Endocrine system: Hypothalamus and Pituitary

What are hormones?

chemical messangers that are released by glans that affect the function of a tissue or system

What are endocrine hormones?

secreted by the endocrine glands into the blood plasma and are then transported to the site of action by the plasma

-secreted into low concentrations into the blood

What are exocrine hormones?

secreted by exocrine glands right at the site of action

-do not have to travel through blood plasma

What is the overarching function of the endocrine system? What other system does it work with to do this function?

maintain homeostasis

-nervous system

What are the major chemical classes of hormones?

-peptide hormone

-amines

-steroid hormone

What type of endocrine hormone is most common?

peptide

What is the biochemical nature/structure of peptide hormones?

made up of amino acid polymers

How are peptide hormones synthesized?

-starts the same as anyother protein synthesis

-during translation it starts as pre-prohormone then converts to prohormone and final it is ready to be secreted as the active hormone

-it is stored in vesicles until ready to be used

What is the mechanism of action for peptide hormones?

bind to membrane receptors on target cells and signal transduction cascade and involve second messangers

WHat is the biochemical nature of steroid hormones?

hydrophobic molecules with fused carbon rings

-cholestrol is precursor to all these hormones

How are steroid hormones synthesized?

-derived from cholesterol

-not stored in vesicles due to hydrophobic nature

What is the mechanism of action for steroid hormones?

due to hydrophobic nature they transverse the cell membrane and bind to receptors in the cytosol or the nucleus

-takes longer to activate the receptor because of this

What is the biochemical nature of amine hormones?

derivatives of tyrosine or tryptophan

-can be hydrophilic or hydrophobic

How are amine hormones synthesized?

carboxyl group on tyrosine or tryptophan are modified

-these are stored in vesicles then secreted

What is the mechanism of action for amine hormones?

-hydrophilic amines will bind to cell membrane receptors like peptide hormones

-hydrophobic amines will bind to nuclear receptors like steroid hormones

What are different signal transduction pathways for peptide hormones?

-phospholipase C mechanism

-adenylyl cyclase mechanism

How is the concentration of circulating hormones controled?

-positve feedback

-negative feedback

What is the purpose of feedback loops that control hormone levels?

ensures the concentration of hormones is matches physiological needs/ is within normal levels

How can the feedback loops exert control on the hormone levels?

direct or indirect control

What is direct control by feedback loops?

feedback directly to gland releasing hormone

What is indirect control by feedback loops?

feedback that affects another gland whos secretions will then affect the gland that needs to be modulated

What does negative feedback do?

inhibits the release of hormone

-regulates level of hormone by varying the strength of signal from feedback system

What are the effects of negative feebback loops?

stabalizing

-bringing hormone levels back into normal levels

What does positive feedback do?

increases the release of hormone

-once the hormone is first released it promotes more hormone to be released

What are positive feedback loops known as?

destabalizing

-bring hormone levels outside of normal range

What factors affect target cell response to hormones?

-type of hormonal receptors

-hormonal concentration

-hormonal interactions

How does type of hormonal receptors affect target cell response to hormone?

-if cell does not have receptor for hormone, it will not be able to affect the cell

-concentration of receptors can also be varied in response to hormone concentrations

What is the permissive effect?

one hormone is required for the action of another hormone

What is synergistic effect?

two hormones have similar effect but not exactly the same funciton

-increases in one of hormones usually causes an increase in the other hormone

What is antagonistic effect?

two hormones have opposing efects with eachother

The hypopthalamus works closely with which other structure to regulate the release of hormones from other glands?

pituitary gland

How is the hypothalamus connected to the pituitary gland?

infundibulum

What is the infundibulum?

-stalk like structure that has blood vessels and nerves running through it

What are the endocrine functions of the hypothalamus?

-regulate hormonal secretion from the anterior pituitary lobe

-create posterior pituitary hormone synthesis

What hormones does the hypothalamus secrete to affect the anterior pituitary gland?

-release hormone (stimulatory)

-release inhibitory hormone (inhibitory)

What non endocrine functions does the hypothalamus have?

-thermoregulation

-sweating

-panting

-shivering

-blood pressure

-satiety

-GI stimulation

-circadian rhythms

-sleep

-arousal

-learning

-memory

What is the anterior pituitary gland known as?

adenohypophysis

What is the posterior pituitary gland known as?

neurohypophysis

What does adenohypophysis mean?

synthesizes its own hormones

What does neurohypophysis mean?

axonal ending bring hormone to the site

What is the role of the superior hypophyseal artery?

provide oxygenated blood to the hypothalamus

What is the role of hypothalamic capillary bed?

this is where hormones from the hypothalamus are released into

What is the role of the long portal vessel?

carries mixed blood containing hormones from the hypothalamus to the anterior pituitary gland

What is the role of anterior pituitary capillary bed?

-brings mixed blood into anterior pituitary gland and deposits the hypothalamic hormones and picks up the anterior pituitary hormones

What is the role of the hypophyseal vein?

drains deoxygenated blood from the entire pituitary gland to the body

How does the hypothalamus communicate with the anterior pituitary gland?

long portal vessel in the infundibulum

How does the hypothalamus communicate with the posterior pituitary gland?

through neurons in the infundibulum

What is responsible for producing the hormones secreted by the posterior pituitary gland?

supraoptic and paraventricular nuclei in the hypothalamus

What is the role of the inferior hypophyseal artery?

gives oxygenated blood to the posterior pituitary

How does the anterior and posterior pituitary gland communicate?

through short portal vessels

What hormones are released from the anterior pituitary gland?

