Pregnancy Physiology PDF

1/16/24, 10:13 PM Realizeit for Student In addition to changes in the reproductive system, the pregnant woman also experiences changes in virtually every other body system in response to the growing fetus. Gastrointestinal System The gastrointestinal (GI) system begins in the oral cavity and ends...

1/16/24, 10:13 PM Realizeit for Student In addition to changes in the reproductive system, the pregnant woman also experiences changes in virtually every other body system in response to the growing fetus. Gastrointestinal System The gastrointestinal (GI) system begins in the oral cavity and ends at the rectum. The secretory and absorptive functions of the GI system are not much affected during pregnancy, but motility is. There is displacement of the intra-abdominal portion of the esophagus into the thorax, in addition to relaxation of the lower esophageal sphincter, causing a decrease in its tone. This leads to gastroesophageal reflux disease of pregnancy (Cunningham et al., 2018). During pregnancy, the gums become hyperemic, swollen, and friable and tend to bleed easily. This change is influenced by estrogen and increased proliferation of blood vessels and circulation to the mouth. In addition, the saliva produced in the mouth becomes more acidic. Some women complain about excessive salivation, termed ptyalism, which may be caused by the decrease in unconscious swallowing by the woman when nauseated. Ptyalism typically resolves spontaneously, though in some women, it endures throughout the pregnancy. Some women get temporary relief from gum chewing or sucking on hard candies (Bianco, 2020). Dental plaque, calculus, and debris deposits increase during pregnancy and are all associated with gingivitis. An increased production of female hormones during pregnancy contributes to the development of gingivitis and periodontitis because vascular permeability and possible tissue edema are both increased. Smooth muscle relaxation and decreased peristalsis occur related to the influence of progesterone. Elevated progesterone levels cause smooth muscle relaxation, which results in delayed gastric emptying and decreased peristalsis. Transition time of food throughout the GI tract may be so much slower that more water than normal is reabsorbed, leading to bloating and constipation. Constipation can also result from low-fiber food choices, reduced fluid intake, use of iron supplements, decreased activity level, and intestinal displacement secondary to a growing uterus. Constipation, increased venous pressure, and the pressure of the gravid uterus contribute to the formation of hemorrhoids. The slowed gastric emptying combined with relaxation of the cardiac sphincter allows reflux, which causes heartburn. Acid indigestion or heartburn (pyrosis) seems to be a universal problem for pregnant women. It is caused by regurgitation of the stomach contents into the upper esophagus and may be associated with the generalized relaxation of the entire digestive system. Over-the-counter antacids will usually relieve the symptoms, but they should be taken only with the health care provider’s knowledge and as directed. The emptying time of the gallbladder is prolonged secondary to the smooth muscle relaxation from progesterone. Hypercholesterolemia can follow, increasing the risk of gallstone formation. Other risk factors for gallbladder disease include obesity, Hispanic ethnicity, and increasing maternal age. Laparoscopic cholecystectomy is a safe procedure in all trimesters of pregnancy if removal of the gallbladder is warranted (Brooks, 2019). Nausea and vomiting, better known as morning sickness, can plague up to 90% of pregnant women. This condition is usually self-limiting, but the symptoms can be distressing and interfere with work, social activities, and sleep. Cardiovascular System https://herzing.realizeithome.com/RealizeitApp/Student.aspx?Token=lqf9HhURQ5RqpgqAkzH2zTYaQRcVeGjlcsXn1BnhV1BdrBMb3lqiFIhL1oNdUK7j0NCYTE… 1/6 1/16/24, 10:13 PM Realizeit for Student Cardiovascular changes occur early during pregnancy to meet the demands of the enlarging uterus and the placenta for more blood and more oxygen. The changes include an increase in heart rate (25%); an increase in cardiac output by 30% to 50% and peaks at 25 to 30 weeks’ gestation; reduced total peripheral resistance; increased blood volume; and increased plasma volume, which leads to physiologic