Hypothalamus and Pituitary Flashcards
What connects the hypothalamus to the pituitary gland?
Infundibulum
How is the hypothalamus connected to the pituitary gland?
Hypothalamic communication with the pituitary gland is both neural (to the posterior pituitary) and endocrine (to the anterior pituitary), hence it’s neuroendocrine function.
What is the name of section of bone the pituitary gland is found?
Located in a pocket in the sphenoid bone (hypophyseal fossa), directly below the hypothalamus
What types of hormones are released from the hypothalamus?
Neurohormones
What types of hormones are released from the anterior pituitary?
Classic endocrine hormones
What types of hormones are released from the posterior pituitary?
Neurohormones (extension of hypothalamus)
What are the two forms of hypothalamic neurohormones?
Tropic – neurohormones secreted into capillaries travelling to anterior pituitary. Govern release of anterior pituitary hormones (can be stimulatory or inhibitory)
Non-tropic – neurohormones produced in the hypothalamus and travel to posterior pituitary (via axons of hypothalamic neurons) where they are released into blood.
Define tropic hormones
Tropic – neurohormones secreted from hypothalamus into capillaries travelling to anterior pituitary. Govern release of anterior pituitary hormones (can be stimulatory or inhibitory)
Define non-tropic hormones
Non-tropic – neurohormones produced in the hypothalamus and travel to posterior pituitary (via axons of hypothalamic neurons) where they are released into blood.
What is the action of hypothalamic tropic hormones?
All hypothalamic tropic hormones bind to receptors on anterior pituitary and stimulate/inhibit release of anterior pituitary hormones
What 7 tropic hormones are produced by the hypothalamus?
5 hypothalamic “releasing hormones”:
– Thyrotrophin Releasing Hormone (TRH)
– Corticotropin Releasing Hormone (CRH)
– Growth Hormone Releasing Hormone (GHRH)
– Gonadotrophin Releasing Hormone (GnRH)
– Prolactin Releasing Hormone (PRH)
2 hypothalamic “inhibiting hormones”
– Growth Hormone Inhibiting Hormone (GHIH) aka somatostatin
– Dopamine aka Prolactin Inhibiting Hormone (PIH)
What are the releasing hormones released by the hypothalamus?
– Thyrotrophin Releasing Hormone (TRH) – Corticotropin Releasing Hormone (CRH) – Growth Hormone Releasing Hormone (GHRH) – Gonadotrophin Releasing Hormone (GnRH) – Prolactin Releasing Hormone (PRH)
What are the inhibiting hormones released by the hypothalamus?
– Growth Hormone Inhibiting Hormone (GHIH) aka somatostatin
– Dopamine aka Prolactin Inhibiting Hormone (PIH)
What kind of hormones are the 7 hormones released by the hypothalamus?
All are peptides, except dopamine, which is an amine hormone
What is the Hypothalamo-hypophyseal portal system?
Network of tiny vessels which transfer trophic hormones from hypothalamus to anterior pituitary
What is responsible for the delivery of tropic hormones from the hypothalamus to the anterior pituitary?
Hypothalamo-hypophyseal portal system
What are the major differences between the anterior and posterior pituitary?
Anterior o True endocrine tissue o Epithelial origin o Connected to hypothalamus via capillary portal system o Also called adenohypophysis o Makes up 2/3rds of the gland
Posterior o Neuroendocrine tissue o Neural tissue origin o Neural connection to hypothalamus o Secretes neurohormones made in hypothalamus o Also called neurohypophysis o Makes up 1/3rd of the gland
What is the other name for the anterior pituitary?
Adenohypophysis
What is the other name for the posterior pituitary?
neurohypophysis
What type of hormones are produced by the anterior pituitary?
Classic endocrine hormones, all peptide hormones
What 6 hormones are released from the anterior pituitary?
- Thyroid Stimulating Hormone (TSH) aka thyrotrophin
- Adrenocorticotrophic Hormone (ACTH) aka corticotrophin
- Follicle Stimulating Hormone (FSH)
- Luteinising Hormone (LH)
- Growth Hormone (GH)
- Prolactin
Which hormone released from the anterior pituitary is non-tropic?
Prolactin
What anterior pituitary hormones make up the gonadotrophins?
FSH and LH both make up the gonadotrophins
Describe the production, target and action of prolactin
Prolactin – produced by AP, directly targets breast for lactation (only non-trophic)
Describe the production, target and action of TSH
Thyroid-stimulating hormone – produced by AP, stimulates thyroid hormone release from thyroid
Describe the production, target and action of Adrenocorticotropic hormone (ACH)
Adrenocorticotropic hormone – produced by AP, targets adrenal cortex for cortisol release (trophic)
Describe the production, target and action of GH
Growth hormone – produced by AP, targets liver for IGF-1 release (trophic) and tissue metabolism (direct)
Describe the production, target and action of FSH and LH
Follicle-stimulating hormone and luteinising hormone – both produced by AP, act on gonads for regulation of reproductive function (direct) and sex hormone release (trophic)
Describe feedback control of AP hormone production
Hormones themselves act as negative feedback signal
Each hormone feeds back to inhibit hormone secretion by integrating centres earlier in the reflex
Feedback from endocrine target = long-loop feedback
Feedback from anterior pituitary to hypothalamus = short-loop feedback
What is short loop feedback?
Feedback from anterior pituitary to hypothalamus = short-loop feedback
What is long loop feedback?
Feedback from endocrine target = long-loop feedback
What hormones are produced by the posterior pituitary ?
Stores and releases 2 peptide neurohormones:
o Vasopressin (aka anti-diuretic hormone; ADH)
o Oxytocin
What types of hormone are produced and stored in the posterior pituitary?
Peptide neurohormones
What neurons in the posterior pituitary produce its hormones and links it to the hypothalamus?
Magnocellular neurons
What is the main function of vasopressin, what triggers its release and where are its sites of action?
Regulates water balance
Triggered by increased plasma osmolarity and decreased blood volume/BP
Increases water resorption at kindey collecting ducts and increases tone of vascular smooth muscle to increase BP
What is the main function of oxytocin, what triggers its release and where are its sites of action?
Milk ejection (not production) and uterine contractions
Triggered by labour (baby head on cervix) and suckling
Contracts milk duct smooth muscle to eject milk and contraction of uterine smooth muscle for child birth
What are primary, secondary and tertiary endocrine disorders?
1° disorders are those in which the defect is in the cells that secrete the hormone e.g. primary thyroid dysfunction
2° disorders are those in which there is too little or too much trophic hormone from pituitary e.g. decreased TSH for the thyroid gland to produce TH
3° disorders relate to hypothalamic defects e.g. affected TRH, leading to altered TSH and therefore TH as well
