Reproduction: fertilisation and implantation - pregnancy and development Flashcards
Where does fertilisation take place?
Uterine tube
When must sperm be introduced to the female and what are the time spans involved? (3)
- sperm must enter 5 days before ovulation
- sperm viable for 5 days
- oocyte available for 12-24 hours
What are the movements of the oocyte in the uterine tube? (4)
- fluid causes oocyte to move at ovulation
- peristaltic contractions move oocyte towards uterus - minutes
- Cilia move oocyte towards uterus - days
- Entire trip takes 4 days
What are the sperm movements in the uterine tube? (4)
- Millions of sperm deposited into vagina during sex
- Swim to uterus and uterine tube
- Survive 5 days in tract
- Only few hundred sperm make it to uterine tube
How can sperm become capacitated and where does this occur?
- Occurs in reproductive tract
- Tail movement causes plasma membrane to be altered
What are the events of fertilisation before the egg is penetrated? (4)
- Several sperm generally reach ovum and penetrate corona radiata
- Sperm bind to sperm-binding protein
- Acrosome reaction triggered - acrosomal enzymes released
- Enzymes break through zona pellicuda allowing sperm to access oocyte
What are the events of fertilisation after the egg is first penetrated? (3)
- First sperm to access oocyte binds to receptor on plasma membrane
- Sperm transported into cytoplasm - fusion
- Sperm-binding proteins become inactivated and zona pellucida hardens to stop other sperm
What are the events of fertilisation once the sperm has fully penetrated the egg and pre zygote formation? (5)
- Fusion stimulates 2nd meiotic division of oocyte
- Oocyte –> ovum
- Sperm plasma membrane disintegrates
- Chromosomes from sperm and ovum migrate to centre
- DNA replication –> zygote
What are the 3 stages 3-4 days post fertilisation?
- Zygote
- Early cleavage (4-cell stage)
- morula (mitotic divisions - still totipotent)
What and when does a blastocyst occur? (5)
- Zona pellucida is lost
- Outer cell layer = trophoblast (becomes placenta)
- Inner cell mass (becomes embryo)
- Fluid filled cavity = blastyocoele
4-5 days post fertilisation
What is implantation and when does it occur? (5)
6-7 days post fertilisation
- Trophoblast responsible for implantation
- Secretes enzymes that provide nourishment for embryo
- Secretes paracrines that stimulate decidual response
- Infiltrates endometrial tissue (placenta)
What does the blastocyst attach itself too and what does this lead to? (2)
- Endometrial lining (increases glycogen stores)
- Trophoblast penetrates endometrium
What disorders can arise from implantation? (3)
Ectopic pregnancy:
- Fertilised ovum implants in fallopian tube
- Growth of fetes and placenta causes issues
- Have to kill/remove fetus
What is gestation and how long does it last? (4)
- Period from conception to birth
- 9 months
- Consists of 3 trimesters
- Dated from last period before conception
What are the 3 components of a blastocyst?
- Single layered sphere of cells (trophoblast) required for implantation
- Fluid filled cavity (blastocoele) develops into amniotic sac
- Inner cell mass - develops into fetus
What does the trophoblast form once implanted? (2)
Chorion (2 layers)
Produces more digestive enzymes which produce more cavities - placenta development
What are the stages of placenta development? (3)
Fetal component - chorionic villi
Maternal component - endometrial tissue
Blood flow to placenta - uterine artery and vein/umbilical
What is the placenta doing after 5 weeks? (2)
Heart beating
Breathing
What is the role of the placenta? (3)
- Allows for free exchange of nutrients, energy & waste
- Provides an immunological barrier between mother and fetus
- Secretes hormones that support the development of the fetus
What are the 6 placental hormones?
Human Chorionic gonadotrophin Estrogen Progesterone Human Chorionic somatotrophin Relaxin Placental PTHrp
What prevents further ovulation during pregnancy?
Progesterone - inhibts GnRH, LH and FSH
What are the maternal changes during the first trimester of pregnancy? (6)
- First trimester - 1-14 weeks
- 1-2kg weight gain
- Increased cardiac output etc
- Increased breast size
- Increase in uterus
- Morning sickness
What are the maternal changes during the second trimester of pregnancy? (5)
- 2nd trimester 14-28 weeks
- Increase of weight
- Heartburn
- Constipation
- Improvement of wellbeing
What are the maternal changes during the third trimester of pregnancy? (3)
- Deeper breaths
- Braxton-Hicks contractions of the uterus
- Tired and anxious
What is eclampsia? (4)
- Pregnancy disorder
- Elevated blood pressure
- Rapid increase
- Life threatening
What are the 2 main disorders of pregnancy?
- Eclampsia
- Diabetes melitus
