The hypothalamus & pituitary gland Flashcards
Where is the hypothalamus arranged?
It is arranged** on both sides of the 3rd ventricle**
What are the different nuclei in the hypothalamus?
-
paraventricular (beside ventricle)
* supraoptic (near optic nerve) - ventromedial
- arcuate
what is a ‘nucleus’ in the CNS?
a cluster of neuronal cell bodies
Describe the** 2 types of hypothalmic neuroendocrine cells**?
- magnocellular - large cell bodies, long axons projecting down the posterior pituitary, release ADH and oxytocin, located at the paraventricular & supraoptic nuclei
- Parvocellular- small cell bodies, short axons projecting to the top of the pituitary stalk, secrete 6 hormones into the blood stream which are released into the hypophyseal portal circulation
What structure facilitates the connection between the hypothalamus and pituitary gland?
the pituitary stalk or infundibulum
what do peptidgeric neuroendocrine cells release?
peptide hormones
what is a ‘trophic’ hormone?
- a hormone that **regulates the production of another hormone **
What are hypophysiotrophic hormones?
note hypophysis is another word for pituitary gland
- they are hormones that regulate hormone production in the anterior lobe of the pituitary gland
What are the hypophysiotrophic hormones released by the hypothalamus?
- GnRH - gonadotrophic releasing hormone
- GHRH
- somatostatin
- CRH - corticotropin releasing hormone
- dopamine
- TRH - thyropin releasing hormone
what is Kallman’s syndrome?
what is it? what is it characterised by?
- an inherited disorder of GnRH deficiency
- KAL1 gene mutations interefere with normal migration of GnRH from hypothalamus during development
- characterised by hypogonadotrophic hypogonadism (HH), infertility, absent/partial pubertal maturation, anosmia
Describe the functional histology of the neurohypophysis (ie the posterior pituitary lobe)
- there are unmyelinated nerve axons whose cll bodies are located in the hypothalamus
- there are** glial cells called pituicytes**
- there are** herring bodies** (swellings along the axon) that contain ADH and oxytocin
- high degree of vascularity - fenestrated capillaries (allowing easy movement of peptides in and out of the nuclei)
what 2 different receptors does ADH act on?
- V1 receptors - vascular smooth muscle cells, activation leads to contraction
- V2 receptors - renal tubule epithelial cells - the activation of these receptors leads to increased renal H20 reabsorption
How does plasma osmolality relate to ADH?
- As the plasma osmolality increasee above 280mOsm/Kg, it is becoming more concentrated and ADH is secreted
what 3 stimuli control ADH release?
- a plasma osmolality above 280mOsm/kg
- hypovolemia (reduced blood volume) - activates strial stretch receptors
- hypotension (low BP) - activation carotid & aortic baroreceptors
Describe the **mechanism of ADH **on renal tubule epithelial cells
- vasopressin binds to the membrane receptor (V2) on basolateral membrane
- receptor then activates cAMP second messanger system
- cell inserts** AQP2 water pores **into the apical membrane
- water is absorbed via osmosis into the blood
What is an example of a disease that involves an ADH deficiency & what are the 2 types of the disease??
-
Diabetes Insipidus
there are 2 types
1. **neural **- no production of ADH - may be due to hypothalamus lesion
2. nephrogenic - resistance to ADH - either by mutations in V2 receptor (inherited) or aquired- drug induced
what is an example of a drug that can cause ADH defiency?
amphotericin B
What** value of urine osmolality **indicates diabetes insipidus after a water deprivation test?
- if after water deprivation test, the urine osmolality is greater than 600mOsm/Kg, DI is excluded
- if urine osmolality is under 400mOsm/Kg after water deprivation test, this indicates DI
What is the syndrome of inappropiate antidiuretic hormone secretion (SIADH)
- a disease that involves excessive secretion of ADH despite a normal or increased plasma volume
- it can be associated with GIT or lung tumours (that are also secreting ADH)
what are the consequences of SIADH?
- increased water reabsorption
- increased urine osmolality
- hyponatremia (conc of Na+ is low)
- plasma hypo-osmolality
what are the** physiological roles of oxytocin**?
- child birth
- lactation
- social/mating
- emotional behaviour
How does oxytocin cause lactation (briefly explain)
- oxytocin stimulates** myoepithelial contractions **to expel milk from the mammary alveoli into ducts/ collecting chamber
- called the milk let down reflex
What is oxytocin’s role in child birth?
- stimulates the** uterus to contract**
- may be used to induce labour
- positive feedback mechanism (furgerson reflex) - ie oxytocin triggers more oxytocin production
what other roles does oxytocin have (other than lactation & birth)
- involved in maternal nurturing behaviour postpartum
- reduces fear and anxiety
- promotes trust & empathy
what is a primary endocrine disorder?
- disorders of the peipheral endocrine gland itself eg thyroid / adrenal
what is a secondary endocrine disorder?
disorders of the pituitary or hypothalamus causing under or over stimulation of peripheral endocrine glands
what kind of symptoms are presented with a hypothalamus/ pituitary gland disorder?
- symptoms of a **deficiency or excess **of one or more of the hormone they produce
*** neurological symptoms **eg headaches or visual disturbances from tumours of these glands
what could be concluded if the the hormone is stimulated but levels dont rise?
there must be a problem with the production of that hormone
what steps can be taken if a tumour is suspected?
*** usually MRI imaging **is used to detect / determine the location of the tumour
* this also determines if the tumour is suitable for surgery
what are the different types of treatment used for** pituitary/hypothalamus disorders**?
- replacement hormones eg for deficiency problems
- surgery or radiotherapy for tumours
- drugs that inhibit hormone production - when surgery isnt suitable
