Pituitary Gland Study Sheet

describe the location and functional significance of the hypothalamic nuceli

1) hypothalamus is area at center of base of brain (part of diencephalon)

2) hypothalamic nuclei located in the hypothalamus

3) regulate pituitary hormone secretion by receiving neural and hormonal input from throughout the brain and body, assessing current conditions

describe the location and functional significance of the median eminence

1) small, vascularized area at the base of the hypothalamus, near the infundibulum

2) acts as the neuroendocrine interface

describe the location and functional significance of the infundibulum

1) stalk like structure

2) provides a physical and vascular connection between the hypothalamus and the posterior pituitary

describe the location and functional significance of the anterior lobe of the pituitary gland

1) pituitary gland is directly beneath the hypothalamus, in the sella turcica of the sphenoid bone

2) Also called: adenohypophysis or pars distalis

3) produces and releases several tropic hormones in response to hypothalamic signals

describe the location and functional significance of the posterior lobe of the pituitary gland

1) pituitary gland is directly beneath the hypothalamus, in the sella turcica of the sphenoid bone

2) Also called: neurohypophysis or pars nervosa

3) stores and releases oxytocin and ADH, which are synthesized in hypothalamus and transported down the infundibulum

describe the location and functional significance of the sella turcica

saddle shaped depression in the sphenoid bone; houses and protects pituitary gland

describe the location and functional significance of the optic chiasm

1) anterior to hypothalamus

2) just superior to pituitary gland and sella turcica

3) optic nerves from CN II partially cross here, allowing for binocular vision and visual field processing

4) pituitary tumors may compress the optic chiasm —> bitemporal hemianopia (loss of peripheral vision)

how many hormones does the pituitary gland secrete

at least 8 different hormones; each hormone has its own distinct function and hypothalamic regulatory mechanism; the 2 lobes of the pituitary gland are also regulated differently by the hypothalamus

describe the functional significance of hypothalamic-pituitary interactions in regulating bodily functions (3)

1) hypothalamus and pituitary gland form the central core of the endocrine system, coordinating signals by the nervous system and endocrine organs to regulate numerous vital bodily functions

2) essential for maintaining homeostasis

3) coordinate endocrine, autonomic, and behavioral responses to internal and external stimuli

explain how hypothalamic neurons and the posterior lobe work together to secrete either oxytocin or ADH when needed

1) ADH is synthesized in cell bodies of one group of hypothalamic neurons, and oxytocin in another group

2) the hormones are transported from the cell bodies down to the axons, then to nerve terminals in the posterior lobe, where they are stored like neurotransmitters

3) hormones then leave the pituitary gland through hypophyseal veins and go through general circulation to the heart

what are other names for ADH

antidiuretic hormone or vasopressin

what are the 2 hormones secreted by the posterior lobe

ADH and oxytocin

what are the 6 hormones secreted by the anterior lobe (give abbreviations and full names and class)

1) gonadotropes/gonadotropins: follicle stimulating hormone (FSH) and luteinizing hormone (LH)

2) thyrotropes: thyroid stimulating hormone (TSH)

3) corticotropes: adrenocorticotropic hormone (ACTH)

4) somatotropes: growth hormone (GH)

5) lactotropes: prolactin (PRL)

describe the roles of the hypothalamic releasing hormones and inhibiting hormones in regulating secretion of the anterior pituitary hormones (5)

1) each anterior pituitary cell type is regulated by a separate hypothalamic hormone

2) each hypothalamic hormone is secreted by a separate population of hypothalamic neurons, each receiving its own neural and hormonal input

3) hypothalamic hormones are secreted when their neurons have action potentials

4) hypothalamic hormones are released at the median eminence, then percolate throughout anterior pituitary, binding to their own specific receptors on specific pituitary cells

5) pituitary cells secrete their hormone

describe the hypothalamic hormones and anterior pituitary hormones in this description layout: hypothalamic hormone name —> (+/-) anterior pituitary hormone name —> end organ (+ meaning stimulating, - meaning inhibit)

1) gonadotropin releasing hormone (GnRH) —> + FSH/LH —> gonads

2) thyrotropin releasing hormone (TRH) —> + TSH —> thyroid

3) corticotropin releasing hormone (CRH) —> + ACTH —> adrenal gland

4) growth hormone releasing hormone (GHRH) —> + GH —> liver

5) dopamine —> - PRL —> breast

describe generally how hypothalamic-anterior pituitary negative feedback loops work

1) hypothalamic neurons and anterior pituitary cells have receptors for "end organ hormone"

2) endocrine organ hormone suppresses secretion of hypothalamic and pituitary hormones

