Topic 7: Endocrine System Flashcards
what is the role of the endocrine system?
-regulate growth, reproduction, and long-term metabolism events
what makes up the endocrine system?
-glands and tissues that secrete hormones
how do hormones travel through the endocrine system?
-through blood
-make their way to target cells where they bind to receptors (proteins) and change the target cell’s activity
what are target cells?
-cells of an effector tissue/organ that have specific receptors for a hormone
where are receptors found on the target cell?
-cell membrane
-intracellular (nuclear)
what are water soluble hormones?
-hormones including peptides, proteins, catecholamines
-act as 1st messengers that bind to receptors on the target cell membrane
-take place in a signalling cascade because they cannot enter the cell (b/c of hydrophobic areas)
what is the mechanism of action taken by a water soluble hormone?
-hormone binds to cell membrane receptors
-hormone - receptor complex activates membrane proteins
-membrane proteins will then activate a 2nd messenger system
what are 2 examples of 2nd messengers?
-cAMP
-Ca++
what is a general example of a water soluble hormone mechanism using cAMP?
-hormone binds to a cell membrane receptor and activates a G-protein (membrane protein)
-G - protein activates adenylate cyclase (another membrane protein/enzyme)
-adenylate cyclase converts ATP to cAMP (2nd messenger)
-[cAMP] in the cytosol increases
-cAMP activates protein kinases in the cytosol
-protein kinase phosphorylates other proteins to alter their activity (change in cell activity)
what is cAMP?
-cyclic adenosine monophosphate
what hormone takes action on liver cells? what is the resulting process of this?
-epinephrine
-activates cAMP (2nd messenger)
-cAMP activates protein kinase A
-protein kinase A activates metabolic proteins (enzymes) that cause breakdown of glycogen to glucose
-glucose is then released to the blood
what is the purpose of using second messenger systems?
-hormone cannot enter the cell
-rapid acting (enzymes just need activation)
-1 hormone molecule can activate many enzyme molecules (multiplies the signal)
-they are limited and can be broken down or removed (easy to change the activity)
how is cAMP broken down in the cell?
-by phosphodiesterase
what are lipid soluble hormones?
-hormones including steroids (cortisol) and thyroid hormones
-trigger protein synthesis (take more time than water soluble hormones, but have a longer acting response)
-can enter the cell (attaches to nuclear receptors)
what is the mechanism of action taken by a lipid soluble hormone?
-hormone enters the target cell and binds to intracellular (nuclear) receptors in the cytosol or nucleus
-hormone receptor complex binds to a specific region on DNA (activates genes)
-transcription is started (messenger mRNA is produced)
-mRNA attaches to ribosomes to produce proteins (translation)
what are the 3 types of stimuli acting on an endocrine gland that regulate the secretion of hormones into the blood?
-humoral stimulus (fluid)
-neural stimulus
-hormonal stimulus
what kind of feedback mechanism takes place in a humoral stimulus?
-negative feedback mechanism
what is a humoral stimulus?
-change in the concentration of a particular ion or nutrient in the blood stimulates the release of a hormone
what are 2 examples of a humoral stimulus?
-ex: an increase in blood glucose after eating carbs
-pancreatic beta-cells (islets of langerhans) detect glucose and release insulin to decrease blood glucose
-ex: a decrease in blood Ca++
-parathyroid gland detects decreased Ca++ and releases parathyroid hormone (PTH)
-this increases bone resorption (breakdown) by decreasing osteoblast activity and increasing osteoclast activity to increase blood Ca++
what are 2 examples of a neural stimulus?
-ex: heart rate
-you start at resting heart rate
-someone yells surprise
-your sympathetic NS preganglionic neuron releases Ach directly to the adrenal medulla
-adrenal medulla releases epinephrine and norepinephrine
-this increases the heart rate and forces contraction of ventricles/cardiac output
-moving out of homeostasis in a controlled manner
-ex: uterine contractions
-uterine contraction triggeres the hypothalamus to release oxytocin from the posterior pituitary
-this increases uterine contractions more
-keeps going until a big event occurs (positive feedback)
what is an example of a hormonal stimulus?
-ex: metabolism
-you start with low metabolism
-trigger the hypothalamus to release thyrotropin-releasing hormone (TRH)
-this triggers the anterior pituitary to release thyroid stimulating hormone (TSH)
-this then triggers the thyroid gland to release thyroxin (T4)
-T4 is converted to T3 (in the target tissue or liver)
-this increase metabolism
-overall a negative feedback mechanism
what will thyroxin eventually inhibit once enough thyroxin is produced?
