Endocrinology and Thyroid Flashcards
Endocrinology
The study of the endocrine system, the hormones it secretes and its disorders
Endocrine gland
Organs that secrete hormones, which play an important role in homeostasis, into the blood or lymph e.g. pancreas
Hormone
A chemical messenger dispersed by the blood that act on target organs to produce effects distant from their point of release e.g. insulin
Exocrine gland
A gland that secretes its products through a duct to the outer surface of the body or an organ e.g. salivary gland
Endocrine signalling
Secretory cells release hormone through the blood to initiate response in distant target cells e.g. growth hormone from pituitary
Paracrine signalling
Secretion of a substance by one cell, which then acts on adjacent cells e.g. release of acetlycholine
Autocrine signalling
Secretion of a substance by a cell, which acts on surface receptors of the same cell
Main endocrine glands
Hypothalamus Pituitary Thyroid Pancreas Kidney Ovary testes
Types of hormones
Polypeptides e.g. insulin
- synthesised on the RER and sent to golgi for packaging and excretion
- stimulus for exocytosis due to membrane depolarisation as a result of increase cAMP and protein kinase action
- water soluble
Modified amino acids e.g. thyroid hormones
- thyroid hormones synthesise in glandullar cells by adding iodine to tyrosines
- secreted when amines split from thyroglobulin
- combines with plasma proteins for transport
Steroid hormones e.g. glucocorticoids
- secreted by adrenal cortex, ovaries, testes
- lipid soluble molecules synthesised from cholesterol
- rapidly mobilised in cytosol due to large stores of cholesterol readily available
- simply diffuse across the membrane due to high lipid solubility
Endocrine system
- Receives chemical and physical stimuli
- Releases a chemical signal that will elicit a change in tissue
Steroid hormone synthesis
- No gene activation
- Regulated by increased conc. of cAMP and Ca2+
- Cholesterol is converted to pregnenolone which undergoes further enzymatic transformation in synthesis of derivative steroid hormones
- Steroidogenic acute regulatory protein mediates acute regulation of steroid hormone
Water-soluble hormones
- Dissolved in the blood plasma
- Transported from their sites of synthesis to target tissues
- Cannot pass through membranes therefore bind to cell surface receptors including G-Protein-coupled protein receptors and Tyrosine-Kinase receptor system
Hydrophobic (fat soluble) hormones
- Transported in the blood bound to plasma protein
- Biologically inactive hormone is protected from degradation
Hormone receptors
- Hormones need to bind to specific protein receptors found either in or on cell membranes; in the cytoplasm or in the nucleus of the target cell
- Down-regulation: Increased hormone concentration and increased binding between hormone and target cell can decrease number of active cells
- Up-regulation: Stimulating hormone induces greater than normal formation of receptors by the target cell
Protein hormone signalling
- Peptide hormones bind to membrane receptors
- Binding activates an effector protein
- Signal is transmitted intracellularly via second messengers such as cAMP, which amplify the signal
- Stimulation or inhibition of a G-protein subunit can activate or inhibit an effector enzyme
- Effector enzyme increases or decreases the intracellular second messenger
- The second messenger then initiate a series of phosphorylation or dephosphorylation reactions
