Physiology of Pregnancy PDF 4th Class 2022

Assistant professor Dr Alaa Ibrahim 4th Class 2022 Physiology of pregnancy During pregnancy there is progressive anatomical, physiological and biochemical change not only confined to the genital organs but also to all systems of the body. This is principally a phenomenon of maternal adaptation to...

Assistant professor Dr Alaa Ibrahim 4th Class 2022 Physiology of pregnancy During pregnancy there is progressive anatomical, physiological and biochemical change not only confined to the genital organs but also to all systems of the body. This is principally a phenomenon of maternal adaptation to the increasing demands of the growing fetus. GENITAL ORGANS VULVA: Vulva becomes edematous and more vascular; superficial varicosities may appear especially in multiparae. VAGINA: Vaginal walls become hypertrophied, edematous and more vascular. The secretion becomes copious, thin, and curdy white due to marked exfoliated cells and bacteria. UTERUS There is the enormous growth of the uterus during pregnancy. The uterus which in a nonpregnant state weighs about 60 g, but at term, weighs 900–1,000 g. The enlargement of the uterus is affected by the following factors: „ Changes in the muscles—(1) Hypertrophy and hyperplasia (2) Stretching. Arrangement of the muscle fibers: Three distinct layers of muscle fibers are evident: (1) Outer longitudinal (2) Inner circular (3) Intermediate—It is the thickest and strongest layer arranged in a crisscross fashion through which the blood vessels run. Apposition of two double curve muscle fibers give the figure of ‘8’ form. Thus, when the muscles contract, they occlude the blood vessels running through the fibers and hence called the living ligature. increase in number and size of the supporting fibrous and elastic tissues. 1 There is marked spiraling of the arteries, reaching the maximum at 20 weeks; which increases the blood supply. As the uterus enlarges, the shape once more becomes pyriform or ovoid by 28 weeks and changes to spherical beyond 36th week Position: Normal anteverted position is exaggerated up to 8 weeks. Thus, the enlarged uterus may lie on the bladder rendering it incapable of filling, clinically evident by frequency of micturition. CERVIX Stroma: There are hypertrophy and hyperplasia of the elastic and connective tissues. Vascularity is increased which is responsible for its bluish coloration. All these lead to marked softening of the cervix. OVARY Both ovaries are enlarged due to increased vascularity and oedema particularly that containing the corpus luteum. Corpus luteum starts to degenerate after the 10th week when the placenta is formed. Corpus luteum secretes oestrogen, progesterone and relaxin. Ovulation ceases during pregnancy due to pituitary inhibition by the high levels of oestrogen and progesterone. BREASTS Increased size of the breasts becomes evident even in early weeks, due to marked hypertrophy and proliferation of the ducts (estrogen) and the alveoli (estrogen and progesterone). Vascularity is increased which results in appearance of bluish veins running under the skin. The nipples become larger, erectile and deeply pigmented. Variable number of sebaceous glands (5–15), become hypertrophied and are called Montgomery’s tubercles. Secretion (colostrum) can be squeezed out of the breast at about 12th week which at first becomes sticky. Later on, by 16th week, it becomes thick and yellowish. CUTANEOUS CHANGES PIGMENTATION: The distribution of pigmentary changes is selective. 1. Face (chloasma gravidarum or pregnancy mask): It is an extreme form of pigmentation around the cheek, forehead and around the eyes disappears spontaneously after delivery. 2. Abdomen: Linea nigra: It is a brownish black pigmented area in the midline stretching from the xiphisternum to the symphysis pubis. pigmentary changes are probably due to melanocyte stimulating hormone from the anterior pituitary. However, estrogen and progesterone may be related to it as similar changes are observed in women taking oral contraceptives. The pigmentation disappears after delivery. Striae 2 gravidarum: "ese are slightly depressed linear found in the abdominal wall below the umbilicus, sometimes over the thighs and breasts. Initially, these are pinkish but after delivery, they become glistening white in appearance and are called striae Albicans. vascular spider and palmar erythema which are due to high estrogen level. WEIGHT GAIN WEIGHT GAIN: The total weight gain during the course of a singleton pregnancy for a healthy woman averages 11 kg (24 lb).This has been distributed to 1 kg in first trimester and 5 kg each in second and third trimester. Increased sodium retention during pregnancy are: (1) increased estrogen and progesterone, (2) increased aldosterone consequent on the activation of the renin- angiotensin system and possibly (3) due