Chapter 45 – Hormones and the Endocrine System
Chemical signals: A molecule released by one cell that may influence the activity of
Local Regulator: The molecule travels a short distance through the interstitial fluid. The
cell influenced is nearby.
• Paracrine signal
o Histamine, cytokines, growth factors
• Autocrine signals
Hormones: The molecule travels through the circulatory system, the cell influenced may
be far away.
Pheromone: The organism releases the molecule; the cell influenced is in another
• Steroid: Never polar, lipid soluble
• Polypeptide: water soluble
• Amine: lipid and water soluble
• Hormones are specific and only excite target cells
• Required for a cell to respond to a chemical signal and these are very specific
Endocrine signalling maintains
• Mediates responses to environmental stimuli
• Regulates growth and development
Paracrine signalling is where the target cells are in close proximity to the secreting cell
Autocrine signalling is where the target cell is the same cell as the secreting cell. The
Hormones are released from the cell and then get a response from the same cell.
Paracrine and Autocrine play a major role in many physiological processes such as
blood pressure regulation, nervous system functioning and reproduction.
Synapse signalling: Neurotransmitters are diffused across a synapse and get a response
from binding with a target cell.
• Cognition • Movement
Neuroendocrine signalling: specialized neurons called neurosecretory cells secrete
molecules out of the endings and into the bloodstream where it travels to the target cell.
These types of hormones are called neurohormones.
• Antidiuretic hormone (vasopressin)
o Kidney and water balance
Signal Transduction: The linage of a mechanical, chemical, or electromagnetic stimulus
to a specific cellular response
1. Reception: binding of epinephrine to Gproteinlinked receptor
2. Transduction: activates G protein, then activates cAMP which activates multiple
Second messengers: protein that transmits the message from the first messenger.
• Hormone system
• Endocrine glands: not all connected to one another like other systems
o Ductless glands that secretes hormones directly into the interstitial fluid,
from which they are carried into the bloodstream.
• Coordinates the activity of cells in different parts of the body
• Each hormone may have several effects
o Epinephrine (adrenalin)
o Several hormones may influence the same process
Breakdown of glycogen in liver cells
• Epinephrine, glucagon
Ion uptake by nephrons
• The effect of a hormone may change depending on conditions