CASE 1 Flashcards
steroid hormones: where are they secreted, what are they derived from, key characteristics
- secreted by 3 steroid glands: adrenal cortex, testes and ovaries
- derived from cholesterol
- lipid-soluble
- transported through blood stream
how do steroid hormones work?
- pass through the cell membrane of the target cell —> lipid-soluble so can diffuse directly through the phospholipid bilayer
- binds with receptor in the cytoplasm, forming a receptor-hormone complex
- complex enters nucleus and triggers gene transcription
- transcribed mRNA is translated into proteins
peptide hormones: what are they made of, where are the made, key characteristics
- made of amino acids
- made by specialised endocrine glands
- water-soluble therefore cannot pass through cell membranes
- short half life so break apart easily (used to direct processes quickly and efficiently)
how do peptide hormones work?
- bind to receptor on cell’s surface
- the hormone-receptor complex triggers a series of biochemical reactions that produces the second messenger
- the second messenger triggers a series of reactions that leads to altered cell functions
name 3 steroid hormones and 3 peptide hormones
steroid —> androgens, progesterone, oestrogen
peptide —> insulin, FSH, LH
FSH: origin, endocrine target, function, regulation
- origin: anterior pituitary
- endocrine target: testes and ovaries
- function: promotes follicle development in females, and with LH stimulates the secretion of estrogens by ovarian cells
- regulation: inhibited by inhibin, regulated by GnRH.
what is GnRH?
gonadotropin-releasing hormone
- pulsatile
- released by hypothalamus
- binds to receptors in the anterior pituitary gland
LH: origin, endocrine target, function, regulation
- origin: anterior pituitary
- endocrine target: ovaries and testes
- function: induces ovulation. promotes the secretion of estrogens and the progestins by the ovaries. FORMATION OF CORPUS LUTEUM
- regulation: regulated by GnRH
what is the effect of a mid-cycle surge of LH?
triggers the rupture of the mature follicle with release of the oocyte
progesterone: origin, function, regulation and how is it formed
- origin: ovary (corpus luteum), placenta
- function: preparation of uterus for pregnancy, maintenance of pregnancy, inhibit LH secretion
- regulation: corpus luteum is formed under LH stimulation and the lipids contained within it are used to from progesterone. Placenta produces sufficient amounts of progesterone to maintain the endometrial lining and continue pregnancy.
oestrogen: origin, function, regulation (what’s it stimulated by?)
- origin: ovary, testes, placenta
- function: stimulates bone and muscle growth, development of secondary female sexual characteristics. initiates growth and repair of endometrium during the menstrual cycle
- regulation: FSH and LH stimulate
inhibin: origin, endocrine target, function, regulation (what is it stimulated by?)
- origin: follicular cells of the ovaries (F = granulosa cells, M = sertoli cells)
- endocrine target: anterior pituitary gland
- function: inhibits secretion of FSH
- regulation: stimulated by FSH from anterior pituitary gland (negative feedback)
hCG: origin, endocrine target, function, regulation (when does it stop being secreted?)
- origin: syncytiotrophoblasts (placental barrier between maternal and foetal blood)
- endocrine target: corpus luteum
- function: maintains the integrity if the corpus luteum and promotes continued secretion of progesterone. appears in blood soon after implantation. the presence of hCG reduces after 3-4 months, but by now the placenta actively secretes both estrogen and progesterone.
- regulation: once placental secretion is sufficient, the cells stop secreting hCG
relaxin: origin, function
- origin: corpus luteum and placenta
- function: increase the flexibility of the pubic symphysis, permitting the pelvis to expand during delivery. causes dilation of the cervix and suppresses the release of oxytocin by the hypothalamus - delaying onset of labour contractions
what is the role of leptin and where is it found?
leptin (in fats) facilitates the production of kisspeptin (the main GnRH generator in females) which pushes the pulsatile secretion of GnRH from the hypothalamus
the menstrual cycle: what are the 4 phases, key days
4 phases = menstruation, follicular phase, ovulation, luteal phase
cycle usually lasts 28 days. cycle begins on 1st day of menstruation and ovulation occurs on approx day 14
orchestrated by the endocrine system via the hypothalamus, pituitary and gonads
what is the result of rising FSH levels at the beginning of the menstrual cycle?
causes stimulation of a few ovarian follicles
as the follicles develop they compete for dominance. how is the dominant follicle selected?
the 1st follicle to fully mature starts to produce large amounts of oestrogen. This causes negative feedback on both the pituitary and hypothalamus which sense the increasing levels of oestrogen and thus hinder the production of FSH and LH —> ensures only one follicle develops to a sufficient level as humans are monofollicular (other follicles become erratic and die off)
what is the single follicle that reaches full maturity called?
the Graafian follicle
the Graafian follicle continues to secrete large amounts of oestrogen. what is the result of this increasing amount of circulating oestrogen?
