Physiology of Pregnancy 2024-1 PDF

PHYSIOLOGY OF PREGNANCY Dra. Torres, modified by Dra. Romo Objectives Describe the process of fertilization, and the movement of the blastocyst to the uterus. Describe the process of implantation. Describe the development and the major physiological functions of the placenta. List the protein hormon...

PHYSIOLOGY OF PREGNANCY Dra. Torres, modified by Dra. Romo Objectives Describe the process of fertilization, and the movement of the blastocyst to the uterus. Describe the process of implantation. Describe the development and the major physiological functions of the placenta. List the protein hormones secreted by the placenta and describe the role of human chorionic gonadotropin (hCG) in the rescue of the corpus luteum in maintaining pregnancy early postimplantation. Describe the role of Estrogens, Progesterone, Human Chorionic Somatomammotropin, Prolactin and Oxytocin. Describe the interactions between the placenta and the fetal adrenal cortex in the production of estrogens during pregnancy. Describe the maternal changes along pregnancy. EXAM LIKE QUESTION Before implantation, the blastocyst obtains its nutrition from the uterine endometrial secretions. How does the blastocyst obtain nutrition during the first week after implantation? A) It continues to derive nutrition from endometrial secretions B) The cells of the blastocyst contain stored nutrients that are metabolized for nutritional support C) The placenta provides nutrition derived from maternal blood D) The trophoblast cells digest the nutrient-rich endometrial cells and then absorb their contents for use by the blastocyst Ejaculation → vagina → upper part (5-10 min) to ampulla of fallopian tubes. Ampulla is most common site of fertilization. Transport is helped by: Weak fluid current (epithelial secretion). Ciliated epithelium (beating toward the uterus). Probably also contraction of fallopian tubes. Progesterone → relaxes smooth muscle of the isthmus → ovum enters the uterus. Enters the uterus as Blastocysts (about 100 cells). Before implantation, the blastocyst obtains nutrition from endometrial secretion called uterine milk. IMPLANTATION Implantation results from: Trophoblasts cells, developed over the surface of the blastocyst. The trophoblasts cells secrete proteolytic enzymes. Actively transport nutrients to the blastocyst. NUTRITION OF EMBRYO Endometrial cells increases size stimulated by progesterone. Rich in: glycogen, proteins & lipids. The trophoblastic cells invade decidua breaking it, the embryo takes nutrients from it, being the only nutrient source during the first weeks. On the 16th day after fertilization placenta starts forming, and at initiates to provide nutrients (less than decidual cells). TROPHOBLASTIC NUTRITION & PLACENTA “Nutrients and O2 pass through placenta mainly by diffusion” Function of the placenta: 1. Carry nutrients and O2 from mother to fetus. 2. Excrete products from fetus to mother. Early months → thick → low permeability. Latest months → thin → high permeability. MATURE PLACENTA Around the 21 day after fertilization, blood begins to be pumped from embryo. Blood also comes from maternal circulation forming blood sinuses that surround the trophoblastic cords. OXYGEN DIFFUSION O2 transported by simple diffusion. Near end of pregnancy: mean PO2 in maternal placental sinuses is about 50 mmHg and mean PO2 in fetal blood after oxygenation in the placenta is about 30 mmHg. Fetal PO2 of 30mmHg (?) 3 main reasons: 1. Fetal hemoglobin can carry 20 – 50% more O2 than can maternal hemoglobin. 2. The Hb concentration of fetal blood is about 50% greater than that of the mother. 3. Bohr effect. BOHR EFFECT Hb can carry more O2 at low PCO2 than at high PCO2. Fetal blood entering placenta carries large amounts of CO2, but much of this diffuses from the fetal blood into the maternal blood. DIFFUSION OF NUTRIENTS In latest stage of pregnancy the fetus uses as much glucose as the mother: Glucose is transported by facilitated diffusion. Fatty acids also diffuse from maternal blood, but much less than glucose. There are other substances which diffuse relatively easy from maternal blood into fetal blood like ketone bodies, K, Na, Cl, Ca. INSULIN – RESISTANT STATE Gestational diabetes Increased ingestion of 3000 kcal/day. Sex steroid increase tissue glycogen storage and increase hepatic glucose production. Corticoids reduce liver glycogen storage and increase hepatic glucose production. Increase insulin secretion. Reduced glucose tolerance from increased production of human placental lactogen. Increase insulin secretion, but reduces insulin sensitivity. PREGNANCY HORMONES EXAM LIKE QUESTION Which of the following is produced by the trophoblast cells during the first 3 weeks of pregnancy? A) Estrogen B) Luteinizing hormone C) Oxytocin D) Human chorionic gonadotropin E) None of the above EXAM LIKE QUESTION