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DEVELOPMENT DEVELOPMENT DURING I, II, & III DURING I, II, & III WEEK OF GESTATIONWEEK OF GESTATION

LECTURE BY PROF. ANSARI,LECTURE BY PROF. ANSARI,

Tuesday, 11-03-08, 8.30-9.30 am.Tuesday, 11-03-08, 8.30-9.30 am.

( for BDS students)( for BDS students)

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MALE & FEMALE MALE & FEMALE REPRODUCTIVE ORGANSREPRODUCTIVE ORGANS

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Development during Development during I week of gestation I week of gestation

Fertilisation.Fertilisation. Implantation.Implantation. Blastocyst formation.Blastocyst formation. Trophoblast Trophoblast

formation.formation.

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IMPLANTATION OF IMPLANTATION OF ZYGOTEZYGOTE

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FERTILISATIONFERTILISATION

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SEMENSEMEN

Human semen contains spermatozoa, prostatic Human semen contains spermatozoa, prostatic secretions, secretions from seminal vesicles secretions, secretions from seminal vesicles and bulbourethra glands.and bulbourethra glands.

2.5 to 5 ml of seminal fluid is excreted. ½ -1 2.5 to 5 ml of seminal fluid is excreted. ½ -1 teaspoonful.teaspoonful.

180 millions of sperms are present in the 180 millions of sperms are present in the ejaculate.ejaculate.

If it is less than 20 million sperms/ml, it leads to If it is less than 20 million sperms/ml, it leads to infertility.infertility.

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Egg & Egg & SpermatozoaSpermatozoa

1. size…over 100 1. size…over 100 /Um in diameter./Um in diameter.

2. No. of egg 2. No. of egg produced:- one produced:- one egg /month.egg /month.

3.Mobility..ovum gets 3.Mobility..ovum gets moved along the moved along the fallopian tube by fallopian tube by cilia.cilia.

1. about 25 /Um 1. about 25 /Um long.long.

2. 180 millions per 2. 180 millions per ejaculate.ejaculate.

3. Moves themselves 3. Moves themselves with the tail.with the tail.

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fertilizationfertilization

After deposition of semen into the female After deposition of semen into the female reproductive tract, the spermatozoa reproductive tract, the spermatozoa travels through the cervix, passes travels through the cervix, passes through the uterine cavity and reaches through the uterine cavity and reaches the fallopian tube, where fertilization the fallopian tube, where fertilization occurs.occurs.

The spermatozoa penetrates the collar of The spermatozoa penetrates the collar of cells surrounding the ovum and fuses cells surrounding the ovum and fuses with the female gamete.with the female gamete.

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ImplantationImplantation

After fertilization the fertilized egg moves After fertilization the fertilized egg moves toward the uterine cavity by the ciliary toward the uterine cavity by the ciliary actions of the fallopian epithelium, and actions of the fallopian epithelium, and peristaltic movements of the smooth peristaltic movements of the smooth muscles of the tubes.muscles of the tubes.

On the 6On the 6thth day after fertilisation it embeds day after fertilisation it embeds into the endometrium by eroding it, into the endometrium by eroding it, posterior wall of uterus/ fundus of uterus posterior wall of uterus/ fundus of uterus is the commonest site of implantation.is the commonest site of implantation.

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Cleavage stageCleavage stage

The single cell of zygote divides many times The single cell of zygote divides many times and a ball of cells is formed, blastomeres.and a ball of cells is formed, blastomeres.

Blastocyst leads to inner cell mass and outer Blastocyst leads to inner cell mass and outer cell trophoblasts.cell trophoblasts.

Inner cell mass form the embryoblast/formative Inner cell mass form the embryoblast/formative cells from which the entire embryo develops.cells from which the entire embryo develops.

The outer cell trophoblast cells form the The outer cell trophoblast cells form the placenta.placenta.

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II WEEK DEVELOPMENTII WEEK DEVELOPMENT

Bilaminar germ disc formation.Bilaminar germ disc formation. The germ disc is flattened structure.The germ disc is flattened structure. The surface epiblast cells are external germ The surface epiblast cells are external germ

layer, ectoderm.layer, ectoderm. The hypoblast cells are cuboidal cells forming The hypoblast cells are cuboidal cells forming

the endoderm germ layer.the endoderm germ layer. The trophoblast cells form cytotrophoblast The trophoblast cells form cytotrophoblast

cells, and syncytial trophoblast layer, forming cells, and syncytial trophoblast layer, forming the primary villus of the placenta. the primary villus of the placenta.

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The two cavities areThe two cavities are

Amniotic cavity &Amniotic cavity & Yolk sac cavity.Yolk sac cavity. These changes occur during 8-14 days.These changes occur during 8-14 days.

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Uteroplacental Uteroplacental circulation is established circulation is established by day 13.by day 13.

Chorionic villi developmentChorionic villi development Primary villi:- day 13-Primary villi:- day 13-

Cytotrophoblast+syncitiotrophoblast.Cytotrophoblast+syncitiotrophoblast. Secondary villi:- day 16- Secondary villi:- day 16-

cyto+Syncytio+core of extra embryonic cyto+Syncytio+core of extra embryonic mesoderm.mesoderm.

Tertiary villi:- day 21- all+foetal blood Tertiary villi:- day 21- all+foetal blood vessels.vessels.

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III WEEK DEVELOPMENTIII WEEK DEVELOPMENT

Tri-laminar germ disc- gastrulation/ primitive Tri-laminar germ disc- gastrulation/ primitive streak formation.streak formation.

The third germ layer is created from the The third germ layer is created from the epiblast cells migrating through the primitive pit epiblast cells migrating through the primitive pit forming the mesoderm.forming the mesoderm.

Heart tube is formed from mesoderm on 20Heart tube is formed from mesoderm on 20 thth day of development.day of development.

The heart tube starts beating at 21-22 days.The heart tube starts beating at 21-22 days. Primitive intestine, a neural tube is also visible.Primitive intestine, a neural tube is also visible.

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III week III week development..cont.ddevelopment..cont.d

Circulation for brain begins,Circulation for brain begins, Back bone – spinal column is formed,Back bone – spinal column is formed, Nervous system is formed.Nervous system is formed.

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2020

The ectodermal derivatives The ectodermal derivatives are as follows:-are as follows:-

Epidermis of the skin, hairs, nails, Epidermis of the skin, hairs, nails, sebacious and sweet glands and sebacious and sweet glands and mammary glands.mammary glands.

Lens, cornea & retina.Lens, cornea & retina. Nervous system.Nervous system. Neural crest cells.Neural crest cells. Tooth enamel.Tooth enamel. Otic & olfactory placodes.Otic & olfactory placodes.

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The mesodermal derivatives The mesodermal derivatives are as follows:-are as follows:-

Somites, vertebral column, all bones and Somites, vertebral column, all bones and cartilages.cartilages.

Heart and blood vessels.Heart and blood vessels. All muscles any where, except iris.All muscles any where, except iris. Testis/ovaries.Testis/ovaries. Kidneys/ suprarenal gland- cortex part.Kidneys/ suprarenal gland- cortex part. Dermis part of skin.Dermis part of skin.

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The endodermal derivatives The endodermal derivatives are as follows:-are as follows:-

Mucosal lining of whole GIT.Mucosal lining of whole GIT. Trachea, larynx and lung parenchyma.Trachea, larynx and lung parenchyma. Liver, gall bladder, pancreas.Liver, gall bladder, pancreas. Urinary bladder.Urinary bladder. Thyroid glands/ parathyroid glands.Thyroid glands/ parathyroid glands.

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Thank u.Thank u.