before and after fertilization ...
Transport of spermatozoa in the male tractSperm undergo maturation.*Seminiferous tubules . The fluid of the seminiferous tubules is secreted constantly by the Sertoli cells. In the rete testis, changes in ionicand small molecule composition occur by diffusion.*In the vasa efferentia and epididymis, major changes occur in the fluid and sperm.
(1)The sperm are concentrated 100-fold by fluid absorption (from 50�106/ml to 50�108/ml).
(2)The epididymis adds some secretory products and also modifies the glycoprotein coat on the surface of thesperm. Instead of a saturated lipid membrane, they end up with a more fluid membrane structure that is stabi-lised by adsorbed glycoproteins.





(3)Before this stage, spermatozoa were incapable of movement and of attaching to and fertilizing eggs. After theepididymis, they can swim effectively. An increase in cAMP in the tail is involved.
(4)The sperm become capable of metabolising fructose.*Note that the anatomical divisions of the epididymis (caput, corpus, cauda) are not consistently related to the histol-ogy (initial segment ­ absorptive; middle segment ­ secretory; terminal segment ­ storage) across species.*The epididymis is a target organ for testosterone and depends on it. It bears intracellular testosterone receptors and on ABP.*The vas deferens is muscular and can propel the sperm along (there is hardly any fluid for them to swim in).Thevas deference serves as a storage reservoir of spermatozoa. In the absence of ejaculation, spermatozoa dribblethrough the terminal ampullaof the vas deferens into the urethra and are washed away upon urination.*Semen = spermatozoa + seminal fluid.Seminal fluid is not essential for effective sperm function, but is importantas a transport medium and may supply nutritional and protective factors. Boars make ~0.5l; humans make ~3ml.Semen volume is 10% from the vas deferens, 60% from the seminal vesicles, 30% from the prostate and smallamounts from the mucous glands (esp. the bulbourethral glands).*The seminal vesiclessecrete a mucoid material containing an abundance of fructose and other nutrients, prosta-glandins and fibrinogen. They empty their contents into the ejaculatory duct shortly after the vas deferens has emp-tied the sperm. This adds greatly to the ejaculated volume and washes the sperm out of the ejaculatory duct. Thefunction of the nutrients is obvious; the prostaglandins :
(1) react with cervical mucus to make it more receptive;
(2)may cause reverse peristaltic contractions in the uterus and oviducts (a few sperm reach the upper end of the Fallo-pian tubes within 5 minutes).
The prostatesecretes a thin, milky, alkaline fluid containing citrate, calcium, acid phosphate, a clotting enzymeanda profibrinolysin.Its capsule contracts simultaneously with the vas deferens to expel this fluid during ejaculation.The alkalinity may be very important for successful fertilization: the fluid of the vas deferens is quite acidic with theend products of sperm metabolism, as is the vaginal fluid (pH 3.5­4.0), while sperm are not optimally motile untilthe pH rises to 6­6.5.
The clotting enzyme acts on fibrinogen to form a weak coagulum that holds the semen in thevagina, and then lyses over then next 15­30 min thanks to fibrinolysin (formed from the profibrinolysin). As thishappens the sperm become highly mobile.
*Semen also contains reducing agents (including ascorbate); sperm are made in a low pO2environment and are thenexposed to oxygen; they are sensitive to oxidation.*Sperm can live for weeks in the male (though in practice they spend 4­5 days there) but once they are ejaculatedtheir maximal lifespan is 24­-48h at body temperature.Ligation of the vasa efferentia causes enormous damming up of fluid, but ligation of the vas deferens (as in vasectomy) does not. Spermatozoa dobuild up, though; they must be removed by phagocytosis or leakage.
CoitusPronunciation: co-it-us, not coytus.*Has a social as well as a sexual function in higher primates; obviously humans (menstruation is concealed and thefemale is receptive throughout the cycle) but archetypally bonobo chimpanzees.
1.Excitement.Psychogenic or somatogenic stimuli cause sexual arousal.
