NCM107 MIDTERMS REV.docx

**PREGNANCY** - The state of carrying a developing embryo or fetus within the female body from conception to birth. **FERTILIZATION** - ***CONCEPTION/FERTILIZATION*** is the penetration of one ovum by one sperm resulting in a fertilized ovum called zygote. The sex of a child is de...

**PREGNANCY** - The state of carrying a developing embryo or fetus within the female body from conception to birth. **FERTILIZATION** - ***CONCEPTION/FERTILIZATION*** is the penetration of one ovum by one sperm resulting in a fertilized ovum called zygote. The sex of a child is determined at the moment of conception by the male gamete. - ***NIDATION*** is the process of burrowing of the developing zygote into the endometrial lining of uterus. This usually takes place 7-10 days after fertilization. - The union of the spermatozoon with the mature ovum. - It begins with when a sperm cell collides and ends with production of mononucleated single cell called the zygote **OBJECTIVES** - To initiate the embryonic development of the egg - To restore the chromosome number of the species **SPECIAL STRUCTURES OF PREGNANCY** **FETAL MEMBRANES** - Arise from the zygote and holds the developing fetus as well as the amniotic fluid **AMNIOTIC FLUID** - Clear yellowish fluid surrounding the developing fetus. - Average amount = 1000 ml - Allows free movement of the fetus - Maintains the temperature - Provides oral fluid **UMBILICAL CORD** - The connecting link between fetus and placenta. - Contains 2 arteries and 1 vein supported by mucoid material (Wharton's jelly) to prevent kinking and knotting - There are no pain receptors in the umbilical cord **PLACENTA** - Transient organ allowing passage of nutrients and water materials between mother and fetus - Also acts as an endocrine organ and as a protective barrier against some drugs and infectious agents **STAGES OF FETAL DEVELOPMENT** **AGE OF VIABILITY** -- the earliest age at which a fetus survives, if born, accepted as 20 weeks or at a point the fetus weighs at least 500 grams. **APPROXIMATION OF THE GAMETES** - The ovum is fertilizable and capable only for 24 to 48 hours; the lifespan of the sperm is 48 to 72 hours. - *[Site]*: the outer third of the fallopian tube, ***AMPULLA*** -- the widest part of the tube. - Out of the millions of sperm cells in the vagina at a single ejaculation, only thousands capacitated spermatozoa enter the uterine tube while only 300 to 500 reach the ovum. - Tubal transport is facilitated by muscular contraction and aspiration action of the uterine tube - It takes only a few minutes for the sperm to reach the fallopian tube **CONTACT & FUSION OF THE GAMETES** **CAPACITATION** - The process of physiological changes in a spermatozoa in order to have the ability to penetrate and fertilize the ovum. - This is the process of undertaking in the sperm when inside the female genital tract influenced by the secretion of the uterine tube. - The sperm must be in the female genital tract 4-6 hours before they can fertilize an ovum. The sperm undergoes changes in the removal of the glycoprotein coat. **ACROSOMAL REACTION** - The acrosomal layer of the sperm becomes reactive and releases the enzyme hyalurodinase known as the acrosome reaction. - It disperses the corona radiata (the outer layer of the ovum) allowing access to the zona pellucida. **CORTICAL REACTION** - The first sperm that reaches the zona pellucida penetrates it. - Penetration of the zona pellucida occur with the aid of several enzymes processed by the sperm which break down the proteins of the zona layer. - Upon penetration, a chemical reaction known as the cortical reaction occurs which makes it impermeable to other sperms. - When a sperm unites with the egg's plasma membrane, it alters the zona pellucida preventing other sperm from binding to and entering the egg. - Acrosome reaction is the release of hydrolytic enzymes to soften the zona pellucida (jelly coat). - Cortical reaction is the hardening of the jelly coat after fertilization to prevent the entry of the other sperm cells. **ZYGOTE DEVELOPMENT** - The male and the female gametes each contribute half the complement of the chromosomes to make a total of 46. The new cell is called zygote. - The zygote contains both the paternal and maternal genetic materials - The sex of a child is determined by the pattern of the sex chromosome supplied by the spermatozoon. **Zygote development happens in [three periods]:** 1. **Pre -- embryonic period**: first two weeks after fertilization a. The implantation of the zygote into the endometrium. b. The embryo takes 3 days to travel through the fallopian tube to reach the uterus. c. It takes another 3 days to get implanted, usually in the dorsal wall of the uterus. d. The embryo is about 1 week old when it gets implanted. 2. **Embryonic period**: 2 to 8 weeks 3. **Fetal period**: 8 weeks to birth The zygote undergoes mitotic division and cellular replication known as cleavage resulting in the formation of smaller cells known as [**BLASTOMERE**.] **Pre-embryonic period happens first 2 weeks after fertilization:** - 2 cells at day 1 -- 30 hours - 4 cells at 2 days, 8 by 2.5 days, 16 by 3 days and called MORULA (resembling a mulberry at 16 to 64 cell stage) - Cells bind tightly together in a process known as compaction. - Next, cavitation occurs where the outermost cells secrete fluid into the morula and fluid filled cavity or blastocele appears and becomes blastocyst comprising of 58 cells. **BLASTULATION** - Development of the morula to the blastocyst has occurred by day 4. - The blastocyst either becomes a trophoblast or inner cell mass - The trophoblast becomes the placenta and chorion - The inner cell mass becomes the fetus, amnion and the umbilical cord **IMPLANTATION** - Embedding of the embryo to the wall of the uterus - Also called NIDATION - Occurs in the endometrium of the anterior or posterior wall of the body near the fundus on the 6th day which corresponds to the 20th day of regular menstrual cycle. Implantation occurs through stages. 