Hypothalamic Pituitary Axis - 2/2 Lopez Flashcards
What is the connection between the hypothalamus and posterior lobe like?
Neural
The connection between the hypothalamus and anterior lobe are what?
Neural and endocrine
How do hormones get from the hypothalamus to the anterior lobe of the pituitary?
Hypothalamic-hypophysial portal vessels
What is a primary endocrine disorder due to a defect in?
Peripheral endocrine gland (target tissue i.e. Thyroid gland)
What is a secondary endocrine disorder due to?
Defect in pituitary gland
What is a tertiary endocrine disorder due to?
Defect in hypothalamus
What are some examples of primary endocrine disorders?
Thyroid, adrenal cortex, liver, gonads
What are the most prominent cell types within the pituitary gland?
Somatotrophs (50%)
What do corticotrophs release?
Somatotrophs?
ACTH
growth hormone
What hormone has melanocyte-stimulating hormone activity?
INC in blood levels of what can cause skin pigmentation?
ACTH
MSH
What disease is associated with INC levels of ACTH?
Symptoms?
Addison’s disease
Skin pigmentation
What is a main regulator of the HPA axis that stimulates it?
Stress (physical, emotional, chemical)
What does ACTH cause the release of in the adrenal gland that can cause negative feedback of the system?
Cortisol or aldosterone
What 2nd messenger does the HPT axis use once TRH is released?
What does this activate?
PLC
INC in Ca and PKC
After the pituitary thyrotrope has been activated, what does it release?
TSH
Once TSH has been released from the pituitary thyrotrope what does it stimulate?
What are its effects?
Ultimate end secretion product?
PKA
Thyroid hormone synthesis and secretion, cell growth
T3, T4
What inhibits TRH secretion?
What end product can also inhibit the HPT axis via negative feedback?
Stress
T3
What stimulates the synthesis and secretion of GH And where is this initial stimulus located?
What does this hormone act on to release GH?
GHRH from the hypothalamus
Acts on ant. Pituitary
What inhibits the secretion of GH?
How?
Somatostatin
Blocks response of ant. Pituitary to GHRH
When GH acts on target tissues (liver) what is produced?
How do they inhibit further secretion of GH?
Somatomedins (IGF)
Inhibit release from ant. Pituitary AND stimulate secretion of somatostatin from hypothalamus
How is GH secreted?
Pulsatile pattern, burst of secretion every 2 hours
What tissues are the main targets of direct effect of GH?
Indirect?
Skeletal m., liver, adipose
Liver
What are the direct effects of GH?
What is the net result?
Diabetogenic: DEC glucose uptake into cells
INC lipolysis in adipose
INC protein synthesis in muscle
INC production of IGF
INC in blood [glucose] and blood insulin levels
What are the indirect effects of GH?
INC Protein synthesis and organ growth (INC uptake of a.a.)
INC linear growth (INC metabolism in cartilage-forming cells and chondrocytes)
What causes GH deficiency?
Lack of ant. Pituitary GH
DEC GHRH due to hypothalamic dysfunction
Failure to generate IGF in liver
GH receptor deficiency
GH excess causes what?
Mostly due to what?
Acromegaly
GH-secreting pituitary adenocarcinoma
What does excess GH cause before puberty?
After?
Gigantism (INC linear growth)
INC periosteum bone growth, INC organ size, glucose intolerance
How to treat GH deficiency?
Excess?
HGH
Somatostatin analogue (octreotide)
What does lactogenesis induce the synthesis of?
Lactose, casein and lipids
What inhibits lactation during pregnancy even though prolactin levels are high?
High levels of estrogen and progesterone down-regulate prolactin receptors
What does prolactin suppress?
How?
Ovulation
DEC synthesis and release of GnRH
What causes prolactin deficiency?
Result?
Destruction of ant. Pituitary or lactotrophs
Inability to lactate
What causes prolactin excess?
Result?
Destruction of hypothalamus or hypophysial tract, prolactinomas,
Galactorrhea and infertility
How to treat prolactin excess?
DA receptor agonist (bromocriptine)
What is Sheehan syndrome?
Pituitary in pregnancy is enlarged and more vulnerable to infarction
What is Cushing’s disease?
Pituitary tumors stimulating an increase in cortisol
Pituitary adenomas develop in 25% of patients with what?
MEN 1
What is the precursor peptide for ADH?
Oxytocin?
Preprossophysin
Prepro-oxyphysin
What are the triggers for ADH secretion?
DEC BP
DEC arterial stretch due to low blood volume
INC Osmolarity (>280) MAIN stimulus
What are the actions of ADH?
Ultimate result?
INC H20 reabsorption via V2 receptors
Vasoconstriction via V1 receptor
INC BP and INC blood volume
What mechanism do the V1 receptors work through?
V2?
IP3/Ca
cAMP
What channel does ADH activate?
Where?
aquaporin 2 (AQP2)
Principal cells of the late DCT and CD
What is ADH secretion like in hyper osmolarity?
Urine concentration?
ADH INC
urine more concentrated
What happens to ADH in hypoosmolarity?
Urine concentration?
Less ADH secreted
Urine more dilute
What are the characteristics of General DI?
Lack of effect of ADH
Frequent urination
Large volume of urine is diluted
What is the cause of central DI?
From what?
Lack of ADH
Pituitary damage or destruction of the hypothalamus
What is happening nephrogenic DI?
Cause?
Kidneys unable to respond to ADH (INC plasma ADH)
Lithium, polycystic kidney disease, sickle cell anemia
What drug is used to treat central DI?
Nephro DI?
Desmopressin
NONE
What is SIADH?
What is it characterized by?
excessive secretion of ADH, excessive water secretion
Hypoosmolarity and hyponatremia
How to treat SIADH?
Fluid restriction
IV hypertonic saline (3%)
V2 receptor antagonist
Demeclocycline (inhibits cAMP)
What are the 3 hypothalamic-pituitary axises?
What do they control?
thyroid, adrenal, gonads (HPT, HPA, HPG)
Growth, milk production/ejection, osmoregulation
