Main Understandings

• Endocrine glands secrete hormones directly into the bloodstream
• Steroid hormones bind to receptor proteins in the cytoplasm of the target cell to form a receptor-hormone complex
• The receptor-hormone complex promotes the transcription of specific genes
• Peptide hormones bind to receptors in the plasma membrane of the target cell
• Binding of hormones to membrane receptors activates a cascade mediated by a second messenger inside the cell
• The hypothalamus controls hormone secretion by the anterior and posterior lobes of the pituitary gland
• Hormones secreted by the pituitary control growth, developmental changes, reproduction and homeostasis

Hypothalamus

The hypothalamus is the section of the brain that links the nervous and endocrine systems in order to maintain homeostasis

• It receives information from nerves throughout the body and other parts of the brain and initiates endocrine responses
• It secretes neurochemicals (called releasing factors) into a portal system which target the anterior lobe of the pituitary gland
• It also secretes hormones directly into the blood via neurosecretory cells that extend into the posterior pituitary lobe

Pituitary Gland

The pituitary gland lies adjacent to the hypothalamus and is in direct contact due to a portal blood system

• The pituitary gland receives instructions from the hypothalamus and consists of two lobes (anterior and posterior lobe)

Anterior Lobe

• The anterior lobe is also called the adenohypophysis (‘adeno’ = relating to glands)
• The hypothalamus produces releasing factors, which are released into portal vessels by neurosecretory cells
• The releasing factors cause endocrine cells in the anterior pituitary to release specific hormones into the bloodstream
  • An example of a releasing factor is GnRH, which triggers the release of LH and FSH from the anterior pituitary

Posterior Lobe

• The posterior lobe is also called the neurohypophysis (‘neuro’ = relating to nerves)
• The posterior lobe releases hormones produced by the hypothalamus itself (via neurosecretory cells)
• These neurosecretory cells extend into the posterior lobe from the hypothalamus and release hormones into the blood