Endocrine & Neuroendocrine: The Long Distance Travelers
Types of Cellular Secretion of Hormones Types of Hormones Action of Hormone Example Autocrine Acts on cells that synthesized them Insulin-like Growth Factor (IGF-1)- stimulates cell division in the cell which produced it. Paracrine Acts on nearby cells Insulin, secreted by pancreatic βcells-affects secretion of glucagon by pancreatic α cells Endocrine Carried in bloodstream or thru lymph to target cells in organs Insulin, Estradiol, Cortisol Neuroendocrine Hormones synthesized in neuron: a) releases hormone next to a) releases hormone next to target cell OR target cell OR b) releases it into bloodstream, b) releases it into bloodstream, which carries it to target cell. which carries it to target cell. Hormone synthesized in neuron, goes from hypothalamus to anterior pituitary gland thru the portal system Neural Chemical released by 1 neuron, & acts on adjacent neuron. Neurotransmitters: Acetylcholine Pheromonal Release of volatile hormones (into atmosphere; are transmitted to another individual & recognized as olfactory signal. Pheromones
Regulation of Hormone Secretion: NEGATIVE FEEDBACK If hormone A acts to raise the plasma concentration of substrate B, a decrease in substrate B will stimulate the secretion of hormone A. Whereas an increase in substrate B will suppress secretion of hormone A. Maintains homeostasis.
Blood Transport of Hormones When hormones are secreted into blood, many are immediately bound to plasma proteins. Proteins can recognize hormone specifically & bind it w/high affinity (ex: binding of sex hormones by sex hormone binding globulin- SHBG).
Blood Transport of Hormones Equilibrium btw free & bound hormone –a fixed proportion of hormone travels free/unbound, while most is carried bound. Bound hormone is Bound hormone is –physiologically inactive –protected from metabolic enzymes in organs (liver) Drugs, (aspirin) can displace other substances like anticoagulants from their binding sites –may cause hemorrhage.
General Mechanisms of Hormonal Action Hormones interact w/target cells thru primary interaction w/receptors that recognize the hormones. Several receptor systems: differ in mechanism & timing. 1) Membrane Receptors 1) Membrane Receptors 2) Intracellular Receptors
bind to receptors on cell membrane conformational change in other membrane proteins activates enzymes in cell Synthesis of second messengers that activate phosphorylating enzymes Charged ions (peptides, neurotransmitters ) MEMBRANE RECEPTORS
INTRACELLULAR RECEPTORS Uncharged molecules (steroid hormones) diffuse into cell & bind to intracellular receptors hormone-receptor complex binds to specific hormone response elements (HREs) on DNA Modulates gene expression in target cell. RNA & protein synthesis altered.
TO WRAP IT UP: Types of Cell Secretion 1.Autocrine 2.Paracrine 3.Endocrine 4.Neuroendocrine 5.Neural 6.Pheromonal Blood Transport –binding of hormone to plasma protein Membrane Receptors Intracellular Receptors
Bibliography Endocrinology-At A Glance Medical Physiology-Guyton