"Medical Physiology Introduction to Endocrinology Mary Lou Vallano" 3/16 Flashcards
What is chorionic gonadotoprin (HCG)?
HCG is a peptide hormone that stimulates the corpus luteum to produce estrogen and progesterone during early pregnancy. It is secreted by the fetal placental unit.
The fetal-placental unit also secretes human placental lactogen, HPL, which is another peptide hormone, and estrogens (estriol) and progesterone.
Name two places steroid hormone receptors are found.
Cytoplasm
Nucleus
What is the defect in pseudohypoparathyroidism? What are the effects?
The defect in pseudohypoparathyroidism is a problem with the alpha subunit of the GPCR, resulting in low serum Ca, and high serum phosphate, which resembles hypoparathyroidism.
The difference between patients with hypo-PTH and pseudohypoPTH is that the latter have (increased) circulating levels of PTH, whereas the former have had the gland removed, and so have no PTH.
The faulty alpha subunit also affects thyroid function and gonadal function, and puts patients at risk for hypothyroidism and other endocrine effects.
Provide an example of a hormone that is secreted in a cyclical fashion.
Growth hormone (GH), and most hypothalamic and pituitary hormones are released in strenuous times, cyclically throughout the day, and during sleep.
GH, for example, is most released during exercise, and during the first few hours of sleep.
What connections does the hypothalamus make to the anterior and posterior pituitary?
The hypothalamus is connected to the anterior pituitary via a portal system, and to the posterior pituitary via axons.
What is the releasing factor for GH? On what cells does it act?
The releasing factor for GH is GHRH, made by the hypothalamus, which acts on somatotrophs in the anterior pituitary.
GHRH is inhibited by somatostatin.
On what cells does TRH (thyrotropin-releasing hormone) act? What hormone does it stimulate?
TRH, released by the hypothalamus, acts on thyrotrophs in the anterior pituitary. The resulting release is TSH (and prolactin).
TSH acts on thyroid follicular cells, which are stimulated to make thyroid hormone.
What stimulating factor acts on corticotrophs in the anterior pituitary?
CRH, corticotropin-releasing hormone, acts on corticotrophs in the anterior pituitary. The result is the release of ACTH, adrenocorticotropin-releasing hormone.
ACTH acts on the fasciculata and reticularis cells of the adrenal cortex.
What are the functions of FSH? From where is it released? What stimulates the release of FSH?
FSH is released by the gonadotrophs of the anterior pituitary. This release is stimulated by GnRH, gonadotropin-releasing hormone which is released by the hypothalamus.
FSH functions in females in concert with LH to make estrogens and progestin ovarian cells.
FSH functions in males to stimulate spermatogenesis in sertoli cells.
In females, LH functions in concert with FSH. In males, the function of LH is independent of FSH function. What is this function of LH in males?
LH is released by gonadotrophs in the anterior pituitary, same as FSH. Its release is also stimulated by GnRH made by the hypothalamus, same as FSH.
In males, LH stimulates Leydig cells to make testosterone. In females, FSH and LH function together to make estrogen and progestin in ovarian cells.
Dopamine, released by the hypothalamus, inhibits the release of what hormone by the anterior pituitary?
Dopamine inhibits the release of PRL, prolactin, by lactotrophs in the anterior pituitary. Prolactin, when not inhibited, stimulates the production of milk in the mammary glands.
TRH stimulates prolactin release.
Prolactin also inhibits ovulation, and promotes breast development during puberty and pregnancy.
What hormones are synthesized in the hypothalamus and delivered to the posterior pituitary?
ADH (or AVP, vasopressin), stored in the posterior pituitary, which increases water collection in the collecting ducts of the kidney. ADH also causes an increase in TPR via the contraction of vascular smooth muscle by stimulating V1 receptors.
Oxytocin, also stored in the posterior pituitary, which acts on the uterus during parturition, and the breast during breast feeding.
What is “short-loop feedback?”
Short-loop feedback refers to a negative feedback loop specifically between the anterior pituitary and the hypothalamus.
Feedback of hormones released from peripheral glands onto the hypothalamic-pituitary axis is called “long-loop feedback.”
In general, the hormone released at the peripheral tissue has an inhibitory effect on the hypothalamus. For example, testosterone inhibits further release of GnRH from the hypothalamus. Give an example of a positive feedback loop, in which the target hormone stimulates further hormone production.
During the menstrual cycle, high levels of estradiol cause greater secretion of GnRH, resulting in a hormone surge that produces ovulation.
Give two examples that can cause pathologic hyperprolactinemia.
- Serving the pituitary stalk (neoplasm or trauma), which prevents the tonic inhibition of prolactin provided by dopamine
- Antipsychotic agent, such as a D2 receptor antagonist
Dopamine receptor agonists such as bromocriptine, can correct excessive prolactin secretion.
