1. Introduction to Embryology is book of science
- 1. Introduction to the study of Embryology By:- Dr. Alazar. E JUNE 15/2023
- 2. What is Embryology What is Embryology • • • • origin and development fertilization of the ovum birth of the fetus. origin and development fertilization of the ovum birth of the fetus. origin and development fertilization of the ovum birth of the fetus. origin and development fertilization of the ovum birth of the fetus. The study of origin and development of human being from fertilization of the ovum to the birth of the fetus. Prenatal development Could be divided into three periods During the first 2 weeks 3rd-8th weeks (Embryonic period) 9th -38th weeks (Fetal period)
- 3. Pre-fertilization Events Pre-fertilization Events SEXUAL REPRODUCTION Sexual reproduction Sexual reproduction occurs when female and male gametes fertilization. female and male gametes fertilization. female and male gametes fertilization. female and male gametes fertilization. female (oocyte) and male gametes (spermatozoon) unite at fertilization. • • • Gametes Gametes are direct descendants of primordial germ cells first observed in the wall of the yolk sac at week 4 of embryonic development and subsequently migrate into the future gonad region. gametogenesis produced by gametogenesis oogenesis in the female and spermatogenesis in the male. employs a specialized process of cell division, meiosis, which uniquely distributes chromosomes among gametes.
- 4. • – – CHROMOSOMES CHROMOSOMES two characteristic regions A single chromosome consists of two characteristic regions called arms which are separated by a centromere. p arm = short arm q arm = long arm • – meiosis I DNA replication, meiosis I DNA replication, During meiosis I, single chromosomes undergo DNA replication, which duplicates the arms. sister chromatids sister chromatids sister chromatids This forms duplicated chromosomes, which consist of two sister chromatids attached at the centromere.
- 5. – – Ploidy and N number. Ploidy- Number of chromosomes in a cell. N - Amount of DNA in a cell. • • • • • • somatic cells germ cells 46 single chromosomes amount of DNA. somatic cells germ cells 46 single chromosomes amount of DNA. somatic cells germ cells 46 single chromosomes amount of DNA. somatic cells germ cells 46 single chromosomes amount of DNA. somatic cells germ cells 46 single chromosomes amount of DNA. somatic cells germ cells 46 single chromosomes amount of DNA. Normal somatic cells and primordial germ cells contain 46 single chromosomes and 2N amount of DNA. The chromosomes occur in 23 homologous pairs maternal origin, paternal origin. maternal origin, paternal origin. maternal origin, paternal origin. one pair is of maternal origin, and the other is of paternal origin. “diploid” “diploid” “diploid” The term “diploid” is classically used to refer to a cell containing 46 single chromosomes. Chromosome pairs 1–22 are autosomal (non-sex) pairs. Chromosome pair 23 consists of the sex chromosomes (XX for a female and XY for a male).
- 6. • • • Gametes Gametes contain 23 single chromosomes (22 autosomes and 1 sex chromosome) and 1N amount of DNA. The term “haploid” is classically used to refer to a cell containing 23 single chromosomes. • • • • • Female gametes Female gametes contain only the X sex chromosome. Male gametes Male gametes contain either the X or Y sex chromosome the male gamete determines the genetic sex of the individual.
- 7. • • The Y chromosome A normal male somatic cell contains one X chromosome and one Y chromosome (XY). • • • • • The X chromosome. A normal female somatic cell contains two X chromosomes (XX). week 1 The female cell permanently inactivates one of the X chromosomes during week 1 of embryonic development. The choice of which X chromosome (maternal or paternal) is inactivated is random. The inactivated X chromosome is called the Barr body.
- 8. MEIOSIS
- 9. • Meiosis production of gametes female ovary male testes. production of gametes female ovary male testes. production of gametes female ovary male testes. production of gametes female ovary male testes. is a specialized process of cell division that occurs only during the production of gametes within the female ovary or male testes. • – – Meiosis consists of two divisions Meiosis I and II Meiosis I and II four gametes, Results in the formation of four gametes, each containing half the number of chromosomes (23 single chromosomes) and half the amount of DNA (1N) found in normal somatic cells (46 single chromosomes, 2N).
- 10. • Meiosis I Events that occur during meiosis I include the following: Synapsis: pairing of 46 homologous duplicated chromosomes. Crossing over: exchange of large segments of DNA. Alignment: alignment of 46 homologous duplicated chromosomes at the metaphase plate. Disjunction: separation of 46 homologous duplicated chromosomes from each other; centromeres do not split. Cell division: formation of two secondary gametocytes (23 duplicated chromosomes, 2N).
- 12. • Meiosis II Events that occur during meiosis II include the following: 1. Synapsis: absent. 2. Crossing over: absent. 3. Alignment: alignment of 23 duplicated chromosomes at the metaphase plate. 4. Disjunction: separation of 23 duplicated chromosomes to form 23 single chromosomes; centromeres split. 5. Cell division: formation of four gametes (23 single chromosomes, 1N).
