Endocrine System Flashcards
What does the endocrine system do?
- regulates growth, reproduction and metabolism which are long term events
What is the second major control system?
Endocrine System
In the endocrine system, what does the glands and tissues do?
- they secrete hormones which travel in blood to target cells which contain specific receptors for that hormone
When the hormones bind to their designated receptors, what happens?
Change in cell activity
In the endocrine system, where are the receptors found?
- cell membrane
- intracellular (nucleus)
What are the types of hormones present in the endocrine system?
Water soluble hormones and lipid soluble hormones
What water soluble hormones are present in the first messenger system?
- peptides, proteins, catecholamines
What happens in the first messenger system?
- hormones bind to the cell membrane receptors
- the hormone-receptor complex then activates membrane proteins such as G-proteins
- the G-proteins then activate the second messenger system (cAMP, Ca2+)
what does the cAMP stand for?
cyclic adenosine monophosphate
Explain in detail how the second messenger system is activated and what happens afterwards?
- hormones bind to cell receptor membrane which activates the G-Protein
- the G-protein then activates the membrane protein adenylatecyclase
- which turns ATP to cAMP (therefore cAMP concentration increases)
- the cAMP activates protein kinases in cytosol
- protein kinases activates other proteins via phosphorylation to alter their activity
What activates the cAMP on liver cells and what happens after they are activated?
- epinephrine
- this causes the breakdown of glycogen to glucose which is then released to the blood
What use the second system?
- rapid acting (enzymes are are already present they just needed to be activated)
- hormones can’t enter cell since they are water soluble
- for 1 hormone molecule, many enzyme molecules are activated which multiplies the signal
- limited - messenger is broken down or removed (eg. cAMP is broken down by phosphodiesterase)
What do lipid soluble hormones do?
- they trigger protein synthesis, it takes time but it’s a long lasting response
Give examples of lipid soluble hormones.
Steroid (cortisol) & thyroid hormones
Explain the steps to lipid soluble hormones
- hormone enters target cell and bind to the intracellular (nuclear) receptors in the cytoplasm or nucleus of the cell.
- the hormone-receptor complex binds to a specific region of DNA
- this activates the genes
- which starts transcription
- mRNA is produce which attaches to a ribosome to make protein (translation)
Stimuli acting on an endocrine gland can be….
- humoral stimulus
- neural stimulus
- hormonal stimulus
What is a humoural stimulus? Give examples
when the stimulus is the ions/concentration of bodily fluids like blood.
- when the blood glucose increases after eating carbs, the pancreatic B-cells of Islets of Langerhans detect and release insulin which decreases blood glucose
- when the blood Ca2+ is decreased, the parathyroid gland detects this change and releases parathyroid hormone (PTH) which increases bone resorption and deceases osteoblast activity (osteoclasts still working to breakdown bone) = as a result, blood Ca2+ increases
What is a neural stimuli? Give an example
when the stimuli is coming from the nerves or the nervous system
- when the heart rate is at rest and there’s a surprising event that happens –> Sympathetic Nervous System functions - preganglionic neurone —> nt = AcH –> adrenal medulla –> nt = epinephrine & NE -> increased heart rate + forced contraction
- this is an example of the nervous system departing from homeostasis in a controlled manner…
What is a hormonal stimuli? Give examples. Are they negative feedbacks or positive feedbacks
When the stimuli is a hormone
1) in a low metabolism, the hypothalamus secretes thyrotropin-releasing hormone (TRH) –> anterior pituitary gland secrete thyroid stimulating hormone (TSH) –> thyroid gland secretes thyroxin (T4) –> T4 to T3 (in target tissues or liver) –> increase in metabolism
- negative feedback
2) in uterine contractions, hypothalamus –> posterior pituitary gland secretes oxytocin –> increases urine contraction
- positive feedback
What is stress? Give examples
any extreme internal or external stimulus such as surgery, infections, strong emotions, exams
what does stress do to the body?
triggers set of body changes called General Adaptation Syndrome
stress is co-ordinated directly or indirectly by what?
hypothalamus
What are the three phases/levels of stress?