-it will inhibit the release of thyrotropin-releasing hormone (TRH) and thyroid stimulating hormone (TSH)
-considered a negative feedback mechanism
what is stress? how does stress express itself?
-any extreme external or internal stimulus
-ex: surgery, infections, strong emotions, exams
-express by triggering a set of body changes called General Adaptation Syndrome
-coordinated by the hypothalamus directly or indirectly
what are the 3 phases of stress/general adaptation syndrome?
-alarm reaction (fight or flight response)
-resistance reaction
-exhaustion
what is the pathway of the alarm reaction?
-immediate reaction created by the nervous system
-CNS receives sensory input from change detection
-hypothalamus activates the reticular activating system (increasing alertness) and leads to the sympathetic nervous system
-the sympathetic nervous system affects organs and the adrenal medulla
-the adrenal medulla releases epinephrine and norepinephrine to prolong the fight or flight response
what are the effects on the body from the SNS + endocrine in the alarm reaction?
-blood glucose increases because the SNS inhibits insulin release and epinephrine and norepinephrine trigger the conversion of glycogen to glucose in the liver
-heart rate will increase due to force of contraction (increased cardiac output)
-respiration rate will then increase (need more O2 to use muscles)
-blood flow to the skin and abdominal viscera decreases so more blood is available to skeletal and cardiac muscle and the brain (O2 and glucose goes to working organs)
-digestion and urine production decrease (not needed + blood flow decrease)
what is the pathway of the resistance reaction?
-long term reaction created by the endocrine system
-permits recovery from the effects of the alarm reaction (tissue repair)
-acts as a response to longer term stress (starvation)
-initiated by hypothalamus hormones (growth hormone releasing hormone + corticotropin releasing hormone)
-these hormones trigger the anterior pituitary to release growth hormone and adrenocorticotropic hormone
-adrenocorticotropic hormone triggers the adrenal cortex to release cortisol (glucocorticoid)
what is the role of growth hormone?
-stimulates growth (protein production) and cell reproduction (mitotic divisions)
what is the role of corisol?
-inhibits insulin release to conserve glucose for rebuilding
how long does it take for cortisol to be released? when does the response occur?
-within 30 seconds of stress
-response does not occur for hours (steroid hormone that acts at nuclear receptors)
how does the release of the hormones in the resistance reaction affect the body short term?
-increases blood glucose
-liver is stimulated to produce new glucose from fats and later from proteins (controlled by growth hormone and cortisol)
-glucose is spared for use by the nervous system
-non-nervous tissue is directed by growth hormone and cortisol to use fats for energy in metabolism
-if the stress continues then cortisol will inhibit growth hormone release and proteins are then used for energy as well
-there is little insulin as well, glucose is not taken up well by skeletal muscle tissue (at rest) or adipose tissue
-overall creates an increase in blood fatty acids and amino acids for energy use (except for within the brain)
-immune system, bone formation, CT formation is inhibited (delayed healing)
-causes the release of aldosterone and antidiuretic hormone which will reduce salt and water loss at the kidney to maintain blood volume
how does the release of the hormones in the resistance reaction affect the body long term?
-decreases weight
-increases blood pressure
-increases heart rate
-immune suppression (due to cortisol)
-decrease in bone density
-increased risk of type 2 diabetes (due to increased blood glucose)
what does the exhaustion phase result from?
-depletion of body resources (ex: lipid reserves)
-loss of K+ (b/c of aldosterone effects)
-damage to organs (heart, liver, kidneys)
what is the pathway of reproductive hormones after puberty for males (testicular hormones)?
-hypothalamus will release gonadotropin releasing hormone (GnRH)
-GnRH will act on the anterior pituitary to release leutenizing hormone (LH) and follicle stimulating hormone (FSH)
-LH causes the release of testosterone in leydig cells in the testes
-testosterone (influences) and FSH (causes) spermatogenesis (work together)
-spermatogenesis will take place in the seminiferous tubules of the testes
-this is a slow acting process because you do not want large spikes of testosterone
-overall negative feedback mechanism
what are the functions of testosterone?
-development of organs of the reproductive tract and secondary sex characteristics
-stimulates bone growth at the epiphyseal plate
-promotes protein anabolism (building)
-directly stimulates spermatogenesis
what occurs to testosterone at the epiphyseal plate when the bone no longer needs to grow longitudinally?
-it is converted to estrogens to stop growth (closure of the plate)
what is the pathway of reproductive hormones after puberty for females (ovarian hormones)?
