Please enable JavaScript.
Coggle requires JavaScript to display documents.
Thyroxine and body temperature - Coggle Diagram
Thyroxine and body temperature
Control of the rate of metabolism
Thyroxine in the form T3 increases the rate of cell metabolism in almost all cells in the body. T3 increases heart rate, breathing rate and rate of cellular respiration.
Thyroxine (T4) is produced by the thyroid gland, converted to T3 which is secreted into blood and carried by blood to all parts of the human body.
Thyroxine is lipid soluble and enters target cells and enters target cells by passing through the cell membrane
When thyroxine/ T3 binds to specific complementary receptors in the nucleus of target cells, the binding results in increased metabolism in the target cells. The steps include increased transcription of many different genes
Thyroid hormone
Triiodothyronine (T3) and thyroxine (T4) are amino acid derivative hormones produced and secreted by follicle cells in the thyroid glands in response to changes in body temperature.
When body temp is below the tolerance limit, thermoreceptors in the hypothalamus detect the change and stimulate neurosecretory cells to secrete thyrotropin-releasing hormone - (TRH) into the anterior pituitary.
TRH stimulates secretory cells in the pituitary gland to release thyroid-stimulating hormone (TSH) which travels to follicular cells in the thyroid gland.
TSH binds to complementary receptors and activates key enzymes that synthesise T3 and T4 in follicular cells.
T3 and T4 travel to target cells where they increase the rate of metabolism and generate heat which increases body temp and reduce the original stimulus.
An imbalance in thyroxine hormone can cause disorders called hyperthyroidism and hyperthyroidism.
In hyperthyroidism, too much T3 and T4 circulate in the blood which increases the rate of metabolism in target cells resulting in overheating, high weight loss and high blood pressure and Grave's disease.
In hypothyroidism too little t3 and T4 circulate in the blood, which decreases the rate of metabolism in target cells resulting in low body temperature, lethargy, weight gain, low blood pressure and goitre.
One cause of hyperthyroidism is a lack of dietary iodine which is required for the synthesise of T3 and T4 in thyroid follicular cells.
Control of thyroxine production by TSH
Thyroid stimulating hormone (TSH) is synthesised by the pituitary gland.
TSH stimulates the thyroid gland to produce thyroxin (T4). T4 is converted to T3(triiodothyronine) before binding to thyroxine receptors.
The blood concentration of T4 regulates the production of thyroid releasing hormone (TRH) from the hypothalamus which then regulates TSH production and release by the pituitary gland
TSH causes the thyroid gland to produce T4.
High levels of T4 inhibits the production of TRH and TSH
There is a negative feedback loop between thyroid gland and the hypothalamus and pituitary gland, with the blood concentration of T4 maintained within a tolerance range
The stimulus for TRH production (hence TSH production) is low blood concentration of T4
However high levels of T4 inhibit both TRH and TSH
Control of body temperature in humans
Thermoreceptors for body temp occur in skin, corena(eyes) and urinary bladder and blood vessels of the hypothalamus (part of the brain)
These receptors detect the stimulus of an increase or decrease in body temp
Tolerance limit of body temp: 36-38
Homeostatic mechanisms involve several effectors operating together to keep the body temp with tolerance range
Transmission of messages to these effectors may be nervous or hormonal