Flashcards in Thyroid and and Parathyroid Function Deck (79)
What's a Positive Feedback Loop?
Positive Feedback Loop – increase in one action triggers increase in target
Example of a (+) Feedback Loop
Childbirth contractions trigger oxytocin, which in turn amplifies the contractions
What's a Negative Feedback Loop?
Negative Feedback Loop – response is opposite to the perturbation
Example of a (-) Feedback Loop
Pituitary TSH and thyroid T4
What are the glands responsible for regulating the activity of the Thyroid?
Hypothalamus and pituitary regulate thyroid, as well as intrinsic regulation by the gland itself
How does Hypothalamus and Pituitary regulate Thyroid activity?
Hypothalamus produces thyroid releasing hormone (TRH), which acts on anterior pituitary
Thyroid stimulating hormone (TSH) released by anterior pituitary into blood stream
What are the 3 thyroid hormones?
Calcitonin (Weak effect on calcium-phosphorus balance)
Function of T3 and T4 (2)
T3 and T4
-regulate metabolic rate of body
-increase protein synthesis
What is Calcitonin's function?
Weak effect on calcium-phosphorus balance
Name 2 routes that aid in Thyroid stimulation:
Vascular supply (iodine) and Sympathetic nervous system
Trace the mechanism of Thyroid stimulation (negative loop) from the Iodine in the blood stream to the TRH from the hypothalamus.
Iodine traveling in blood (from diet) absorbed into thyroid follicle cell to combine with Thyroglobulin (TGB) to form T3 and T4 (thyroid hormones)
Stimulated by TSH released by anterior pituitary into blood stream
Stimulated initially by hypothalamus TRH
What's the best stimulus for TRH?
Exposure to cold
What's the end result of the Thyroid negative feedback loop?
Negative feedback loop control
T3 and T4 in circulation limit production
Name 4 major actions of T3 and T4.
1. Enter cell and bind with receptors in nucleus
DNA stimulated for gene expression
Altered protein synthesis within cells
2. Brain growth and development
3. Bone growth and development
4. Function of metabolism, cardiac system, heat production, glucose and fat metabolism
What are the 3 main functions of the Thyroid?
Metabolism, growth, and development
Explain how is Thyroid involved in metabolism?
Basal metabolic rate and heat production
Metabolic effect- Energy substrate utilization
Glucose absorption and enzyme enhancement
Lipolysis and lipolytic hormone use
Explain how is Thyroid involved in growth and development?
Growth and development
Stimulate GH release and enhanced effects
What is the cardiovascular effect of Thyroid activity?
Increase HR and contractility possibly by enhancing effect of epi and norepi (release by the medulla of adrenal glands)
What are some confounding variables when trying to diagnose Thyroid dysfunction at an older age?
After age 60, thyroid may be mistaken for dementia, depression, heart disease
Name 3 risk factors for Thyroid dysfunction
Name a few effects of alterations in Thyroid functioning
Alterations in thyroid can produce changes in hair, nails, skin, eyes, GI, respiratory tract, cardiovascular, neuromuscular, musculoskeletal systems – virtually everything
What test diagnoses thyroid dysfunction?
TSH (thyroid stimulating hormone) test
What is the normal range of TSH?
0.5 - 4.70 µIU/mL
Name 8 sets of characteristics specific to hypothyroidism
Fatigue, feeling run down or tired, difficulty concentrating, depression, slowed heart beats
Non tender swelling around the neck
Muscle cramps, muscle weakness
dry, coarse itchy skin
dry, coarse thinning hair
intolerance to cold especially in the hands and feet
increased menstrual flow, irregular periods, infertility / miscarriage
Name 8 sets of characteristics specific to hyperthyroidism
Nervousness, irritability, restlessness, increased perspiration, palpitation, insomnia, heart racing, panic
Non tender swelling around the neck
Muscular weakness and tremor especially the upper arms and thighs. In later Grave's disease eyes may bulge
fine and brittle hair
intolerance to heat
less frequent periods with lighter flow
frequent bowel movements
Describe hormonal levels in hypothyroidism
High TSH, low T3, T4
Antibodies to TPO in Hashimoto's thyroiditis
Describe hormonal levels in hyperthyroidism
Low TSH, High T3, T4
Antibodies to TSH receptors in Grave's disease
Goiter, enlargement commonly due to lack of iodine in diet
Describe the feedback loop present in goiter in relation to dietary lack of iodine
Inhibits normal thyroid hormone production, causing hypersecretion of TSH due to lack of negative feedback loop
Almost eradicated in US due to iodized salt