1. The Placenta
חתכים והסברים

2. After 20 days the bundle of cells had changed into an early kind of body, an embryo.

3. By one month you were the size of an apple seed and needed more food to grow so the cell clump made you a food factory - the placenta.  

4. חתך
Maternal Side
Fetal Side

5. Fetal Side Villi generally cut in cross-section showing trophoblastic shell with mesenchyme core. Shell (dark border) consists of an outer variable thickness of syncitiotrophoblasts with and inner layer of cytotrophoblast cells. Core (pale interior, space is artefact) consists of mesenchymal cells forming an undifferentiated connective tissue with fetal blood vessels coursing through this region.
Note region closest to maternal side shows large syncitiotrophoblast clumps (dark purple regions).
Maternal Side Notice the decidual reaction glycogen deposits (bright magenta/red) close maternal surface. on right of image lumenal space of endometrial glands with precipitated contents. Compare the thickness of the endometrial layer with that seen during the menstrual cycle.

6. Fetal Side Maternal Side
Section through the junction between the fetal and maternal portions of the placenta. Note the chorionic villi and the highly vascular stratum basale into which the villi anchor
Fetal Side
Maternal Side

7. The exchange functions of the placenta
Exchanges across the placenta are of vital importance to the growth and development of the fetus. The transport of a substance from the mother to the fetus or visa versa depends on:- i.
The concentration of the substance in the maternal circulation (Faber and Hart, 1966).
ii.
The mechanism of transfer across the placental cell membranes, e.g. diffusion, active transport or receptor sites (Sibley and Boyd, 1988)
iii.
The concentration of the substance in the lacunae
iv.
The availability of appropriate carrier proteins if they are required (Stephenson et al., 1993) v.
The placental consumption of the substance
vi.
The concentration in the blood feeding the fetal side of the placenta (Stephenson et al., 1990)

8. links http://www.simba.rdg.ac.uk/Dave/Lit%20review.html