2.Plateau.Arousal is intensified; if stimulation is sufficient and prolonged, orgasm occurs.
3.Orgasm.Brief moment of involuntary climax; intense pleasure; often myotonia.
4.Resolution.Sexual arousal fades. Pelvic haemodynamics return to normal. Occurs rapidly (minutes) following orgasm but may take hours otherwise.This model applies to both sexes.
In the male, there is an absolute refractory period following orgasm in which sexual rearousal and orgasm is impossible; its duration varies with age (young=quick), and psychological factors in-cluding novelty of partner/context.
The male.
Erection results from tactile stimulation the penis and adjacent perineum. The reflex involves the internal pudendalnerves (afferent) and the parasympathetic outflow from S-2­4 (efferent).
Psychogenic stimuli (e.g. visual cues) canal cause erection so there is descending control.Erection is caused by relaxation of the smooth muscle of the dorsal artery and the arteries to the corpus cavernosum.The arteries dilate, allowing an inflow of blood. Arterio-venous shunts are closed to prevent drainage and the SM ofthe cavernosum relaxes, decreasing resistance to the increase in blood volume there. Venous `bleed' valves close(and the veins are compressed by the increased pressure). Low volume, low pressure .The corpus spongiosum does not increase in turgor as much as the c.c., so compression of the urethra is avoided.*Signalling pathways are still not certain. Autonomic NS involves NA and ACh. Injection of VIP causes erection, butmay ultimately end up as a nitric oxide (NO) signal (enter Viagra).*The testes are drawn reflexively towards the perineum and the dartos muscle contracts the scrotum. Testicular vol-ume may increase by 50% due to vasocongestion.*Further stimulation leads to emission, in which the contents of the vas deferens, prostate and seminal vesicles areexpelled into the urethra.4This is followed by ejaculation, in which semen is expelled from the posterior urethra(urethral smooth muscle + bulbocavernosus + ischiocavernosus). Retrograde ejaculation into the bladder is pre-vented by contraction of the vesical urethral sphincter.*Other changes of sexual arousal ­ nipple erection, HR, BP, skin rashes immediately prior to ejaculation, musclespasms etc.The female.*Psychogenic stimulation, stimulation of the vaginal walls and particularly the clitoris leads to genital changes verysimilar to the male. Vasocongestion of genitalia, including clitoral erection. Other effects are also similar, thoughtimecourse differs from the male (i.e. longer). Subjective descriptions of orgasms are very similar in men andwomen.*Vaginal lubrication is by transudationof fluid through the vaginal wall.*The vagina increases in width and length and the uterus elevates, lifting the cervical os to cause tentingof the va-gina.*At orgasm, vaginal and uterine contractions occur. The cervix may be actively dipped into the pool of semen bythese contractions.*Behavioural differences in sexual excitability probably reflect differences in reproductive strategy (see Ridley). Or-gasm following coitus occurs in 100% of normal men but surveys suggest 30­50% of women.2The Coolidge effect,named after the US President. The story goes that the Coolidges were on a tour of a chicken farm and Mrs Coolidge saw acockerel mounting one of the hens. "How often does he do that?" she asked. "Oh, a good ten times a day, ma'am," replied the farmer. "Please tell thatto the President," said Mrs Coolidge. On being appraised of this fact, the President asked "Always the same hen?" "Oh, no, Mr President, a differenthen every time," came the reply, to which he responded "Tell that to Mrs Coolidge."3Point and Shoot ­ parasympathetics for erection, sympathetics for ejaculation. This is oversimplified but useful.4Sympathetic NS. Alpha-blockers lead to `dry orgasms'3Transport of spermatozoa in the female tractSperm undergo capacitationand activation.*The ovum has halted in the ampullary­isthmic junction of the oviduct. Fertilization occurs here.