anemia. Perhaps the most striking cardiac alteration occurring during pregnancy is the increase in blood volume. BLOOD VOLUME Blood volume increases by approximately 1,500 mL, or up to 50% above nonpregnant levels, by the 32nd week of gestation and remains more or less constant thereafter (Webster et al., 2018). The increase is made up of 1,000 mL plasma plus 450 mL red blood cells (RBCs). It is not clear how this occurs, but retention of sodium seems to be involved. It begins at weeks 10 to 12, peaks at weeks 32 to 34, and decreases slightly by week 40. Take Note! The rise in blood volume correlates directly with fetal weight, supporting the concept of the placenta as an arteriovenous shunt in the mat This increase in blood volume is needed to provide adequate hydration of fetal and maternal tissues, to supply blood flow to perfuse the enlarging uterus, and to provide a reserve to compensate for blood loss at birth and during the postpartum period. The maternal blood volume expansion occurs at a larger proportion than the increase in RBC mass, which results in physiologic anemia and hemodilution. This dilution of RBCs is termed physiologic anemia of pregnancy. This is reflected in a lowered hematocrit and hemoglobin. These changes cannot be prevented by giving iron supplementation, and they are considered a normal adaptation of pregnancy (Blackburn, 2018). This increase is also necessary to meet the increased metabolic needs of the mother and to meet the need for increased perfusion of other organs, especially the woman’s kidneys since she is excreting waste products for both herself and the fetus. CARDIAC OUTPUT AND HEART RATE Cardiac output, the product of stroke volume and heart rate, is a measure of the functional capacity of the heart. It increases from 30% to 50% over the nonpregnant rate by the 32nd week of pregnancy and declines to about a 20% increase at 40 weeks’ gestation. The increase in cardiac output is associated with an increase in venous return and greater right ventricular output, especially in the left lateral position (Ikeda & Aoki-Kamiya, 2019). Heart rate increases by 10 to 15 bpm between 14 and 20 weeks’ gestation, and this persists to term. There is slight hypertrophy or enlargement of the heart during pregnancy. BLOOD PRESSURE Blood pressure, especially the diastolic pressure, declines slightly during pregnancy as a result of peripheral vasodilation caused by progesterone. It usually reaches a low point mid-pregnancy and thereafter increases to prepregnancy levels until term. During the first trimester, blood pressure typically remains at the prepregnancy level. During the second trimester, the blood pressure decreases 5 to 10 mm Hg and thereafter returns to first-trimester levels. This decrease in blood pressure begins at about 7 weeks’ gestation and persists until 32 weeks’ gestation, when it begins to rise to prepregnancy levels (Jordan et al., 2019). Any significant rise in blood pressure during pregnancy should be investigated to rule out gestational hypertension. Gestational hypertension is a clinical diagnosis defined by the new onset of hypertension (systolic of 140 mm Hg or higher and/or diastolic of 90 mm Hg or higher) after 20 weeks’ gestation. BLOOD COMPONENTS The number of RBCs also increases throughout pregnancy to a level that is 20% to 30% higher than nonpregnant values, depending on the amount of iron available. This increase is necessary to transport the additional oxygen required during pregnancy. Although there is an increase in RBCs, there is a greater increase in the plasma volume as a result of hormonal factors and sodium and water retention. Because the plasma increase exceeds the increase of RBC production, normal hemoglobin and hematocrit values decrease, resulting in physiologic anemia of pregnancy. Changes in RBC volume are due to increased circulating erythropoietin and accelerated RBC production. The rise in erythropoietin in the last two trimesters is stimulated by progesterone, prolactin, and human placental lactogen (Blackburn, 2018). Iron requirements during pregnancy increase because of the demands of the growing fetus and the increase in maternal blood volume. The fetal tissues prevail over the mother’s tissues with respect to use of iron stores. With the accelerated production of RBCs, iron is necessary for hemoglobin formation, the oxygen-carrying component of RBCs. Take Note! Many women enter