Maternal and Newborn Health Nursing Course - Physiology of Normal Pregnancy PDF

Physiology of Normal Pregnancy  Outline I. Conception and fetal development. II. Actions of placental hormones. III. Physiological adaptation during pregnancy Changes in the reproductive system Changes in the urinary tract. Chang...

Physiology of Normal Pregnancy  Outline I. Conception and fetal development. II. Actions of placental hormones. III. Physiological adaptation during pregnancy Changes in the reproductive system Changes in the urinary tract. Changes in the alimentary tract. Weight gain. Changes in the respiratory system. Changes in the skin. Changes in the skeleton and joints. Changes in the cardiovascular system. Endocrine changes. IV. Calculation of the expected date of delivery  Conception & fetal development Every human beign starts out as two separate germ cells, or gametes. The female gamete is the ovum, and the male gamete is the sperm. At conception the gametes unite to form the cell that eventually becomes the developing fetus. Human development is an ongoing process that begins at the moment of fertilization and continues even after birth.  Developmental stages 1-Pre-embryonic stage. 2-Embryonic stage. 3- Fetal stage.  I - Pre-embryonic stage This stage begins at fertilization and lasts through the end of the second week after fertilization. During pre-embryonic stage, cellular division and implantation occur  Fertilization or Conception Fertilization Is the union of the mature sperm from the male with the mature ovum from the female (e.g., the ovum is receptive to fertilization for approximately 24 to 48 hours after release from ovary). While the sperm is viable for 24 to 72 hours after ejaculation into the vagina. At ovulation, the ovum is expelled from the graafian follicle and picked up by the fimbria of the fallopian tube on the side. The spermatozoa meet the ovum near the fimbriated end of the tube.  During intercourse, the man ejaculates approximately 300:600 million sperm deposited in 3 ml of seminal fluid into the vagina. However, only one sperm will fertilize the mature ovum, but several millions are necessary to supply their substance hyaluronidase, which softens the corona radiata (the cells surrounding the ovum).   A large number are destroyed by the acidity of the vagina, and several more die on the journey to the fallopian tubes. After the sperm are ejaculated into the vagina, they travel through the cervix, into the uterus, and then into the Fallopian tubes. Prostaglandins in the semen increase smooth muscle contractions of the uterus, thus facilitating the transport of sperm.  Conception usually occurs when the ovum is in the ampulla. Once the single sperm has penetrated the thick membrane that surrounds the ovum (i.e. Zona pellucida), a chemical reaction occurs causing the ovum to be impenetrable to other sperm.  Cellular Reproduction The zygote begins the process of division or cleavage through mitotic division. It occurs every 12 hours. As the cells divide, the zygote transforms from one cell into two cells the uterus., and then each cell further divides to form a total of four cells. Each of these cells in turn divides to form a total of eight cells and so on. Each new cell contains the diploid number of chromosomes (46) beginning with the first mitotic division. During cleavage , the zygote is traveling through the Fallopian tubes toward the uterus.  Morula Formation Nearly, at about the 3rd day after fertilization, the total cell count has reached 32. The solid cell mass cluster is now referred to as a morula. The morula continues its journey toward the uterus while cleavage of cells continues.  Blastocyst At about the 5th day after fertilization, the dividing cell mass has developed a hollow, fluid-filled core and is now called a blastocyst. The blastocyst has an outer layer of cells, the trophoblast; a fluid- filled hollow core, and an inner cell mass. The trophoblast will go on to become the structures that nourish and protect the developing conceptus. By the end of the pre-embryonic period, the inner cell mass has become the embryonic disc, which will eventually become the fetus.  Implantation Almost on the 6th day after fertilization, the trophoblast develops finger-like projections that help the blastocyst to burrow itself into the nutrient-rich endometrium. By the 10th day, the blastocyst is completely buried in the uterine lining, and the endometrium is known as the decidua.  The blastocyst begins to produce human chorionic gonadotropin (HCG), which signals the corpus luteum to continue producing progesterone to maintain the endometrial lining and the pregnancy. Implantation normally occurs in the upper part of the posterior wall of the uterus.  II-Embryonic Stage The embryonic stage lasts from the end of the second week after fertilization until the end of the 8th week. By the end of the embryonic stage, all of the organ systems and major structures are present, and the embryo is fully recognizable as human in form.  During the embryonic period, differentiation process occurs in which the cells and tissues of the embryo multiply to form organs and organ systems. In the 3rd week, three germ layers develop in the embryo, these layers are ectoderm, mesoderm, and endoderm. Ectoderm layer: It is the outer layer of cells, develops to form skin, hair, nails, and the nervous system. Mesoderm layer: It is the middle layer, which will form the skeletal, muscular, and circulatory systems. Endoderm layer: It is the inner layer, which will form the glands, lungs, and urinary and digestive tracts.  