1. Physiology of Pregnancy
Department of Physiology
School of Medicine
University of Sumatera Utara

2. Endometrium and Desidua
3 days to move to uterus
3 -5 days in uterus before implantation

3. Implantation results from the action of trophoblast cells that develop over the surface of the blastocyst.
These cells secrete proteolytic enzymes that digest and liquefy the adjacent cells of the uterine endometrium.
Once implantation has taken place, the trophoblast cells and other adjacent cells (from the blastocyst and the uterine endometrium) proliferate rapidly, forming the placenta and the various membranes of pregnancy.

4. Making the connection to Mom

6. Blastocyst: Inner Cell Mass: Trophoblast:
A fluid filled sphere of cells formed from the morula which implants in the endometrium.
Inner Cell Mass:
A group of cells inside of the blastocyst from which the three primary germ layers will develop.
Objective 11
A blastocyst * is a hollow, fluid filled sphere of cells formed from the morlula. * The blastocyst implants in the thickened uterine wall, the endometrium. *
The inner cell mass * is the mass of cells inside the blastocyst * from which the three primary germ layers develop. *
A trophoblast * is the name of the single layer of cells making up the outer wall of the blastocyst. * The trophoblast cells, eventually form the chorion. * *
Trophoblast:
One of the cells making up the outer wall of the blastocyst which will form the chorion.

7. Implantation

8. Following implantation the endometrium is known as the decidua and consists of three regions: the decidua basalis, decidua capuslaris, and decidua parietalis.
The decidua basalis lies between the chorion and the stratum basalis of the uterus. It becomes the maternal part of the placenta.
The decidua capsularis covers the embryo and is located between the embryo and the uterine cavity.
The decidua parietalis lines the noninvolved areas of the entire pregnant uterus.

9. Decidua

10. Parts of Endometrial Lining

11. When the conceptus implants in the endometrium, the continued secretion of progesterone causes the endometrial cells to swell further and to store even more nutrients.
These cells are now called decidual cells, and the total mass of cells is called the decidua. As the trophoblast cells invade the decidua, digesting and imbibing it, the stored nutrients in the decidua are used by the embryo for growth and development.
Figure 82–4 shows this trophoblastic period of nutrition, which gradually gives way to placental nutrition.
Medical Physiology, Guyton 6 ed, 2006, p.1029

12. Implantation
Viability of the corpus luteum is maintained by human chorionic gonadotropin (hCG) secreted by the trophoblasts
hCG prompts the corpus luteum to continue to secrete progesterone and estrogen
Chorion – developed from trophoblasts after implantation, continues this hormonal stimulus
Between the second and third month, the placenta:
Assumes the role of progesterone and estrogen production
Is providing nutrients and removing wastes

13. Hormonal Changes During Pregnancy
Figure 28.6

14. Fetal Membrane
and
Placenta

15. Fetal Membranes Called the Bag of Waters Consists of two layers
1) Amnion- inner membrane, next to fetus
2) Chorion- outer membrane, next to mother
Function: to house the fetus for the duration of pregnancy, protects from outside world, prevents vertical transmission of infection.

16. Chorion:
Outermost embryonic membrane which forms the placenta & produces human chorionic gonadotropin.
Objective 11
The chorion * is the outermost embryonic membrane * which protects the developing embryo. * The Chorion eventually produces the placenta which provides for the exchange of nutrients and wastes between the mother and the embryo. * *

17. Amnion:
Membrane which surrounds embryo to form the amniotic cavity & produces amniotic fluid.
Objective 11
The amnion * is the membrane * which surrounds the embryo to form the amniotic cavity. * The amnion produces amniotic fluid which bathes the embryo to protect it. * *

18. Amnionic Fluid:
Protects fetus from trauma & permits free movement without adhesion.
Objective 11
The amniotic fluid * bathes the embryo/fetus * protecting it from trauma * and permitting free movement without adhesions. * *

19. Yolk Sack:
Provides initial nutrients, supplies earliest RBCs and seeds the gonads with primordial germ cells.
Objective 11
The yolk sack * provides initial nutrients while the placenta is developing, * supplies the first RBC’s * and seeds the gonads with primordial germ cells.* *

20. Properties of Amniotic Fluid
Amniotic fluid is the fluid medium that the fetus is surrounded within the amniotic cavity.
The volume ranges from 400-1,200 ml, depending on the week of pregnancy.
Mainly composed of water.
Also composed of ions including sodium, chlorine, and calcium.
Amniotic fluid contains urea, which comes from the fetus.

21. Variations Of Substances In Amniotic Fluid

22. Amniotic Fluid Volume Versus Gestation Period In Weeks
1. Amniotic fluid  rapidly from an average vol. of 50ml by 12 weeks of pregnancy to 400ml at mid-pregnancy.
The 24th week of pregnancy, the vol. of amniotic fluid continues to 
3. Maximum of about 1 liter of fluid at 36 to 38 weeks.

