Endocrine System Flashcards
endocrine system
the cells, tissues, and organs that are endocrine glands, as well as the hormones they secrete
exocrine glands
glands that secrete their products by way of a duct onto an epithelial surface
- extracellular effects
endocrine glands
glands that are ductless and release their secretions into the bloodstream
- intracellular effects
differences between nervous and endocrine systems
- neurons release neurotransmitters into a synapse; endocrine glands release hormones into the bloodstream
- nervous system responds quickly and stops at the end of the stimulus; endocrine system may have a longer response time and can persist for days or weeks after the stimulus ends
- efferent nerve fiber innervates one organ and a limited number of cells; hormones have more widespread effects
steroid hormones
- derived from cholesterol, differ in the functional groups attached to four-ringed steroid backbone
- sex hormones and corticosteroids (cortisol)
- enter target cell nucleus and act directly on genes by activating or inhibiting transcription
monoamines (biogenic amines)
- made from amino acids and retain an amino group
- include several neurotransmitters as well as hormones
- dopamine, epinephrine, norepinephrine, melatonin, thyroid hormone
peptide hormones (water soluble)
- chains of 3 to 200+ amino acids
- synthesized the same as other proteins
- oxytocin and antidiuretic hormone, angiotensin
negative feedback of hormones
hormone itself inhibits further secretion by binding to the pituitary or hypothalamus
positive feedback of hormones
the change produced by the hormone causes more hormone to be released
- oxytocin
humoral stimuli
stimuli that are critical ions or nutrients
- low calcium in blood leads to secretion of parathyroid hormone
neural stimuli
nerve fibers stimulate hormone release
- epinephrine
hormonal stimuli
secretion of a hormone is in response to hormones produced by other endocrine glands
- tropic hormones and anterior pituitary gland
hypothalamus
major integrating link between the nervous and endocrine systems
- receives input from cortex, thalamus, limbic system, and internal organs
- control pituitary gland
anterior pituitary
stimulated by hypothalamic hormones to release or not release other hormones
- master gland
hypophyseal portal system
connects the hypothalamus to the anterior pituitary
- made up of capillaries in the hypothalamus, portal venules, and capillaries in the anterior pituitary
posterior pituitary
nerve endings in posterior pituitary gland are stimulated by nerve impulses from the hypothalamus to release hormones
- nervous tissue and not a true gland
- does not made hormones
tropic hormones
hormones that stimulate other glands to release their hormones
- produced by the anterior pituitary gland
growth hormone (GH)
- produced by anterior pituitary
- stimulates mitosis and cellular differentiation to promote tissue growth
- stimulates secretion of insulin-like growth factors (IGFs) that promote growth, protein synthesis, and fat breakdown
- levels decline with age
gigantism
increased linear growth of bones in childhood
acromegaly
increased growth usually due to pituitary tumor in adulthood
pituitary dwarfism
caused GH hyposecretion in childhood or adolescence
thyroid-stimulating hormone
- produced by anterior pituitary
- stimulates growth of thyroid gland and synthesis and secretion of thyroid hormones
gonadotropins
- produced by anterior pituitary
- follicle-stimulating hormone (FSH)
- luteinizing hormone (LH)
follicle-stimulating hormone (FSH)
- stimulates secretion of ovarian estrogen and the development of follicles
- in testes, stimulates sperm production
luteinizing hormone (LH)
- stimulates ovulation in females
- stimules secretion of progesterone
- stimulates secretion of testosterone in males
prolactin (PRL)
- produced by anterior pituitary
- secretion increases during pregnancy but has no effect until after birth
- stimulates mammary glands to synthesize milk
- in males, makes testes more sensitive to LH and thus enhances testosterone secretion
adrenocorticotropic hormone (ACTH)
- produced by anterior pituitary
- stimulates glucocorticoid (cortisol) secretion by adrenal cortex
oxytocin (OT)
- produced by hypothalamus
- stored and released by posterior pituitary
- surges during sexual arousal and orgasm
- stimulates labor contractions and enhances uterine muscle contraction (positive feedback loop)
- stimulates flow of milk from mammary gland to nipple
- plays a role in bonding between sexual partners and between mother and infant
- suckling reflex
antidiuretic hormone (ADH)
- produced by hypothalamus
- stored and released by posterior pituitary
- also functions as a neurotransmitter and called vasopressin in neuroscience
- stimulates water reabsorption by kidneys, which decreases urine volume and conserves body water
- increases blood pressure
- controlled primarily by osmotic pressure of the blood
- alcohol and other diuretics inhibit ADH
thyroid gland
- largest endocrine gland in adults
- two lateral lobes, lies just below the larynx
- produces thyroid hormone, calcitonin, parathyroid hormone
thyroid hormone (T3 and T4)
control conversion of glucose to energy or heat and regulate growth of reproductive and nervous tissue
- secreted in response to TSH from anterior pituitary
- primary effect: increase metabolic rate
goiter
a pathological enlargement of the thyroid
- lack of iodine lead to oversecretion of TSH, and the thyroid gland undergoes hypertrophy
hypothyroidism
hyposecretion of TH leads to decreased metabolic rate
- reduced BMR and low tolerance to cold
- fat accumulation and sluggisness
hyperthyroidism
- oversecretion of T3 and T4
- increased metabolic rate and oxygen consumption = increased use of metabolic fuels
- increased BMR, sweating, poor heat tolerance, and CV abnormalities
- thinness and nervousness
calcitonin
- decreases blood calcium levels by depositing calcium in bone
- stimulates osteoblast activity
- antagonizes the action of parathyroid hormone
- important mainly in children
parathyroid glands
- four ovoid glands found partially embedded in the posterior surface of the thyroid
- secrete parathyroid hormone in response to low blood calcium
parathyroid hormone (PTH)
- increases blood calcium by stimulating osteoclasts, increasing calcium reabsorption from urine, and promoting formation of calcitrol, which increases absorption of calcium from the GI tract
adrenal glands
- sit atop each kidney
- contains an adrenal medulla (10-20% of the gland) and an adrenal cortex (80-90%)
adrenal cortex
- surrounds the adrenal medulla and produces over 25 hormones known as corticosteroids or corticoids
- zona glomerulosa, zona fasciculata, zona reticularis
zona glomerulosa
- thin layer located just beneath the capsule at the gland surface
- secretes mineralocorticoids, mainly aldosterone
aldosterone
- mineralocorticoid produced by the adrenal cortex
- stimulates kidneys to retain sodium and excrete potassium
- helps maintain blood volume and pressure
- controlled by sodium levels, BP and blood volume
RAAS
renin, angiotensin, aldosterone system
zona fasciculata
- thick middle layer making up about 3/4 of the adrenal cortex
- releases cortisol
- anti-inflammatory effect
Addison’s Disease
- adrenal cortex slows release of cortisol
- results in excess ACTH
- bronzing of skin due to buildup of melanin
- develop low blood pressure
- severe dehydration and a mild infection can lead to death
zona reticularis
- narrow, innermost layer of adrenal cortex that is adjacent to the renal medulla
- releases androgens
androgens
- secreted by zona reticularis
- responsible for development of secondary sexual characteristics in puberty
- DHEA: precursor of testosterone
- estradiol: estrogen that is most important after menopause
adrenal medulla
- acts as both an endocrine gland and as a ganglion of the sympathetic nervous system
- sympathetic preganglionic nerve fibers extend through the cortex to reach cells in the medulla
- upon stimulation by nerve fibers, releases catecholamines