-the hypothalamus will release gonadotropin releasing hormone (GnRH)
-GnRH will act on the anterior pituitary to release leutinizing hormone (LH) and follicle stimulating hormone (FSH)
-LH triggers ovulation and the production of estrogens
-FSH triggers follicles to develop (primary + secondary) which will then trigger the production of estrogens
what is the function of FSH?
-stimulates the primary follicle to become a secondary follicle
what inhibits FSH?
-progesterone
-FSH increases when progesterone decreases and vice versa
-why progesterone increases when you’re pregnant
what is the function of LH?
-stimulates estrogen production from theca and granulosa cells of the follicle
what does a surge in LH cause?
-ovulation and formation of the corpus luteum from remnants of the follicle
what causes a surge in LH?
-estrogen from the secondary follicle rises for a few days
-LH is released due to GnRH which stimulates the follicle to increase estrogen secretion
-estrogen secretion becomes a positive feedback mechanism on LH production (causing a surge)
what is the function of estrogen?
-required for ovulation and the development of secondary sex characteristics
-stimulates the growth of endometrium and maintains it
-stimulates bone growth during puberty and later in life closes the epiphyses (18-20 years old)
what is the function of progesterone?
-releases from the corpus luteum
-prepares the uterus for pregnancy
what occurs within the ovary on days 1-14 of the uterine cycle?
-follicular (preovulatory) phase
-early on in the cycle, progesterone is low, therefore LH and FSH are secreted causing some primary follicles to become secondary follicles
-secondary follicles will secrete estrogen causing estrogen levels in the blood to rise
-later on in the cycle, one secondary follicle will become a vesicular follicle
what occurs within the uterus on days 1-14 of the uterine cycle?
-menstrual phase (days 1-5)
-stratum functionalis sheds and the shedded areas bleed
-proliferative phase (days 6-14)
-estrogen repairs and proliferates the stratum functionalis (mitosis in the stratum basalis)
what do estrogen levels in the proliferative phase depend on?
-if pregnancy occured
what is menstrual flow made up of?
-blood
-cells
-secretions
what is the stratum functionalis?
-outer layer of the endometrium
what occurs on day 14 of the uterine cycle?
-ovulation
-LH triggers the completion of meiosis I (secondary oocyte is formed)
-LH triggers the rupture of the vesicular follicle with the release of the secondary oocyte
what occurs in the ovary on days 15-28 of the uterine cycle?
-luteal phase
-high progesterone from the corpus luteum which inhibits GnRH (causes a drop in LH and FSH
-therefore no follicles will develop
what occurs in the uterus on days 15-28 of the uterine cycle?
-secretory phase
-progesterone from the corpus luteum prepares the endometrium for implantation
-progesterone inhibits uterine contractions
how does the endometrium prepare for implantation?
-becomes vascular and thick
-stores glycogen
what will happen if fertilization of the secondary oocyte occurs?
-the placenta will secrete human chorionic gonadotropin (hCG)
-the corpus luteum will secrete progesterone and estrogen for about 6 weeks until the placenta takes over
-FSH and LH are inhibited by high progesterone levels (no follicles develop)
what will happen if fertilization of the secondary oocyte does not occur?
-corpus luteum becomes the corpus albicans (no hCG and low LH)
-progesterone and estrogen levels decrease (LH + FSH are no longer inhibited, so they increase)
-endometrium no longer needs to be maintained (menstruation takes place)
what is the role of hCG?
-maintains the corpus luteum (has a similar structure to LH) for approximately 6 weeks post-fertilization
-detected in pregnancy tests
-stimulates testosterone secretion by fetal testes
how do oral contraceptives work?
-cause high estrogen and progesterone to inhibit GnRH secretion
-therefore FSH and LH levels are low
-the luteal phase is mimicked (no follicle maturation, no ovulation)
how does the implant work as a contraceptive?
-uses progestin
-similar mechanisms to oral contraceptives
how does the morning after pill work?
-high estrogen and progestin or progestin only
-prevents implantation, ovulation, or fertilization
what forms the placenta?
-the chorion from the fetus and endometrium from the mother
what does the placenta allow for?
-blood vessels of the mother and fetus to be in close proximity (blood does not mix)
what are the 2 main functions of the placenta?
-exchange site
-secretes hormones
how does the placenta act as an exchange site?
-gases, nutrients/wastes, hormones, antibodies are passed between the fetus and the mother
-drugs such as alcohol, morphine, and nicotine can also be passed
-viruses such as measles polio can be passed as well
what type of immunity is created when antibodies pass from the mother to the fetus?
-passive immunity because the fetus is not actively making antibodies
what hormones does the placenta secrete?
-estrogen + progesterone
-hCG
