Term
| How much does the pituitary gland weigh and what is the name of the skull depression within which it is located? |
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Definition
| in the adult it weighs, 600mg; sella turcica ("Turkish Saddle"); |
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Term
| what are the different parts of the adenohypophysis? |
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Definition
| The adenohypophysis is further divided into the main pars distalis (most distal to the hypothalamus), pars tuberalis (extension of the glandular tissue up the infundibular stalk) and pars intermedia (along the fold line remnant of Rathke’s pouch). |
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Term
| what are the different parts of the neurohypophysis? |
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Definition
| The posterior lobe (neurohypophysis) is composed of the axons of hypothalamic neurons that extend downward as a large bundle behind the anterior pituitary. The neurohypophysis is also divided into the main pars nervosa and the infundibulum. The pituitary stalk or infundibulum connects the pituitary gland with the hypothalamus. |
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Term
| what are the embryological origins of the hypophysis? |
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Definition
| The two lobes have different embryological origins. The anterior lobe is derived from an out pocketing (Rathke’s pouch) of the floor of primitive oral cavity ectoderm. The posterior lobe is an out pocketing from the diencephalon neuroectoderm. Remnants of Rathke’s pouch (Rathke’s pouch cysts) can often be found as cystic cavities sandwiched between the adenohypophysis and neurohypophysis. |
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Term
| what borders the pituitary? |
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Definition
| The pituitary gland is bordered inferiorly by the sella turcica, which is a depression in the sphenoid bone, and superiorly by a tough dural covering, the diaphragm sella through which passes the infundibulum. The cavernous sinuses form the lateral borders of the pituitary. Cranial nerves 3, 4, and 5 pass through the cavernous sinuses. The optic chiasm also runs superiorly to the pituitary. Growth of the pituitary laterally can cause cranial nerve palsies or growth upward can cause visual compromise, most notably loss of vision in the temporal field. |
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Term
| what artery supplies the anterior pituitary? |
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Definition
| A branch of the superior hypophyseal artery -> capillary bed in the lower hypothalamus (median eminence), and hypothalmic hormones destined for the anterior pituitary are secreted into that capillary blood -> hypothalamic-hypophyseal portal veins-> capillaries within the anterior pituitary carry hormones secreted by that gland, coalesce into veins (cavernous sinus veins) that drain into the systemic venous blood. |
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Term
| what provides the major blood supply for the posterior pituitary? |
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Definition
| inferior hypophysial arteries. |
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Term
| what are six major hormones synthesized and secreted by the anterior pituitary? |
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Definition
| polypeptides: GH, PRL, ACTH; Dimeric glycoproteins: TSH, FSH, LH. |
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Term
| in the anterior pituitary Somatotrophs produce |
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Definition
| GH; they compose 50% of cells. |
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Term
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Definition
| PRL; and compose about 15% of cells |
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Term
| Individual cells within the anterior pituitary secrete a single hormone except |
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Definition
| gonadotropes , in which one cell produces FSH and LH |
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Term
| what are direct effects of GH? |
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Definition
| stimulates adipocytes to break down triglyceride and suppresses their ability to take up and accumulate circulating lipids. |
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Term
| The indirect effects of GH are mediated by what? |
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Definition
| IGF, which mediates the majority of the growth promoting effects of GH. |
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Term
| what stimuates proliferations of chondrocytes and what stimulates their differentiation? |
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Definition
| IGF-1 stimulates proliferation of chondrocytes (cartilage cells), resulting in bone growth. Growth hormone does seem to have a direct effect on bone growth in stimulating differentiation of chondrocytes. |
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Term
| what stimulates both the differentiation and proliferation of myoblasts? It also stimulates amino acid uptake and protein synthesis in muscle and other tissues |
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Definition
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Term
| what are the effects of GH on protein, lipid, and carb metabolism? |
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Definition
protein - anabolism: amino acid uptake, increased protein synthesis and decreased oxidation of proteins. fat - enhances the utilization of fat by stimulating triglyceride breakdown and oxidation in adipocytes. carbs - maintain blood glucose within a normal range, has anti-insulin activity - because it supresses the abilities of insulin to stimulate uptake of glucose in peripheral tissues and enhance glucose synthesis in the liver. Somewhat paradoxically, administration of growth hormone stimulates insulin secretion, leading to hyperinsulinemia. |
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Term
| what is a hypothalamic peptide that stimulates both the synthesis and secretion of growth hormone? |
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Definition
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Term
| what is a peptide produced by several tissues in the body including the hypothalamus, inhibits growth hormone release in response to GHRH and to other stimulatory factors such as low blood glucose concentration? |
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Definition
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Term
| what is a peptide hormone secreted from the stomach. Ghrelin binds to receptors on somatotrophs and stimulates secretion of growth hormone? |
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Definition
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Term
| how does negative feedback loop work to control GH secretion? |
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Definition
0. normally GHRH->GH->IGH-1 1. excess GH probably feeds back @ somatotroph to inhibit secretion of GH & @ hypothalamus to inhibit release of GHRH. 2. High blood levels of IGF-1 lead to decreased secretion of growth hormone not only by directly suppressing the somatotroph, but by stimulating release of somatostatin from the hypothalamus. |
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Term
| what are 6 facts about GH secretion and levels? |
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Definition
- pulsatile pattern
- basal concentrations in blood very lo.
