exam purpose what is the vertebral label of thyroid gland now the next comes is the weight of thyroid gland the weight is again the question for your multiple choice question it is vary from 20 to 25 grams and the weight depends upon the body weight of individual person and iodine intake now this is very particular uh thing about the thyroid gland that it is highly vascular endocrine gland and because of the high vascularity it is brown in color now when you will talk about the consistency it is firm inconsistency and you know that the thyroid gland secrete two hormone one which stimulate and increase the rate of cellular metabolism that is known as thyroxine and second hormone which is concerned with the calcium level in the blood that is the calcitonin and when the high level of calcitonin is there it decreases the blood calcium level then what are the parts of the thyroid gland now in this diagram you can appreciate that thyroid gland is classically h shaped land now when you will have this edge shape gland you can appreciate that this gland is having sidely placed two lobes and these lobes are connected in the middle portion by horizontal part is known as isthmus of thyroid gland so it is a h-shaped gland which is having the two symmetrical lobes and the lobes are united by the isthmus isthmus lies in front of the tracheal rings now here in this diagram you can see that these are the tracheal rings and when we are having the thyroid gland it is occupying the front of your trachea with the side of your larynx so this is lies in front of the second third and fourth tracheal ring so this is the label of isthmus second thing is the lobes lies on both the side of the larynx and trachea now again you have to understand which i just told you that lobes are not anteriorly placed and you have to understand that whenever you are palpating the thyroid gland you should not palpate around this laryngeal prominence you have to go below this prominence to palpate the thyroid gland each lobe extending from the oblique line of the thyroid cartilage to the sixth tracheal ring now when you will see the thyroid cartilage on the thyroid cartilage you are having a oblique line now this oblique line is the upper limit of the apax or the upper part of the lobe and when you will see the lower limit of the lobe it correspond to the sixth tracheal ring lope covers the intro lateral surface of the trachea cricoid cartilage and the lower part of thyroid cartilage now you are able to understand that again and again you are having the word lower part of the thyroid cartilage not in the upper part of thyroid cartilage now there is one more terms come and that is pyramidal process now pyramidal process is nothing but it is a extra tissue which is sometime present from extension of isthmus now when you will see the thyroid gland in 30 percent of the cases you have the pyramidal process which extends upward from the stomach and may reach the higher bone so it may be long enough to approach this bone which is known as hyoid bone or sometimes what will happen that between this pyramidal lobe and the hyoid bone you have a connection which is a fibrous band and this connection is known as levator glandular thyroid or levator thyroid glandular so when you are having this pyramidal process you have to understand that pyramidal process is a normal tissue in function wise and it is nothing but just a extra gland or extra part of the thyroid gland which is present from the esthemous and sometimes its upper part is connected to the higher bone by fibrous band now what this pyramidal process represent this process actually representing the remnant of thyroglossal duct now we will move to the capsule of thyroid gland now thyroid gland is covered by the two capsule one is known as true capsule another is known as false capsule now whenever you are having the capsule of thyroid gland here always you have the comparison with the capsule of prostate now why we are having the comparison of prostate capsule with the capsule of thyroid gland it is because of the presence of plexus of veins now you have to understand that when you will have the prostate gland it is surrounded by again the true and false capsule and the thyroid gland is also surrounded by true and false capsule but in case of the thyroid gland you know that it is an endocrine gland so the secretion will pour into the blood so you need the venous plexus inside the parenchyma so you will have the venous fluxes which is present inside the true capsule but in case of the prostate we have this plexus inside the false capsule that means in this gap between the true and false capsule so when you will have the prostate gland you have to understand that in prostate gland the venous fluxes lies outside the true capsule but in case of the thyroid gland this venous plexus lies inside the true capsule so the difference comes when we are talking about the surgery the difference is that when you want to remove the prostate when you have to do the turp that is trans urethral resection of prostate we always start to do the dissection from the center and we will take out the prostate tissue in bits and pieces through the urethra and the only important thing which you have to keep in mind that we are not going to tear this true capsule because outside the true capsule you have the venous fluxes so if there is injury on the plexus there is a severe hemorrhage but in case of the thyroid gland because the flux is present deep to the true capsule so you can remove this false capsule and take out this gland whole without any manipulation