pediagenosis: Reproductive
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Showing posts with label Reproductive. Show all posts
Showing posts with label Reproductive. Show all posts

Saturday, April 3, 2021

Fertilization, Pregnancy And Parturition

Fertilization, Pregnancy And Parturition


Fertilization, Pregnancy And Parturition
Fertilization
The unfertilized ovum can survive for up to 24 h after ovulation, and sperm remain viable in the uterus for up to 5 days after ejaculation. The environment of the female tract triggers the capacitation of sperm. This is a prerequisite for fertilization that involves remodelling of the lipids and glycoproteins of the sperm plasma membrane, coupled with increased metabolism and motility. The ovum is surrounded by the zona pellucida, an acellular membrane bearing the glycoprotein ZP3 that acts as a sperm receptor. Fertilization occurs in the oviduct, when a single capacitated sperm binds to ZP3 and under-goes the acrosome reaction. The acrosome is a body containing proteolytic enzymes that is attached to the sperm head (Fig. 52a). When a sperm binds to ZP3, the acrosomal enzymes are released to digest a pathway for the sperm to penetrate the ovum, within which the contents of the sperm head, including its genetic material, are deposited. This event leads to a chain of reactions that denies access to further sperm penetration. The ovum first undergoes electrical depolarization and then discharges granules that impair further sperm binding at the zona pellucida (the cortical reaction). In this way, fertilization is normally restricted to one sperm per ovum. Some 2–3 h after penetrating the ovum, the sperm head forms the male pronucleus which joins with the female pronucleus from the ovum (Fig. 52a). Fusion of the pronuclei combines the parental genetic material from the gametes to form the zygote.

Fertilization, Pregnancy And Parturition

Pregnancy
The zygote is propelled by cilia and muscular contractions of the Fal-lopian tube into the uterus, where it implants in the endometrium. During this journey, the zygote undergoes a number of cell divisions to form the morula, a solid ball of 16 cells that ‘hatches’ from the zona pellucida and develops into the blastocyst, in which embryonic cells are surrounded by trophoblasts (Fig. 52a). The trophoblasts are responsible for implantation, digesting away the uterine endometrial wall to form a space for the embryo, opening up a pathway to the maternal circulation (via the spiral arteries of the uterus) and forming the fetal portion of the placenta. The tissue engineering activities of trophoblasts are mediated by epidermal growth factor (EGF) (Chapter 46) and interleukin-1β. Implantation is complete within 7–10 days of fertilization, at which time the embryo and early placenta begin to secrete human chorionic gonadotrophin (hCG). The appearance of hCG in the plasma and urine is one of the earliest signs of successful conception, and its detection forms the basis of pregnancy testing kits. hCG is a glycoprotein similar to LH that stimulates progesterone secretion from the corpus luteum. Progesterone levels rise steadily throughout pregnancy and fall sharply at term (Fig. 52b). This steroid ensures that the smooth muscle of the uterus remains quiescent during gestation (essential for a successful pregnancy), stimulates mammary gland development and prepares the maternal brain for motherhood. The  placenta  also  secretes  chorionic  somatomammotrophin,  a growth hormone-like protein that mobilizes metabolic fuels (Chapter 43) and promotes mammary gland growth, and oestrogen (mainly oestriol) that stimulates uterine expansion to accommodate the growing fetus. Fetal development occurs within a fluid-filled sac, known as the amniotic membrane, which provides a protective buffer against physical trauma. Pregnancy makes many physiological demands on the mother. The ventilation rate, cardiac output and plasma volume increase to supply fetal–maternal oxygen and water demands; the gastrointestinal absorption of minerals is enhanced; and the renal glomerular filtration rate (Chapter 32) rises to cope with fetal waste production.
Endocrine Control Of Reproduction

Endocrine Control Of Reproduction


Endocrine Control Of Reproduction
Reproductive function in males and females is controlled by common hormonal systems based on the hypothalamic control of the pituitary gonadotrophins, individually known as luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These glycoproteins are released from the gonadotrophs of the anterior pituitary gland under the influence of gonadotrophin-releasing hormone (GnRH; Chapter
44) (Fig. 50a,b). Failure of GnRH release is one cause of infertility. It is released in pulses at intervals of 1–3 h in both males and females, a pattern that is accurately reflected in plasma levels of LH. The pulsatile pattern of GnRH secretion is essential for normal reproductive activity, as continuous exposure of gonadotrophs to the hormone leads to a rapid desensitization of the gonadotrophs and a reduction in the release of gonadotrophins. The releasing hormone acts through receptors coupled to Gq (Chapter 3) to stimulate the release and manufacture of the gonadotrophins.

Endocrine Control Of Reproduction

Actions of gonadotrophins
The gonadotrophins produce their effects via interactions with guanosine triphosphate-binding protein (G-protein)-coupled receptors that activate the intracellular production of cyclic adenosine monophosphate (cAMP) (Chapter 3). In the male, LH acts on the Leydig cells of the testes to stimulate the production of the steroid testosterone, which acts in concert with FSH on Sertoli cells of the seminiferous tubules to support spermatogenesis (Fig. 50a). Sperm are generated in a two-stage meiosis from spermatocytes via spermatids. Spermatogenesis proceeds most efficiently at a temperature of 34 °C, which is why the testes are located outside the body cavity. A normal adult male produces some 2 × 108 sperm per day, a process that carries on from puberty until the end of life. Sertoli cells also produce inhibin, a peptide feedback signal that specifically inhibits the release of FSH from the anterior pituitary.

