Physiology Lecture 26 PDF

Physiology Lecture 26 menstral cycle if there is fertilizations no menstral bleeding The inhibition of FSH (follicle-stimulating hormone) and LH (luteinizing hormone) The zygote remains in the fallopian tube for ap...

Physiology Lecture 26 menstral cycle if there is fertilizations no menstral bleeding The inhibition of FSH (follicle-stimulating hormone) and LH (luteinizing hormone) The zygote remains in the fallopian tube for approximately 3 days What happens to the zygote while it is in the fallopian tube? the zygote undergoes mitotic divisions (mitosis) and develops into a blastocyst consisting of approximately 100 cells. Upon reaching the uterus, the blastocyst typically remains in the uterine cavity for an additional 1 to 2 days before it implants into the endometrium. What are the two main types of cells in the blastocyst? the inner cell mass and an outer epithelial-like layer of trophoblasts. What types of cells are included in the trophoblast layer? syncytiotrophoblasts and cytotrophoblasts. What is the role of syncytiotrophoblasts? crucial for fetal and placental development. What is the role of cytotrophoblasts? initially provide a supportive layer for cell division. What is the region of the trophoblast layer adjacent to the inner cell mass and function The embryonic pole attaches to the uterine endometrium during implantation. Physiology Lecture 26 1  What prepares the uterus to receive the blastocyst during the secretory phase? High levels of progesterone released from the corpus luteum during the luteal phase of the ovaries prepare the uterus to receive the blastocyst. What is the role of syncytiotrophoblasts during implantation? secrete proteolytic enzymes that digest adjacent cells of the uterine endometrium, facilitating the embedding of the blastocyst and forming the fetal portion of the placenta. What maternal response occurs following implantation? decidualization occurs, transforming endometrial stromal cells into decidual cells, which are rich in glycogen, proteins, lipids, and minerals essential for embryo development. What are decidual cells, and what do they form? Decidual cells are transformed endometrial stromal cells that form the decidua, which constitutes the maternal portion of the placenta. approximately 8 days after ovulation. syncytiotrophoblasts begin secreting human chorionic gonadotropin (HCG)? What is the function of HCG in early pregnancy? HCG acts similarly to luteinizing hormone (LH), preventing the regression of the corpus luteum and allowing it to continue producing progesterone and estrogen to support the implanted embryo. How does the sustained release of estrogen and progesterone affect ovarian follicle development? Sustained release of estrogen and progesterone inhibits pituitary secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), preventing the development of new ovarian follicles. What do mature villi contain? Mature villi contain both fetal umbilical arteries and veins. What covers the surface of villi, and what is their role? Physiology Lecture 26 2  The surface of villi is covered with syncytiotrophoblasts, which contain carrier molecules for transporting nutrients. What is the function of villi in the placenta? Villi function as fetal placental capillaries. What is the intervillous space filled with, and what is its function? The intervillous space is filled with maternal blood and serves as functional maternal placental capillaries. Are there structural capillaries between maternal arterioles and venules within the placenta? No, there are no structural capillaries. The intervillous space functions as the capillary interface for maternal blood. What does the fetal umbilical vein carry? The fetal umbilical vein carries oxygenated blood rich in nutrients obtained from maternal arteries. What do fetal umbilical arteries carry? Fetal umbilical arteries carry deoxygenated blood containing fetal metabolized waste products, returning it to maternal veins. Placenta Functions Delivering Oxygen and Nutrition: Draining CO2 and fetal metabolites Hormone release Storage of nutrition The protective barrier function of HCG Human chorionic gonadotropin (HCG): 1. Maintaining corpus luteum function to release progesterone and estrogen in the first trimester. Physiology Lecture 26 3  2. Promoting testes release of testosterone and antimullerian hormone for male phenotypic formation 3. Stimulating maturation of fetal adrenal gland and liver (essential for placenta synthesis of estrogen). 