ENDOCRINE SYSTEM Flashcards by Nicole Cano

a system of glands &
hormone-secreting
cells that regulate
body functions
through chemical
messages called
hormones.

ENDOCRINE SYSTEM

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controls & integrates
the functions of other
organ systems in the
body
together with the
nervous system, is a
major regulator of
homeostasis

ENDOCRINE SYSTEM

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a substance secreted by
an endocrine gland

HORMONE

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released into the
circulation & distributed
to distant organs/tissues

HORMONE

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target organ/tissue: an
organ /tissue which
contains specific
receptor sites to a
particular hormone

HORMONE

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only exerts its effects on
target organs or tissues

HORMONE

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alters the cellular
activity of target
organs/tissues

HORMONE

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formed from cholesterol
are lipid-soluble
examples: cortisol,

aldosterone

Steroidal hormones

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receptor is located in the

target cell’s nucleus

Steroidal hormones

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mechanism of action:

a) diffuses through plasma
membrane of target cell
b) once in ICF, enters the
nucleus & binds to a
receptor protein to form a hormone-receptor complex
c) hormone-receptor complex
binds to specific sites on DNA
d) certain genes are activated to
transcribe mRNA , w/c is then
translated in cytoplasm
e) new proteins are synthesized
& produce a response

Steroidal hormones

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are amino acid-based &

water-soluble

example: norepinephrine

Non-steroidal hormones

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could not enter cell
receptor is located on the target cell’s plasma
membrane

Non-steroidal hormones

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needs a second messenger
(usually cyclic adenosine
monophosphate or cAMP)
to bring about a response

Non-steroidal hormones

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mechanism of action:

a) binds to the membrane
receptor
b) a reaction starts inside the cell
that converts ATP into cAMP.
c) cAMP activates several
proteins
d) activated proteins cause
reactions that produce
physiological responses

Non-steroidal hormones

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glands secrete their
hormones in direct response
to changing levels of ions or nutrients in the blood

Humoral regulation

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Changing level of substance in plasma-> endocrine gland-> target cells-> action

process of humoral regulation

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glands secrete their
hormones when directly
stimulated by the nervous system
example: adrenal medulla

Neural regulation

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Nervous system-> endocrine gland-> target cells-> action

process of neural regulation

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glands secrete their
hormones in response to
hormones released by other
endocrine glands
* example: thyroid gland

Hormonal regulation

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hypothalamus-> anterior pituitary gland-> peripheral endocrine gland-> target cells-> action

process of hormonal regulation

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the feedback system
controlling most hormones
example: PTH & calcitonin

Negative feedback

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oxytocin is regulated via this feedback mechanism

Positive feedback

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 or deficient
supply of the
hormone
e.g.:
hypothyroidism

HYPOSECRETION

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 or excessive
supply of the
hormone
e.g.:
hyperthyroidism

HYPERSECRETION

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* located in the brain * serves as the major link bet. the nervous & endocrine system

HYPOTHALAMUS

* although NOT a gland, it regulates the secretory activity of the pituitary gland

HYPOTHALAMUS

* target organ: pituitary gland

HYPOTHALAMUS

* hormones produced: releasing hormones o TRH o CRH o GnRH o GHRH o PRH

HYPOTHALAMUS

* hormones produced: inhibiting hormones o GHIH or somatostatin o PIH

HYPOTHALAMUS

* also called, “hypophysis” * lies in the sella turcica of the sphenoid bone at the base of the brain

PITUITARY GLAND

* divided into 2 lobes - the anterior & posterior pituitary glands

PITUITARY GLAND

* infundibulum: a stalk-like structure that attaches the pituitary gland to the hypothalamus

