What key components does the endocrine system contain?

The endocrine system is primarily responsible for hormone production and regulation, which is crucial for maintaining homeostasis within the body. The key components that make up the endocrine system include glands that secrete hormones directly into the bloodstream. Among these, the pituitary, adrenal, and thyroid glands play essential roles.

The pituitary gland, often dubbed the "master gland," regulates various endocrine functions by controlling other glands. The adrenal glands are responsible for producing hormones that help regulate metabolism, the immune response, and stress. The thyroid gland plays a critical role in regulating metabolism, energy generation, and overall growth and development through its production of thyroid hormones.

In contrast, the other options contain organs and systems that either do not have significant roles in hormonal regulation or belong to different physiological systems, such as the cardiovascular or nervous systems. Therefore, the inclusion of the pituitary, adrenal, and thyroid glands accurately reflects the core components of the endocrine system.