The pituitary gland (11)

Question 1

What is a hormone?

Answer 1

chemical messengers carried in the bloodstream to target organ

Question 2

How are peptide hormones synthesised?

Answer 2

synthesised as prohormones- require further processing (e.g. cleavage) to be activated

Question 3

How are peptide hormones stored?

Answer 3

stored in vesicles and only released in response to a signal (regulatory secretion)

Question 4

How do peptide hormones work in terms of receptors?

Answer 4

bind to receptors on cell membrane and usually activate a secondary messenger system

Question 5

How are steroid hormones synthesised?

Answer 5

made from precursor cholesterol in a series of reactions

Question 6

How are steroid hormones stored?

Answer 6

released immediately (constitutive secretion)

Question 7

How do steroid hormones work in terms of receptors?

Answer 7

bind to intracellular receptors- alter gene expression

Question 8

Where is the pituitary gland located and what is its structure?

Answer 8

• pituitary gland hangs from infundibulum (stalk)
• sits in sella turcica of sphenoid bone
• anterior and posterior portions- posterior continuous with hypothalamus
• at front is optic chiasm

Question 9

What are the 5 endocrine cell types in the anterior pituitary and what hormones do they produce?

Answer 9

• somatotrophs: produce growth hormone (somatotrophin)
• lactotrophs: produce prolactin
• thyrotrophs: produce thyroid stimulating hormone (TSH)
• gonadotrophs: produce luteinising hormone (LH) and follicle stimulating hormone (FSH)
• corticotrophs: produce adrenocorticotrophic hormone (ACTH)

Question 10

How does the hypathalmo-pituitary portal system work?

Answer 10

1. axon terminals of parvocellular neurons release hormones/factors (releasing/inhibitory) into median eminence- rich in blood vessels
2. factors leak into portal system–> transported through blood stream into anterior pituitary
3. factors bind to relevant anterior pituitary hormone cells (e.g. thyrotrophs)–> causes them to release their hormones into circulation

Question 11

What hypothalamic factor regulates the production of prolactin?

Answer 11

dopamine- inhibiting, so less dopamine–> more prolactin

Question 12

What 2 hypothalamic factors regulate the production of growth hormone?

Answer 12

growth hormone releasing hormone- releasing
AND
somatostatin- inhibiting

Question 13

Where are the main target cells/receptors of growth hormone?

Answer 13

muscle tissue, bone, liver

Question 14

Where are the main target cells of gonadotrophins (LH+FSH)?

Answer 14

ovaries and testes

Question 15

Where are the main target cells of prolactin?

Answer 15

mammary glands

Question 16

Where are the main target cells of corticotrophin?

Answer 16

adrenal gland- specifically adrenal cortex

Question 17

Where are the main target cells of thyrotrophin?

Answer 17

thyroid gland

Question 18

What happens when a pituitary tumour compresses the optic chiasm?

Answer 18

lose peripheral vision
‘bitemporal hemianopia’- common presentation
–> fibres from nasal retinae cross at the optic chiasm
–> tumour prevents transmission of sensory info from lateral visual fields to occipital lobe

Question 19

What is the mechanism of milk production (a neuroendocrine reflex)?

Answer 19

1. mechanical stimulation of nipple and surrounding area activates afferent pathways
2. afferent signals integrated in the hypothalamus and inhibit dopamine release from dopaminergic neurons
3. less dopamine in hypothalamic-pituitary portal system–> less inhibition of anterior pituitary lactotrophs
4. more prolactin in plasma–> more milk secretion in mammary glands

Question 20

What are the 2 ways in which growth hormone can stimulate growth?

Answer 20

GH binds to body tissues directly
BUT ALSO to GH receptors on liver–> causes production of insulin-like Growth Factor (IGF-1 and IGF-2)

so skeleton has IGF receptors and GH receptors

–> both leads to growth and development

Question 21

What conditions are a result of too much growth hormone?

Answer 21

gigantism= children
acromegaly= adults (can't get taller, but large jaw/prognathism, macroglossia, prominent nose, increased hand and foot size)

Question 22

What are the posterior pituitary hormones?

Answer 22

arginine vasopressin (AVP/ADH)
and oxytocin

Question 23

How does regulation of the posterior pituitary gland work?

Answer 23

• 2 sets of distinct populations of hypothalamic neurosecretory cells producing AVP and oxytocin
• excitation of neuronal populations stimulates release of hormones–> transported into posterior pituitary
• diffuse into blood capillaries and leave via blood

Question 24

What is the physiological action of vasopressin?

Answer 24

/Anti-Diuretic Hormone
*diuresis= production of urine

–> binds to V2 receptor in collecting duct–> stimulates intracellular cascade–> promotes Aquaporin-2 movement to membrane- then inserted–> water flows along conc. gradient (from urine) through collecting duct to Aquaporin 3–> water reabsorbed into plasma–> urine concentrated

Question 25

What are hypothalamic magnocellular neurons?

Answer 25

• long
• originate in supraoptic (AVP) and paraventricular (oxytocin) hypothalamic nuclei
• flow down from hypothalamus–> through infundibulum–> posterior pituitary

N.B. posterior pituitary made of neural tissue- anatomically continuous w/ hypothalamus

Question 26

What are the physiological actions of oxytocin?

Answer 26

milk ejection and delivery of baby

induces contraction of myometrial cells (delivery of baby) and myoepithelial cells (milk ejection)

Question 27

What is the mechanism of milk ejection (a neuroendocrine reflex)?

Answer 27

1. mechanical stimulation of nipple activates ascending sensory pathways
2. afferent signals integrate into hypothalamus–> stimulate oxytocin neurons in posterior pituitary–> release oxytocin from nerve endings
3. oxytocin secreted into bloodstream–> inc. milk ejection in mammary glands

Question 28

What are hypothalamic parvocellular neurons?

Answer 28

• short, terminate on median eminence
• release hypothalamic releasing/inhibitory factors into capillary plexus in median eminence–> factors carried by portal circulation to anterior pituitary

Question 29

What hypothalamic factor regulates the production of TSH?

Answer 29

Thyrotrophin releasing hormone

Question 30

What hypothalamic factor regulates the production of both LH and FSH?

Answer 30

Gonadotrophin releasing hormone

Question 31

What hypothalamic factor regulates the production of ACTH?

Answer 31

Corticotrophin-releasing hormone