Conception Fertilisation (also known as conception, fecundation and syngamy), is the fusion of gametes to produce a new organism. In animals, the process involves the fusion of an ovum with a sperm, which eventually leads to the development of an embryo. Depending on the animal species, the process can occur within the body of the female in internal fertilisation, or outside in the case of external fertilisation. 2
Sperm transport Semen is ejaculated into vagina, cervical and may reach cervical canal Semen coagulate by coagulating enzymes from prostate gland which interacts with fibrinogenous substrate from seminal vesicles Coagulum protects spermatozoa from vaginal acidity and prevent loss of spermatozoa Coagulum liquefies after 15 to 20 minutes Liquefaction time is one criteria for semen quality Sperm may live up to 48 – 72 hours in female reproductive tract. 5
Barriers (1) Spermatozoa have to confront three barriers before reaching ampulla, the site for fertilization First barrier – cervical mucus Mucus will filter and choose spermatoza – dead and immotile spermatozoa are discarded, normal spermatozoa are stored in the cervical crypts (first reservoir) Filtered spermatozoa discarded in the vaginal secretion post-coital Consistency of cervical mucus assist in sperm motility upwards Mucus thick, sperm could not penetrate Mucus thin and more stringy, sperm is assisted in motility by swimming in channels form by the mucus
Barriers (2) Endometrial glands – second barrier Will choose and filter spermatozoa Chosen spermatozoa are stored here (second reservoir) Here, capacitation occurs due to prostaglandins from endometrium
Barriers (3) Third barrier – utero-tubal junction Chosen spermatozoa are finally stored in the isthmus (third reservoir) to wait for the ovum to travel down Ovulated ovum will be caught by infundibulum when fimbriae comes close to ovary Ovum will travel down the infundibulum to the ampulla by oviductal contraction and presence of cilia
Capacitation (1) A time dependent phenomenon which is species- specific Takes more than 24 hours in human Reversible process (if capacitated spermatozoa are placed in epididymal fluid or seminal plasma, will be decapacitated – contains decapacitating factor) only in vitro Must occur to enable acrosome reaction to occur Substances like cholesterol, glycosaminoglycans and glycoproteins are stripped from plasma membrane of sperm head
Capacitation (2) Two elements in this process:t Hyperactivated motility – sperm starts to show whiplashing movement to enable sperm to move forward fasterr Change to membrane surface – membrane stability decreases. More permeable to calcium ions. Tyrosine kinase activity increases. Adenyl cyclase activity in spermatozoa heightens and causes protein phosphorylation which are cAMP dependent
Acrosome reaction Occurs right after capacitation Totally dependent on calcium uptake into cells and increase in intracellular pH (pH 7.1 to pH 7.5) The acrosome swells and the outer acrosomal membrane fuses with the overlying plasma membrane Vesiculation occurs and pores are formed Acrosomal contents (hyaluronidase, acrosin etc) are released
Acrosome reaction Two types: True acrosome reaction – reaction occurs at zona pellucida False acrosome reaction – degeneration of sperm due to death (enzymes from acrosome will self-desctruct sperm)
Initiators of the acrosome reaction (1) High calcium influx ZP3 (zona pellucida glycoprotein 3) Progesterone etc ZP3 in ovum will bind to sperm binding protein (receptor) on sperm plasma membrane This binding site may contain galactosyl transferase activity When binding occurs, G protein involvement will stimulate calcium influx and the rise in pH initiates the acrosome reaction
Initiators of the acrosome reaction (2) Progesterone will also stimulate calcium influx which then stimulates adenyl cyclase and cAMP Progesterone can stimulate acrosomal leakage to release hyaluronidase Hyaluronidase will digest hyaluronic acid which binds cumulus cells When these cells breaks apart, spermatozoa can bind to zona pellucida Progesterone has been reported to initiate capacitation also
Sperm binding properties to zona Outer acrosomal membrane has receptor to ZP3 Inner acrosomal membranes has receptor to ZP2 Equatorial segment and post-acrosomal region is the part of the spermatozoon that enters the ovum Tail and midpiece left outside ovum
Gamete fusion Sperm penetration of the zona takes between 5-20 minutes Sperm lies tangent at the ovum surface between the zona pellucida and oolemma at the perivitelline space Microvilli at the oocyte surface will engulf the sperm head The equatorial segment and the post-acrosomal region of the sperm fuses with the ovum After fusion, zygote forms and male and female pronuclei Syngamy occurs when both male and female chromosomes combines and then form 2-cell conceptus