*The cervixis a physical and a physiological filter for sperm. It is in the female's interests to select high-qualitysperm; only the best shall pass?*Ejaculated sperm are poor at ­ or at least slow to ­ fertilize eggs in vitro. Sperm recovered from the oviduct a fewhours after coitus are capable of immediate fertilization; they have undergone capacitationin the female tract. Ca-pacitation involves the stripping off of the sperm's glycoprotein coat, acquired in the epididymis. An oestrogen-primed uterus is an optimal medium for this. Several factors probably contribute: the high ionic strength and theproteolytic enzymes present are important. These conditions elute the glycoproteins. This leads to increased mem-brane fluidity at the head and tail, and increases the calcium conductance.*The sperm are still not fully capable of fertilization. The final change is activation, which is a Ca2+-dependent eventand involves three changes.1.The acrosome reaction.The acrosome swells and its membrane fuses with the plasma membrane at severalpoints. This can release the contents of the acrosome.2.Tail movement. While ejaculated sperm move by undulating their flagella, capacitated sperm move with apowerful whiplash motion.3.The membrane overlying the middle (equatorial region) and the posterior half of the spermatozoal headchanges. The change allows the membrane to fuse with the surface of the egg (it becomes `fusible').Fertilization*After the acrosome reaction, the sperm will live for 15­30 minutes, so it needs to be near the egg when this happens.The exocytosis of the acrosome contents depends on a further internal rise in both Ca2+and cAMP. The egg is sur-rounded by the cumulus cells, which act like a sponge and carry progesterone. Progesterone can elicit the acrosomereaction.*(The method of depositing a reservoir of sperm in the cervix and then letting them trickle towards the egg wherethey are activated may be a mechanism of increasing fertility. You don't want them all dying straight away if theegg isn't there yet.)*The acrosome reaction releases hyaluronidase.This can digest the intercellular matrix of hyaluronic acid holdingthe cumulus mass to the egg. The cumulus falls off. Some sperm may be sacrificed getting through the cumulus soothers can make it further.*The sperm is now next to the zona pellucida, which contains glycoproteins ZP1, ZP2 and ZP3.*ZP3 binds the apical membrane of sperm that have not undergone the acrosome reaction. This binding is species-specific;it is the only species-specific binding in the whole process. ZP3 elicitsthe acrosome reaction.*ZP2binds the inneracrosomal membrane. This allows sperm to attach and digest a pathway through the ZP usingthe proteolytic enzyme acrosin.The hyper-activated tail pushes it forwards.*The sperm enters the subzonal (perivitelline) space,next to the oolemma. Microvilli on the surface of the egg en-velop the sperm head, which lies on its side and fusesat its mid- (equatorial) region, which is next to its nucleus.Sperm can only fuse if they have undergone the acrosome reaction. They can fuse with the egg anywhere exceptover the meiotic metaphase spindle.*Fusion triggers cessation of tail movement.From entry into the cumulus mass to fusion takes 10­20 minutes.*The oocyte is now fertilized and is a zygote.It faces two immediate problems: (1) stop more sperm coming in ­ theblock to polyspermy­ as that would cause androgenetic triploidy/polyploidy, and (2) complete its second meioticdivision, to prevent gynogenetic triploidy.*Fusion triggers a Ca2+ wavespreading over the egg. A secondary series of Ca2+spikes occurs every 5­10 minutesfor several hours and is due to release and resequestration of Ca2+from internal stores. These stores are sensitive toIP3and Ca2+itself (positive feedback). Mechanism unclear ­ currently favoured idea is that a G-protein-coupled re-ceptor detects the sperm and causes IP3formation. Ca2+has two roles:1.It causes exocytosis of vesicles ("cortical granules"). These vesicles contain enzymes which target the ZP.