CONCEPTION,NIDATION AND PLACENTAL DEVELOP0MENT

CONCEPTION FERTILIZATION OR UNION OF THE MALE AND FEMALE GAMETES(SPERM AND OVUM) SAME AS PREGNANCY

NIDATION IMPLANTATION OR EMBEDDING OF THE PRODUCT OF FERTILIZATION OR ZYGOTE INTO THE UTERINE CAVITY A NIDUS IS A CAVITY IN WHICH PLANT SPORES DEVELOP

NIDATION

SPERMATOGENESIS STAGES OF DEVELOPMENT OF THE SPERM OCCURING IN THE TESTIS. STAGES OF DEVELOPMENT OF THE SPERM OCCURING IN THE TESTIS. THE PROCESS STARTS AT PUBERTY IT TAKES ABOUT 72 DAYS FROM SPERMATOGONIUM TO MATURE SPERM.

OOGENESIS STARTS DURING INTRAUTERINE LIFE. ALL THE PRIMARY OOCYTES ARE FORMED BEFORE BIRTH. THE PRIMARY OOCYTE BEGINS THE FIRST MEIOTIC DIVISION JUST BEFORE BIRTH. COMPLETION OF THE PROPHASE OCCURS JUST BEFORE PUBERTY.

OOGENESIS BEFORE PUBERTY, THE PRIMARY OOCYTE INCREASES IN SIZE AND ZONA PELLUCIDA FORMS AROUND IT. BEFORE PUBERTY, THE PRIMARY OOCYTE INCREASES IN SIZE AND ZONA PELLUCIDA FORMS AROUND IT. BEFORE OVULATION, PRIMARY OOCYTE COMPLETES FIRST MEIOTIC DIVISION,RESULTING IN SECONDARY OOCYTE AND FIRST POLAR BODY

OOGENESIS WITH THE ONSET OF OVULATION,THE NUCLEUS OF THE SECONDARY OOCYTE ENTERS THE SECOND MEIOTIC DIVISION AND PROCEEDS TO METAPHASE UNTIL FERTILIZATION. THE SECONDARY OOCYTE RELEASED AT OVULATION IS CALLED OVUM. IT IS SURROUNDED BY ZONA PELLUCIDA AND CORONA RADIATA. SECOND POLAR BODY IS FORMED AFTER FERTILIZATION AND IS EXPELLED.

SPERMATOGENSIS AND OOGENESIS

STRUCTURE OF SPERM STRUCTURE OF SPERM

STRUCTURE OF SECONDARY OOCYTE 1.OVUM 2. ZONA PELLUCIDA 3. CORONA RADIATA

COMPOSITION OF SEMEN FROM THE FOLLOWING ORGANS 1.TESTIS 2. SEMINAL VESICLE 3.PROSTATE 4.URETHRAL GLANDS

TRANSPORT OF SEMEN ALKALINE SEMEN DEPOSITED IN THE VAGINA AFTER SEXUAL INTERCOURSE COAGULATES THEN LIQUIFIES. AFTER 30MINS IN THE VAGINA WHICH IS ACID THEY LOOSE MOTILITY AND UNABLE TO PENETRATE THE CERVICAL MUCUS AND DIE. SPERMS CAN SURVIVE FOR 1-3 DAYS IN THE CERVICAL MUCUS AND FURTHER 2 DAYS IN THE FALLOPIAN TUBE

TRANSPORT OF SPERM BY PERISTALSIS ASSISTED BY TUBAL FLUID,CILIA AND MUSCULAR CONTRATION. DURING THE JOURNEY TO THE TUBE THE SPERMS GAIN ABILITY TO FERTILIZE THE OVUM BY PROCESSES OF CAPACITATION AND ACROSOMAL REACTION

CAPACITATION AND ACROSOMAL REACTION CAPACITATION-THE PROCESS WHICH REMOVES THE SPERM MEMBRANES. ACROSOMAL REACTION IS THE PROCESS WHEREBY THE CAPACITATED SPERM LOOSES ITS ACROSOMAL MEMBRANES RELEASING THE ENZYMES WHICH HELPS THE PENETRATION OF THE ZONA PELLUCIDA

OVUM AT OVULATION, THE FIMBRIAL END OF THE TUBE COMES VERY CLOSE TO THE OVARY. WHEN THE OVUM IS RELEASED, IT IS CARRIED BY PERITONEAL FLUID INTO THE TUBE BY CILIARY ACTION OF EPITHELIAL CELLS AND MUSCULAR CONTRACTIONS. THE FERTILE LIFE OF THE OVUM IS ABOUT 24 HRS

FERTILIZATION NORMALLY OCCURS AT THE AMPULLA OF THE FALLOPIAN TUBE INVOLVES FUSION OF OVUM AND SPERM. INVOLVES FUSION OF OVUM AND SPERM. ONLY ONE SPERM FERTILIZES THE OVUM SPERM IS ATTRACTED TO OVUM BY CHEMOTAXIS.