PITUITARY GLAND

: blood vessels w/in the infundibulum that connect the capillaries of the hypothalamus to the capillaries of the anterior pituitary gland

hypophyseal portal veins

: specialized form of nerve cells that secrete a “neurotransmitter” into the bloodstream rather than into a synaptic cleft; found in the hypothalamus & some may extend to the posterior pituitary

neurosecretory cells

* the smaller lobe of the pituitary gland * contains the axons & axon terminals of neurosecretory cells whose cell bodies are in the hypothalamus * also called “neurohypophysis” * does not synthesize hormones but stores & releases two hormones: oxytocin & ADH

Posterior Pituitary Gland

* plays a role in childbirth & lactation * primarily regulated via positive feedback * partly responsible for the feelings of sexual pleasure during and after intercourse

Oxytocin

target tissue: smooth muscles in the walls of the uterus stimulus: pressure on cervix response: uterine contraction to expel fetus & placenta

during childbirth

target tissue: mammary glands stimulus: stimulating/sucking of mother’s nipples response: milk ejection or “let down”

lactation (after childbirth)

* also called “vasopressin” * controlled by hypothalamus (neural regulation) * stimuli: ✓ dehydration/ water content ✓  blood osmolality or concentration

Antidiuretic hormone (ADH)

* main function: to conserve body water * target organs: kidneys, sweat glands & arterioles

Antidiuretic hormone (ADH)

specific action:  water retention/reabsorption by kidney tubules response: less water loss from the blood into the urine, &  urine volume

kidneys

specific action:  perspiration response:  water loss from sweat

sweat glands

specific action:  perspiration response:  water loss from sweat

sweat glands

specific action: smooth muscles contract → vasoconstriction response:  blood pressure

arterioles

* factors that inhibit ADH release: ✓ alcohol intake ✓ caffeine intake ✓ cold weather

Antidiuretic hormone (ADH)

* also called “adenohypophysis” * the larger lobe of the pituitary gland * controlled by the releasing & inhibiting hormones of the hypothalamus (hormonal regulation)

Anterior Pituitary Gland

* secretes the tropic hormones (TSH, ACTH, FSH & LH) * also secretes GH, PRL & MSH

Anterior Pituitary Gland

* also called “somatotropin” * its release is promoted by GHRH & inhibited by GHIH from hypothalamus (hormonal regulation) * target organs: liver, adipose tissue, muscles, bone, cartilage,

Growth hormone (GH)

specific action: lipolysis or breakdown of fat for energy &  glucose synthesis by the liver response: maintained or blood glucose levels

liver & adipose tissue

specific action:  rate of mitosis, amino acid transport & protein synthesis response: growth until puberty & tissue repair

muscles, bone & cartilage

* stimulus: excess CRH secretion from hypothalamus (hormonal regulation) * target cell: melanocytes on skin * response: skin darkening (occurs only in hyposecretion of adrenal cortex)

Melanocyte-stimulating hormone (MSH)

* promotes lactation * its release is promoted by PRH & inhibited by PIH from hypothalamus (hormonal regulation) * target tissue: mammary glands * response: milk production

Prolactin (PRL)

* also called “thyrotropin” * stimulus: TRH from hypothalamus (hormonal regulation) * target organ: thyroid gland * response: release of thyroid hormones

Thyroid-stimulating hormone (TSH)

* also called “corticotropin” * stimulus: CRH from hypothalamus (hormonal regulation) * target organ: adrenal cortex * response: release of hormones from adrenal cortex

Adrenocorticotropic hormone (ACTH)

* stimulus: GnRH from hypothalamus (hormonal regulation) * target organ: testicles & follicles of ovaries * response: females: development or maturation of egg cells & secretion of estrogen * response: males: development of sperm cells

Follicle-stimulating hormone (FSH

* stimulus: GnRH from hypothalamus (hormonal regulation) * in males, also called interstitial cell-stimulating hormone (ICSH) * target organ: interstitial cells of testicles & follicles of ovaries * response: females: release of mature egg cell (ovulation) & secretion of progesterone * response: males: secretion of testosterone

Luteinizing hormone (LH)

