Introduction:
Hormones are chemical messengers that are produced by glands and are released into the bloodstream. They play a vital role in regulating various bodily functions and maintaining homeostasis. In order for hormones to exert their effects, they need to reach their target sites in the body.

Explanation:
- Target Site: Target sites are specific tissues or organs in the body that are responsive to a particular hormone. These sites have receptors that can recognize and bind to the hormone. The hormone-receptor interaction triggers a series of cellular events that ultimately lead to the hormone's intended effect. Hormones can have multiple target sites in the body.
- Bloodstream: The bloodstream is the major transportation system in the body, carrying oxygen, nutrients, waste products, and hormones to various tissues and organs. Hormones are released into the bloodstream by endocrine glands and are transported throughout the body to reach their target sites.
- Hormone Transport: Once hormones are released into the bloodstream, they bind to carrier proteins to ensure their stability and proper transport. These carrier proteins protect the hormones from degradation and help regulate their release and availability. Hormones can circulate in the bloodstream for varying durations, depending on factors such as their half-life and the body's metabolic processes.
- Blood-Brain Barrier: It is important to note that not all hormones can freely cross the blood-brain barrier, which separates the bloodstream from the brain. Certain hormones, such as insulin, cannot easily pass through this barrier and require alternative mechanisms for reaching their target sites in the brain.
- Active Site: The active site refers to the specific location on a hormone receptor where the hormone binds. This binding is highly specific and is crucial for initiating the cellular response. The active site is typically a pocket or cleft on the receptor protein that perfectly complements the hormone's shape and chemical properties.

Conclusion:
In summary, hormones reach their target sites in the body through the bloodstream. They are released by endocrine glands and circulate in the bloodstream, bound to carrier proteins. Once they reach their target sites, hormones bind to specific receptors at the active site, triggering cellular responses and exerting their effects. It is through this process that hormones regulate various physiological processes and maintain homeostasis in the body.