Introduction to Endocrine Flashcards
What hormone is released by the pineal gland and what are its 3 roles?
Melatonin
Regulates circadian rhythm, involved in maintaining immune function and acts as an antioxidant
What hormone is released by the parathyroid glands and what is its role?
PTH
Increases plasma calcium and decreases plasma phosphate levels
What hormones are released by the thymus and what are their roles?
Thymosin and thymopoietin
Involved in lymphocyte development
What hormone is released by the heart and what is its role?
Atrial natriuretic peptide
Acts on the kidneys to increase Na+ excretion
What hormones are released by the liver and what are their roles?
Angiotensinogen: acts on adrenal cortex to stimulate aldosterone secretion, and on blood vessels to cause vasoconstriction and increase BP
IGFs: act on many tissues, involved in growth promotion
Where does an autocrine signal act?
On the same cell that secreted it
Where does a paracrine signal act?
Diffuses to act on adjacent cells
What is a neurohormone? What are the 3 major groups of neurohormones?
A neurocrine signal secreted into the bloodstream
Hypothalamic neurohormones acting on the anterior pituitary, hypothalamic neurohormones acting on the posterior pituitary, and catecholamines made by modified adrenal medulla neurons
What is a tropic hormone?
A hormone that controls the secretion of another hormone
What is a trophic hormone?
Usually a hormone that stimulates growth and development
Are peptide hormones made on demand or stored in advance?
Precursor stored in advance
What is the difference peptide and steroid hormones in terms of their half-life?
Steroid hormones have a longer half-life than peptide hormones
Do thyroid hormones resemble peptide or steroid hormones in terms of their structure and action?
Steroid
Do catecholamines resemble peptide or steroid hormones in terms of their structure and action?
Peptide
What are the amine hormones mostly derived from?
Tyrosine
List 4 factors influencing the plasma concentration of free, biologically active hormone
Rate of secretion
Rate of metabolic activation (only for a few hormones)
Extent of binding to plasma proteins (for steroid and thyroid hormones)
Rate of metabolic inactivation and excretion
How are steroid hormones removed from the circulation?
They are conjugated and removed via the urine and bile
How are amine hormones removed from the circulation?
They are degraded by specific circulating degrading enzymes
How are large peptides removed from the circulation?
Via receptor-mediated endocytosis
How are most small peptides removed from the circulation?
Via the kidneys
What is the role of antagonism in hormone regulation? Give an example
The hormones act together but in opposite directions, which allows for fine tuning (e.g. insulin and glucagon)
What is synergism in terms of hormone regulation? Give an example
Multiple stimuli producing an effect that is more than additive (e.g. glucagon, cortisol and adrenaline in the control of blood glucose)
What does “permissive” refer to in terms of hormone action? Give an example
1st hormone requires the presence of a 2nd hormone to exert its effects (e.g. cortisol and adrenaline, thyroid hormone and IGFs)
What is the difference between a primary and secondary endocrine disorder?
In a primary endocrine disorder, the gland is abnormal
In a secondary endocrine disorder, the gland is abnormal but the tropic hormone is abnormal
What are the advantages of the hypothalamic-hypophyseal portal system between the hypothalamus and the anterior pituitary?
Less hormone secretion is required to elicit a response
There is direct delivery of hormone
What is another name for the posterior pituitary? How is this related to its embryological origin?
Neurohypophysis
An outgrowth of the brain, composed of nervous tissue
What is another name for the anterior pituitary? How is this related to its embryological origin?
Adenohypophysis
Originated from glandular epithelial tissue and ectodermal cells (true endocrine gland)
What is the infundibulum?
The stalk connecting the pituitary to the brain
What 2 hormones are released by the posterior pituitary?
Vasopressin/ADH
Oxytocin (OT)
What is the role of ADH?
Increases collecting duct permeability to decrease urinary output
What is the role of OT?
Causes ejection of milk by the breasts, and contraction of the uterus
What nuclei are involved in the control of the posterior pituitary?
Supraoptic and paraventricular nuclei
What nuclei are involved in control of the anterior pituitary?
Arcuate and other nuclei
List 7 hormones secreted by the hypothalamus to target the anterior pituitary
CRH TRH GnRH GHRH GHIH (somatostatin) PRF PIH (dopamine)
What are somatomedins?
IGFs
List 8 hormones secreted by the anterior pituitary
ACTH B-lipotropin TSH (thyrotropin) Prolactin LH FSH GH
Which hypothalamic hormone, besides PRF, can stimulate prolactin secretion from the anterior pituitary?
TRH
Besides tropic hormones, what other controls can affect hormone production?
Higher centres in the brain
Changes in diurnal/circadian rhythm
What causes Kallman syndrome? What are the symptoms?
The failure of embryological GnRH neurons to migrate via the olfactory pathway
Causes hypogonadotropic hypogonadism, and hyposmia/anosmia
What % of brain growth occurs in the first 2 years of life?
Postnatal growth spurt results in 70% of brain growth
What occurs during the pubertal growth spurt?
Lengthening and epiphyseal fusion of long bones
Production of testosterone and oestrogen
What are the metabolic effects of GH?
Increase blood fatty acid and glucose (anti-insulin)
Increase protein synthesis
What effect does GH have on soft tissues and the skeleton?
Hyperplasia and hypertrophy of cells
What effect does GH have on the liver?
Stimulates production and release of IGFs
What hormone is responsible for closing the epiphyseal plates of long bones? (Think about the timing of epiphyseal fusion)
Oestrogen
What are the 4 actions of IGFs?
Insulin-like activity (opposes GH)
Anti-lipolytic activity (opposes GH)
Protein synthesis
Epiphyseal growth
What is the role of GH in early growth?
Plays a permissive role (required from birth)
What is the effect of GH deficiency in children?
Dwarfism
What is the cause of Laron dwarfism?
GH receptors are unresponsive despite normal GH
What are the effects of adult onset GH deficiency?
Few effects
How is GH deficiency treated?
Using genetically engineered hGH
List 6 GH-independent causes of short stature
Cretinism (TH deficiency) Precocious/early puberty Gonadal dysgenesis (XO chromosomes) Constitutional delayed/stunted growth Psychosocial dwarfism (due to chronic abuse or neglect) Achondroplasia
What is achondroplasia and what is the underlying cause?
The most common form of dwarfism
Caused by FGFR-3 mutation
What is the result of GH excess in childhood vs adulthood?
Gigantism in childhood
Acromegaly in adulthood
What are the clinical signs of acromegaly?
Bone and soft tissue deformities
Increased viscera size and protein content