(a)a proteolytic enzyme cleaves ZP2 no more sperm can bind to it(b)hexosaminidase digests the galactose-rich oligosaccharide chain on ZP3 no more acrosomereactions induced(c)an enzyme cross-links ZP2 to ZP3 renders ZP indigestible to acrosomal contents no moresperm can get through (any sperm halfway through get stuck)2.Meiosis is reactivated. The egg was arrested in 2nd meiotic metaphase. Now the second polar body forms(with one set of chromosomes in it) and is jettisoned. This is the first time the female gamete is haploid!Meiosis completes.55A protein called maturation promotion factor (MPF), unique to the egg, has stabilized the meiotic spindle thus far. In turn it is stabilized by cyto-static factor (CSF). Ca2+destroys CSF, destabilizing MPF and the spindle, and off we go to interphase. Anyway, enough of this molecular stuffbr>

Both problems solved!*The reason it's so hard for sperm to get to the egg is because only one must be allowed to do it.*If the spindle fails its task, chromosomes come adrift and monosomy and trisomy can result.6If the oocyte is keptwaiting around for a few days before fertilization, p(abnormalities of somy/ploidy) increases. Maybe this accountsfor the increases in trisomy in older women (eggs've been hanging around for years! J). The optimum is a freshlyovulated egg from a young woman.*Now the spermatozoal chromosomes are `unpacked' and the two pronuclei migrate to the centre of the egg. Thisis a zygote ­ the chromosomes are not mingled.*At the end of the first cell cycle, the pronuclei break down and the chromosomes mingle to form a diploid nucleus ­the process of syngamy. This is now an embryo.The chromosomes form up on the equator and undergo mitosis.They will not be transcriptionally active until the 4-cell stage.Implantation*As cell cleavage is occurring, the embryo moves towards the uterus (it's wafted there by the cilia of the oviduct andthe intramural sphincter opens; this is dependent solely on steroid hormones). It arrives just as the blastocyst is aboutto form ­ at the 4½­5½ day stage.*The blastocyst grows (5½­10½ d).*Luteal regression will cause loss of the embryo. Probably 50­80% of embryos are lost this way.*Human embryos make a luteotrophic signal.They put an enormous effort into making human chorionic gonado-trophin (hCG),which resembles LH.7*Before attachment, embryonic nutrition is obtained histiotrophically from uterine secretions.*In humans, attachment occurs at 7 days. The ZP is shed ­ in the human, the blastocyst digests a hole and `hatches'from the ZP.*The size of the attachment (placental structure) and the intimacy of tissue interaction depends on the species. Hu-mans have a small, discrete placenta, but the embryo invadesthe endometrium and is enveloped.8It erodes maternaltissue, including blood vessels, creating lakes of blood in which to dip its placental `fingers'. The maternal responseis called decidualization.(It probably prevents the embryo invading too far!)*Decidualization requires a uterus exposed to high progesterone levels (to maintain secretion/state of endometrium)plus a secondary oestrogen exposure (changes the secreted material; alters the surface epithelium so it can respondto the embryo9).*Up to the primitive streak stage, MZ twinning can occur. (Dizygotic twins ­ two eggs, two sperm. Monozygotictwins ­ one egg, one sperm, splits. If it splits at the 2-cell stage, you get two blastocysts; at the ICM stage you gettwo amnions and one placenta; still later, you get one amnion and one placenta.)*0.1% of the gastrulated conceptus becomes the fetus. The rest... nutritional support systems.Know this:trophectodermchorionic ectodermchorion & placenta(cyto- & syncytiotrophoblast)(together with someextra-embryonic mesoderm)inner cell mass (ICM) ^extra-embryonic ectoderm} amnion{mesoderm} }{endoderm} yolk sac & allantois{{ embryonic ectoderm}{mesoderm} embryo / fetus{endoderm}6Triploidy = 3 of all chromosomes. Trisomy = 3 of one chromosome.
Other animals: a close apposition of surface epithelium, but no invasion.
Heparin-binding epidermal growth factor (HBEGF) is made locally. The blastocyst has receptors for this and is stimulated to hatch and attach.

