Endocrine Flashcards by Cal Schiller

Close to site of release, at synapse

Muscle (smooth, cardiac, and skeletal) cells, gland cells, other neurons

Typically within milliseconds

Brief (milliseconds-seconds)

Neurotransmitters

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Far from site of release (usually)

Cells throughout the body

Seconds to hours to days

Longer (seconds to days)

Endocrine

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can be both a neurotransmitter and a hormone

Norepinephrine

Epinephrine

Oxytocin

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Neurotransmitter: released throughout the brain and expressed by neurons

Hormone: released from the pituitary gland into blood, acting on breast and uterine tissue

Oxytocin

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Secrete hormones into interstitial fluid and blood surrounding the secretory cells (TSH for example)

ENDO- “Within”

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Secrete their product into ducts that release into body cavities, lumen of organs, or to outer surface (skin)

Sudoriferous (sweat), sebaceous (oil), mucous, salivary, mammary, ceruminous, lacrimal

EXO- “Outside”

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Hormone receptors are cellular __

proteins

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Hormone receptors are___ and broken down like other cellular components

synthesized

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Occurs when too much hormone present

Reduction of receptors means less sensitivity to the circulating hormone

Receptor Down-regulation

If not enough receptors, some of the hormone will get metabolized unused…not as effective

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Occurs when not enough hormone present

Increase of receptors means more sensitivity to the circulating hormone

Receptor Up-regulation

If more receptors present, better chance at all of the circulating hormone being used

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___ pituitary releases thyroid stimulating hormone (TSH) which binds to receptors on cells of the thyroid as no other cells in the body should have receptors for this hormone

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Circulating hormones (the majority) – pass from secretory cells to the interstitial fluid into the ___

blood stream

tend to linger in blood stream minutes to hours

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act on a neighboring cell or the same cell without entering the bloodstream

Local hormones

act quickly

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hormones that act on neighboring cells

paracrines

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hormones that act on same cell

Autocrines

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___ hormones: Most use transport proteins (synthesized in the liver)

Lipid-soluble

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Make the hormone temporarily water-soluble

Retard the passage of smaller hormone molecules through the kidney filter therefore reducing the amount lost in urine

Provide a ready reserve of hormone in the bloodstream
Free fraction- 0.1-10% are not bound to a transport protein; these diffuse from capillaries, bind to receptors immediately

Lipid-soluble hormones

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transported in their free (unbound) form in blood

Water-soluble hormones

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Control of Hormone Secretion regulated by

Signals from nervous system

Chemical changes in the blood

Other hormones

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Ex: Nerve impulses to adrenal medullae regulate release of epinephrine

Signals from nervous system

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Ex: Blood Ca2+ level regulates secretion of parathyroid hormone

Chemical changes in the blood

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Ex: Release of a hormone (ACTH) from the anterior pituitary stimulates release of cortisol by adrenal cortex

Other hormones

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Reverses a change in the controlled condition

Hormone “A” secreted by anterior pituitary

Blood levels of hormone “A” increase

Sends signal to anterior pituitary to stop/slow production of Hormone “A”

Negative feedback

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Strengthens or reinforces the change in the controlled condition

Oxytocin causes uterine contractions

Uterine contractions cause oxytocin to be released

Positive feedback

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Types of hormones Divided into three major groups based on chemical structure

Proteins and Polypeptide hormones Steroid hormones Tyrosine derivative hormones

Other ways to classify hormones

By solubility By gland By function

The majority of the hormones in the body fall into this category

Proteins and Polypeptides

Are made from the joining of three or more amino acids

Proteins and Polypeptides

Are all water soluble Can travel unbound in blood Finds their receptors on the cell membrane

Proteins and Polypeptides

Derived from cholesterol Very little concentration of these are stored

Steroid Hormones

Are lipid-soluble Have to be bound to transport proteins while in blood (because blood is water-based) Can freely pass through cell membrane Binds to receptors on the inside of the cell

steroid hormones

Derived from some form of tyrosine (amino acid)

Tyrosine Derivative Hormones

Thyroid hormones Adrenal medullary hormones (catecholamines) Prolactin Inhibiting Hormone (PIH)

Tyrosine Derivative Hormones

Triiodothyroinine (T3) | Thyroxine (T4

Thyroid hormones

Epinephrine | Norepinephrine

Adrenal medullary hormones (catecholamines)

Controls the autonomic nervous system through neural and hormonal approaches

The Hypothalamus

Location: anterior and inferior to the thalamus

The Hypothalamus

Connected to the posterior pituitary gland by the __ stalk. | hypothalamus

infundibular

There is a partial sheath that wraps up the infundibular stalk from the anterior pituitary gland called the pars tuberalis These two things entwined become the ____ (hypothalamus)

infundibulum

Every hormone synthesized in the hypothalamus is transported to the ___ gland, where it will either be stored or cause another hormone to be synthesized

pituitary

Hypothalamus + ___ = regulation of growth, development, metabolism, and homeostasis