Embryonic development (1) Germinal period (movement of zygote and implantation in uterus) lasts two weeks Cleavage occurs - 1 cell to 2 daughter cells after 36 hours post fertilization Daughter cells called blastomeres Zygote still covered by ZP ZP inhibits blastomeres from falling apart If this happens, two possibilities occur7. Monozygotic twins8. Chimaeras Chimaeras is the fusion of two different zygotes from two fertilized ovum – two sets of two different genotype
Embryonic development (2) Blastomeres becomes morula on day 3 Progesterone from functioning CL will stimulate the release of glycogen from endometrium for energy to developing embryo (histiotropic nutrition) High levels of progesterone also inhibit oviductal constriction to enable morula to move towards the uterus by peristaltic contraction and cilia movement Becomes blastocyst on day 4 - 5
Embryonic development (3) Blastocysyt has fluid-filled cavity (blastocoele) Has inner cell mass (ICM) surrounded by trophodectum (trophoblast) ICM will form extra embryonic membranes (amnion, yolk sac etc) and fetus Trophoblast forms chorion Blastocyst floats in uterine cavity for 1 – 2 days Prior to implantation, will shed ZP by enzymatic digestion
Implantation (1) A nutritional and physical contact between fetus and mother Blastocyst surface becomes sticky Trophoblastic cells (cytotrophoblast) releases enzymes to digest proteins on endometrium Syncytiotrophoblast enters endometrium to suck up metabolic fuel and nutrients Deep invasion into endometrium occurs Change to endometrium occurs (stromal reaction/primary decidualization reaction) Endometrium releases prostaglandins to stimulate vascularization causing edema and increasing nutrient stores
Implantation (2) The invaded part of the endometrium is called decidua 2 –3 days post invasion, decidua enlarges to become secondary decidua Blastocyst enters this decidua After entry, a layer of endometrial cells will cover and bury the blastocyst Syncytiotrophoblast on the other hand keep on digesting endometrial cells to get nutrients until the placenta is formed
Multiple pregnancy Multiple pregnancy is a pregnancy with two or more fetuses. Twins - 2 fetuses, Triplets - 3 fetuses, Quadruplets - 4 fetuses, Quintuplets - 5 fetuses, Sextuplets - 6 fetuses and Septuplets - 7 fetuses Naturally occurring factors causing multiple pregnancy are: heredity A family history of multiple pregnancy increases the chances of having twins older age Women over 30 have a greater chance of multiple conception. high parity Having one or more previous pregnancies, especially a multiple pregnancy, increases the chances of having multiples. race African-American women are more likely to have twins than any other race. Asian and Native Americans have the lowest twinning rates. Caucasian women, especially those over age 35, have the highest rate of higher-order multiple births (triplets or more).
How to detect pregnancy? Urine test – detect hCG Blood test – detect hCG Ultrasound Milk test – P4 Blood test - PMSG
•The hCG Urine Pregnancy TestStrip is a test kit based on a visual,qualitative principle for thedetermination of hCG (HumanChorionic Gonadotropin) aglycoprotein hormone secreted bythe developing placenta afterfertilization in urine specimens.• Pregnancy Test Strips are over99% accurate and are capable ofdetecting hCG, at levels of just20mIU/ml/hCG. Can test accurately6 to 8 days after conceiving - and 7days after missed period.•The appearance of hCG soon afterconception and its subsequent risein concentration during earlygestational growth make it anexcellent marker for the earlydetection of pregnancy
hCG The developing placenta begins releasing hCG into blood as early as 6 days after implantation.Some hCG also gets passed in the urine. HCG helps to maintain pregnancy and affects the development of fetus. Levels of hCG increase steadily in the first 14 to 16 weeks following last menstrual period (LMP), peak around the 14th week following LMP, and then decrease gradually. The amount that hCG increases early in pregnancy can give information about pregnancy and the health of the baby. Shortly after delivery, hCG can no longer be found blood. More hCG is released in a multiple pregnancy, such as twins or triplets, than in a single pregnancy. Less hCG is released if the fertilized egg implants in a place other than the uterus, such as in a fallopian tube. This is called an ectopic pregnancy.
