ПЕРВАЯ НЕДЕЛЯ РАЗВИТИЯ ГАМЕТОГЕНЕЗ ОПЛОДОТВОРЕНИЕ ДРОБЛЕНИЕ СПЕРМАТОГЕНЕЗ

ПЕРВАЯ НЕДЕЛЯ РАЗВИТИЯ ГАМЕТОГЕНЕЗ, ОПЛОДОТВОРЕНИЕ, ДРОБЛЕНИЕ.

СПЕРМАТОГЕНЕЗ Сперматогенез – последовательность событий, путем которых сперматогоний трансформируется в сперматозоид. Этот процесс начинается в период полового созревания. Оогенез - последовательность событий, путем которых оогоний трансформируется в зрелую ооцит.

СТАДИИ СПЕРМАТОГЕНЕЗА Spermatogonia are transformed into primary spermatocytes, the largest germ cells in the seminiferous tubules. Each primary spermatocyte subsequently undergoes a reduction division-the first meiotic division-to form two haploid secondary spermatocytes, which are approximately half the size of primary spermatocytes. Subsequently, the secondary spermatocytes undergo a second meiotic division to form four haploid spermatids, which are approximately half the size of secondary spermatocytes. The spermatids are gradually transformed into four mature sperm by a process known as spermiogenesis. The entire process of spermatogenesis, which includes spermiogenesis, takes approximately 2 months. When spermiogenesis is complete, the sperms enter the lumina of the seminiferous tubules.

КЛЕТКИ СЕРТОЛЛИ. ПОЛОВЫЕ ОРГАНЫ МУЖЧИНЫ Sertoli cells lining the seminiferous tubules support and nurture the germ cells and may be involved in the regulation of spermatogenesis. Sperms are transported passively from the seminiferous tubules to the epididymis, where they are stored and become functionally mature. The epididymis is the elongated coiled duct along the posterior border of the testis. It is continuous with the ductus deferens (vas deferens), which transports the sperms to the urethra.

ООГЕНЕЗ. ПРЕНЕТАЛЬНОЕ СОЗРЕВАНИЕ ООЦИТА During early fetal life, oogonia proliferate by mitosis. Oogonia enlarge to form primary oocytes before birth. As a primary oocyte forms, connective tissue cells surround it and form a single layer of flattened, follicular epithelial cells. The primary oocyte enclosed by this layer of cells constitutes a primordial follicle. As the primary oocyte enlarges during puberty, the follicular epithelial cells become cuboidal in shape and then columnar, forming a primary follicle. The primary oocyte soon becomes surrounded by a covering of amorphous acellular glycoprotein material, the zona pellucida. Scanning electron microscopy of the surface of the zona pellucida reveals a regular meshlike appearance with intricate fenestrations. Primary oocytes begin the first meiotic division before birth, but completion of prophase does not occur until adolescence. The follicular cells surrounding the primary oocyte are believed to secrete a substance, oocyte maturation inhibitor, which keeps the meiotic process of the oocyte arrested.

ООГЕНЕЗ. ПОСТНАТАЛЬНОЕ СОЗРЕВАНИЕ ООЦИТА. Beginning during puberty, usually one follicle matures each month and ovulation occurs, except when oral contraceptives are used. The long duration of the first meiotic division (up to 45 years) may account in part for the relatively high frequency of meiotic errors, such as nondisjunction (failure of paired chromatids to dissociate), that occur with increasing maternal age. The primary oocytes in suspended prophase (dictyotene) are vulnerable to environmental agents such as radiation. No primary oocytes form after birth in females, in contrast to the continuous production of primary spermatocytes in males. The primary oocytes remain dormant in the ovarian follicles until puberty.

As a follicle matures, the primary oocyte increases in size and, shortly before ovulation, completes the first meiotic division to give rise to a secondary oocyte and the first polar body. Unlike the corresponding stage of spermatogenesis, however, the division of cytoplasm is unequal. The secondary oocyte receives almost all the cytoplasm , and the first polar body receives very little. The polar body is a small, nonfunctional cell that soon degenerates. At ovulation, the nucleus of the secondary oocyte begins the second meiotic division, but progresses only to metaphase, when division is arrested. If a sperm penetrates the secondary oocyte, the second meiotic division is completed, and most cytoplasm is again retained by one cell, the fertilized oocyte. The other cell, the second polar body, also a small nonfunctional cell, soon degenerates. As soon as the polar body is extruded, maturation of the oocyte is complete.

