Introduction to Human Embryology PDF

introduction to human embryology Dr. Hanan Al-Lataifeh references 1. Keith L. Moore & T.V.V Persaud, Before we are born, Latest Edition 2. Gerard J. Tortora & Mark T. Niels, Principles of Human Anatomy, Latest Editionen 3. Langman embryology objectives Define the topic of...

introduction to human embryology Dr. Hanan Al-Lataifeh references 1. Keith L. Moore & T.V.V Persaud, Before we are born, Latest Edition 2. Gerard J. Tortora & Mark T. Niels, Principles of Human Anatomy, Latest Editionen 3. Langman embryology objectives Define the topic of embryology including male and female gametogenesis Understand the process of fertilization and embryo implantation introduction Embryology: is the science that is concerned with humans’ origin and development from the zygote to birth Human development begins by fertilization of an ovum by a sperm to form the zygote, then it will undergo changes to produce a human introduction Puberty age begins when secondary sex characteristics appear (pubic hair) 12-15 in females and 13-16 in males introduction Puberty age begins when secondary sex characteristics appear (pubic hair) 12-15 in females and 13-16 in males Menarch: first menstruation introduction Puberty age begins when secondary sex characteristics appear (pubic hair) 12-15 in females and 13-16 in males Menarch: first menstruation Gametogenesis: is the process of producing gametes introduction Puberty age begins when secondary sex characteristics appear (pubic hair) 12-15 in females and 13-16 in males Menarch: first menstruation Gametogenesis: is the process of producing gametes Gametes have haploid number of chromosomes introduction Puberty age begins when secondary sex characteristics appear (pubic hair) 12-15 in females and 13-16 in males Menarch: first menstruation Gametogenesis: is the process of producing gametes Gametes have haploid number of chromosomes They are sex cells Sperms in males ( from testes) Oocytes in females ( from ovaries) introduction Gametogenesis: is the process of producing gametes Spermatogenesis: Oogenesis : introduction Oocyte: the female germ cell produced by ovaries introduction Oocyte: the female germ cell produced by ovaries Secondary oocyte : the mature oocyte introduction Oocyte: the female germ cell produced by ovaries Secondary oocyte : the mature oocyte Sperm : the male germ cell produced by testes(pl. spermatozoa) introduction Oocyte: the female germ cell produced by ovaries Secondary oocyte : the mature oocyte Sperm : the male germ cell produced by testes(pl. spermatozoa) Embryo: is the developing human during all early stages of development introduction Oocyte: the female germ cell produced by ovaries Secondary oocyte : the mature oocyte Sperm : the male germ cell produced by testes(pl. spermatozoa) Embryo: is the developing human during all early stages of development Zygote: the diploid cell (2n) formed by union of an oocyte and a sperm. It is the beginning of a humanbeing. introduction Oocyte: the female germ cell produced by ovaries Secondary oocyte : the mature oocyte Sperm : the male germ cell produced by testes(pl. spermatozoa) Embryo: is the developing human during all early stages of development Zygote: the diploid cell (2n) formed by union of an oocyte and a sperm. It is the beginning of a humanbeing. Fertilized ovum: secondary oocyte impregnated by a sperm introduction it is difficult to determine when fertilization occurred exactly introduction Cleavage of the zygote: mitotic cell division will form embryonic cells called blastomeres The size of early embryo = that of the zygote (cells of blastomeres become smaller with divisions) Zygote--cleavage continues -morula introduction Morula: an embryo at day 3, consists of 12-32 cells. (cluster of cells resembling a mulberry) At day 3 an embryo is formed of cluster of cells that resembles a mulberry Blastocyct: 1. Morula enters the uterus 2. Inside morula a fluid filled cavity (blastocystic cavity) is formed 3. Blastocyst contains inner cell mass (= embryoblast) that will for the embryo introduction There are 2 ways for calculation: 1. Gestational age : from the first day of last normal menstrual period 2. Fertilization age: since fertilization occurs ( 2 wks < gestational age ) introduction Conceptus: is the whole products of conception since fertilization = embryo + membranes (placenta) introduction Conceptus: is the whole products of conception since fertilization = embryo + membranes (placenta) Primordium: the first indication of an organ or structure introduction Conceptus: is the whole products of conception since fertilization = embryo + membranes (placenta) Primordium: the first indication of an organ or structure Embryonic period: till end of week 8 introduction Conceptus: is the whole products of conception since fertilization = embryo + membranes (placenta) Primordium: the first indication of an organ or structure Embryonic period: till end of week 8 Fetal period: ninth week to birth introduction Differentiation