- frequency & amplitude higher in sleep than waking.
- increases during puberty & declines in middle age.
- increased by stress & exercise
- lower in obese subjects than lean subjects.
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Term
| How is GH deficiency different in children than in adults? What is used in treating either? |
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Definition
GH deficiency in children results in short stature and subnormal growth rate. GH deficiency in adults produces increased fat mass, decreased muscle mass, decreased exercise capacity and muscle strength, osteopenia, decreased quality of life (social isolation, fatigue, depression), and elevated cholesterol. Recombinant hGH is approved for treating GH-deficient children and adults. |
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Term
| Why are random GH measurements not diagnostic of GH deficiency? |
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Definition
| because GH secretion is pulsatile. |
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Term
| what is used to diagnose GH deficiency in children? |
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Definition
| IGF-1 levels are used to diagnose GH deficiency in children but are less helpful in adults because the normal elderly have low values as well. |
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Term
| Why should patients with childhood onset isolated GH deficiency be retested in adulthood before continuing adult GH replacement? |
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Definition
| because isolated GH deficiency during adolescence is often transient and normalization of GH responses are seen in 25-50% of cases. |
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Term
| What defines a GH deficiency? |
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Definition
| lack of increase of plasma GH to 5 ng/ml on two pharmacological stimulation tests. |
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Term
| How many amino acids make up GH? |
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Definition
you gotta b kidding, right? 190. |
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Term
- How many amino acids make up Prolactin?
- What is the critical cell specific factor that activates PRL gene transcription?
- Is PRL secreted in bursts that increase in frequency and amplitude with sleep?
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Definition
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Term
| what stimulates prolactin release? |
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Definition
| Stimulation of the nipples and mammary gland. |
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Term
| What the two roles of prolactin in milk production? |
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Definition
- Induction of lobuloalveolar growth of the mammary gland. Alveoli are the clusters of cells in the mammary gland that actually secrete milk.
- Stimulation of milk production after giving birth. Prolactin, along with cortisol and insulin, act together to stimulate transcription of the genes that encode milk proteins.
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Term
- Unlike the rest of the hormones, what is the one hormone released by the pituitary that is under tonic inhibition?
- What is the predominant Prolactin inhibitory factor produced by the hypothalamus?
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Definition
- Prolactin, of course.
- Dopamine.
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Term
| What 3 hormones that positively regulate the release of prolactin? |
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Definition
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Term
| What are the effects of hyperprolactinemia on women & men? |
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Definition
Women: amenorrhea (lack of menstrual cycles) and galactorrhea (excessive or spontaneous secretion of milk). Men with hyperprolactinemia typically show hypogonadism, with decreased sex drive, decreased sperm production and impotence. |
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Term
| a mutation in the Pit-1 gene results in what? |
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Definition
| Congenital PRL deficiency, which also includes deficiencies in GH & TSH. |
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Term
| What polypeptide hormone is the smallest of the three produced in the anterior pituitary? |
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Definition
| ACTH, a 39 amino acid peptide. |
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Term
| what stimulates and inhibits ACTH secretion? |
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Definition
| CRH stimulates ACTH release. Stress in turn stimulates release of CRH. Glucocorticoids (cortisol) eventually released by the adrenal negatively feeds back to inhibit CRH & ACTH release. |
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Term
| A large precursor protein named proopiomelanocortin (POMC) is synthesized and proteolytically cleaved into several fragments. The hormones other than ACTH that are produced in this process are: |
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Definition
- Beta-endorphin and Met-enkephalin: Opioid peptides with pain-alleviation and euphoric effects.
- Melanocyte-stimulating hormone (MSH): Controls melanin pigmentation in the skin of most vertebrates.
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Term
| When is ACTH production highest, when is it lowest? |
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Definition
| 4:00 am highest, lowest at midnight. |
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Term
| what are the signs of ACTH deficiency? |
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Definition
Common symptoms are fatigue, muscle weakness, anorexia and weight loss.
Hyponatremia and hypoglycemia may be present, but severe dehydration and hyperkalemia do not occur. |
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Term
| How is ACTH deficiency diagnosed? |
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Definition
- A low random serum cortisol level must be confirmed with an ACTH stimulation test unless the value exceeds 18 ug/dl excludes ACTH deficiency.
- ACTH stimulation test (250 ug) (Cortrosyn test) Subnormal response is a cortisol level < 18 ug/dl
- ACTH levels helpful to distinguished primary vs. secondary.
