Anterior Pituitary

Question 1

what does hypophysectomy cause

Answer 1

stops growth and lactation
atrophy (thyroid/adrenal cortex/gonads)
disruption to (salt and water balance, carb and protein metabolism)

Question 2

anatomy of the pituitary

Answer 2

adenohypophysis/anterior - glandular
neurohypophysis/posterior - neuronal processes in SON/PVN
intermediate lobe - forms MSH, not in adults (in animals/babies)

Question 3

posterior lobe formation

Answer 3

forebrain (diencephalon) invagination

Question 4

anterior lobe formation

Answer 4

buccal cavity outgrowth (rathke’s pouch)

Question 5

formation steps

Answer 5

1) outgrowth of tissue forms at diencephalon (FB becomes thalamus and hypothalamus)
2) outgrowths combine
3) anterior and posterior lobes begin to form (Rathke’s pouch removal)
4) posterior lobe (neural tissue) anterior lobe (non-neural tissue) sella turcica (skull) protects pituitary gland

Question 6

posterior vs anterior pituitary connections

Answer 6

posterior pituitary has neural connections
anterior pituitary has no neural connections - connected to median eminence via pituitary portal system

Question 7

blood supply

Answer 7

blood passes capillary loops through long/short hypophyseal portal vessels (specific to anterior pituitary)
superior hypophyseal artery supplies ME and stalk
inferior hypophyseal artery supplies posterior lobe directly / indirectly to the anterior lobe via short portal veins
inferior and superior artery connected via trabecular artery
A and P lobes drain into venous sinuses

Question 8

2 features of the anterior pituitary

Answer 8

hypothalamic hypophysiotropic hormones (very diluted released into wider circulation)
feedback by target gland hormones

Question 9

where are hypothalamic hypophysiotropic hormones synthesised

Answer 9

in the cell body and transported to axon terminal to be stored until release in adjacent capillary

Question 10

control of hypothalamic hypophysiotropic hormone release

Answer 10

1) 1 or more neurons in neural pathway converge on 1 neurosecretory hormone
2) direct synapse on soma/dendrite of neurosecretory hormone
3) axo-axonic synapse on nerve ending of neurosecretory hormone
4) neuron releases NT into portal vessels which modifies action of neurohormone

Question 11

5 cells in the anterior pituitary

Answer 11

gonadotroph cells
corticotroph cells
somatotroph cells
lactotroph cells
thyrotroph cells

Question 12

tropic vs trophic

Answer 12

tropic = hormone release
trophic = stimulates growth of downstream tissue

Question 13

hormone release

Answer 13

TSH/LH/FSH/ACTH - tropic
GH - stimulates growth of liver hormones/somatomedians - trophic
PRL - not trophic/tropic

Question 14

episodic hormone secretion

Answer 14

not secreted at a constant rate
secreted in a pulsatile pattern

Question 15

GH secretion

Answer 15

spontaneous surges throughout the day
occurs 3-4hrs (undetectable inbetween)
GHRH and somatostatin determine GH rhythm (peak during sleep)

Question 16

what causes pulsatile secretion

Answer 16

intrinsic rhythm generators in hypothalamus

Question 17

why is episodic secretion important

Answer 17

desensitisation of hormone receptors when challenged with partner hormone (maintains sensitivity of system)

Question 18

negative feedback system

Answer 18

y (circulating hormone concentration) is sensed and compared to set point
difference in feedback is sensed and produces an error signal
hormone maintained in a narrow range

Question 19

CNS negative feedback

Answer 19

specific signal e.g. stress
CRH release acts on corticotroph cells in anterior pituitary cells
ACTH release
ACTH acts on adrenal glands to release cortisol
negative feedback to hypothalamus

high glucocorticoids = CRH and ACTH low (vice versa)

Question 20

positive feedback

Answer 20

occurs when increase in a hormone’s levels leads to enhancement of its effect by stimulating further release

Question 21

oestrogen release

Answer 21

normally uses negative feedback
high oestrogen levels use positive feedback, stimulates gonadotropin release from pituitary, rapid surge of FSH and LH (needed for ovulation)

Question 22

circadian rhythm

Answer 22

endogenous oscillations across a period of ~ 24hrs
synchronised precisely 24hrs rhythm by environmental signals L/D

Question 23

anterior pituitary hormones and CR

Answer 23

GH/PRL/ACTH pulses are larger amplitude/more frequent during sleep
larger TSH peaks in morning/peak in males
CRH/TRH/GnRH show CRs

Question 24

SCN

Answer 24

suprachiasmatic nucleus
in anterior hypothalamus

retina sends daylight info to SCN via optic nerve and optic chaism (retinohypothalamic tract)

Question 25

SCN projections

Answer 25

medial hypothalamus
ARC
ME
parvocellular portion of PVN

Question 26

melatonin secretion from pineal gland

Answer 26

NA nerves from superior cervical ganglia project to pineal gland
NA release regulated by SCN controls melatonin release
melatonin synthesised and released during darkness

light onto retina inhibits output from SCN

Question 27

what controls oestrous and menstrual cycles

Answer 27

GnRH release
modulated by steroid feedback

Question 28

what are seasonal rhythms

Answer 28

supression of rhythm generators for discrete periods of the year - suppression related to changes in daylength (photoperiod)

Question 29

what characteristics does daylength affect

Answer 29

coat colour
food intake
fattening
hibernation

Question 30

seasonal changes driven by photoperiod

Answer 30

no of hours of light/darkness
driven by changes in melatonin release