Hormones and Response PathwaysKayla OwensMichael 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▫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