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

Tuesday, April 13, 2021

Central Nervous System

Central Nervous System


Central Nervous System
Time period: day 22 to postnatal development
Introduction
Ectoderm is induced by the notochord to form neuroectoderm during neurulation (see Chapter 17). This neuroectoderm in turn produces the neural tube and neural crest cells from which the central nervous system develops. The central nervous system comprises the brain and spinal cord.

Central Nervous System

Spinal cord
The caudal end of the neural tube continues to elongate and form the spinal cord. A lumen through the centre of the spinal cord, the neurocoel (or neural canal), forms by week 9 and will become the central canal. The neurocoel is lined with thickening layers of neuroepithelia known as the ventricular zone (Figure 44.1) or ependymal layer.
Peripheral Nervous System

Peripheral Nervous System


Peripheral Nervous System
Time period: day 27 to birth
Introduction
The peripheral nervous system develops in tandem with the brain and spinal cord. It connects the central nervous system to structures of the body as they form and includes the spinal nerves, cranial nerves and autonomic nervous system.
This process begins with neurulation (see Chapter 17), when ectoderm is induced by the notochord to form neuroectoderm. This neuroectoderm in turn produces neuroblasts (primitive neurons) and neural crest cells.
Spinal nerves

Spinal nerves
Neural crest cells migrate out from the neural tube, passing towards multiple targets throughout the embryo (see Chapter 18). Some neural crest cells only migrate a little way from the developing spinal cord, collect together and differentiate to form neurons of the dorsal root ganglia (Figure 45.1). Located bilaterally to the spinal cord, the dorsal root ganglia send afferent processes back towards the alar plate of the spinal cord (see Figure 44.1), eventually passing to the dorsal horn. The dorsal root ganglia also send processes out to run alongside processes of neurons of the ventral root. Their combined bundle of neuronal axons become the spinal nerve.
The Ear

The Ear


The Ear
Time period: 22 day to birth
Internal ear
The function of the internal ear is to receive sound waves and interpret them into nerve signals, and to identify changes in balance.

The Ear, Internal ear, Membranous labyrinth

Membranous labyrinth
At about 22 days, a thickening of ectoderm on either side of the hindbrain develops; this is the otic placode (Figure 46.1). The placode invaginates forming a pit that later becomes separated from the ectoderm, forming the otic vesicle (or otocyst) deep to the ectoderm. The otic vesicle is surrounded by mesoderm that will become the otic capsule, the cartilaginous precursor of the bony labyrinth.
The Eye

The Eye


The Eye
Time period: weeks 3–10
Introduction
The development of the eye begins around day 22 with bilateral invaginations of the neuroectoderm of the forebrain (Figure 47.1).
Optic cup and lens
As the neural tube closes these invaginations become the optic vesicles and remain continuous with the developing third ventricle (Figure 47.1). Contact of these optic vesicles with the surface ectoderm induces the formation of the lens placodes (Figures 47.1 and 47.2).
As the optic vesicle invaginates it forms a double‐walled structure, the optic cup (Figure 47.2). At the same time the lens placode invaginates and forms the lens vesicle which lies in the indent of the optic cup and is completely dissociated from the surface ectoderm. Epithelial cells on the posterior wall of the lens vesicle lengthen anteriorly and become long fibres that grow forwards. It takes about 2 weeks for these fibres to reach the anterior cell wall of the vesicle. These are primary lens fibres (Figure 47.3). Secondary lens fibres form from epithelial cells located at the equator of the lens and are continuously added throughout life along the scaffold made by the primary fibres from the centre of the lens. These cells elongate and eventually lose their nuclei to become mature lens fibres. This occurs in early adulthood.
The Eye, Optic cup and lens, Retina, Optic nerve, Meninges, Cornea, Extraocular muscles,

Retina
In the optic cup there is an outer layer that develops into the pigmented layer of the retina and an inner layer that becomes the neural layer.
Antenatal Screening

