24- Neurohormones

Question 1

define a neurohormone

Answer 1

type of hormone produced and released by neurosecretory cells into circulation - travel to target cells for long-distance communication and effect

e.g. vasopressin, oxytocin

Question 2

define a neurotransmitter

Answer 2

chemical messenger released at neurone synapses - transmit signals between neurons and bind to receptors for point-to-point communication

e.g. Ach, dopamine, 5-HT

Question 3

define the neuroendocrine system

Answer 3

system consisting of glands and neurons - release hormones into circulation to act on target cells

Question 4

physiological significance of the neuroendocrine system

Answer 4

stress response via the HPA axis, release of adrenaline and cortisol

metabolism regulation through insulin and glucagon release - maintain blood glucose levels

reproductive function through hypothalamic GnRH release, pituitary FSH and LH release, regulating oestrogen, progesterone and testosterone production

growth development through growth hormone release - stimulates bones and tissues

ADH and aldosterone in fluid and electrolyte balance

circadian rhythm regulation through melatonin release - influences sleep-wake cycle

Question 5

what are the four different sorts of communication in the nervous system?

Answer 5

point-to-point communication = neurone to neurone, fast but restricted

diffuse modulatory system = slow, widespread communication with neurone cell bodies within a core projecting to other brain regions

neurons of the secretory hypothalamus = endocrine glands secrete neurohormones into circulation, leak out of capillaries to diffuse into the environment and act on receptors. slower, more widespread communication

networks of interconnected neurons = fast, widespread communication

Question 6

the three types of neurohormones

Answer 6

peptide hormones - vary in size, synthesised as a precursor and then processed/modified before secretion (e.g. insulin)

amino acid derivatives - mostly tyrosine derived (e.g. adrenaline, NA, dopamine)

steroid hormones - lipids derived from cholesterol (e.g. oestrogen, cortisol, aldosterone)

Question 7

function of somatostatin

Answer 7

growth hormone inhibiting hormone

inhibits release of growth hormones, VIP, glucagon, insulin, TSH and prolactin

Question 8

function of dopamine as a neurohormone

Answer 8

inhibits prolactin release

Question 9

what do anterior pituitary lactotroph cells respond to?

Answer 9

TRH, somatostatin and dopamine

somatostatin and dopamine inhibit PL release
TRH stimulates PL release

Question 10

describe regulation of the HPA axis

Answer 10

CRH from hypothalamus enters median eminence and hypophyseal portal capillary system

anterior pituitary corticotrophs respond - ACTH synthesised form its large glycoprotein precursor POMC

ACTH released into circulation - acts on adrenal cortex receptors

stimulates cortisol, sex hormones and glucocorticoid synthesis

dysfunction can lead to stress-related disorders, regulated my negative feedback mechanism with cortisol receptors on hypothalamus and anterior pituitary

Question 11

name the three hypothalamic nuclei involved in the HP (anterior and posterior) axis

Answer 11

medial pre-optic, paraventricular and arcuate for the hypothalamus-anterior pituitary system

supraoptic and paraventricular nuclei for the hypothalamus-posterior pituitary nuclei (magnocellular neurones project from these nuclei)

Question 12

describe the regulation of the HPT axis

Answer 12

TRH released from hypothalamic nuclei - enters median eminence and hypophyseal portal capillary system

acts on anterior pituitary thyrotrophic cells - TSH released

TSH binds to thyroid gland receptors = secretion of T4 and T3. T4 converted to its active form of T3

T3 increases basal metabolic rate and heat rate

Question 13

what stimulates ADH release?

Answer 13

changes in activity of osmoreceptor complex in hypothalamus

Question 14

effects of ADH release

Answer 14

controls plasma osmolality - regulates water excretion and drinking behaviour

stimulates vascular smooth muscle of kidney tubules to contract = reduce water loss, increase retention

Question 15

what stimulates oxytocin release?

Answer 15

suckling detected by nipple mechanoreceptors

peripheral stimuli of cervical stretch receptors

Question 16

effects of oxytocin release?