and growth occurs in fetal period Functional maturation of organs and rate of body growth are high in 3rd and 4th months Increase in weight in terminal months introduction Trimester : period of pregnancy consists of 3 calendar months 9 months are divided into 3 trimesters introduction Conceptus: is the whole products of conception since fertilization = embryo + membranes (placenta) Primordium: the first indication of an organ or structure Embryonic period: till end of week 8 Fetal period: ninth week to birth Differentiation and growth occurs in fetal period Functional maturation of organs and rate of body growth are high in 3rd and 4th months Increase in weight in terminal months Trimester : period of pregnancy consists of 3 calendar months 9 months are divided into 3 trimesters introduction Abortion: expulsion of embryo or fetus before being viable Viable: mature enough to survive outside the uterus introduction embryology…… why? To understand the normal ……reasons of anomalies Human embryonic stem cells are pluripotent : able to differentiate into different cell type directional terminology and body planes Anatomical position Anterior /Posterior Superior /Inferior Lateral /Medial Caudal /Cranial Dorsal /Ventral Sagittal plane – Coronal section- frontal plane Transverse section types of cells Somatic cells: have 2 sets of chromosomes= diploid number= 2n= 46 Divide by mitosis Germ line cells= have 2 sets of chromosomes= diploid number= 2n= 46 Divide by meiosis giving ….. Gametes are produced from germ cells have 1 set of chromosomes= haploid number= 1n= 23 chromosomes in embryos Gametes are derived from primordial germ cells that are formed in the epiblast later they migrate to the wall of the yolk sac….. migrate from the yolk sac toward the developing gonads( reach by week 5)….. Mitosis to increase in their number…then ….gametogenesis produces gametes  Traits are determined by specific genes on chromosomes Humans have 23,000 genes on 46 chromosomes.  In somatic cells, chromosomes appear as 23 homologous pairs to form the diploid number of 46. There are 22 pairs of matching chromosomes, the autosomes, and one pair of sex chromosomes. If the sex pair is XX, the individual is genetically female; if the pair is XY, the individual is genetically male. One chromosome of each pair is derived from the maternal gamete, the oocyte, and one from the paternal gamete, the sperm. each gamete contains a haploid number of 23 chromosomes, and the union of the gametes at fertilization restores the diploid number of https://s3-us-west-2.amazonaws.com/courses- images/wp- centromere vs. kinetochore centromere : the region where the two sister chromatids are held together after the replication of chromosome Kinetochore: the protein complex on the chromosome where spindle fibers are attached during cell division Image from https://ibiologia.com cell division 2 types 1. Mitosis: 2. Meiosis  mitosis Mitosis is the process of cell division ending with two daughter cells that are identical to the parent cell Before a cell enters mitosis, each chromosome replicates its DNA (chromosomes are extremely long, they are spread diffusely through the nucleus, and they cannot be recognized with the light microscope). prophase chromosomes begin to coil, contract, and condense. Each chromosome consists of two parallel chromatids, joined at a narrow region (centromere). chromosomes continue to condense, shorten, and thicken. Metaphase:the chromosomes line up in the equatorial plane, doubled structure is visible Anaphase: mitotic spindles are formed. the centromere of each chromosome divides, Telophase: migration of chromatids to opposite poles of the spindle. Cytokinesis: cytoplasm division  meiosis Meiosis is the cell division that takes place in the germ cells to produce gametes meiosis I & meiosis II to reduce the number of chromosomes to the haploid number of 23 Cells replicate their DNA at the beginning of meiosis I (each of the 46 chromosomes is duplicated into sister chromatids). homologous chromosomes then aline a themselves in pairs(synapsis). The pairing is exact and point for point except for the XY combination. Homologous pairs then separate into two daughter cells, thereby reducing the chromosome number from diploid to haploid. Each gamete then contains 23 chromosomes.  