Endocrinology Flashcards
What are the different types of chemical messengers and what do they involve?
Neurocrines: Chemical messengers that are released by neurons. (Neurotransmitters are a subclass of this). Endocrines (Hormones): Chemical messengers that are released into the bloodstream and synthesized by a specific tissue. Paracrines: Chemical messengers that affect nearby cells and travel through the extracellular fluid. Autocrines: Like paracrines, except act only on cells of the same type as their secreting cell. Cytokines: Chemical messengers secreted by immune cells, they can act in a paracrine, autocrine, or endocrine manner. Pheromones: Chemical messengers that are released by an animal into the environment to affect the behavior or physiology of another animal of the same species.
What different structural types can water soluble hormones be subdivided into? Describe them briefly.
Water-soluble hormones: These are usually stored in vesicles then released into the blood. They travel directly in the blood without the need for a transporter. They usually elicit short-term effects from targeted cells, however, they can result in longer-term effects in some cases (eg: GH).
Peptide/polypeptide/protein hormones: Examples include: Insulin, leptin, ADH, the somatomammotropins, and POMC derivatives.
Glycoprotein hormones: These have oligosaccharide groups covalently bonded to the protein portion of the molecule. Examples include LH, FSH, TSH, and hCG. These hormones are closely related and are made up of two subunits; alpha and beta. The alpha subunit is the same for all of the hormones but the beta subunit differs between them.
Catecholamines: These are made from tyrosine (amino acid). They are not all hormones, for example, noradrenaline and dopamine work as neurotransmitters, while adrenaline is a hormone.
What different structural types can lipid-soluble hormones be subdivided into? Describe them briefly.
Lipid-soluble hormones: These diffuse out of cells once made. They travel through blood with transporters to target cells. They diffuse through membranes of target cells and then bind to intracellular receptors. Then they usually lead to a change in gene expression. Longer lasting change.
Steroid hormones: These are made from cholesterol. Examples include testosterone and oestrogen, as well as corticosteroids made by the adrenal cortex.
Thyroid hormones: thyroxine and triiodothyronine are made from tyrosine in the thyroid gland and, unusually, include iodine in their structures. triiodothyronine is the active hormone, made from thyroxine.
Fatty acid derivatives: prostaglandins, often acting as inflammatory mediating signals in the local area. Because they are unstable, they are usually paracrines. Synthesis of prostaglandins requires the enzyme cyclooxygenase.
Indoleamines: These are all made from a similar structure. Example: melatonin, serotonin, histamine.
How do G-Protein coupled receptors work? Mention the three types of G protein as well.
The water-soluble hormone binds to the receptor extracellularly.
This activates the Gs (stimulating) protein. The alpha subunit dissociates from GDP and binds to GTP. It then dissociates from the beta and game subunits. The alpha subunit binds to the adenylate cyclase enzyme, which is also anchored to the cell membrane. The adenylate cyclase enzyme then catalyzes the reaction of ATP to cAMP. cAMP then activates a protein kinase enzyme, which phosphorylates various molecules, resulting in a variety of responses. This is a cascade reaction as a small amount of hormone can result in a proportionally larger response. To terminate the response, GTP will be hydrolyzed to GDP, and the alpha subunit will bind to the beta and gamma subunits because of this. A phosphodiesterase will hydrolyse cAMP. There is also a Gi protein that inhibits the action of adenylate cyclase and reduces the production of cAMP. There is also another type of G protein, Gq that works in a different way. It activates the inositol phospholipid pathway, which results in the release of intracellular Ca2+.
Describe briefly lipid-soluble hormone receptors
These are usually intracellular and are called ligand modulated transcription factors. The hormones will bind to them and they will travel to the DNA to act as a transcription factor. Many lipid-soluble hormones also have rapid effects mediated via plasma membrane receptors.
How are hormones destroyed?
Most are broken down in the liver or kidneys. Some are excreted in the urine. Some are taken up, into the cell by endocytosis along with their receptor, then broken down.