Phase 1 = alarm reaction
Phase 2 = long term reaction
Phase 3 = exhaustion
What system is mostly working during the phase 1 of stress?
Nervous system = Sympathetic Nervous System
Explain the mechanism of stress in phase 1
CNS receives sensory input and detects change -> hypothalamus secretes RAS which increases alertness in the body –> Sympathetic Nervous System –> organs associated with it work & adrenal medulla secretes (NE + epinephrine) which prolongs flight or fight response
What are the effects of Phase 1 of stress
-
- increase in blood glucose because SNS inhibits the production of insulin to breakdown the glucose & the NE, E converts glycogen to glucose in the liver
- the heart rate increases + forced contraction
- respiration rate increases
- decrease blood flow skin and abdominal viscera because they are more available to skel. muscle, cardiac muscle and brain
- digestion decreases and so does urine production
What system is mostly working now in phase 2 of stress?
- endocrine system
What happens in phase 2 of stress
- the endocrine system permits recovery from the effects of phase 1 (eg. tissue repair)
- responds to long term stress
Explain the mechanism of the endocrine system during phase 2 of stress
hypothalamus
/ \
growth hormone corticotropin releasing hormone (GHRH)releasing hormone (CRH)
\ /
anterior pituitary gland
/ \
growth hormone (GH) adrenocorticotropic
hormone (ACTH)
l
adrenal medulla
l
cortisol (glucocorticoid)
What does the GH do in phase 2 of stress?
stimulations growth (protein reproduction) and cell reproduction
What does the cortisol do in phase 2 of stress?
- it’s released in 30 seconds of stress but response is slow
- steroid hormones act on nuclear receptors
- inhibits insulin production
Overall what are the effects of the hormones released during phase 2 of stress
1) blood glucose increases = due to little insulin (inhibition)
- skel. muscle + adipose tissue aren’t taking glucose very well
- spared glucose is used by NS
- metabolism of non NS directed to use fat as source of energy
- if stress continues, cortisol level increases which then inhibits production of GH, as a result protein is used for energy as well
- OVERALL: the FA blood and AA increase and are used for energy
2) inhibition of immune system. bone & CT formation (delays healing)
3) release of hormones aldosterone and ADH (Antidiuretic hormone) = reduces salt and water loss at kidney to maintain blood volume
What are the long term effects of stress during phase 2?d
- weight loss
- increased risk of type 2 diabetes due to increase of glucose
- increased blood pressure
- increased heart rate
- immune system suppression
- decreased bone density
During phase 3 of stress what happens?
exhaustion due to:
- depletion of body resources (lipid reserves)
- loss of K+ (aldosterone effect)
- damage to organs such as heart, liver, kidney
Explain hormonal regulation of the male reproductive function. (after puberty)
- at the hypothalamus, Gonadotropin Releasing Hormone is released (GnRH)
- this stimulates the anterior pituitary gland, which releases the Lutenizing Hormone (LH) & Follicle Stimulating Hormone (FSH)
- the LH stimulates the testes to secrete testosterone which directly stimulates spermatogenesis in the seminiferous tubules
- the FSH INDIRECTLY stimulates spermatogenesis
What is the role of testosterone?
- directly stimulates spermatogenesis
- development of organs or reproduction tract & 2 degree sex characteristics
- stimulates bone growth at epiphyseal plate (converted to E to stop growth = closing of the plate)
- promotes protein anabolism
Why is the hormonal regulation of male reproductive function considered a negative feedback.
Because the increase of sperm count (spermatogenesis) inhibits the secretion of hypothalamic GnRH and FSH
Explain the steps of the hormonal regulation of the female reproductive function after puberty.
- at the hypothalamus, GnRH or Gonadotropin Releasing Hormone stimulates the anterior pituitary gland to release LH and FSH.
- Then the LH stimulates ovulation in the ovaries and signals the production of estrogen
- FSH stimulates the production of follicles (primary and secondary) which then simulates production of estrogen at the signal of LH
What is the role of the FSH in the hormonal regulation of the female reproduction function?
