Hormones and Response
Pathways
Kayla Owens
Michael Drew Turner
Types of Secreted Signaling Molecules
• Hormones, local regulators, neurotransmitters,
pheromones, and neurohormones
• Trigger responses by binding to specific receptor
proteins in or on the target cells
• Only target cells have receptors for these
secreted signaling molecules, other types of cells
are unresponsive to that type of molecule
Hormones and Endocrine Signaling
• Endocrine glands—a group of endocrine cells in
a ductless organ
• Hormones are secreted through the blood
stream
▫ Maintain homeostasis, mediate responses to
environmental stimuli; regulate growth,
development, and reproduction
▫ Used in endocrine signaling
Local Regulators
• Local regulators—secreted molecules that act over
short distances and reach their target cells by
diffusion
▫ Play roles in many processes such as blood pressure
regulation, nervous system function, and reproduction
▫ Function in paracrine and autocrine signaling
• Paracrine and autocrine signaling
▫ Paracrine—target cells lie near the secreting cell
▫ Autocrine—secreted molecules act on the secreting
molecule itself
Neurotransmitters and Synaptic
Signaling
• Neurotransmitters—neurons secrete these that
diffuse a very short distance to bind receptors on
the target cells
▫ These are very important for sensation, memory,
cognition, and movement
Neuroendocrine Signaling and
Neurohormones
• Use neurosecretory cells that are specialized
neurons typically found in the brain; they then
secrete molecules that diffuse from nerve call
endings into the blood stream
• Neurohormones—travel through bloodstream to
reach target cells, a special class of hormone
Chemical Classes of Hormones
• Hormones are often divided into three groups
▫
▫
▫
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Polypeptides—ex. Insulin—water soluble
Amines—ex. Epinephrine—water soluble
Steroids—ex. Cortisol—lipid soluble
*differ in form and solubility
Cellular Response Pathways
• Water soluble hormones travel through the bloodstream and bind to
cell-surface receptors
• This triggers a cytoplasmic response or change in gene expression
• Lipid soluble hormones travel through the bloodstream and are
bound to transport proteins
• Enter target cells and bind to a receptor in the cytoplasm or nucleus
• Binding of water soluble hormones initiates signal transduction—
converts extracellular signals to specific intracellular responses
▫ Epinephrine (adrenaline)—released in response to stress by the adrenal
gland, results in release of glucose into bloodstream
▫ Steroid hormones—bind to cytoplasmic receptors; this complex moves to
the nucleus and stimulates transcription of specific genes; ex. Thyroxin,
vitamin D, testosterone, etc.
Multiple Effects of Hormones
• A given signal can have different effects on
different target cells and can produce different
effects in different species
• Differences may result from
▫ Types of receptors
▫ Specific signal transduction pathways present
▫ Particular transcription factors that are activated
Signaling by Local Regulators
• Cytokines—polypeptide regulators involved in immune
responses
• Growth factors—polypeptides that are required in the
extracellular environment for many types of cells to divide and
develop
• Nitric oxide—a gas that can serve as a neurotransmitter and as a
local regulator that produces vasodilation, increasing blood flow
• Prostaglandins—modified fatty acids that have a wide range of
effects on nearby target cells; help to induce labor
▫ Aspirin and ibuprofen inhibit the synthesis of prostaglandins
and thus reduce their fever and inflammation inducing and
pain intensifying actions