5.2 HPT Axis Flashcards
Physiologically pituitary gland is divided into
Ant. Pituitary
Pars intermedia
Post. pituitary
Hypophysis is connected to the hypothalamus via
Hypophysial stalk
Differentiate anterior and posterior pituitary glands regarding their secretion
Anterior - release of RELEASING HORMONES from hypothalamus brings about secretion
Posterior - reception of NERVE SIGNALS from hypothalamus brings about secretion of stored ADH and Oxytocin
Anterior pituitary is the site where the anterior pituitary hormones are SYNTHESIZED, STORED, and RELEASED. However, in the posterior pituitary, hormones are NOT synthesized, ONLY STORED and RELEASED. What synthesized ADH and Oxytocin?
ADH - supraoptic nuclei
Oxytocin - paraventricular nuclei
The negative feedback is only applicable to the ANTERIOR pituitary because
The ANTERIOR Pituitary is responsive to hypothalamic RELEASING HORMONES (not nerve signals –> POSTERIOR)
Type of negative feedback where X-stimulating hormone inhibits the hypothalamus
Short loop
Type of negative feedback where X-releasing hormone inhibits the hypothalamus
Ultra short loop
Type of negative feedback where X-hormone inhibits hypothalamus or ant. Pituitary gland
Long loop
For most anterior pituitary hormones, the hypothalamic releasing hormones are MOST important as well EXCEPT _______, an inhibitory hormone exerts more control
Prolactin
Hormone that stimulates ACTH secretion
CRH - corticotropin releasing hormone
TRH or thyrotropin releasing hormone stimulates which hormone secretion
stimulated TSH secretion and PRL - Prolactin secretion
Precursor of ADH
Prepropressophysin
It is a carrier protein during axonal transport
Neurophysin
ADH and Oxytocin are both SECRETORY PEPTIDES, synthesized as larger precursor and cleaved into: 1. _________, 2. _________, and 3. __________.
- Active hormone
- Neurophysin
- Glycopeptide
It is the PRIMARY trigger of ADH secretion
Plasma osmolarity changes.
High plasma osm: increase ADH secretion
Low plasma osm: decrease ADH secretion
“Only a change of 1-2% plasma Osmolarity is needed to trigger ADH release.”
It is secreted in response to plasma osm changes and DECREASE in blood volume
ADH
TRUE or FALSE
Increased level of plasma osmolarity (>280 mosm/kg) increases the release of ADH
TRUE.
Why?
^ plasma osm -> ^osmoreceptors (w/c draws out water and causes shrinkage) -> signals sent to posterior pituitary -> ADH secretion occurs -> ^cAMP -> recruitment of aquaporins -> ^ permeability of H2O -> ^H2O absorption -> v plasma osm back to normal
True or False. In the presence of ADH, collecting tubules are impermeable to water, meaning no reabsorption occurs.
False.
In the ABSENCE of ADH, collecting tubules are IMpermeable to water, meaning NO reabsorption occurs.
In the PRESENCE of ADH, aquaporins are able to reabsorb water, increased PERMEABILITY.
Three factors that influence decrease in ADH secretion
Low plasma osm
High ECF volume
Alcohol
Characterized by excess ADH
Effects are increase water retention, low plasma osm, hyponatremia, inappropriately concentrated urine
SIADH Syndrome of inappropriate ADH secretion
Secretion of growth hormone is described as
Pulsatile - secretion is in pulses with MAXIMAL burst during SLEEP
Lifetime pattern - increasing with progression from birth, HIGHEST during PUBERTY, after which GH decreases
Growth effects of GH. Is also mediated by
IGF-1
True or false. GH inhibiting the hypothalamus is a long loop regulation.
FALSE.
GH inhibiting the hypothalamus is a SHORT loop regulation.
IGF-1 inhibiting the hypothalamus is a LONG loop regulation.
Test used to determine excess of hormones
Suppression test
Test used to determine deficit of hormones
Stimulation test
excess GH
Gigantism: open epiphyseal plate; __________: closure of epiphyseal plate
Gigantism: open epiphyseal plate; ACROMEGALY: closure of epiphyseal plate
GH: cytokine receptor; ACTH: ___________
GH: cytokine receptor; ACTH: G-protein coupled receptor
GH: lifetime pattern; ACTH : _______ pattern
GH: lifetime pattern; ACTH : DIURNAL pattern
ACTH can be altered by changing wake-sleep cycle
NOTE: both GH and ACTH. Are pulsatile
________ secretion follows ACTH secretion
Cortisol
Request for cortisol administration is during
explain why
6-8AM because this is the peak of the diurnal pattern of ACTH secretion
How can diurnal pattern of ACTH secretion be altered
Changing sleep wake cycle
What does hypothalamus secrete to stimulate synthesis of ACTH
Corticotrophin Releasing Hormone (CRH)
CRH increases the transcription of
POMC gene
Effects of a lack in CRH
- Impair the ACTH diurnal rhythm
2. Affects the response to stress
Function of BNP
Inhibits ACTH secretion and causes the expulsion of sodium and water in the urine
Stimulates ACTH secretion
Stress Transition from sleep to wake Norepinephrine Ach Serotonin
Inhibit secretion of ACTH
GABA
Endorphins
LH: estrogen and progesterone; FSH:
LH: estrogen and progesterone; FSH: estradiol and inhibin
When there is an excess of one hormone, it can “sit” on the other hormones. Explain what “sit” on means
An excess in one hormone may sit on the receptor of another hormone causing the effects of that other hormone to be manifested
Ex. Excess HCG can sit on the TSH receptor and cause some of the effects of TSH such as stimulation of the thyroid gland
The way by which releasing hormones of the hypothalamus reach the anterior pituitary
Hypophyseal portal system via the median eminence
ADH is synthesized by
Supraoptic nuclei of hypothalamus
Oxytocin is synthesized by
Paraventricular nuclei of hypothalamus
Oxytocin and ADH have the same amino acid residues except for two aa residues:
ADH: arginine and phenylalanine
Oxytocin: leucine and isoleucine
Direct metabolic effects of growth hormone
Protein synthesis Fat lipolysis Inhibited uptake of blood glucose Gluconeogenesis Insulin resistance
Indirect effects of growth hormone
Postnatal linear growth and somatic development
Proliferation of chondrocytes
Bone forming and soft tissue growth
