Hormones and the Endocrine System

Vocabulary Endocrine System: the sum of all its hormone-secreting cells and tissues. Endocrine Glands: ductless and secrete hormones directly into body fluids. Hormone: chemical signals that cause a response in target cells. Positive and Negative Feedback: regulate most endocrine secretion.

Human Endocrine Glands

Basic patterns of simple hormonal control pathways. In each pathway, a receptor/sensor (blue) detects a change in some internal or external variable—the stimulus—and informs the control center (gold). The control center sends out a signal, either a hormone (red circles) or a neurohormone (red squares). An endocrine cell carries out both the receptor and control center functions.

Mechanisms of hormonal signaling: a review. A water-soluble hormone binds to a receptor protein on the surface of a target cell. This interaction triggers a signal transduction pathway that leads to a change in a cytoplasmic function or a change in gene transcription in the nucleus. Example: The binding of epinephrine to liver cells causes a cascade that leads to the conversion of glycogen to glucose. Lipid Soluble hormone penetrates the target cell’s plasma membrane and binds to an intercellular receptor, either in the cytoplasm or in the nucleus (shown here). The signal-receptor complex acts as a transcription factor, typically activating gene expression. Example: Testosterone enters the cell and binds to its specific receptor; this complex then enters the nuclei of target cells, binds to the DNA, and stimulates the transcription of a gene.

Production and release of posterior and pituitary hormones Production and release of posterior and pituitary hormones. The posterior pituitary gland is an extension of the hypothalamus. Certain neurosecretory cells in the hypothalamus make antidiuretic hormone (ADH) and oxytocin, which are transported to the posterior pituitary where they are stored. Nervous signals from the brain trigger release of these neurohormones. Bozeman Science Explains All!