Hypothalamic-Pituitary Physiology Flashcards
What does the posterior pituitary regulate as part of the hypothalamus-pituitary complex (2)?
Lactation
Water metabolism
What does the anterior pituitary regulate as part of the hypothalamus-pituitary complex (4)?
Thyroid gland
Adrenal glands
Reproductive glands
Somatic growth
What is the function of the hypothalamus?
Collect and integrate signals and funnel them to the pituitary gland.
Where does the pituitary lie?
In a depression of the sphenoid bone called the sella turcica.
Why are vision problems (mainly peripheral vision) associated with tumors of the pituitary?
Tumors cause the pituitary to be pushed upward, compressing the optic nerves at the optic chiasm
Where are the anterior and posterior pituitaries derived from? What are their technical names?
Rathke’s pouch (oral ectoderm) grows upward into the adenohypophysis
Neural down growth from the diencephalon (infundibulum) gives rise to the neurohypophysis
What are the six hormones secreted by the hypothalamus to the adenohypophysis?
Growth hormone-releasing hormone (GHRH)
Thyroid-releasing hormone (TRH)
Corticotropin-releasing hormone (CRH)
Gonadotropin-releasing hormone (GnRH)
Dopamine (DA)
Somatostatin (SST)
The supraoptic nucleus secretes what hormone to the neurohypophysis?
Oxytocin
The paraventricular nucleus secretes what hormone to the neurohypophysis?
Antidiuretic hormone (ADH/vasopressin)
What are the five cell types of the adenohypophysis and what six peptide hormones do they secrete?
Lactotrophs: prolactin (PRL)
Somatotrophs: growth hormone (GH)
Corticotrophs: (ACTH)
Gonadotrophs: follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
Thyrotrophs: thyroid-stimulating hormone (TSH)
Somatostatin and dopamine are inhibiting hormones of the hypothalamus and pituitary. What do they inhibit?
Somatostatin: GH and TSH
Dopamine: PRL
Releasing hormones are secreted into what structure?
Median eminence
The first capillary bed in the hypophyseal portal system
Long-acting GnRH analogs (leuprolide) have been used in the treatment of what (4)? How do they work?
Treats:
Precocious puberty
Manipulation of reproductive cycles (IVF)
Treatment of endometriosis
PCOS
Acts as an agonist to GnRHr to decrease gonadotropin as well as sex hormones
What are some factors that can lead to hyperprolactinemia? (4)
Drugs that block dopamine (D2 receptors)
Lesions that interfere with portal blood flow
Primary hyperthyroidism (high TRH)
Lactotroph adenomas (prolactinomas; ~40% of all pituitary tumors)
What are the two primary actions of prolactin?
Enhanced breast development during pregnancy
Induce lactogenesis
What are the symptoms caused by prolactinomas? Men? Women? Both?
Both: headache, visual disturbance, hypopituitarism
Women: loss of menstrual periods, breast milk reduction, acne, excessive body/facial hair
Men: erectile dysfunction, enlarged breasts, diminished sexual interest
How many amino acids long is prolactin?
99
How many amino acids long is growth hormone? What other special characteristic does it have?
191 amino acids longs
2 disulfide bridges
What is the function of growth hormone after puberty is complete?
Modulate metabolism, body composition, and functional capabilities
What are the direct and indirect effects of GH?
Direct: GH binds to its receptor on target cells (ex: lipolysis in adipocytes)
Indirect: mediated by insulin-like growth factor-1 (IGF-1), which is secreted from the liver in response to growth hormone (ex: bone growth)
What pituitary hormone is an antagonist for GHRH?
Somatostatin
What are the effects of GH? (4)
*Postnatal growth of bones (cartilage in epiphyseal plates)
Increases organ size and fucntion
Increase lean body mass and decreases fat cell size
Increase blood glucose concentration
What is the average rate of secretion of GH? When does it peak?
~10 pulses/day
Regular nocturnal peak (deep sleep)
At approximately what rate do GH levels drop over the course of a lifetime?
~50% drop every 7 years
What conditions can cause a decrease in GH secretion? (3)
Obesity
Non-alcoholic fatty liver disease (NAFLD)
Type 2 diabetes
What disorder is caused by GH deficiency before puberty?
Dwarfism:
Retarded skeletal growth
Delayed sexual development
Poorly developed muscles
Excess subcutaneous fat
What disorder is caused by a resistance to GH due to dysfunction of the GH receptor?
Laron syndrome
350 cases worldwide
Autosomal recessive
Patients do not grow past 4 feet but are very well protected against cancer, diabetes, and potentially heart diseases and Alzheimer’s
Why is GH deficiency difficult to diagnose in adults?
“generic” symptoms
reduced well-being
increased fat mass (central obesity)
Dyslipidemia
Increased cardiovascular disease
Decreased bone density
What disorder is caused by an increase in GH before puberty (before closure of epiphyseal plates)? Symptoms? Life expectancy?
Gigantism:
Glucose intolerance and hyperinsulinism
Cardiovascular problems
More susceptible to infections
30-40 year life expectancy
What disorder is caused by an increase in GH after puberty? Symptoms? Treatment?
Acromegaly:
Enlargement of hands, feet, forehead, jaw, nose, and heart (oppositional growth)
Thick skin and large tongue
Treatment: surgery or somatostatin analogs
