Phys II- Endocrine II Flashcards
Follicular Cells
- functional unit of thyroid
- lumen filled with colloid (stores TH)
Describe TH
- T4 (thyroxine) or T3
- made of tyrosine (made by body) and iodine (from diet), amine
- lipophilic
- tropic
C Cells
- secrete calcitonin
- peptide hormone
TH Synthesis (4 steps)
- thyroglobulin uses exocytosis to move from follicular cells to colloid)
- Iodine to colloid from blood via pump
- Iodine attaches to tyrosine
- iodinated tyrosine molecules couple up to form TH
TH Storage
- in colloid until secretion
- usually enough for several months
TH Secretion
- follicular cells phagocytize thyroglobulin colloid
2. T3 and T4 are now free to diffuse across plasma mem into blood using plasma protein (thyroxine-binding globulin)
Is T3 or T4 more potent? How much?
T3 (4x)
How is TH used?
- target cells cleave iodine
- liver/kidney
- long term but slow acting
3 Effects of TH
- Metabolic
- Permissive
- Developmental
Metabolic Effects of TH
- basal metabolic rate
- stimulates Na/K+
- heat generation
- calorigenic
Permissive Effects of TH
- works w SNS
- increase target cells responsiveness toE and NE
- increase HR and force by increasing beta-adrenoreceptors on heart
Developmental Effects of TH
- normal NS development
- essential for normal growth
- stimulates release of GH
- stimulates IGF-1 production
- enhances effect of GH and IGF-1
Congenital Hypothyroidism
- absence of TH in fetus
- poorly developed NS (compromised intellectual function)
What is the one condition resulting from hypothyroidism?
atrophy
What are the three conditions resulting from hyperthyroidism?
- Hypertrophy
- Hyperplasia
- Goiter
Hyperthyroidism
- primary failure of thyroid
- secondary to deficiency of TRH, TSH or both
- too much iodine in diet
- low TSH in blood
- high T4/T3 in blood
- often caused by Graves (autoimmune)
- often goiter present
Cretinism
hyperthyroidism at birth causing CNS effects
How is Hyperthyroidism treated?
- surgical removal
- radioactive iodine
- antithyroid
Symptoms of Hyperthyroidism
- weight loss
- heat intolerance
- increased appetite
Hypothyroidism
- high TSH
- low T4 and T3
Symptoms of Hypothyroidism
- weight gain
- cold sensitivity
- fatigue
- slow weak pulse
- impaired mental function