endocrine Flashcards
what is the difference between an endocrine and ex0crine gland?
Endocrine glands secrete into ducts
Exocrine glands secrete directly into blood/lymph
What are the 4 types of chemical messengers?
HORMONES: long distance chem signals that travel in the blood or nymph.
AUTOCRINES: local chem messengers that exert their effects on the cells that produce them.
PARACRINES: local chem messengers that effect other cells.
SECONDARY MESSENGERS: produced inside a cell and cause a response by that cell
What is the endocrine system’s primary goal?
to collaborate with the CNS to maintain homeostasis
What part of the brain exerts control over the endocrine system?
hypothalamus
What are the two major classes of hormones?
Amino acid based: vary in size from small peptides to polypeptides
-water soluble
Steroid based: synthesized from cholesterol
-not water soluble
Give an example of a amino acid based hormone
amines, thyroxine, peptides, proteins
Give an example of a steroid based hormone
gonadal, adrenocortical hormones
What are the 5 ways that a hormone can alter target cell activities?
CHANGE permeability or potential (ion channels)
STIMULATE synthesis of enzymes or other regulatory molecules
ACTIVATE/DEACTIVATE enzymes
INDUCE secretion
STIMULATE mitosis
What are the two mechanisms that hormones use convey their message to target cells?
indirect: used by amino acid hormones (water-soluble which can’t get through the phospholipid bilayer)
- involves a G protein and 2nd messenger in cell
Direct: used by lipid soluble hormones (can get through the phospholipid bilayer)
- directly act on intracellular receptors
Describe the indirect mechanism for hormones
1) hormone binds to receptor -> receptor changes shape and binds to G protein
2) G protein binds to GTP and is activated
3) Activated G protein binds to and activates adenylate cyclase
4) this enzyme converts ATP to cyclic AMP (cAMP)
5) cAMP (second messenger) riggers response of target cell via protein kinases which activate/inactivate other proteins
6) cAMP is rapidly destroyed by phosphodiesterase
What is meant by indirect mechanisms can have an amplifying effect?
one hormone can cause multiple effects within a cell
Describe the direct mechanism for hormone signalling using cAMP (cyclic AMP).
- hormone passes through cell membrane and nuclear membrane
- binds to receptor chaperonin complex
- moves to DNA and binds to receptor protein on DNA
- turns on gene and stimulates transcription to produce mRNA
- mRNA directs protein synthesis
What are the 8 characteristics of hormones?
1) Specific
2) act like triggers; turn cells on or off
3) degree of response to hormone is variable
4) hormones can influence the number of their receptors on the target cells
5) hormones can also influence the number and affinity of receptors for other hormones
6) hormones are effective at very low concentrations and are quickly destroyed after binding to receptors
7) speed of response of target cells vary
8) duration of response of target cells vary
What is the average half-life of a hormone?
30 minutes
What is the one amino acid based hormone that does not use indirect mechanisms?
thyroid hormone
What are the three factors that the degree of response to a hormone depend on?
Concentration of hormone in the blood
Number of receptors on target cells
Affinity of receptors to the hormone
Explain what up and down regulation is.
Target cell’s receptors are influenced by hormones in one of two ways:
UP-REGULATION: develop more receptors in response to rising hormone, therefore, become more sensitive
DOWN-REGULATION: lose receptors in response to rising hormone levels to prevent over reaction
What is hormone permissiveness?
an interaction between to hormones where….
one hormone cannot act without the presence of another hormone
ex. thyroxine must be present before reproductive hormones can cause development of the reproductive organs
What is hormone synergism?
an interaction between hormones where…
two or more hormones together exert a greater effect than either one alone
ex glucagon and epinephrine each cause increased blood sugar, but together have a 150% greater increase
What is hormone antagonism?
a hormone interaction where…
two hormones have an opposite effect on target tissue
ex glucagon and insulin
What are the three stimuli that can cause the release of hormones?
HUMORAL: changing levels of some constituent of the blood directly stimulates secretion
ex. low blood sugar triggers release of glucagon
NEURAL: nerve fibers stimulate the release
ex: release of epinephrine and norepinephrine
HORMONAL: hormones trigger secretion of other hormones by endocrine glands.
ex. hypothalamic hormones stimulate anterior pit
What protects/houses the pituitary gland?
the sella turcica of the sphenoid bone
What is the hypophysis?
pituitary gland
What is the neurophysis?
the posterior pituitary and the infundibulum that descends from the hypothalamus
What are the two lobes of the pituitary gland?
anterior and posterior pituitary
What are the 2 hormones secreted by the posterior pituitary?