Antenatal Screening


Antenatal Screening
Introduction
Modern antenatal care is based on the assessment of risk and identification of the most appropriate care pathway for a pregnant woman. Obstetric ultrasound is a routine tool in antenatal screening for detecting foetal anomalies. Low risk women are offered ultrasound screening in the first and second trimesters, and as these are anomaly scans appropriate care and counselling should be immediately available.
Primary care practitioners will refer a pregnant woman to ante- natal care and aim for a first appointment with ultrasound scanning at approximately 10 weeks into the pregnancy from the date of the last menstrual period (8 weeks after fertilisation). A full obstetric history should be taken and it is good practice to take full gynaecological and medical histories. At the booking appointment the midwife will initiate a close relationship with the mother, and for primigravida women this is the opportunity to discuss the effects of early pregnancy and non‐specific symptoms. Tiredness, nausea and vomiting may be worrying, but hyperemesis gravidarum (excessive nausea and vomiting) should be identified and treated. The mother will be weighed at this meeting, but normally weight is not monitored throughout pregnancy.
Antenatal Screening

The first scan
The first‐trimester ultrasound scan, sometimes referred to as the ‘dating scan’, is performed at a minimum of 10 weeks’ gestation and usually before 14 weeks. Scanning at this stage will confirm foetal viability, give gestational dating information, identify multiple pregnancy, define chorionicity (see Chapter 11) and look for indicators of anomalous development (Figure 48.1). These indicators include nuchal translucency, abdominal wall defects (see Chapter 35) and brain anomalies (see Chapter 44). Nuchal translucency screening is not reliable in smaller foetuses and other anomalies may also be missed. Nuchal translucency measures the thickness of fluid between the cervical spine and skin, and is associated with a number of chromosomal anomalies such as Down syndrome, Turner syndrome, trisomy 18 and trisomy 13, and with cardiac anomalies (Figure 48.2). Skeletal dysplasias may be detectable by ultrasound in the first trimester, and in the near future cardiac defects may be screened for as the resolution of ultrasound scanning improves.

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.

Monday, February 15, 2021

SUPPORT OF PELVIC VISCERA

SUPPORT OF PELVIC VISCERA

SUPPORT OF PELVIC VISCERA

To clarify the relationships of muscles and fasciae in supporting the pelvis, with particular reference to the vagina and internal female genitalia, the uterus, in the accompanying picture, has been elevated upward and backward.  The plane chosen for the section (small upper diagram) runs from a point anterior to the body of the uterus down through the anterior vaginal fornix and along the longitudinal axis of the vagina to the perineum. At this level, the large iliac vessels run close to the superior pubic rami which form the lateral pelvic walls. These pubic rami are connected to the ischiopubic rami across the obturator foramen by the obturator membrane, the obturator internus muscle, and the obturator fascia. The broad ligaments begin at the lateral pelvic walls as double reflections of the parietal peritoneum, forming large wings, which divide to include the uterus and separate the pelvic cavity into anterior and posterior compartments. They are continuous with the peritoneum of the bladder anteriorly and the rectosigmoid posteriorly. The broad ligaments contain fatty areolar tissue, blood vessels, and nerves, and at their apices invest the round ligaments, which are condensations of smooth muscle and fibrous tissue holding the uterus forward and inserting below and anterior to the fallopian tubes. The left ovary has been lifted up to demonstrate the uteroovarian and infundibulopelvic ligaments, the latter containing the ovarian blood supply. The bladder peritoneal reflection has been detached from the uterus, revealing the endopelvic or uterovaginal fascia, which runs laterally to the pelvic wall as the cardinal ligament, and with the associated blood vessels, nerves, and fat forms the parametrium. The uterine arteries and veins extend medially from their origins in the hypogastric vessels to the lateral vaginal fornices. The ureters (cross-sectioned) at this point pass beneath the uterine vessels and then continue in the uterovaginal fascia medially and anteriorly across the upper vagina into the bladder. The close proximity of the ureters to the uterine blood supply and vagina explains why they may easily be injured during hysterectomy and in operations to repair lacerations of the endopelvic fascia.

PELVIC DIAPHRAGM II—FROM ABOVE

PELVIC DIAPHRAGM II—FROM ABOVE

PELVIC DIAPHRAGM II—FROM ABOVE

The pelvic diaphragm forms a musculotendinous, funnel-shaped partition between the pelvic cavity and the perineum and serves as one of the principal supports of the urethra, vagina, rectum, and pelvic viscera. It is composed of the levator ani and coccygeus muscles, sheathed in a superior and inferior layer of fascia. The muscles of the pelvic diaphragm extend from the lateral pelvic walls downward and medially to fuse with each other and are inserted into the terminal portions of the urethra, vagina, and anus. Anteriorly, they fail to meet in the midline just behind the pubic symphysis, exposing a gap in the pelvic floor, which is completed by the urogenital diaphragm. This gap is partially filled by the subpubic ligament that is pierced by the dorsal vein of the clitoris. In this area, the inferior fascia of the pelvic diaphragm fuses with the superior fascia of the urogenital diaphragm.