Saturday, March 6, 2021

CERVICAL INSUFFICIENCY

CERVICAL INSUFFICIENCY

CERVICAL INSUFFICIENCY

Cervical insufficiency is characterized by asymptomatic dilation of the internal os during pregnancy. This generally leads to dilation of the entire cervical canal during the second trimester with subsequent risk of rupture of the membranes and/or expulsion of the fetus. This affects 1/54 to 1/1842 pregnancies (resulting from uncertain diagnostic criteria). Though uncommon, it is thought to be involved with as many as 20% to 25% of all second-trimester pregnancy losses.

ABORTION

ABORTION

ABORTION

Abortion is the loss or failure of an early pregnancy and it is defined in several forms: complete, incomplete, inevitable, missed, septic, and threatened. A complete abortion is the termination of a pregnancy before the age of viability, typically defined as occurring at less than 20 weeks from the first day of the last normal menstrual period or involving a fetus of weight less than 500 g. Most complete abortions generally occur before 6 weeks or after 14 weeks of gestation. An incomplete abortion is the spontaneous passage of some, but not all, of the products of conception. A pregnancy in which rupture of the membranes and/or cervical dilation takes place during the first half of pregnancy is labeled an inevitable abortion. Uterine contractions typically follow, ending in spontaneous loss of the pregnancy for most patients. A missed abortion is the retention of a failed intrauterine pregnancy for an extended period. A septic abortion is a variant of an incomplete abortion in which infection of the uterus and its contents has occurred. A threatened abortion is a pregnancy that is at risk for some reason. Most often, this applies to any pregnancy in which vaginal bleeding or uterine cramping takes place but no cervical changes have occurred. Estimates for the frequency of complete abortions are as high as 50% to 60% of all conceptions and between 10% and 20% of known pregnancies. Less than 2% of fetal losses are missed abortions. Septic abortions occur in 0.40 to 0.6 of 100,000 spontaneous pregnancy losses. Threatened abortions occur in 30% to 40% of pregnant women.

ECTOPIC PREGNANCY III— INTERSTITIAL, ABDOMINAL, OVARIAN

ECTOPIC PREGNANCY III— INTERSTITIAL, ABDOMINAL, OVARIAN

ECTOPIC PREGNANCY III— INTERSTITIAL, ABDOMINAL, OVARIAN

When, during the process of abortion or rupture, the trophoblast, after total separation, implants itself again somewhere in the peritoneum, as happens on rare occasions, it may grow and develop into a secondary abdominal pregnancy. The embryo in such cases may have remained in its original amniotic sac, or a new sac may have formed from the surrounding tissues. A secondary abdominal pregnancy may also result from a beginning tubal implantation that ruptured and became inserted between the leaves of the broad ligament. If the latter should rupture again, the embryo in the fetal sac may extrude into the peritoneal cavity, with the placenta remaining in the extraperitoneal position between the broad ligament sheets. In still more exceptional cases, the fertilized ovum may escape through the open end of the tube, attaching itself to the parietal or visceral peritoneum or the omentum, developing into a primary abdominal pregnancy. It has even been reported that an abdominal pregnancy has originated from a defect in the uterine wall, which had been filled and closed up by the omentum during the healing period after cesarean section. The remarkable feature of these abdominal pregnancies is that they may continue to near term before an occasion for diagnosis may even arise, even in the face of repeated ultrasonographic studies. The incidence of abdominal pregnancy is estimated to be roughly 1 in 10,000 live births.

ECTOPIC PREGNANCY II—RUPTURE, ABORTION

ECTOPIC PREGNANCY II—RUPTURE, ABORTION

ECTOPIC PREGNANCY II—RUPTURE, ABORTION

Very rarely does a tubal pregnancy develop longer than into the fourth or fifth month without symptoms and signs that ultimately lead to the diagnosis. The most frequent outcome of tubal pregnancy is abortion through the tube into the peritoneal cavity. It usually occurs between the middle of the second and the end of the third month, but it may come earlier. A partial or total separation of the trophoblast from the tubal walls occurs, leading to death of the embryo. Blood extravasation and later extrusion of the embryo with blood clots into the peritoneal cavity follow, where they may slowly be absorbed, provided the hemorrhage was slight. The uterine decidua may sometimes separate as a whole and be eliminated as a decidual cast of the uterine cavity. Passage of the decidual cast can be confused with an early spontaneous abortion, and hence the passed tissue should be carefully examined.

ECTOPIC PREGNANCY I—TUBAL PREGNANCY

ECTOPIC PREGNANCY I—TUBAL PREGNANCY

ECTOPIC PREGNANCY I—TUBAL PREGNANCY

Ectopic pregnancy refers to the implantation of the embryo in any place outside the uterine cavity. According to the site of implantation, four kinds of ectopic pregnancy are distinguished: tubal, ovarian, abdominal or peritoneal, and cervical. Between 10 and 15 of every 1000 pregnancies are ectopic, with the rate varying with age, race, and geographic location (highest in Jamaica and Vietnam).

HORMONAL FLUCTUATIONS IN PREGNANCY

HORMONAL FLUCTUATIONS IN PREGNANCY

HORMONAL FLUCTUATIONS IN PREGNANCY

In addition to its function as the agent of transfer of gases and nutrients, the placenta also has significant endocrine activity. It produces progesterone, which is important in maintaining the pregnancy; somatomammotropin (also known as placental lactogen), which acts to increase the amount of glucose and lipids in the maternal blood; estrogen; insulin-like growth factors; relaxin; and –human chorionic gonadotrophin (β-hCG). This hormonal activity is the main cause of the increased maternal blood glucose levels seen in pregnancy, which results in an increased transfer of glucose and lipids to the fetus.

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