Female Reproductive System: Anatomy and Cycle

Female Reproductive System Anatomy

• The internal female genitalia consists of the vagina, uterus, fallopian tubes, and ovaries.
• The uterus consists of the cervix, body, and fundus.
• Two bilateral tubes connect to the uterus with connections to the peritoneum.
• External genitalia include the clitoris, mons pubis, labia majora, and labia minora.

Reproductive Cycle

• The female reproductive cycle involves producing an ovum and preparing the uterus for pregnancy.
• If the produced ovum is not fertilized and implanted, the cycle resets through menstruation.
• FSH triggers early follicular growth.
• Mature follicles form during ovulation, when the oocyte is released into the fallopian tube.
• After ovulation starts the luteal phase prepares the uterine lining for implantation.
• Progesterone levels decrease and thinning occurs if fertilization and implantation do not happen, resulting in menstruation.

Oogenesis and Ovulation

• Under the influence of FSH and LH, the ovaries produce a mature ovum through ovulation.
• Around day 14 of the reproductive cycle, the oocyte matures and is released.
• Normal menstrual cycle length is twenty eight days give or take seven days
• Menstrual cycle lasts about 21 to 35 days
• After implantation of the egg, human chorionic gonadotropin is produced.
• HCG can be detected in a pregnancy test about 3 days post-fertilization.
• One sperm can fertilize only one oocyte.
• Monozygotic twins can occur if the oocyte divides after fertilization.
• Two oocytes can be fertilized but it is uncommon

The Umbilical Circulation

• The umbilical circulation transports fetal blood to and from the placenta for gas and nutrient exchange.
• The umbilical arteries carry deoxygenated blood from the fetus to the placenta.
• Oxygenated blood returns to the fetus through the umbilical vein, leading to the fetal liver.
• The umbilical cord contains 3 vessels with 2 umbilical arteries and 1 umbilical vein.
• A small amount of the blood is oxygenated by the liver.
• The ductus venosus bypasses the liver, joining the inferior vena cava (IVC) that enters the right atrium.
• The ductus venosus is narrow and has high blood velocities.
• A membranous valve in the right atrium, the crista dividens, prevents mixing of well-oxygenated blood from the ductus venosus with desaturated blood from the IVC.
• The ductus venosus blood flows across the right atrium to the left atrium through the foramen ovale.
• Blood goes through the mitral valve to the left ventricle and then to the aorta.
• About 50% of the blood goes to the head and upper extremities.
• The remainder goes down the aorta and mixes with blood of lower oxygen saturation coming from the right ventricle.
• Deoxygenated blood returns from the fetal head and lower body through the right atrium and ventricle to the pulmonary artery.
• Blood bypasses the lungs to enter the descending aorta via the ductus arteriosus that connects two vessels.
• Desaturated blood from the right ventricle goes down the aorta for arterial circulation and returns to the placenta to be reoxygenated.
• Prior to birth, the ductus arteriosus remains open due to the production of prostaglandin E2 and prostacyclin, which act as local vasodilators.
• Premature closure of the ductus arteriosus has been reported with the administration of cyclooxygenase inhibitors.
• At birth, umbilical blood flow cessation leads to cessation of flow in the ductus venosus.
• A fall in pressure in the right atrium leads to closure of the foramen ovale.
• Ventilation of the lungs opens the pulmonary circulation, decreasing pulmonary vascular resistance, which dramatically increases the pulmonary circulation.
• The ductus arteriosus functionally closes within a few days of birth.

Decidua

• After fertilization and implantation, the endometrium becomes the decidua.
• 3 types of decidua are: decidua basalis, decidua capsularis, and decidua parietalis.
• The decidua basalis is located between the embryo and the uterine wall
• The decidua capsularis surrounds the embryo
• The decidua parietalis lines the rest of the uterine cavity

Central Nervous System

• The early central nervous system (CNS) begins as a simple neural plate that folds to form a groove and then a tube, open at each end.
• Failure of these openings to close results in neural tube defects (NTDs).
• Later development of the fetal brain involves folding of the neurocortex during the second half of pregnancy.
• Folate deficiency is the predominant cause of NTDs
• Meningoceles are congenital anomalies.