with this venous fluxes so you have to always keep this question in mind because whenever you are having the exam this is very commonly asked question now in this diagram you can appreciate that this is your thyroid gland and this thyroid gland is having a outer layer and this outer layer is the false capsule and inside this you have the true capsule of thyroid gland now what about the true capsule now true capsule is thin and it is formed by the condensation of the fibrous stoma and the most important thing about the true capsule that it is densely adherent to the gland and this capsule sand the septa inside the gland and that septals divide the gland into the pseudo lobules so this is the true capsule and this true capsule is very intimately related to the gland and it is not you cannot strip this layer of true capsule from the gland what is false capsule now in the class of d fish of the neck we discussed that there is a layer is known as pre tracheal fascia now this pre tracheal fascia modify here and the splitting of this pre tracheal fascia is going to form a covering and that is known as thyroid fascia sometimes or it is also known as false capsule of thyroid gland now this fascia is different from the true crab capsule because you can easily separate it from the capsule during the surgery i just told you that the true capsule of the thyroid gland cannot be separated from the gland but the false capsule you can cut the false capsule and you can very easily separate this capsule from the gland because in this diagram you can see that this capsule is not adherent to the gland there is a layer of fat which is present between the true and false capsule when you will trace this pre-tracheal fascia above you will realize that this pre-tracheal fascia after enclosing the gland will reach to the your oblique line of thyroid cartilage and further it will go above ultimately approach the higher bone so when you will see the midline extension of the pre tracheal fascia this is your hired bone and this is your thyroid cartilage so this pre tracheal fascia is approaching till this part of the structure in the midline and this is one of the reason that we will always discuss why the thyroid swellings move with the degrutation then there is one more important modification is seen with the pre tracheal fascia and that is known as ligament of berries now this ligament of berry the most important question is that it connect which surface of the thyroid gland with the midline structure so answer is that it condensation at the postero medial part and it connects the postero medial surface of the thyroid gland with the cartilage of larynx that is mainly the cricoid cartilage so whenever you are having the ligament of berry it is a connection of thyroid gland which surface of thyroid gland answer is postero medial surface with the cricoid cartilage so this is the first important thing which you always keep in mind whenever you are having this question so the ligament of berry connecting the cricoid cartilage and sometimes the first tracheal ring to the postero medial aspect of each thyroid lobe it is the primary point of the fixation of the thyroid to the surrounding structure now this is the question which is again the question of your viva that why the thyroid gland move up and down during swallowing so when you will have the saliva or whatever you are swallowing there is a movement of the thyroid swelling occurs now why the only answer is because of this pre tracheal fascia modification that is we are talking about the false capsule it is responsible for the connection of the thyroid gland with the laryngeal cartilages and above it is connected with the higher bone so whenever the deglution will occur the floor of mouth pulls the head bone up upside and when there is a upward movement of the higher bone it is again pull the thyroid cartilage in the upper direction so this is the important thing which is again the question of your exam then what is the surgical importance of ligaments of berry so ligament of berry is having very important surgical importance because of its relation with recurrent laryngeal now so it is important surgically because of the relation with recurrent laryngeal now and the now pass deep or sometime through the ligament and this now is also having a relation with the small branch of inferior thyroid artery and during the surgery when we are cutting this ligament of berries with the hype uh this keeping this in mind that there is a high chances of the injury of recurrent lymph will now there are some time the injury occurs to this artery and this will become the cause of bleeding so you have to understand that ligament of berry is very important structure in the thyroidectomy because it is more prone and there are high chances of the injury second thing is if there is a bleeding occurs while cutting the ligament of berry then the source of bleeding is the branch of inferior thyroid artery then what are the different parts and relation of the thyroid gland so each lobe of the thyroid gland is roughly pyramidal or conical in shape and that is having the apax base so when you will see the gland this is the gland so this is the one lobe so this will become this part become the base this is the isthmus which is connecting the both side of the lobe and when you will see the surfaces of the lobe you have to take the transfer section now in this transfer section you can see that this surface is known as the lateral surface or the superficial surface of the thyroid lobe this surface is known as the medial surface of the thyroid