to increased antidiuretic hormone. The amount of water retained during pregnancy at term is estimated to be 6.5 liters. HEMATOLOGICAL CHANGES BLOOD VOLUME: Blood volume is markedly raised during pregnancy. And starts to increase from about 6th week, expands rapidly thereafter to maximum 40–50% above the nonpregnant level at 30– 34 weeks and remains almost static till.Total plasma volume increases to the extent of 1.25 liters. The RBC mass is increased to the extent of 20–30%. Reticulocyte count increases by 2%. Erythropoietin level is raised. The disproportionate increase in plasma and RBC volume produces a state of hemodilution (fall in hematocrit) during pregnancy. Thus, even though the total hemoglobin mass increases during pregnancy to the extent of 18–20%, there is apparent fall in hemoglobin concentration. The advantages of relative hemodilution are: (1) Diminished blood viscosity ensures optimum gaseous exchange between the maternal and fetal circulation. (2) It protects the woman against the adverse effects of supine and erect posture. (3) Protection of the mother against the adverse effects of blood loss during delivery. Neutrophilic leukocytosis occurs to the extent of 8,000/mm3 and even to 20,000/mm3 in labor. The increase may be due to rise in the levels of estrogen and cortisol. BLOOD COAGULATION FACTORS: Pregnancy is a hypercoagulable state. Fibrinogen level is raised by 50%. As a result of rise in fibrinogen and globulin level and diminished blood viscosity, erythrocyte sedimentation rate (ESR) gives a much higher value. 3  Platelets count, however, gives a conflicting picture. Recent studies show a static or a slight fall. Gestational thrombocytopenia may be due to hemodilution and increased platelet consumption. Fibrinolytic activity is depressed till 15 minutes after delivery. ANATOMICAL CHANGES: Due to elevation of the diaphragm consequent to the enlarged uterus, the heart is pushed upward and outward with slight rotation to left. Abnormal clinical findings: The displacement may, at times, be responsible for palpitation. The apex beat is shifted to the 4th intercostal space Pulse rate is slightly raised, often with extrasystoles. A systolic murmur may be audible in the apical or pulmonary area. This is due to decreased blood viscosity and torsion of the great vessels. CARDIAC OUTPUT: The cardiac output (CO) starts and reaches its peak 40–50% at about 30–34 weeks. increases further during labor (+50%) and immediately following delivery. BLOOD PRESSURE: Systemic vascular resistance (SVR) decreases due to smooth muscle relaxing effect of progesterone. In spite of the large increase in cardiac output, the maternal BP is decreased due to decrease in SVR. SUPINE HYPOTENSION SYNDROME (POSTURAL HYPOTENSION): During late pregnancy, the gravid uterus produces a compression effect on the inferior vena cava when the patient is in supine position. the venous return of the heart may be seriously curtailed. This results in production of hypotension, tachycardia and syncope. GENERAL METABOLIC CHANGES: Total metabolism is increased due to the needs of the growing fetus and the uterus. Pregnancy is an anabolic state. CARBOHYDRATE METABOLISM: Insulin secretion is increased in response to glucose and amino acids. There is hyperplasia and hypertrophy of beta cells of pancreas. SYSTEMIC CHANGES RESPIRATORY SYSTEM: Total lung capacity is reduced by 5% due to diagrammatic elevation. Total pulmonary resistance is reduced due to progesterone effect. The mucosa of the nasopharynx becomes hyperemic and edematous. This may cause nasal stuffiness and rarely epistaxis. It is probably due to progesterone acting on the respiratory center and also to increase in sensitivity of the center to CO2. The woman feels shortness of breath. URINARY SYSTEM: Kidney—There is dilatation of the ureters, renal pelvis and the calyces. 4 Renal plasma flow is increased by 50–75%. The glomerular filtration rate (GFR) is increased by 50% all throughout pregnancy. ALIMENTARY SYSTEM: The cardiac sphincter is relaxed, and regurgitation of acid gastric content into the esophagus may produce chemical esophagitis and heartburn. Dyspepsia is common. Atonicity of the gut leads to constipation. CALCIUM METABOLISM AND SKELETAL SYSTEM: During pregnancy there is increase in the demand of calcium by the growing fetus to the extent of 28 g, 80% of which is required in the last trimester for fetal bone mineralization. Calcium absorption from intestine and kidneys are doubled Pregnancy does not cause hyperparathyroidism. Calcitonin levels increase which protects the maternal skeleton from osteoporosis. There is increased mobility of the pelvic joints due to softening of the ligaments caused mainly by hormone. This along with increased lumbar lordosis during later months of pregnancy due to enlarged uterus produces backache and waddling gait. 5