The Pituitary Gland Flashcards
Two classes of hormones?
Peptide and steroid.
How are peptide hormones synthesised?
Synthesised as pro hormones. Further processing such as cleavage to activate.
How are peptides hormones stored?
Stored as vesicles.
How do peptides hormones create a signal?
Transduce signal using 2nd messenger systems.
How are steroids synthesised?
Synthesised from cholesterol.
How are steroids released compared to peptides?
Released immediately while peptide secretion is regulated.
How do steroids create a signal?
Bind to intracellular receptors and alter gene expression directly.
What bone holds to pituitary gland?
Sella turcica of sphenoid bone.
Another name for the anterior pituitary?
Adenohypophysis.
Another name for the posterior pituitary?
Neurohypophysis.
What is the optic chiasm?
Optic nerve crossover. Where neurones from the nasal retina cross over.
Where does the anterior pituitary gland grow from during fetal development?
Upgrowth from oral ectoderm.
Where does the posterior pituitary gland grow from during fetal development?
Downwards growth from diencephalon.
What is Rathke’s pouch?
Is an ectodermal invagination of the roof of the developing embryonic mouth.
What controls the anterior pituitary?
Hypothalamus.
What endocrine cells are present in anterior pituitary?
Somatotrophs, Lactotrophs, Corticotrophs, Thyrotrophs and Gonadotrophs.
What hormones are secreted by the anterior pituitary gland?
Growth hormone. Prolactin, TSH, LH and FSH, Adrenocorticotrophic hormone.
What hormones are secreted by the hypothalamus?
GHRH, Somatostatin, Dopamine, Thyrotrophin releasing hormone, Gonadotrophin releasing hormone and Corticotrophin releasing hormone.
What does growth hormone do?
Body tissues growth and release of IGF-1 from liver.
What does somatostatin do?
Inhibit release of growth hormone.
What does a decrease in dopamine do?
Increase in prolactin.
What can a pituitary tumour result in?
Compression of optic chiasm can lead to bitemporal hemianopia. Prevents transmission of information from lateral visual fields to occipital lobes.
What is acromegaly?
Excess growth hormone production.
Symptoms of agromegaly?
Increased hand and feet size. Macroglossia. Prominent nose.
Key difference between posterior pituitary gland and anterior?
Posterior doesn’t produce hormones.
What hormones does the posterior pituitary gland store?
Oxytocin and arginine vasopressin.
Where are oxytocin and arginine vasopressin produced?
Hypothalamus.
Explain the release of thyroxine
Axon terminals of parvocellular neurones release thyrotrophin releasing hormone (TRH) into hypophyseal portal system. TRH travels through the capillaries of the portal system to anterior pituitary gland. TRH binds to thyrotrophs and stimulates release of TSH. TSH leaves pituitary gland via the blood and travels to thyroid gland to stimulate release of thyroid hormone.
Explain release of arginine vasopressin and oxytocin
Arginine vasopressin produced in supraoptic nucleus. Oxytocin produced in paraventricular nucleus. Hormones travel down neuronal axons in pituitary stalk. Enter posterior pituitary and stored. Excitation of hypothalamic magnocellular neurones releases AVP or oxytocin. These diffuse into capillaries.
Physiological action of arginine vasopressin?
Anti-diuretic hormone, vasoconstrictor and stimulates ACTH release from anterior pituitary.
Arginine vasopressin anti diuretic mechanism?
AVP binds to V2 receptor. Leads to aquaporin-2 channels bind to apical membrane of kidney duct cell. Allows water to move into duct cell from urine and so this leads to more concentrated urine.
Physiological action of oxytocin?
Causes contraction of myometrial and myoepithelial cells leading to delivery of baby and milk ejection.
Explain process of lactation?
Mechanical stimulation of nipple. Action potentials in ascending sensory pathway, inhibit dopamine release from dopaminergic neurones and stimulate oxytocin releasing neuron activity. Inhibition of dopamine leads to less inhibition of anterior pituitary lactotrophs. Oxytocin produced in hypothalamus and released from posterior pituitary. Increased plasma prolactin leads to increased milk production in mammary glands. Increased plasma oxytocin leads to increased milk ejection.
What is T3?
Triiodothyronine.
Description of parvocellular neurones?
Short hypothalamic neurones that release stimulatory/inhibitory factors into capillary plexus.
What nuclei is AVP produced in?
Supraoptic nucleus.
What nuclei is oxytocin produced in?
Paraventricular nucleus.