pregnancy with insufficient iron stores and thus need supplementation to meet the extra demands of pregnancy. https://herzing.realizeithome.com/RealizeitApp/Student.aspx?Token=lqf9HhURQ5RqpgqAkzH2zTYaQRcVeGjlcsXn1BnhV1BdrBMb3lqiFIhL1oNdUK7j0NCYTE… 2/6 1/16/24, 10:13 PM Realizeit for Student Both fibrin and plasma fibrinogen levels increase along with various blood clotting factors. These factors make pregnancy a hypercoagulable state. These changes, coupled with venous stasis secondary to venous pooling, which occurs during late pregnancy after long periods of standing in the upright position with the pressure exerted by the uterus on the large pelvic veins, contribute to slowed venous return, pooling, and dependent edema. These factors also increase the woman’s risk for venous thrombosis (Ikeda & Aoki-Kamiya, 2019). Respiratory System Pregnancy puts less stress on the respiratory system than on the cardiovascular system, but adaptations to this system do take place during pregnancy. The primary changes occur in lung volume and ventilation. Oxygen consumption reflects the uptick of maternal metabolism by increasing between 20% and 30% by the time full term is reached. During pregnancy, the amount of space available to house the lungs decreases as the uterus puts pressure on the diaphragm and causes it to shift upward by 4 cm above its usual position. The growing uterus does change the size and shape of the thoracic cavity, but diaphragmatic excursion increases, chest circumference increases by 2 to 3 in, and the transverse diameter increases by an inch, allowing a larger tidal volume, as evidenced by deeper breathing. Tidal volume, or the volume of air inhaled, increases by 30% to 40% (from 500 to 700 mL) as the pregnancy progresses. This increase results in maternal hyperventilation and hypocapnia. As a result of these changes, the woman’s breathing becomes more diaphragmatic than abdominal. Concomitant with the increase in tidal volume is a 30% to 40% increase in maternal oxygen consumption due to the increased oxygen requirements of the developing fetus, placenta, and maternal organs. Anatomic and physiologic changes of pregnancy predispose the mother to increased morbidity and mortality and increase the risks of a less than optimal outcome for the fetus. The frequency and significance of acute and chronic respiratory conditions in pregnant women have increased in recent years. Because of these various changes, pregnant women with asthma, pneumonia, or other respiratory pathology are more susceptible to early decompensation (Namazy & Schatz, 2019). A pregnant woman breathes faster and more deeply because she and the fetus need more oxygen. Oxygen consumption increases during pregnancy even as airway resistance and lung compliance remain unchanged. Changes in the structures of the respiratory system take place to prepare the body for the enlarging uterus and increased lung volume (Jarvis & Eckhardt, 2020). As muscles and cartilage in the thoracic region relax, the chest broadens with a conversion from abdominal breathing to thoracic breathing. This leads to a 50% increase in air volume per minute. All of these structural alterations are temporary and revert back to their prepregnant state at the end of the pregnancy. Increased vascularity of the respiratory tract is influenced by increased estrogen levels, leading to congestion. Rising levels of sex hormones and heightened sensitivity to allergens may influence the nasal mucosa, precipitating epistaxis (nosebleed) and rhinitis. This congestion gives rise to nasal and sinus stuffiness and changes in the tone and quality of the woman’s voice (Jordan et al., 2019). Renal/Urinary System The renal and urinary systems undergo dramatic change in response to pregnancy. The kidneys must adapt to an increase in blood volume and increased maternal and fetal waste. Hormonal changes during pregnancy allow for increased blood flow to the kidneys. The renal system must handle the effects of increased maternal intravascular and extracellular volume and metabolic waste products as well as excretion of fetal wastes. The predominant structural change in the renal system during pregnancy is dilation of the renal pelvis and uterus. Changes in renal structure occur as a result of the hormonal influences of estrogen and progesterone, pressure from an enlarging uterus, and an increase in maternal blood volume. Dilation of the