Fertilization, Pregnancy and Parturition - Physiology and Anatomy - Lecture Slides, Slides for Physiology. Amity Business School

Physiology

Description: This lecture is taken from the slides of Physiology. Key important points are: Fertilization, Pregnancy and Parturition, Fallopian Tubes, Capacitation, Female Reproductive Tract, Acrosome of Sperm, Acrosomal Reaction, Cleavage and Blastocyst Formation, Trophoblast Cells
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Fertilization, Pregnancy, & Parturition

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Fertilization

• Normally occurs in fallopian tubes • Ejaculation produces ~300 million sperm; only 100

reach each fallopian tube • Freshly ejaculated sperm are infertile

– Must spend >7hrs in female reproductive tract to be fertile

• Process is called capacitation

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Fertilization continued

• Acrosome of sperm contains enzymes that digest a channel through zona pellucida to oocyte (acrosomal reaction)

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Fertilization continued • As 1st sperm fuses

with membrane of 2o oocyte, changes occur preventing another fertilization

• 2o oocyte completes meiosis II, producing a mature ovum + polar body

• Sperm enters ovum cytoplasm, ovum nuclear membrane disappears & diploid zygote forms

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Fig 20.40 Docsity.com

Cleavage and Blastocyst Formation • About 30-36 hrs after

fertilization, zygote divides by mitosis (= cleavage) into 2 cells

• About 50-60 hrs after fertilization, early embryo develops into 8 cell morula – Which enters uterus 3 days

after ovulation

• Morula becomes a blastocyst which implants on 6th day

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Fig 20.42 Docsity.com

Blastocyst

• Blastocyst has inner cell mass which will become fetus & surrounding chorion whose trophoblast cells form placenta

• Trophoblast secretes enzymes that allow blastocyst to digest its way into endometrium – 75% of lost pregnancies

result from failure to implant

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Embryonic Stem Cells and Cloning • Only fertilized egg cells & early cleavage cells are totipotent

– That is, has ability to create an entire organism • Reproductive cloning involves transplanting adult nucleus

into cytoplasm of a totipotent cell – Which reprograms it to be totipotent – This has been used to clone many animals

• Embryonic stem cells (ESCs) are derived from inner cell mass of blastocyst – These are pluripotent (can give rise to all cells except trophoblast)

• Adult stem cells are multipotent (can give rise to a limited number of cell types)

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Human Chorionic Gonadotropin (hCG) • CL survives & pregnancy is

maintained because blastocyst secretes hCG even before implantation

• hCG is similar to LH & keeps CL from degenerating – Maintains E & P levels

• Early pregnancy tests detect hCG

• hCG declines by 10th wk – Is only required for 1st 6 wks

at which time E & P from placenta take over

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Amniocentesis

• Usually performed at ~16 wks

• Amniotic fluid contains cells sloughed off fetus, placenta, & amniotic sac – Genetic abnormalities can

be detected by aspiration of this fluid (amniocentesis) & examination of cells

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Exchange of Molecules Across Placenta

• Embryo & placenta are immunologically privileged (protected from rejection) – In part because fetal &

maternal blood do not mix • Placental circulation is via

umbilical artery & vein • Maternal blood is delivered

to cavities of decidua basalis

• Gas, nutrients, & wastes are exchanged without mixing of blood

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Placental Hormones

• Include hCG & hCS (chorionic somatomammotropin) – hCS acts like GH & prolactin – hCS & maternal GH cause diabetic-like effect, promoting

lipolysis & glucose sparing in mother • This increases blood glucose, resulting in polyuria, thirst, &

dehydration • Ensures supply of glucose for placenta & fetus

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Placental Hormones continued • After CL regresses, placenta secretes large amounts of E & P

– That are derived from precursors supplied by fetus & mother • P is synthesized from cholesterol from mother • Fetus converts some of this P to androgens which placenta converts to E

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Labor

• Is physical work necessary to expel fetus during parturition (childbirth)

• Uterine contractions are stimulated by oxytocin & prostaglandins (PGs) – Oxytocin comes from Post Pit & uterus – PGs come from uterus

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Labor continued

• Initial stimulus for labor is not understood but involves rising levels of androgens from fetus being converted to high levels of estrogens from placenta – Which induce gap junctions in uterine smooth muscle

• & oxytocin & PG receptors in uterus – Making it more sensitive to these hormones

– Initiation may start with CRH from placenta stimulating ACTH release from Ant Pit

• Which increases cortisol & androgen secretion by adrenal

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Lactation

• Nursing is part of neuroendocrine reflex

• Suckling causes release of prolactin & oxytocin – Oxytocin from Post

Pit causes milk letdown reflex

• By stimulating contraction of lactiferous ducts

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