- stimulates primary to become a secondary follicle
What happens when level of progesterone rises?
- it inhibits the production of FSH and LH
What roles does the LH play in the hormonal regulation of the female reproduction function?
- stimulates estrogen production from theca + granulosa cells of follicle
- in an LH surge, it causes ovulation and formation of corpus luteum from the remnants of the follicle
- during the follicular phase, the estrogen from the secondary follicle stimulates the release of LH via the GnRH which then stimulates the follicle to create more estrogen (an example of a positive feedback = as a result, LH surge occurs
What is the luteal phase?
When the rising progesterone levels inhibit the production of LH
What is the role of estrogen in the hormonal regulation of the female reproduction function?
- required for ovulation
- develops secondary sex characteristics
- requires for bone growth and closure of the epiphysis
- stimulates growth and maintains endometrium
What is the role of progesterone in the hormonal regulation of the female reproduction function?
- prepares uterus for pregnancy
Where does progesterone come from?
corpus luteum
What happens to the ovarian/uterus cycle in day 1-14
1) Ovary - goes through follicular phase (preovulatory phase)
- early on, there’s low levels of Progesterone therefore secretion of LH and FSH is high.
- some primary follicle becomes secondary due to lFSH
- the follicles secrete estrogen, therefore estrogen levels in blood increases
- one (usually) secondary follicle becomes a Graafian follicle
2) Uterus
- Menstrual phase (day 1-5)
= the stratum functionalis shed (outer layer of endometrium) & the denuded areas bleed
= therefore, menstrual flow happens = blood, cell + secretions
- Proliferative phase (day 6-14)
= Estrogen repairs and proliferates the stratum functionalis due to the mitosis of stratum basalis
What happens in the ovarian/uterine cycle in day 14?
Ovulation caused by the LH surge.
- the LH triggers:
- completion of meiosis I –> secondary oocyte
- breakdown of the Graafian follicle to release secondary oocyte
What happens during day 15-28 in the ovarian/uterine cycle?
1) The ovary goes through:
- Luteal Phase = high levels of P inhibits the GnRH therefore no secretion of LH and FSH = as a result, no follicles are developed
2) The uterus goes through:
- Secretion Phase = the progesterone from corpus luteum prepares the endometrium for implantation = becomes vascular, thick and stores glycogen
= inhibits uterine contraction
What happens when fertilization occurs?
- the placenta secretes human chorionoic gonadotropin (hCHG) which maintains corpus luteum
- for about 6 weeks, the corpus luteum secretes estrogen and progesterone and then the placenta takes over
- FSH and LH is inhibited the high levels of P so no follicles develop
The human chorionic gonadotropin has a similar structure to?
Lutenising hormone
If no fertilization what happens?
- the corpus luteum becomes corpus albican = no hCG & low LH
- decrease in progesterone and estrogen = therefore, no inhibition of LH and FSH (so they increase), no longer maintain endometrium = menstruation
What are some contraceptives?
- oral contraceptives
- implants
- morning after pill
What do oral contraceptives do?
high secretion of E and P which inhibits the GnRH causing low levels of LH and FSH (mimics fertilization) = no follicle maturation and ovulation
Give an example of implants?
- progestin which has a similar mechanism to oral contraceptives
What do morning after pills do?
they increase Estrogen production and progestin OR progestin alone. It prevents implantation, ovulation and fertilization
Placenta is formed from?
- chorion of the fetus and endometrium of the mother
Is there blood mixing between the fetus and the mother in the placenta?
no
What is the role of the placenta?
1) exchange site
= gases, nutrients, wastes, antibodies (passive immunity), hormones, viruses, drugs (eg. alcohol, morphine, nicotine)
2) secretes hormones = progesterone and estrogen
= hCG: maintains the corpus luteum for about 6 weeks post-fertilization
- detected by pregnancy test
- stimulates testosterone secretion by fetal testes