4. Immunosuppression. Human placental lactogen/human chorionic somatomammotropin (hPL/HCS) function 1. Reducing insulin sensitivity (increase in insulin resistance) of mother, which is the major cause of diabetogenicity of pregnancy. 2. Facilitating fetal use of glucose by increasing fetal glucose uptake. 3. Converting glucose to fatty acids and ketones as additional energy sources of fetus. 4. Preparing maternal mammary glands for the lactation after parturition. What is the role of prostaglandins in pregnancy? Prostaglandins trigger and participate in parturition (childbirth). How does progesterone contribute to pregnancy? Progesterone facilitates implantation and suppresses uterine smooth muscle cell (SMC) contraction preventing preterm labor. What functions do estrogens, particularly estriol (E3), serve during pregnancy? Estrogens, including estriol (E3), promote uterine growth and breast development, working in concert with the maternal-placenta-fetal unit. progesterone in placenta Maternal cholesterol, primarily supplied as LDL particles, serves as a precursor for progesterone synthesis. The placenta utilizes this maternal cholesterol supply to produce substantial amounts of progesterone, which is then distributed to both the fetus and the mother. This mechanism ensures that maternal progesterone levels are maintained even when the corpus luteum's capacity diminishes Physiology Lecture 26 4  estrogenic placenta The placenta collaborates with the mother (providing cholesterol) and the fetal adrenal cortex and liver to produce estrogen/E3 enzymes 17α-hydroxylase and 17,20- Desmolas 16α- hydroxylase uteal-placenta shift the transition from progesterone and estrogen production by the corpus luteum to their production by the placenta. around 8 weeks of pregnancy, marking the point when the embryo is defined as a fetus estrogen to progesterone ratio (E/P ratio) Maintaining a low estrogen to progesterone ratio (E/P ratio) during pregnancy is crucial for maintaining normal and mature gestation. Progesterone relaxes uterine smooth muscle, while estrogen constricts it. The E/P ratio increases later in pregnancy in preparation for parturition. the E3 to E2 ratio erves as an index for evaluating fetal health and placental function. A higher ratio indicates well fetal development facilitated by placental function Placenta synthesis of estriol dependent on the fetal adrenal gland and liver, which provide the enzymes essential for the estrogen synthesis. Maternal Responses weight gain primarily due to an increase in uterus size from approximately 50 grams (10 cm) to 1100 grams (1-2 cm), as well as growth in breasts, fetus, amniotic fluid, placenta, extra blood and extracellular fluid, and accumulation of fat. Maternal Responses Metabolism Increase in basal metabolic rate Development of insulin resistance due to human placental lactogen (hPL), which underlies the diabetogenic effect of pregnancy and is a significant Physiology Lecture 26 5  metabolic change. Maternal Responses Circulatory system Increase in cardiac output during mid-pregnancy (around 27-30 weeks), followed by a decline in the later stages. Expansion of blood volume by 1-2 liters, primarily influenced by elevated estrogen and aldosterone levels that enhance kidney fluid retention. Increased activity of bone marrow to produce additional blood cells to match the expanded blood volume. Maternal Responses Respiratory system Increased alveolar ventilation due to heightened metabolic demands and increased circulating load. Progesterone-induced sensitivity of the respiratory center to CO2, leading to increased CO2 exhalation and a shift towards respiratory alkalosis. Uterine enlargement pressing upwards on the diaphragm, reducing its excursion and causing shallow breathing with increased respiratory rate Maternal Responses renal system Approximately 50% increase in renal tubular reabsorption of sodium chloride and water Increased renal blood flow and glomerular filtration rate to compensate for enhanced tubular reabsorption of salt and water. Maternal Responses nutrition increased demand for nutrition causes of parturition initiation Locally, as pregnancy nears its end, uterine distention itself can stimulate increased contractility Systemically, hormonal (1) and mechanical changes (2) work synergistically to trigger uterine contractions and facilitate parturition Parturition Prostaglandins Physiology Lecture 26 6  Prostaglandins, synthesized in the placenta, play a key role in labor by: i) Softening, dilating, and thinning the cervix (cervical ripening). ii) Stimulating uterine contractions. iii) Enhancing oxytocin-induced contractions by increasing oxytocin receptors in the uterus. estrogen to progesterone ratio (E/P ratio) in parturition functional progesterone withdrawal The increase in the estrogen to progesterone ratio (E/P ratio), also known as 'functional progesterone withdrawal,' involves reduced uterine progesterone receptor expression and/or enhanced progesterone metabolism time dependent ueteurus contract better how does estrogen make uterus contract better Increasing the number of gap junctions between smooth muscle cells, promoting synchronized contractions. Stimulating local production of prostaglandins (PGs). Upregulating oxytocin and prostaglandin receptors to enhance uterine responsiveness. Parturition Oxytocin Oxytocin receptor and oxytocin release increase significantly during entire laboring process in response to increases in estrogens and PGs, and cervical stretch (next slide) CRH in parturition? CRH stimulates the fetal pituitary to release ACTH. ACTH then stimulates the fetal adrenal cortex to release cortisol, which enhances estrogen production. ACTH also promotes the placenta's release of estrogen. Physiology Lecture 26 7  This process helps increase the estrogen to progesterone (E/P) ratio, facilitating functional progesterone withdrawal and the onset of labor. Progressive mechanical changes, as a function of oxytocin Oxytocin stimulates uterine contractions. These contractions lead to cervical stretching as the fetus moves downward. Cervical stretching excites fundic contractions (stronger contractions in the upper part of the uterus). This sends neurogenic signals to the neurohypophysis (posterior pituitary), triggering the release of more oxytocin. This creates a positive feedback cycle that intensifies contractions and progresses labor. lactation positive feedback During pregnancy, estrogen, progesterone, and prolactin increase, but lactation is inhibited because: Estrogen and progesterone block prolactin’s action on the breasts. Prolactin inhibitory hormone (PIH, or dopamine) from the hypothalamus suppresses prolactin release. After parturition, estrogen and progesterone levels drop, removing their inhibitory effects. A reduction in PIH release allows prolactin to stimulate milk production, initiating lactation. lobule A lobule consists of multiple alveoli (milk-producing sacs). These alveoli are connected by one or more excretory ductules, which converge to form a lactiferous duct. The lactiferous ducts merge to form the lactiferous sinus, located just before the nipple. Physiology Lecture 26 8  The nipple is highly innervated, allowing it to serve as a sensor for suckling alveolus types of cells Epithelial Cells: These cells have prolactin receptors and are responsible for milk synthesis and secretion into the alveolar lumen. Myoepithelial Cells: Located on the outer surface of the alveoli, these cells contain oxytocin receptors. Oxytocin stimulates their contraction, helping to eject milk into the lactiferous ducts (milk let-down). lactation essential Prolactin: Stimulates milk synthesis by acting on epithelial cells in the alveoli, leading to milk secretion into the alveolar lumen. Oxytocin: Triggers milk ejection (let-down) by stimulating myoepithelial cells to contract, pushing milk from the alveolar lumen into the ductules. Positive Feedback Loop: Baby suckling sends signals that increase pituitary release of prolactin and oxytocin, reinforcing milk synthesis and ejection. Inhibition of GnRH: High prolactin and oxytocin levels suppress GnRH release from the hypothalamus, reducing FSH and LH, and suppressing the ovarian cycle in nursing mothers. Resumption of Menstrual Cycle: After several months, especially in partial breastfeeding, the inhibitory effect on GnRH declines, allowing FSH and LH to rise and restart the menstrual cycle. Psychogenic Factors: Factors like postpartum depression or sympathetic nervous system activation can decrease prolactin and oxytocin release, reducing milk production and ejection. Physiology Lecture 26 9