ADH and Oxytocin
What stimulates the release of hormones from the posterior pituitary?
nerve impulses from the hypothalamus
What is the nerve tract between the hypothalamus and the posterior pituitary called?
hypothalamic - hypohphyseal tract
Describe the stimulus for release, the target, and the effect of ADH.
Stimulus: neural and humoral (blood levels are monitored by HT)
Target: kidney tubules
Effect: inc reabsorption of water from filtrate
What happens with hyposecretion of ADH? What can this cause?
causes diabetes insipidus
- excrete large volumes of dilute urine
- Low BP and BV (dehydration and acute thirst)
What happens with hypersecretion of ADH? What can cause this?
decreased urine output, water retention
results in increased BV and BP
neurosurgery, trauma, or cancer cells can cause this
What is the effect of alcohol on ADH?
it inhibits the release
Describe the stimulus for release, the target, and the effect of oxytocin.
Stimulus: neural (cervical stretching, suckling
Targets and Effects: uterus (contraction, labour), breasts (milk ejaculation)
Other effects:
- plays a role in sexual arousal for both sexes
- in non-sexual relationships promotes nurturing and affectionate behaviour (cuddle hormone)
What are the hypophyseal portal veins?
they are a local blood circuit between the hypothalamus and the anterior pituitary.
carry releasing/inhibiting hormones from the HT to the ant pit that direct secretion
What are the 6 hormones that are secreted by the anterior pituitary (hypophysis)?
4 TROPIC hormones:
- TSH (thyroid stimulating hormone)
- FSH and LH
- ACTH
2 others:
- GH (growth hormone)
- Prolactin
Are the hormones secreted by the anterior pituitary (hypophysis) direct or indirect?
all are indirect and uses cAMP except GH
Describe the stimulus for release, the target, and the effect of GH.
Stimulus: GNRH from HT
Target: liver, skeletal musc, bone, and cartilage
Effect:
- causes them to release insulin like growth factors that stimulate bone and muscle growth
- exerts anti-insulin effects; mobilizes fats, raises blood glucose by decreasing glucose uptake and encouraging glycogen breakdown (all to provide E for growth)
When is the most GNRH released from the HT?
usually greatest release during sleep, but can be effected by stress, nutrition, and sleep patterns
What happens in hyposecretion of GH?
dec long bone growth that can result in PITUITARY DWARFISM
What does hypersecretion of GH cause?
in children: GIGANTISM (increased growth of longs bones)
in adults: ACROMEGALY (overgrowth of bones in face, hands and feet that are still sensitive to GH)
Describe the stimulus for release, the target, and the effect of TSH (thyroid stimulating hormone)
Stimulus: TRH (thyroid releasing hormone) from the HT
Target: thyroid gland
Effect: normal development of and normal secretion from thyroid gland
Describe the stimulus for release, the target, and the effect of ACTH.
Stimulus: CRH from the HT
Target: adrenal cortex
Effect: production and release of corticosteroids
** cyclic release with greatest release in early AM **
Describe the stimulus for release, the target, and the effect of FSH and LH.
Stimulus: after puberty, GnRH from HT
Target: gonads
Effect:
FSH - gamete formation
LH (ISCH in males) - stimulates gonadal hormone production
in females, the two combine to regulate the menstrual cycle
Describe the stimulus for release, the target, and the effect of prolactin
Stimulus: PRH from HT
target: milk ducts
effect: stimulates lactation
Describe the structure of the thyroid gland. What are the two types of cells in the thyroid?
2 lobes connected by isthmus
FOLLICLE cells: produce thyroglobulin
PARAFOLLICULAR cells: produce calcitonin
What do the lumens of the follicles in the thyroid gland do?
store colloid: thyroglobulin + Iodine needed to make thyroxine
What happens in hyposecretion of PRL (prolactin)?
poor milk production
What happens in hypersecretion of PRL (prolactin?
menses stop, inappropriate lactation, female infertility. development of breasts and impotence for males
What are the two thyroid hormones (thyroxines)? Which one is more active?
T4 and T3
T3 is ten times more reactive than T4
What two hormones are produced by the thyroid?
thyroxines (or thyroid hormones, specifically T4 and T3)
calcitonin
What is the molecular structure for T4 hormone?
2 tyrosine molecules + 4 bound iodine atoms
What is the molecular structure for T3 hormone?
2 tyrosine molecules + 3 bound iodine atoms
Describe the steps of synthesis of thyroxines.
after TSH binds to receptors on follicle cells:
1) thyroglobulin produced in follicle cells and stored as colloid in lumen of follicle
2) Iodide actively transported out of blood into colloid and oxidized to I2
3) I2 added to thyroglobulin to form T1 (monoiodotyrosine) and T2
4) T1 and T2 merge to form T3 and T4 (more T4 than T3)
5) enzymes split T4 and T3 from colloid and hormones diffuse out of cells into the blood
6) bind to transport proteins in the blood and go to target cells.