-growth hormone (GH)

-prolactin

-thyroid stimulatiing hormone (TSH)

-adrenocorticotropic hormone (ACTH)

-follicle stimulating hormone (FSH)

-lutenizing hormone (LH)

What type of cell secretes growth hormone?

somatotropes

What is another name for growth hormone?

somatotropin

What is the function of growth hormone?

stimulate longitudinal growth of the body

What type of cells secrete prolactin?

lactotropes or mammotropes

What is the function of prolactin?

stimulatio of milk production

What type of cell secretes thyroid stimulating hormone?

thyrotropes

What is the function of thyroid stimulating hormone?

growtha nd stimulation of the thyroid follicular cells

What type of cell secretes adrenocorticotropic hormone?

corticotropes

What is the function of adrenocorticotropic hormone?

stimulation of glucocorticoids, minerelocorticoids, and androgens from adrenal cortex

What type of cells secrete follicle stimulating hormone?

gonadotropes

What is the funciton of follicle stimulating hormone?

-stimulates the development of the ovaries

-stimulates spermatogenesis in testis

What type of cell secretes lutenizing hormone?

gonadotropes

What is the function of lutenizing hormone?

-stimulates ovulation

-formation of corpus luteum

-stimulates estrogen and progesterone

-stimulates testosterone

What are the posterior pituitary hormones?

-antidiuretic hormone (ADH)

-oxytocin

What is the function of antidiuretic hormone?

regulate body fluid osmolarity and vascular smooth muscle contraction

-when blood pressure falls blood vessels constrict to increase TPR and water retension increases

What si the function of oxytocin?

-milk ejection

-uterine contraction

(both of these are positive feedback mechanisms)

What class of hormone are all anterior pituitary hormones?

peptide hormones

What is the patten of growth hormone secretion?

in a diurnal pattern

-released about every 2 hours

-largest secretion is right after falling asleep

How does growth hormone secretion vary over lifetime?

-increase form birth to puberty steadily

-large burst during puberty

-declines from puberty into adulthood

-secretion reduces greatly during senescence

What causes an increase in growth hormone secretion?

-reduced glucose concentration

-reduced fatty acid concentration

-exercise

-puberty

-stress

-fever

-trauma

-alpha adrenergic agonist

What causes a decrease in growth hormone secretion?

-beta adrenergic agonist

-somatostatin

-somatomedin

What hormone is released to stimulate growth hormone secretion? Where does it come from?

growth hormone releasing hormone from the hypothalamus

What is another name for somatostatin? What does it do?

somatotropin (growth hormone) release inhibiting factor

-inhibit release of growth hormone

What type of feedback is caused by the release of growth hormone?

negative feedback

What are the negative feedback loops for growth hormone?

-ultra short loop

-short loop

-long loop

What is the ultra short loop for growth hormone?

release of growth hormone releasing hormone causes a decrease in its own production

What is the short loop for growth hormone?

tissue targeted by growth factor releases somatomedins that act directly on the anterior pituitary gland to prevent growth hormone release

What is the long loop for growth hormone?

tissue targeted by growth factor releases somatomedins that act directly on the hypothalamus to produce somatostatin which inhibits the pituitary glands production of growth hormone

Where is somatomedin produced?

the target tissue; created when liver metabolizes somatotropins

(acts directly and indirectly on anterior pituitary gland)

Where is somatostatin produced?

hypothalamus

(acts directly on anterior pituitary gland

What are the action of growth hormone?

-powerful metabolic hormone

-combined effect with other hormones

-promotes linear growth of cartilage and bone

-enhances lean body mass (by increasing protein synthesis and lipolysis)

-promotes insulin resistance

-increases blood glucose levels

What happens when there is excess growth hormone released before puberty?

excessive growth of long bones leading to tall stature

-can lead to acromegaly if not treated

What is gigantism?

tall stature due to excess growth hormone before puberty

What is aracogmegaly? What does it cause?

excess growth hormone after puberty

-increased periosteal bone growth

-excessive growth of soft tissue

-peripheral insulin resistance

What happens when there is periosteal bone growth?

broaden face

-protrusion of jaw

-enlargement of hands/feet

How do you treat excessive growth hormone?

somatostatin analogues

What causes growth hormone deficiency?

-decreased secretion of growth hormone releasing hormone

-reduced growth hormone secretion from pituitary

-failure to generate somatomedins

-deficiency pf receptors of growth hormone or somatomedin

What happens when there is a growth hormone deficiency as a child?

-short stature

-proinent forehead

-underdeveloped nose bridge

-mild obesity

-delayed puberty

What happens when there is a growth hormone deficiency as an adult?

-reduced bone density (tendency to fracture)

-a higher level of body fat

-fatigue

-anxiety and depression

How do you treat deficient growth hormone?

growth hormone injections

What type of hormone is prolactin?

peptide hormone

How is prolactin secretion regulated?

hypothalamic-pituitary axis

What stimulates the pituitary gland to release prolactin?

thyrotropin releasing hormone which comes from hypothalamus

What inhibits the release of prolactin?

dopamine (also called prolactin inhibiting hormone)

What is the main source of dopamine for prolactin control?

hypothalamus

-posterior pituitary releases a little and so does the anterior pituitary

What type of feedback mechanism does prolactin have?

negative feedback

-prolactin promotes dopamine secretion

What factors will stimulate prolactin secretion

-pregnancy

-breast feeding

-sleep

-stress

-thyrotropin releasing hormone

dopamine antagonist

What factors will inhibit prolactin secretion?

-dopamine

-bromocriptine

-somatostatin

-prolactin

What does prolactin do?

-breast development

-lactogenesis

-inhibits ovulation