Reproduction 2: Pregnancy and Lactation Flashcards
(29 cards)
Prolactin is synthesized by ? and is under the control of ?
Prolactin is synthesized in the ant pit by LACTOTROPHS and it secretion is under the control of hypothalamus.
What are the 2 regulatory pathways in which the hypothalamus controls the secretion of PRL?
- an inhibitory pathway thru dopamine.
- a stimulatory pathway through Thyrotropin releasing hormone [TRH]
In persons who are not pregnant/lactating,PRL secretion by ANT PIT is TONICALLY INHIBITED BY DOPAMINE. In other words, PRL is maintained at low levels b/c inhibition of PRL secretion by dopamine overrides stimulation of PRL secretion by TRH.
How does the inhibitory dopamine reach the lactotrophs of the ant pit?
Dopaminergic neurons secrete dopamine into median eminence of the hypothalamus. The hypothalamic-hypophysial portal vessels deliver dopamine directly, and in high concentration, to the lactotrophs of the ant. pit.
Why amenorrhea with a prolactinoma?
PRL inhibits the secretion of GnRH which leads to decreased LH. The surge in LH initiates ovulation.
What drugs can inhibit or lower PRL levels? And what is its mechanism of action?
Dopamine agonists such as Bromocriptine, inhibit PRL secretion by ant pit. Systemically, acts just like dopamine.
Gonadotropin secretion over the life-span:
Begins during fetal stage. During childhood LH starts steroidal hormone synthesis by increasing activity of P450scc. During menopause,there is little neg feedback to hypothal/ant pit with few developing follicles. In older men, testosterone secretion diminishes somewhat→ less neg feedback also.
Why must fertilization occur soon after ovulation?
Oocyte only lives 12-24 hrs and sperm live 2-5days. Oocyte-cumulus complex is ovulated into peritoneal space. Fimbriae of the oviduct recognize the cumulus and sweep the complex into the ampulla where ferilization takes place. Hyaluronidase enzymes on the sperm head hydrolyze the ECM around the cumulus cells to permit the sperm(with acrosome intact) to make its way to the zone pellucida.
Before sperm can fertilize the ovum, they must undergo CAPACITATION in the female reproductive tract. What is the process and how long does it take?
Capacitation takes 4-6 hours and involves biochemical and structural modifications of the sperm that result in:
- Tails develop hyperactive motility
- Changes in membrane of the head make it capable of reaching the cell membrane of the egg and fusing with it. Fusing with the membrane involves the acrosomal reaction.
How long do human sperm remain capacitated for?
1-4 hrs. In not “called into action” they lose ability to fertilize the oocyte. Not all sperm undergo capacitation at once, so a population that is no longer fxnl is replaced by a new one. (Sperm stored in oviduct go through waves of capacitation)
How does motility develop during capacitation?
Cytoplasm of sperm is acidic and enters alkaline environment of vagina. Protons leave the sperm cytoplasm through Hv1 channels in the flagellum. As more protons are lost, the flagellum starts to beat in a whip like manner. The change in pH influences role of Ca2+ channels and the calcium influx-permits flagellar motion.
Are sperm motile in the male reproductive tract?
NO! They become motile in the alkaline environment of the vagina and undergo capacitation and are capable of undergoing acrosomal reaction.
What happens to the sperm in the vicinity of the egg? ECF pH is 7-8
Alkaline pH triggers opening of Ca channels. Influx of Ca ions contributes to increasingly whip-like tail motions. Hv1 may be used as a target for controlling male fertility.
Only 100-1000 sperm reach the oviduct. What facilitates the sperm reaching oviduct?
High sperm count, must be 20x10^6.
Uterine & oviduct contractions may be stimulated by ↑estrogen, oxytocin released during intercourse, prostaglandins in semen.
Sperm dysfunction-most common cause of infetility
How does progesterone as an attractant(chemoattractant/chemotaxis) for the sperm to find the egg?
Progesterone initially influences the direction of the sperm’s movement by initially binding to a sperm transmembrane receptor assoc. with adenylyl cyclase and exerting it’s effects via genomic actions.
Which cells secrete the chemical attractant?
cumulus cells or gr cells. The chemical attractant secreted by the oocyte itself is unknown.
Thermotaxis?
Traveling along a temperature gradient appears to be caused by increased [Ca]i mediated by PLC and IP3.
How do the sperm cells get through the cloud of gr/cumulus cells to get to the zona pellucida in order to initiate the acrosomal reaction?
the sperm heads secrete hyaluronidase enzymes to get through cumulus cells to the z. pellucida. Hyaluronidase enzymes forge a path through granulosa cells.
How do sperm cells undergo the acrosomal reaction?
Bind to specific sites on the z. pellucida and undergo the acrosomal reaction. The enzymes released cut a path through the z. pellucida.
Acrosomal rxn: SNARE dependent exocytosis of proteolytic enzymes requires Ca. Since sperm do not possess ER for Ca storage, where does the Ca come from?
Instead Ca stores are maintained at 2 different sites.
1.Ca stored in the acrosome regulates the acrosomal rxn.
2.Ca stored in the neck or mid piece-regulate motility and hyperactivation.
Sperm also possess Ca channels, pumps, and transporters.
What happens once fertilization occurs?
the oocyte completes the 2nd meiotic division and releases the 2nd polar body. The sperm and oocyte pronuclei fuse to form the zygote nucleus.
Fusion of egg and sperm membrane triggers the CORTICAL REACTION of the oocyte. What is the cortical rxn?
Cortical granules in the peripheral cytoplasm release their contents into the perivitelline space. The cortical substances alter the membrane and z. pellucida to prevent more than 1 sperm from fusing with the oocyte. This accomplishes “block to polyspermy”
The ENTIRE sperm cell enters the oocyte! What happens next?
the flagellum and mitochondria are degraded within the cytoplasm. The centriole becomes an organizing element of the mitotic spindle. The 2nd meiotic division which was arrested in metaphase will be completed. Upon fertilization, the zygote produces enzymes that contribute to the development of the conceptus-a ball of cells resulting from repeated mitotic divisions of the zygote. Fetilization is often referred to as conception.
What is estriol?
Androgens secreted by the fetus are converted to estriol by the placenta. Its an estrogen.
Where is estriol synthesized?
estriol is synthesized by steps in the placenta, fetal adrenal gland, and fetal liver.