1. **APPOSITION** a. Occurs through pinopod formation. Pinopods are long finger-like projections (microvilli) from the endometrial cell surface b. The pinopods absorb the endometrial fluid which is secreted by the endometrial gland cells. This fluid rich in glycogen and mucin provides nutrition to the blastocyst initially 2. **ADHESION** c. Unless this fluid is absorbed, adhesion phase cannot occur d. Adhesion of blastocyst to the endometrium occurs through the adhesion molecules like integrin, selectin and cadherin (glycoproteins) 3. **PENETRATION & INVASION** e. Occur through the stromal cells in between the gland and is facilitated by the histolytic action of the blastocyst. f. With increasing lysis of the stromal cells, the blastocyst is burrowed more and more inside the stratum compactum of the decidua. **EMBRYONIC AND FETAL STRUCTURES** **DECIDUA** - The endometrium during pregnancy - It has 3 layers: - ***BASALIS*** -- lies directly under the embryo (portion where trophoblast establish communication with maternal blood vessels) - ***CAPSULARIS*** -- stretches or encapsulates the surface of the trophoblast - ***VERA*** -- the remaining portion of the uterine lining; parietalis **CHORIONIC VILLI** - Miniature villi similar to probing fingers that appear on the 11th or 12th day. - They begin the formation of the placenta. - Consists of a central core of connective tissue and fetal capillaries. **Consists of 2 layers of trophoblast cells:** - ***CYTOTROPHOBLAST*** (middle or Langhan's layer) -- functions in early pregnancy to protect the growing embryo and fetus from infection. - ***SYNCYTIOTROPHOBLAST*** (syncytial layer) -- produces HCG, somatomammotropin (HPL), estrogen and progesterone. **HORMONES PRODUCED:** - **HCG (human chorionic gonadotropin)** -- ensures that the corpus luteum of the ovary continues to produce estrogen and suppresses maternal immunologic response to avoid placental tissue rejection. - **ESTROGEN** -- helps in mammary gland development, stimulates uterine growth - **PROGESTERONE** -- maintains endometrial lining, reduce contractility of uterine muscle preventing premature labor, decreases intestinal peristalsis = constipation. - **HPL (human placental lactogen)** -- promotes mammary gland growth, regulates maternal glucose, protein, and fat levels; acts as glucose antagonist, so that glucose will be available for the fetus; diabetogenic hormone: can cause gestational diabetes. **PLACENTA** - Serves as fetal lungs, kidneys, and GIT. - Exchange happens thru selective osmosis thru the chorionic villi. - Placental circulation most efficient when mother lies on her left. - Weighs 400-600 grams at term, 15-20 cm in diameter, 2-3 cm deep. - Mother transmits immunoglobulin G to fetus, limited passive immunity. - Has 25-30 cotyledons (placental compartments that lie on the maternal side) - Has 2 sides: - ***MATERNAL*** -- dirty rough - ***FETAL*** -- shiny smooth - It also secretes endocrine hormones. - **HCG** -- 1 st placental hormone Ensures corpus luteum to continuously produce progesterone and estrogen - Suppresses maternal immunologic reaction so that placental tissue is not detected and rejected as a foreign substance - If fetus is male, stimulates the testes to begin producing testosterone - At 8 weeks, begins progesterone production and as a result, disintegrates corpus luteum and HCG production decreases **ESTROGEN (estriol)** - hormone of women. - Contributes to mammary gland development of mother in preparation for lactation. - Stimulates uterine growth to accommodate growing fetus. **PROGESTERONE** -- - hormone for mothers - Necessary to maintain endometrial lining of the uterus during pregnancy - Reduces contractility of uterus during pregnancy preventing preterm labor **HUMAN PLACENTAL LACTOGEN** - With both growth promoting and lactogenic (milk production) properties - Promotes mammary gland growth in preparation for lactation - Regulates maternal glucose, protein and fat levels so that adequate amounts of these are always available to the fetus **THE PLACENTA BARRIER** - Sugar, fats and oxygen diffuse from mother's blood to fetus - Urea and CO2 diffuse from fetus to mother - Maternal antibodies are actively transported across the placenta. Some resistance to disease is passed to the fetus (passive immunity) - Most bacteria are blocked - Many viruses can pass including rubella, chickenpox, sometime HIV - Many drugs and toxins pass including alcohol, heroin, and mercury **UMBILICAL CORD** - Transports oxygen and nutrients to fetus and returns waste products from fetus to placenta. - Has 1 vein & 2 arteries: probably with congenital anomaly if incomplete. - About 55 cm long 2 cm diameter. - **Wharton's jelly** -- a gelatinous mucopolysaccharide that forms the bulk of the umbilical cord giving its body: prevents pressure on the vein and arteries **AMNIOTIC MEMBRANES** - **CHORIONIC MEMBRANE** -- the outermost fetal membrane forming the sac that contains the amniotic fluid. - **AMNIOTIC MEMBRANE** -- 2nd membrane lining the chorionic membrane formed beneath the chorion. - Produces amniotic fluid. - Produces phospholipids that initiates the formation of prostaglandins causing uterine contractions and trigger labor. **AMNIOTIC FLUID** - 800 -- 1,200 ml at term - *POLYHYDRAMNIOS* (\>2,000 ml) - *OLIGOHYDRAMNIOS* (\