The Pituitary Gland Flashcards
What a messenger?
A messenger, carried from the organ where they are produced to the organ which they affect by means of the blood stream
What are the types of hormones?
Peptide and steroid
What is the difference between peptide and steroid hormones?
- synthesis, storage, receptors
Label this diagram of the pituitary gland.
What is another name for the anterior pituitary gland and what did it derive from?
aka adenohypophysis
Derived from an upgrowth from the oral ectoderm of the primitive oral cavity called Rathke’s pouch
Epithelial origin
What is another name for the posterior pituitary gland and what did it derive from?
neurohypophysis
Formed from a downgrowth of the diencephalon that forms the floor of the third ventricle
Neural origin
Label this diagram of the pituitary gland.
What do hypothalamic parvocellular neurones regulate?
Anterior pituitary function
Where is the median eminence?
Base of the hypothalamus
Why does the median eminence have lots of capillaries?
They are leaky, so they allow things to flow into them so they can encounter circulation (the portal circulation)
What are hypothalamic parvocellular neurones?
Short, terminate on median eminence
Release hypothalamic releasing/inhibitory factors into capillary plexus in median eminence
These hypothalamic regulatory factors carried by portal circulation to anterior pituitary
Label this diagram of the pituitary gland.
How would you describe the anterior pituitary gland to the hypothalamus?
Anatomically distinct
What cells is the anterior pituitary gland made of?
Somatotrophs
Lactotrophs
Corticotrophs
Thyrotrophs
Gonadotrophs
How is the activity of the cells in the anterior pituitary gland regulated?
Regulated by hypothalamic releasing/inhibiting factors via hypophyseal-pituitary portal system
What are the steps of the hypothalamo-pituitary portal system?
- Axon terminals of hypothalamic neurosecretory cells release hormones (RHs and IHs) into the hypothalamo-pituitary portal system
- The RHs and IHs travel in the portal system to the anterior pituitary
- The RHs and IHs stimulate or inhibit the release of hormones (black dots) from anterior pituitary cells
- Anterior pituitary hormones leave the gland via the blood
Give an example of the hypothalamo-pituitary portal system with the regulation of thyroid hormone production.
- Axon terminals of hypothalamic neurosecretory cells release Thyrotropin Releasing Hormone (TRH) into hypothalamo-hypophysial portal system
- TRH travels in the portal system to the anterior pituitary
- TRH stimulates the release of Thyroid Stimulating Hormone (TSH) from anterior pituitary thyrotrophs
- TSH leaves the gland via the blood to travel to the thyroid gland to stimulate thyroid hormone release (thyroxine)
what hormone do somatotrophs release?
Growth hormone
What hormone do lactotrophs release?
Prolactin
What hormone do thyrotrophs release?
Thyroid stimulating hormone (TSH)
What hormone do gonadotrophs release?
Luteinising hormone (LH)
Follicle stimulating hormone (FSH)
What hormone do corticotrophs release?
Adrenocorticotrophic hormone (ACTH)
What is the hormone regulating somatotrophs?
Releasing= growth hormone releasing hormone
inhibitory= somatostatin
What is the hormone regulating lactotrophs?
Inhibitory= dopamine
what is the hormone regulating thyrotrophs?
releasing= THYROTROPHIN RELEASING HORMONE (TRH)
What is the hormone regulating gonadotrophs?
Releasing= GONADOTROPHIN RELEASING HORMONE
What is the hormone regulating corticotrophs?
releasing= corticotrophin-releasing hormone
Give an overview of the cells of the anterior pituitary gland and what they do.
What is the target for growth hormone?
General body tissues (particularly the liver)
What is the target for prolactin?
breast (lactating women)
What is the target for thyroid stimulating hormone?
thyroid
What is the target for gonadotrophins (LH and FHS)?
testes (males)
ovaries (females)
What is the target for adrenocorticotrophic hormone (ACTH)?
Adrenal cortex
What do you take to check if someone has a pituitary tumour?
