Reproduction 3 Flashcards
Where does fertilisation usually take place?
In the uterine tube
When must sperm be introduced to the female reproductive tract & why?
5 days before ovulation
- Sperm viable for 5 days
-Oocyte vibale for 12-24 hours
Sperm is initially incapable of fertilisation, what is required?
It requires ‘capacitation’
How do oocyte and sperm compare?
Oocyte is much larger than sperm cells
How does oocyte move in the uterine tube?
- At ovulation, fluid movement causes oocyte to enter of uterine tube
- Peristaltic contractions move oocyte toward uterus for several minutes
- Activity of cilia move oocyte toward uterus for a few days
How long does it take for the oocyte to travel down the uterine tube?
Entire trip takes 4 days
Sperm must meet ovum during these 4 days
What happens if oocyte movement in the uterine tube goes wrong?
This is how an eptopic pregnancy occurs (sperm fetrilises the egg in the uterine tube
How does the sperm move in the unterine tube?
- Millions of sperm deposited into the vagina during copulation
- Swim to uterus
- Survival time in reproductive tract usually abt 5 days
- Only a few hundered sperm make it to uterine tubes
How many sperm need to break through the barrier of an oocyte?
Only 1
Where does sperm capacitation happen?
- Deposited sperm cannot fertilise oocyte
- Capacitation occurs in female reproductive tract
What happens during sperm capacitation?
- Tail movement
- Plasma membrane altered
What are the events of fertilisation? (Part 1)
- Several sperm generally reach ovum & try preventing corona radiata
- When through, bind top sperm-binding protein
- Acromosome reaction triggered, with acromosomal enzymes released
- Enzymes break thru zona pellucida allowing sperm to access oocyte
What are the events of fertilisation?
- First sperm to access oocyte binds to receptor on oocyte plasma membrane
- Sperm transported into cytoplasm = fusion
- Sperm-binding proteins become inactivated & zona pelludica hardens preventing polyspermy
What happens in fertilisation?
- Fusion stimulates 2nd meiotic division of oocyte = oocyte –> ovum
- Sperm plasma membrane disintegrates
- Chromosomes from sperm and ovum migrate to centre
- DNA repliated - zygote
What do capiciated sperm release
enzymes from their acrosomes in order to penetrate their cells and son pelludisa surrounding the egg
What happens in the fusion of sperm and egg to form zygote?
Egg and sperm nuclei fuse to form zygoye nucleus & a second polar body is produced as well
What happens in early embryonic development and implantation?
- Mitotic divisions - morula
- Cell cleavage (no increase in overall size)
- Totipotent up to 16-32 cell stage
What is a blastocyst?
- Lost zona pellicuda
- Outer cell layer = trophoblast –> will become fetal placenta
- Inner cell mass –> willl become embryo
- Fluid dilled cavity = blastocoele
What can happen in the development of the blastocyst?
At this stage quite alot of miscarrriages can happen
What happens in the implantation stage?
Occurs 6-7 days post fertilisation
Trophobast responsible for implantantation:
- Secretes enzymes that digest endometrial cellls to provide nourishment for embryo
- Secretes paracrines that stimulate decidual respone
- Infiltraes endometrial tissue to develop into placenta
What are the steps that happen during implantation?
1 - Ovulation
2 - Day 1: fertilisation
3 - Days 2-4: Cell division takes place
4 - Days 4-5: Blastocyst reaches uterus
5 - Days 5-9: Blastocyst implants
What happens when the Blastocyst Attaches to Endometrial Lining?
Endometrium swells, increases glycogen stores
What happens when the Trophoblast Penetrates Endometrium?
Trophoblast and endometrial cells will form placenta
What are the Disorders of Implantation?
Ectopic Pregnancy (1 in 300 pregnancies):
- Fertilised ovum implants in the fallopian tube
- Growth of fetus and placenta causes distension, bleeding and possible rupture
- Treat with drugs to kill fetus (subsequently reabsorbed) or surgical removal
What is gestation/preganancy?
- Covers the period from conception to birth of the fetus * Approx 9 months
- Consists of 3 (uneven) Trimesters
- The first is dated from the day of the last period - i.e. 2 weeks before conception
What are the 3 components of the blastocyst?
- Single layered sphere of cells - Trophoblast - required for implantation and develops into the fetal placenta
- Fluid filled cavity - Blastocoele - develops into the amniotic sac
- Inner cell mass - develops into fetus
After implantation what does the trophoblast form?
The two cell layer ‘chorion’
What does the two layer ‘chrorion’ do?
Produces more digestive enzymes which produce more cavities - which allows development of placenta
What are the stages of placenta development?
- Fetal component –> Chorionic Villi
- Maternal component –> Endometrial tissue
- Blood flow to placenta –> Maternal uterine artery and vein & Fetal umbilical artery and vein located in umbilical cord
What does the developing embryo float in & how does this help the embryo?
In the Amniotic fluid;
- It obtains oxygen & nutrients from the mother thru the placenta & umbilical cord
How is material exchanged into the placenta?
- Some material is exchanged across placental membrane by diffusion
- Other material must be transported
Look at the diagram of the placenta (may have to laebel it)
:)
What is the fetus like by 5 weeks?
