Lecture 17 - Endocrine Systems: Pituitary Hormones and Axes Flashcards
What are the 2 distinct components that secrete hormones in the pituitary?
- Adenohypophysis - anterior lobe of the pituitary gland
- Neurohypophysis - posterior lobe of the pituitary gland. Made of neural tissue
NOTE: there is also the intermediate lobe, but it doesn’t secrete hormones in adults
Pituitary gland (aka hypophysis)
An endocrine organ that consists of a stalk of tissue dangling from the inferior side of the forebrain
Hypothalamus
Part of the diencephalon and is an endocrine organ. Has many functions and is known to release 9 hormones
5 functions of the hypothalamus and give examples for each
- Regulating alertness through the limbic system and basal forebrain (ex. wakefulness, emotional state)
- Controlling behavioural “drives” (ex. generating motivation for eating, drinking, aggression, social actions)
- Regulating circadian rhythms by affecting the release of melatonin from the pineal gland
- Regulating autonomic functions through the brainstem and ANS (ex. control of temps, BP, HR)
- Secreting both regulatory and effector neurohormones through the pituitary gland
Name the 2 effector hormones that the hypothalamus directly releases and which part are they released from?
Vasopressin (ADH) and oxytocin (OT) are released from the posterior lobe of the pituitary gland
Function of vasopressin (ADH) and oxytocin (OT) and what are their target organs?
Vasopressin - antidiuresis (water conservation); kidney
Oxytocin - uterine contraction and milk ejection; uterus
They are very different hormones because of their target organs
Name the 6 hormones released from the anterior pituitary and their target organs
- Thyroid stimulating hormone (TSH) - thyroid gland
- Adrenocorticotropic hormone (ACTH) - adrenal gland
- and 4. Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH) - ovary and testis
- Growth hormone (GH) - musculoskeletal system
- Prolactin (PRL) - mammary gland
What are regulatory hormones?
Most hypothalamic regulatory hormones are “releasing hormones,” meaning they stimulate secretion of their anterior pituitary hormone
True or False? Growth hormone is the only hormone known to have an antagonistic hypothalamic regulator hormone
False - growth hormone and prolactin each have antagonistic hypothalamic regulator hormones, GH-IH and PIH, respectively
ie. they inhibit the release of the hormones released by the pituitary
Describe the hierarchy of the HPE (hypothalamus, pituitary, effector) axis and how it is regulated
It consists of hypothalamic neurons, anterior pituitary cells, and their target organs that form the axis. The HPE axis involves 3 hormones:
- the releasing (regulatory) hormones
- the pituitary hormones
- the effector hormones
All of which are regulated by negative feedback by their effector hormones on their regulatory hormones
Name 3 examples of HPE axes
- HPT axis: TRH -> TSH -> thyroid gland -> thyroid hormones
- HPA axis: CRH -> ACTH -> adrenal cortex -> glucocorticoids
- HPG axis, 2 types:
GnRH -> FSH -> testes/ovaries -> inhibin/inhibin and estrogens
GnRH -> LH -> testes/ovaries -> andorgens/progesterone and estrogens
What is a tropic hormone?
It is a regulatory hormone; it acts to affect the secretion of another hormone
What is a trophic hormone?
A hormone that stimulates cell division in its target cells
Give 3 examples of anterior pituitary hormones that are both trophic and tropic
ACTH, TSH, and LH/FSH
4 potential causes of hormone hyposecretion?
- Tumour - (esp. on the optic nerve) can compress the axons and/or blood vessels, which can block the transmission of the hormone
- Physical damage to the pituitary gland can destroy some or all tropes - can’t release the hormone to the target organ
- Damage to the target organ (often by antibodies created by autoimmune disease) can destroy effector producing cells
- Strokes or other causes of brain damage can destroy hypothalamic neurons
