The central endocrine system

Question 1

Define the hypothalamus

& its importance

Answer 1

is a collection of brain ‘nuclei’ or centres which have important control and integrative functions

• importance for homeostasis and primitive functions
• controls ANS via brainstem centres
• controls endocrine function via pituitary gland
• posterior part of pituitary more related to CNS than anterior

Question 2

The hypothalamus responds to

Answer 2

• light (circadian rhythm) - interactions with retina and pineal gland (melatonin)
• stress, fear and noise
• Neural signals
• secretes release factors (RF)
• Visceral afferents from intestines/heart/liver
• glutamate, Ach, GABA, DA

Question 3

Hypothalamic hormones include

Answer 3

• small peptides with short half life
• release is pulsatile
• rapid effects on the release of cognate anterior pit H
• TRH, CRH, DA, GnRH, GHRH, somatostatin

Question 4

The anterior pituitary gland

Answer 4

• adenohypophysis
• different embryological origins
• regulated by secreted hypothalamic factors
• hormones synthesised in specialised cells

tropic hormones

Thyrotroph (5%) - TSH- TH regulation- TRH
Corticotroph (10%)- ACTH- adrenal cortex - CRH
Gonadotroph (5-10%) - LH/FSH- reproductive control- GnRH
60% secrete both, 18% only LH, 22% FSH
Somatotroph (50%) - GH- growth
Lactotroph (15-20%)- Prolactin - milk

Question 5

The posterior pituitary gland

Answer 5

• hormones synthesised in the HP, transported via neuronal projections
• structurally continuous with HP, remains attached via hypophyseal stalk

ADH - water regulation (osmolality)
neurophysins - ADH synthesis
oxytocin - birth, breast milk

Question 6

glycoproteins secreted from the anterior PG include?

Answer 6

• TSH
• FSH
• LH -
• made up of a/b SU
• B SU that differs
• 2 chains (Heterodimers)

Question 7

proteins/ PP secreted include ?

Answer 7

ACTH (POMC)
GH
prolactin
- single chain

Question 8

TSH is produced in response to?

Answer 8

• TRH from HP

Question 9

What is the role of FSH/ LH?

Answer 9

• regulation of menstrual cycle and fertility in ovary
• regulate testosterone synthesis
• spermatogenesis
• act via cAMP/PKA
• pulsatile secretion

Question 10

effects of ACTH?

Answer 10

• stimulates GPCR - cAMP
• upregulation of sTAR
• rises in response to hypoglycaemia /stress

Question 11

How do PRL levels rise?

Answer 11

• during pregnancy
• due to oestrogen
• major control exerted via DA- negative feedback also via SST
• can be regulated by TRH VIP (stimulates)

Question 12

prolactinomas are

Answer 12

• most common pit tumour
• interferes With HPG axis resulting in infertility, amenorrhoea, galactorrhoea
• treatment with DA agonist

Question 13

hypothyroidism can affect PRL in what way

Answer 13

• increased secretion of TRH

- hyperprolactinaemia

Question 14

Growth hormone

Answer 14

released throughout life

• pulsatile release
• stimulated by low glucose , exercise and sleep
• effects mediated by GH and IGF-1
• produced via somatotrophs

Question 15

GH deficiency can be caused by

Answer 15

Gh R mutations - laron syndrome (dwarfism)- treated with IGF-1
- GH deficiency treated with recombinant GH

Question 16

causes of hypopituitarism include?

Answer 16

• a tumour
• brain surgery
• trauma
• radiotherapy
• blocked blood supply
• autoimmunity
• infection

Question 17

IGF-1 mediates

Answer 17

• cartilage growth
• increased blood glucose
• bone and tissue growth
• inhibits GH release via neg feedback loop

Question 18

ADH is synthesised how?

Answer 18

• packaged with a carrier protein neurophysin in secretory granules in the magnocelluplar neutrons or paraventricular and supraoptic nuclei
• granules move down ends of fibres upon stimulation

Question 19

oxytocin

Answer 19

• stimulates contraction of smooth muscle (myoepithelial cells) of breast and uterus
• induces labour
• milk ejection reflex and parturition (birth)