Lecture Quiz 8 Flashcards
What is the hypothalamo-pituitary axis formed by and what does it do (broadly)?
Formed by the hypothalamus and pituitary gland
exerts control over many parts of the endocrine system
How does the hypothalamo-pituitary axis facilitate interaction between the nervous and endocrine systems?
nervous system regulates the endocrine system
endocrine activity modulates the activity of the CNS
receives signals from many parts of the brains
Where is the hypothalamus located?
directly underneath the thalamus at the base of the brain
What does the hypothalamus consist of?
many interconnected nuclei, some of which produce neurohormones that affect the pituitary gland
What are the two functions of the hypothalamus?
produces releasing hormones and inhibition hormones which regulate the activity of the anterior pituitary
produces substances that are delivered to the posterior pituitary via axonal transport where they are released into the bloodstream becoming hormones
Where is the pituitary gland located?
aka hypophysis
located in the cranial cavity and occupies the sella turcica
How is the pituitary gland connected to the hypothalamus?
via pituitary stalk infundibulum which carries both axons and blood vessels
What are the regions of the pituitary gland?
anterior pituitary (adenohypophysis) which acts as a true endocrine gland posterior pituitary (neurohypohysis) which acts as an extension to the hypothalamus
What do all hormones produced in the pituitary gland have in common?
they are peptides and therefore hydrophilic
How do the adenohypophysis (anterior pituitary) interact with the hypothalamus?
receives polypeptide hormones via pituitary portal vessels located in the pituitary stalk
How do hypothalamus hormones affect the anterior pituitary?
hypothalamic releasing hormones stimulate
hypothalamic inhibiting hormones (statins) decrease its activity
What are hormones produced by the anterior pituitary called and why?
tropic hormones because they stimulate other endocrine glands
What does growth hormone do? I.e. where does it come from, where does it go
aka somatotropin
comes from adenohypophysis
induces increased levels of sugar in the blood
stimulates the production of insulin-like growth factors (somatomedins) by muscle, liver, and b one (where it goes)
What do insulin-like growth factors do?
induce protein synthesis, cellular growth, and cellular division
How does inadequate secretion of growth hormone affect humans?
leads to pituitary dwarfism
What does overproduction of growth hormone do?
in childhood - leads to gigantism
as an adult - acromegaly (large extremities)
What does adrenocorticotropic hormone do? (to its effector organ)
stimulates the production of glucocorticoids (cortisol) by the adrenal cortex
How is ACTH/corticotropic regulated?
hypothalamic corticotropin releasing hormone increases ACTH production
cortisone decreases production of both CRH and ACTH
How is ACTH released throughout the day?
in a pulsatile fashion from the pituitary
follows a circadian rhythm, peaking in the morning and then declining
What does thyroid stimulating hormone do to its effector organ?
stimulates normal development and the secretory activity of the thyroid gland
How is TSH regulated?
thyrotropin-releasing hormone from the hypothalamus stimulates pituitary to produce TSH
TSH stimulates thyroid glad
thyroid gland produces thyroxin that aces on target cells and inhibits the pituitary and the hypothalamus
What does prolactin do to its effector organ?
stimulates milk production in the breasts
also related to growth, reproduction, and parental behavior
What is the main inhibitor of prolactin production?
prolactin inhibiting hormone (PIH, dopamine)
Describe prolactin-producing tumors
common
often asymptomatic
may cause inappropriate lactation or altered menstrual cycle in females, or impotence in males
What does lutenizing hormone do?
gonadotropin
promotes the synthesis of the gonadal hormones ovaries and testes
What does follicle stimulating hormone do?
gonadotropin
promotes the development of egg and sperm
When are gonadotropins produced?
only after puberty
GnRH stimulates their production
What are the two hormones released by the neurohypohysis?
oxytocin and antidiuretic hormone
What is the posterior pituitary gland made up of?
neuronal processes and glia as an extension of the hypothalamus
there are no vascular connections between the neurohypophysis and the hypothalamus
How are the two hormones of the neurohypophysis released?
hypothalamus produces hormones transported via axon transport released in neurophyophysis ADH and oxytocin bind to protein carriers called neurophysins for axonal transport hormones released into the blood stream
Where is oxytocin produced and stored, and what stimulates it?
synthesized in the paraventricular nucleus
stored in the neurohypophysis
responds to neural stimuli originating in the uterus or breast
Describe oxytocin as a molecule
small peptide of 9 amino acids
exerts its effect via PiP2 messenger mechanism
What affects the numbers of oxytocin receptors?
increases during the third trimester of pregnancy
What is oxytocin’s role during birth?
stretching of cervix stimulates oxytocin release
oxytocin increases uterine contractions
positive feedback mechanism
What is oxytocin’s role during breastfeeding?
infant suckling stimulates oxytocin production
oxytocin stimulates contraction of the smooth muscle in the mammary glands causing milk ejection (not milk production)
“bonding” hormone since it is associated with nurturing and affectionate behavior
What does oxytocin cause in males?
ejaculation
“bonding” hormone
Where is antidiuretic hormone and what does it cause?
synthesized in the supraoptic nucleus and stored in the neurohypophysis
causes the kidneys to retain water, producing concentrated urine
How is ADH production controlled?
osmoreceptors monitor the concentration of electrolytes in the blood
when concentration is too high (high osmalarity), supraoptic neurons of the hypothalamus are stimulated
ADH is produced, which is then transported to the posterior pituitary and then released into the bloodstream
How does antidiuretic hormone affect the kidneys?
it activates the receptors in target cells via PiP2 mechanism
in the kidneys it stimulates V2 receptors causing distal renal tubules to reabsorb water and return it to the bloodstream
How does ADH affect visceral organs?
causes casoconstriction by acting on V1a receptors
What is the overall effect of ADH?
increase the systemic blood pressure
How is ADH production increased? When is it inhibited?
