Pituitary Gland Flashcards
Where is the pituitary gland?
within sella turcica (Turk’s saddle) of sphenoid bone, just below hypothalamus
What is the pituitary gland connected to?
connected to hypothalamus by infundibulum (connecting stalk)
What are the two lobes of the pituitary gland?
- anterior lobe or adenohypophysis
- posterior lobe or neurohypophysis
What is the anterior lobe or adenohypophysis composed of?
glandular tissue that produces and releases 6 major hormones
What is the posterior lobe or neurohypophysis?
part of brain composed of neurons and supporting cells (neural tissue) that is the site of storage and release of 2 neurohormones produced by hypothalamus
Anterior Pituitary
What is activity regulated by?
hypothalamus
Anterior Pituitary
How does it communicate with hypothalamus? (2)
through vascular connection:
- primary capillary plexus
- secondary capillary plexus
Anterior Pituitary
Where is the primary capillary plexus?
in inferior hypothalamus (part of hypothalamus)
Anterior Pituitary
Where is the secondary capillary plexus?
in anterior pituitary
Anterior Pituitary
What is the hypothalamic-hypophyseal portal system?
primary and secondary plexuses + network of hypophyseal portal veins that connects them
Anterior Pituitary
What produces hormones?
neurosecretory neurons in hypothalamus (hypothalamic neurons)
Anterior Pituitary
Where are hypothalamic hormones stored?
in axon terminals that synapse on capillaries of primary plexus
Anterior Pituitary
Upon stimulation, where are hypothalamic hormones released?
released into primary capillary plexus and delivered, via hypophyseal portal veins, to secondary capillary plexus where they can stimulate or inhibit activities of hormone-producing anterior pituitary cells
Anterior Pituitary
What do hypothalamic hormones act on?
can stimulate or inhibit activities of hormone-producing anterior pituitary cells
Anterior Pituitary
What are hormones regulated by?
one or more hypothalamic hormones (+ stimulatory or – inhibitory)
Anterior Pituitary
What are the 6 hormones?
- growth hormone (GH) or somatotropin (STH)
- thyroid-stimulating hormone (TSH) or thyrotropin
- adrenocorticotropic hormone (ACTH) or corticotropin
- follicle-stimulating hormone (FSH)
- luteinizing hormone (LH)
- prolactin (PRL)
Anterior Pituitary
What hypothalamic hormones regulate growth hormone (GH) or somatotropin (STH)? (+/-)
+ GH-releasing hormone (GHRH)
- GH-inhibiting hormone (somatostatin)
Anterior Pituitary
What hypothalamic hormones regulate thyroid-stimulating hormone (TSH) or thyrotropin? (+/-)
+ thyrotropin-releasing hormone (TRH)
- thyrotropin-inhibiting hormone (somatostatin)
Anterior Pituitary
What hypothalamic hormones regulate adrenocorticotropic hormone (ACTH) or corticotropin? (+)
+ corticotropin-releasing hormone (CRH)
Anterior Pituitary
What hypothalamic hormones regulate follicle-stimulating hormone (FSH)? (+)
+ gonadotropin-releasing hormone (GnRH)
Anterior Pituitary
What hypothalamic hormones regulate luteinizing hormone (LH)? (+)
+ gonadotropin-releasing hormone (GnRH)
Anterior Pituitary
What hypothalamic hormones regulate prolactin (PRL)? (+/-)
+ PRL-releasing hormone (TRH and undefined PRHs)
- dopamine (predominant) – primary
What is thyroid-stimulating hormone (TSH) produced by?
thyrotrophs
What does thyroid-stimulating hormone (TSH) control?
controls each step in the production of thyroid hormones by the thyroid gland
What is adrenocorticotropic hormone (ACTH) produced by?
corticotrophs
What does adrenocorticotropic hormone (ACTH) stimulate?
stimulates cortex of adrenal gland to produce glucocorticoid hormones, especially cortisol
What is FSH and LH (gonadotropins) produced by?
single type of anterior pituitary cells called gonadotrophs
What does FSH and LH (gonadotropins) regulate?
regulate functions of gonads (testes and ovaries), including production of gametes (sperm or ova) and sex steroids
What is prolactin produced by?
lactotrophs
What is the main function of prolactin during pregnancy?
to stimulate breast development and lactogenesis (production of milk), but there many more functions (300+)
sucking → decrease dopamine → increase PRL → decrease GnRH → decrease LH and FSH → decrease fertility
What is the function of prolactin in mean?
