Introduction to Endocrinology Flashcards
what makes up the endocrine system?
discrete glands/cells that secrete hormones
what do the hormones of the endocrine system do?
regulate chemical reactions in cells - controls functions of other organs, tissues and cells
what are the principle functions of the endocrine system?
Homeostasis of the internal environment of the body (Maintenance of optimum biochemical environment)
Integration and regulation of growth and development
Control of sexual reproduction, including gametogenesis, fertilisation, foetal growth and development and nourishment of the newborn
what are the endocrine organs?
- Pituitary gland
- Pineal gland
- Thyroid gland
- Parathyroid glands
- Adrenal: 2 glands
- Cortex
- Medulla
where are endocrine glands present in other organs?
- Pancreas
- Thymus
- Gonads
- Hypothalamus
what are the endocrine cells in the GI tract?
Diffuse neuroendocrine system (DNES)
what are the endocrine cells in the heart?
atrial natriuretic peptide (ANP)
what is the function of the ANP?
Stimulates kidney to secrete more salt & decreases excess blood volume, high BP and high blood sodium concentration
what is the role of the endocrine cells in the kidneys?
Juxtaglomerular cells secrete renin
– Renin indirectly signals adrenal cortex to secrete aldosterone
Erythropoietin: signals bone marrow to increase RBC production
what are hormones?
Chemical messengers act as molecular triggers
what are the effects of hormones dependent on?
The effects are dependent on the programmed response of the target cells
what are the basic categories of hormones?
modified amino acids polypeptides glycoproteins steroids fatty acid derivatives - eicosanoids
how is hormone secretion controlled?
controlled by receptor-mediated feedback loops
what are the 3 mechanisms of hormone release?
- humoral
- neural
- hormonal
what hormone is released through the humoral mechanism?
PTH
what hormone is released through the neural mechanism?
catecholamines
how does the humoral mechanism of hormone release work?
low concentrations of Ca2+ stimulates secretion go PTH
how does the neural mechanism of hormone release work?
preganglionic SNS fibres stimulates adrenal medulla cells to secrete catecholamines
how does the hormonal mechanism of hormone release work?
the hypothalamus secretes hormones that –> stimulates the anterior pituitary gland to secrete hormones–> that stimulate other endocrine glands to secrete hormones
where is the hypothalamus?
Located at the base of the brain
how does the hypothalamus control the endocrine system?
by controlling the pituitary gland
what does the hypothalamus do?
provides communication between the nervous system & the endocrine system
how does the hypothalamus control the pituitary gland?
- Secretes releasing hormones to cause the pituitary to release hormones
- Secretes inhibiting hormones to turn off secretion of pituitary hormones
what does TRH (thyroid releasing hormone) stimulate?
release of TSH
what does CRH (corticotropin releasing hormone) stimulate?
release of ACTH
what does GnRH (gonadotropin releasing hormone) stimulate?
release of FSH & LH
what does PRF (prolactin releasing hormone) stimulate?
release of PRL
what does GHRH (growth hormone releasing hormone) stimulate?
release of GH
what does PIF (prolactin inhibiting factor) inhibit?
PRL
what does GH inhibiting hormone inhibit?
growth hormone
what hormones does the posterior pituitary release?
ADH (antidiuretic hormone or vasopressin)
oxytocin
what is the function of ADH?
stimulates the kidneys to reclaim more water from the urine, raises blood pressure
what is the function of oxytocin?
prompts contraction of smooth muscle in reproductive tracts, in females initiating labor and ejection of milk from breasts
what does the anterior pituitary gland release>
- Melanocyte stimulating hormone (MSH)
- Adrenal corticotropic Hormone (ACTH)
- Thyroid stimulating hormone (TSH)
- Luteinizing Hormone (LH)
- Follicle stimulating Hormone (FSH)
- Prolactin (PRL)
- Growth Hormone (GH)
what are tropic hormones?
hormones that regulate other hormones
what does TSH do?
stimulates thyroid to produce thyroid hormone
what does ACTH do?
stimulates the adrenal cortex to produce corticosteroids: aldosterone & cortisol
what does FSH do?
stimulates follicle growth and ovarian oestrogen production; stimulates sperm production & androgen-binding protein
what does LH do?
has a role in ovulation and the growth of the corpus luteum; stimulates androgen secretion by interstitial cells in testes
what does GH do?
(somatrotropic hormone) stimulates growth of skeletal epiphyseal plates and body to synthesize protein
what does PRL do?
stimulates mammary glands in breast to make milk (lactation)
what does MSH do?
stimulates melanocytes (pigmentation)
what does the pineal gland secrete?
Produces serotonin by day, converts it to melatonin at night
what is the role of melatonin?