gland and this is known as posterior surface of the thyroid gland so whenever you are having the lobe lobes are having the three surfaces posterior surface lateral surface and medial surface then it is having the two border anterior border and posterior border so what about the apex of thyroid gland so apex of thyroid gland is directed upward so this is the first thing which you have to keep in mind second thing is that it extend up to the oblique line of thyroid cartilage where it is limited above by the attachment of a muscle is known as sternothyroid now here on this image of the larynx you can appreciate that this is the outer surface of thyroid cartilage on the lateral side of the thyroid cartilage we are having a line and this line is known as oblique line now this oblique line is having the relation with the three muscle one muscle is coming from the lower down and this is coming from the sternum to approach the cartilage so this is known as sterno this muscle is known as sterno thyroid because it is coming from the sternum and approaching to this cartilage second muscle arising from here and approaching to the higher bone and that is known as thyroid and then you have one more muscle which is horizontally placed and it is a constrictor and this is the inferior constrictor and this inferior constrictor is going backward and it is also having some origin from the cricoid cartilage so that is the inferior constrictor so when you will see this area you will find that there are three muscles on the oblique line one is coming from the lower down that is sternothyroid then you will have thyroid and you have horizontally placed muscle is known as inferior constrictor so if i will take the section here and suppose this is your hired bone this is your cartilage thyroid cartilage now we have seen that there is a muscle which is coming from lower down to approaching this oblique line coming from the sternum so it is sterno thyroid then you will have the muscle from thyroid to the hyoid bone that is thyroid now here you have the cricoid cartilage and in between you will have the muscle arising and this is your inferior constrictor so the important thing which you have to understand that when you will keep the thyroid gland here the lobe of the thyroid gland become sandwich between the two muscle this is the outer muscle which is known as sternothyroid and this is the inner muscle which is known as your constrictor that is inferior constrictor so that's why it is written here that the apex cannot go beyond this oblique line because it is overlapping by the attachment of this muscle is known as sternothyroid muscle the apex become sandwich or it lies between the inferior constrictor and the sternothyroid i hope now it is clear the external branch of the superior laryngeal now is medial to this part of the gland as it passes to supply crico thyroid now why it is medial because you have to understand that whatever the nerves are reaching they have to enter into the larynx and they become medial whenever they are approaching towards the larynx now in this diagram you can see that this is the strap muscles which are present in the midline now this is your gland now this gland is having this superficially placed muscle which is coming from the sternum approaching this oblique line of the thyroid cartilage and this is known as sterno thyroid muscle now superficial to this is sternothyroid you will have one more muscle which is directly approaching the higher bone that is known as sternohyoid so right now we are not talking about estranohyoid we are talking about sternothyroid muscle so sternothyroid muscle is the important muscle which prevent the upward extension of thyroid lobes then what about the base now base is the broad lower part of the gland and this base is extend up to the fifth or sixth tracheal ring it is related with the inferior thyroid artery and recurrent laryngeal know in this diagram you can see that this is the inferior thyroid artery and this is the recurrent angel now both are approaching this lower part of the gland which is known as base of the gland then you will have the lateral surface now lateral surface is actually the superficial surface of the lobes which you are able to see after removing the strap muscles so it is convex and it is covered by the three strap muscles what are the name of these muscles sternothyroid sternohyoid and the superior belly of omohyoid a small portion of the sternocleidomastoid also overlap but it is only in the lower part the sternothyroid muscle do not completely meet in the midline above the level of isthmus but the sternohyoid muscle meet at the midline and in the form of the roughly which you have to cut at the time of thyroidectomy so what is the meaning of these two lines now see this is your thyroid gland now here you are able to see the deep strep muscle that is sterno thyroid which is approaching this oblique line now you can see that there is a gap that means the sterno thyroid muscles are not closer to each other but superficial to this you have one more muscle that is known as sterno hyoid now these sternohyoid muscles which are coming from the sternum and directly passing to the hyoid bone they are actually making a rough in the midline and when you are doing the thyroidectomy you have to cut this raphe and you have to separate these superficial muscles which is known as sternohyoid so this is again the question of your exam or even though when you are doing the dissection you have to first remove the sternohyoid muscle rather than sternothyroid when you are removing the