- 13. FIGURE 1.2. Oogenesis: female gametogenesis. Note that only one pair of homologous chromosomes is shown (red, maternal origin; blue, paternal origin). Synapsis is the process of pairing of homologous chromosomes. The point at which the DNA molecule crosses over is called the chiasma and is where exchange of small segments of maternal and paternal DNA occurs. Note that synapsis and crossing over occur only during meiosis I. The polar bodies are storage bodies for DNA unnecessary for the further function of the cell and probably degenerate. There is no evidence that polar bodies divide or undergo any other activity.
- 14. Gametogenesis • • Occurs in the gonads (ovary & testis) By meiosis
- 15. OOGENESIS: FEMALE GAMETOGENESIS • – Occurs in the cortex of the Ovary from the oogonia which becomes primary oocytes when begin meiosis Found as follicles of various stages
- 16. Primary follicles 1. – – 2. – Unilamina Unilaminar primary follicles Oocyte is surrounded by one layer of follicular cells The follicles are surrounded by zona pellucida Multilaminar Multilaminar primary follicles Theca follicli formes around the follicles by differentiations of the fibroblasts of the stroma
- 17. Secondary (antral) follicles • • • 1. 2. Antrum filled by liquour folliculi Cumulus oophorus and corona radiata appear Theca folliculi differentiates into: Theca interna containing a rich vascular network and steroid- secreting cuboidal cells (cells of theca interna) separated from granulosa cells by a thick basement membrane. Theca externa consisting mainly of vascular connective tissue with layers of fibroblasts surrounding theca interna.
- 18. • • 25 mm or more, protrude from the surface of the ovary. As follicle grows, granulosa cells layer becomes thinner. Mature (graafian or preovulatory) follicles
- 19. Ovulation • • • By a surge of LH production from pituitary in response to high levels of circulating estrogen from growing follicles Just before ovulation 1st meiotic division is completed giving the ovum (secondary oocyte) and first polar body. Second meiotic division begins, but arrested at metaphase stage about 3 hrs before ovulation to complete the division if fertilized
- 20. Corpus Luteum • • 1. – – 2. – – By remnants of the follicle after ovulation Contains: Granulosa lutein cells By pale staining cells with characteristics of steroid secreting cells Secrete progesterone. Theca lutein cells Smaller in size than granulosa cells and secrete estrogen. Stain more intensely and are located in the folds of the wall of the corpus luteum.
- 21. • Is maintained for 6 months, & declines afterwards, although still present until end of pregnancy. Corpus Luteum of pregnancy (corpus lutem graviditatis)
- 22. • • Reaches to its maximum development approximately by the 9th days after ovulation. Shows apoptotic degeneration 14 days after ovulation if fertilization has not taken place because of lack of stimulation from human chorionic gonadotrophin. Corpus Luteum of menstruation
- 23. • • – – Is about 12 cm long, and has four pats: infundibulum with fimbriae, ampulla, isthmus and intramural or interstitial part. Lining epithelium of: Simple ciliated columnar cells Simple nonciliated columnar secretory cells The oviduct (uterine tube)
- 24. • Has body (corpus), fundus and cervix parts. The uterus
- 25. • 1. 2. 3. Has three layers: Endometrium Myometrium Perimetrium Body and funds of uterus
- 26. • – – • – • 1. 2. Lining epithelium of: Simple ciliated columnar cells Simple nonciliated columnar secretory cells Lamina propria Contains vascularized connective tissue with simple tubular glands (branched in deeper portion) Subdivided into: Stratum functionale (pars functionalis) Stratum basale (pars basalis) Endometrium
- 27. • • • a. • • Undergoes cyclic changes in response to the ovarian hormones Receives the coiled (spiral) arteries Subdivided based on the density of the lamina propria Stratum compactum Superficial and with large number of stromal cells b. Stratum spongiosum Deeper portion. Stratum functionale (pars functionalis) of endometrium
- 28. Menstrual cycle • • Regulated by estrogen and progesterone from the follicles. Has 3 phases.
- 29. The male reproductive system • 1. 2. 3. 4. • 1. 2. 3. Is consisted of: Testes Genital ducts Accessory glands Penis. Accessory Genital Glands Seminal vesicles (glands) Prostate gland Bulbourethral glands (Cowper’s glands)
- 30. The Testis – – Divided into about 250 pyramidal shaped incomplete lobules. Each contains 1-4 seminiferous tubules packed in a loose connective tissue containing interstitial cells (of Leydig). Produce about 200-300 million spermatozoa
- 31. Seminiferous Tubules • 1. 2. Lined by germinal or seminiferous epithelium which contains 4-8 layers of cells of the spermatogenic lineage. Supporting (sertoli) cells
- 32. Spermatogenesis • • At puberty primordial germ cells differentiate into spermatogonia to develop into the spermatozoa through 3 phases. Takes about 74 days.
- 33. Spermiogenesis • – – – – Spermatids are transformed into spermatozoa with: Formation of the acrosome – from Golgi bodies Condensation and elongation of the nucleus Development of the flagellum - from one of the centrioles Lose of much of the cytoplasm as residual bodies