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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.

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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

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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

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Barriers (2)

Endometrial glands – second barrierWill choose and filter spermatozoaChosen spermatozoa are stored here

(second reservoir)Here, capacitation occurs due to

prostaglandins from endometrium

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Barriers (3)

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

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Capacitation (1)

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

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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

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Acrosome reaction

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

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Acrosome reaction

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)

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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

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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

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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

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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

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Formation of male and female pronuclei

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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

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Fertilized egg 2 cell stage

4 cell stage 8 cell stage

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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

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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

enzymatic digestion

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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

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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

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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).

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How to detect pregnancy?Urine test – detect hCGBlood test – detect hCGUltrasoundMilk test – P4Blood test - PMSG

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•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

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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.

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•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.

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Week 5

Week 8

Week 11

Twins

Twins kicking

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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

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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

birth

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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

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Factors affecting fetal growthGenetic (species, breed, genotype)Environmental (nutrition, size, parity, size

and blood circulation of placenta)Fetal hormones (thyroid, growth hormone,

somatomedins)

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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

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Factors affecting gestation lengthMaternal factor – age of motherFetal factor – number of fetuses, gender,

adrenal and pituitary functionGenetic – species, breed, fetal genotypeEnvironmental factors – nutrition,

temperature, season

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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.)

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Development of embryo and fetus

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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.

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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.