Hypothalamus and Pituitary Flashcards
What connects the hypothalamus and pituitary?
A stalk called the infundibulum
Why is the hypothalamic communication with the pituitary gland neuroendocrine?
It is a neural connection (to posterior pituitary)
AND an endocrine connection (to the anterior pituitary)
What is the function of the hypothalamus?
It is an integration centre for the endocrine systems
Where is the hypothalamus located?
At the base of the brain, below the thalamus
What is the pituitary gland?
Bean shaped and sized gland located in a pocket in the sphenoid bone
What are the two parts of the pituitary gland?
The posterior and anterior pituitary
These are two distinct tissues
What are trophic hormones?
Hormones that govern the release of another hormone
What kind of hormones does the hypothalamus and posterior pituitary release?
Neurohormones
What kind of hormones does the anterior pituitary release?
Classic endocrine hormones
What are the two kinds of hypothalamic neurohormones?
- Trophic - secreted into capillaries travelling to the anterior pituitary (govern release of anterior pituitary hormones)
- Non-trophic - neurohormones produced in hypothalamus + travel to posterior pituitary (via axons of hypothalamic neurons) where they are released into the blood
What are the 5 main hormones produced by the hypothalamus that travel to the anterior pituitary and cause the release of another hormone? i.e. they are trophic
Thyrotropin releasing hormone (TRH) Corticotropin releasing hormone (CRH) Growth hormone releasing hormone (GHRH) Gonadotrophin releasing hormone (GnRH) Prolactin releasing hormone (PRH)
What are the two hypothalamic inhibiting hormones?
Growth hormone inhibiting hormone (GHIH) aka. somatostatin
Dopamine (aka prolactin inhibiting hormone)
What are the kind of hormones are released by the hypothalamus?
Peptide (expect dopamine)
What does PRH stimulate?
Release of prolactin from anterior pituitary
What does TRH stimulate?
Release of thyroid stimulating hormone from anterior pituitary
What does CRH stimulate?
Release of ACTH from anterior pituitary
What does GHRH stimulate?
Release of HG from the anterior pituitary
What does GnRH stimulate?
Release of FSH and LH from the anterior pituitary
What does ACTH do?
Stimulates release of cortisol from adrenal cortex
What is the hypothalamo-hypophyseal system?
Network of tiny vessels which transfer trophic hormones from hypothalamus to anterior pituitary
Where are the hypothalamic hormones released in the hypothalamo-hypophyseal portal system?
Released from neurosecretory neurons at the median eminence
What kind of tissue is the anterior pituitary?
True endocrine tissue
What is the origin of the anterior pituitary tissue?
Epithelial
What kind of tissue is the posterior pituitary?
Neuroendocrine
What is the origin of the posterior pituitary tissue?
Neural tissue
How is the anterior pituitary connected to the hypothalamus?
Via a capillary portal system
How is the posterior pituitary connected to the hypothalamus?
Neural connection (it secretes neurohormones made in the hypothalamus)
What are the other names for the anterior and posterior pituitary?
Anterior - adenohypophysis
Posterior - neurohypophysis
What % of the pituitary gland is anterior and posterior?
1/3 posterior, 2/3 anterior
How does the hypothalamus control the release of anterior pituitary hormones?
By producing releasing or inhibiting hormones (e.g. TRH stimulates TSH secretion)
How many hormones are released from the anterior pituitary? How many of these are trophic?
6 (all peptide)
5 are trophic
What hormones are released by the anterior pituitary?
Thyroid stimulating hormone Adrenocorticotrophic hormone Follicle stimulating hormone Lutenising hormone Growth hormone Prolactin
Which of the anterior pituitary hormones is NOT trophic and what is its role?
Prolactin
Directly stimulates milk production from the breast during lactation
What is a portal system?
Two capillary beds in series
What does growth hormone do?
Goes to liver and stimulates IGF-1 release and also directly affects tissue metabolism
What is involved in anterior pituitary feedback control?
Hormones themselves act as negative feedback signal
Feedback from endocrine target (long-loop feedback)
Feedback from anterior pituitary to hypothalamus (short-loop feedback)
What kind of hormones does the posterior pituitary store and release?
2 peptide neurohormones -
Vasopressin (ADH)
Oxytocin
Where are oxytocin and ADH synthesised?
In magnocellular neurons (which have their cell bodies in specific areas of the hypothalamus), their terminals end directly on capillaries in the posterior pituitary
What is the function of vasopressin?
Regulates water balance
What triggers the release of vasopressin?
Increased plasma osmolarity
Decreased plasma volume or BP
Where does vasopressin act?
Kidney collecting ducts to increase water reabsorption and vascular smooth muscle to increase BP
What is the action of oxytocin?
Milk ejection + uterine contraction
What triggers the release of oxytocin?
Labour (baby’s head pushing against cervix)
Suckling
Where does oxytocin act?
Milk duct smooth muscle (contracts muscle ejecting milk)
Uterine smooth muscle (–> childbirth)
Define hyposecretion
Too little hormone secreted
Define hypersecretion
Too much hormone secreted
Define hyporesponsiveness
Reduced response of target cell
Define hyperresponsiveness
Increased response of target cell
What are primary disorders?
Those in which the defect is in the cells that secrete that hormone
What are secondary disorders?
Those in which there is too little or too much trophic hormone from the pituitary
What are tertiary disorders?
These relate to hypoththalamic defects
What may cause hyporesponsiveness?
Alterations in receptors for that hormone, disordered post-receptor events or failure of metabolic activation of hormone
What may cause hyperresponsiveness?
Permissive effects