- T4 and T3 both bind to target cells, T3 much more active
- most tissues have enzymes that convert T4 to T3
Describe the stimulus for release, the target, and the effect of thyroxines.
Stimulus: low thyroxine levels trigger HT to release TSH
Target: almost all body tissues/cells
Effect: increases metabolism, aids normal functioning of heart, muscles, skeleton, digestive tract, reproduction, regulation of tissue growth, and development of the nervous system
What happens when thyroxine is hyposecreted in adults?
MYXEDEMA: low basal metabolic rate -> feel cold, constipation, physically and mentally sluggish
GOITER: same symptoms, but thyroid also enlarges. caused by lack of dietary iodine
What happens when thyroxine is hyposecreted in infants?
CRETINISM: irreversible mental and physical retardation.
however, completely preventable if detected early and treated with thyroid hormone
What happens when thyroxine is hypersecreted?
HYPERTHYROIDISM: “turning up the furnace”
eyes bulge
What is Grave’s disease?
an autoimmune disease where antibodies bind to receptors in the thyroid stimulating production of thyroxine.
results in hyperthyroidism
What secretes calcitonin and what does it do?
thyroid gland
lowers blood calcium by inhibiting osteoclasts and stimulating osteoblasts (stimulates bone deposits)
Where are the parathyroid glands located?
2 in each lobe of the thyroid gland (can have more, it varies)
What hormone is secreted by the parathyroid glands?
PTH (parathyroid hormone)
What type of cell secretes PTH?
parathyroid chief cells
Describe the stimulus for release, the target, and the effect of PTH (parathyroid hormone)
Stimulus for secretion: humoral -> dec in blood Ca2+ detected by parathyroid hormones
Targets:
- skeleton: stimulates osteoclasts (release of Ca by breaking down bone)
- kidneys: inc reabsorption of Ca2+ from urine and activation of vit D
- Digestion: vit D inc absorption of Ca from food
Effect: raises blood Ca2+
What happens when PTH is hypersecreted?
- loss of bone salts
- bones becomes spongy
- excess blood Ca interferes with the nervous system
- can cause kidney stones
this is a rare condition that can be caused by a tumour
What happens when PTH is hyposecreted?
low blood calcium: hyper excitability of neurons, tetany, respiratory paralysis, death if untreated
Describe the structure of the adrenal glands.
2 main layers
Outer: cortex (glandular tissue), secretes steroid hormones
Inner: medulla (part of the sympathetic nervous system) secretes catcholamines
Outer cortex has three different layers that secrete different hormones
What are the hormones secreted by the adrenal glands?
Outer cortex:
- mineralcorticoids
- glucocorticoids
- gonadocorticoids
Inner medulla:
- catecholamines
Describe the stimulus for secretion for mineralcorticoids.
HORMONAL: low BP, BV, NA, high K activates renin - angiotensin mechanism -> inc aldosterone (the primary mineralcorticoid) release
NEURAL: HT responds to stress -> secretes CRH -> ant pit releases ACTH -> adrenal cortex releases aldosterone
HUMORAL: low blood Na, high blood K can be directed by the adrenal cortex itself
describe the effect and target of mineralcorticoids.
Target: kidney tubules
Effect: kidney tubules secrete K and reabsorb Na. Water follows with it -> inc BP, volume, and Na while decreasing K
What happens with hypersecretion of mineralcorticoids?
can be caused by Addison’s disease, results in:
- wt loss
- dec blood Na and glucose
- hypotension
- dehydration
Describe the inhibition of release for mineralcorticoids.
Occurs when BP is too high:
heart secretes ANP -> inhibits renin and aldosterone - less Na and water absorbed
What is alderstonism?
hypersecretion of mineralcorticoids:
- excess Na and Water retention
- inc BP and edema
- loss of blood K
- neurons non-functional -> muscle weakness -> paralysis
Describe the stimulus for release and the effect of glucocorticoids.
Stimulus: HT releases CRH -> ant pit releases ACTH -> adrenal cortex secretes glucocorticoids
Effect: helps resist stressors.
Stimulates gluceogenesis - proteins and fats converted to glucose or catabolized for E.
