lecture 23

Hormone Regulation

• Hormones regulate various bodily processes, including circadian rhythms, metabolism, "fight, flight, freeze" responses, and blood sugar regulation.
• The pancreas, an endocrine organ, regulates blood sugar levels via negative feedback loops.

Hormone Characteristics

• Hormones target specific cells that have a receptor for the hormone.
• Hormone receptors can be on the cell surface or inside a cell, depending on the molecular makeup of the hormone.
• Hydrophilic hormones (e.g., peptides and amines) cannot cross cell membranes, while hydrophobic hormones (e.g., steroids) can.

Hormone Types

• Amines and peptide hormones are more abundant and diverse, working in minutes to hours and typically initiating signal cascades that activate or repress enzymes.
• Hormone amplification occurs along a hormonal pathway, where one gland releases a hormone that triggers a second gland to release a hormone, amplifying the signal until the final impact on the target cell.

Evolutionary Conservation of Hormones

• Vertebrates and invertebrates share a number of hormones, although their functions differ between the groups.
• Some hormones also function as neurotransmitters.

Vertebrate Endocrine System

• The hypothalamus responds to sensory input from the nervous system by secreting releasing hormones, which signal the anterior or posterior pituitary.
• The pituitary gland, formed from epithelial cells in the roof of the mouth and neural tissue at the base of the brain, releases hormones to regulate the rest of the endocrine system.

Pituitary Gland

• Hormones released by the anterior pituitary act on other glands to cause the release of other hormones (tropic hormones).
• Hormones released by the anterior pituitary include TSH, FSH, LH, and ACTH.
• Hormones released by the posterior pituitary gland include oxytocin and antidiuretic hormone (ADH).

Other Body Glands

• The parathyroid gland controls the level of calcium in the blood by signaling bone to be built or broken down.
• The pineal gland controls circadian rhythms by secreting melatonin.
• The adrenal medulla secretes epinephrine and norepinephrine, regulating fight, flight, freeze responses.

Local Chemical Communication

• Paracrines are chemical signals that act on nearby cells.
• Autocrine signals are chemical signals that act on the cell that secreted them.
• Histamines are paracrines released when a cell is damaged, causing inflammation and dilating blood vessels.

Endocrine System

• The endocrine system regulates responses to the environment, growth and development, homeostasis, and reproduction.
• The system is often triggered by sensory input from the nervous system.

Growth Regulation

• Sex hormones are released to trigger the development of secondary sex characteristics as an animal approaches adulthood.
• Molting and metamorphosis in insects are triggered by the release of hormones in tissues in the head.
• In humans, growth regulation is primarily controlled by the pituitary gland, which produces Human Growth Hormone (hGH or somatotropin).