3) ex: thyroid hormone suppresses secretion of TRH and TSH

what is the goal of hypothalamic-anterior pituitary negative feedback loops

to keep end organ hormone concentration constant! but note that hypothalamic neurons have additional neural and hormonal inputs, so end organ hormone concentration may be increased or decreased depending on the situation (ex: thyroid hormone concentration increases in a cold env to elevate metabolic rate and heart rate)

explain how hypothalamic-anterior pituitary negative feedback loops can be modified by other factors in order to increase or reduce the secretion of an anterior pituitary hormone (5)

1) external or internal factors can override or modulate the negative feedback loop to meet physiological needs

2) external stimuli could be things like temp, stress, pregnancy

3) can alter hypothalamic input, increasing or decreasing release of releasing hormones

4) it influences the sensitivity of anterior pituitary to hypothalamic signals

5) modifies the set point of feedback threshold to allow for temporary elevations or suppressions of hormone levels

give 2 examples of external/internal factors modifying the hypothalamic-anterior pituitary negative feedback loops

1) a cold environment —> increase hypothalamic release of TRH —> anterior pituitary releases more TSH —> increases TH production —> boost basal metabolic rate and heat production

2) pregnancy/lactation —> suckling inhibits dopamine —> increases prolactin despite normal levels

define the 3 categories of pituitary tumors: non-functional, hyperfunctional, and hypofunctional

1) nonfunctional: no hormone secretion; most common

2) hyperfunctional: secretes excess hormone; tumor cells are not regulated in the usual way

3) hypofunctional: prevents hormone secretion by mass effect

what is the mass effect of pituitary tumors?

the mass effect occurs when there is a pituitary tumor that is large enough to intrude on other structures inside the skull

what are some common symptoms of the mass effect and why do these symptoms occur?

1) symptoms: headache, hormonal hypofunction/dysfunction, visual field changes, cranial nerve palsies (CN III, IV, V1, V2, VI)

2) occur primarily due to tumor location and size, can cause stretch or compression of other structures

describe where the optic nerves travel in relation to the optic chiasm

1) optic nerves meet at the optic chiasm

2) from the optic chiasm, optic tracts go to the right and left sides of the brain

3) the optic chiasm is immediately adjacent to the pituitary gland

describe how a large pituitary tumor can interfere with peripheral vision

1) pituitary tumors grow up and out of the sella turcica

2) as pituitary tumor grows, it may compress the optic chiasm

3) with compression of the optic chiasm, the medial parts of the optic nerves that transmit peripheral visual fields are compressed

4) symptoms: trouble w driving, running into door jambs, double vision, headache

surgical removal of pituitary tumors is indicated when?

when the tumor is secreting GH, ACTH, or TSH

nonfunctional pituitary tumors are treated with surgery when? (5)

1) causing mass effect

2) causing low hormones

3) optic chiasm compression

4) cavernous sinus invasion w cranial nerve palsies

5) tumors are growing over time

when might surgery NOT be needed for a pituitary tumor?

small, stable, non-secretory tumors

what is hypopituitarism and defects causing this can occur at which 3 areas

1) complete or partial failure of secretion of anterior and/or posterior pituitary hormones

2) defects can occur at the: hypothalamus, infundibulum, or pituitary gland

hypopituitarism can be congenital or acquired. what are 2 congenital causes

1) genetic defects leading to abnormal formation of hypothalamus, anterior lobe, or posterior lobe

2) mutation in gene coding for a hormone receptor

what are 5 acquired causes of hypopituitarism

1) tumors or metastases

2) vascular: hemorrhage or infarction

3) infection, inflammation

4) radiation

5) traumatic brain injury

what is treatment for hypopituitarism

synthetic hormone replacement for the individual hormones

list the synthetic hormones used to treat hypopituitarism

1) ADH deficiency —> desmopressin

2) GH deficiency —> rhGH for children; controversial for adults

3) TSH deficiency —> levothyroxine

4) ACTH deficiency —> cortisol

5) FSH/LH deficiency —> estrogen or testosterone

explain how the hypothalamus regulates growth hormone secretion (3)

1) hypothalamic neurons secrete GHRH and somatostatin in response to neural and hormonal inputs to the neurons that secrete them

2) GHRH stimulates GH secretion

3) somatostatin inhibits GH secretion

explain how growth hormone affects IGF-1 secretion (2)

1) GH stimulates the liver to secrete IGF-1 (insulin like growth factor 1)

2) GH and IGF-1 exert negative feedback

describe growth hormone and IGF-1 levels in children, pubertal teens, and adults

1) children: moderate

2) teens: highest at puberty (stimulation by sex hormones)

3) adults: lowest, with continuing decline w age

GH is secreted in __________, why?

pulses; probably in response to pulses of GHRH. this is typical of most pituitary hormones

when is GH most secreted?

during sleep!

what are some other stimuli for increased GH and IGF-1 secretion

stress, exercise, fasting, hypoglycemia

list some normal actions of GH and IGF-1 (3)

1) stimulates bone growth in children

2) stimulates protein synthesis and growth in many tissues

3) stimulates release of glucose from liver and fatty acids from adipose tissue

note: IGF-1 is synergistic w some GH actions and antagonists for other GH actions

growth hormone excess is rare and is usually caused by what?

a pituitary tumor

what does GH excess lead to prior to the closure of the epiphyseal plates?

gigantism

what do we see in gigantism?