Женские половые пути Матка толстостенный, грушевидный мышечный орган 7 -8 см в длину, 5 -7 см в ширину. Состоит из двух основных частей 1. Тело, расширенная верхняя 2/3 2. Шейка, цилиндрическая нижняя 1/3

СТРОЕНИЕ МАТКИ 1. 2. 3. Тело матки сужается от дна, округлой верхней части тела, до шейки - сужения в области между телом и шейкой матки. Стенки тела матки состоит из трех слоев Периметрий, тонкий наружный слой Миометрий, толстый гладкий мышечный слой Эндометрий, тонкий внутренний слой

Овуляция

Illustrations of ovulation. When the stigma ruptures, the secondary oocyte is expelled from the ovarian follicle with the follicular fluid. After ovulation, the wall of the follicle collapses and is thrown into folds. The follicle is transformed into a glandular structure, the corpus luteum.

Illustrations of the movement of the uterine tube that occurs during ovulation. Note that the infundibulum of the tube becomes closely applied to the ovary. Its fingerlike fimbriae move back and forth over the ovary and "sweep" the secondary oocyte into the infundibulum as soon as it is expelled from the ovary during ovulation.

нормальный гаметогенез Оогонии не показаны т. к. они дифференцируются в первичные ооциты до рождения.

Микрофотография первичного ооцита во вторичном фолликуле

Micrographs of ovarian cortex. A - Several primordial follicles are visible (Ã— 270). Observe that the primary oocytes are surrounded by follicular cells. B - Secondary ovarian follicle. The oocyte is surrounded by granulosa cells of the cumulus oophorus (Ã— 132).

мейоз А-D профаза E – метафаза F – анафаза G –телофаза

Второе деление мейоза

Ненормальный гаметогенез

Последняя стадия сперматогенеза Потеря цитоплазмы, развитие хвоста, и формирование акросомы. Митохондрии располагаются в виде плотной спирали, образуя воротник типа митохондриальной оболочки.

Мужские и женские гаметы оплодотворение

Акросомная реакция и проникновение спермия в ооцит

Оплодотворение - сложная последовательность согласованных молекулярных событий, которая начинается с контакта спермы и яйцеклетки и заканчивается смешением материнских и отцовских хромосом в метафазе первого деления митотической зиготы одноклеточного эмбриона. Занимает около 24 часов.

СТАДИИ ОПЛОДОТВОРЕНИЯ 1. 2. 3. 4. 5. 6. Passage of a sperm through the corona radiata. Penetration of the zona pellucida Fusion of plasma membranes of the oocyte and sperm. Completion of the second meiotic division of oocyte and formation of female pronucleus. Formation of the male pronucleus. As the pronuclei fuse into a single diploid aggregation of chromosomes, the ootid becomes a zygote.

ОПЛОДОТВОРЕНИЕ Стимулирует яйцеклетку завершить второе деление мейоза. Восстанавливает нормальное количество хромосом (46) в зиготе. Определяет хромосомный пол эмбриона. Вызывает метаболическую активацию оотид и инициирует деление зиготы (дробление)

ПРЕДОПРЕДЕЛЕНИЕ ПОЛА ЭМБРИОНА 1. 2. 3. 4. Т. к. X - и Y - содержащие сперматозоиды формируются в равных количествах, ожидается, что соотношение полов при оплодотворении (первичное соотношение полов) будет равно 1, 00 (100: 100) Однако младенцев мужского пола рождается больше (105: 100) При искусственном оплодотворении возможен выбор пола с помощью отбора сперматозоидов по особым признакам: Раличная «плавучесть» X - и Y - содерж. сперматозоидов. Внешние различия Отличия по массе ДНК (2, 8% больше при Х) Разные скорости миграции в электрическом поле

ОПЛОДОТВОРЕНИЕ The steps: 1. Ovarian follicles are stimulated to grow and mature by the administration of clomiphene citrate or gonadotropin (superovulation). 2. Several mature oocytes are aspirated from mature ovarian follicles during laparoscopy. 3. The oocytes are placed in a Petri dish containing a special culture medium and capacitated sperms. 4. Fertilization of the oocytes and cleavage of the zygotes are monitored microscopically for 3 to 5 days. 5. One or two of the resulting embryos (four- to eight-cell stage or early blastocysts) are transferred by introducing a catheter through the vagina and cervical canal into the uterus. Any remaining embryos are stored in liquid nitrogen for later use.

