General Embryology (PDF) - Griffith University

General embryology Dr. Umesh Bindal Copyright © Griffith University. Griffith University claims copyright ownership of all material on this video unless expressly stated otherwise. No part of the video may be copied (except as allowed by the copyright law of your country) or further disseminated wit...

General embryology Dr. Umesh Bindal Copyright © Griffith University. Griffith University claims copyright ownership of all material on this video unless expressly stated otherwise. No part of the video may be copied (except as allowed by the copyright law of your country) or further disseminated without the express and written permission of Griffith University. To seek copyright permission, email: [email protected]. Module Learning outcomes Outline the key stages of embryonic development from fertilization to flexion of the embryo (First four weeks of embryonic development) Clinical correlation Lecture- series 1. 2. 3. 4. 5. Fertilization First week Second week Third week Fourth week Fertilisation Before we start fertilization we will review the process of gametogenesis Gametogenesis It is a process of formation of male and female gametes Male gametes called sperms forms in testis Female gametes called oocyte forms in the ovary Oogenesis Oocytes ~2 million at birth ~40,000 at puberty ~400 ovulated over a lifetime Structure of the primordial follicle Oogenesis At the time of birth primary oocyte is arrested in the prophase of meiosis I At puberty, the female begins to undergo regular monthly cycles (menarche). About 15 to 20 primordial follicles from the pool will begin to mature Primary oocyte in the follicle will pass through the stages of Meiosis 1 and 3 hours before ovulation it will complete Meiosis 1 and forms a secondary oocyte and smaller cell forms the first polar body. The secondary oocyte is arrested in the metaphase of Meiosis 2 which will complete at the time of fertilization. Menstrual cycles are controlled by the hypothalamus. Gonadotropin-releasing hormone (GnRH) produced by the hypothalamus acts on cells of the anterior pituitary gland, which in turn secrete gonadotropins. These hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), stimulate and control cyclic changes in the ovary. Precocious puberty? https://www.uptodate.com/contents/image?imageKey=PEDS%2F98701~PEDS%2F98702&topicKey=PEDS%2F5849&source=see_link Reference: https://www.histology.leeds.ac.uk/female/FRS_ova.php https://youtu.be/KXmx958r33A Summary Under the influence of Progesterone (and Oestrogen), the endometrium undergoes a secretory change to receive the embryo It becomes Thicker, with Increased vascularity, Increased glandular secretions, cervical mucus → Thick ovulation Clinical correlation of ovulation Middle pain Increase in basal body temperature Ovulation stimulation in case of low gonadotropin levels- for exampleclomiphene citrate Product of ovulation: During ovulation, the secondary oocyte arrested in metaphase of meiosis 2 is covered by Zona pelucida & a bunch of supporting cells (cumulus oophorus) is released into the peritoneal cavity. Spermatogenesis https://youtu.be/6fBa8UqEano Spermatogenesis Spermiogenesis is the process by which haploid round spermatids complete an extraordinary series of events to become streamlined spermatozoa capable of motility. Mature sperm Abnormal germ cells: Reference reading Please read chapter-1 from the book Fertilization The product of the ovulation is transported to the ampullary part of the fallopian tubes The fimbriae of the fallopian tube grasp the ovum and take it into the fallopian tube. The transportation of the ovum through the tube is facilitated by the smooth muscle contractions and the ciliary action of the tubes. If healthy sperms are available, fertilization takes place usually in the ampullary region usually within 24 hrs after ovulation. Fertilization Fertilization, the process by which male and female gametes fuse, occurs in the ampullary region of the uterine tube. Video: https://youtu.be/_5OvgQW6FG4 Result of fertilisation: 1. Restoration of the diploid number of chromosomes, half from the father and half from the mother. Hence, the zygote contains a new combination of chromosomes different from both parents. 2. Determination of the sex of the new individual. An X-carrying sperm produces a female (XX) embryo, and a Y-carrying sperm produces a male (XY) embryo. Hence, the chromosomal sex of the embryo is determined at fertilization. 3. Initiation of cleavage. Without fertilization, the oocyte usually Degenerates 24 hours after ovulation Timing of pregnancy/ calculation of EDD Embryologists Fertilization age: a moment of fertilization Division of pregnancy corresponding to development: 0-3 weeks –early development 3-8 weeks –embryonic period (organogenesis) 8 wks-term –fetal period Total gestation time = 38 weeks Clinicians Menstrual age: last menses Division of pregnancy into trimesters Total gestation time = 40 weeks Clinical correlation: Contraceptives to prevent pregnancy/fertilization Barrier Contraceptive pills Intrauterine device Permanent methods- vasectomy or tubectomy Drugs for abortion in the initial 8 weeks of pregnancy: RU-486 (mifepristone) Infertility IVF First and Second weeks of development https://www.toppr.com/ask/en-ae/question/name-the-embryonic-phase-which-changes-zygote-into-blastula/ Once the zygote has reached the two-cell stage, it undergoes a series of mitotic divisions, increasing the number of cells. These cells will become smaller with each cleavage division, known as blastomeres. Play the following video and select the part zygote till implantation in the video https://youtu.be/8312a32dcQc Timeline in the video start from the first day of the menstrual cycle for exact timing please follow the timeline as mentioned in this lecture. The animation in the video is to understand the