Endocrine System Helen is a 45-year-old housewife, lately she\'s noticed that sh
ID: 3522640 • Letter: E
Question
Endocrine System Helen is a 45-year-old housewife, lately she's noticed that she has been losing weight but maintaining her caloric intake and still going for her 2 powerwalks a week, although she feels like she needs to start running as when she gets home she is full of beans. She has also been increasingly irritated with her husband Timothy who has been putting the electric blanket on in bed when she is already overheating Helen goes to her local clinic to see Dr. Dresden, who notes that her body temperature is above average and she has in fact lost 10 kg since her regular check-up 4 months ago. Dr Dresden orders a blood test to check Helen's thyroid hormone levels T4 concentration 15.2 ug/dl (N-4.5-12.5), T3 concentration- 194.6 ng/dl (N 80-160) What affect would Helen's current levels of T4 and T3 have on her levels of TRH and TSH, with respect to homeostasis and explain the feedback system.Explanation / Answer
The hypothalamus - potutary - thyroid (HPT) axis is crucial for the maintenance of hokeostatic physiological levels of hormoces. The HPT axis is a feedback system and is composed of multiple loops. The control of the feedback loop lies with the thyrotrophic hormones. In pathologies, there is an anomalous functionality in the HPT feedback system. Any up-regulation or decrease in the HPT axis or hormonal levels is directly fed back to the system for review of the HPT functionaly. the HPT axis controls the release of the thyroid hormones, T3 and T4. The thyrotropin releasing hormone, (TRH), is responsible for the release of the thyroid stimlating hormone (TSH). thyrotropin - release horomone (TRH) is responsible for synthesising, releasing and the biological activities of TSH.
Clinical information :
Thyroxine (T4) is synthesized in the thyroid gland. T4 metabolized to triiodothyronine (T3) peripherally by deiodination. T4 is considered a reservior or prohormone for T3, the biologically most active thyroid hormone. About 0.05% of circulating T4 is in the free or unbound portion. The remainder is bound to thyroxine - binding globulin (TBG),prealbumin and albumn.
the hypothalamus secretes thyrotropin releasing harmone (TRH), which stimulates the pitutary to release thyroid - stimulating hormone (TSH). TSH stimulated the thyroid to secrete T4. T4 is primary converted peripherally to T3. High amounts of T3 and T4 cause of hyper thyroidsm.
T3 and T4 cause positive feedback to the pitutary and hypothalamus with resultant suppressin or stimulation of the thyroid gland as follows : decrease of TSH if T3 or T4 is high (hyperthyroidism), and increase of TSH if T3 or T4 is low (hypothyroidism).
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