The process whereby the blastocyst initially attaches to the uterine endometrium at a particular site and then begins the process of implantation is still being studied. Implantation begins first with attachment (adplantation) of the blastocyst through the outer trophopoblast cells to the uterine lining. Following adplantation, trophoblast cells on the outside differentiate into syncitiotrophoblasts which invade the uterine endometrium. The blastocyst then moves moves into the endometrium, initially partially buried, and on completion of implantation, is fully buried in the endometrium. The site of implantation is marked on the surface by a "plug".There are many different sites of implantation, some of which may not even be within the uterus.Physically, following attachment, the inner cell mass is usually juxtaposed (beside) the uterine wall with the blastoceal cavity away from the wall.The uterine wall is hormonally regulated in preparation for implantation (see menstrual cycle notes) and a recent study (Stewart et al., 1992) has also shown that leukaemia inhibitory factor (LIF) secreted by the uterine glands aids in normal blastocyst implantation. This LIF may either act autocrinely on the wall or alter the blastocyst.Following Implantation the blastocyst secretes human chorionic gonadotrophin (HCG) which maintains the endometrium and therefore no menstruation occurs. The detection of HCG in the urine is the most reliable and basis of nearly all pregnancy tests.
Blastocyst has reached uterus
- remains free for short time
- zona pellucida disintegrates

- nourished by 'uterine milk' from endometrial glands
trophoblast cells
- important role in implantation:
secrete proteolytic enzymes � cavity in endometrium
sticky so adhere to endometrium
- also secretes hCG - prevents menstruation

At least 30% of all human pregnancies spontaneously fail for unknown causes. The research performed by Dr. Elliott Bedows� laboratory is dedicated to improving women�s health by clarifying the molecular basis by which the hormone human chorionic gonadotropin (hCG) facilitates embryo implantation. In doing so, he hopes to determine why this critical event in early pregnancy is so sensitive to adverse outcome.
Trophoblasts (cells surrounding the embryo which attach to the uterine wall and provide nutrition) undergo dramatic transformation during the first several days of pregnancy and ultimately lead to the development of the placenta. Dr. Bedows feels that "monitoring biochemical changes that occur within the trophoblast cells during this period will allow him to characterize events that will be predictive of pregnancy outcome." The pregnancy-induced hormone hCG is secreted by the trophoblast. Human CG appears to have two distinct roles in maintaining pregnancy. First, the earliest form of hCG expressed by trophoblasts seems to facilitate embryo implantation. This form of hCG, which is expressed 6-10 days following conception, does not efficiently stimulate ovarian progesterone production. Over the course of the subsequent week, hCG matures into a form that is capable of stimulating ovarian progesterone secretion. The second role of hCG is to stimulate ovarian progesterone secretion in quantities sufficient for the maintenance of pregnancy. If hCG does not mature from its early form into a form capable of stimulating progesterone secretion, early pregnancy loss occurs. Dr. Bedows indicated, "It is the earliest detectable form of hCG that interests us most because the genes that are regulated during embryo implantation may be the key to determining a successful pregnancy. We are now determining the identity of the genes being regulated following hCG exposure in human endometrial tissues in an attempt to better understand the role of hCG in normal pregnancy and why alterations in this process may lead to early pregnancy loss." Dr. Bedows� research is currently testing the hypothesis that the early form of hCG modulates the expression of enzymes that promote tissue remodeling (matrix metalloproteases) and proteins that stimulate new blood vessel growth, both of which contribute to embryo implantation.

At least 30% of all human pregnancies spontaneously fail for unknown causes. The research performed by Dr. Elliott Bedows� laboratory is dedicated to improving women�s health by clarifying the molecular basis by which the hormone human chorionic gonadotropin (hCG) facilitates embryo implantation. In doing so, he hopes to determine why this critical event in early pregnancy is so sensitive to adverse outcome.