- endometrial thickening
- thinning of cervical mucus to allow easier passage of sperm
- inhibition of LH production by the pituitary gland
what does the graafian follicle begin to release and what is the consequence of this?
progesterone and inhibin - inhibin inhibits the release of FSH so oestrogen levels continue to rise and soon reaches a threshold at which point negative feedbacks turns into positive feedback —> leads to a surge in LH and FSH (although FSH is much less due to the inhibin)
what does the high amounts of LH cause?
causes the membrane of the Graafian follicle to become thinner so within 24-48 hours of the surge, the follicle ruptures releasing a secondary oocyte.
what does the secondary oocyte develop into?
quickly matures into an ootid and then into a mature ovum
what happens to the mature ovum?
it is released into the peritoneal space and is taken into the uterine tube via fimbriae (ovulation)
what do you need for successful implantation?
synchronisation of ovulation with endometrial preparation
once ovulation has occurred, what do LH and FSH stimulate?
stimulate the remaining Graafian follicle to develop into the corpus luteum (yellow body)
what does the newly formed corpus luteum begin to do?
begins to produce progesterone. as it is no longer a follicle, it stops releasing oestrogen
what do increased levels of progesterone released from the corpus luteum result in?
- the endometrium becoming receptive to implantation of blastocyst
- negative feedback causing decreased FSH and LH (both needed to maintain the corpus luteum)
- an increase in the woman’s basal body temperature
what happens as a result of falling LH and FSH levels?
the corpus luteum degenerates as it needs both FSH and LH to survive
what does the degeneration of the corpus luteum result in?
the loss of progesterone production —> menstruation = superficial stratum functionalis is shed due to constriction of spiral arteries
what happens if fertilisation occurs?
- fertilised ovum produces hCG
- hCG prevents the degeneration of the corpus luteum —> continued production of progesterone
- the continued progesterone prevents mentruation
- the placenta eventually takes over the role of the corpus luteum (from 8 weeks gestation)
what is menstruation and how does reduced progesterone result in menstruation?
- the degeneration of the endometrial lining as a result lowered progesterone
- lowered progesterone levels causes the contraction of spiral arteries (progesterone keeps the arteries dilated)
- constricted arteries = reduced blood flow to the endometrium
- doesn’t receive oxygen or nutrients
- stratum functionalis becomes necrotic and degenerates
- blood fills the uterine cavity from the broken vessels
what are theca cells?
found in the ovary, stimulated by LH: make androgens — androstenedione
what are granulosa cells?
form a single layer around the oocyte, many layers around the Graafian follicle. stimulated by FSH
what is atresia?
the degeneration of those ovarian follicles which do not ovulate during the menstrual cycle.
name the 4 steps leading to fertilisation
- sperm binding = sperm binds to zona pellucida
- acrosome reaction = acrosomes leak out and digest the zona pellucida
- cortical reaction = cortical granules modify zona pellucida so it can function as a block to polyspermy (it becomes impenetrable to other sperm)
- genetic material of sperm released into egg
- when genetic material meets, fertilisation occurs
when does the acrosomal head of a sperm rupture?
when a spermatozoon binds to a sperm receptor on the zona pellucida
what is the importance of the cortical reaction?
ensures that only one sperm’s DNA can get in
what is conception?
the fertilisation of an ovum by a spermatozoon
what helps accelerate sperm to its destination and what is this stimulated by?
uterine contractions of uterine musculature, stimulated by prostaglandins in seminal fluid and oxytocin secreted from woman’s posterior pituitary gland during her orgasm.
what is cleavage in embryogenesis?
- a series of cell divisions that sub-divides the cytoplasm of the zygote
- splitting without growth — stays within the zona pellucida
what is a zygote?
the single cell formed when an egg and a sperm cell fuse