1 DEVELOPMENT DURING I, II, & III WEEK OF GESTATION LECTURE BY PROF. ANSARI, Tuesday, , am. ( for BDS students)

2 MALE & FEMALE REPRODUCTIVE ORGANS

3 Development during I week of gestation  Fertilisation.  Implantation.  Blastocyst formation.  Trophoblast formation.

4 IMPLANTATION OF ZYGOTE

5 FERTILISATION

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8 SEMEN  Human semen contains spermatozoa, prostatic secretions, secretions from seminal vesicles and bulbourethra glands.  2.5 to 5 ml of seminal fluid is excreted. ½ -1 teaspoonful.  180 millions of sperms are present in the ejaculate.  If it is less than 20 million sperms/ml, it leads to infertility.

9 Egg & Spermatozoa  1. size…over 100 /Um in diameter.  2. No. of egg produced:- one egg /month.  3.Mobility..ovum gets moved along the fallopian tube by cilia.  1. about 25 /Um long.  millions per ejaculate.  3. Moves themselves with the tail.

10 fertilization  After deposition of semen into the female reproductive tract, the spermatozoa travels through the cervix, passes through the uterine cavity and reaches the fallopian tube, where fertilization occurs.  The spermatozoa penetrates the collar of cells surrounding the ovum and fuses with the female gamete.

11 Implantation  After fertilization the fertilized egg moves toward the uterine cavity by the ciliary actions of the fallopian epithelium, and peristaltic movements of the smooth muscles of the tubes.  On the 6 th day after fertilisation it embeds into the endometrium by eroding it, posterior wall of uterus/ fundus of uterus is the commonest site of implantation.

12 Cleavage stage  The single cell of zygote divides many times and a ball of cells is formed, blastomeres.  Blastocyst leads to inner cell mass and outer cell trophoblasts.  Inner cell mass form the embryoblast/formative cells from which the entire embryo develops.  The outer cell trophoblast cells form the placenta.

13 II WEEK DEVELOPMENT  Bilaminar germ disc formation.  The germ disc is flattened structure.  The surface epiblast cells are external germ layer, ectoderm.  The hypoblast cells are cuboidal cells forming the endoderm germ layer.  The trophoblast cells form cytotrophoblast cells, and syncytial trophoblast layer, forming the primary villus of the placenta.

14 The two cavities are  Amniotic cavity &  Yolk sac cavity.  These changes occur during 8-14 days.

15 Uteroplacental circulation is established by day 13.  Chorionic villi development  Primary villi:- day 13- Cytotrophoblast+syncitiotrophoblast.  Secondary villi:- day 16- cyto+Syncytio+core of extra embryonic mesoderm.  Tertiary villi:- day 21- all+foetal blood vessels.

16 III WEEK DEVELOPMENT  Tri-laminar germ disc- gastrulation/ primitive streak formation.  The third germ layer is created from the epiblast cells migrating through the primitive pit forming the mesoderm.  Heart tube is formed from mesoderm on 20 th day of development.  The heart tube starts beating at days.  Primitive intestine, a neural tube is also visible.

17 III week development..cont.d  Circulation for brain begins,  Back bone – spinal column is formed,  Nervous system is formed.

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20 The ectodermal derivatives are as follows:-  Epidermis of the skin, hairs, nails, sebacious and sweet glands and mammary glands.  Lens, cornea & retina.  Nervous system.  Neural crest cells.  Tooth enamel.  Otic & olfactory placodes.

21 The mesodermal derivatives are as follows:-  Somites, vertebral column, all bones and cartilages.  Heart and blood vessels.  All muscles any where, except iris.  Testis/ovaries.  Kidneys/ suprarenal gland- cortex part.  Dermis part of skin.

22 The endodermal derivatives are as follows:-  Mucosal lining of whole GIT.  Trachea, larynx and lung parenchyma.  Liver, gall bladder, pancreas.  Urinary bladder.  Thyroid glands/ parathyroid glands.

23 Thank u.