•An ultrasound test is a radiologytechnique, which uses high- frequencysound waves to produce images of theorgans and structures of the body. Itinvolve no radiation and studies havenot revealed any adverse effects.•The sound waves are sent throughbody tissues with a device called atransducer placed directly on top of theskin, which has a gel applied to thesurface.•The sound waves that are sent by thetransducer through the body are thenreflected by internal structures as"echoes." which return to thetransducer and are transmittedelectrically onto a viewing monitor.
Fetus formation Gene dependant Size dependant on nutrition and health of mother, parity (primiparous mothers have small babies as compared to multiparous mothers), mother’s size, pregnant more than one baby and self-damage caused by smoking, drug addiction, alcoholic etc Small sized baby is due to prematurity or even if full-term, there must be a factor to cause a retarded growth for the baby
Fetal Development Heart and brain develop from 3rd week Heart starts to pump blood from week 4-5 Feet and hands starts to develop and tail at coccxy starts to shrink Embryo is less than an inch long at week 5 Hands and feet is visible and nose also starts to form At week eight, it is about an inch long By week 9, embryo is called a fetus Sexual organs starts to form but sex is not yet determine Other organs also starts to form and develop until birth
Rate of fetal growth is slow until week 20 but accelerate to a maximum at week 30-36 Peak of growth velocity is on week 8 Fetal nutrition is from CHO (glucose), amino acids and lactate. Fatty acids, vitamins and minerals are also transferred to the fetus via the placenta
Gestation length: 280 days or 40 weeks or 9 months and 10 days LMP – Last Menstrual Period EDD – Estimated Delivery Date (First day of last menstrual period plus 280 days) Trimester – 3 months Human – 3 trimesters
Factors affecting gestation length Maternal factor – age of mother Fetal factor – number of fetuses, gender, adrenal and pituitary function Genetic – species, breed, fetal genotype Environmental factors – nutrition, temperature, season
Physical changes during pregnancy No menstruation Nausea in first trimester Back and hip pains Increase in body weight Pigmentation of skin especially in fair-skinned women (choalasma – mask of pregnancy) especially at the facial region ‘Quickening’ or baby movements in uterus – occurs at 5 months pregnancy onwards ‘Braxton-Hicks contraction at 6-7 months pregnancy Others eg pica (Pica is a pattern of eating non-food materials such as dirt or paper and should last at least 1 month to fit the diagnosis of pica.)
Abnormal pregnancies – Ectopicpregnancy Occurs when a fertilized egg attaches somewhere other than in the uterus, usually in a fallopian tube (tubal pregnancy). Because an ectopic pregnancy can cause life-threatening complications, the pregnancy must be ended with medicine or surgery. An ectopic pregnancy, especially a tubal pregnancy, can be dangerous because the fallopian tube does not stretch as the fertilized egg grows. If a tubal pregnancy is not detected and treated early, the tube may burst. This can be a life-threatening situation and requires emergency surgery. Pelvic inflammatory disease or tubal surgery increases the risk of having an ectopic or tubal pregnancy by creating scar tissue that may block the fallopian tube.
Abnormal pregnancies – Molar pregnancy A mass of abnormal tissue (hydatidiform mole) that comes from the placenta inside the uterus, which triggers symptoms of pregnancy. About 1 out of 1,000 women with early pregnancy symptoms has a molar pregnancy. There are two types of molar pregnancy: complete and partial. Complete molar pregnancy. In place of a normal placenta/embryo, the hydatidiform mole is abnormal placental tissue that grows into a grapelike cluster that can fill the uterus. Partial molar pregnancy. The placenta grows abnormally into molar tissue. Any fetal tissue that develops is likely to have severe defects.