FERTILIZATION MANY SPERMS ENTER THE ZONA PELLUCIDA BUT AS SOON AS ONE SPERM GETS INTO THE CYTOPLASM, THE OVUM SEPERATES FROM THE ZONA. THE HEAD OF THE SPERM WHICH IS THE NUCLEUS FUSES WITH THE NUCLEUS OF THE OVUM TO FORM THE ZYGOTE.

FERTILIZATION THE ZYGOTE IS CARRIED DOWN THE TUBE BY PERISTALSIS AND CILIARY ACTION AND REACHES THE UTERINE CAVITY ABOUT 5-6 DAYS AFTER OVULATION.

FERTILIZATION

IMPLANTATION

EARLY DEVELOPMENT AND EMBEDDING OF BLASTOCYST ZYGOTE UNDERGOES MITOTIC DIVISION FORMING TWO DAUGHTER CELLS CALLED BLASTOMERES WITHIN 30 HRS AFTER FERTILIZATION LATER DIVISION OCCURS ABOUT EVERY 24HRS UNTIL A MORULA FORMS WHICH IS ABOUT 16 BLASTOMERES.

CAVITY APPEARS IN THE MORULA AND IS NOW CALLED BLASTOCYST. THE BLASTOCYST CONSISTS OF 1.OUTER LAYER CALLED TROPHOBLAST 2.INNER CELL MASS WHICH GIVES RISE TO THE EMBRYO THE TROPHOBLAST ERODES AND DIGEST THE ENDOMETRIUM NOW CALLED DECIDUA.

EARLY DEVELOPMENT

DEVELOPMENT OF THE PLACENTA FORMS FROM TROPHOBLAST WHICH DIFFERENTIATES TO 1.INNER CYTOTROPHOBLAST 2.OUTER SYNCYTIOTROPHBLAST

FORMATION OF PLACENTA EARLY DEVELOPMENT

TROPHOBLAST PENETRATES THE ENDOMETRIUM NOW CALLED DECIDUA. DECIDUA BASALIS IS UNDERNEATH THE CONCEPTUS AND IS INVOLVED IN THE MATERNAL SIDE OF THE PLACENTA. CYTOTROPHOBLAST PROLIFERATES AND FORM CLUMPS THAT EXTENDS TO THE SYNCYTIOTROPHOBLAST TO FORM THE PRIMARY VILLI.

FORMATION OF PLACENTA LATER DEVELOPMENT

Placenta: Later de velopment Placental growth continues to term Until week 16 the placenta grows both thickness and circumference due to the growth of the chorionic villi with accompanying expansion of the intervillous space. Until week 16 the placenta grows both thickness and circumference due to the growth of the chorionic villi with accompanying expansion of the intervillous space. After 16 weeks growth occurs mainly circumferentially. The placenta at term Circular, diameter 15-20, thickness~2.5cm at the centre. Weight~500g (the ratio of fetal: placental weight at term is about 6:1) It occupies about 30% of the uterine wall at term and has two surfaces:

Fetal surface  Covered by a smooth, glistening amnion with the umbilical cord usually attached at or near its centre.  The branches of the umbilical blood vessels are visible beneath the amnion as they radiate from the insertion of the cord.  The amnion can be peeled off from the underlying chorion except at the insertion of the cord.

Maternal surface  Has a rough and spongy appearance and is divided into several velvety bumps called the cotyledons (15-20) by septa arising from the maternal tissues.  Each cotyledon may be supplies by its own spiral artery.  Numerous small greyish spots may be visible on the maternal surface representing calcium deposition in degenerated areas.

Umbilical cord Vascular cable that connect the fetus to the placenta. Varies from 30 to 90cm long, covered by amniotic epithelium. Contains two umbilical arteries and one umbilical vein embedded into the Wharton's jell. The arteries carry deoxygenated blood from the fetus to the placenta and the oxygenated blood return to the fetus via the umbilical vein. In a full-term fetus, the blood flow in the cord is approximately 350ml\min

PRIMARY VILLI BRANCHES EXTENSIVELY INTO SECONDARY AND TERTIARY VILLI AND FINALLY CHORION FRONDOSUM.(fetal portion of the placenta) MORE INVASION OF THE DECIDUA BASALIS TAKES PLACE,WITH THE FORMATION OF THE COTYLEDON(15-20)

PLACENTAL FUNCTION 1. LUNG FUNCTION-GASEOUS EXCHANGE 2.KIDNEY FUCTION-EXCRETION OF HYDROGEN IONS AND BREAKDOWN PRODUCTS OF OTHER SUBSTANCES 3. GI. FUNTION-NUTRIENT FUNCTION 4.HORMONE PRODUCTION 5.IMMUNE FUNCTION-TRANSFER OF IMMUNOGLOBULINS TO THE FETUS 6.LIVER FUNCTION-DETOXIFICATION OF DRUGS

PLACENTA