Placentation & Endocrinology of Pregnancy
ANS 3319C Reproductive Physiology and Endocrinology Placentation Placentation & Endocrinology of Pregnancy 1) Placenta (eutherian mammals) (Figs. 14-1, 14-2, 14-3) ♦ Transient organ of pregnancy • __________________________________________________________________________ ♦ Transient endocrine gland • __________________________________________________________________________ • __________________________________________________________________________ • __________________________________________________________________________ ♦ Types of placentation • _____________________________: conceptus buries into endometrium ♦ Totally invasive or semi-invasive • _____________________________: placenta attaches to uterine epithelium 2) Placental classifications ♦ Based on villi distribution over chorion • _____________________: uniform villi distribution ♦ Sow: initial attachment day 12, established day 18-20 ♦ Mare (micocotelydons): initial attachment day 24, established day 36-38 • _____________________: villi form zone around middle of chorion ♦ Dogs & cats • _____________________: villi form a regionalized disc ♦ Humans, primates, rodents • _____________________: villi on button-like structures called cotyledons ♦ _________________________________: interface maternal caruncle & fetal cotyledons • Fetal cotyledon: ________________________________________________________ • Maternal cotyledon: _____________________________________________________ ♦ Sheep: 90-100 cotyledons, day 16 initial attachment, established day 30 • 128 Concave caruncles ANS 3319C Reproductive Physiology and Endocrinology Placentation ♦ Cattle: 70-120 cotyledons, day 25 initial attachment, established day 40 • Convex caruncles ♦ ________________________________________________ (cow: up to 5-6 cm diameter) • _______________________________________________________________________ ♦ Number of placental layers between fetal & maternal circulations Fig 14-4, 14-5 • Nomenclature based “prefix” & “suffix” • _____________________: maternal side “epithelio” & fetal side “chorial” ♦ Sow, mare (attachment) can include cow • _____________________: endometrial epithelium transiently erodes & regrows (ruminant) ♦ Intermittent exposure of maternal capillaries to chorionic epithelium ♦ _________________________________________________________________________ • Sheep: day 14 • Migrate from chorionic epithelium, invade endometrial epithelium • Secrete placental lactogen, estrogen, progesterone • ______________________________________________________________________ ∗ • Cow: day 18-20 Unique to ruminants, pregnancy test via blood sample (See BioPryn) ____________________: complete erosion endometrial epithelium/underlying interstitium ♦ ________________________________________________________________ • ____________________: chorionic epithelium in direct apposition to maternal blood ♦ ____________________________________________________ 129 ANS 3319C Reproductive Physiology and Endocrinology Placentation Fig 14-5 Epithelial chorial Endothelial chorial Hemo chorial Hemo endothelial Endothelium + + ¬ ¬ Connective tissue + ¬ ¬ ¬ Epithelium + ¬ ¬ ¬ Trophoblast + + + ¬ Connective tissue + + + ¬ Endothelium + + + + pig, horse, ruminant dog, cat human rat, rabbit Tissue Maternal Fetal Species 130 ANS 3319C Reproductive Physiology and Endocrinology Placentation 3) Placental function ♦ Classical function • Apposition of fetal membranes to maternal endometrium to permit physiologic exchange of gasses & other nutrients between fetus & mother ♦ Specific functions: similar to postnatal animal organ systems • Transmits & provides nutrients: ___________________________ • Exchange of water & gasses: _____________________________ • Excretion of fetal waste: _________________________________ • Modifies fetal & maternal metabolism, maintenance of pregnancy: ___________________ 4) Placental circulation ♦ Characteristics • ___________________________________________________________________________ ♦ Maternal uterine blood flow: _______________________________________________ ♦ Placental & fetal blood flow: _______________________________________________ • Interface between circulations allow for exchange ♦ Maternal substrates & gasses for fetal growth ♦ Fetal waste elimination 5) Placental substrate exchange Mechanism Substance Functions Oxygen, carbon dioxide, water Free fatty acids, Na, K, Cl Homeostasis Substrate for growth Drugs Toxic Glucose Fetal nutrition Amino Acids Fe, Ca, P, Zn Fetal nutrition Endocytosis Transferrin (carries Fe) Source fetal iron Pinocytosis Antibodies (species specific) Immunity Diffusion (simple) Diffusion (facilitated) Active transport 131 ANS 3319C Reproductive Physiology and Endocrinology Placentation ♦ Nutrient/gas exchange • O2 & CO2 ♦ ____________________________________________________________________ • Diffusion O2 from maternal to fetal circulations ♦ ____________________________________________________________________ • Glucose (1° energy source) ♦ ____________________________________________________________________ • Amino acids ♦ ____________________________________________________________________ • Lipid transport limited ♦ ____________________________________________________________________ • Antibodies ♦ DO NOT cross placental barrier: _____________________________________________ • Newborn gets antibodies: _______________________________________________ ♦ DO cross placental barrier: _________________________________________________ • Vitamins: transferred across placenta ♦ Vitamins B, C: water soluble cross more easily ♦ Vitamins A, D, E: lipid soluble cross more slowly • Minerals: transferred across placenta ♦ Under fetal control • Toxic/potentially pathogenic substances ♦ Ethyl alcohol, lead, phosphorus, mercury, opiate drugs, barbiturates, antibiotics ♦ Viruses, bacteria • Teratogenic substances: abnormal development (birth defects) ♦ Amphetamines, lithium, diethylstilbesterol (DES), thalidomide, alcohol 132 ANS 3319C Reproductive Physiology and Endocrinology Placentation 6) Placenta as endocrine organ ♦ Maintains pregnancy ♦ (+) ovarian function ♦ (+) fetal growth ♦ (+) mammary function ♦ Assist in parturition ♦ Mare: eCG (pregnant mare serum gonadotropin-PMSG) • ________________________________________________________ ♦ 5-10 over surface of chorion (trophoblast & endometrial origin; Fig 14-6) ♦ Develop day 35-60 ♦ Secrete eCG from attachment to day 120 (Fig 14-6) • _________________________________________________________________________ ♦ ______________________________________________________________________ ♦ ______________________________________________________________________ • • (+) progesterone to assist in maintaining pregnancy (Fig. 14-7 Powerful FSH like actions: (+) superovulation in cow, sheep, rabbit ♦ Human placenta: hCG (human chorionic gonadotropin) • _________________________________________________________________________ • _________________________________________________________________________ ♦ ______________________________________________________________________ • _________________________________________________________________________ • hCG administered to non-primates induces ovulation 133 ANS 3319C Reproductive Physiology and Endocrinology Placentation Fig 14-7 Fig 14-8 ♦ Placental progesterone (Fig 14-9) • Primary function: block of myometrial contractions • CL of pregnancy (Table 14-1) ♦ Ewe, cow, mare, human: CL NOT REQUIRED for entire gestation, placenta takes over ♦ Sow, rabbit: CL REQUIRED for entire gestation 134 ANS 3319C Reproductive Physiology and Endocrinology Placentation Table 14-1 Gestational length and time of placental takeover for progesterone production in various species Species Gestation length Time of placental take over Alpaca 11.4 mo None Bitch 2 mo (65 days) None Camel 12.3 mo None Cow 9 mo (283 days) 6-8 mo Ewe 5 mo 50 days Goat 5 mo None Llama 11.3 mo None Mare 11 mo Queen 2 mo (65 days) None Rabbit 1 mo None Sow 3.8 mo (113 days) None Woman 9 mo 70 days 60-70 days ♦ Placental Lactogen (somatomammotropin; Fig 14-10) • Secreted in rats, mice, sheep, cows, humans • Growth hormone like actions (species specific) • Lactogenic actions: stimulates mammary gland (species specific) 135
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