23. The Placenta
The placenta consists of thousands of tiny branched fingers of tissue called CHORIONIC VILLI these project into the endometrium. The maternal blood vessels surrounding the chorionic villi break down forming maternal blood sinuses

24. The Placenta
Allows female mammals to carry the young inside their bodies during early development.
During pregnancy, the developing foetus receives all its nutrients via the placenta.
All the waste products in the foetus’s blood are removed via the placenta.
The placenta also produces hormones.

25. Implantation of the Blastocyst

26. Implantation of the Blastocyst

27. Chorionic Villi:
Finger-like growths of the trophoblasts into the endometrium to form the placenta.
Objective 11
The chorionic villi * are the finger-like extensions of the trophoblasts * which grow into the endometrium * to acquire nutrients for the preembryo. * The chorionic villi eventually form the placenta. *

28. Placentation
Figure 28.7a-c

29. Placenta and Further Embryonic Development

30. Umbilical Cord Contents 2 arteries that carry blood to the placenta
1 umbilical vein that carries oxygenated blood to the fetus
primitive connective tissue
Stub drops off in 2 weeks leaving scar (umbilicus)

32. Placenta - function Delivery and excretion Endocrine organ Delivers O2
Removes CO2
Delivers amino acids
Removes urea
Delivers sugars and fats
Delivers hormones
T3 to fetus (early)
To promote growth
Estrogen (estriol = E3) to mother
Endocrine organ

33. Placental Function O2 Minerals Glucose Vitamins Objective 12
The function of the placenta is to provide for the exchange of nutrients from the maternal blood into the fetal blood, without direct mixing of the two. Nutrients move by simple diffusion from areas of higher concentration of each nutrient into the area of lower concentration. Thus O2 diffuses from the mother’s blood into the blood of the fetus. * The same is true of glucose,* vitamins *, minerals *, etc. * O2
Minerals
Glucose
Vitamins

34. Table showing exchange of materials across the placenta
Mother to Foetus
Foetus to Mother
Oxygen
Glucose
Amino acids
Lipids, fatty acids & glycerol
Vitamins
Ions : Na, Cl, Ca, Fe
Alcohol, nicotine + other drugs
Viruses
Antibodies
Carbon dioxide
Urea
Other waste products

36. The Placenta

37. The Placenta
Fetal Side of placenta
Maternal side of placenta

39. Placenta’s Hormons

40. Chorionic gonadotropin (for humans ® hCG)
Produced by cells of the chorion or trophoblast
Chorion develops from the trophoblast
Cytotrophoblast produces hCG very early in embryonic life
Most early pregnancy tests confirm pregnancy by binding to hCG with a specific antibody and then to a color producing molecule (chromagen)
hCG prolongs the life of the corpus luteum and maintains the production of P
hCG stimulates placental production of E and P

41. hCG during pregnancy

42. Progesterone Maternal blood supplies cholesterol
Placenta converts cholesterol to progesterone
Produces enough to support pregnancy by 5-6 wks in humans
Necessary for endometrial support and secretion
\ necessary for support of pregnancy
Exerts negative feedback on LH and FSH
Ovarian follicles do not grow
No stimulation for ovarian steroid production
Increases fat deposition
Stimulating appetite
Diverting energy stores from sugar to fat

43. Feto-Placental Unit - Estrogens
Progesterone from placenta to fetal adrenal gland
Through umbilical and fetal vasculature
Outer layers (cortex)
fetal adrenal zone converts P to DHEA
DHEA circulates to fetal liver ® converted to 16a-OH-DHEA sulfate
Converted to estriol in the placenta
E3 is the primary estrogen during pregnancy
Fetus and placenta cooperate to produce maternal estrogens

44. Chorionic Somatomammotropin (hCS) = Placental Lactogen (PL)
hCS = hPL, both like PRL help prime mammary glands for later milk secretion
With estrogens and progesterone
Has effects similar to GH
Placenta also secretes PRL

45. Relaxin Secreted by the corpus luteum and then the placenta
Levels rise late in pregnancy
Loosens connective tissue
Widens pubic symphysis so head can pass through
Inhibits spontaneous uterine contractions
Promotes cervical effacement
Flattening, spreading, dilation of cervical os

46. Endocrinology of pregnancy
Placenta also secretes
Chorionic GnRH
Chorionic CRH and Corticotropin (ACTH)
Chorionic Thyrotropin (TSH)
Increased need for iodine by embryo from 20 wks on
May be related to fetal brain development
Thyroid hormones appear to have their most profound effects on the terminal stages of brain differentiation, including synaptogenesis, growth of dendrites and axons, myelination and neuronal migration
Chorionic Endorphins

47. Change in hormone levels during pregnancy