* butterfly-shaped organ on anterior neck * located inferior to the larynx (voicebox) & anterior & lateral to the trachea * isthmus: narrow, central portion of thyroid gland dividing it into left & right lobes * thyroid follicles: microscopic sacs that make up most of the gland * follicular cells: cells in the walls of the follicles that secrete thyroxine (T4) & triiodothyronine (T3)

THYROID GLAND

lie bet. the follicles & produce calcitonin

parafollicular cells:

* produced from iodine * stimulus: release of TSH from anterior pituitary (hormonal regulation) * target cells: various body cells

T3 & T4

* effects/response:  ATP production →  basal metabolic rate (BMR) →  energy consumption from all food types &  oxygen consumption →  body temp. * effects/response:  rate of protein synthesis (maintains normal growth & development together w/ GH) control of T3 & T4 secretion: a)  metabolic rate &  T3 & T4 in the blood stimulates release of TRH from hypothalamus b) TRH is carried along hypophyseal portal veins c) TRH stimulates anterior pituitary gland to secrete TSH. d) TSH is released into circulation. e) TSH stimulates follicular cells of thyroid gland to secrete T3 & T4. f) T3 & T4 is released into circulation &  metabolic rate g) elevated levels of T3 & T4 inhibit release of TRH & then of TSH (negative feedback)

T3 & T4

* important for Ca++ homeostasis * stimulus: hypercalcemia or  Ca++ levels in the blood (humoral regulation) * target cells: osteoclasts & osteoblasts * specific actions: inhibits osteoclasts to  bone resorption stimulates osteoblasts to  Ca++ deposition from the blood to the bones * response: Ca++ level of blood  & returns to normal * negative feedback: calcitonin release is inhibited once Ca++ levels in blood return to normal

Calcitonin

Four (4) small glands embedded on posterior side of thyroid gland

Parathyroid Gland

* also called “parathormone” * important for Ca++ homeostasis * stimulus: hypocalcemia or  Ca++ levels in the blood (humoral regulation) * target cells: osteoclasts & kidneys

Parathyroid Hormone (PTH)

* also called “parathormone” * important for Ca++ homeostasis * stimulus: hypocalcemia or  Ca++ levels in the blood (humoral regulation) * target cells: osteoclasts & kidneys * specific actions: stimulates osteoclasts to  bone resorption & move Ca++ from the bones to the blood * specific actions: stimulates kidneys to produce calcitriol , the active form of vitamin D which  absorption of Ca++ & PO4- from the small intestine * specific actions:  reabsorption of Ca++ in the kidneys to  its excretion  excretion of PO4- from the kidneys * response: Ca++ level of blood  & returns to normal * negative feedback: PTH release is inhibited once Ca++ levels in blood return to normal

Parathyroid Hormone (PTH)

* flattened organ located on LUQ of abdominal cavity, posterior to the stomach & in curve of the duodenum * has both exocrine & endocrine functions

PANCREAS

* Islets of Langerhans or pancreatic islets: the endocrine portion of the pancreas w/c contains 2 types of cells w/c produce hormones that regulate metabolism of glucose

PANCREAS

* produced by the alpha cells of the pancreatic islets * stimulus: hypoglycemia or  glucose levels in the blood (humoral regulation) * target cells: liver

Glucagon

* specific actions: glycogenolysis ( breakdown of glycogen to glucose) gluconeogenesis (conversion of fatty acids & excess amino acids into glucose)

Glucagon

* produced by the beta cells of the pancreatic islets * stimulus: hyperglycemia or  glucose levels in the blood (humoral regulation) * target cells: various body cells

Insulin

* specific actions:  diffusion of glucose into the cells &  utilization by the cells glycogenesis (conversion of glucose to glycogen in liver cells & skeletal muscles)

Insulin

* response: glucose level of blood  & returns to normal * negative feedback: insulin release is inhibited once glucose levels in blood return to normal