process. At the end of the first week of development, the blastula enters the uterine cavity and hatches out of the zona pellucida. Inner cell mass- Embryoblasts Blastocoele- Yolk sac Outer cell mass- Trophoblast Day- 5-6 after fertilisation Implantation to Bilaminar germ disc (Week 2) Implantation Blastocysts will start invading the uterine wall by attaching it at the embryonic pole Implantation occurs around 7- 8 days after fertilization. Site: a posterosuperior wall of the uterine cavity Endometrial changes to receive the Embryo Decidualization is a process that results in significant changes to cells of the endometrium in preparation for, and during, pregnancy. By this time (the second half of the menstrual cycle) the uterine endometrium is ready to accept the embryo. The first half is oestrogen dominant for the proliferation of the endometrium. – 2nd half – Progesterone dominant – converts proliferated endometrium to a secretory type; one capable of providing nutrition to the early embryo. Ultrasonographic assessment of the endometrium Echogenic uterine cavity Thin hypoechoic functional layer A thick hypoechoic functional layer A thick hypoechoic functional layer Trophoblasts, HCG and Pregnancy Test The trophoblast cells secrete a hormone, Human chorionic gonadotrophin (HCG), Which is essential for the maintenance of the corpus luteum which in turn secretes progesterone and oestrogen to maintain pregnancy. HCG appears in maternal blood after implantation (7-8 days) and takes another 2-3 days to appear in the urine. Abnormal Implantation & ectopic pregnancy The rate of ectopic pregnancy is 11 per 1000 pregnancies, with a maternal mortality of 0.2 per 1000 estimated ectopic pregnancies. Risk factors Tubal abnormalities (Pelvic inflammatory disease & Pelvic surgeries) IUCD Previous ectopic Previous abortions Increasing age 35< Smoking ……… Locations Fallopian tube - Commonest Peritoneal cavity Ovary Cervical Broad ligament Presentation of Ectopic pregnancy. female of reproductive age, with a history of a missed period, presenting with Lower abdominal pain. Bleeding PV. May present with symptoms of shock. Ix - HCG test/USS scan https://radiologykey.com/ectopic-pregnancy-7/ Ectopic pregnancy in the ampullary portion of a fallopian tube. Week 2 of embryonic development Animation video of events taking place in week 2 https://youtu.be/bIdJOiXpp9g Cross section of placental villi CTB proliferates into STB core. 1ry Villi – 2nd week EEM proliferates into CTB and STB core. 2ry Villi – end of 2nd week Fetal capillaries develop within the EEM  fetomaternal 3ry Villi – end of 3rd week circulation starts Placental membrane (PM) 3wks < - Trimester 1 12wks < -Trimester2 36 wks < - Term STB nuclear knots STB CTB Fetal endothelium STB CTB start disappearing. Some fetal capillaries (Saprse) are directly in contact with STB. PM Fetal endothelium +EEM + CTB + STB CTB start disappearing. EEM become thinner. Fetal capillaries grow & are directly in contact with STB. PM Fetal endothelium + STB with Nuclei STB/EEM become thinner and nuclei form knots that are placed away from the capillaries. Highly vascular. PM Fetal endothelium STB (Thinner, No nuclei) End of Week 3 End of Week 2 Connecting stalk Chorion Note only a narrow band of EEM connects (connecting stalk – Future Umbilical cord) the developing embryo to the Chorion. Note the 2ry villi Note the embryo- BL Disc Connecting stalk Chorion Note the development of fetal placental vessels within EEM forming the 3ry villi. Note the embryo - BL disc has been changed ……. Endometr site of placenta (Decidua Basalis) encircles gestational sac Umbilical vessels Amnion Amniotic cavity Chorionic cavity Uterine Cavity Chorion Note during early development, chorionic villi surround the whole embryo. With the rapid growth, embryo is pushed into the uterine cavity with its coverings. The surrounding chorionic villi disappear except at the future location of the placenta. Post implantation - Components of the maternal Endometrium (Decidua) Decidua basalis Decidua basalis Decidua Parietalis Decidua Capsularis http://www.embryology.ch/anglais/fplacenta/circulplac01.html Fused capsularis and parietalis Maternal surface of the placenta Fetal surface of the placenta Functions of the Placenta Gas & Nutrient exchange. Elimination of metabolic waste products (Bilirubin). Hormone production – HCG – 1st 2 months – Progesterone – (produce enough quantity to maintain the pregnancy) – Oestriol – Somatomammotropin Immunological - maternal antibodies transfer (IgG). Barrier for certain chemicals and organisms. The placenta is not an absolute barrier, Some chemicals & organisms can cross the placental barrier. Gases Carbon monoxide Infectious agents Viruses (HIV, cytomegalovirus, rubella, Coxsackie, varicella, measles, poliomyelitis), bacteria (tuberculosis, Treponema), and protozoa (Toxoplasma) Alcohol, Cocaine, caffeine, nicotine, Drugs Ig warfarin, trimethadione, phenytoin, tetracycline, cancer chemotherapeutic agents, anesthetics, sedatives, analgesics, Steroids Anti Rh antibodies Clinical conditions associated with membrane and placental development 1. Placenta praevia (PP) Condition where the placenta is formed in the lower segment of the uterus. Based on whether the placenta occludes the internal Os or not, PP is categorised into minor and major groups. Presentation – Third trimester bleeding. https://doi.org/10.1017/CBO9781107585799.003 3. Molar Pregnancy Abnormal proliferation of chorionic villi giving rise to either a partial mole (with fetal tissue) or complete mole (without fetal tissue). associated with chromosomal abnormalities (Eg. presence of only paternal chromosomes) Presentation First trimester bleeding, Hyperemesis Ix – high levels of HCG Rarely do these cells may remain in the uterus after pregnancy. give rise to a malignant variety of C h o r i o c a rc i n o m a. Snowstorm appearance