Answer 16

regulates uterus smooth muscle contractions - positive feedback mechanism during labour where it binds to uterus receptors and induces uterus stretching

affects activity of myoepithelial cells lining the mammary duct - affects milk ejection

antidepressants, antipsychotic, induces trust

Question 17

describe the cellular mechanisms of peptide hormones

Answer 17

peptide hormones - e.g. insulin, growth hormone

peptide hormone binds to its cell surface receptor

receptor dimerises and recruits tyrosine kinases

phosphorylates target protein

induces biological respose

Question 18

describe the G-protein & adenylyl cyclase pathway

Answer 18

e.g. TSH and ACTH

bind to N-terminal of cell surface GCPR

activates Gs coupled protein = activates adenylyl cyclase activity = increases cAMP production and PKA activity

PKA phosphorylates target proteins - initiates specific gene expression and biological processes

Question 19

describe DAG & IP3 pathway

Answer 19

e.g. oxytocin and GnRH

Gq coupled - activates phospholipase C

converts PIP2 to IP3 and DAG

IP3 binds to receptors = stimulates Ca”+ release from intracellular stores

DAG activates PKC = phosphorylates proteins, alters enzyme activity

Question 20

describe the steroid/ nuclear receptor pathway

Answer 20

steroid hormones are lipophilic - pass through the plasma membrane and bind to their intracellular cytosolic receptor forming a complex

bind to a target region of DNA in the nucleus - affect gene expression and regulation

Question 21

what are the three key features of a nuclear receptor?

Answer 21

zinc finger domain

hormone/ligand binding domain

transcription activation domain AF1

Question 22

differentiate Addison’s disease and Cushing’s syndrome as aspects of adrenal pathology

Answer 22

Addison’s - primary adrenal insufficiency where adrenal glands lack cortisol and aldosterone production

caused by autoimmune destruction of adrenal glands

Cushing’s - excessive cortisol secretion, overproduction by adrenals or prolonged use of glucocorticoid meds

caused by tumours in adrenals, excess ACTH production or iatrogenic/ meds

Addison’s disease has symptoms of low blood pressure, fatigue, weakness and weight loss

Cushing’s syndrome has symptoms of high blood pressure, central obesity, muscle weakness and fatigue

Question 23

what is Addison’s disease?

Answer 23

primary adrenal insufficiency where adrenal glands lack cortisol and aldosterone production

caused by autoimmune destruction of the adrenal glands

Question 24

symptoms of Addison’s disease?

Answer 24

fatigue and weakness
weight loss
low blood pressure
dizziness, fainting
hyperpigmentation

Question 25

what is Cushing’s syndrome?

Answer 25

excessive cortisol production from overproduction by the adrenals or prolonged use of glucocorticoid meds

caused by:
- adrenal tumour/ carcinoma
- excessive ACTH production by anterior pituitary
- glucocorticoid meds

Question 26

symptoms of Cushing’s syndrome?

Answer 26

central obesity
thinning of skin, easy bruising
muscle weakness and fatigue
high blood pressure

Question 27

differentiate Hashimoto’s disease and Graves’ disease as aspects of thyroid dysfunction

Answer 27

Hashimoto’s - autoimmune disease, antibodies made against thyroid gland, resulting in low thyroxine/ hypothyroidism

Graves’ - autoimmune disease, antibodies mimic TSH and bind to thyroid gland receptors, resulting in hyperthyroidism

Hashimoto’s results in low thyroxine and basal metabolic weight = causes weight gain, lack of energy and goitre

Graves’ results in high thyroxine and basal metabolic rate = causes weight loss, goitre, anxiety, irritability and bulging eyes

Question 28

what is Hashimoto’s disease?

Answer 28

autoimmune disease, antibodies made against thyroid gland, resulting in low thyroxine/ hypothyroidism

Question 29

symptoms and complications of Hashimoto’s?

Answer 29

symptoms: weight gain, lack of energy, goitre

complications: birth defects, heart failure and slow growth

Question 30

what is Graves’ disease?

Answer 30

autoimmune disease, antibodies mimic TSH and bind to thyroid gland receptors, resulting in hyperthyroidism

Question 31

symptoms and complications of Graves’?

Answer 31

symptoms: weight loss, anxiety and irritability, goitre, difficulty breathing and bulging eyes

complications: rapid/irregular heart beat, heart failure, greater risk of miscarriage

Question 32

name different disorders that can be caused by a pituitary adenoma

Answer 32

loss of vision due to pressure on the optic nerve

Cushing’s syndrome from ACTH overproduction = excess cortisol secretion

hyperprolactinaemia = too much prolactin

hypogonadism and infertility

acromegaly from too much GH