Endocrinology: Pituitary gland

Question 1

peptide hormones

Answer 1

• synthesised as prohormones (need processing like cleavage to activate)
• Stored in vesicles (regulatory secretion)
• Bind receptors on cell memb; use 2nd messenger syst

Question 2

Steroid hormones

Answer 2

• Synthesised from cholesterol in multistep reaction
• Released immediately (constitutive secretion)
• Bind to intracellu. recep. to change gene expression directly

Question 3

Where does pit gland sit

Answer 3

Sella turicica

Turkish saddle !

bony dish

Question 4

Function of hypothalamic parvocellular neurons

Answer 4

Regulate ant pit function

short and End on median eminence

Release hypo releasing/inhib factors to capillary plexus in m.e.

These are carried by portal circulation to ant pit

Cause action eg hormone release

Question 5

Ant pit (adenohypophysis) made up of 5 diff endocrine cells :

Answer 5

Somatotrophins

Lactotrophins

Corticotrophins

thyrotrophs

Gonadotrophs

Question 6

what is ant pit regulated by and how is it anatomically in relation to hypoth

Answer 6

• hypothalamic relea/inhib factors via hypophyseal - pituitary portal system
• Anatomically distinct from hypo

Question 7

Hypothalamo-pit portal system - describe

Answer 7

1. hypo neurosecretary cells release RHs and IHs into hypo pit portal system
2. RHs and IHs go to ant pit
3. These stimulate or inhib release of hormones from ant pit cells
4. Ant pit hormones leave gland via blood

Question 8

Example of hypothalamopit portal system - reg of thyroid hormone production

Answer 8

• Axon term of neurosecre cells release Thyrotophin releasing hormone (TRH) into hypothalamo-hypophysial portal system
• TRH travels to ant pit
• Stimulates release of thyroid stimulating hormone (thyrotrophin) from ant pit thyrotrophs
• TSH leaves gland via blood to go to thyroid gland to stimulate thyroid hormone release (thyroxine)

Question 9

Chain of comand in thyroid system

Answer 9

Thyroid gland. msut be told what to do by ant pit so :

Hypo

Pit

Thyroid

Question 10

Ant pit cells and hormones

Answer 10

Somatotrophs : growth hormone (somatotrophin)

Lactotrophs : prolactin

Thyrotrophs : thyroid stimulating hormone (TSH) (thyrotrophin)

Gonadotrophs : Lutenising hormone (LH) and follicle stimulating hormone (FSH)

Corticotrophs : Adenocorticotrophic hormone (ACTH, corticotrophin)

Question 11

Which RHs or IRs affect which hormones

Answer 11

• gRowth hormone releaasing hormone (RH) and Somatostain (IH) - growth hormone
• Dopamine (IH) - prolactin
• Thryotrophin releasing hormone (RH) - TSH
• Gonadotrophin releasing hormone (RH) - LH and FSh
• Corticotrophin releasing horm (RH) - ACTH
• dop is only one that causes inhib stimulus

Question 12

ant pit hormones and therir main target cells

Answer 12

• Growth hormone : general body tissues (especially liver)
• Prolactin : breasts
• Thyrotophin : thyroid
• Gonadotrophins : Testes and ovaries
• Adenocorti.. : adrenal cortex

Question 13

How is optic chiasm affected in tumour and what is name for visual field defect

Answer 13

• Tumour in one of ant pit cells - affects optic chiasm
• can cause bitemporal hemianopia - half of visual field cut off
• Because in optic chiasm fibres from nasal restinae cross at optic chiasm - compression of this by tumour prevents transmission of sensory info from lateral visual fields to occipital lobe

Question 14

Neuroendocrine reflex arc

Answer 14

1. stimulation of nipple activates afferent path
2. Integrate signals in hypo and inhib dop release from dopaminergic neurones
3. LEss dop in hypopit portal sys so less inhib of ant pit lactotrophs
4. Increased plasma prolactin - increased milk secretion

Question 15

Growth hormone mechanism and effects of too much growth hormone

Answer 15

• binds to liver
• Stimulates IGF-1 - main insulin like growth factor (Somatomedin) (IGF-2 mostly produced in foetus)
• Binds to own receptors on muscle and bone stimulating growth
• Too much growth horm before puberty: gigantism
• Too much after : acromegaly but no change in height

Question 16

Acromegaly

Answer 16

• Xs growth hormone
• INCreased size of hands and feet
• Larger and more prominent nose, jaw (prognathism), tongue (macroglossia)
• Sweatiness and headaches
• No increase in height because epiphyseal plates fully fused
• Caused usually by Tumour in somatotrophs

Question 17

Post pit gland

Answer 17

• neurohypophysis
• Two hormones : Arginine vasopressin (AVP) also known as Antidiuretic hormone (ADH) and oxytocin
• Anatomically continuous with hypo
• Long and originate in supraoptic (AVP) and paraventricular (oxytocin) hypo nuclei
• Nuclei - stalk - posterior pit

Question 18

Reg of post pit gland

Answer 18

Two sets of hypo neurosecre cells produce AVP and oxytocin and transport them to post pit

Excitation of hypo magnocellular neurones - stimulates release of AVP or oxytocin into posterior pit - diffuse into blood capillaries

Then leave the post pit via blood

Question 19

Action of vasopressin

Answer 19

• Diuresis - produces urine
• Stimulates water reabsorbtion in renal collecting duct
• Concentrates urine
• AVP binds to v2 receptor in kidney
• This causes more aquaporin to attach to memb of collecting duct causing more water to pass - less concentrated urine
• Also a vasoconstrictor via V1 receptor
• Stimulates ACTH release from ant pit (minor role )
• Reabsorption of water into plasma leads to concentration of urine

Question 20

actions of oxytocin

Answer 20

• in uterus - myometrial cells - contract - delivery of baby
• In breast during lactation - myoepithelial cells - contract - milk ejection

Question 21

Neuroendocrine reflex arc - milk ejection

Answer 21

• Stimulation of nipple - activates afferent path
• Afferent signals integ in hypo and stimulate oxytocin releasing neuron activity
• A.p. travel down oxytocin neurones and this is secreted into blood
• Increased plasma oxytocin increases milk ejection