Pituitary gland

Responds to signals from internal AND external environment (Temperature, hunger, satiety, blood pressure, levels of hormones, stress)

Hypothalamus + Pituitary gland

Controls daily bodily rhythms such as melatonin secretion from pineal gland, cortisol secretion, body temperature Collects and combines information from the body and makes changes to correct any imbalances

Hypothalamus + Pituitary gland

Hormones produced in hypothalamus, placed into ____ system (capillaries), transported via portal system down to anterior pituitary gland (anterior)

pituitary portal

Once at anterior pituitary gland, these hormones CAUSE ___ hormones to be synthesized in the anterior pituitary

other

Hypothalamic Releasing Hormones include

GHRH: growth hormone-releasing hormone TRH: thyrotropin-releasing hormone CRH: corticotropin-releasing hormone GnRH: gonadotropin-releasing hormone PRH: prolactin-releasing hormone

Function is to stimulate release of particular anterior pituitary hormones

Hypothalamic Releasing Hormones

Function is to inhibit release of particular anterior pituitary hormones (from hypothalamus)

GHIH: growth hormone-inhibiting hormone PIH: prolactin-inhibiting hormone

AKA somatostatin

GHIH: growth hormone-inhibiting hormone

AKA dopamine

PIH: prolactin-inhibiting hormone

Once produced, these hormones are sent via axons from the hypothalamus down through the ____, into the posterior pituitary gland, where they are stored for future use (Transport to Posterior Pituitary Gland)

infundibular stalk

Hormones synthesized in the hypothalamus but stored in the posterior pituitary gland

Oxytocin Antidiuretic hormone (ADH/Vasopressin)

A small, pea-sized endocrine gland located within the ___ of the sphenoid bone (pituitary)

sella turcica

Posterior pituitary gland is connected to the hypothalamus via the ____

infundibular stalk

AKA: adenohypophysis or pars distalis

Anterior pituitary

AKA: neurohypophysis or pars nervosa

Posterior pituitary

Pars distalis & pars tubereralis

Anterior Pituitary Gland

glandular tissue (the largest portion) anterior pituitary

Pars distalis

partially covers the infundibulum (like a sheath) anterior pituitary

Pars tuberalis

Four of the tropic hormones released from the anterior pituitary gland exert their effect on another endocrine gland. Exception? (Ant. Pit.)

The exception to this is human growth hormone as it acts directly on almost all tissues found in the body, not a particular gland

Once anterior pituitary hormones are synthesized they are released into general circulation?

Venous

Also known as somatotropin

Human Growth Hormone (hGH)

Most abundant anterior pituitary hormone

Human Growth Hormone (hGH)

Secreted by somatotrophic cells (most abundant cell) Usually secreted in bursts every few hours

Human Growth Hormone (hGH)

Starts to decline production after adolescence Found to be approximately 25% production after age of 70

Human Growth Hormone (hGH

Is produced and released in a pulsatile manner Characteristic increase during the first two hours of deep sleep

Human Growth Hormone (hGH)

HGH secreted by?

somatotrophs

Main function is to promote synthesis and secretion of small protein hormones called Insulin-like Growth Factors (IGF’s; also known as somatomedins)

Human Growth Hormone (hGH)

In response to hGH, cells in the liver, skeletal muscle, cartilage, bones synthesize and secrete ___

IGF’s (somatomedins)

IGF enters bloodstream via the ___ or may act locally as autocrines or paracrines

liver

It is believed that all of the changes seen in the body are due to the presence of these IGF’s, not ___ directly

hGH This means that someone can have a normal hGH level but if there is a deficiency in the production of IGF’s, they will have some abnormalities

Increases protein synthesis Increases uptake of amino acids into cells

IGF

Decreases protein catabolism Decreases breakdown of proteins by limiting use of amino acids for ATP production and instead uses free-fatty acids

IGF

Stimulates growth in childhood Especially of bone, and muscle

IGF

Enhances lipolysis (break down of adipose tissue) Releases free-fatty acids (FFA’s) into the bloodstream for use as a source of energy in cells rather than glucose

IGF

Influences carbohydrate metabolism

IGFs

____ glucose uptake into cells (to an extent), leaving it in the bloodstream readily available for neurons to use (if needed). With increased FFA’s, cells will use these as their main energy source (hGH/IGF)

Decreases

Also stimulates the liver to release ____ (glycogenolysis) into the blood if serum levels are low (hypoglycemia) (hGH/IGF)

glucose IGF’s attempt to keep glucose available for neurons at all times during states of hypoglycemia While doing this, they mobilize glucose stores from liver to increase blood glucose levels

Insulin secreted in abundance in high blood glucose situations ___ produced and secreted in abundance in low blood glucose situations

IGF

____ stimulates GHRH secretion and inhibits GHIH secretion (hypothalamus) Anterior pituitary increases secretion of hGH resulting in increased ___ concentration

