Lec 24 Flashcards
Hypophysis
the two parted pituitary:
Anterior and Posterior Pituitary
Neurosecretory Neurons
Paraventricular nucleus
Supraoptic nucleus
Paraventricular nucleus
located in the hypothalamus, produces oxytocin that is stored in the posterior pituitary.
Supraoptic nucleus
located in the hypothalamus, produces vasopressin that is stored in the posterior pituitary.
“adenohypophysis”
anterior pituitary that is formed from glandular epithelial tissues.
“neurohypophysis”
posterior pituitary - release of hormones is determined by electrical activity from the hypothalamus.
During fetal development, the posterior lobe:
comes from neural tissue
During fetal development , the anterior lobe:
comes from Rathke’s pouch (as well as intermediate)
Hypophysiotropic hormone
a hormone from the hypothalamus that is released into the pituitary stalk and eventually into the hypothalamo-hypophyseal portal system. this controls the release of anterior pituitary hormones.
hypothalamohypophyseal portal system
the vascular link that passes hormones from the hypothalamus to the anterior pituitary through systemic arterial inflow.
“tropic” hormone
a hormone that regulate the release of another hormone
5 Types of hormone-producing cells in the anterior pituitary:
Somatotrophs (30-50%) - Growth Hormone
Corticotrophs (20%) adrenocorticotropic Hormone (ACTH)
next 3 Make up 5% –summed
Thyrotrophs - thyroid stimulating hormone (TSH)
Lactotrophs - prolactin (PRL),
Gonadotrophs - lueteinizing hormone (LH) & Follicle-stimulating Hormone (FSH)
Somatotrophs
30-50% - make GH
Corticotrophs
20% - make ACTH
Thyrotrophs
(summed 5%) - make TSH
Lactotrophs
(summed 5%) - make PRL
Gonadotrophs
(summed 5%) - make LH & FSH
Synonym for GH
somatotropin (STH)
GH
general targets - promotes growth by stimulating protein anabolism and fat mobilization
PRL
Mammary glands (alveolar secretory glands ) targeted to promote milk secretion
TSH
thyroid glands targeted to stimulate development and secretion in the thyroid gland
ACTH
adrenal cortex targeted to promote development and secretion in the adrenal cortex.
FSH
targets Gonads (primary sex organs)
Female: triggers ovulation; promotes development of corpus luteum
Male: stimulates production of testosterone
MSH
targets skin and adrenal glands to possibly stimulate production of melanin pigment in skin. (function unknown)
ADH
Targets the kidney to promote water retension by kidney tubules
OT
targets uterus and mammary glands to stimulate uterine contractions; stimulates ejection of milk into mammary ducts
Peptide hormones
GH & PRL - closely related peptide sequence
TSH, FSH, LH - a-subunits are identical!
(specificity of their actions is determined by the different B subunits)
[most hormones are tropic]
Peptide hormones: identical a-subunits
TSH, FSH, LH
specificity of their actions is determined by the different B subunits
Peptide hormones: closely related peptide sequence
GH&PRL
Functions of the Anterior Pituitary
reproduction growth energy metabolism stress response (most hormones are tropic)
Metabolic rate
determined by TSH –> Thyroid gland –> T3+T4
Metabolic actions; Stress Response
determined by ACTH –> adrenal cortex –> cortisol
Breast Milk and milk Secretion
determined by PRL –> Mammary glands
Growth
determined by GH –> Liver –> Somatomedins –> Bone & soft tissues
Sex hormone secretion
determined by LH –> gonads = estrogen and progesterone in females & testosterone in males
Gamete production
determined by FSH –> gonads = ova in females & sperm in males
Pituitary dwarfism
GH hyposecretion during childhood
Gigantism and 3 treatments
GH hypersecretion during childhood - treated by 1.surgery to remove the source of the hormone (tumor)
- somatostatin analogues, and
- GH antagonists.
Laron Syndrome (dwarfism)
abnormal GH receptors - treated with IGF-1 but only prior to puberty
[lower rates of cancer and diabetes]
Gh insufficiency treatment
replacement therapy
acromegaly
An excess of GH - thickening of bones, the feet, hands, and face, and enlargement of certain organs such as the heart and liver.
Inhibits GH
somatostatin
PRL inhibition
PRL release is soley inhibitory and that this occurs through release of Dopamine
Hypothalamic releasing hormones
Corticotropin-releasing hormone (CRH)
Thyrotropin-releasing hormone (TRH)
Growth Hormone - releasing hormone (GHRH)
Luteinizing hormone - releasing hormone (LHRH or GnRH)
Somatostatin , somatotropin releasing hormone (SRIF)
Dopamine
CRH
stimulates ACTH secretion by corticotrphs; stimulates expressino of POMC gene
TRH
stimulates TSH secretion by thyrotrophs; stimulates expression of genes for alpha and Beta subunits of TSH in thyrotrophs; stimulates PRL synthesis by lactotrophs
GHRH
Stimulates GH secretion by somatotrophs; stimulates expression of GH gene in somatotrophs
LHRH
stimulates FSH and LH secretion by gonadotropin-releasing hormone (GNRH) gonadotrophs (another name for LHRH)
SRIF
INHIBITS GH secretion by somatotrophs; inhibits TSH secretion by thyrotrophs
Dopamine
inhibits PRL synthesis and secretion by lactotrophs
