Hypothalamus/pituitary Flashcards
What are the two lobes of the hypothalamus called and what is found in them?
Adenohypophysis (anterior pituitary):
Pars tubealis
Pars intermedia
Pars distalis
Neurohypophysis (posterior pituitary):
Median eminence Pars nervosa
What is the hormonal feedback mechanism of the hypothalamus and anterior pituitary?
Stimulus (+/-) -> Hypothalamus -> Hormone 1 (GnRH) -> Anterior pituitary -> Hormone 2 (LH, FSH) -> Gonads -> Hormone 3 (17-bea estradiol=E2) -> Target tissue
Both negative and positive feedback. Long loop feedback is from the 17 beta estradiol to the hypothalamus. The two short feedback loops are from the 17 beta estradol to the anterior pituitary and from the LH or FSH to the hypothalamus.
What are the surrounding structures for the hypothalamus?
Anterior: anterior commissure and lamina terminalis
Posterior: mammillary bodies and midbrain
Superior: thalamus
What is the blood supply to the pituitary gland?
Inferior hypophyseal artery to the capillary plexus of infundibular process to the posterior hypophyseal veins
Superior hypophyseal artery to hypopharyngeal portal veins to the secondary plexus of hypophyseal portal system and then to the anterior hypophyseal veins
Why is there high vascularity to the pituitary?
To allow fast feedback and fast, effective endocrine function.
Where do neurons from the hypothalamus release hormones to?
Into the median emmenence, which i part of the hypophyseal portal system supplied by the superior hypophyseal artery. This delivers the hormones to the capillaries in the anterior lobe of the pituitary and can influence the release of other hormones (indirect)
What are the non-hypotalamic neurons that secrete in the pituitary?
Supraoptic and paraventricular neurons. These produce anti-diuretic hormone and oxytocin, respectively and are released into the posterior lobe - these are direct release hormone
What is the path to the release of growth hormone?
Neurons from he arcuate nucleus release growth hormone releasing hormone into the anterior pituitary resulting in the synthesi and production of growth hormone. In this process, the growth hormone inhibitory hormone needs to be inhibited. These are produced by neurons from the periventricular nucleus.
Growth hormone in the liver leads to secretion of somatomedins (insulin-like growth factor 1), which has a feeback on both neurons to produce growth hormone inhibitory hormone.
Somatomedins induce the growth of skeletal muscle and other tissues
What does prolactin and ocytocin regulate?
Prolactin for preparing milk production
Both important for milk ejection.
How is prolactin regulated?
Produced prolactin regulates its own synthesis and release by acting back on he neurons in the arcuate nucleus. This regulates dopamine release in the median eminence causing inhibition of prolactin release/
During pregnancy and lactation this changes to a positive feedback loop. Reduced dopamine signaling.
The suckling stimulus and placental prolactin.
Reduced dopamine is secreted, increased prolactin transport to the brain, placental lactogens as an additional source of lactogen, and secretion of prolactin releasing factor in response to a suckling stimulus. Increased estrogen also increases lactotropes and increased sensitivity of lactotropes.
What are the final output cells for he hypothalamo-pituitary-gonadal axis?
Th GnRH neurons in the hypothalamus. Essential for fertility. They are spread out because they are too important to keep in one place. Only need a small number functional.
Where to the GnRH neuons project to?
From the hypothalamus to the median emenence to get access to the anterior lobe of the pituitary
What does GnRH do?
It induces the release of LH and FSH in the anterior lobe that then act on the ovaries.
What modulates the release of FSH and LH?
In the anterior pituitary
Females: estrogen
Males: testosterone
Neurons up stream of the GnRH neurons regulate secretion. These are influenced by stress, starvation etc.
What cells does LH act on?
Thecal cells or leydig cells in the testis.