1) abnormally large growth due to excess GH in childhood

2) excess growth in bone length bc GH excess occurs prior to closure of epiphyseal plates

what does GH excess lead to in adults

acromegaly (occurs after closure of epiphyseal plates)

what do we see in acromegaly?

1) facial bone growth

2) soft tissue swelling

3) dental problems

4) joint pain

5) paresthesia (carpal tunnel syndrome)

6) impaired glucose tolerance/diabetes

7) congestive HF

8) HTN

9) fatigue, headaches

10) irregular menses, decreased libido

11) excessive sweating

dentists might see what in a pt with either gigantism or acromegaly

prognathism, macrodontia, large mandible, etc

what are some ways that GH excess can be treated? (2)

1) drugs: block GH production or block GH receptors (anatagonists); either of these also prevent IGF-1 secretion by liver

2) removal of tumor: surgery, radiation (takes a long time)

what are the 3 main known functions of prolactin

1) stimulates growth of mammary gland tissue, esp during the early weeks of lactation

2) stimulates milk production by mammary epithelial cells

3) essential for lactation

how is prolactin secretion stimulated during lactation? (3)

1) hypothalamic regulation is predominantly inhibitory by dopamine (prolactin inhibiting hormone)

2) sensory stimuli from nipple and areola during suckling communicate to hypothalamus, inhibiting dopamine, and eliciting secretion of prolactin

3) some prolactin is always in the blood

what 3 things can cause prolactin excess

1) pregnancy

2) prolactin secreting pituitary tumor

3) tumor that blocks flow thru infundibulum of dopamine (ex of mass effect)

what are some clinical features/symptoms of prolactin excess (4)

1) breast pain, tenderness, lactation (galactorrhea)

2) prolactin inhibits GnRH secretion, causing reduced FSH and LH secretion from pituitary —> reduced estrogen/testosterone secretion by gonads

3) irregular/absent menses

4) infertility, erectile dysfunction, decreased libido, osteopenia

how is prolactin excess treated (3)

1) first check for pregnancy or meds that could affect prolactin secretion

2) pituitary imaging to check for tumor

3) tx w dopamine agonist drug (inhibitor)

what are the 2 best known functions of oxytocin

1) participates in stimulation of uterine contraction during parturition (process of childbirth)

2) stimulates contraction of mammary gland myoepithelial cells to cause milk ejection

how is oxytocin secretion stimulated during lactation?

1) suckling stimulates sensory receptors in breast —> sensory signals sent to hypothalamus —> hypothalamus signals posterior pituitary to release oxytocin into bloodstream —> oxytocin causes contraction of myoepithelial cells in mammary glands —> milk ejection

2) this is a positive feedback loop! (continued suckling leads to continued oxytocin release)

what are 2 alternate names for ADH and how do the names for this hormone reflect its actions

1) anti-diuretic hormone: reflects its primary renal action to prevent diuresis (urine production) by increasing water reabsorption in kidneys

2) vasopressin: reflects its vascular action which causes vasoconstriction to raise BP, esp during hypovolemia or shock

what are the main stimuli for secretion of ADH (3)

1) increased osmolarity of bodily fluids (sensed by hypothalamic osmoreceptors)

2) low mean arterial pressure (sensed by baroreceptors)

3) angiotensin-II

these are all signals that reflect low fluid volume!

what are the 2 main actions of ADH

1) reduce urinary water loss by reducing diuresis by actions at thick ascending loops of henle (NKCC2 transporters) and at collecting ducts (aquaporins and urea transporters)

2) vasoconstriction throughout vascular system

what is the main problem to be solved by ADH

1) maintain fluid balance and stable BP

2) these are in situations such as dehydration, low blood volume, high blood osmolality

what does ADH contribute to solving the main problem of maintaining fluid balance and stable BP?

conserves water and stabilizes BP by acting on kidneys (V2 receptors) and acting on blood vessels (V1 receptors)

what is diabetes insipidus

ADH deficiency is also known as diabetes insipidus —> is essentially the inability to concentrate urine

what are the symptoms of diabetes insipidus

polyuria (copious amounts of dilute urine), hypernatremia (increased plasma sodium concentration), and polydispia (increased thirst)

what are the 2 types of DI

1) central DI

2) nephrogenic DI

what causes central DI and how can it be treated

1) defect in ADH synthesis and secretion

2) etiology: surgery, trauma, tumor, infection

3) tx w synthetic ADH

what causes nephrogenic DI and how can it be treated

1) impaired renal tubule response to ADH (receptor resistance)

2) difficult to treat