Which of the following is not an effect of thyroid hormones?
a. Regulation of the metabolic rate
b. Promotion of growth and development
c. Thermoregulation
d. Synergism with the parasympathetic nervous system

Verified step by step guidance

1. Step 1: Begin by understanding the primary functions of thyroid hormones. Thyroid hormones, such as thyroxine (T4) and triiodothyronine (T3), play a critical role in regulating the body's metabolic rate, promoting growth and development, and maintaining thermoregulation.
2. Step 2: Analyze each option provided in the question. For example, 'Regulation of the metabolic rate' is a well-known effect of thyroid hormones, as they increase the rate of energy production and consumption in cells.
3. Step 3: Consider 'Promotion of growth and development.' Thyroid hormones are essential for normal growth and development, especially in children, as they influence protein synthesis and the development of the nervous system.
4. Step 4: Evaluate 'Thermoregulation.' Thyroid hormones help maintain body temperature by regulating heat production through metabolic processes, making this another valid effect.
5. Step 5: Examine 'Synergism with the parasympathetic nervous system.' This option is not an effect of thyroid hormones, as thyroid hormones primarily interact with the sympathetic nervous system to enhance its effects, such as increasing heart rate and energy mobilization, rather than synergizing with the parasympathetic nervous system.

Key Concepts

Thyroid Hormones

Thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3), are crucial for regulating various physiological processes in the body. They influence metabolism, energy production, and overall growth and development. These hormones are produced by the thyroid gland and play a significant role in maintaining homeostasis.

Metabolic Rate Regulation

The metabolic rate refers to the speed at which the body converts food into energy. Thyroid hormones are key regulators of this process, increasing the basal metabolic rate and influencing how the body utilizes carbohydrates, fats, and proteins. An imbalance in thyroid hormone levels can lead to conditions such as hyperthyroidism or hypothyroidism, affecting energy levels and weight.

Thermoregulation

Thermoregulation is the process by which the body maintains its core internal temperature. Thyroid hormones contribute to thermoregulation by increasing metabolic activity, which generates heat. This is particularly important in maintaining body temperature in response to environmental changes, ensuring that physiological processes function optimally.