kidneys and ureters increases the potential for urinary stasis and infection. Like the heart, the kidneys work harder throughout the pregnancy. Changes in kidney function occur to accommodate a heavier workload while maintaining a stable electrolyte balance and blood pressure. As more blood flows to the kidneys, the glomerular filtration rate (GFR) increases, leading to an increase in urine flow and volume, substances delivered to the kidneys, and filtration and excretion of urea, uric acid, creatinine, water, and solutes (Webster et al., 2018). Anatomically, the kidneys enlarge during pregnancy. Musculoskeletal System Changes in the musculoskeletal system are progressive, resulting from the influence of hormones, fetal growth, and maternal weight gain. Pregnancy is characterized by changes in posture and gait. By the 10th to 12th week of pregnancy, the ligaments that hold the sacroiliac joints and the pubis symphysis in place begin to soften and stretch, and the articulations between the joints widen and become more movable (Santos-Rocha, 2019). The relaxation of the joints peaks by the beginning of the third trimester. The purpose of these changes is to increase the size of the pelvic cavity and to make delivery easier. https://herzing.realizeithome.com/RealizeitApp/Student.aspx?Token=lqf9HhURQ5RqpgqAkzH2zTYaQRcVeGjlcsXn1BnhV1BdrBMb3lqiFIhL1oNdUK7j0NCYTE… 3/6 1/16/24, 10:13 PM Realizeit for Student The postural changes of pregnancy—an increased swayback and an upper spine extension to compensate for the enlarging abdomen— coupled with the loosening of the sacroiliac joints may result in lower back pain. The woman’s center of gravity shifts forward, requiring a realignment of the spinal curvatures. Factors thought to contribute to these postural changes include the alteration to the center of gravity that come with pregnancy, the influence of the pregnancy-related hormone relaxin on the pelvic joints, and the increasing weight and position of the growing fetus. An increase in the normal lumbosacral curve (lordosis) occurs and a compensatory curvature in the cervicodorsal area develops to assist her in maintaining her balance (Fig. 11.3). In addition, relaxation and increased mobility of joints occur because of the hormones progesterone and relaxin, which lead to the characteristic “waddle” gait that pregnant women demonstrate as they near term. Increased weight gain can add to this discomfort by accentuating the lumbar and dorsal curves (Santos-Rocha, 2019). FIGURE 11.3 Postural changes during (A) the first trimester and (B) the third trimester. Integumentary System There are a variety of integumentary changes that are associated with pregnancy including changes in pigment, vascular supply, connective skin tissue, hair growth, nail structure, and gland functions. Increased activity of the maternal adrenal and pituitary glands, along with a contribution for the developing fetal endocrine glands, increasing cortisone levels, accelerated metabolism, and enhanced production of progesterone and estrogenic hormones, are responsible for most skin changes in pregnancy (Keltz, 2019; Zaidi et al., 2019). Up to 90% of pregnant women will show signs of hyperpigmentation during pregnancy, typically generalized and mild. The skin of pregnant women undergoes hyperpigmentation primarily resulting from estrogen, progesterone, and melanocyte-stimulating hormone levels. These changes are mainly seen on the nipples, areola, umbilicus, perineum, and axilla. Although many integumentary changes disappear after giving birth, some only fade. Many pregnant women express concern about stretch marks, skin color changes, and hair loss. Little is known about how to avoid these changes. Complexion changes are not unusual. The increased pigmentation that occurs on the breasts and genitalia also develops on the face to form the “mask of pregnancy,” which is also called facial melasma. It occurs in up to 70% of pregnant women. There is a genetic predisposition toward melasma, which is exacerbated by the sun, and it tends to recur in subsequent pregnancies. This blotchy, brownish pigment covers the forehead and cheeks in dark-haired women. Most facial pigmentation fades as the hormones subside at the end of the pregnancy, but some may linger. The skin in the middle of the abdomen may develop a pigmented line called the linea nigra, which extends from the umbilicus to the pubic area (Fig. 