Coronal MRI pictures from front to back
(tumour is usually benign)
What can a pituitary tumour compress?
optic chiasm
WHat can compression on the optic chiasm cause?
bitemporal hemianopia
What is a bitemporal hemianopia?
Fibres from the nasal (medial) retinae cross at the optic chiasm
Compression of the optic chiasm by a pituitary tumour/suprasellar tumour prevents transmission of sensory information from lateral (TEMPORAL) visual fields to the occipital lobe
Where is the sella turcica?
In the sphenoid bone
What is the mechanism of growth hormone action?
Indirectly inducing growth via IGF-1 receptors
Directly promotes growth by releasing growth hormone
What is excess growth hormone called in adults?
Acromegaly
What is too much growth hormone in children called?
gigantism
What are the symptoms/ features of acromegaly?
Coarsening of facial features
Macroglossia= large tongue
Prominent nose
Large jaw - prognathism
Increased hand and feet size
Sweatiness
Headache
What happens to bones when there is excess growth hormone after puberty? (what else can happen as a symptom of too much GH- not to do with bones)
It is impossible to grow taller at the end of puberty as the bones fuse
- Instead soft tissue gets bigger
- Can stop insulin from working properly
What are the hormones of the posterior pituitary gland?
Arginine vasopressin (AVP) (also known as Anti-diuretic hormone)
Oxytocin
How would you describe the relationship between the hypothalamus and the posterior pituitary gland?
anatomically continuous with hypothalamus
what are the hypothalamic magnocellular neurones?
Long, originate in supraoptic (AVP) and paraventricular (oxytocin) hypothalamic nuclei
Nuclei → stalk →posterior pituitary
Does the posterior pituitary gland make its hormones?
Does not make hormones itself, stores arginine vasopressin and oxytocin produced in the hypothalamus
Describe the regulation of the posterior pituitary gland.
- Two sets of hypothalamic neurosecretory cells produce AVP and oxytocin and transport them to the posterior pituitary
- Excitation of these hypothalamic magnocellular neurons stimulates release of AVP or oxytocin into the posterior pituitary where they diffuse into blood capillaries…
- …then leave the posterior pituitary via the blood
What is a word for production of urine?
Diuresis
What are the physiological actions of vasopressin?
Other name = Anti-Diuretic Hormone
Main physiological action = stimulation of water reabsorption in
the renal collecting duct
- This concentrates urine
Also a vasoconstrictor (via V1 receptor)
Stimulates ACTH release from anterior pituitary
What does arginine vasopressin act through to concentrate urine?
Acts through the V2 receptor in the kidney
How does arginine vasopressin concentrate urine?
- AVP binds to V2 receptor on basolateral membrane of cell
- This activates a G protein, which activates adenylate cyclase, forming cAMP, forming protein kinase
- This triggers vesicles containing aquaporin-2 to fuse with the apical membrane of the cell
- the apical membrane is closer to the urine, this causes water from the urine to enter the cell (down a concentration gradient? (idk about this part))
- It then leaves the cell via aquaporin-3 on the basolateral membrane side and enters the plasma
What are the physiological actions of oxytocin?
What is the role of the anterior pituitary gland in lactation?
- Mechanical stimulation of nipple & surrounding area activates afferent pathways
- Afferent signals integrated in the hypothalamus and inhibit dopamine release from dopaminergic neurons
- Less dopamine in the hypothalamic-pituitary portal system causes less inhibition of anterior pituitary lactotrophs
- Increased plasma prolactin increases milk secretion in mammary glands
What is the role of the posterior pituitary gland in lactation?
- Mechanical stimulation of nipple & surrounding area activates afferent pathways
- Afferent signals integrated in the hypothalamus and stimulate oxytocin- releasing neuron activity
- Action potentials travel down oxytocin neurons and oxytocin is secreted into the bloodstream
- Increased plasma oxytocin increases milk ejection in mammary glands
What is the overall anterior and pituitary roles?