thyroid gland now what about the medial surface of the gland now in this diagram you can see that this is the medial surface of the gland and this medial surface is related with the two tubes one is the trachea anteriorly and some part of the esophagus apart from that there are two muscles which we discussed one is the inferior constrictor of the pharynx and and the cricothyroid muscle of the larynx then there are two cartilage one is the cricoid cartilage and the thyroid cartilage and there are two muscles now which are related to the medial surface one is coming from the above that is external laryngeal one is coming from the below that is recurrent laryngeal now then what about the posterolateral surface now where is the postero lateral surface now this is the postero lateral surface now this posterolateral surface is having the parathyroid gland apart from that it is related with the medial side of carotid sheath now here is the carotid sheath and this surface is related with only the medial aspect of this carotid sheath but if the gland become enlarged if the thyroid gland become enlarged then it has the lateral extension at that time it can approach the anterior aspect of internal jugular vein and this surface is also related with the parathyroid the parathyroid gland usually lies in contact with the surface between it and fascia what does it means that this is your pre-tracheal fascia which is forming the false capsule and the parathyroid gland lies inside the false capsule then what about the borders of the gland you have anterior water and the posterior water anterior border is here now this is the anterior border now this anterior border actually separating the medial surface from the anterior or the lateral surface and this is related with the superior thyroid artery now superior thyroid artery is one of the branch of external carotid artery and these superior thyroid artery runs downward and they are running along the anterior border of thyroid gland then you will have the posterior water posterior borders are the round and thick borders and this separates the medial and posterior surface so this is the medial surface this is the posterior surface and here you will have the posterior borders which are not sharp or well defined as compared to the anterior border and they are related with the longitudinal arterial anastomosis between the branches of superior and inferior thyroid artery so here you can see that this is the branch of superior thyroid and these are the branches of inferior thyroid so the anastomosis will take place posteriorly and it is said that this area is considered as a posterior border of thyroid gland then what about the estherous now esthemas is a horizontally placed structure which is connecting the right and left lobe this is having the two border this is known as the superior border of the estimas this is the inferior border of the estimas apart from that it is having the two surfaces this is the anterior surface and the one is posterior surface of isthmus so what are the relations of isthmus so first is about the anterior surface now anterior surface of the estimates is related with the strap muscles that is sternohyoid and sternothyroid it is not at all related with the homohyde it is not at all overlapped by the sternocleidomastoid so this is the basic difference whenever you are writing the short note anterior relation of the low and anterior relation of the esthetis here only the two muscles which you can appreciate apart from that near the midline you will have the anterior jugular vein so you can see that these are the anterior jugular vein which are the superficial veins so these veins are running near the midline and they are crossing the anterior aspect of isthmus posteriorly now posteriorly we have already seen that posteriorly you will have a tube is known as trachea and there are second third fourth tracheal rings which are lies in the posterior relation of isthmus then you will have the relations of the superior and inferior border of the estimas now this superior border related with the anastomosis between the branches of superior thyroid artery only not the inferior thyroid so there are the two branches one is coming from the right side one is coming from the left side so this is the right superior thyroid branch this is the left superior thyroid branch and these branches are enasting along the upper or superior border of isthmus where we'll have the inferior border inferior border is having the branches uh not the arterial but it is giving the mainly exit of a vein is known as inferior thyroid vein so in this diagram in this lower border you can see that there is no arterial anastomosis but there is a exit of this vein and this vein is known as inferior thyroid vein now sometimes you have a aberrant artery which is known as thyroidia emma artery now if the thyroidia emma artery is present then it is arising from the lower part and it enters into the thyroid gland through the inferior part of isthmus so whenever you are writing the relation of the estimas along the upper and lower border you have to understand that arterial anastomosis present along the upper border while the vein leave through the inferior or lower border of isthmus so at the end of this class what we are able to understand that how you will divide the thyroid gland into the different parts what are the different presenting areas of the thyroid gland and what is ligament of berries why thyroid move with the deglution and what are the important relations of thyroid gland so this is all for today's class thank you