Introduction to endocrinology Flashcards
Define endocrinology
The study of endocrine glands (tissues) and the substances they secrete
Define endocrine gland
A gland that makes and secretes hormones into the bloodstream, through which they travel to affect distant targets
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 exocrine gland
A gland that secretes its products through ducts opening onto an epithelium rather than directly into the blood.
What is endocrine secretion?
Secretion of a hormone into the bloodstream to act on a distant target
Define paracrine
of, relating to, promoted by, or being a substance secreted by a cell and acting on adjacent cells.
Define autocrine
of, relating to, promoted by, or being a substance secreted by a cell and acting on surface receptors of the same cell.
What are the 4 types of chemical messengers?
1) Neurotransmitters (act like paracrine)
2) Neuroendocrine messengers
3) Hormones (ie. endocrine messengers)
4) Cytokines (peptides with autocrine, paracrine or endocrine functions)
List the main endocrine organs
- Hypothalamus
- Pituitary (anterior and posterior)
- Thyroid
- Thymus
- Adrenal
- Pancreas
- Kidney
- Testes
- Ovary
- Uterus
List the main hormones
- Glucocorticoids
- Insulin, glucagon
- Thyroid hormones
- Gastric hormones
- Intestinal hormones
- ADH, RAAS
What are the major molecular types of hormones?
- Modified single amino acids eg. catecholamines (adrenaline, noradrenaline, dopamine and serotonin).
- Peptides eg. Thyrotropin Releasing Hormone, Antidiuretic hormone, Somatostatin, Insulin, PTH, gonadotrophs (FSH, TSH, LH)
- Steroids (derives from cholesterol) eg. cortisol, sex steroids (eg. testosterone), vitamin D
Describe the characteristics of amino acids and peptides
- water soluble
- rapid changes in [plasma]
- Short (sec-to-min) plasma half life
- cell membrane receptor
- mechanism: activate preformed enzymes, secretory granules, constitutive + bursts
- rapid (sec-to-min) speed of effect
Describe the characteristics of steroids and thyroid hormones
- lipid soluble
- slow fluctuations in [plasma]
- long (min-to-days) plasma half life
- intracellular receptor
- mechanism: stimulate protein synthesis, direct rapid passage, related to secretion rate
- Slow (hrs-to-days) speed of effect
Describe how catecholamines, peptides and proteins are transported in the blood
Water-soluble hormones are carried in free form in the blood. Dissolve in blood
Describe how steroids and thyroid hormones are transported in the blood
Hydrophobic (fat-soluble) hormones.
- Transported bound to plasma binding proteins. Binding affinity is important
- The hormone is:
1) Considered inactive
2) Protected from degradation
3) Acts as a reservoir
What are the signalling mechanisms of water-soluble hormones?
Are large and hydrophilic (water-soluble)
Cannot pass through membranes
Bind to cell surface receptors, e.g. G protein-coupled receptors (GPCR) –> Adenylyl cyclase or phospholipase C; tyrosine kinase receptors
What are the signalling mechanisms of hydrophobic hormones?
Are large and hydrophobic (lipid soluble) can diffuse across the plasma membrane
Bind to intracellular and cell surface receptors
What is negative feedback?
Output reduces the original stimulus
What is positive feedback?
Output enhances the original stimulus
What is the difference between a tropic hormone and a trophic hormone?
A tropic hormone affects other endocrine glands.
A trophic hormone affects growth and development directly
What is primary endocrine dysfunction?
Too much of effector hormone from endocrine organ
What is secondary endocrine dysfunction?
Overstimulation of the effector endocrine organ by excessive tropic hormone
What effects does cortisol (a glucocorticoid) have on the body?
1) Decrease bone function, increase bone resorption
2) Decrease connective tissue
3) Inhibit inflammatory and immune response
4) Maintain cardiac output, decrease endothelial permeability, increase arteriolar tone
5) Facilitate maturation of the foetus
6) Increase glomerular filtration and water clearance
7) Modulate emotional tone, wakefulness
8) Maintain muscle function, decrease muscle mass
What is Cushing’s syndrome?
Glucocorticoid excess
Symptoms:
- Central weight gain
- Change in appearance – moon face
- Depression
- Psychosis
- Insomnia
- Amenorrhoea
- Poor libido
- Thin skin
- Bruising
- Growth arrest
- Back pain
- Polyuria/polydipsia
Treatment is surgery to remove tumour or drugs to inhibit cortisol production
What is Addison’s syndrome?
Hypoadrenalism - reduced glucocorticoids and mineralocorticoids
Symptoms:
- Weight loss
- Anorexia
- Weakness
- Fever
- Depression
- Impotence/amenorrhoea
- Nausea/vomiting
- Diarrhoea/constipation
- Confusion
- Abdominal pain
- Back pain
Causes:
- Destruction of adrenal cortex
- Reduced glucocorticoid, mineralocorticoid and sex steroid production
