GAMETOGENESIS FERTILIZATION CLEAVAGE Dr Katalin Gallatz THE HUMAN

GAMETOGENESIS, FERTILIZATION, CLEAVAGE Dr. Katalin Gallatz

THE HUMAN DEVELOPMENT STARTS WITH THE FERTILIZATION During this process the oocyte and sperm unite. New organism, the ZYGOTA develops. Before fertilization both male and female gametes pass through meiotic division and cytodifferentiation. The aim of these processes: 1. To decrease the number of chromosomes (somatic cells 46 diploid number, gametes 23 haploid). . 2. To change the form of gametes, prepar them for the fertilization The human somatic cells contain 23 pair (diploid) chromosomes , 22 pair homolog autosome and 1 pair szexchromosome (or XX or XY)

1. Mitotic division - before the cell starts to divide all chromosomes replicate their DNA, it becomes duplicated. - During division the dauther cells get the half of chromosomes, therefore all cells have the same number of of chromosomes as the mother cell. 1. Meiotic division - homológ chromosomes form pairs (synapsis) - crossing, 2. Meioticus osztódás - chage of chromatidsegments - there is not DNA synthesis before it - all dauther cells contain leánysejt only 1 from a - dauther cells contain 23 chromatids chromosome pair 23 chromosomes

Gametogenesis: conversion of germ cells into male and female gametes - Primordial germ cells appear in the wall of the yolk sac at the end of the 3 rd week of development. - Germ cells migrate from the yolk sac toward the developing gonads (genital ridges), they arrive at the end of the 4 th or the beginning of the 5 th week.

Human gametes Spermium (spermatozoa) fej nyak középdarab fődarab végdarab oocyte farok

Convoluted seminiferous tubules Spermatogenesis Spermatogonia → mitosis, growth primer spermatocyte → first meiosis secunder spermatocyte →second meiosis spermatides

Spermiohistogenesis: differentiation of the sperm 1. Golgi phase: - acrosome formation: granule, vesicle, cap (contains enzimes importants in fertilazation) 2. Cap phase: - condensation of the nucleus, - acrosome connected to it. 3. Acrosomal phase: - further condensation of the nucleus 4. Maturation phase: - differentiation of the neck, the middle piece and tail, - the remaining parts of cytoplasm are phagocyted by Sertoli cells

1. SPERMATOGENETIC CELLS 2. SERTOLI cells: from the basement membrane to the lumen, trigone-shaped nucleus, well-seen nucleolus, Function: spermiohistogenesis, in their cytoplasm they secrete inhibin, androgen-binding protein, piruvate and lactate. spermatids

Primordial gametes differentiate into Spermatogonia just before the puberty in the wall of seminiferous tubules.

1. Oogenesis : development of the oocyte 2. Maturation of the follicle Graafian follicle

MATURATION OF THE FOLLICLE OVARIUM

PRIMORDIAL, PRIMER AND SECONDER FOLLICULUS PRIMORDIAL FOLLICLE PRIMER FOLLICLE SECUNDER FOLLICLE GRAAFIAN FOLLICLE

TERTIER FOLLICLE - OOCYTA INCREASES IN SIZE - STRATIFIED GRANULOSA EPITHELIUM, - CAVUM FOLLICULI, - LIQUOR FOLLICULI - THECA FOLLICULI

Before birt the a primer oocyte is in the prophase of the az 1 st meiotic division, Than it remain in resting stage or diploten stage, it doesn’t finish the 1. meiotic division before puberty. Oocyta maturation inhibitor (OMI), is produced by the follicular cells.

Human gametes Spermium (spermatozoa) fej nyak középdarab fődarab végdarab oocyte farok

From the primer oocyte 1 matured oocyte develops, from the primer spermatocyte 4 matured spermium develops

Ovulation

OVULATION

BEFORE FERTILIZATION 200 -300 million spermatozoa arrive in the female genital tract → 300500 reach the site of fertilization → only 1 fertilize Oocyte and spermatozoa remain viable for approximately 24 hours and 4 5 days respectively. Spermatozoa are not capable of fertilizing oocyte!!! They must undergo (a) Capacitation (b) Acrosomal reaction

CAPACITATION AND ACROSOMAL REACTION Capacitation: conditioning in the female reproductive tract (approx 7 hours), glycoprotein coat and seminal plasma proteins are removed that overlies the acrosomal region → hyperactivation of motility Acrosomal reaction: after binding to zona pellucida, release of enzymes (acrosin, trypsin like substances) induced by zona pellucida proteins

FERTILIZATION: the fusion of the a spermium and oocyte PHASES OF FERTILAZATION 1. Penetration of corona radiata. 2. Penetration of zona pellucida. 3. Fusion of the plasma membrane of the oocyta and sperm. 4. Completion of the second meiotic division of the oocyte and formation of the female pronucleus. 5. Formation of the male pronucleus.

1. Phase: Penetration of corona radiata. In the penetration of the corona radiata the acrosomal enzymes has important role: -hiauronidase and a CPE-(corona penetratin enzyme)

FERTILIZATION 2. phase: Penetration of zona pellucida. 3. phase: Fusion of the plasma membrane of the oocyta and sperm. The outer membrane of the acrosome binds to the receptor (ZP 3) of zona pellucida. Tthe acrosomal reaction starts, the plasmamembrane unites with the acrosomal membrane. Acrosomal enzyme secretion: acrosin, esterases, neuraminidase) A ZP opens, the spermium is connected wih the membrane of the oocyte.

Cortical reaction When fertilin (can be found on the apical part of the 1 st spermium) becomes connected with the integrine molecules of the oocytamembrane, from corticalis granules of the oocyta lysosomal enzymes liberate and the membrane of the oocyte becomes impermiable for further sperms. A structure of the zona pellucida is also changed.

The membrane of the oocyta and inner acrosomal membrane of the spermium unite. The head and tail enters the cytoplasm of the oocyta. The plasmamembrane and mitochondria are phagocyted The second meiotic divison of the oocyta is completed. Definitive oocyta (22+X) and 2. polar body is formed. Following decondensation of the maternal chromosomes, the nucleus of the mature oocyte becomes the female pronucleus. The nucleus of the sperm enlarges to form the male pronucleus and the tail of the sperm degenerates. As the pronuclei fuse into a single diploid aggregation of chromosomes the ootid becomes the ZYGOTE. Metabolic activation CLEAVAGE

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