Hypothalamic and Pituitary Function (F) Flashcards
What is pituitary (/ pituitary gland)?
It is the “master gland”
What is the fxn of pituitary?
It secretes hormones
What is the fxn of hormones secreted by the pituitary?
These regulate other glands
The pituitary is needed for what?
1) Metabolism
2) Gonadal fxn
3) Thyroidal fxn
4) Adrenal fxn
What is the action of pituitary?
It is a transponder that translates neural input into a hormonal or endocrinologic product
What are the distinguishing features of pituitary fxn?
1) Feedback loops
2) Pulsatile secretions
3) Diurnal rhythms
4) Environmental or external modification of its performance
What are the 3 distinct parts of pituitary?
1) Anterior pituitary or adenohypophysis
2) Intermediate lobe or pars intermedialis
3) Posterior pituitary or neurohypophysis
What are the characteristics of anterior pituitary or adenohypophysis?
1) It is the largest portion of the pituitary gland
2) It originates from Rathke’s pouch
What are the characteristics of intermediate lobe or pars intermedialis?
1) It is poorly developed in humans
2) It has little fxnal capacity
What is the characteristic of posterior pituitary or neurohypophysis?
It arises from diencephalon
What are the responsibilities of posterior pituitary or neurohypophysis?
It is responsible for storage and release of:
1) Oxytocin
2) Vasopressin
Where does pituitary reside?
It resides in a pocket of sphenoid
The pituitary is surrounded by what?
It is surrounded by dura mater
The afferent pathways (inputs) to hypothalamus are integrated in what (in connection to fxnal aspects of the hypothalamic-hypophysial unit)?
These are integrated in various specialized nuclei
What is done to the afferent pathways (inputs) to hypothalamus w/c are integrated in various specialized nuclei?
These are processed and resolved into sp. patterned responses
What are the characteristics of hypothalamic response patterns?
1) It is similar for each sp. pituitary hormone
2) Open-loop (-) feedback mechanisms (like thermostat)
3) Pulsatility
4) Cyclicity
What are the most common products of hypothalamus (in connection to hypophysiotropic or hypothalamic hormones)?
1) Peptides
2) Bioactive amines
What are the multiple actions that are often done by hypothalamic hormones?
1) TRH stimulates secretion of both TSH and prolactin
2) GnRH stimulates both LH and FSH production
3) Somatostatin inhibits GH and TSH release from pituitary
4) Vasopressin stimulates H2O metabolism and ACTH secretion
Where are hypophysiotropic hormones found?
These are found throughout:
1) Central nervous system (CNS)
2) Gut
3) Pancreas
4) Other endocrine glands
What are the characteristics of anterior pituitary hormones?
These are larger and more complex > those from hypothalamus
What are the 2 types of anterior pituitary hormones?
1) Tropic
a. GH
2) Direct effectors
a. LH
b. FSH
c. TSH
d. ACTH
What is the characteristic of tropic?
Its actions are sp. for another endocrine gland
What are the actions of GH?
1) It affects substrate metabolism
2) It stimulates liver to produce growth factors
What is the action of direct effectors?
It acts directly on peripheral tissue
What is the action of LH?
It directs testosterone production from Leydig cells
What are the actions of FSH?
1) Ovarian recruitment
2) Folliculogenesis
3) Spermatogenesis
What is the action of TSH?
It directs thyroid hormone production from thyroid
What is the action of ACTH?
It regulates adrenal steroidogenesis
In connection to pituitary tumors, how many percent of people harbor clinically silent pituitary adenomas?
Up to 20%
Findings consistent w/ pituitary tumors are observed in how many percent of normal individuals undergoing MRI exams?
10 - 30%
Pituitary tumors account for how many percent of lesions from pts who have undergone transsphenoidal surgery?
91%
When is physiologic enlargement of pituitary (in connection to pituitary tumors) can be seen?
During:
1) Puberty
2) Pregnancy
What are the actions of growth hormone (GH)?
1) It is amphibolic (influences both anabolic and catabolic processes)
2) It allows effective transition from a fed state to a fasting state (w/out shortage of substrates)
3) It directly antagonizes effect of insulin on glucose metabolism
4) It provides hepatic gluconeogenesis
5) It stimulates lipolysis
6) It enhances protein synthesis (in skeletal muscle and other tissues)
7) It stimulates production of insulin-like growth factors
How can GH be tested?
It can be tested based on dynamic physiology of GH axis
Testing for autonomous production of GH relies on what?
Normal suppressibility of GH
How can normal suppressibility of GH (where testing for autonomous production of GH rely on) can be done?
By oral glucose loading
What are the strategies to stimulate GH?
1) Insulin-induced hypoglycemia
2) Combination infusions of GHRH and amino acid L-arginine
3) Infusion of L-arginine coupled w/ oral L-DOPA
What is the characteristic of insulin-induced hypoglycemia (as 1 of the strategies to stimulate GH)?
It is an outdated method
In connection to GH, acromegaly results from what?
It results from pathologic or autonomous GH excess (in most cases, a pituitary tumor)
Acromegaly causes what?
1) Gigantism
2) Bony and soft tissue overgrowth
3) Progressive enlargement of:
a. Hands
b. Feet
c. Mandible
d. Skull
4) Arthritis
5) Diabetes
6) Hypertension
7) Atherosclerosis
8) Muscle weakness
9) Sleep apnea
10) Shortened life expectancy
To whom does GH deficiency occur?