meiosis Crossover: are the interchange of chromatid segments between paired homologous chromosomes a critical events in meiosis I Segments of chromatids break and are exchanged as homologous chromosomes separate. As separation occurs, points of interchange are temporarily united and form an X-like structure, a chiasma  meiosis A. Homologous chromosomes approach each other. B. Homologous chromosomes pair, each consists of two chromatids. C, Paired homologous chromosomes interchange chromatid segments [crossover]. D. Double - structured chromosomes pull apart. E. Anaphase of the first meiotic division. F,G. During the second meiotic division, the double— structured chromosomes split at the centromere. At completion of division, chromosomes in each of the four daughter cells are different from each  meiosis Results of meiotic divisions: Genetic variability (Crossover redistributes genetic material ) Random distribution of homologous chromosomes to the daughter cells Each germ cell contains a haploid number of chromosomes so that at fertilization, the diploid number of 46 is restored  gametogenesis The process of formation & development of gametes Spermatogenesis in males starts at puberty (13-16y) Oogenesis in females starts during fetal period stop during meiosis 1, resume at puberty  spermatogenesis Transformation of spermatogonia into spermatozoa Takes place at puberty within seminiferous tubules of testes I. Spermatocytogenesis: division & growth of primitive sperm cells (spermatogonia) into spermatocytes II. Meiosis: division of spermatocytes (2n) into haploid cells (spermatids, 1n) III. Spermiogenesis: transformation (Metamorphosis) of spermatids into sperms (spermatozoa) spermatocytogenesis & meiosis Spermatogonia (primitive germ cells): Present during fetal period After puberty mitosis and increase in size to form Primary spermatocytes Primary spermatocytes: Largest germ cell in seminiferous tubules (2n). Enter the first meiotic division to form Secondary spermatocytes Secondary spermatocytes: chromosomes (1n) Enter the 2nd meiotic division to produce spermatids Spermatids: (1n) spermiogenesis The transformation of spermatids into elongated sperms (spermatozoa) mature sperm Head: nucleus & acrosome Neck Tail: middle piece: mitochondria Principal piece end piece spermatogenesis Spermatogenesis process requires 2 months (64 days) oogenesis oogenesis Is the formation of gametes in the ovaries occurs 1. Primordial germ cells will develop to give diploid (2n) oogonia 2. Diploid oogonia divide by mitosis during early fetal development to produce millions of germ cells; before birth, most of the latter degenerate by atresia. 3. few oogonia will develop into larger cells, called primary oocytes 4. primary oocytes enter prophase of meiosis I during fetal development but do not complete this phase until after puberty. 5. Each month during a woman’s reproductive years, several primordial follicles ( primary oocyte and single layer of follicular cells) start to grow and become primary follicles( surrounded by several layers of follicular cells) 6. Follicle grows and cells around oocyte secrete a fluid in a cavity ( antrum), follicle is now secondary follicle 7. After puberty, each month meiosis I resume in several secondary follicles, only one will mature fully to give two haploid cells ( secondary oocyte and 1st polar body) 8. secondary oocyte and 1st polar body begin meiosis II and stop at metaphase ii 9. Ovulation occurs 10. If fertilization occurs, meiosis II will resume and the secondary oocyte divides into two haploid cells: the ovum and a 2nd polar body 11. The sperm will unite with the ovum to give the zygote Secondary oocyte is a large cell can be seen by naked eye Secondary oocyte at ovulation begins 2nd miotic division and stop at metaphase If fertilization occurs it will resume meiosis II If no fertilization it will degenerate A new born ovary contains up to 1 million primary oocyte At puberty only 40000 remain 400 mature secondary oocytes ovulated during life of females During follicle development the secondary oocyte is surrounded by a covering of a material known as Zona pellucida and a layer of follicular cells (corona radiata) Cumulus oophorus : follicular cells project into antrum Image from : Gerard J. Tortora & Mark T. Niels, Principles of Human Anatomy, 13th Editionen gametogenesis Male gametes Female gametes Highly motile Not motile Small sized Large sized Two types: x- chromosomes’ One type with X- sperms and y- chromosomes’ chromosome sperms 4 sperms result from 1 oocyte result from cell division division transport An oocyte will enter the first part of Fallopian tube as fimbriae will move making a current , then to ampulla and isthmus through peristaltic movement of the tube and finally enter the uterus transport Sperms will move from epididymis by peristaltic movement Secretions from the gland will be added to form semen and then semen ejaculated No. of sperms is 200-600 million sperms are highly motile and they will travel in the vagina vaginal plug will be formed by semen to prevent backflow of it out 200 sperms reach fertilization site maturation of sperms capacitation Fresh sperms are unable to fertilize an ovum There is about 7 hours conditioning period Glycoprotein coat and seminal proteins removed from surface of acrosome No morphological changes but increased activity Occurs in uterus or uterine tubes viability of gametes Oocytes should be fertilized within 12 hours They can not do so after 24 hours as they will degenerate Invetro fertilization (outside the body) can occur even if gametes were frozen for many years  Fertilization: Fusion of male gamete & female gamete to form the zygote begins with the contact between the oocyte and the sperm, and ends with intermingling of maternal & paternal chromosomes at metaphase of the 1st mitotic division of the zygote. Locations : ampulla of uterine tube phases of fertilization 1-Passage of sperm through corona radiata. 