WEEK 7: 7.4 Hypothalamus and Pituitary Flashcards
What is the pituitary gland?
a small, bulbous structure that dangles off the hypothalamus
How is the pituitary gland attached to the hypothalamus?
a thinner piece of tissue called a pituitary stalk
What significant structure is very close to the pituitary gland, and how can this cause visual discrepancies?
The optic chiasm, where enlargement of the pituitary gland can prevent the OC from transporting neurons that bring info from the eyes to the brain
Why can the hypothalamus be referred to as a ‘post office’
It receives lots of info from different places, sources that info and then relays info to various body organs and systems that help respond to the external environment, and maintain homeostasis
What is the name of the lobe associated with emotion that the hypothalamus is connected to
limbic lobe
What two lobes is the geriatric gland composed of?
the larger vascular anterior lobe and the smaller neural posterior pituitary
What is the posterior pituitary and what is it comprised of?
an extension of the hypothalamus, comprised mainly of neural tissue and supporting cells called pitcher sites
Where do the terminals of neurons in the posterior pituitary have their cell bodies located?
in the hypothalamus, arranged within clusters
Where are oxytocin and ADH synthesised?
in the cell bodies of these hypothalamic neurons
What happens to the neurohormones?
they are packaged into vesicles and transported down via long axons to the posterior pituitary, where they are released into circulation
Does the posterior pituitary synthesise or store hormones?
It stores hormones
What is a diuretic?
a substance which increases the amount of water excreted from the body as urine
Hence, what is an anti diuretic hormone?
It reduces the loss of water in urine
What is the release of ADH stimulated by?
- increase in osmolality
- decrease in BP
- increased stressors
briefly describe the negative feedback loop in response to an increase in osmolality
- increase in osmolality activates neurons in hypothalamus sensitive to changes in molality
-triggers action potential firing in hypothalamic neuron, projecting to posterior pituitary
-ADH acts on collecting ducts of kidneys to promote insertion of water channels (aquaporins)
-Permits more water to be reabsorbed from the kidney filtrate and back into the bloodstream
-decreased osmolality and increased plasma volume
how does ADH influence vasoconstriction
it can act on smooth muscle walls and promote vasoconstriction hence increase BP
What are the 3 distinct G protein couples receptors that have been identified for ADH and where are they located
V2 on kidney tubules
V1 on blood vessels
V3 on anterior pituitary corticotrophs
What happens when V2 receptors bind and activate to ADH
- increase in cyclic AMP
- triggers insertion of aquaporin
- increased water reabsorption in bloodstream
What happens when V1 receptors bind and activate to ADH
- production of IP3/DAG second messengers
- lead to release of calcium
- influx of calcium into vascular smooth muscle cells promotes contraction
-increased vascular tone - constriction of blood vessels
What happens when V3 receptors bind and activate to ADH
- secretion of the adrenal trophic hormone, which stimulates the secretion of aldosterone hormone from the adrenal cortex, which then acts on the kidney to increase the absorption of sodium and water.
what hormone promotes contraction of the wall of the uterus?
oxytocin
What else is oxytocin involved in?
ejection of milk from mammary glands and other behaviours like bonding and attachment
T or F: chemical messengers like vassopressin and oxytocin are both structurally and functionally similar
F: they can be structurally similar, but play different functions in the body
What pituitary cells make up the anterior pituitary?
50%- somatotrophs
20%- corticotrophs
15%- gonadotrophs and lactotrophs
5%- thyrotrophs
