Neurohormone Flashcards
What is the difference between the endocrine system and the nervous system?
endocrine
- mediators travel within blood vessels (released directly into blood from neurosecretory cells)
- utilises chemical mediators (hormones)
- slow communication
- effects can be long lasting and wide spread
nervous
- signalling travels along nerve fibres (released from neurones)
- transmission of electrical impulses
- fast communication
- effects are short acting and restricting
What are the principle endocrine organs of the body? What do they release?
hypothalamus
- somatostatin, corticotrophin releasing hormone
pituitary gland
- anterior pituitary = prolactin, thyroid stimulating hormone
- posterior pituitary = vasopressin, oxytocin
thyroid gland - thyroxine, triiodothyronine parathyroid glands adrenal gland - adrenal cortex = aldosterone, cortisol - adrenal medulla = adrenaline, noradrenline
pancreas - insulin, glucagon, somatostation ovary (females) - oestrogen, progesterone testes (males) - testosterone
What are the different types of hormones?
protein and peptide hormones
- can be synthesised as a large precursor and processed prior to secretion (growth hormone, somatostatin)
- can be post translationally modified (glycosylation)
- can have multiple subunits synthesised independently and assembled (follicle stimulating hormone)
amino acid derivatives
- are mostly tyrosine derived
- neurotransmitters that can act as hormones (DA, NA)
steroid hormones - class of lipids derived from cholesterol (cortisol, aldosterone, testosterone, progesterone)
What is the hypothalamic pituitary adrenal axis (HPA axis)?
describes the interaction between the hypothalamus, pituitary gland, and adrenal glands
- pituitary gland is made up of the anterior pituitary (adenohypophysis) and posterior pituitary (neurohypophysis)
it is a system which regulates the production and secretion of cortisol
= mediates the body’s stress response
- controlled by negative feedback loop
What is the anterior pituitary gland? What is its function? How does it work?
also known as the adenohypophysis
- produces and releases hormones
hypopthalamic neurones have cells bodies in the hypothalamus which project into the capillary network of the hypothalamus
- release neurohormones into the capillary network
- neurohormone are transported by the hypophyseal portal vessels (are within the infundibulum)
- neurohormones activate and bind to receptors of specialised cells in the anterior pituitary
- these produce and release other types of neurohormones into the blood to act on organs
What is the posterior pituitary gland? What is its function? How does it work?
also know as the neurohypophysis
- does not produce hormones but does store and release them
have magnocellular neutrons known as
- paraventricular nucleus - produce oxytocin
- supraoptic nucleus - produce vasopressin/ADH
released neurohormones move down the axon of the nucleus to be released into the blood
How are hormones delivered from the hypothalamus to the pituitary gland?
the hypothalamus and the pituitary gland are connected via the infundibulum
- a think stalk
delivery of neurohormones is dependent on this stalk being intact
What specialised cells does the anterior pituitary have? What neurohormones do they release?
corticotrophs
- control adrenocorticotrophin (ACTH) release in response to corticotrophin releasing hormone (CRH)
thyrotrophs
- controls thyroid stimulating hormone (TSH) in response to thrytotrophin releasing hormone (TRH)
lactotrophs
- control prolactin release in response to TRH, somatostatin and dopamine (DA)
gonadotrophs
- control luteinising hormone (LH) and folic stimulating hormone (FSH) release in response to gonadotrophin releasing hormone (GnRH)
somatotrophs
- control growth hormone (GH) release in response to growth hormone releasing hormone (GHRH) and growth hormone release inhibiting hormone (somatostatin)
How is the hypothalamic pituitary adrenal axis stimulated to release cortisol? What is the negative feedback mechanism?
stress activates the hypothalamus and induces corticotrophin releasing hormone (CRH)
CRH travels to the anterior pituitary via the infundibulum and activates corticotroph cells to release adrenocorticotrophin (ACTH)
ACTH is released into the blood and travels to the adrenal cortex
- binds to ACTH receptors to induce cortisol release
excess cortisol activates the cortisol receptors in the
- pituitary
- hypothalamus
this inhibits further release of ACTH
What is cortisol?
is the main glucocorticoid released fro the bona fasciculata layer of the adrenal cortex
follow a circadian rhythm
- are highest in the morning and lower through the day
= must be taken into account when considering cortisol replacement therapy
How is thyroid stimulating hormone (TSH) and thyroid secretion regulated in the HPA axis?
hypothalamus is stimulated and releases thyrotrophin releasing hormone (TRH) into the hypophyseal portal vessels
TRH stimulates the anterior pituitary to release thyroid-stimulating hormone (TSH)
TSH acts on the thyroid to increase T3/T4 secretion
- T3 (triiodothyronine) is the most potent thyroid hormone and targets tissues (e.g. liver) containing a deiodinase enzyme (DI) to convert T4 (thyroxine) to T3
T4 and T3 can act on thyroxine receptors on the hypothalamus and pituitary to inhibit TRH and TSH release
What is oxytocin?
is normally undetectable but is elevated during parturition (giving birth), lactation and mating
- released in response to peripheral stimuli of the cervical stretch receptors and sucking at the breast
regulates the contraction of smooth muscles
What is vasopressin?
also known as anti-diuretic hormone
releases stimulated by changes in the activity of the osmoreceptor complex in the hypothalamus
- subfornical organ stimulates the hypothalamus
controls plasma osmolarity by regulating water excretion and drinking behaviour
stimulates vascular smooth muscle contraction in the distal tubules of the kidney
- reduces water loss and raises blood pressure
What is the effect of pituitary adenoma?
gigantism and acromegaly
- excess growth hormone (GH)
hyperprolactinaemia
- excess prolactin (PL)
cushing syndrome
- excess adrenocorticotrophin (ACTH) and cortisol
addison’s disease
- adrenal insufficiency = too little cortisol
hypothyroidism
- too little thyroxine (T4)
hyperthyroidism
- excess thyroxine (T4) = grave’s disease
What causes hypothyroidism and hyperthyroidism? What are the symptoms?
hypothyroidism
- caused by insufficient thyroxine (T4)
= Hashimoto’s disease creates antibodies that destroy T4
- slow growth, cold hands/feet, weight gain, reduced heart rate, goitre
hyperthyroidism
- caused by excessive thyroxine (T4)
= Grave’s disease where the immune system attacks your thyroid gland, causing it to make more thyroid hormones
- goitre, difficulty breathing, weight loss, excess perspiration, difficulty sleeping
