[Music] men and especially women possess various organs that are optimally suited for the creation of another human being [Music] the ovary possesses about half a million eggs embedded in follicles several follicles and therefore eggs mature in each cycle the dominant follicle grows to about two centimeters and defibriated end of the fallopian tube which eventually catches the egg moves to the site of ovulation [Music] the egg consists of an outer layer called the corona radiata underneath is another protective layer the zona pellucida both layers must be penetrated by the sperm cell in order to reach the
cell nucleus that contains 23 different chromosomes [Music] each chromosome contains dna dna is the blueprint for building our body cells eye color body size arrangement and function of our organs it's all in there [Music] if two identical chromosomes occur in one cell we can later speak a trisomy [Music] the egg cell is transported inside the fallopian tube with the help of cilia and mucus produced by glands in the walls of the fallopian tube additional contractions of the muscle layers help to transport the ovum [Music] at a speed of about three to four millimeters per minute
something else makes its way from the other side of the fallopian tube sperm cells thousands of them and barely visible they all have only one goal reaching the ovum [Music] a sperm cell's nucleus contains the male's genetic information through messenger substances emitted by the egg cell the remaining sperm cells find their way to the oval [Music] the goal of all sperm cells is to penetrate the two outer layers to reach the chromosomes [Music] do [Music] the sperm cell penetrates corona radiata and zona pellucida resulting in the degradation of the acrosome cap upon entering the cytoplasm
fertilization occurs resulting in activation activation causes among other things a structural chains of the zona pellucida so that no further sperm can penetrate in addition activation causes the ovum to complete its second maturation division in this process the sister chromatids are pulled into opposite poles and a female pro-nucleus and a polar body are formed [Music] the sperm's tail and head gradually degenerate into cytoplasm the condensed sperm nucleus rapidly increases enormously in size and the chromatin decondenses thus a male pro nucleus is formed with 23 unreplicated chromosomes that possess the genetic information of the father as
the two pronuclei approach both doubled their dna resulting in replicated chromosomes [Music] [Music] finally synchrome occurs in which the pro nuclei dissolve and the chromosomes of male and female are properly aligned in the spindle apparatus [Music] now the cell is called a zygote which is the very first cell of the new human being the stage of cleavage begins in this process the cell continues to divide two cells then four then eight at a 16 cell to 32 cell stage embryo we speak of a murala since the shape resembles a mulberry the cells are still enclosed
by the zona pellucida thus after each cell division whilst the number of cells increases the size of each cell diminishes finally the blastocyst is formed the blastocyst consists of a fluid-filled cavity the cells of the embryoblast and the trophoblast the embryoblast is the initial structure of the new human being whereas the trophoblast is the origin of placenta and membranes let's see the individual stages in the fallopian tube fertilization occurs at the end of the tube the first cell division takes place about a day after fertilization eventually further cell divisions happen forming the mirala and in
the uterus the blastocyst is created at this stage the mucous membranes of the uterus or womb has already been prepared for the implantation of the blastocyst usually the blastocyst implants in the posterior wall of the uterus however implantation can also occur on the side as we will see in a moment the blastocyst floats in the protective and nourishing uterine mucus for implantation in the uterus the blastocyst must first hatch from the protective zona pellucida then the blastocyst barrels further and further into the uterine lining like a parasite [Music] [Music] let's take a closer look at
this the endometrium has a protective epithelium and capillaries filled with blood as well as mucus-producing glands the trophoblast cells fuse with the endometrium and a central trophoblast is formed that will nourish the embryo in addition hypoblast and epiblast arise from the embryoblast the embryo burrows further into the endometrium rapidly increasing in cell mass and leaving a wound which may result in a completely harmless implantation bleeding finally the amniotic cavity is formed as the process continues the yolk sac is created as well as a non-cellular plug that is later sealed by migrating uterine epithelial cells the
trophoblast rapidly increases in size with the amniotic cavity and yolk sac remaining relatively small this gives rise to the chorionic cavity and the body stalk [Music] [Music] three germ layers form from the primitive streak and node this process is called gastrulation the germ layers ectoderm mesoderm and endoderm eventually differentiate into various tissues and organs [Music] [Music] [Applause] [Music] [Music] in the course of the third week of development neuralation occurs at that time the foundation for the central nervous system is laid the neural groove is formed closing from the center to the sides at the sides
small bumps called somites can be seen the neural groove becomes the neural tube which later forms for example spinal cord and brain [Music] those cells later become the neural networks which enable us to think [Music] [Music] in the fourth week of development this process is almost complete the embryo is still in the amnion which is filled with amniotic fluid that has numerous functions the optic plaques which are the bases for the inner ear can be seen and a heart is already pumping blood through the intra-embryonic blood vessels [Applause] [Music] [Applause] [Music] the yolk sac and
the body stalk continue to nourish the embryo [Music] the chorion is the outer membrane and is connected to the body stalk the chorionic villi are surrounded by maternal blood this allows them to carry nutrients to the embryo and nourish it we'll see more on this later during the fourth week three pairs of pharyngeal arches appear in addition the upper limb buds are visible first followed by the lower limb buds the embryo is now curved in a c-shape the caudal imminence is till-like in shape the somites which give rise to the cells forming the skeletal muscles
and components of the skin among other things can still be identified [Music] the embryo continues to grow rapidly measuring approximately four to five millimeters by the end of the fourth week the lens placodes and olfactory pits are formed the later arms and hands as well as legs and feet can be already well identified the hands will develop from paddles to separate fingers by the eighth week [Music] [Applause] [Music] the embryo is about 23 millimeters long by the middle of the eighth week the legs will not lose their webbed feet until a few days after the
hands [Music] embryogenesis turns into fetal genesis in the ninth week and in the third month that is from the twelfth week on the fetus already has a human-like appearance [Music] the eyelids are closed the skin is translucent in the following weeks the fetus grows and the ossification of the fetal skeleton takes place so that the bones are clearly visible on ultrasound images by the 16th week [Music] in addition the body is completely covered with downy lanugo hairs which help among other things to keep the vernix secreted by dedicated cells on the skin the vernix protects
the skin from direct contact with the amniotic fluid from about the 18th week the mother can feel the baby's movements in addition the sucking reflex has already been established by the 28th week the hair on the head eyebrows and eyelashes continue to grow in addition the eyes open the fetus gains a lot of mass in the last few months and the latter go hairs and the vernix gradually fade away it is also slowly getting tighter and tighter in mom's belly at first the fetus is supplied by the body stalk and yolk sac but then more
and more by the umbilical cord and placenta since the fetus possesses both the dna of the mother and of the father the blood of the fetus must not mix with the blood of the mother the placenta is responsible for this it is responsible for the exchange of substances between mother and fetus the chorionic villi which were previously completely distributed over the corion have regressed to other parts of the uterus the remaining villi are part of the placenta maternal blood rich in oxygen and nutrients enters the intervilla space via the arteries veins carry away the oxygen
and nutrient poor blood [Music] the chorionic villi extract oxygen and necessary nutrients from the mother's blood nutrients include carbohydrates amino acids fats vitamins and iron oxygen and nutrients are then transported to the fetus via the veins with the help of the umbilical cord however waste products also reach the villi via the arteries this allows the fetus to release its waste products such as carbon dioxide and urea into the maternal blood the mother's organism then takes over the excretion of these substances after about 38 weeks the fetus is fully developed it measures 50 centimeters and weighs
around 3000 grams the birth takes place now or in the next two to four weeks you
