LECTURE 9 (Pregnancy and lactation) Flashcards
Describe the fertilisation of the Ovum
1) Transport of sperm to the AMPULLA of Fallopian tubes is aided by contractions of uterus + Fallopian tubes stimulated by PROSTAGLANDINS in male seminal fluid + OXYTOCIN released during female orgasm
2) In ampulla, sperm penetrates the CORONA RADIATA + binds to and penetrates the ZONA PELLUCIDA
3) Sperm enters ovum (still in secondary oocyte stage), oocyte divides to form MATURE OVUM + SECOND POLAR BODY that is expelled. Female pronucleus + male pronucleus combine to form FERTILISED OVUM (46 chromosomes)
Describe the transport of the fertilised ovum in the Fallopian tube
- normally takes 3-5 days to transport into uterus
- effected by fluid current from epithelial secretion + ciliated epithelium + weak contractions of Fallopian tube
- isthmus is contracted to prevent entry into uterus until increase in progesterone relaxes muscle cells to allow entry
- delayed transport allows cell division of ovum into BLASTOCYST
Before implantation, where does the blastocyst obtain its nutrition from?
Uterine endometrial secretions, also called “uterine milk”
How does Implantation occur?
1) It happens from the action of the TROPHOBLAST CELLS that develop over the surface of the blastocyst -> cells secrete proteolytic enzymes that digest + liquefy adjacent cells of uterine endometrium
2) Fluid + nutrients released are actively transported by trophoblast cells into blastocyst
[sustenance for growth]
3) Once implantation has occurred, trophoblast cells and other cells proliferate rapidly forming the PLACENTA
ADDITIONAL INFO:
developing blastocyst remains in uterine cavity for 1-3 days so implantation usually occurs 5th-7th day after ovulation
Where does the embryo get its early nutrition from?
- Continuous secretion of progesterone cause endometrial cells to swell further + store even more nutrients and are now called “decidual cells”/decidua
[embryo uses for growth + development] - Placenta
[from 16th day after fertilisation]
Describe the development of the placenta
Trophoblastic cords from the blastocyst attach to uterus + blood capillaries grow into cords from vascular system -> 21 days after fertilisation, blood is pumped by heart of human embryo -> Blood sinuses supplied with blood from mother develop around outside of trophoblastic cords -> Trophoblast cells send out more projections becoming PLACENTAL VILLI -> Villi carrying foetal blood are surrounded by sinuses that contain maternal blood
Describe the physiological anatomy of the placenta
FOETUS: Foetus’ blood flows through two umbilical arteries, then into the CAPILLARIES OF THE VILLI and through a single UMBILICAL VEIN into the foetus
MOTHER: Mother’s blood flows from her UTERINE ARTERIES into large MATERNAL SINUSES that surround villi + back into UTERINE VEINS of mother
What is the major function of the placenta?
To provide for diffusion of nutrients and oxygen from the mother’s blood into the foetus’ blood and diffusion of excretory products from the foetus back into the mother
What are the properties of the placenta during pregnancy?
- In early pregnancy has low diffusion conductance since thick + small surface area -> diffusion increases since surface area expands + thinning of membrane
- “breaks” occur in membrane, allows foetal blood to pass into mother or transport as much oxygen to foetal tissues as much as the mother’s
[foetal blood carries more O2 than mother]
How is the foetus capable of receiving more than adequate oxygen through the placental membrane?
- Foetal haemoglobin is shifted to the LEFT of the curve -> at the low Po2 levels in foetal blood, foetal haemoglobin can carry 20-50% more oxygen than maternal haemoglobin
- Haemoglobin concentration is 50% greater than that of mother
- “DOUBLE BOHR EFFECT”
[haemoglobin can carry more O2 at a low Pco2 than at a high Pco2 -> foetal blood entering the placenta carries large amounts of CO2 which diffuses into mother’s blood -> loss of CO2 makes foetus blood more alkaline, increase CO2 makes maternal blood more acidic -> capacity of foetal blood to combine with O2 increases + maternal blood decreases -> forces more O2 from maternal blood + enhance O2 uptake by foetal blood]
How does glucose diffuse from the mother to the foetus?
Trophoblast cells lining the placental villi provide for facilitated diffusion of glucose through the placental membrane via carrier molecules in the trophoblast cells
ADDITIONAL INFO:
In the late stages of pregnancy, the foetus uses as much glucose as the entire body of the mother uses
What waste product is significantly higher in the foetus than the mother?
Creatinine
EXPLANATION: urea diffuses across the placenta with great ease but creatinine does not diffuse as easily. There is continual diffusion of these substances into the mother’s blood though since its higher in the foetus’ blood (diffusion gradient)
What is the importance of the Human Chorionic Gonadotropin hormone?
- prevents menstruation which could terminate pregnancy (stabilises endometrium lining)
- secreted by SYNCYTIAL TROPHOBLAST CELLS
- can be measure 8-9 days after ovulation (shortly after blastocyst implantation)
- maximum at 10-12 weeks then decreases at 16-20 weeks and continues at this level for remainder of pregnancy
What is the function of the Human Chorionic Gonadotropin hormone?
- prevents involution of corpus luteum
[removal of corpus luteum up to 12th week can cause spontaneous abortion] - causes corpus luteum to secrete more oestrogens + progesterone
[prevent menstruation + cause endometrium to continue to grow + store large amounts of nutrients forming “decidual cells”] - results in production of testosterone in male foetus -> formation of male sex organs + near end of pregnancy, causes testes to descend from scrotum
Where are oestrogens and progesterone secreted in the placenta?
Syncytial trophoblast cells
