Hypothalamo-adenohypophysical axis Flashcards
Where is the pituitary gland
Attached to the base of the brain in a bony dip (sella turcica)
Draw a diagram of the brain showing the hypothalamus and pituitary glands
diagram
What grows into the posterior and anterior pituitary glands
anterior: upwards growth from the buccal cavity
Posterior: downwards growth from neural tissue
what structure is close to the anterior pituitary gland
Optic chiasm
What are the hypothalamic nuclei
Clusters of neural cell bodies
Describe the how the axons reach the pituitary glands
posterior- axon extends all the way down to the gland
Anterior - axon extends to the median eminence where hormones may enter the primary capillary plexus
What feature of the plexus make them important for secretion
Leaky walls (large SA?|)
Give the route of blood flow through the hypothalamus
Superior hypophysial artery primary capillary plexus long portal veins secondary capillary plexus Cavernous sinus Jugular veins
Which 5 hormones are secreted by the adenohypophysis
Somatotrophs Lactotrophs Thyrotrophs Gonadotrophs Corticotrophs
What are somatotrophs and what is the target
Growth hormones, proteins and general body tissue
What are Lactotrophs and what is the target
Prolactins, proteins, breasts in lactating women
What are thyrotrophs and what is the target
Thyroid stimulating hormone (TSH), glycoproteins and thyroid
What are gonadotrophs and what is the target
Luteinising hormone and follicle stimulating hormone, glycoprotein and testes/ovaries
What are corticotrophs and what is the target
adrenocorticotrophic hormone (ACTH), polypeptide and adrenal cortex
How are somatotrophs controlled
Growth hormone releasing hormone to increase or somatostatin to decrease
How are lactotrophs controlled
Negatively by dopamine and a bit by TRH
How are thyrotrophs controlled
thyrotrophin releasing hormone
How are gonadotrophs controlled
gonadotrophin releasing hormone
How are corticotrophs controlled
corticotrophin releasing hormone or vasopressin
Where can somatotrophs bind
Liver or other body tissues
What happens when somatotrophs bind to the liver
release of somatomedin - IGF I and IGF II
What can somatotrophs do
stimulate amino acid transport to cells and increase protein synthesis
Increase gluconeogenesis
Increase lipolysis and fatty acid synthesis
increase cartilaginous growth and somatic cell growth
IGF I can give direct feedback to the adenohypophysis or indirect feedback to the hypothalamus
What factors effect release of growth hormone releasing hormone
Stress Sleep Certain amino acids Ghrelin Oestrogens Fasting Hypoglycaemia
How does dopamine normally affect hormone release
Dopamine is released from the hypothalamic nuclei. It inhibits lactotrophs so that prolactin is not released
How does milk form when a baby suckles on the mother
- When the baby suckles, tactile receptors on the nipple feedbacks to the hypothalamus.
- hypothalamic dopaminergic neurones are suppressed
- Less dopamine released
- Prolactin released into the circulation
- milk formation in the breast
Where do the neurones that lead to the neurohypophysis originate from
Supraoptic and paraventricular nuclei
What is the name of the neurone that extends to the gland
Magnocellular neuron
Describe the route from the supraoptic nuclei
Supraoptic nuclei
Pass the median eminence
Terminate in the neurohypophysis
Oxytocinergic or vasopressinergic
Describe the route from the paraventricular nuclei
Paraventricular nuclei
Some terminate at the median eminence
Some travel to other parts of the brain
Some terminate at the neurohypophysis: vasopressinergic or oxytocinergic
Which amino acids differ between vasopressin and oxytocin
Phe vs Ile
Arg vs Leu
How is vasopressin synthesised
- pre-provasopressin transcribed
- signal peptide directs it to the golgi
- cleavage produces provasopressin
- As vesicles move along the axon, enzymes split provasopressin to produce vasopressin, glycopeptide and neurophysin
- vesicles may be stored in herring bodies along the way
How does the oxytocin pathway differ from vasopressin
It is the same but no glycopeptides are produced and the neurophysin is different
What are the two types of vasopressin receptor
V1 and V2
Compare V1 to V2
Linked to G proteins via phospholipase C vs adenyl cyclase
Production of IP3 and DAG vs cAMP, PKA, aquaporins (AQP2)
Increase in calcium vs cAMP
What are the two types of V1
V1a - arterial smooth muscle, hepatocytes, CNS neurones
V1b - corticotrophs
Where is V2 found
collecting duct cells
endothelial cells
What is the other name for vasopressin
Anti-diuretic hormone (ADH)
What its the main effect of vasopressin
Stimulation of water reabsorption in the renal collecting ducts
What is the vasopressin mechanism
- vasopressin binds to V2
- G-protein action activates adenyl cyclase
- ATP turns into cyclic AMP
4 protein kinase A activated - synthesis of aquaporin molecules (AQP2)
- aggraphores move to the apical membrane
- insertion of aquaporins onto the membrane
- Water moves through down its concentration gradient
- AQP 3 and 4 are less sensitive to vasopressin but attach to the basolateral (serosal) membrane
What are aggraphores
They store AQP2
Which structures does oxytocin have an effect on
uterus and mammary gland
What are the minor (unwanted) effects of oxytocin
cardiovascular and kidney
What are the additional effectsnof oxytocin
CNS
What are the effects of oxytocin on the uterus
Rhythmic contraction (funds to urine)
Increase in prostanoid production
dilation of the cervix
At baby delivery the uterus becomes very sensitive to oestrogen
suppression of progesterone, enhancing of oestrogen
What is the mechanism for baby delivery on release of oxytocin
- release of oxytocin
- Acts on the uterus at the parturition
- Travels to the myometrial cells
- Contraction
- Baby delivery
What is the effect of oxytocin on the mammary gland
Contraction of myoepithelial cells, leading to milk ejection
What is the mechanism for milk ejection on release of oxytocin
- oxytocin release
- Acts on the breasts during lactation
- Travels to myoepithelial cells
- Contraction
- Milk ejection
What are the clinical uses of oxytocin
induction of labour at term (controlled IV)
Prevention treatment of postpartum haemorrhage
Facilitation of milk let-down (nasal spray)
Autism
Describe the reaction to an increase in osmolality
- osmoreceptors shrink as they lose fluid to the blood
- stimulation neurones
- stimulation of vasopressin secretion
- vasopressin travels to the kidney
- increase in aquaporins
- increase in water absorption
- osmolality brought back to normal levels
Describe the reaction to a decrease in blood pressure
- baroreceptors firing rate drops
- baroreceptor neurone causes less inhibition of vasopressin secretion
- more vasopressin released
- increase in vasoconstriction
- blood pressure returns to normal levels
How is oxytocin release regulated
- stimulus = baby suckling on the nipple
- Nipple receptors linked to neural afferent limb
- oxytocin release from neurohypophysis
- activation of the endocrine efferent limb
- milk ejection
What is the consequence of lack of oxytocin
Parturition and milk ejection can be induced or replaced by other means
What is the consequence of lack of vasopressin
Diabetes insipidus
What is syndrome of inappropriate ADH
Too much vasopressin.g. tumours absorb water
What are the two type of diabetes insipidus
Central/ cranial and nephrogenic
What causes central/cranial DI
Lack of vasopressin
What causes nephrogenic DI
Kidneys are resistant to vasopressin
What are the symptoms of DI
polydipsia (increased thirst)
polyuria (large urine volume)
Dilute urine (hypo-osmolar)