Hypoglycemia IGF

Hyperglycemia does the opposite Stimulates the hypothalamus to secrete GHIH Reduced levels of hGH result which also reduces the IGF action – plasma glucose levels reduce because the IGF’s are no longer working to keep integral glucose in the blood stream for neurons (there is enough already there)

Aight

Hypoglycemia Sympathetic nervous system stimulation (stress, strenuous exercise) Deep sleep

Factors that stimulate hGH secretion

Decreased serum fatty acids Increased serum amino acids Starvation/fasting or protein deficiency

Factors that stimulate hGH secretion

Factors that stimulate hGH secretion from Increased levels of:

Testosterone Estrogen Ghrelin – hormone secreted by stomach right before meals

Hyperglycemia Increased serum fatty acids Decreased serum amino acids Emotional deprivation Obesity When plasma T3 and T4 levels are low (thyroid) hGH (somatotropin) itself (negative feedback) GHIH (somatostatin) Aging

Factors that inhibit hGH secretion

ACTH secretion stimulated by

Corticotropin-releasing hormone (CRH) from hypothalamus and/or stress-relate stimuli (trauma, low BGL)

controls production of cortisol, other glucocorticoids and certain androgens produced by the cortex of adrenal glands

Adrenocorticotropic Hormone (ACTH)

Prolactin (PRL) controlled by

Prolactin-releasing hormone (PRH) Prolactin-inhibiting hormone (PIH) (AKA dopamine)

Prolactin (PRL) causes milk _____

production

Ejection of milk is caused by

oxytocin (posterior pituitary)

Low levels of estrogen and progesterone just prior to menstruation inhibits secretion of ____ and stimulates prolactin secretion (this likely accounts for breast tenderness at this time)

PIH (dopamine)

During the rest of the female cycle: as ____ increases, PIH (dopamine) secretion increases

estrogen secretion

____ from the hypothalamus stimulates the anterior pituitary to secrete FSH

Gonadotropin-Releasing Hormone (GnRH)

initiates follicle production in women monthly Also stimulates ovarian follicular cells to produce estrogen

FSH

stimulates production of sperm cells in men

FSH

____ from the hypothalamus stimulates the anterior pituitary to secrete LH

Gonadotropin-Releasing Hormone (GnRH)

____ from the hypothalamus stimulates the anterior pituitary to secrete LH

Gonadotropin-Releasing Hormone (GnRH)

LH triggers ____ in women as well as formation of the corpus luteum and therefore the secretion of progesterone by the corpus luteum

ovulation

With FSH, ___ triggers secretion of estrogen by ovarian follicular cells

LH stimulates cells in the testes to produce and secrete ____ in males

testosterone

Collective name for group of peptide hormones produced in the skin, the anterior pituitary and other parts of the brain

Melanocyte Stimulating Hormones

____ inhibits MSH release from anterior pituitary only

Dopamine (PIH)

Pigmentation of skin cells (i.e. increased melanin causing tanned skin) (This MSH is made locally in the skin) Possible suppression of appetite

MSH

Release of Thyrotropin Releasing Hormone (TRH) from the ___ stimulates the release of Thyroid Stimulating Hormone (TSH) from the anterior pituitary

hypothalamus

TRH is inhibited by increased levels of ___ in the bloodstream which when reduced, causes a reduced amount of TSH to be produced in the anterior pituitary

T3 and T4 This reduction in TRH and subsequently TSH reduces the amount of T3/T4 to be made

The ___ segment of the pituitary gland comprises ~ 25% of the total weight of the gland

posterior

nerve tissues encompassing the “bulbar” part of the posterior pituitary

Pars Nervosa-

connection to the pituitary gland

Infundibular stalk-

Hormones stored in posterior pituitary

Antidiuretic Hormone (ADH) (also known as vasopressin) Oxytocin

Produced in the hypothalamus, stored in the posterior pituitary gland “Against urination” – decreases urine production/excretion

Antidiuretic Hormone (ADH; Vasopressin)

Also causes vasoconstriction of arterioles (causing an increase in blood pressure) hence the alternative name vasopressin

Antidiuretic Hormone (ADH; Vasopressin)

Normal urine output daily is ____, without ADH this increases 10 fold to 20 liters a day

1-2 liters

Amount of ADH secreted varies with ___ and blood volume

blood osmotic pressure

High blood osmotic pressure stimulates osmoreceptors in the ____

hypothalamus

ADH action at Kidneys:

increased water reabsorption by tubules

ADH action at sudoriferous glands:

decreased sweating

ADH action at vascular smooth muscle:

artieriolar constriction

ADH secretion altered by other means:

Pain, stress, trauma, anxiety Drugs

During delivery of a child, stretching of the cervix stimulates release of ___ from posterior pituitary

oxytocin

After delivery of the child, it stimulates milk ejection or “let-down” from the mammary glands

oxytocin

Suggested to help with parental caregiver behavior

oxytocin

Many autistic children have reduced levels of ___ when compared to those without autism

oxytocin