11.4). FIGURE 11.4 Linea nigra. https://herzing.realizeithome.com/RealizeitApp/Student.aspx?Token=lqf9HhURQ5RqpgqAkzH2zTYaQRcVeGjlcsXn1BnhV1BdrBMb3lqiFIhL1oNdUK7j0NCYTE… 4/6 1/16/24, 10:13 PM Realizeit for Student Striae gravidarum, or stretch marks, are irregular reddish streaks that appear on the abdomen, breasts, and buttocks in up to 90% of pregnant women. Estrogen, relaxin, and adrenocorticoids contribute to these changes. Striae are most prominent by 6 to 7 months. Vascular-Related Skin Changes Vascular changes during pregnancy manifest in the integumentary system include varicosities of the legs, vulva, and perineum. Varicose veins are commonly the result of distention, instability, and poor circulation secondary to prolonged standing or sitting and the heavy gravid uterus placing pressure on the pelvic veins, preventing complete venous return. BOX 11.2 PREGNANCY, INSULIN, AND GLUCOSE During early pregnancy, maternal glucose levels decrease because of the heavy fetal demand for glucose. The fetus is also drawing amino acids mother's ability to synthesize glucose. Maternal glucose is diverted across the placenta to assist the growing embryo/fetus during early pregna As a result, maternal glucose concentrations decline to a level that would be considered “hypoglycemic” in a nonpregnant woman. During early pregnancy there is also a decrease in maternal insulin production and insulin levels. The pancreas is responsible for the production o into cells. Although glucose and other nutrients easily cross the placenta to the fetus, insulin does not. Therefore, the fetus must produce its o into its own cells. After the first trimester, hPL from the placenta and steroids (cortisol) from the adrenal cortex act against insulin. hPL acts as an antagonist agai must be secreted to counteract the increasing levels of hPL and cortisol during the last half of pregnancy. Prolactin, estrogen, and progesterone are also thought to oppose insulin. As a result, glucose is less likely to enter the mother's cells and is m fetus. Cunningham, F. G., Leveno, K. J., Bloom, S. L., Dashe, J. S., Hoffman, B. L., Casey, B. M., & Spong, C. Y. (2018). Williams obstetrics (25th ed.). McGraw-Hill Professional Publishing; Blackburn, S. T. (2018). Materna Prostaglandin Secretion During Pregnancy Prostaglandins are not protein or steroid hormones; they are chemical mediators, or local hormones. Although hormones circulate in the blood to influence distant tissues, prostaglandins act locally on adjacent cells. The fetal membranes of the amniotic sac—the amnion and chorion—are both believed to be involved in the production of prostaglandins. Various maternal and fetal tissues, as well as the amniotic fluid itself, are considered to be sources of prostaglandins, but details about their composition and sources are limited. It is widely believed that prostaglandins play a part in softening the cervix and initiating and/or maintaining labor, but the exact mechanism is unclear. What is theorized is that when progesterone levels drop at term, an increased production of prostaglandins occurs, which facilitates uterine contractions and increases myometrial sensitivity to oxytocin that is needed for the labor process (Steegers et al., 2019). Along with oxytocin, the influence of prostaglandins on the uterine myometrium predominates to promote uterine contractile activity. Placental Secretion The placenta is an organ that serves to prevent the direct exchange between the blood of the fetus and the blood of the mother. The placenta is not only a transfer organ but a factory as well. It is capable of synthesizing enzymes and proteins, and manufactures fats and carbohydrates that serve as a source of stored energy. The placenta also functions as an endocrine gland, manufacturing and secreting hormones. The placenta has a feature possessed by no other endocrine organ—the ability to form protein and steroid hormones. Very early during pregnancy, the placenta begins to produce the following hormones: https://herzing.realizeithome.com/RealizeitApp/Student.aspx?Token=lqf9HhURQ5RqpgqAkzH2zTYaQRcVeGjlcsXn1BnhV1BdrBMb3lqiFIhL1oNdUK7j0NCYTE… 5/6 1/16/24, 10:13 PM Realizeit for Student hCG hPL Relaxin Progesterone Estrogen Table 11.3 summarizes the role of these hormones. https://herzing.realizeithome.com/RealizeitApp/Student.aspx?Token=lqf9HhURQ5RqpgqAkzH2zTYaQRcVeGjlcsXn1BnhV1BdrBMb3lqiFIhL1oNdUK7j0NCYTE… 6/6