PELVIC DIAPHRAGM I—FROM BELOW

PELVIC DIAPHRAGM I—FROM BELOW

PELVIC DIAPHRAGM I—FROM BELOW

Removing the superficial muscles and fasciae of the pelvic floor, the pelvic diaphragm, viewed from below, forms a hammock of muscle from the pelvic brim, investing the urethra, vagina, and rectum and attaching posteriorly to the sacrum and coccyx. The principal muscles of this group are the levatores ani, consisting of both medial and lateral components on each side and supplied by the pudendal nerve. The larger medial component, the pubococcygeus, arises from the posterior surface of the superior ramus of the pubis adjacent to the symphysis, whence the fibers pass downward and backward around the lateral walls of the vagina, with some fibers reaching the coccyx, some terminating in the fascia forming the central tendinous point of the perineum, and others blending with the longitudinal muscle coats of the rectum. The pubococcygei are separated medially by the interlevator cleft through which pass the dorsal vein of the clitoris, the urethra, vagina, and rectum. These organs are supported by musculofascial extensions from the pubococcygei, their inferior fascia being continuous with the superior fascia of the urogenital diaphragm.

THE VAGINA

THE VAGINA

THE VAGINA

The vagina (from Latin, literally “sheath” or “scabbard”) serves as the portal to the internal female reproductive tract and a route of egress for the fetus during delivery. The viscera contained within the female pelvis minor include the pelvic colon, urinary bladder and urethra, uterus, uterine tubes, ovaries, and vagina. These structures surround the vagina and interact with it in the clinical setting. Therefore, the vagina also provides a convenient portal to understanding the female pelvic viscera.

FEMALE CIRCUMCISION

FEMALE CIRCUMCISION

FEMALE CIRCUMCISION

Female circumcision is a culturally determined practice of ritually cutting a female’s external genitals that results in removal of part or all of the external genitalia including the labia majora, labia minora, and/or the clitoris. This activity is illegal in many locations. Female circumcision (female genital mutilation, infibulation) is generally performed as a ritual process, often without benefit of anesthesia and frequently under unsterile conditions, generally near the time of puberty or soon after. The resulting scarring may preclude intromission or normal vaginal delivery should pregnancy be achieved. In rare cases, scarring and deformity may be sufficient to result in amenorrhea or dysmenorrhea. The ritual is often performed to reinforce a woman’s place in her society, to establish eligibility for marriage and entry into womanhood. It is sometimes also performed to safeguard virginity or to paradoxically improve fertility. Although the ritual can have devastating effects on the woman’s sexual pleasure, it is some- times performed to enhance the husband’s pleasure.

Sunday, February 14, 2021

MALIGNANT TUMORS

MALIGNANT TUMORS

MALIGNANT TUMORS

About 5% of the malignant tumors of the female genital organs originate on the vulva. (The incidence of vulvar cancer rose by approximately 20% between 1973 and 2000, likely related to increased exposure to human papillomavirus [HPV].) Primary carcinoma is almost always seen in elderly women with an average age for in situ tumors being 40 to 49 years, and 65 to 70 for invasive lesions. The vast majority of these tumors are of the squamous cell variety. Histologic types include squamous cell (90%), melanoma (5%), basaloid, warty, verrucous, giant cell, spindle cell, acantholytic squamous cell (adenoid squamous), lymphoepithelioma-like, basal cell, and Merkel cell. Sarcoma accounts for approximately 2% of vulvar cancers. Metastatic tumors from other sources are rare but do occur.

BENIGN TUMORS

BENIGN TUMORS

BENIGN TUMORS

Benign tumors of the vulva include the fibroma, fibromyoma, lipoma, papilloma, condyloma acuminatum, urethral caruncle, hidradenoma, angioma, myxoma, neuroma, and rarely endometrioid growths.

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