Date post: | 31-Dec-2015 |
Category: |
Documents |
Upload: | britney-richard |
View: | 218 times |
Download: | 0 times |
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