Transcript of Tot presentation
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.
Sperm transportSemen is ejaculated into vagina, cervical and
may reach cervical canalSemen 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 minutesLiquefaction time is one criteria for semen
qualitySperm 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 mucusMucus 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 penetrateMucus thin and more stringy, sperm is
assisted in motility by swimming in channels form by the mucus
Endometrial glands – second barrierWill choose and filter spermatozoaChosen spermatozoa are stored here
(second reservoir)Here, capacitation occurs due to
prostaglandins from endometrium
Third barrier – utero-tubal junctionChosen 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
A time dependent phenomenon which is species-specific
Takes more than 24 hours in humanReversible 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:1. Hyperactivated motility – sperm
starts to show whiplashing movement to enable sperm to move forward faster
2. 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
Occurs right after capacitationTotally 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
Two types:True acrosome reaction – reaction
occurs at zona pellucidaFalse acrosome reaction –
degeneration of sperm due to death (enzymes from acrosome will self-desctruct sperm)
Initiators of the acrosome reaction (1)
High calcium influxZP3 (zona pellucida glycoprotein 3)Progesterone etcZP3 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 fusionSperm penetration of the zona takes between
5-20 minutesSperm 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
Formation of male and female pronuclei
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 occur1. Monozygotic twins2. Chimaeras
Chimaeras is the fusion of two different zygotes from two fertilized ovum – two sets of two different genotype
Fertilized egg 2 cell stage
4 cell stage 8 cell stage
Embryonic development (2)Blastomeres becomes morula on day 3Progesterone 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
daysPrior to implantation, will shed ZP by
Implantation (1)A nutritional and physical contact between
fetus and motherBlastocyst surface becomes stickyTrophoblastic cells (cytotrophoblast)
releases enzymes to digest proteins on endometrium
Syncytiotrophoblast enters endometrium to suck up metabolic fuel and nutrients
Deep invasion into endometrium occursChange 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 decidua2 –3 days post invasion, decidua
enlarges to become secondary decidua Blastocyst enters this deciduaAfter entry, a layer of endometrial cells
will cover and bury the blastocystSyncytiotrophoblast 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:i. heredity
A family history of multiple pregnancy increases the chances of having twins
ii. older ageWomen over 30 have a greater chance of multiple conception.
iii. high parityHaving one or more previous pregnancies, especially a multiple pregnancy, increases the chances of having multiples.
iv. raceAfrican-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 hCGBlood test – detect hCGUltrasoundMilk test – P4Blood test - PMSG
•The hCG Urine Pregnancy Test Strip is a test kit based on a visual, qualitative principle for the determination of hCG (Human Chorionic Gonadotropin) a glycoprotein hormone secreted by the developing placenta after fertilization in urine specimens.
• Pregnancy Test Strips are over 99% accurate and are capable of detecting hCG, at levels of just 20mIU/ml/hCG. Can test accurately 6 to 8 days after conceiving - and 7 days after missed period.
•The appearance of hCG soon after conception and its subsequent rise in concentration during early gestational growth make it an excellent marker for the early detection of pregnancy
hCGThe 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 radiology technique, which uses high- frequency sound waves to produce images of the organs and structures of the body. It involve no radiation and studies have not revealed any adverse effects.
•The sound waves are sent through body tissues with a device called a transducer placed directly on top of the skin, which has a gel applied to the surface.
•The sound waves that are sent by the transducer through the body are then reflected by internal structures as "echoes." which return to the transducer and are transmitted electrically onto a viewing monitor.
Fetus formationGene dependantSize 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 DevelopmentHeart and brain develop from 3rd weekHeart starts to pump blood from week 4-5Feet and hands starts to develop and tail at coccxy
starts to shrinkEmbryo is less than an inch long at week 5Hands and feet is visible and nose also starts to formAt week eight, it is about an inch longBy week 9, embryo is called a fetusSexual organs starts to form but sex is not yet
determineOther organs also starts to form and develop until
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 8Fetal nutrition is from CHO (glucose), amino
acids and lactate. Fatty acids, vitamins and minerals are also transferred to the fetus via the placenta
Factors affecting fetal growthGenetic (species, breed, genotype)Environmental (nutrition, size, parity, size
and blood circulation of placenta)Fetal hormones (thyroid, growth hormone,
Gestation length: 280 days or 40 weeks or 9 months and 10 days
LMP – Last Menstrual PeriodEDD – Estimated Delivery Date (First day of
last menstrual period plus 280 days)Trimester – 3 monthsHuman – 3 trimesters
Factors affecting gestation lengthMaternal factor – age of motherFetal factor – number of fetuses, gender,
adrenal and pituitary functionGenetic – species, breed, fetal genotypeEnvironmental factors – nutrition,
Physical changes during pregnancyNo menstruationNausea in first trimesterBack and hip painsIncrease in body weightPigmentation 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 pregnancyOthers 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.)
Development of embryo and fetus
Abnormal pregnancies – Ectopic pregnancyOccurs 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 pregnancyA 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.