AP BIOLOGY

Detailed explanation-1: -Here, a soluble signaling molecule secreted by one cell diffuses to another cell in the local neighborhood. For instance, neurotransmitters secreted by neurons diffuse a few nanometers before binding to receptors on target neurons or muscle cells.

Detailed explanation-2: -Paracrine signaling occurs when a ligand diffuses in a small area and only acts on neighboring cells. Neural signals are a specialized subset of paracine signals, diffusing a very short distance within the synaptic cleft between adjacent neurons (more on neural communication in a future class session).

Detailed explanation-3: -Specificity of signaling can be controlled if only some cells can respond to a particular hormone. Endocrine signaling involves the release of hormones by internal glands of an organism directly into the circulatory system, regulating distant target organs.

Detailed explanation-4: -Autocrine signals bind to receptors on cells that secrete them. Paracrine signals bind to receptors and stimulate nearby cells. Exocrine signaling occurs when cells secrete signaling molecules into the blood.