Respiratory System

• The lung first appears as an outgrowth from the primitive foregut by 3–4 weeks postconception.
• By 4–7 weeks epithelial tube branches and vascular connections are forming.
• By 20 weeks the conductive airway tree and parallel vascular tree is well developed.
• By 26 weeks type I and II epithelial cells are developing.
• Pulmonary surfactant reduces surface tension at the air-liquid interface of the alveolus and made by type II cells starting at about 30 weeks.

Alimentary System

• The primitive gut is there by week 4.
• The primitive gut consists of the foregut, midgut, and hindgut.
• The foregut endoderm gives rise to the esophagus, stomach, proximal duodenum, liver, and pancreas.
• The midgut endoderm gives rise to the distal duodenum, jejunum, ileum, caecum, appendix, ascending colon, and transverse colon.
• The hindgut endoderm develops into the descending colon, sigmoid colon, and rectum.
• Between 5 and 6 weeks, due to lack of space in the abdominal cavity, the midgut is pushed into the umbilical cord as a physiological hernia.
• Failure of the gut to reenter the abdominal cavity by 12 weeks results in omphalocele.
• Intestinal peristalsis occurs from the second trimester.
• The large bowel contains meconium at term.

Liver, Pancreas and Gall Bladder

• The pancreas, liver, and biliary tree derive from the endoderm of the foregut.
• The liver and biliary tree appear late in the third week or early in the fourth week.
• By the sixth week, the fetal liver performs haematopoiesis and peaks at 12-16 weeks, and continues until approximately 36 weeks.

Kidney and Urinary Tract

• The pronephros starts at about 3 weeks in a ridge and form on sides the embryo.
• The pronephros degenerates while the mesonephric (Wolffian) duct extends towards the end of the embryo, attaching to the cloaca.
• During the fifth week of gestation, the ureteric bud grows as an out-pouching from the Wolffian duct and forms the collecting duct system of the kidney.
• The ureteric bud induces formation of the renal secretory system

Skin & Homeostasis

• The epidermis comes from the surface ectoderm. The dermis and hypodermis attach dermis layers to tissues.
• By the 4th week mesencyhmal cells both grow.
• Single layers of ectoderm are around the embryo
• Protective coats grow as vernix, which coats the skin.
• All layers of the epidermis are developed during weeks 16-20.

Blood and Immune System

• In the beginning of implantation, the yolk sac comes from trophoblastic tissue and its primary action is haematopoietic until replaced after about 6-7 weeks.
• Red blood cells and immune effector cells are made from pluripotent haematopoietic cells.
• They come from the yolk sac the first noted in the blood islands.
• At 8 weeks the yolk sac is replaced by the liver as the source of these cells. Near 20 weeks the yolk cells are produced by the bone marrow.
• Thymus growth begin near the start of pregnancy in first trimester

Immunoglobulins in the Fetus

• Most of the mother's immunoglobulin G (IgG) is produced for the fetus
• Mother's placenta produces a passive immunity to the fetus and neonate.
• In small amounts the fetus makes only amounts of IgM and IgA, which don't mix with the placenta..
• No IgG means the fetus has an infection

Endocrine System

• The hypothalamic-pituitary axis is completed within 12 weeks
• Interstitial cells of the testis creates Testosterone throughout the first trimester
• The range for it has increases from 17-21 weeks
• The growth of Thyroid glands produces T4 during 10-12 weeks

Amniotic Fluid

• In the start it goes through amnion
• It is mainly a trandate through 10 weeks, through skin and naval cord
• Near week 16 weeks of growth occurs in the amniotic fluid
• It is like it is a small imbalance in kidneys and swaps fluid
• Volume goes up through 10 weeks measuring 30 ml, near 20 weeks it measures near 300 ml
• 30 through weeks marks 600 ml during growth and for 38 weeks the growth reaches 1,000 ml.
• At 40 weeks it drops to 800 ml and lowers further to 350 ml at 42 weeks.