Gametogenesis PDF

A s s o ci at e P r o f e s s o r V D e p a r t m e n t o f M o r p h o p h y s i o l o g y and P h a r m a c o l o g y C o l l e g e o f V e t e r i n a r y S c i ence and M e d i c i n e C e n t r a l Luzon S ta t e U n i v e r s i t y  Developm...

A s s o ci at e P r o f e s s o r V D e p a r t m e n t o f M o r p h o p h y s i o l o g y and P h a r m a c o l o g y C o l l e g e o f V e t e r i n a r y S c i ence and M e d i c i n e C e n t r a l Luzon S ta t e U n i v e r s i t y  Development and maturation of sex cells called gametes Gametes - matured sex cells of male and female a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells Includes meiosis and cytodifferentiation After the process of fertilization in animals, a single-celled organism called the zygote is formed. Specifically termed: spermatogenesis for male oogenesis for female GERM LINE The lineage of cells from which gametes arise PRIMORDIAL GERM CELLS (PGCs) The cells which produce the gametes SOMATIC CELLS The non- germ line cells  only present in the development of the urinary and reproductive organs. carries sperm from testicle to urethra during ejaculation convoluted tubular accessory glands accomodates fetal and embryonic development produce a small amount of lubricating fluid that helps protect the urethra during ejaculation. This fluid also neutralizes the acidity of the male urethra and semen PGC MIGRATION In mammals, primordial germ cells arise from yolk sac endoderm. The cells migrate around the gut to the mesentery into the gonad. In birds and reptiles, they travel through the blood stream and into the gonads. PGC MIGRATION  Two successive meiosis occur during gametogenesis to reduce the diploid number of chromosome of germ cells into haploid. Stages of meiosis is similar with the stages of mitosis, i.e. P I,II ; M I,II ; A I,II and T I,II.  Timing of meiosis differ in males and females. In males, meiosis starts from the onset of puberty throughout the entire reproductive life. In females, meiosis starts before birth and completion of meiosis is upon fertilization.  MITOSIS vs MIEOSIS Mitosis is a process where a single cell divides into two identical daughter cells (cell division) with the same diploid number of chromosomes. When you say diploid number it refers to the 2N number of chromosomes of the cell in contrast to the N, haploid number, ex. in human 2N=46 and N=23chromosomes. The major purpose of mitosis is for growth and to replace worn-out cells. What part or cell organelles are involved in mitosis?  MITOSIS vs MIEOSIS Answer: Cell membrane, nucleus, nuclear membrane, and centriole What cells in the body are diploid, which are haploid Answer: the diploid cells are the somatic cells and the haploid cells are the sex cells(gametes) How do the cells become haploid? Answer: During meiosis the sex cells become haploid  MITOSIS vs MEIOSIS What is meiosis then Meiosis is a process where a single cell divides twice to produce four cells containing half the original amount of genetic information. Why the sex cells ( gametes: sperm & egg) are haploid During fertilization where the egg and sperm cell unite will not result to polyploidy ( more than 2 sets of chromosomes)  Cell Cycle and Cell Division Cell cycle is a repeating series of events that include growth, DNA synthesis, and cell division. in prokaryotes is quite simple: the cell grows, its DNA replicates and the cell divides (asexual reproduction) in eukaryotes, the cell cycle is more complicated and has several phases.  Cell Cycle and Cell Division he mitotic phase (M) actually includes both mitosis and ytokinesis. This is when the nucleus and then the ytoplasm divide. he other three phases (G1, S, and G2) are generally rouped together as interphase. During interphase, the ell grows, performs routine life processes, and prepares o divide Cell Cycle and Cell Division  Cell Cycle and Cell Division The Interphase of the eukaryotic cell cycle can be subdivided into the following three phases: Growth Phase 1 (G1): Longest phase cell undergoes rapid growth synthesize amino acids needed for DNA replication. If a cell is not dividing, the cell enters the G0 phase from this phase.  