168. Hypothalamic-Pituitary Basic Physiology Flashcards
Confers the biologic specificity of hormones
beta-subunit
Essential for boney growth and has effects on fat, muscle, and CHO GHRH (+) and somatostatin (-)
Growth hormone
High estrogen levels of pregnancy result in hyperplasia of lactotrophs and high ___ levels
Prolactin
Stimulates gonadal steroid production
Midcycle surge triggers ovulation (release of egg) GnRH (+)
LH
Derive from an evagination of neural ectoderm of the ventral diencephalon
Posterior lobe of pituitary
Stimulates mild let-down and postpartum uterine contraction
Stimulated by suckling
Oxytocin
Mutations in these peptides give rise to combined pituitary hormone deficiency through lack of development of certain pituitary cells but hypothalamic structures are normal
Pit-1 and PROP-1
Stimulates follicle and sperm development GnRH (+)
FSH
Under tonic inhibition by the hypothalamus via dopamine
Cutting of the stalk causes hypopituitarism but also an increase in this hormone
Prolactin
Secreted by the somatotrophs (50% of pituitary cells)
Promotions of linear growth at the growth plates of bones
Increases osteoclast differentiation and activity
Increases osteoblast activity
Increases bone mass by endochondral bone formation
Growth hormone
Converts electrical signals from the retina into hormonal signals
Pineal gland
Need ___ secretion instead of continuous for adequate hormone release
Pulsatile
Localized in hypothalamic nuclei that project to the median eminence to secrete peptide and bioamine releasing and inhibiting hormones into the proximal end of the hypothalamic-pituitary portal vessels
Hypophysiotropic neurons
Made by Liver and bones after Growth Hormone has acted on them
- most comes from liver
Then acts in a negative feedback loop on the pituitary and hypothalamus
IGF-1
Primary regulator of ADH secretion
Senses hyperosmolality (hypernatremia) which stimulates ADH release
Senses hypoosmolality (hyponatremia) which suppresses ADH release
Osmoreceptors in hypothalamus
Produced by corticotrophs (10-20% of pituitary cells)
Derived from POMC
Main product in pituitary
Stimulates adrenal cortex to produce cortisol and adrenal androgens
Little effect on aldosterone
Stimulated by CRH Stress mediated
ACTH
Secreted by pituitary lactotrophs (15% of pituitary cells)
Stimulates breast epithelium to proliferate
- in conjunction w/ estrogen, progesterone, thyroid hormone, cortisol, and insulin
Induces milk production in the puerperium
Dopamine-receptor blockers can increase levels of this hormone
Suckling is the normal stimulus for secretion in the puerperium
Prolactin
Produced by gonadotrophs (10-15% of pituitary cells)
In ovary, binds to receptors on theca cells where it stimulates the production of androgens and steroid precursors that are transported to granulosa cells for aromatization to estrogen
In testes, binds to receptors on Leydig cells where it stimulates testosterone production
Triggers ovulation if properly timed
LH
Primary regulation of aldosterone is performed by ___ along with from the adrenal gland after ACTH stimulation
Renin-Angiotensin System
Provide negative feedback at both the pituitary and hypothalamic levels with decreases in TRH and increases in somatostatin
T4 and T3
Originate in the supraoptic and paraventricular nuclei
Traverse the pituitary stalk
Release vasopressin and oxytocin from nerve endings in the posterior pituitary
Neurohypophysial neurons
Main androgen responsible for closing of epiphyseal growth plates
Estrogen
Derives from Rathke’s pouch
Anterior lobe of pituitary
TRH, VIP, and maybe other peptides release ___ in the setting of low dopamine
Prolactin
Synthesized in magnocellular neurons in the supraoptic and paraventricular nuclei of the hypothalamus
Acts by binding V2 receptors in renal collecting ducts making them more water permeable
- activation of aquaporin 2 channels
Primary action it to maintain normal serum osmolality through water reabsorption
Also acts on V1 receptors on vascular smooth muscle to cause muscle contraction and an increase in BP
ADH (vasopressin)
From sertoli cells and ovarian granulosa cells that feeds back to inhibit FSH release
Acts on pituitary gland to inhibit FSH and LH secretion
Inhibin
Controlled only by water balance
- controlled by vasopressin and thirst
Serum osmolality
Produced by the thyrotrophs (5% of pituitary cells)
Glycoprotein with an alpha and beta subunit
Stimulates all aspects of thyroid function as well as thyroid gland growth
TSH (Thyrotrophin)
Stimulates amino acid uptake into tissue and increases muscle
Promotes lipolysis with fat breakdown
Causes resistance to the action of insulin (a counter-regulatory hormone)
Growth Hormone
Stimulates thyroid hormone production and thyroid growth TRH (+) and somatostatin (-)
Thyrotropin (TSH)
Linear growth is dependent on the stimulation of this protein from the liver and locally in other tissues, such as the epiphyseal growth plate
Measure this when wanting to assess GH status
IGF-1
Can override osmotic regulation in extreme conditions
- 10-15% blood volume or pressure drop to override the osmolality control
Baroreceptors (volume receptors) in chest
Influences hormone cycles in humans more than light-dark
Sleep-wake cycles
Common to TSH, LH, FSH, and chorionic gonadotrophin
alpha-subunit
Act as carriers of IGF in plasma Prolong the half-life of IGF in circulation
Regulate IGF access to receptor in extracellular fluid
IGFBPs (IGF binding proteins)
Binds to receptors in the breast, causing contraction of myoepithelial cells around the alveoli and ductules to eject milk
Suckling stimulates tactile receptors, sending signal to hypothalamus to release __
Released during vaginal stretching with delivery of infant and is important in causing uterine contraction then to prevent blood loss
Oxytocin
Hyperglycemia suppresses __ secretion
Growth hormone
Produced by gonadotrophs (10-15% of pituitary cells)
In ovary, binds to receptors on granulosa cells where it induces enzymes that are involved in estrogen synthesis and promotes follicle growth
In testes, binds to receptors on Sertoli cells where it stimulates spermatogenesis and inhibin-related proteins
FSH
Stimulates water reabsorption in the kidney collecting duct
Stimulated by hyperosmolality and intravascular volume/pressure loss
Vasopressin
Stimulates cortisol and adrenal androgen production and adrenal growth
Strong diurnal rhythm
CRH (+) and vasopressin (+)
ACTH
