Endocrinology Flashcards
Define endocrine gland
A gland that makes and secretes hormones into the blood stream through which they travel to distant targets
Define exocrine
A gland that makes and secretes hormones through ducts opening onto an epithelium rather than directly into the blood.
Define paracrine
Substance secreted and acting on adjacent cells. (e.g. neurotransmitters)
Define autocrine
Substances secreted by cell and act on the receptors on the surface of the same cell.
Define hormone
A chemical substance produced by cells and released especially into the blood and having a specific effect on cells or organs usually at a distance from the place of origin.
Define endocrine
Hormones secreted and act on distant targets
Define cytokines
Peptides with autocrine, paracrine and endocrine functions
What are the main endocrine organs?
Hypothalamus Pituitary Thyroid Thymus Pancreas Adrenal glands Kidneys Ovaries Uterus Testes
What other tissues have endocrine functions?
Heart Gut Liver Adipocytes Placenta
What are the major molecular types of hormones?
Proteins
Modified amino acids
Steroids
Name examples of amino acid derived hormones
Catecholamines and serotonin (single amino acids)
Thyroid hormones (dipeptides)
TRH, vasopression, somatostatin (small peptides)
Insulin and PTH (intermediate peptides)
Gonadotrophs (complex polypeptides)
Name hormones derived from lipid precursors
Steroids (cortisol, sex steroids, vitamin D)
Prostaglandins
Describe the process of protein and peptide hormone synthesis
1) Gene transcription
2) mRNA to rER
3) Translation on rER
4) Post-translational processing
5) Packaging into secretory vesicles in golgi apparatus
6) Exocytosis
Describe the process of steroid hormone synthesis
1) hydrolysis of esters and release of cholesterol (or by direct uptake of cholesterol)
2) Cholesterol modified to prenenolone in mitochondrion
3) Processing in sER
4) Diffusion through cell membrane (hydrophobic)
How are hormones transported in the blood?
Hydrophilic (water soluble- dissolve in water
Hydrophobic (fat soluble):
-Transported bound to plasma binding proteins (inactive when bound, protected, acts as reservoir)
Describe the mechanism of action of water soluble hormones
Bind to G-protein coupled receptors:
acts on either adenylate cyclase to activate cAMP to activate protein kinases; or activates phospholipase C which activates IP3 which stimulates Ca2+ release from ER which further signals downstream events.
Tyrosine-kinase receptor system:
Receptor binding causes phosphorylation and activation of receptors which activates nearby proteins which causes a signalling cascade (e.g. insulin)
Describe the mechanism of action of fat soluble hormones
Bind to intracellular receptors:
Intracellular receptors take hormone to nucleus and DNA where transcription produces mRNA which is translated by ribosomes on rER and new proteins are produced.
Or cell surface receptors (same action as water soluble receptors)
Give an example of postive feedback
Release of egg from ovaries (oestrogen causing surge of luteinising hormone)
Define tropic hormone
Affects other endocrine glands to produce a response
Define trophic hormone
Affects growth and development directly
What are the actions of glucocorticoids?
Decrease muscle mass
Modulate emotions and wakefulness
Increase glomerular filtration
Initiate maturation of foetus
Increase bone resorption and reduce bone function
Decrease inflammatory and immune response
Decrease connective tissue
What are the symptoms of excess glucocorticoid production? (Cushing’s syndrome)
Central weight gain Depression, psychosis, insomniia Amenorrhoea Decreased libido Bruising Growth arrest Polyuria/polydipsia
What are the symptoms of underproduction of glucocorticoids?
e.g. Addison's disease (hypoadrenalism) Weight loss Anorexia Weakness Fever Depression Impotence Amenorrhoea Nausea/vomiting Confusion Back/abdo pain
Define primary endocrine dysfunction
Excess effector hormone from an endocrine organ