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Term
True or False: The alpha subunit of TSH is also present in two other pituitary glycoprotein hormones, FSH and LH, and, in primates, in the placental hormone chorionic gonadotropin. Each of these hormones also has a unique beta subunit, which provides receptor specificity. In other words, TSH is composed of alpha subunit bound to the TSH beta subunit, and TSH associates only with its own receptor. Free alpha and beta subunits have essentially no biological activity. |
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Definition
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Term
| What inhibits secretion of TSH & TRH? |
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Definition
| Secretion of TRH, and hence, TSH, is inhibited by high blood levels of thyroid hormones (T3 + T4) in a classical negative feedback loop. |
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Term
| How is TSH a marker of thyroid disease? |
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Definition
| In disorders of the thyroid producing hypothyroidism, the production of TSH rises, and in hyperthyroidism from thyroid disease (e.g. Grave’s Disease) TSH is suppressed. |
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Term
| What is the diurnal variation of TSH secretion? |
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Definition
| TSH is secreted in a circadian pattern with peak levels between 9 PM and 5 AM. |
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Term
| What is secondary hypothyroidism and how is it diagnosed? |
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Definition
- Hypothyroidism occurs with TSH deficiency.
- Lack of energy, weight gain, cold intolerance and constipation may occur but are usually less severe than in primary hypothyroidism.
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- Diagnosis is made with a low free thyroxine and normal or low TSH.
- Note that the TSH alone cannot be used as a screening test for TSH deficiency.
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Term
| What is the effect of LH hormone in both males and females? |
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Definition
In both sexes, LH stimulates secretion of sex steroids from the gonads. In the testes, LH binds to receptors on Leydig cells, stimulating synthesis and secretion of testosterone. Theca cells in the ovary respond to LH stimulation by secretion of testosterone, which is converted into estrogen by adjacent granulosa cells.
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Term
| What are the effects of LH & FSH? |
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Definition
| in females LH is responsible for formation and continued development and function of corpora lutea. FSH is stimulates the maturation of ovarian follicles. it also induces superovulatoin - development of more than the normal number of gametes. it supports the function of Sertoli cells, which in turn support many aspects of sperm cell maturation. |
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Term
| What is a ten amino acid peptide that is synthesized and secreted from hypothalamic neurons and binds to receptors on gonadotrophs? |
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Definition
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Term
True or False: GnRH stimultes secretion of LH, which in turn stimulates gonadal secretion of the sex steroids testosterone, estrogen and progesterone. In a classical negative feedback loop, sex steroids inhibit secretion of GnRH and also appear to have direct negative effects on gonadotrophs.
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Definition
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Term
True or False: The regulatory loop for LH leads to pulsatile secretion, to a much lesser extent, FSH. The number of pulses of GnRH and LH varies from a few per day to one or more per hour. In females, pulse frequency is clearly related to stage of the cycle. |
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Definition
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Term
| the gonads secrete at least two hormones which selectively inhibit and activate FSH secretion from the pituitary. what are they? |
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Definition
| inhibin and activin, respectively. |
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Term
| what does diminished secretion of LH and FSH cause? |
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Definition
| Diminished secretion of LH or FSH can result in failure of gonadal function (hypogonadism). This condition is typically manifest in males as failure in production of normal numbers of sperm. In females, cessation of reproductive cycles is commonly observed. |
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Term
True or False: Elevated blood levels of gonadotropins usually reflect lack of steroid negative feedback. Removal of the gonads from either males or females, as is commonly done to animals, leads to persistent elevation in LH and FSH. In humans, excessive secretion of FSH and/or LH is most commonly the result of gonadal failure. |
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Definition
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Term
| How do oral contraceptives work? |
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Definition
| Oral contraceptive pills contain a progestin (progesterone-mimicking compound), usually combined with an estrogen. Progesterone and estrogen inhibit LH secretion, and oral contraceptives are effective because they inhibit the LH surge that induces ovulation. |
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Term
| How is orchidectomy or oophorectomy induced without surgery? |
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Definition
| By administering long acting GnRH analogs, such as leuprolide, which down-regulate LH and FSH synthesis and secretion. No LH/FSH, no ovulations or spermatogenesis. |
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Term
True or False:
Fertility can also be stimulated in men and women with hypopituitarism with recombinant pituitary hormones. HCG is used as an LH-like molecule because it has a long half-life whereas the half-life of LH is only 20-30 min.
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Definition
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Term
| What is Kallmann's Syndrome? |
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Definition
An X-linked form of Isolated Hypogonadotropic Hypogonadism (IHH) which is thought to be due to a mutation in a neural cell adhesion protein which guides axon growth and allows GnRH neurons to migrate from their site of origin in the cribriform plate to the anterior hypothalamus. Anosmia (inability to smell) and low plasma levels of LH and testosterone.Because GnRH neurons are not in their appropriate anatomical location, axons to the anterior pituitary do not develop.
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Term
| In multitropic failure, what is the common sequence of hormone loss? |
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Definition
- In multitropic failure a common sequence of hormone loss is GH, LH/FSH, TSH, ACTH and PRL.
- Prolactin is often increased from compression of the pituitary stalk and interruption of dopamine, which normally inhibits prolactin.
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Term
| What are 4 rules to management of hypothyrodism? |
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Definition
- replacing target gland products is easier than replacing pituitary peptide hormones;
- if multiple deficits exist, start replacing cortisol first, followed by thyroxine (allows a normal environment for ADH and sex steroids, thyroid accelerates the catabolism of cortisol); and
- avoid over replacement, which can contribute to morbidity and excess mortality.
- Mineralocorticoids need no supplementation.
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