Cell cycle_yazan-inroduction anatomy-embryo-1.pdf

Cell cycle Gametogenesis Anatomy Unit201 Anatomy Unit  Objectives 1. To understand the cell cycle: 2. Steps of (Mitosis and Meiosis cell divisions) 3. Differentiate between Mitosis and Meiosis and their end results. 4. Compare between spermatogenesis and oogenesis ...

Cell cycle Gametogenesis Anatomy Unit201 Anatomy Unit  Objectives 1. To understand the cell cycle: 2. Steps of (Mitosis and Meiosis cell divisions) 3. Differentiate between Mitosis and Meiosis and their end results. 4. Compare between spermatogenesis and oogenesis  Case scenario Q. Concerning maturation of the female gamete (oogenesis), when do the oogonia enter meiosis I and undergo DNA replication to form primary oocytes? A. During fetal life B. At birth C. At puberty D. With each ovarian cycle E. Following fertilization  Cell division ❑ Mitosis: Somatic (body) cell division , for growth and repair. ❑ Meiosis: Reduction division of gametes (sex cells)  Meiosis ❑ Cell division. ❑ Site: in the gonads (testes and ovaries). ❑ Types: meiosis I&II ❑ Results: produce gametes (sperms and ova).  Meiosis-I ❑ Reduction division ❑ Replication of DNA ❑ Cross over ❑ Results: 2 cells each has 23 chromosomes.  Meiosis-II ❑ The same as mitotic division ❑ No DNA replication. ❑ No cross over ❑ Results: 4 cells (each cell contains 23 chromosomes)  Importance of Meiosis ✓ Reduces the Diploid number of chromosome to Haploid. ✓ Allows shuffling of maternal & paternal chromosomes. ✓ ✓ Allows Crossing Over of chromosome segments which redistributes genetic material.. Importance of Meiosis Mitosis & Meiosis  Spermatogenesis Definition: It is the process of transformation of spermatogonia (Primitive germ cells) into spermatozoa (mature sperm). Site: Seminiferous tubules in the testis. Duration: 2 months (roughly 64 days). Onset: From puberty (13 –16 Y) till old age.  Spermatogenesis Steps: A) Spermatocytogenesis. B) Spermiogenesis  Spermatocytogenesis Definition: divisional transformation of the spermatogonium to spermatid.  Spermiogenisis Definition: morphological transformation of the spermatids to mature sperms (spermatozoa).  Seminal fluid Formation: It is a suspension contain: 1) Sperms. 2) Secretions of the epididymis, prostate, bulbourethral glands and seminal vesicle.  Seminal fluid Volume: 3-5cc. Odor: Has characteristic odor. Reaction: Alkaline. Characters: thick, white and gelatinous fluid rich in glucose and fructose.  Seminal fluid Number of sperms: 200-600 millions Motility: more than 80 % of sperms Function: ❑ Contain fructose for sperm nutrition. ❑ Contain prostaglandins for sperm motility and transport. ❑ Alkaline to neutralize the vaginal acidity.  Abnormalities of Seminal fluid 1. In number: ❑ Azospermia: No sperms in semen. ❑ Oligospermia: few numbers of sperms in semen. 2. In motility: ❑ Necrospermia: sperms in semen are dead.  Abnormalities of Seminal fluid 3. In shape: ❑ Giant sperms. ❑ Dwarf sperms. ❑ Sperms with more than one head or with 2 tails. These forms should not exceed 20% & normally present less than 10 %  Oogenesis Definition: It is the process of transformation of oogonia (Primitive germ cells) into mature ovum Site: In the outer cortex of the ovary  Oogenesis The 1ry oocyte (44-XX-4n) starts 1st meiotic division before birth but remains in resting prophase till puberty.  Oogenesis At puberty: 5 -12 primary oocytes resumes 1st meiotic division every month to form two cells: a. Large cell called secondary oocyte. b. Small cell called 1st polar body. 2) At ovulation: The 2ry oocyte and 1st polar body undergoes the 2nd meiotic division but arrested in the metaphase till fertilization  Oogenesis N.B. The are 2 millions 1ry oocytes in the ovaries of the newborn females. There are only 40000 1ry oocytes during adolescence, of these, only about 480 becomes 2ry oocytes and are expelled at ovulation during reproductive life. Q: Compare between male and female gametes? Spermatogenisis & Oogenesis  Case scenario Q. Concerning maturation of the female gamete (oogenesis), when do the oogonia  enter meiosis I and undergo DNA replication to form primary oocytes? A. During fetal life B. At birth C. At puberty D. With each ovarian cycle E. Following fertilization More (Down syndrome, Turner syndrome, Klinefelter syndrome) (Langman's Medical Embryology)