Thyroid Flashcards
What is the thyroid gland shaped like?
Butterfly
Where is the thyroid gland located?
Anterior neck:
From thyroid cartilage to 3rd tracheal ring.
What are the three main areas of the thyroid gland?
L+R lobes
Isthmus
What is an additional 4th area of the thyroid gland sometimes present?
Pyramidal lobe
How many people have a pyramidal lobe?
45%
Where is the isthmus located?
Between lobes anteriorly to 2nd and 3rd tracheal rings
What is found attached to the back of the thyroid gland?
Parathyroid glands
What are the four compartments of the neck?
Prevertebral fascia
Investing fascia
Pretracheal fascia
Carotid sheaths
What muscles are not contained in a fascia compartment?
Platysmal muscles
What do platysma muscles do and what innervates them?
Facial expression
CNVII
What is contained in the prevertebral fascia?
Vertebrae
Postural neck muscles
Where is the investing fascia found?
Surrounding the other compartments of the neck
What is contained within the investing fascia?
Trapezius
Sternocleidomastoid
What is contained in the carotid sheaths?
Vagus nerve
Deep cervical lymph nodes
Carotid artery
Internal jugular vein
What links the carotid sheaths?
Retropharyngeal space
What is important to know about the retropharyngeal space?
Back links with chest lining therefore infection can spread.
What is contained within the paratracheal fascia?
Oesophagus Trachea Thyroid gland Strap muscles Recurrent laryngeal nerves
What are the four strap muscles?
Thyrohyoid
Sternothyroid
Sternohyoid
Omohyoid
What innervates the strap muscles?
Fibres from C1 travelling with hypoglossal- Thyrohyoid
Anas cervicalis from C1-3- Others
How many arteries supply the thyroid gland?
4 or 5
What are the arteries that supply the thyroid gland?
R+L superior thyroid
R+L inferior thyroid
Ima artery (not always present)
Where do the superior thyroid arteries originate from?
Common carotid arteries
Where do the inferior thyroid arteries originate from?
Subclavian arteries
Where does the ima artery originate from?
Brachiocephalic artery
How many veins drain the thyroid gland?
6
What six veins drain the thyroid gland?
R+L Superior thyroid vein
R+L Middle thyroid vein
R+L Inferior thyroid vein
Where do the superior and middle thyroid veins originate from?
Internal jugulars
Where do the inferior thyroid veins originate from?
Brachiocephalic vein
How many groups of lymph nodes drain the thyroid gland?
5
What five groups of lymph nodes drain the thyroid gland?
Superior deep cervical lymph nodes
R+L Inferior deep cervical lymph nodes
Paratracheal
Paratracheal
Which lymph nodes often metastasise?
Tracheal ones.
What two nerves are often impinged by the thyroid gland?
Recurrent laryngeal nerve
Vagus nerve
Where do the recurrent laryngeal nerves run?
In the carotid sheaths then loop under the arch of the aorta (L) and right subclavian artery (R)
Where do the vagus nerves run?
In the carotid sheaths beside the pretracheal fascia
What vertebra levels does the thyroid gland span?
C5-T1
What part of the thyroid gland needs to be moved to perform a tracheostomy?
Isthmus
What are the basic units of the thyroid gland?
Follicles
What are the two areas of a thyroid follicle?
Follicular cells
Colloid
Where are follicular cells found?
As a single cell layer round the outside of the follicle
Where is the colloid found?
In the centre of the follicle
What is stored in the colloid?
Thyroglobulin
What other cells are found in the follicle?
Parafollicular C cells (rare).
Little role in humans
What chemical does the thyroid gland predominantly use?
Iodine
What happens to iodine once it has been taken up into follicular cells?
It is excreted into the colloid along with thyroglobulin where they are conjugated to form T3 and T4.
What are the first products of iodine and thyroglobulin conjugation?
MIT
DIT
What happens to MIT and DIT?
Joined together to form T3 and T4
What are T3 and T4?
Thyroid hormones.
Which thyroid hormone is most abundant?
T4 (makes up 90%)
Which thyroid hormone is most active?
T3 (4x more active)
What happens to T4 in the tissues?
Converted to T3
How is the majority of thyroid hormone transported in the blood?
Bound to proteins
What proteins commonly bind thyroid hormone?
Thyroxine binding globulin/TBG (70%)
Thyroxine binding prealbumin/TBPA (20%)
Albumin (5%)
Free thyroid hormone
What kind of receptor is the thyroid hormone receptor?
Nuclear
What general effects does thyroid hormone have on the body?
Increased met Increased thermogenesis Increased growth Aids development Modifies behaviour
What effect do thyroid hormones have on metabolism?
Increase it
How do thyroid hormones increase metabolism?
Increase mitochondria
Mobilize fats
Build protein
Increase blood glucose
What effect do thyroid hormones have on thermogenesis?
Increase it
How do thyroid hormones increase thermogenesis?
Increase electron uncoupling
What effect do thyroid hormones have on growth?
Increase it
How do thyroid hormones increase growth?
Increase release of GHSH
Is thyroid hormone important for foetal brain development?
Yes
What affect does thyroid hormone have on behaviour?
Can cause Permissive Sympathomimetic activity
What is Permissive Sympathomimetic activity?
Increased sensitivity to adrenalin and noradrenalin bu increasing receptors.
What effect does Permissive Sympathomimetic activity
have?
Increase HR and force
How is thyroid hormone release regulated?
Hypothalamus thyrotropin releasing hormone (TRH) stims pit thyroid stimulating hormone (TSH) which stims thyroid hormone release from thyroid.
How can thyroid hormones regulate their release?
T3/T4 inhibit TRH and TSH release therefore decreasing further thyroid hormone release.
What kind of feedback loop regulated thyroid hormone release?
Negative feedback
What external factors can stimulate thyroid hormone release?
Cold- Increases TRH
Stress- Increases TRH and TSH
Circadian rhythm- Levels highest at night
Where does thyroid hormone metabolism occur?
All tissues
What enzymes cause thyroid metabolism?
Deiodinase 1
Deiodinase 2
Deiodinase 3