Activated PLCβ hydrolyzes membrane phospholipids (as described below) resulting in increased levels of IP and DAG.Downstream signaling proteins are phosphorylated on serine and threonine by PKA and DAG-activated protein kinase C (PKC) leading to alterations in their activities.Activation of these receptors by hormones (the first messenger) leads to the intracellular production of a second messenger, such as c AMP, which is responsible for initiating the intracellular biological response.
Carriers for steroid and thyroid hormones allow these very hydrophobic substances to be present in the plasma at concentrations several hundred-fold greater than their solubility in water would permit.
Carriers for small, hydrophilic amino acid-derived hormones prevent their filtration through the renal glomerulus, greatly prolonging their circulating half-life.
Receptor structure is varied: some receptors consist of a single polypeptide chain with a domain on either side of the membrane, connected by a membrane-spanning domain.
Some receptors are comprised of a single polypeptide chain that is passed back and forth in serpentine fashion across the membrane, giving multiple intracellular, transmembrane, and extracellular domains.
Descriptive Table of Vertebrate Hormones Structure and Function of Hormones Receptors for Peptide Hormones Basics of Peptide Hormones The Hypothalamic-Pituitary Axis The Glycoprotein Hormone Family The Gonadotropins (LH, FSH, h CG) Thyroid Stimulating Hormone (TSH) Pro-Opiomelanocortin (POMC) Family Adrenocorticotropic Hormone, ACTH POMC-Derived Melanocortins & Feeding Behavior The Posterior Pituitary Hormones Vasopressin and Oxytocin The Growth Hormone Family Growth Hormone (GH) Human Chorionic Somatomammotropin (h CS) Prolactin (PRL) The Pancreatic Polypeptide Family: PP, PYY, NPY Melanin-Concentrating Hormone, MCH The Orexins Gastrointestinal Hormones and Peptides Adipose Tissue Hormones and Cytokines Irisin: Exercise-Induced Skeletal Muscle Hormone Natriuretic Hormones Renin-Angiotensin System Parathyroid Hormone (PTH) Calcitonin Family Erythropoietin, EPO The Pancreatic Hormones Insulin and Glucagon Somatostatin Amylin The integration of body functions in humans and other higher organisms is carried out by the nervous system, the immune system, and the endocrine system.
The endocrine system is composed of a number of tissues that secrete their products, endocrine hormones, into the circulatory system; from there they are disseminated throughout the body, regulating the function of distant tissues and maintaining homeostasis.
In addition, systemic feedback mechanisms have evolved to regulate the production of endocrine hormones.
Once a hormone is secreted by an endocrine tissue, it generally binds to a specific plasma protein carrier, with the complex being disseminated to distant tissues.
The G-GTP complex binds adenylate cyclase, activating the enzyme.
The activation of adenylate cyclase leads to c AMP production in the cytosol and to the activation of PKA, followed by regulatory phosphorylation of numerous enzymes. For more information on G-proteins and GPCRs visit the Signal Transduction page.
Additionally, a series of membrane-associated and intracellular tyrosine kinases phosphorylate specific tyrosine residues on target enzymes and other regulatory proteins.