Melatonin helps regulate the circadian rhythm
- The biological clock of the diurnal (night/day) rhythm
- Complicated feedback via visual input (retina)
what 3 hormones are secreted from the thyroid gland?
- calcitonin
- thyroxine T4
- triiodothyronine T3
what is the effect of thyroxine?
increases the basal metabolic rate.
what are the effects of thyroxine on target cells?
- Protein synthesis
- Bone growth
- Neuronal maturation
- Cell differentiation
when is calcitonin secreted?
when blood calcium levels are high
what is function of calcitonin?
lowers calcium
how does calcitonin lower calcium?
by slowing the calcium-releasing activity of osteoclasts in bone and increasing calcium secretion by the kidney
how does PTH increase blood calcium levels?
Stimulates osteoclasts to move bone
Ca2+ from the skeleton into
bloodstream
Stimulates the kidneys to stop excreting Ca2+
Stimulates the intestines to absorb more Ca2+ from diet
Activates vitamin D to increases Ca2+ uptake by intestine
what hormone is released if blood calcium levels are low?
parathyroid hormone
what hormones are produced by the thymus gland?
- thymopoietin
- thymosins
what is the function of the hormones from the thymus glands?
stimulate the production of T cells
what makes up the endocrine pancreas?
Islets of Langerhans
what do the alpha cells secrete?
Glucagon
what are the effects of glucagon?
- increased blood glucose
- increased glycogen breakdown in liver
what do the beta cells secrete?
insulin
what are the effects of insulin?
- decreased blood glucose
- increased glycogen synthesis in liver
what do the delta cells secrete?
inhibiting peptide somatostatin
what are the effects of inhibiting peptide somatostatin?
- Inhibits release of glucagon & insulin
- Slows food absorption + enzyme secretion
what makes up the adrenal gland?
- adrenal cortex (outer layer)
- adrenal medulla (middle layer)
what does the adrenal cortex secrete?
steroid hormones - cholesterol
what does the adrenal medulla secrete?
Neuroendocrine component – epinephrine & norepinephrine (noradrenaline)
what hormone release mechanism does the adrenal medulla use?
neuronal mechanism - it is an extension of the nervous system
what hormone release mechanism does the adrenal cortex use?
hormonal mechanism, apart from aldosterone which uses a humoral mechanism
what are spherical chromaffin cells?
modified postganglionic sympathetic neurons
what are the spherical chromaffin cells responsible for?
- Secrete epinephrine (adrenaline) & norepinephrine (noradrenalin)
- Amine hormones
- Fight, flight, fright
where are hormones stored in the adrenal medulla?
vesicles store the hormones
what is the role of glucocorticoids?
- Regulates or supports important cardiovascular, metabolic, immunologic & homeostatic functions including water balance
- Helps body deal with stressful situations (minutes)
- Keeps blood glucose levels high enough to support brain activity
are glucocorticoids anabolic or catabolic?
catabolic - break down protein
what is the effect of glucocorticoid on lymphocytes?
Redirects circulating lymphocytes to lymphoid & peripheral tissues where pathogens usually are
when is aldosterone secreted?
Secreted by adrenal cortex in response to a decline in either blood volume or blood pressure (e.g. severe hemorrhage)
what is the function of aldosterone?
Prompts distal and collecting tubules in kidney to reabsorb more sodium
what are the adrenal androgens?
Dehydroepiandrosterone (DHEA)
&
Androstenedione (primates)
what are the adrenal androgens used for?
Precursors for testosterone & oestrogen
Source of oestrogen in postmenopausal women
where are the adrenal androgens converted?
in perpherial tissues
when are adrenal androgen levels high?
High in foetus, increases again prior to puberty (adrenarch)
when do adrenal androgen levels drop?
Starts to decline in early 30s
what do the ovaries secrete?
progesterone
oestrogen
what is the role of progesterone?
prepares uterus for pregnancy
what do the testes secrete?
androgens - e.g. testosterone
what are some diseases associated with the pituitary gland?
- Gigantism –too much GH in childhood
- Acromegaly – too much GH in adulthood
- Pituitary dwarfs – too little GH in childhood
what are some diseases associated with the pancreas?
Diabetes mellitus – insulin deficiency (Type 1
what are some diseases associated with the thyroid gland?
- Hyperthyroidism, - commonest is Grave’s disease (autoimmune)
- Hypothyroidism
what are some diseases associated with the adrenal gland?
- Cushing’s syndrome
- Addison’s diseases
what usually causes Cushing’s syndrome?
Usually ACTH-secreting pituitary tumor, rarely by tumor of adrenal cortex
what usually causes Addison’s disease?
Hyposecretion of cortisol and aldosterone - low blood glucose & sodium, severe dehydration, fatigue, abdominal pain
