Harmful Substances that cross the Placental Membrane

Poisonous gases	Carbon monoxide
Infectious agents	Viruses (HIV, cytomegalovirus, rubella, Coxsackie, variola, varicella, measles, poliomyelitis) Bacteria (tuberculosis, Treponema) Protozoa (Toxoplasma)
Drugs	Cocaine, alcohol, caffeine, nicotine, warfarin, trimethadione, phenytoin, tetracycline, cancer chemotherapeutic agents, anesthetics, sedatives, analgesics
Immunoglobulins	Anti-Rh antibodies

 

Placentae in mammals may be classified according to general shape, fine structure, intimacy of fusion between extraembryonic membranes and maternal tissue, source of foetal blood and whether maternal tissue is shed with the placenta and membranes. In these terms the human placenta would be described as diskoidal, labyrinthine, haemo-chorial, chorio-allantoic and deciduate.

In epithelio-chorial placenta (in the pig) the chorionic villi make contact with the epithelium of the uterine gland (Fig.). In desmo-chorial placenta (in ruminating animals) the chorionic villi contact with connective tissue of maternal endometrium. In vaso-chorial placenta (in predatory animals) chorionic villi erode the epithelium and connective tissue and contact with the endothelium of maternal blood vessels.

Table 4

Exchange across the placenta
Maternal blood to foetal blood (supply)	Foetal Blood to maternal blood (excretion)
· Oxygen · Nutrients (Glucose, amino acids, free fatty acids, vitamins) · Electrolytes · Water · Steroid hormones (cortisol, estrogen · Antibodies (IgG – confers fetal passive immunity) · Maternal serum proteins serum albumin, some protein hormones (thyroxin, insulin) · Erythrocytes (a few)	· Carbon dioxide · Metabolites (Urea, uric acid, bilirubin, creatine, creatinine) · Steroid Hormones (hCG, placental progesterone) · Water · Erythrocytes (a few)

 

 

 

Table 6

Differentiation of the Germ Layers

Germ Layer	Adult Derivatives
Ectoderm	Surface ectoderm	Epidermis and its derivatives (hairs, nails, sweat and sebaceous glands); Mammary glands Epithelial lining of the oral cavity structures, ameloblasts, salivary glands; Lens of eye; Adenohypophysis; Epithelial lining of external auditory meatus; utricle, semicircular ducts Olfactory placode; Epithelial lining of lower anal canal
	Neuroectoderm		Nerve tube	CNS (all neurons and glial cells); Retina; Pineal gland
			Nerve crest	PNS end many other structures (table)
Mesoderm	Paraxial (SOMITES)		Dermatome	Skin dermis
			Myotome	Skeletal muscles of trunk, limbs, head and neck; extraocular muscles; intrinsic muscles of tongue
			sclerotome	Vertebrae and ribs; cranial bone
	Intermediate (Nephrogonotome)		Kidneys Reproductive system organs
	Lateral (splanchnotome)		Serous membranes of body cavities (mesothelium) Carddiogenic mesoderm (splanchnic mesoderm) → heart Suprarenal cortex cells
Mesenchyme	Blood, lymph, connective tissue, smooth muscle cells, blood vessels, endocardium
Endoderm	Epithelial lining of the gastrointestinal tract, the liver, the pancreas, the gall bladder; epithelial lining of the respiratory system (trachea, bronchi, lungs), the thymus stroma, the thyroid and the parathyroid glands endocrine cells; epithelial lining of the urinary bladder, the female urethra and most of the male urethra

 

DIAGRAM of CONSECUTIVE STAGES of HUMAN EMBRYOGENESIS

1- uterine mucosa; 2- epithelium; 3- connective tissue; 4- trophoblast;

5- embryoblast; 6- amniotic vesicle (ectoderm material); 7- entoderm material;

8- extraembryonic mesoderm; 9- extraembryonic mesenchyme; 

10- differentiation of trophoblast; 11- yolk sac; 12-amniotic stalk;

13- chorion cavity; 14- lacunae; 15- symplastotrophoblast; 16- cytotrophoblast;

17- intraembryonic mesoderm; 18- primitive streak; 19- chorion frondosum;

20- smooth chorion; 21- amnion; 22- body fold; 23- yolk sac; 24-embryo body;

25- amniotic membrane; 26- allantois; 27- chorionic villi

 

Fig.1 Cleavage in mammals

       1 – blastomere;

       2 – fertilization membrane

 

Fig.2 Implantation. Differentiation of trophoblast.

           

1 – trophoblast; 2 – embryoblast; 3 – epithelium of endometrium;

4 – connective tissue of endometrium; 5 – hypoblast; 6 – epiblast;

7 – roof of amniotic vesicle; 8 – amniotic cavity; 9 – blood vessels of endometrium;

10 – symplastotrophoblast; 11 – cytotrophoblast; 12 – mitosis in cytotrophoblast;

13 – extraembryonic mesoderm; 14 – fibrinoid;

15 – lacunae within symplastotrophoblast; 16 – exocoelomic cavity.

 

 

Fig.5 Extraembryonic organs in human

A – the third week;

B – the beginning of the forth week

1 – amnion wall;

2 – cardiac primordium;

3 – blood islets; 4 – oral membrane;

5 – cloacal membrane;

6 – chorionic plate;

7 – tertiary chorionic villi;

8 – chorionic blood vessels;

9 – allantois; 10 – primitive foregut;

11 – primitive midgut;

12 – primitive hindgut;

13 – yolk sac cavity;

14 – primitive umbilicus;

15 – amniotic cavity;

16 – extraembryonic cavity

(chorion’ cavity)

 

 

Fig.7. Changes in extraembryonic membranes and the embryo’ correlation in

The process of development

1 – amniotic vesicle; 1a – amniotic cavity;

2 – the embryo body;

                   3 – yolk sac;

                   4 – extraembryonic coelom (chorion cavity)

                   5 – primary chorionic villi;

                   6 – secondary chorionic villi

                   7 – connective stalk;

                   8 – tertiary chorionic villi;

                   9 – allantois;

            10 – umbilical cord

Fig.8 HUMAN PLACENTA

           

 

A – General plan of placenta structure (arrows point blood circulation in one of lacunae);

B, C, D – consecutive stages of chorionic villi’ formation;

E – structure of placentar barrier in the first trimester of pregnancy;

F – structure of cotyledon

 

1 – amniotic epithelium; 2 – chorionic plate; 3 – stem villus; 4 – fibrinoid; 5 – reducing yolk sac;

6 – umbilical cord; 7 – septum between cotyledons; 8 – lacuna; 9 – spiral artery;

10 – decidua basalis; 11 – myometrium; 12 - symplastotrophoblast; 13 – cytotrophoblast;

14 – basal lamina of trophoblastic epithelium; 15 – hemocapillar of chorionic villus;

16 – fibroblast; 17 – mesoderm of secondary chorionic villus;

18 – blood vessel of tertiary chorionic villus.

 

Fig.10 Gastrulation and differentiation of the germ layers in human

           

A – the germ disk (15 days);

B – stage of the primitive streak;

C – migration of cells of mesoderm and notochord (17-18 days);

D – trilaminar embryo;