Endocrinology: Pituitary Hormones Flashcards
Location of pituitary gland
sella turcica of sphenoid
The anterior pituitary also called? and the posterior pituitary?
anterior pituitary gland–> adenohypophysis
posterior pituitary galnd –> neurohypophysis
Most cell types of pituitary gland are
somatotropes (about 40%)
Cell types of anterior pituitary gland and the hormones each secretes
*MNEMONIC: Some Think Cody Looks Good.
Somatotropes --> human growth hormone (hGH) Thyrotropes --> TSH Corticotropes -->ACTH Lactotrophes --> PRL (Prolactin) Gonadotropes --> LH and FSH
Location of cells that synthesize posterior pituitary gland hormones
Hypothalamic supraoptic and paraventricular nuclei
Which cells produce posterior pituitary gland hormones?
Magnocelullar neurons
Hypothalamic control of pituitary gland secretion
Release hypothalamic releasing or inibitory factors/hormones which inhibit or cause release of pituitary gland hormones
Travel via hypothalamic hypophyseal portal system to reach anterior pituitary gland, while uses purely neuron signals to affect posterior pituitar gland
Factors affecting release of hypothalamic inhibitory or releasing factors
Emotional or mental excitation
Levels of nutrients and electrolytes
Olfactory stimulus
Pain
Major factors secreted from hypothalamus to anterior pituitary gland
- Growth hormone releasing hormone
- Thyrotropin releasing hormone
- Corticotropin releasing hormone
- Prolactin inhibitory hormone
- Gonadotropin releasing hormone
Unique feature of GH as compared to other pituitary hormones.
Exerts its effects not by affecting other glands, but directly affecting body cells; it doesn’t have a specific target
Which organic molecule’s metabolism is affected in the shortest amount of time by GH?
Protein synthesis
Importance of somatomedin C
Is released when liver is stimulated by GH
It carries out effects of GH because it binds more strongly to plasma proteins so has a longer half life and prolonged effects.
People who have congenital deficiency of somatomedin C are generally short because somatomedin C is important in GH effects to be implemented. This is seen in dwarfs
Stimulators of GH secretion
Stress (exercise/anxiety) Strong emotions Starvation Hyoglycemia Ghrelin
Somatomedin also called
Insulin-like growth factor (IGF)
GHRH is released from
Hypothalamus ventromedial nucleus
Mechanism by which GHRH causes release of GH
by cAMP messenger system
- GHRH binds to its receptors
- activation of adenylyl cyclase
- formation of cAMP
- increase in calcium concentration = exocytosis of vesicle contents
Also has genomic effect of increasing transcription for synthesis of new growth hormone
Regulation of GH secretion
GHRH causes increase in its secretion and Somatostatin causes decrease in its secretion. Feedback mechanism is not clear, but the overall nutritional state determines levels of GH with protein deficiency having greater effect in chronic starvation compared to carbohydrate deficiency in acute starvation
Hypopituitarism
Condition in which there is significant reduction in secretion of all anterior pituitary hormones.
No GH = Dwarfism if it occurs in childhood as well as increased risk of osteoperosis and arthritis because osteoblasts are not being as active in bone remodelling
No LH and FSH means loss of sexual function and failure to undergo puberty if this occurs during childhood
No TH means no thyroid hormones produced by thyroid gland = decrease in metabolism, lethargy, and weight gain
Why is Gigantism often associated with diabetes?
In gigantism excess GH is produced, but because of its diabetogenic effects (increases insulin resistance), the pancreas beta cells work harder to secrete insulin in response to the hyperglycemia and eventually begin to break down leading to total loss of insulin and full blown diabetes mellitus
Normal concentrations of growth hormone
1.6 - 3 ng/ml in adults
6 ng/ml in children and adolescents
Cell types of posterior pituitary gland
pituicytes
ADH is secreted mainly in the
supraoptic nuclei
Why do oxytocin and ADH have slight functional similarities?
Very structurally similar. both have 9 amino acids, but they differ in only two; vasopressin has phenylanine instead of isoleucine and arginine instead of leucine
Composition of oxytocin and ADH
ADH/Vasopressin MNEMONIC: Very Cold Tea *Prevents Gas. And Cinnamon Powder *Alleviates Gas.
Vasopressin; Cys, Tyr, Phe, Gly, Asn, Cys, Pro, Arg, Gly
Oxytocin: Cys, Tyr, Ile, Gly, Asn, Cys, Pro, Leu, Gly
Mechanism of ADH on renal cells
binds to receptors, causes activation of adenylyl cyclase, increases cAMP levels, causes docking of vesicles with aquaporins. exocytosis causes their release making the cell more permeable to water
How is ADH secretion regulated?
When concentration is high in plasma, water moves out of osmoreceptors in or around the hypothalamus causing them to shrink and send signals to hypothalamus to cause increased secretion of ADH.
When concentration is too low, water moves into the osmoreceptors and increases their size causing them to stop sending signals to hypothalamus to cause secretion of ADH
Evidence for which oxytocin could be responsible for causing uterine contractions in pregnancy
- Animals without hypothalamus section responsible for stimulating oxytocin release have prolonged labor
- Oxytocin levels increase at labor when uterine contractions increase
- Stimulation of cervix correlated with increase in oxytocin levels
