Reproduction in Humans Flashcards
The female reproductive system
The female gametes, eggs, are made in the two ovaries. Leading away from the ovaries are the oviduct also known as fallopian tubes. the two oviducts lead to the uterus or womb, which has thick walls, made of muscle, it is small at first but stretches when a women is pregnant. then the cervix of the uterus lead to the vagina. The opening from the bladder, called the urethera, runs in front of the vagina while the rectum is just behind it.
The male reproductive system
The male gametes, called spermatozoa or sperm, are made in the two testes, these are outside the body, in two sacs of skin called scrotum. The sperm are carried away from each testis in a tube called the sperm duct, which join up with urethra just below the bladder, the urethra continues downwards and opens at the tip of the penis. Where sperm duct join the urethra, there is a gland called the prostate gland, which makes fluid which the sperm swims in.
Egg production
Eggs start to form in the ovaries before the girl is born, when she hits puberty some of the egg cells will start to mature, usually one develops at a time.
Ovulation
When the matured egg bursts out of the ovary and into the funnel at the end of the oviduct. In humans it usually happens once a month
Sperm production
sperm is made in testis which contains thousands of very narrowed coiled tubes or tubules. Sperm develops from the cells in the walls of the tubules, which divide by meiosis. Sperm is produced continually from puberty onwards. Sperm production is very sensitive to heat therefore it is located outside the human body surrounded by a cool environment.
Fertilisation and development
after ovulation the funnel of the oviduct, which is lined with cilia beating rhythmically, wafting the egg into the entrance of the oviduct. The egg then travels towards the uterus, cilia lining the oviduct, muscles in the oviduct helps the egg move by peristalsis, if the egg is not fertilises with 8-24 hours after ovulation, it would die. the sperm should reach the top of the oviduct for fertilisation to be successful.
Sexual intercorse
When a man is sexually excited, blood is pumped into the spaces in the penis, making it erect. To bring the sperm as close as to the egg, the penis is inserted into the vagina.
Journey of sperm cel
Sperm is pushed into the vagina, when the muscles in the walls of the tubes containing sperm contract rhythmically. The wave of contraction begins in the testes, travels along the sperm duct into the penis, ejaculation occurs. The sperm fluid is called semen, which is deposited in the top of the vagina, near the cervix by ejaculation. The sperm then swims using its tails, up through the cervix through the uretus, into the oviduct. Once the sperm reached the egg, the head (nucleus) of the sperm enters the egg fusing with the nucleus of the egg, causing fertalisation
Implantation
When the sperm and egg nucleus fuses together it forms a zygote, which continues to move towards the oviduct and is divided along the way by mitosis, after a few hours it has formed a ball of cells known as the embryo, which obtains food from the yolk of the egg. after several hours the embryo reaches the uterus, by the time has 16-32 cell ball. The uterus has a thin, spongy lining, in which the embryo sinks into, this is known as implantation.
The placenta and amnion
The cells of the embryo buried in the walls of the uterus continues to divide, causing a placenta to grow, which connects it to the wall of the uterus. The placenta is soft and dark red, with projections called villi. The placenta is where substances are exchanged between the mother’s blood and the embryo’s blood.
The placenta and amnion (2)
After 11 weeks the embryo has been developed into a fetus, the placenta is joined to the fetus by the umbilical cord, which contain two arteries, which takes blood from the fetus into the placenta and the vein returns this blood.
The placenta and amnion (3)
In the placenta are capillaries filled with fetus’ blood, while the wall of the uterus are large spaces filled with mothers blood. Oxygen and food materials in the mother’s blood diffuses across the placenta into the fetus’s blood which is then caried along the umbilical cord to the fetus, CO2 and waste materials are travelled the opposite
Amniotic fluid
The fetus is surrounded by a strong membrane called the amnion, which produces a liquid known as amniotic fluid, which helps to support the fetus and protect it.
Development of the embryo and fetus
The ball of cells continue to divide, moving into positions to start to form the organs of the new individual. These cells start to develop into new specialised cells to perform different functions. Some becomes skin cells, some becomes muscle cells and some some become blood cells etc.
Birth
The fetus turns its head near the cervix few weeks before birth. Birth begins when the strong muscle in the wall of the uterus start to contract, this is called labour. This contraction stretch the opening of the cervix, the amniotic sac usually breaks during this point. After several hours the cervix is wide enough for the head of the baby to pass through and the muscles push the baby through the cervix out of the vagina, the placenta is fallen from the walls of the uterus as the baby can breath by themselves now.