Cell Cycle and Cell Division Synthesis Phase (S): forms two genetically identical daught cells. During this phase, the amount of DNA in the cell is double though the cell remains in a diploid state. Growth Phase 2 (G2): second gap (growth) (G2) phase is shortened growth period in which many organelles ar reproduced or formed. Parts necessary for mitosis and ce division are made during G2, including microtubules used in th mitotic spindle Cell Cycle and Cell Division G0 phase: The resting phase where the cell has left the cycle an has stopped dividing These cells may remain in G0 for a long period of time, even indefinitely, such as with neurons. Cells that are completely differentiated may also enter G0. Some cells stop dividing when issues of sustainability or viability of their daughter cells arise, such as with DNA damage or degradation, a process called cellular senescence. Cellular senescence occurs when normal diploid cells lose the ability to divide, normally after about 50 cell divisions.  The entire process involved in the transformation of germinal epithelial cells (stem cells) to spermatozoa  The entire process involved in the transformation of germinal epithelial cells (stem cells) to spermatozoa  Occur in the seminiferous tubules of the testis  Can be divided into two phases: spermatocytogenesis spermiogenesis  Proliferative phase whereby spermatogonial cells multiply by a series of mitotic divisions followed by the meiotic divisions which produce the haploid (n) number of chromosomes  Maturation of the spermatids while they are still in the adluminal compartment. Parts of Spermatid Fates in Spermatozoa Nucleus Head Cytoplasm Manchette Golgi apparatus Acrosome Mitochondrion Middle piece Proximal centriole Neck Distal centriole Flagellum/tail  The release of matured spermatids into the lumen of the seminiferous tubules where they stay for a while then migrate in the epididymis for further maturation  boar bull rooster stallion Goat & sheep HEAD Oval structure which includes the nucleus containing the haploid number of chromosomes Also has a cap called the acrosome, which contains enzymes to permit penetration into the ovum. These are the acrosin and hyaluronidase MIDPIECE The power plant of the sperm. Within it are numerous mitochondria that carry out the metabolism that provides adenosine triphosphate (ATP) for the sperm’s locomotion. TAIL Consists of a flagellum for propulsion A. Coiled Tail with Droplet B Coiled Double Tail. C "DAG" defect. D Folded tail. E Filamentous. F. Double Tail G Corkscrew Midpiece with Droplet. H Corkscrew Midpiece.  The process by which oocytes are formed The oogonia follow the same pattern in the sperm cell i. e. from oogonia to primary oocyte to secondary oocyte to ootid to egg or ovum  The developmental sequence of a follicle goes through various follicle stages: Primordial follicle - primary follicle - secondary follicle - tertiary follicle PRIMORDIAL FOLLICLE A follicle containing the primary oocyte enveloped by a single layer of flat, follicular epithelial cells PRIMARY FOLLICLE A follicle little larger than the primordial follicle A primary oocyte surrounded by a single layer of cuboidal follicular cells SECONDARY FOLLICLE An oocyte with two or more layers of cuboidal follicular cells having a small or no antrum. MATURE FOLLICLE (Graafian follicle/ Vesicular follicle/ Tertiary follicle) A very large follicle bulging from the surface of the ovary with a fluid-filled cavity as identifying characteristic VITELLINE MEMBRANE Cell membrane of the oocyte ZONA PELLUCIDA A prominent translucent acellular layer located between the vitelline membrane of the oocyte and the follicular cells. GRANULOSA CELLS Squamous follicular cells which become cuboidal CORONA RADIATA Follicular cells directly adjacent to the zona pellucida of the oocyte CUMULUS OOPHORUS Mound of granulosa cells on which the oocyte sits ANTRUM A fluid-filled cavity containing the liquor folliculi  Release of ovum from the follicle Prior to ovulation, the oocyte and corona radiate detach from the cumulus oophorus and float in the follicular fluid Pressure inside the follicle and hormone, LH are the complementing factors left ovary ovulates more frequently in the mare right ovary in the cow  2 types: Spontaneous ovulation- ova are released without the need for copulation Most species Induced ovulation –the physical act of coitus or mechanical stimulation Cats, rabbits, camels, ferrets  2 types: Induced-female animal ovulates due to an externally-derived stimulus during, or just prior to, mating, rather than ovulating cyclically or spontaneously. Stimuli causing induced ovulation include the physical act of coitus or mechanical stimulation simulating this, sperm and pheromones. Cats, rabbits, camels, ferrets Th a n k y o u !