Lecture 24 (thyroid + parathyroid) Flashcards
Thyroid (main structures + histology)
Structures:
- right + left lobes
- isthmus
Histology of thyroid follicle
- colloid stores thyroglobulin (TGB)
- follicular cell
- parafollicular (C) cell (release calcitonin)
Notes about thyroid surrounding structures + thyroid surgery
- highly vascularized
- many important nerves nearby, risk of losing voice if nerve is damaged during surgery
Actions of thyroid hormone
-
increase BMR (basal metabolic rate): use fuel, consume O2, generate heat
Regulate metabolism: - stimulate synthesis of many proteins: Na+/K pump, increase ATP utilization, increase heat
- glycogenolysis + lipolysis: breakdown into glucose, glycerol + fatty acids
- hepatic excretion of cholesterol
- up-regulates B-receptors
- growth: mental development, reproductive health
which receptors do NE and E stimulate?
NE: preferentially alpha-receptors
E: both alpha and beta
Thyroid hormone (types + features)
T3: benzene ring + tyrosine (also used in catecholamines) has 3 Iodines
T4: same but 4 iodines
- T4 produced more, less potent, more stable
- all cells have enzyme to convert T4 to T3
- lipophilic
Thyroid hormone regulation
TRH: produce TSH
TSH: produce and release stored T3 + T4
T3 + T4: blood levels regulate other hormones
- high T –> decrease TRH + TSH
- low T –> increase TRH + TSH
Synthesis of thyroid hormones
*need tyrosine and iodine
- TGB synthesized
- iodide trapping (pulled into cell)
- oxidize into iodine (via thyroperoxydase:TPO)
- iodination of tyrosine (T1 + T2 on TGB)
- coupling of T1&T2 (into T3 + T4 on TGB)
- removes from colloid
- TH diffuse into blood (detach from TGB)
- travel using TBG (thyroid binding globulin)
Thyroid goiter (main cause)
- insufficient iodine causes
- inability to produce T3 & T4
- triggers excessive TRH + TSH
- triggers hypertrophy & hyperplasia (cells reproduce + grow in size)
- creates a goiter
thyroid pathology
euthyroidal - normal thyroid
hyperthyroidism - high TH
hypothyroidism - low TH
causes of hyperthyroidism + goiter or not
- excessive TRH or TSH –> goiter
- production of auto-antibodies that stimulate TSH receptors (Grave’s disease) –> goiter
- thyroid adenoma/toxic nodule (produces high TH)
symptoms of hyperthyroidism
- lose weight
- exophthalmos (bulging eyes, must be surgically corrected)
- high body temp
- fatigue (due to muscle wasting)
- high HR
- highly alert (may lead to irritability or hyperreflexia)
- may or may not have goiter
causes of hypothyroidism
- inadequate iodine –> goiter
- TRH or TSH deficiency –>
- loss of thyroid follicular cells
- eg: hashimoto’s thyroiditis –> goiter (autoimmune cells flood thyroid)
symptoms of hypothyroidism
- gain weight
- low body temp
- fatigue (lack of energy)
- high blood cholesterol
- low HR and potentially low BP
- hyporeflexia
- puffiness (accumulation of fluid especially in face, hands and feet)
Parathyroid glands (location, features, histology)
- 4 on posterior side of thyroid (#can vary)
- much easier to see in children
Histology - chief cells (secrete parathyroid hormone)
- oxyphil cells
Hormones produced in Thyroid + Parathyroid
T: thyroxin (T3 + T4) and calcitonin (CT)
P: parathyroid hormone (PTH)
*CT and PTH are hydrophillic