not known – but high levels decrease gonadotropin and testosterone secretion, decreasing testicular function
What is growth hormone produced by?
cells of anterior pituitary called somatotrophs
What does growth hormone have important metabolic effects on? (3)
- liver
- adipose
- muscle
What metabolic effects does growth hormone have on liver?
increase gluconeogenesis
What metabolic effects does growth hormone have on adipose tissue?
increase lipolysis
What metabolic effects does growth hormone have on muscle?
increase amino acid uptake and protein synthesis
How are most of growth hormones’ actions related to growth?
indirect actions – mediated by increasing synthesis of insulin-like growth factors (and especially IGF-1) by liver and target tissues, such as bone and cartilage
Growth Hormone
What is the origin of most IGF-1 in circulation?
hepatic origin
Growth Hormone
What does most IGF-1 in circulation do?
has endocrine effect
Growth Hormone
What also synthesizes IGF-1?
several tissues such as muscle, cartilage and bone
Growth Hormone
What does IGF-1 synthesized by tissues (muscle, cartilage, bone) do?
acts in a paracrine or autocrine fashion to promote local tissue growth
What does elevated levels of growth hormone inhibit?
- anterior pituitary (via direct or short loop negative feedback)
- hypothalamus
(elevated IGF-1 has similar negative feedback effect on both regions of the brain)
Anterior Pituitary
Hypothalamic-Pituitary-Liver Axis – DO NOTES ON DIAGRAM
–
What causes dwarfism?
hyposecretion of growth hormone during childhood
What causes gigantism?
hypersecretion of growth hormone during childhood
What is acromegaly?
growth of hands, feet, facial features, and thickening of skin
What causes acromegaly?
hypersecretion of growth hormone as adult
- normally we don’t grow throughout our whole lives – long bones stop responding to IGF-1
- however, some bones have the ability to respond to IGF-1 throughout life and continue to grow
What causes acromegaly?
hypersecretion of growth hormone as adult
- normally we don’t grow throughout our whole lives – long bones stop responding to IGF-1
- however, some bones have the ability to respond to IGF-1 throughout life and continue to grow
What are body sizes at birth of people with dwarfism, gigantism, and acromegaly?
individuals are of normal size at birth, as fetal growth is promoted by hormones produced by placenta
Posterior Pituitary
What type of connection between hypothalamus and posterior pituitary is there?
neural connection – neurons originate from two specific regions of hypothalamus:
- supraoptic nuclei
- paraventricular nuclei
Posterior Pituitary
What is the supraoptic nuclei?
where the neurohormone antidiuretic hormone (ADH) is produced
Posterior Pituitary
What is the paraventricular nuclei?
where the neurohormone oxytocin is produced
Posterior Pituitary
Following synthesis in hypothalamus, where is each hormone transported?
to axon terminals in posterior pituitary and stored in vesicles
Posterior Pituitary
Upon stimulation, where are hormones released?
hormone is released into a capillary bed in posterior pituitary for distribution to specific target tissues
Posterior Pituitary
How are ADH and oxytocin similar?
both composed of 9 amino acids
Posterior Pituitary
How are ADH and oxytocin different?
have very different physiological functions
Posterior Pituitary
What is an antidiuretic?
substance that inhibits formation of urine
What is diuresis?
urine production
Posterior Pituitary
What physiological function is affected in the presence of antidiuretic hormone (ADH)?
distal convoluted tubules and collecting ducts of kidney reabsorb water from urine → decrease water loss and increase blood volume
Posterior Pituitary
What is antidiuretic hormone (ADH) also referred to as, and why?
also referred to as vasopressin, as it causes constriction of arterioles → increases blood pressure
Posterior Pituitary
What are the two hormones produced?
- antidiuretic hormone (ADH)
- oxytocin
Posterior Pituitary
What is the main target tissue of oxytocin? (2)
- uterus during late pregnancy and delivery
- lactating mammary gland
Posterior Pituitary
What does oxytocin do in the uterus?
increase stretching of uterus and cervix shortly before onset of birth → increase release of oxytocin → increase contractions of uterine smooth muscle → birth
Posterior Pituitary
What does oxytocin do in the mammary gland?
sucking by newborn → increase release of oxytocin → contraction of specialized cells surrounding milk-producing glands (myoepithelial cells) → increase milk ejection (“letdown”)
