Thyroid Hormone Function and Metabolism

Study Notes

Under normal conditions, the thyroid hormone receptor is a transcription factor that binds to gene DNA, reducing the transcription of genes linked to metabolic rate.
Cold temperatures trigger the release of thyroxine from the thyroid gland, which activates the receptor, leading to an increase in transcription.
Increased transcription produces proteins that enhance the metabolic rate, resulting in elevated body temperature.

Transcription factors regulate gene transcription by binding to specific DNA sites near gene start points.
Activators boost transcription rates, while repressors diminish them.
Hormones can modulate the activity of transcription factors, influencing gene expression.

Endocrine glands release hormones directly into the bloodstream instead of via ducts, distinguishing them from exocrine glands.
Major endocrine glands include:
- Pituitary Gland: Often termed the "master gland," it regulates various bodily functions.
- Hypothalamus: Controls the pituitary gland and homeostasis, including temperature regulation.
- Thyroid Glands: Produce thyroid hormones that regulate growth and metabolism.
- Parathyroid Glands: Secrete hormones that manage calcium homeostasis.
- Pancreas: Functions as both endocrine (insulin, glucagon) and exocrine (digestive enzymes) gland.
- Adrenal Glands: Generate hormones like adrenaline (fight or flight response) and aldosterone (osmotic balance).
- Kidneys: Involve hormone production that affects red blood cell synthesis and vitamin D metabolism.

The hypothalamus serves a critical role in maintaining constant body temperature through thermoregulation.
It receives temperature data from thermoreceptors distributed throughout the body.
Impulses from thermoreceptors travel via sensory neurons to the hypothalamus, which in turn sends signals through motor neurons to various effectors (muscles and glands).
Effectors act to correct and stabilize body temperature when deviations occur.

Under normal conditions, the thyroid hormone receptor is a transcription factor that binds to gene DNA, reducing the transcription of genes linked to metabolic rate.
Cold temperatures trigger the release of thyroxine from the thyroid gland, which activates the receptor, leading to an increase in transcription.
Increased transcription produces proteins that enhance the metabolic rate, resulting in elevated body temperature.

Transcription factors regulate gene transcription by binding to specific DNA sites near gene start points.
Activators boost transcription rates, while repressors diminish them.
Hormones can modulate the activity of transcription factors, influencing gene expression.

Endocrine glands release hormones directly into the bloodstream instead of via ducts, distinguishing them from exocrine glands.
Major endocrine glands include:
- Pituitary Gland: Often termed the "master gland," it regulates various bodily functions.
- Hypothalamus: Controls the pituitary gland and homeostasis, including temperature regulation.
- Thyroid Glands: Produce thyroid hormones that regulate growth and metabolism.
- Parathyroid Glands: Secrete hormones that manage calcium homeostasis.
- Pancreas: Functions as both endocrine (insulin, glucagon) and exocrine (digestive enzymes) gland.
- Adrenal Glands: Generate hormones like adrenaline (fight or flight response) and aldosterone (osmotic balance).
- Kidneys: Involve hormone production that affects red blood cell synthesis and vitamin D metabolism.

The hypothalamus serves a critical role in maintaining constant body temperature through thermoregulation.
It receives temperature data from thermoreceptors distributed throughout the body.
Impulses from thermoreceptors travel via sensory neurons to the hypothalamus, which in turn sends signals through motor neurons to various effectors (muscles and glands).
Effectors act to correct and stabilize body temperature when deviations occur.