ДРОБЛЕНИЕ ЗИГОТЫ Cleavage consists of repeated mitotic divisions of the zygote, resulting in a rapid increase in the number of cells. These embryonic cells-blastomeresbecome smaller with each successive cleavage division. Cleavage normally occurs as the zygote passes along the uterine tube toward the uterus. During cleavage, the zygote is within the rather thick zona pellucida. Division of the zygote into blastomeres begins approximately 30 hours after fertilization. Subsequent cleavage divisions follow one another, forming progressively smaller blastomeres After the nine-cell stage, the blastomeres change their shape and tightly align themselves against each other to form a compact ball of cells. This phenomenon, compaction, is probably mediated by cell surface adhesion glycoproteins. Compaction permits greater cell-to-cell interaction and is a prerequisite for segregation of the internal cells that form the inner cell mass or embryoblast of the blastocyst When there are 12 to 32 blastomeres, the developing human is called a morula. Internal cells of the morula (inner cell mass) are surrounded by a layer of cells that form the outer cell layer. The spherical morula forms approximately 3 days after fertilization and enters the uterus.

ФОРМИРОВАНИЕ БЛАСТОЦИСТЫ Shortly after the morula enters the uterus (approximately 4 days after fertilization), a fluid-filled space called the blastocystic cavity appears inside the morula. The fluid passes from the uterine cavity through the zona pellucida to form this space. As fluid increases in the blastocystic cavity, it separates the blastomeres into two parts: A thin, outer cell layer, the trophoblast, which gives rise to the embryonic part of the placenta A group of centrally located blastomeres, the inner cell mass, which gives rise to the embryo; because it is the primordium of the embryo, the inner cell mass is called the embryoblast

2, 3 и 8 клеточный зародыш

Photomicrographs of sections of human blastocysts recovered from the uterine cavity (Ã— 600). A, At 4 days: the blastocystic cavity is just beginning to form and the zona pellucida is deficient over part of the blastocyst. B, At 4 ½ days; the blastocystic cavity has enlarged and the embryoblast and trophoblast are clearly defined. The zona pellucida has disappeared.

1. 2. During this stage of development-blastogenesis-the conceptus is called a blastocyst The embryoblast now projects into the blastocystic cavity and the trophoblast forms the wall of the blastocyst. After the free blastocyst has floated in the uterine secretions for approximately 2 days, the zona pellucida gradually degenerates and disappears Shedding of the zona pellucida and hatching of the blastocyst have been observed in vitro. Shedding of the zona pellucida permits the hatched blastocyst to increase rapidly in size. While floating in the uterus, this early embryo derives nourishment from secretions of the uterine glands. Approximately 6 days after fertilization (day 20 of a 28 -day menstrual cycle), the blastocyst attaches to the endometrial epithelium, usually adjacent to the embryonic pole. As soon as it attaches to the endometrial epithelium, the trophoblast starts to proliferate rapidly and gradually differentiates into two layers: An inner layer of cytotrophoblast An outer layer of syncytiotrophoblast consisting of a multinucleated protoplasmic mass in which no cell boundaries can be observed

Attachment of the blastocyst to the endometrial epithelium during the early stages (6 days) of its implantation

At 7 days: the syncytiotrophoblast has penetrated the epithelium and has started to invade the endometrial connective tissue.

ПОДВЕДЕМ ИТОГИ Oocytes are produced by the ovaries (oogenesis) and expelled from them during ovulation. The fimbriae of the uterine tube sweep the oocyte into the ampulla where it may be fertilized. Sperms are produced in the testes (spermatogenesis) and are stored in the epididymis. Ejaculation of semen during sexual intercourse results in the deposit of millions of sperms in the vagina. Several hundred sperms pass through the uterus and enter the uterine tubes. When an oocyte is contacted by a sperm, it completes the second meiotic division. As a result, a mature oocyte and a second polar body are formed. The nucleus of the mature oocyte constitutes the female pronucleus. After the sperm enters the oocyte, the head of the sperm separates from the tail and enlarges to become the male pronucleus. Fertilization is complete when the male and female pronuclei unite and the maternal and paternal chromosomes intermingle during metaphase of the first mitotic division of the zygote. As it passes along the uterine tube toward the uterus, the zygote undergoes cleavage (a series of mitotic cell divisions) into a number of smaller cells-blastomeres. Approximately 3 days after fertilization, a ball of 12 or more blastomeres-a morula-enters the uterus. A cavity forms in the morula, converting it into a blastocyst consisting of the embryoblast, a blastocystic cavity, and the trophoblast. The trophoblast encloses the embryoblast and blastocystic cavity and later forms extraembryonic structures and the embryonic part of the placenta. Four to 5 days after fertilization, the zona pellucida is shed and the trophoblast adjacent to the embryoblast attaches to the endometrial epithelium. The trophoblast at the embryonic pole differentiates into two layers, an outer syncytiotrophoblast and an inner cytotrophoblast. The syncytiotrophoblast invades the endometrial epithelium and underlying connective tissue. Concurrently, a cuboidal layer of hypoblast forms on the deep surface of the embryoblast. By the end of the first week, the blastocyst is superficially implanted in the endometrium.

Summary of the ovarian cycle, fertilization, and human development during the first week