ADH increases with shock, pain, fluid loss, and low blood pressure
alcohol inhibits production causing dehydration
What does underproduction of ADH lead to?
diabetes insipidus
excessive amounts of urine are produced due to the kidneys inability to make concentrated urine
leads to electrolyte imbalance and the loss of glucose
shock and death may results
What does overproduction of ADH cause?
can occur due to brain trauma
leads to water retention, serum hypo-osmolarity, hyponatremia, and high urine osmolarity
What are the symptoms of low ADH production?
headache apathy nausea and vomiting impaired consciousness can be fatal in extreme cases
What happens when there is too much Na+?
hypernatremia not enough K+ hypothalamus stimulated ADH released kidneys retain water
Where is the thyroid gland located?
on the anterior surface of the neck, below the Adams apple
anterior to the trachea and larynx
Describe the thyroid gland
consists of two lobes connected by the isthmus
made of many follicles - a single layer of cuboidal epithelial cells surrounding a space
space is filled with colloid, composed of the protein thyroglobulin
Describe the synthesis of thyroid hormones
synthesized in the follicular cells of the thyroid
thyroglobulin contains remnants of the amino acid tyrosine
Iodine is added to make it T4
Where are thyroid hormones stored?
as a part of the thyroid
What is the most essential ingredient in thyroid synthesis and how do we get it in our diets?
Iodine
in the US, it is abundantly available in foods (salt, milk, baked goods)
What happens to people with diets with low iodine?
simple goiter
the thyroid gland is stimulated by the increased production of TSH
Describe the differences between the two thyroid hormones
90% produced is T4
10% produced is T3
T3 possesses 10x the biological activity of T4
peripheral tissues (especially kidneys and liver) convert T4 into T3
How are thyroid hormones transported?
T4 and T3 are water insoluble
thyroid hormones are attached to plasma proteins for transport
albumin and thyroxin-binding globulin
How are the thyroid hormones received by the rest of the body (cellularly)?
TH are required by all cells of the body
receptors are found in the nucleus
stimulation activates the transcription of different genes
What are the two major physiological affects of thyroid hormones?
increase protein synthesis in virtually every body tissue
increase oxygen consumption dependent upon Na+/K+-ATPase (sodium pup)
What are the overall effects of thyroid hormones
T3 and T4 act as metabolic stimulants increase O2 consumption increase glucose consumption increase ATP production increase fat consumption increase of the body temperature
What do T3 and T4 regulate?
growth and development, which is especially critical for the fetus and infants
impact muscle, bones, and CNS development
increases heart rate and the force of cardiac contractions to achieve increased cardiac output
What does hypothyroidism cause during early development?
leads to cretinism
causes a failure to grow and mental retardation
What does hypothyroidism in adults cause?
myxoedema
sx include lethargy, low blood pressure, low temperature, weight gain
can by caused by Hashimoto’s (autoimmune disease) or low iodine diet
What causes hyperthyroidism?
autoimmune disease - Grave’s disease
or TSH overproduction
sx - high body temperature, weight loss, exophthalmoses (fat builds up behind eye), high blood pressure
Describe calcitonin
produced by parafollicular C-cells in thyroid
polypeptide that participates in Ca2+ metabolism - lowers blood Ca2+
amino-acid deriver water-soluble hormone
eliminated by kidneys and liver
What does calcitonin do?
stimulates osteoblasts to deposit calcium ions from the blood to the bone
regulated by PTH
Describe parathyroid glands
located within the lateral loves of the thyroid gland
3-4 on each side
produce parathyroid hormone
Describe parathyroid hormone
polypeptide of 84 amino acids
synthesized in the parathyroid hormone
How is PTH regulated?
decrease in Ca2+ concentration in blood stimulates PTH production via stimulation of Ca2+ receptors of parathyroid glands and C-cells of thyroid gland
Ca2+ acts via 2nd messenger (cAMP)
HUMORAL
What effects does PTH have in the body?
stimulates Ca2+ released from the bone by stimulating osteoclasts and inhibiting osteoblasts
increases Ca2+ reabsorption by the kdineys
induces the production of calcitriol in the kidneys
calcitriol increases the absorption of Ca2+ by the small intenstines
How do tropic hormones affect regulation of PTH?
control thyroxine secretion, but exert no influence on calcitonin or PTH secretion
control is strictly humoral - based on Ca2+ levels in the blood
What can happen after a thyroidectomy and what can it lead to?
PTH production may drop
decreased blood calcium causes an inability to transmit neural impulses at the synapse, leading to uncontrollable muscle contraction