Insulin

* located on top of each kidney * also called “suprarenal glands” * separated into adrenal cortex & adrenal medulla

ADRENAL GLANDS

* outer shell of adrenal gland * subdivided into 3 zones: ✓ zona glomerulosa (outer zone) ✓ zona fasciculata (middle zone) ✓ zona reticularis (inner zone)

ADRENAL CORTEX

* major mineralocorticoid secreted by cells of zona glomerulosa * stimulus: angiotensin II (as a result of  BP,  blood volume or  Na+) * target organ: kidneys

Aldosterone

* specific actions:  Na+ reabsorption by thekidneys to  blood volume & BP  K+ excretion by the kidneys * response: Na+ level of blood, blood volume & BP  & returns to normal * negative feedback: aldosterone release is inhibited once blood volume, Na+ & BP return to normal

Aldosterone

* most abundant glucocorticoid secreted by cells of zona fasciculata * stimulus: ACTH from anterior pituitary gland (hormonal regulation) * active in periods of prolonged stress * target cells: various body cells * response: gluconeogenesis →  blood glucose levels keeps blood glucose levels high enough to support brain’s activities * in high doses: blocks histamine → depresses inflammatory response suppresses immune system by inhibiting WBCs

Cortisol

* secreted by cells of zona reticularis * converted to estrogen or testosterone in peripheral tissues * action: stimulate growth of axillary & pubic hair in males & females

Androgens

* inner core of adrenal gland * innervated by sympathetic division of ANS

ADRENAL MEDULLA

* stimulus: impulses from hypothalamus (neural regulation) in response to short-term stress * produces the fight or flight response

Epinephrine & Norepinephrine

* female gonads * located in pelvic cavity

OVARIES

* secreted by the follicle cells of the ovary * stimulus: FSH from anterior pituitary (hormonal regulation) functions: female secondary sex characteristics promotes maturation of egg cell/ovum

Estrogen & Progesterone a) Estrogen

* secreted by the corpus luteum (remnant of the ovarian follicles ) * stimulus: LH from anterior pituitary (hormonal regulation) * function: maintains pregnancy

Progesterone

* male gonads * located in scrotum

TESTES

* secreted by the interstitial cells of the testicles * stimulus: LH from anterior pituitary (hormonal regulation)

Testosterone

* small endocrine gland posterior to the thalamus

PINEAL GLAND

* hormone produced: melatonin * secretion is during darkness &  when light enters eye * fxn: stimulates the onset of sleep

PINEAL GLAND

* located posterior to the sternum, and superior to the heart * extends from lower neck to anterior thorax

THYMUS

* hormone produced: thymosin * fxn: promotes maturation of T-cell lymphocytes

THYMUS

* functions (depend on specific type): inflammation pain mechanisms blood clotting contraction of the uterus secretion of mucus in GIT * produced by: virtually all cells in the body (except RBCs) * PGs involved in pain are made in response to tissue injury → pain receptors become more sensitive to painful stimuli

Prostaglandins (PGs)

* produced by: kidneys * stimulus: low O2 levels in blood * response:  rate of RBC production in bone marrow

Erythropoietin

* produced by: GI tract * examples: gastrin, secretin, cholecystokinin * response: regulate digestive functions by influencing the activity of the stomach, intestines, liver, & pancreas.

GI hormones

* produced by: heart * stimulus:  blood volume * target organ & response: stimulates Na+ excretion from kidneys to  blood volume & BP

Atrial natriuretic peptide (ANP)

* produced by: heart * stimulus:  blood volume * target organ & response: stimulates Na+ excretion from kidneys to  blood volume & BP

Atrial natriuretic peptide (ANP)

* produced by: placenta (during pregnancy) * fxn: maintains pregnancy by stimulating the ovaries to continue producing estrogen & progesterone

Human chorionic gonadotropin (hCG)

the hormone tested during a pregnancy test

Human chorionic gonadotropin (hCG)