3.3.1 Thyroid Gland Physiology Flashcards
What type of receptors respond to THs? What are the downstream effects of a bound receptor? Which TH has greater affinity
Type of receptor: nuclear
Downstream effect: alter gene expression
Greater affinity: T3
What dietary substance is required for the synthesis of TH?
Iodine
Minimum: 75 ug/day
RDA: 150 ug/day
In excess, how will TH affect glucose metabolism?
Glyconeogenolysis, altered glucose utilization, enhances actions of epinephrine through upregulation of beta-adrenergic receptors
TBG has high affinity for what molecules?
T4/T3
How does TH affect Bone, skin and hair, and GIT?
Bone: linear growth and development
Skin and hair: required for follicle development and epidermis renewal
GIT: increase GI motility
What are some conditions that favor SRIF?
Galphai
Decreased adenylyl cyclase
Decreased Ca++
Who is most at risk for thyroid disorders?
Women, 10:1
What are the effects of TH on the heart and reproductive system?
Heart: sensitivity of Beta-adrenergic receptors, increase CO via HR and SV, excess TH causes vasodilation
Reproductive system: TH required for normal function
What is the effect of TH on basal metabolic rate?
Regulates oxidative phosphorylation
Low TH: decrease in BMR
Excess TH: increase in BMR
Where is thyroid binding globulin (TBG) produced? States that increase its production? States that decrease its production?
Liver
Increase: pregnancy, newborns, oral contraceptives (estrogen)
Decrease: androgens, large dose of GCs, chronic liver dz, severe systemic illness, active acromegaly, kidney dz w/ proteinuria
What type of role does TH play in protein metabolism
Plays a permissive role by stimulating GH expression, metabolic proteins and ezymes while promoting calcification within cartilage
Only substances in the body that have iodine in their structure
THs
Name the important membrane-bound enzyme for idodide?
Thyroperoxidase (I and H2O2)
How much of T4/T3 is in the free form?
Less than 1%
What are some conditions that favor TRH?
Galphaq
PLC (PKC, Ca++)
What are the 4 functions of TH?
Regulate:
- Protein metabolism
- Glucose metabolism
- Lipid metabolism
- Basal metabolic rate (BMR)
What are some of the symptoms associated w/ hypo- and hyperthyroidism?
I WANT AN EXHAUSTIVE LIST!!!!
Compare the potencies of T3 and T4.
T3 > T4 (x10)
What are the components of the thyrotroph axis?
What effect does TH play in lipid metabolism?
Stimulates cholesterol synthesis and its conversion to bile
Low: hypercholestrolemia
High: increased fat metabolism
What are the negative feedback loops within the H-P-T axis?
What upregulates the activity of the thyrotroph? Downregulates the thyrotroph?
Upregulates: TRH
Downregulates: SRIF
What are some of the treatment methods for hyperthyroidism?
radioactive iodine, thyroidectomy, antithyroid drugs (propylthiouracil (PTU), carbimazole/methimazole (TPO inhib)
What are the three molecules that can bind thyroid hormone?
TBG, Transthyretin/thyroxine binding pre-albumin (TBPA), Albumin (low affinity, high capacity)
What are some of the causes of hypothyroidism? (6)
Cretinism - deficiency in utero
Iodide deficiency
Hashimoto’s Dz - AI dz
Non-thyroidal illness - shift in conversion of T4 to rT3
Endemic goiter
Sporadic goiter - rare, mutation in thyroglobulin/TPO
What is Lil Doc’s favorite song?
Hello by Adelle
Once again, this may not be factual. Yet, it is highly probable considering her willingness to share this photo on the internet
Where is 5’ deiodinase type II found?
Pituitary, brain, brown adipose
How does TH affect brain development?
Promotes:
- dendritic branching
- proliferation of axons
- formation of synapses
Regulates myelinization within the cortex
How is iodide taken up into the body?
Na/I symporter
Active process that requires energy
What are the half-lives of T4 and T3
T4: ~8 days
T3: 1-3 days
What comprises the thyroid?
Numerous follicles
What idonates thyroglobulin?
Thyroperoxidase (TPO)
How does TH affect glucose metabolism?
Pontentiates actions of insulin (stimulates glycogen and glucose utilization)
What is the treatment for hypothyroidism?
exogenous T4 (L-thyroxine)
What are some of the other causes of hyperthyroidism?
Adenomas of the thyroid gland, pituitary adenomas - excessive TSH, thyrotoxicosis - excessive TH
Describe some of the characteristics of Grave’s Dz?
AI dz (lack of negative feedback)
Diffuse toxic hyperplasia
Prediposing factors: Female, stress, [smoking]
Symptoms: nervousness, fatigue, rapid HR or palpitations, heat intolerance, weight loss, opthalmopathy
An excess of TH will lead to what irregularity regarding protein metabolism?
protein catabolism
What is the standard conversion b/t THs in the periphery
40% of secreted T4 is converted to T3
What are some of the secretion methods of TH, which is stimulated by TSH?
pinocytosis
lysosome fusion
hydrolysis
secretion
deiodination
TH plays an important role in which three processes?
CNS development, growth, metabolism