III-Fetal Stage The fetal stage starts from the beginning of the 9th week after fertilization and continues until birth. During the fetal stage, there is additional growth and maturation of the organs and body systems.  Supportive structures development Fetal membranes There are two fetal membranes, amnion and chorion. The amnion is a thin fibrous lining, made up of several layers, that helps to protect the fetus and forms the inner part of the sac in which the fetus grows. The chorion is a second layer of thick fibrous tissue that surrounds the amnion. Both amnion and chorion are not fused together, but lie in close contact with each other. Professional Midwifery , Third Level  Amniotic fluid Serves as a cushion to protect the fetus from injury. A temperature control mechanism. A medium that allows for free movement and unrestricted growth. Amniotic fluid is clear and is mainly composed of water. It also contains proteins, carbohydrates, lipids, electrolytes, fetal cells, lanugo, and vernix caseosa.  Amniotic fluid during the first trimester is produced from the amniotic membrane. During the second and third trimesters, the fluid is produced by the fetal kidneys. Amniotic fluid increases during pregnancy and peaks around 34 weeks at 800 to 1,000 mL and then decreases to 500 to 600 mL at term.  Placenta The placenta at term Circular, diameter 15–20cm, thickness 2.5cm at the center. Weight 500g (ratio of fetal: placental weight at term is about 6:1). Occupies 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 center. Branches of the umbilical blood vessels are visible beneath amnion as they radiate from the insertion of the cord. Amnion can be peeled off from underlying chorion, except at insertion of cord. Maternal surface Rough and spongy appearance, divided into several velvety bumps called cotyledons (15–20) by septa arising from the maternal tissues. Each cotyledon may be supplied by its own spiral artery. Numerous small greyish spots may be visible on the maternal surface representing calcium deposition in degenerated areas. Function of Placenta: Placenta: essential functions The placenta is directly responsible for mediating and/or modulating the maternal environment necessary for normal fetal development.  Principal Functions of the Placenta To anchor the fetus and establish the fetoplacental unit. To act as an organ for gaseous exchange. Endocrine organ to bring the needed changes in pregnancy. Transfer of substances to and from the fetus. Barrier against infection.  Metabolic and gas exchange: In the placenta, fetal waste products and CO2, urea are transferred from the fetal blood into the maternal blood sinuses by diffusion. Nutrients, such as glucose and amino acids, and O2 are transferred from the maternal blood sinuses to the fetal blood through the mechanisms of diffuse and active transport.  The Placenta as a Barrier The placenta acts as a barrier for the fetus against pathogens and the maternal immune system.  Infection The placenta forms an effective barrier against most maternal blood-borne bacterial infections. However, some important organisms, such as syphilis, parvovirus, hepatitis B and C, rubella, human immune deficiency virus (HIV), and cytomegalovirus (CMV) are able to cross it and infect the fetus during pregnancy.  Drugs Many drugs administered to the mother will pass across the placenta into the fetus; exceptions include low-molecular-weight heparin (LMWH). Some drugs may have little effect on the fetus and be considered ‘safe’ (e.g. paracetamol), but others (e.g. warfarin) may significantly affect development, structure, and function of the fetus.  The Placenta as an Endocrine Organ As an active endocrine organ, the placenta produces a number of hormones as (Hcg), Estrogens, And Progesterone  Umbilical Cord The umbilical cord extends from the umbilicus of the fetus to the fetal surface of the placenta. In the cord are two arteries that bring deoxygenated blood from the fetus to the placenta and one vein that carries oxygenated and nourished blood from the placenta to the fetus.  These three vessels are surrounded by Wharton's Jelly, which is a clear gelatinous substance that gives support to cord and helps prevent compression of the cord, which could impair blood flow to the fetus.  Actions of Hormones Estrogen Breast and nipple growth, and pigmentation of the areola. Promote uterine blood flow, myometrial growth, cervical softening. Sensitivity and expression of myometrial oxytocin receptors. Water retention and protein synthesis.  Progesterone Synthesized by the corpus luteum until 35 days and by the placenta thereafter. Progesterone promotes smooth muscle relaxation (gut, ureters, uterus) and raises body temperature. It is the principal hormone that prevents preterm labour and is now increasingly administered to prevent preterm labour.  Other Placental Hormones In addition to chorionic gonadotrophin, oestrogens and progesterone, the placenta produces two other specific hormones-placental lactogenic hormone and relaxin. Placental lactogenic hormone promotes growth, stimulates development of the breast and is important in maternal fat metabolism. Relaxin has a relaxant effect, especially upon connective tissue