Transcript Section 4
Isfahan University of Technology College of Agriculture, Department of Animal Science Advanced Reproduction Physiology (Part 4) Prepared by: A. Riasi http://riasi.iut.ac.ir Placentation, the Endocrinology of Pregnancy and Parturition Reference: Pathways to Pregnancy and Parturition (Second revised edition) By: P. L. Senger, 2005 Placenta formation The phenomenon of intrauterine development ensures that the developing conceptus will receive adequate nutrient and protection during its development. Placenta formation The placenta is a transient organ of metabolic interchange between the conceptus and dam. It is also a transient endocrine organ. The placenta in composed from two parts: Fetal component derived from the chorion Maternal component derived from modifications of the uterine endometrium Placenta formation The functional unit of the fetal placenta is the chorionic villus. Specific of mare placenta: It has many specialized microzones of chorionic villi known as microcotyledons It contains unique transitory structure known as endometrial cups. Placenta formation Placenta formation Ruminant have cotyledonary placenta. Placentome consists of: Fetal cotyledon contributed by the chorion Maternal cotyledon, originating from caruncular regions of uterus Placenta formation The migrating binucleate giant cells (BGC) in the ruminat placenta Placenta formation The characteristics and functions of BGC: They are quite large and two nuclei originated from trophoblast cells. They are formed continuously throughout gestation. The BGC migrate from the chorionic epithelium and invade the endometrial epithelium. Placenta formation The characteristics and functions of BGC (continue): They are believed to transfer complex molecules from the fetal to maternal placenta. These cells secrete pregnancy specific protein B (PSPB) and placental lactogen. Placenta functions The placenta regulate the exchange between fetus and dam. Placental exchange ways: Simple diffusion Facilitated diffusion Active diffusion Placenta functions Placental transportation: Gases Water Minerals and vitamins Glucose and Amino Acids Proteins Lipids Placenta functions Placental transportation (continue): Large peptide hormones (TSH, ACTH, GH, insulin, glucagon) Smaller molecular weight hormones (steroids, T3 and T4) and catcholamines Toxic substances Bacteria and viruses Placenta functions In addition to serving as a metabolic exchange organ, the placenta serves as a transitory endocrine organ. Hormones from the placenta gain accesss to both the fetal and the maternal circulation. Placenta functions The placenta produces hormones that can affect: Stimulate ovarian function Maintain pregnancy Influence fetal growth Stimulate mammary function Assist in parturition Placenta functions Placenta functions Placenta functions Placenta functions The placenta secretes progesterone and estrogen Progesterone provides the stimulus for elevated secretion by the endometrial glands Progesterone inhibits (progesterone block) myometrial contraction Placenta functions Placenta functions In addition to progesterone, estrogens are also an important product of the placenta. The placental estrogens are particularly important during the last part of gestation and in most species signals the early preparturient period. Placenta functions The placenta produce placental lactogen or somatomammotropin. This hormone have two major effect: Promoting the growth of fetus Stimulating the mammary gland of the dam Placenta functions Placenta functions Relaxin This is also a product of placenta. hormone is produce in some species: Humans Mares Rabbits Pigs and monkeys Cats and dogs Placenta functions Relaxin cause: Softening of the connective tissue in the cervix Promotes elasticity of pelvic ligaments Physiology of parturition The fetal hypothalamo-pituitary-adrenal axis is obligatory for initiation of parturition. During the conclusion of gestation, fetal mass approaches the inherent space limitations of the uterus. Physiology of parturition Limited space for fetus Fetus cortisol Fetus hypothalamus Fetus ACTH Placental estrogen Uterus PGF2α Induction of parturition Progesterone Physiology of parturition Plasma cortisol concentration changes during sheep gestation (Yuen et al. 2004) Physiology of parturition Prepartum increase in sheep circulating cortisol is required for the differentiation and maturation of key fetal organs: Lung Liver Kidney Brain Physiology of parturition A positive relationship between the level of activation of the fetal hypothalamus-pituitaryadrenal axis and leptin synthesis and/or secretion in late gestation. Physiology of parturition The endocrine changes cause two major events to occur: Removal of the myometrial “progesterone block” enabling myometrial contractions to begin Increased reproductive tract secretions particularly by the cervix Physiology of parturition Three stages of parturition are: Initiation of myometrial contractions Expulsion of the fetus Expulsion of the fetal membranes Physiology of parturition Effect of fetal corticoids: Converting progesterone to estradiol Synthesizing PGF2α by placenta As both estradiol and prostaglandin become elevated, the myometrium becomes increasingly more active The CL of pregnancy regress Physiology of parturition Physiology of parturition Physiology of parturition Relative hormone profiles in the cow during the periparturient period Physiology of parturition Physiology of parturition Physiology of parturition Follistatin and activin may be also involved in the mechanism of natural parturition (Xia et al. 2009) Physiology of parturition In pre-parturition period birth canal is lubricated by: Mucus secretion in cervix and vagina Fetal membrane rupture and loss of amniotic and allantoic fluid Physiology of parturition As the fetus enters the birth canal, it becomes hypoxic Hypoxia promotes fetal movement that, in turn, promotes further myometrial contraction Physiology of parturition In most species, expulsion of the fetal membranes quickly follows expulsion of the fetus It is believed that vasoconstriction of arteries in villi reduces pressure and thus allows the villi to be release from the crypts Physiology of parturition Prolonged parturition can result in serious complications to both the fetus and dam. Different causes for dystocia: Excessive size of fetus Failure of proper fetal ritation Multiple births in monotocous species Some research papers associated to this lecture 1. Leibovicha, H., et al. 2001. Effects of recombinant ovine placental lactogen and recombinant ovine growth hormone on growth of lambs and milk production of ewes. Livestock Production Science 68: 79–86. 2. Probo, M., et al. 2011. Peripartal Hormonal Changes in Alpine Goats: a Comparison Between Physiological and Pathological Parturition. Reprod Dom Anim 46: 1004– 1010. 3. Leury, B. J., et al. 2003. Effect of insulin and growth hormone on plasma leptin in periparturient dairy cows. Am. J. Physiol. Regul. Integr. Comp. Physiol. 285: 1107– 1115. 4. Murawski, M., et al. 2011. Cortisol, progesterone and estradiol secretion in vitro in postpartum placental cotyledons of ewes that gave birth to single or twin lambs. Ann. Anim. Sci., 11: 53–60.