The Basic Principles of Endocrinology Flashcards
anterior pituitary hormones
- Follicle stimulating hormone (FSH)
- Luteinizing hormone (LH)
- Adrenocorticrotophic hormone (ACTH)
- thyroid stimulating hormone (TSH)
- Prolactin
- Melanocyte stimulating hormone (MSH)
- Growth hormone
posterior pituitary hormones
- Oxytocin
- Anti-diuretic hormone (ADH) / VASOPRESSIN
anterior pituitary hormones
are controlled by substances synthesised in the hypothalamus which are releasing into the portal blood and drain directly down the infundibulum to the anterior pituitary
posterior pituitary hormones
are synthesised in the hypothalamus and are transpired down nerve axons to be released by the posterior pituitary
hypothalamus- pituitary- gonadal axis
- hypothalamus secretes Gonadotrophin releasing hormone (GnRH)
- this stimulates the anterior pituitary which secretes FSH and LH
- in females FSH and LH acts on the ovaries which secrete oestrogen and progesterone
- in males FSH and LH acts on the testes which secrete testosterone
- oestrogen, progesterone and testosterone have negative feedback affects on the anterior pituitary and the hypothalamus
- project inhibits the action of FSH and LH on the ovaries and the testes
hypothalamus- pituitary- thyroid axis
- the hypothalamus secretes thyrotrophin releasing hormone (TRH)
- this stimulates the anterior pituitary to secretes TSH
- this acts on the thyroid gland which secrete T3 and T4
- the T3 and T4 have a negative feedback affect on the anterior pituitary and the hypothalamus
hypothalamus- pituitary- growth hormone axis
- the hypothalamus secretes growth hormone releasing hormone (GHRH) AND growth hormone inhibiting hormone (GHIH otherwise known as SOMATOSTATIN)
- growth hormone releasing hormones stimulates the anterior pituitary which secretes growth hormone
- somatostatin inhibits the release of growth hormones from the anterior pituitary
hypothalamus- pituitary- growth- hormone axis 2
- growth hormones stimulates the liver to secrete IGF- (insulin like growth factor 1) which increased protein synthesis (by uptake of amino acids) causing increased muscle mass and increases lateral and linear bone and increases cartilage , soft tissue and organ size
- IGF-1 has a negative feedback affect on the anterior pituitary
- growth hormone is also a stress hormone so has direct affects: increases blood glucose concentration by hepatic gluconeogenesis , increases lipolysis which increases fatty acid concentration, increases protein synthesis (by uptake of amino acids) so causes increased muscle mass
what causes increased release of growth hormone releasing hormone from the hypothalamus
- sleep
- puberty
- exercise
- hypoglycaemia
hypothalamus- pituitary- adrenal axis
- hypothalamus secretes corticotrophin releasing hormone (CRH)
- this stimulates the anterior pituitary to secrete ACTH
- this stimulate the adrenal gland to secrete cortisol
- cortisol stimulates glycogenolysis and down regulates the immune system
- cortisol has a negative feedback affect on the anterior pituitary and hypothalamus
what causes increased release of portico-trophin releasing hormone from the hypothalamus
stress
what happens if the negative feedback affects of cortisol are reduced because there is reduced levels of cortisol
corticotrophin releasing hormone can also stimulate the pars intermedius of the anterior pituitary which secretes melanocyte stimulating hormone (which is the cause of hyper pigmentation in addison disease)
hypothalamic-pituitary- adrenal axis operates on a
circadian rhythm
at midnight
cortisol levels are 0 and the gradually increase until they reach there maximum at 8am before the slowly fall through the day until they reach 0 again at midnight
physical or mental stress
increases the release of corticotrophin releasing hormone (CRH) from the hypothalamus which increases cortisol levels
prolactin axis
- the hypothalamus secretes TRH and serotonin and dopamine
- the TRH and serotonin stimulates the anterior pituitary to secrete probation
- the dopamine inhibits the release of prolactin from the anterior pituitary
- prolactin acts on breast tissue causing it to lactate
clinical significance of prolactin axis
- anti-psychotics (haloperidol, chlorpromazine) and anti-emetics (metoclopramide and domperidone) are dopamine antagonists and can cause gallactorrhoea as they prevent the inhibitory affect of dopamine on prolactin release from the anterior pituitary
- anti-depressant (citalopram) are selective serotonin reuptake inhibitors so they increase serotonin levels which is a prolactin releasing factor which acts on the anterior pituitary causing prolactin release so can cause gallactorrhoea
- hypothyroidism can also cause galactorrhea as it increases the amount of TRH due to low T3 and T4 levels, so this acts on the anterior pituitary to increase prolactin release
oxytocin
- oxytocin is a posterior pituitary gland hormone therefore it is synthesised in the hypothalamus not in the posterior pituitary
oxytocin axis
- hypothalamus secretes oxytocin
- oxytocine is stored and released form the posterior pituitary in response to suckling or uterine distention
- oxytocin acts on the breasts to let down milk
- oxytocin acts on the uterus to contract it and causes cervical dilatation
anti-diuretic hormone is also known as
vasopressin
anti-diuretic hormone is a
posterior pituitary gland hormone therefore it is created and released from the hypothalamus not the pituitary gland
anti-diuretic hormone axis
- hypothalamus synthesis and secretes ADH in response to various signals
- the ADH is stored and released from the posterior pituitary
- ADH acts on the kidney by binding to principal cells on collecting ducts increasing the number of aquaporins and increasing water resorption
- ADH acts on the vasculature to increase peripheral vasculature resistance
Hypothalamus synthesis and secretes ADH in response to
- high serum osmolality
- angiotensin II
- low blood pressure
- low blood volume
what inhibits the release of ADH from the hypothalamus
atrial natriuretic peptide (ANP) which is released in repose to high blood pressure