During pregnancy, the uterine smooth muscle is quiescent. During the 9th month of gestation, the uterine muscle becomes progressively more excitable. What factors contribute to the increase in excitability? A) Placental estrogen synthesis rises to high rates B) Progesterone synthesis by the placenta decreases C) Uterine blood flow reaches its highest rate D) Prostaglandin E2 synthesis by the placenta decreases E) Activity of the fetus falls to low levels HUMAN CHORIONIC GONADOTROPIN Secreted by syncytial trophoblast cells. Detected 8 – 9 days after ovulation. Peak 9 – 12 w. After delivery disappears with a half life of 12 –24 hours. Stimulates: –LH receptors on the corpus luteum. Maintains high levels of progesterone secretion and estrogens. –Fetal Leydig cells to produce testosterone. –Fetal Adrenal cortex. –Maternal Thyroid gland activity. –In fetus stimulates DHEA-S and Testosterone. –Responsible for “morning sickness”. PROGESTERONE Stimulates secretion and maintains decidual cells. Suppresses maternal immune system against the fetus. “Progesterone maintains pregnancy” Initially produced by the corpus luteum. By the 8th week of gestation placenta becomes the major source. Before the placenta develops, it stimulates production of nutrients needed for embryo survival. After placenta develops and fetus begins to grow, it inhibits contractions of uterine myometrium. Promotes breast growth of lobule-alveolar system. PROGESTERONE Inhibits uterine myometrial contractions by: – Inhibiting electrical excitability and propagation of action potentials. – Inhibiting production of prostaglandins. – Decreasing sensitivity to oxytocin. “Progesterone maintains pregnancy” ESTROGEN Stimulate continuous growth of the myometrium, preparing it for its role in labor. Stimulates growth of the ductal system of the breast. Produces enlargement of external genitalia. Along with relaxin, causes relaxation and softening of pelvic ligaments. Maternal-Placental-Fetal Unit Maternal-Placental-Fetal Unit HUMAN CHORIONIC SOMATOMAMMOTROPIN Human Placental Lactogen. Detected at 4th week. Concentration correlates with placental weight. Only 3% of growth promoted activity. Stimulated by maternal fasting and hypoglycemia. Main function: Maintenance of continuous flow of substrates, principally glucose to the fetus. Stimulates lipolysis & promotes fatty acid release (used by fetus & placenta as energy sources). Decreases insulin sensitivity. Increases plasma glucose levels. Promotes lactation. MATERNAL CHANGES EXAM LIKE QUESTION Which of the following is not a maternal change during pregnancy? A) Heart position (Right axis deviation) B) Bladder capacity decreases C) Midline hyper pigmentation D) Pituitary gland enlarges GENERAL: Increased body mass (25 – 30 pounds). Change posture. Nausea. Fetus Placenta & membranes 0.7 kg Amniotic fluid Maternal contribution – Weight of the uterus – Blood – Breast 2.0 Kg – Adipose tissue & interstitial fluid 3.3 kg 1.0 kg 9.0 kg 0.7 kg 1.3 kg 5.0 Kg. CARDIOVASCULAR: Heart position (Left axis deviation). Increased stroke volume (39%). Increased CO by 27th week. Increased hydrostatic pressure in legs, edema. HEMATOLOGICAL: Increased blood volume (about 50%). RBC mass (20 – 30%). RESPIRATORY: Increased O2 consumption (VO2max). Increased tidal volume (VT) and alveolar ventilation (VA). May or not increase respiratory rate. Decreased pCO2. URINARY TRACT: Bladder capacity decreases. Residual volume and frequency of micturition increase. Increase risk of urinary tract infection. RENAL: Increase reabsorption (50%) of Na, Cl and water. Increased GFR (50%) and renal plasma flow. SKIN: Due to estrogen, progesterone and MSH: Midline hyper pigmentation and dry skin, chloasma. Stria gravidarum (stretch marks). Spider angiomata. ENDOCRINE: Pituitary gland enlarges. Increased production of ACTH, TSH, prolactin. Decreased production of FSH, LH. Increased secretion of glucocorticoids and mineralocorticoids. Enlargement of thyroid gland. Enlargement of parathyroid gland and increase in PTH secretion. EXAM LIKE QUESTION Why is milk produced only after delivery, not before? A. Levels of luteinizing hormone and follicle-stimulating hormone are too low during pregnancy to support milk production. B. High levels of progesterone and estrogen during pregnancy suppress milk production. C. The alveolar cells of the breast do not reach maturity until after delivery. D. High levels of oxytocin are required for milk production to begin, and oxytocin is not secreted until the baby stimulates the nipple Bibliography Guyton, A., Hall, J. (2016). Textbook of Medical Physiology. (14th Ed.). Philadelphia: Elsevier-Saunders. Chapter 83. Pages 1045-1059. Boron, W., Boulpaep, E. (2009). Textbook of Medical Physiology. (11th Ed.). Philadelphia: ElsevierSaunders. Koeppen, S., Stanton, S. (2008). Berne & Levy Physiology. (6th Ed.). Philadelphia: Mosby-Elsevier.