By 5 weeks, placenta is functioning and heart is beating
What are the 3 primary functions the placental serves?
- Allows for the free exchange of energy, nutrients and waste products –> respiratory, digestive & renal functions
- Provides an immunological barrier between mother and fetus
- Secretes hormones that support the development of the fetus and prepare the mother to support the newborn child
How does the placenta providing an immulogical barrier between the mother & fetus beneficial?
Prevents rejection of father’s proteins
What are the placental hormones?
- Human Choionic Gonadotropin (hCG)
- Estrogen
- Progesterone
- Human Chorionic Somatomammotropin
- Relaxin
- Placental PTHrp (parathyroid hormone- related peptide)
What is the role of Placental PTHrp (parathyroid hormone- related peptide) in the placenta?
Inc maternal plasma Ca2+ level for use in calcifying fetal bones –> if necessary promotes localised dissolution of maternal bone
What is the role of Relaxin in the placenta
- Softens the cervix in preparation for cervical dilation at parturition
- Loosens the connective tissue between the pelvic bones
What is the role of Human Chorionic Somatomammotropin in the placenta?
- Believed to reduce maternal use of glucose and to promote breakdown of stored fat (like growth hormones) - more glucose and free fatty acids available to fetus
- Helps prepare the mammary glands for lactiation
What is the role of progesterone in the placenta?
- Suppresses uterine contractions to provide a quiet environment for the fetus
- Promotes formation of a cervical mucus plug to prevent uterine contamination
- Helps prepare the mammary glands for lactation
What is the role of estrogen in the placenta?
- Stimulates growth of the myometrium, increasing uterine strength for parturition
- Helps prepare the mammary glands for lactation
What is the role of Human Chorionic Gonadotropin (hCG)?
- Maintains the corpus luteum of pregnancy
- Stimulates the secretion of testosterone by the developing testes in XY embryos
Look at the hormonal changes during preganancy slide
I can’t insert the graphs
How is ovulation prevented during pregnancy?
Progesterone inhibits GnRH, LH, and FSH release, preventing LH surge
What develops in the fetus at 4 weeks?
Spinal cord & heart
(weight = <1g)
What develops in the fetus at 8 weeks?
- Head & Facial Features (eyes & nose)
- Arms & Legs
- All internal organs - heart beat detectable
-Reflexes develop
(weight = 3g)
What develops in the fetus at 12 weeks?
- Sexual differentiation complete
- Development of bones
- Fine hairs on body
- Fingers & toes discernible
- Splenic production of Red Blood Cells begins
(weight = 48g)
What develops in the fetus at 16 weeks?
- Superficial blood vessels observed
- Ears & hearing develops
- Lungs breathe amniotic fluid
- Finger nails discernible
- Facial expressions observed
(weight = 180g)
What develops in the fetus at 20 weeks?
- Skin sensitive to touch
- Movement more coordinated - stretching, grasping & turning
- Sebaceous glands operational
(weight = 500g)
What develops in the fetus at 24 weeks?
- Brain waves resemble that of newborn child and evidence of patterns of sleep & wake
- Detects and recognises external sound
(weight = 1kg)
What develops in the fetus at 32 weeks?
- Thermoregulatory mechanisms partially operational
- Deposition of adipose tissue
- Plenty of movement
- Lungs able to function ex utero
(weight = 2kg)
What is the 10th & 90th percentile of appropriate size fr gestational age at birth?
10th = 5.5lbs
90th = 8.8lbs
What are the maternal changes during the first trimester of pregnancy (weeks 1-14)?
- Associated w a 10-25% increase in metabolic activity & 1-2 kg weight gain
- Inc in Cardiac Output, Heart Rate, Respiration & Blood Volume
- Inc in breast size (action of hormones)
- Inc in uterus - presses on bladder
- ‘Morning sickness’ and loss of libido
What are the maternal changes during the second trimester of pregnancy (14-28 weeks)?
- Increase in weight (approx 6 kg) - loss of waistline
- Heartburn - progesterone-induced relaxation of oesophageal muscle
- Constipation - progesteron-induced relaxation of intestinal muscle
- General improvement in well-being
- Feel movement of baby, return of libido, improved skin tone
What are the maternal changes during the third trimester of pregnancy (29 weeks - birth)?
- Deeper breaths - baby reduces abdominal movements of diaphragm
- Braxton-Hicks contractions of the uterus - preparation for child birth
- Tired and anxious
What are the 3 disorders of pregnancy?
- Pre-eclampsia & Eclampsia
- Eclampsia = ‘like a flash of lightening’
- Diabetes mellitus
What is Pre-eclampsia & Eclampsia?
Elevated blood pressure in 15% of woman
- Compromises blood flow to fetus
- Requires plenty of bed rest and even sedation
What is Eclampsia (‘like a flash of lightening’)?
Large and rapid increase in blood pressure associated with water and sodium retention
- Life threatening to mother and fetus
- Precipitated by fetal factor as blood pressure drops post parturition
- Yreat aggressively with anti-hypersensitive agents or terminate pregnancy
What is diabetes mellitus?
- 1/350 pregnancies
- Danger to both fetus and mother
