IUHS Student-2-Student USMLE Step 1 Recall

                                                Endocrinology

                                                    Pituitary

Normal Anterior Pituitary

the anterior pituitary, or adenohypophysis, constitutes about 80% of the gland...

it is derived embryologically from rathke pouch, which is an exteniosn of the developing oral cavity...it is eventually cut off from its origins by the growth of the sphenoid bone, which creates a saddle like depression, the sella turcica...along its tract, squamous epithelial rests may be left...

the anterior pituitary has a portal vascular system that is the conduit for the transport of hypothalamic releasing hormones from the hypothalamus to the anterior pituitary...hypothalamic neurons have terminals in the median eminence where the hormones are released into the portal system, which traverses the pituitary stalk and enters the anterior pituitary gland....

produce growth hormone (GH): these acidophilic cells constitute half of all the hormone producing cells in the anterior pituitary...

produce prolactin: these acidophilic cells secrete prolactin, which is essential for lactation...

these basophilic cells produce adrenocorticotropic hormone (ACTH), pro-opiomelanocortin, melanocyte stimulating hormone (MSH), endorphins, and lipotropin...

these pale basophilic cells produce thyroid stimulating hormone (TSH)...

these basophilic cells produce both follicle stimulating hormone (FSH) and luteinizing hormone (LH)...FSH stimulates the formation of graafian follicle in the ovary, and LH induces ovulation and the formation of corpora lutea in the ovary...

the posterior pituitary, or neurohypophysis, consists of modified glial cells (termed pituicytes) and axonal processes extending from nerve cell bodies in the supraoptic and paraventricular nuclei of the hypothalamus, through the pituitary stalk to the posterior lobe, where the two posterior lobe hormones, oxytocin and vasopressin, are stored...

the posterior pituitary is derived embryologically from an outpouching of the floor of the third ventricle, which grows downward alongside the anterior lobe...the neuroectoderm...

herring bodies are formed from neuroectoderm as an extension of the developing diencephalon...

Prolactinomas

most frequent type of hyperfunctioning pituitary adenoma, accounting for about 30% of all clinically recognized pituitary adenomas...

increased serum levels of prolactin, or prolacintemia, cause amenorrhea, galactorrhea, loss of libido, and infertility...the diagnosis of an adenoma is made more readily in women than in men, especially between the ages of 20 and 40 years, presumably b/c of the sensitivity of menses to disruption by hyperprolactinemia...this tumor underlies almost a quarter of cases of amenorrhea...

macroadenoma = prolactin levels greater than 350...

microadenoma = prolactin levels between 200 and 300...

hyperprolactinemia may result from causes other than prolactin secreting pituitary adenomas...physiologic hyperprolactinemia occurs in pregnancy, where serum prolactin levels increase throughout pregnancy, reaching a peak at delivery...

prolactin levels are also elevated by nipple stimulation, as occurs during suckling in lactating women, and as a response to many types of stress...

pathologic hyperprolactinemia can also result from lactotroph hyperplasia, such as when there is interference with normal dopamine inhibition of prolactin secretion...this may occur as a result of damage to the dopeminergic neurons of the hypothalamus, pituitary stalk section (owing to head trauma), or drugs that block dopamine receptors on lactotroph cells...

any mass in the suprasellar comparment may disturb the normal inhibitory influence of the hypothalamus on prolactin secretion, resulting in hyperprolactinemia - a phenomen called the stalk effect...therefore a mild elevation in serum prolactin in a patient with a pituitary adenoma does not necessarily indicate a prolactin secreting tumor...

several classes of drugs can cause hyperprolactinemia, including dopamine receptor antagonists such as the neuroleptic drugs (phenothiazines, haloperidol), and older antihypertensive drugs, such as reserpine, which inhibit dopamine storage...

other cause of hyperprolacintemia include estrogens, renal failure, and hypothyroidism...prolactinomas are treated with bromocriptine, a dopamine receptor agonist, which causes the lesions to diminish in size...

Growth Hormone Adenomas of the Pituitary

GH secreting tumors are the second most common type of functioning pituitary adenoma...these tumors, similar to other pituitary adenomas, arise from a monoclonal expansion of a single cell that has undergone somatic mutation...

corticotroph adenomas are usually small microadenomas at the time of diagnosis..these tumors are basophilic or chromophobic and stain positively with periodic acid schiff (PAS) stains b/c of the presence of carbohydrate in the ACTH precursor molecule...

hypopituitarism refers to decreased secretion of pituitary hormones, which can result from diseases of the hypothalamus or of the pituitary...hypofunction of the anterior pituitary occurs when approximately 75% of the parenchyma is lost or absent...

this may be congenital or the result of a variety of acquired abnormalities that are intrinsic to the pituitary...most cases of hypofunction arise from destructive processes directly involving the anterior pituitray, such as tumors, ischemic necrosis of the pituitary, and the empty sella syndrome, although other mechanisms hae been identified...

Sheehan's syndrome, also known as postpartum pituitary necrosis, results from the sudden infarction of the anterior lobe of the pituitary...this can occur with obstetric complications, such as hemorrhage or shock...

Sheehan's syndrome produces symptoms of hypopituitarism...the initial sign is cessation of lactation, which may be followed by secondary amenorrhea due to the loss of gonadotropins...other signs of hypopituitarism include hypothyroidism and decreased functioning of the adrenal gland...

ADH deficiency causes diabetes insipidus, a condition characterized by excessive urination (polyuria) owing to an inability of the kidney to resorb water properly from the urine...

it can result from a variety of processes, including head trauma, tumors,and inflammatory disorders of the hypothalamus and pituitary as well as surgical procedure involving these organs....

the condition can arise spontaneously, in the absence of an underlying disorder...the clincal manifestations include the excretion of large volumes of dilute urine with an inappropriately low specific gravity....

serum sodium and osmolality are increased owing to excessive renal loss of free water, resulting in thirst and polydipsia...

ADH excess causes resorption of excessive amounts of free water, resulting in hyponatremia...

the most frequent causes of SIADH include the secretion of ectopic ADH by malignant neoplasms (particularly small cell carcinomas of the lung), non-neoplastic diseases of the lung, and local injury to the hypothalamus or posterior pituitary (or both)....

the clinical manifestations of SIADH are dominated by hyponatremia, cerbral edema, and resultant neurologic dysfunction...

the craniopharyngioma is thought to be derived from vestigial remnants of rathke pouch...

although they occur most commonly during childhood and adolescence, about 50% present clinically after age 20...