Endocrine System Overview

Gonads

• Ovaries in females and testes in males produce sex hormones.

Pineal Gland

• Regulates sleep patterns through the release of melatonin.

Types of Hormones based on chemical nature

• Three main hormone types: amino acid-based, steroids, and fatty acid derived.
• Most hormones are amino acid-based, including amines (dopamine & epinephrine) and polypeptide hormones (e.g., insulin, growth hormone).
• Steroid hormones are derived from cholesterol, such as gonadal and adrenocortical hormones.
• Fatty acid-derived hormones include eicosanoids, which are derived from arachidonic acid, such as leukotrienes and prostaglandins.

Intracellular Hormone Receptors and Activation of Genes

• Hormone receptors can be located in the cell membrane, cytoplasm, or nucleus.
• Cell membrane receptors are primarily for protein, peptide, and catecholamine hormones.
• Cytoplasmic receptors are primarily for steroid hormones.
• Nuclear receptors are for thyroid hormones.

Hormone Action

• Hormones circulate to all tissues but activate only target cells.
• Target cells have specific receptors for particular hormones.

G Protein–Linked Hormone Receptors

• A hormone (first messenger) binds to the receptor, which activates a G protein inside the cell.
• G protein then activates an enzyme called adenylyl cyclase.
• Adenylyl cyclase converts ATP to cyclic adenosine monophosphate (cAMP), which acts as a second messenger.
• cAMP then activates protein kinases.
• Protein kinases activate other proteins that ultimately produce a specific cellular effect.