What happens if glucocorticoid levels are elevated for too long? (hyper secretion)
reduced inflammatory and immune responses
Could be Cushings’s syndrome/disease: moon face
syndrome caused by adrenal tumour
disease caused by pit tumour
What happens when glucocorticoids are hyposecreted?
can be caused by Addison’s disease
- dec blood glucose, and Na
- wt loss
- severe dehydration and hypotension
- hypoglycemia
What are gonadotropins?
most are androgens converted to either testosterone or estrogens
- role not well known
- may contribute to onset of puberty and development of secondary sex characteristics
- in woman, androgens may cause sex drive and then be converted to estrogens after menopause
What happens in hypersecretion of gonadocorticoids?
masculinization of females or prepubertal males
What is the type of cell in the adrenal medulla? What do they secrete?
CHROMAFFIN cells: secrete 80% epinephrine, 20% epinephrine
these are Catcholamines
What do catcholamines do? (epinephrine and norepinephrine)
reinforce effects of the sympathetic nervous system in fight or flight response
- inc HR, BP, blood sugar, peripheral vasoconstriction, etc
What happens in hyposecretion and hypersecretion of catcholamines?
hyposecretion is not a problem since sympathetic nervous system can make up the difference
Hypersecretion is very rare - effects are like massive uncontrolled sympathetic nervous stimulation
- hyperglycemia
- high BMR
- rapid HBR
- hypertension
describe the structure of the pancreas and the function of each aspect
it is both a exocrine (digestion) and endocrine gland
Islets of Langerhans contain endocrine cells:
- alpha cells produce GLUCAGON
- beta cells produce INSULIN
What do glucagon and insulin do together?
regulate blood glucose level
they are antagonistic to each other
Describe the stimulus for release, the target, and the effect of glycagon
stimulus: drop in blood glucose
Target: Liver
Effects:
GLYCOGENOLYSIS - conversion of glycogen to glucose, release of glucose into the blood
GLUCOGENESIS - conversion of lactic acid, fats and proteins to glucose
results in raising blood glucose
What results from hyposecretion of glucagon?
chronic hypoglycemic conditions
Describe the stimulus for release, the target, and the effect of insulin.
Stimulus: inc blood sugar
Targets:
- LIVER - stims storage of glucose by converting it to glycogen
- MUSCLE and FAT cells take up glucose
- inhibits gluconeogenesis
Effect: lowers blood glucose
What happens in hyposecretion of insulin?
can be caused by diabetes mellitus
symptoms: polyuria, polydipsia, polyphagia
glucose can’t enter cells without insulin, therefore dec fuel for ATP production resulting in more glucose being released, but with no effect
- inc release of glucose -> inc blood glucose -> glucose lost in urine and pulls water with it
more fats mobilized -> inc fatty acids in blood -> ketone bodies (organic acids) -> acidosis and ketouria -> if untreated leads to coma and death
What happens when insulin is hypersecreted?
hypoglycemia -> less glucose to brain -> convlusions -> unconsciousness -> death if untreated
What does the pineal gland secrete?
MELATONIN: may affect
- timing of sexual maturation and puberty
- day and night cycles
- circadian rhythms of body
What do the ovaries secrete? What do these hormones do?
Ovaries: ESTROGENS & PROGESTERONE
- stimulate normal growth/maturation of reproductive system and development of secondary sex characteristics
- together control menstrual (uterine and ovarian) cycle
What do the testes secrete? What does this hormone do?
Testosterone:
- normal growth and development of reproductive system, development of secondary sex characteristics
- spermatogenesis
- sex drive
What does the placenta secrete during pregnancy?
estrogens, progesterone, and human chorionic gonadotropin (HCG) which act on uterus to influence pregnancy
What does the thymus secrete? what do these do?
Thmopoietin, thymic factor and thymosin
- assist development of T lymphocytes to become immunocompetent
What are enteroendocrine cells and what do they do?
They are cells in the mucosal lining of the digestive tract that secrete local hormones that control activities of digestion
some examples of hormones:
gastrin, CCK, secretin
What do the kidneys secrete? what does this do?
ERYTHROPOIETIN in response to low blood 02
target is red bone marrow, stims RBC prod.
What hormone does the skin secrete? what does this do?
CHOLECALCIFEROL:
inactive precursor of vit D - activated in liver and kidney
What hormone does the adipose tissue secrete? what does this do?
LEPTIN:
secreted after uptake of glucose and lipids
target is CNS neurons - gives feeling of satiety
also produces resistin (an antagonist of insulin)
What are three developmental aspects of hormones?
1) hormone function can be disrupted by environmental exposures to things like pesticides, industrial chems…. etc
2) Pollutants effect: sex hormones, thyroid hormone, and glucocorticoids
3) high cancer rates in certain areas may be due to interference with glucocorticoids
