The Thyroid And Adrenal Gland

Thyroid-binding globulin (TBG) is the main transporter of thyroid hormones. TBG is a protein produced by the liver that binds to thyroid hormones, such as thyroxine (T4) and triiodothyronine (T3), in the bloodstream. This binding allows the hormones to be transported throughout the body to their target tissues, where they play important roles in regulating metabolism, growth, and development. Therefore, TBG is crucial for the proper functioning of thyroid hormones in the body.

Adrenaline is produced by chromaffin cells of the adrenal medulla. These cells are specialized neuroendocrine cells found in the adrenal glands. They secrete adrenaline, also known as epinephrine, in response to stress or stimulation of the sympathetic nervous system. Adrenaline plays a crucial role in the fight-or-flight response, increasing heart rate, blood pressure, and energy availability to prepare the body for action.

Very high T3 levels promote net anabolism of muscle and fat. Anabolism refers to the process of building up complex molecules from simpler ones, resulting in growth and development. In this context, high T3 levels would stimulate the synthesis of proteins and lipids, leading to an increase in muscle mass and fat accumulation. This is in contrast to catabolism, which involves the breakdown of complex molecules into simpler ones, resulting in the release of energy.

Thyroxine has the highest affinity for intracellular and transport proteins compared to T3. This is because thyroxine is the major form of thyroid hormone in the bloodstream and it binds tightly to transport proteins, such as thyroxine-binding globulin (TBG), which helps to carry it through the bloodstream to target tissues. Once inside the cells, thyroxine is converted to T3, the active form of the hormone. However, T3 has a lower affinity for binding proteins and is more readily taken up by cells, where it exerts its biological effects.

Deiodinase is an enzyme that is responsible for converting the inactive thyroid hormone T4 into the active form T3 inside the cells. This conversion is crucial for regulating metabolism, growth, and development. Deiodinase removes an iodine atom from the T4 molecule, resulting in the formation of T3. Without deiodinase, T4 would remain inactive and unable to exert its effects on the body. Therefore, deiodinase plays a vital role in ensuring proper thyroid hormone function within the cells.

Noradrenaline stimulates both α-adrenoceptors and β1-adrenoceptors. α-adrenoceptors are found in smooth muscle, and their stimulation leads to vasoconstriction. β1-adrenoceptors are found in the heart, and their stimulation increases heart rate and contractility.

TSH (thyroid-stimulating hormone) is released by the pituitary gland and acts on the follicular cells of the thyroid gland to regulate thyroid hormone production. TSH stimulates the release of thyroid hormones (T3 and T4) from the thyroid gland, which in turn negatively feedback inhibits the release of TRH (thyrotropin-releasing hormone) from the hypothalamus. This feedback loop helps maintain the balance of thyroid hormones in the body. Therefore, the correct answer is "Decreased TRH release" because TSH does not directly act on the hypothalamus to decrease TRH release.

Cold via the hypothalamus causes an increase in TSH release. The hypothalamus senses the decrease in body temperature due to cold and stimulates the release of thyrotropin-releasing hormone (TRH). TRH then stimulates the anterior pituitary gland to release thyroid-stimulating hormone (TSH), which in turn stimulates the thyroid gland to produce and release more thyroid hormones (T3 and T4). This feedback loop helps to increase the metabolic rate and generate heat, thus helping to raise body temperature back to normal.

T3 and T4 are thyroid hormones that have inhibitory effects on the pituitary gland. They decrease the number of TRH receptors, which reduces the sensitivity of the pituitary gland to TRH (thyrotropin-releasing hormone). This leads to a decrease in TSH (thyroid-stimulating hormone) production by the pituitary gland. Therefore, the correct answer is that T3 and T4 cause a decrease in TRH receptors and a decrease in TSH production.

Cortisol increases medullary production of adrenaline by increasing the activity of the enzyme PNMT. PNMT, or phenylethanolamine N-methyltransferase, is responsible for converting norepinephrine to adrenaline in the adrenal medulla. Cortisol stimulates the synthesis of PNMT, leading to an increase in adrenaline production. This is an important regulatory mechanism in the body's stress response, as adrenaline plays a crucial role in the fight-or-flight response.

ACTH, or adrenocorticotropic hormone, stimulates the production of cortisol in the adrenal glands. Cortisol is a steroid hormone that helps regulate various body functions, including metabolism, immune response, and stress response. Noradrenaline and dopamine are neurotransmitters produced in the brain and are not directly stimulated by ACTH. Therefore, the correct answer is Noradrenaline and Dopamine.

Thyroid hormones stimulate both anabolism and catabolism simultaneously, creating a futile cycle. In this cycle, the body continuously breaks down and builds up molecules, resulting in a net energy loss. This process is inefficient and does not contribute to the overall energy balance of the body.