It occurs in both:
1) Children
2) Adults
What are the causes of occurrence of GH deficiency in children?
1) It is genetic
2) Or due to tumors
Why does GH deficiency occur in adults?
It is a result of structural / fxnal pituitary abnormalities
GH deficiency results in what in children?
Growth failure
What are the various genetic defects w/c are associated w/ GH deficiency?
1) Recessive mutation in GHRH gene, failure of GH secretion
2) Loss of GH gene
3) GH insensitivity
4) Structural lesions of pituitary or hypothalamus
What are the characteristics of prolactin?
1) It is structurally related to:
a. GH
b. Placental lactogen
2) It is considered as a stress hormone
3) It has vital fxns in reproduction
4) It is classified as a direct effector hormone
5) It regulates via tonic inhibition (not intermittent stimulation)
6) Its secretion is inhibited by dopamine
7) Its physiologic effect is lactation
8) Excess prolactin usually leads to hypogonadism
In connection to prolactin, what is prolactinoma?
It is a pituitary tumor that directly secretes prolactin
What is the characteristic of prolactinoma?
It is the most common type of fxnal pituitary tumor
The clinical presentation of prolactinoma depends on what?
1) Pt’s age
2) Pt’s gender
3) Tumor size
What are the clinical presentations of prolactinoma to premenopausal women?
1) Menstrual irregularity / amenorrhea
2) Infertility
3) Galactorrhea
What are the clinical manifestations of prolactinoma to men / postmenopausal women?
1) Headaches
2) Or visual complaints
What are the other causes of hyperprolactinemia (in connection to prolactin)?
1) Pituitary stalk interruption
2) Dopaminergic antagonist medications
3) Thyroidal failure
4) Renal failure
5) Polycystic ovary syndrome (PCOS)
How can hyperprolactinemia be clinically evaluated (in connection to prolactin)?
1) Careful history
2) Physical examination
3) Obtain TSH and free T4 lvls
4) Careful assessment of other anterior pituitary fxn and evaluation of seller anatomy w/ MRI (if pituitary tumor is suspected)
What are the therapeutic goals in connection to management of prolactinoma?
1) Reduce tumor mass
2) Restore normal gonadal fxn and fertility
3) Prevent osteoporosis
4) Preserve normal pituitary fxn
What are the therapeutic options in connection to management of prolactinoma?
1) Simple observation
2) Surgery
3) Radiotherapy
4) Medical management w/ dopamine
What is idiopathic galactorrhea (in connection to prolactin)?
Lactation in women w/ normal prolactin lvls; dx of exclusion
Failure of either pituitary or hypothalamus (in connection to hypopituitarism) results in what?
Loss of anterior pituitary fxn
What is panhypopituitarism (in connection to hypopituitarism)?
Complete loss of fxn
What is monotropic hormone deficiency (in connection to hypopituitarism)?
Loss of only a single hormone
Hypopituitarism is associated w/ what?
Low / normal lvls of tropic hormone
When should both tropic and target hormone lvls be measured?
These should be measured when there is any suspicion of pituitary failure
What should be done if 1 secondary deficiency is documented (in connection to hypopituitarism)?
Search for other deficiency states and cause for pituitary failure
What are the etiologies of hypopituitarism?
1) Tumors
a. Pituitary
b. Parasellar
c. Metastatic
d. Hypothalamic
2) Postpartum ischemic necrosis of pituitary
3) Infiltrative diseases
a. Hemochromatosis
b. Sarcoidosis
c. Histiocytosis
4) Fungal infections
5) Tuberculosis (TB)
6) Syphilis
7) Lymphocytic hypophysitis
8) Severe head trauma
9) Pituitary surgery
10) Radiotherapy
What are the treatments for panhypopituitarism?
1) Thyroxine
2) Glucocorticoids
3) Gender-specific sex steroids
What is posterior pituitary?
1) It is an extension of forebrain
2) It represents storage region for oxytocin and vasopressin
What are the 2 posterior pituitary hormones?
1) Oxytocin
2) Vasopressin
What are the characteristics of oxytocin?
1) It is a cyclic nonapeptide, w/ a disulfide bridge connecting amino acid residues 1 & 6
2) It has a critical role in lactation
3) It likely plays a major role in labor and parturition
4) It has been shown to have effects on pituitary, renal, cardiac, and immune fxns
In connection to oxytocin, what is used in obstetrics to induce labor?
Synthetic oxytocin, Pitocin
What are the characteristics of vasopressin?
1) It is a cyclic nonapeptide w/ an identical disulfide bridge
2) It is structurally similar to oxytocin (it differs by only 2 amino acids)
3) It is a potent pressor agent
4) It affects blood clotting
What is the major action of vasopressin?
Its major action is to regulate renal free H2O excretion and H2O balance
What is the action of hypothalamic osmoreceptors and vascular baroceptors (in connection to vasopressin)?
Regulate release of vasopressin from posterior pituitary
The deficiency of vasopressin can lead to what condition / disorder?
Diabetes insipidus (DI)
What are the characteristics of DI (where deficiency of vasopressin can lead to)?
1) Excessive urine production (polyuria)
2) Intense thirst (polydipsia)