2-Penetraton of the zona pelleucida. 3- Fusion of plasma cell membaranes of the oocyte and the sperm. 4- Completion of the second meiotic division of the oocyte. 5- Formation of the male pronulceus. 6-Break down of pronuclear membaranes. Figure 3-1 Acrosome reaction and sperm penetration of an oocyte. 1, Sperm during capacitation. 2, Sperm undergoing the acrosome reaction. 3, Sperm forming a path through the zona pellucida. 4, Sperm entering the cytoplasm of the Downloaded oocyte. from: StudentConsult (on 29 September 2012 08:44 AM) © 2005 Elsevier  phases of fertilization 1. Passage of the sperm through corona radiata Hyaluronidase from acrosome of the sperm 2. Penetration of zona pellucida Acrosomal enzymes (Acrosin, esterases, & neuraminidase)  lysis of zona pellucida  path for the sperm  phases of fertilization 3. Fusion of plasma membranes of oocyte & sperm * Zona reaction: changes in the properties of Z.P. that makes it impermeable to other sperms  phases of fertilization 4. Formation of female pronucleus Completion of the second meiotic division of the oocyte & forms 5. Formation of male pronucleus Sperm nucleus enlarge & become rounded Tail degenerates  phases of fertilization 6. Pronuclei replicate DNA 7. Breakdown of the pronuclear membranes Condensation of the chromosomes,  mitotic cell division first cleavage division of the zygote occurs. results of fertilization 1- stimulates the secondary oocyte to complete the 2nd meiotic division producing the second polar body. 2- restores the normal diploid number (46) in the zygote. 3- results in variation of human sepcies. 4- determines the chromosomal sex of the embryo. 5- causes metabolic activation of the oocyte , which initiates cleavage of the zygote.  cleavage of the zygote Repeated mitotic divisions of the zygote into many cells (Blastomeres) Compaction: compact ball of tightly aligned cells after 8 cell stage Morula (like mulberry): 12 to 32 blastomeres surrounded by zona pellucida 4 days after fertilization * time to enter the uterine cavity blastogenesis Early blastocyst: (late Day 4) Fluid-filled space is formed Fluid comes from uterine fluid Late blastocyst: (Day 5) Z.P. is shed at day 5 hatching blastomeres differentiate into: 1. Trophoblast: outer cell layer = embryonic part of placenta 2. Inner cell mass (embryoblasts): a group of blastomeres gathered at periphery give rise to the embryo cleavage Occurs in the uterine tube Once the zygote has reached two cell stage it undergoes a series of mitotic divisions, increasing the number of cells. These cells which become smaller with each cleavage division, are known as blastomeres. Division of the zygote begins approximately 30 hrs. After fertilization. During cleavage the zygote is still surrounded by zona pellucida. Until the eight cell stage , they form a loosely arranged clump. After the 3rd cleavege blastomeres form a compact ball of cells  morula Approximately 3 days after fertilization, cells of the compacted embryo divide again to form a 16-cell morula (mulberry). Inner cells of the morula constitute the inner cell mass, and surrounding cells compose the outer cell mass. The inner cell mass gives rise to tissues of the embryo proper, and the outer cell mass forms the trophoblast, which later contributes to the placenta. blastocyst Once the morula enters the uterine cavity, fluid will penetrate through the zona pellucida into the intercellular spaces of the inner cell mass. Gradually, the intercellular spaces become confluent, and finally, one cavity (blastocele), forms and the embryo is a blastocyst.  Blastomeres separated into two parts:- A. embryoblast: Cells of the inner cell mass are at one pole B. trophoblasts: the outer cell mass flatten and form the epithelial wall of the blastocyst. The zona pellucida has disappeared, allowing implantation to begin. trophoblastic will penetrate endometrium the uterus on about the sixth day (implantation) Downloaded from: StudentConsult (on 29 September 2012 08:44 AM) © 2005 Elsevier implantation The entrance of the blastocyst into the thick endometrium of the uterus Time: Starts at 6th-8th day and completed at 12th day.  implantation 1. Blastocyst attaches to endometrial epithelium 2. Trophoblast proliferate & differentiate into two layers: 1. Cytotrophoblasts inner layer of cells 2. Syncytiotrophoblast layer: outer layer of multinucleated protoplasmic mass of tissue (no cell boundaries) Erode the endometrium 3. The blastocyst becomes embedded into the endometrium The site of implantation is closed by a fibrin clot. 4. the blastocyst is completely embedded in the endometrium & the surface epithelium covers the original defect in the uterine wall Syncytiotrophoblast Multinucleated protoplasmic mass Have a phagocytic function