Trophoblasts (cells surrounding the embryo which attach to the uterine wall and provide nutrition) undergo dramatic transformation during the first several days of pregnancy and ultimately lead to the development of the placenta. Dr. Bedows feels that "monitoring biochemical changes that occur within the trophoblast cells during this period will allow him to characterize events that will be predictive of pregnancy outcome." The pregnancy-induced hormone hCG is secreted by the trophoblast. Human CG appears to have two distinct roles in maintaining pregnancy. First, the earliest form of hCG expressed by trophoblasts seems to facilitate embryo implantation. This form of hCG, which is expressed 6-10 days following conception, does not efficiently stimulate ovarian progesterone production. Over the course of the subsequent week, hCG matures into a form that is capable of stimulating ovarian progesterone secretion. The second role of hCG is to stimulate ovarian progesterone secretion in quantities sufficient for the maintenance of pregnancy. If hCG does not mature from its early form into a form capable of stimulating progesterone secretion, early pregnancy loss occurs. Dr. Bedows indicated, "It is the earliest detectable form of hCG that interests us most because the genes that are regulated during embryo implantation may be the key to determining a successful pregnancy. We are now determining the identity of the genes being regulated following hCG exposure in human endometrial tissues in an attempt to better understand the role of hCG in normal pregnancy and why alterations in this process may lead to early pregnancy loss." Dr. Bedows� research is currently testing the hypothesis that the early form of hCG modulates the expression of enzymes that promote tissue remodeling (matrix metalloproteases) and proteins that stimulate new blood vessel growth, both of which contribute to embryo implantation


At least 30% of all human pregnancies spontaneously fail for unknown causes. The research performed by Dr. Elliott Bedows� laboratory is dedicated to improving women�s health by clarifying the molecular basis by which the hormone human chorionic gonadotropin (hCG) facilitates embryo implantation. In doing so, he hopes to determine why this critical event in early pregnancy is so sensitive to adverse outcome.
Trophoblasts (cells surrounding the embryo which attach to the uterine wall and provide nutrition) undergo dramatic transformation during the first several days of pregnancy and ultimately lead to the development of the placenta. Dr. Bedows feels that "monitoring biochemical changes that occur within the trophoblast cells during this period will allow him to characterize events that will be predictive of pregnancy outcome." The pregnancy-induced hormone hCG is secreted by the trophoblast. Human CG appears to have two distinct roles in maintaining pregnancy. First, the earliest form of hCG expressed by trophoblasts seems to facilitate embryo implantation. This form of hCG, which is expressed 6-10 days following conception, does not efficiently stimulate ovarian progesterone production. Over the course of the subsequent week, hCG matures into a form that is capable of stimulating ovarian progesterone secretion. The second role of hCG is to stimulate ovarian progesterone secretion in quantities sufficient for the maintenance of pregnancy. If hCG does not mature from its early form into a form capable of stimulating progesterone secretion, early pregnancy loss occurs. Dr. Bedows indicated, "It is the earliest detectable form of hCG that interests us most because the genes that are regulated during embryo implantation may be the key to determining a successful pregnancy. We are now determining the identity of the genes being regulated following hCG exposure in human endometrial tissues in an attempt to better understand the role of hCG in normal pregnancy and why alterations in this process may lead to early pregnancy loss." Dr. Bedows� research is currently testing the hypothesis that the early form of hCG modulates the expression of enzymes that promote tissue remodeling (matrix metalloproteases) and proteins that stimulate new blood vessel growth, both of which contribute to embryo implantation.

nvasion of the trophoblast into the endometrium, an essential element of
embryo implantation, resembles invasion of malignant tumors in many aspects,
including destruction of host tissue, erosion of blood vessels, and angiogenesis.
At the initial phase of implantation, the trophoblast and the uterine epithelium
establish their first contact via their respective apical cell membranes. Knowledge of
the mechanisms that underlie this adhesive cell-cell contact will enable us to better
understand the nature of both the trophoblast-endometrium interaction and tumor
invasion.We have identified new molecules, trophinin, tastin, and bystin, that mediate
cell adhesion between trophoblastic cells and endometrial epithelial cells at therespective apical cell membranes. Trophinin is an intrinsic membrane protein, and
tastin and bystin are cytoplasmic proteins. Bystin binds directly to trophinin, tastin, and
cytokeratin, suggesting that these molecules form a complex in trophoblastic cells and
endometrial epithelial cells. All of these molecules are strongly expressed in cells
involved in implantation whereas they are not expressed in many other
cell types in the tissues