Sexual Reproduction in Humans/ Human Reproduction System

• The male reproductive system consists of the testis, epididymis, sperm duct, prostate gland, penis and urethra
• Testes: Produces sperm and testosterone.

  
• Epididymis: a mass of tubes where sperm cells are stored to mature

  
• Sperm duct: A tube that carries sperm cells from the testes to the urethra

  
• Prostate gland: produces fluid rich in carbohydrates (energy for sperm cells), prostate liquid + sperm cells

  
• Urethra: A tube that carries urine from the bladder and passes semen through the penis

  
• The female reproductive system consists of the uterus, ovaries, oviduct (fallopian tube), cervix, endometrium, and vagina.
• Ovaries: produce egg cells (ova) and two hormones - estrogen and progesterone

  
• Fallopian tube: a pathway for egg cells and site of fertilization

  
• Uterus: site of embryo development

  
• Cervix: a ring of muscles closing and protecting the uterus and separating it from the vagina

  
• Endometrium: The inner lining of the uterus that is shed at the end of the menstrual cycle

  
• Vagina: organ of copulation; receives sperm from the penis during intercourse

  
• Sperm cell structure is: head, mid-peace and tail (flagellum)
• The head of the sperm cell contains the genetic material in a nucleus.

  
• The acrosome in the head contains enzymes so that sperm can penetrate an egg.

  
• The middle piece is packed with mitochondria to release energy needed to swim and fertilize the egg.

  
• The tail enables the sperm to swim.

  
• Egg cell production: one follicle starts to develop in the ovary. It takes 12-14 days
• Follicles produce estrogen, which is important for the egg cell maturation.
• Ovulation: On day 12th–14th, an egg cell is released from the ovary to the Fallopian tube
• After ovulation, the ruptured follicle turns into a yellow body, which produces progesterone and a small amount of estrogen. This is important to prepare the uterus for a future pregnancy. If there is no pregnancy, the yellow body turns into a white body.
• Menstrual cycle phases: follicular phase, ovulation, luteal phase (yellow body develops), menstrual bleeding

  
• Hormones and the menstrual cycle: Ovaries secrete two hormones:

  -estrogen

  -progesterone.

  The secretion of these hormones is under the control of two other hormones produced by the pituitary gland located at the base of the brain.

  The pituitary hormones are also two:

  -follicle-stimulating hormone (FSH) -luteinizing hormone (LH).

  
• Changes in the Female's reproductive organs during the cycle

  
• Fertilization is the union of two gametes (a sperm cell and an egg cell) in order to form a new cell called zygote.
• Fertilization takes place in the 1st third of the Fallopian tube. When sperm cells enter the female reproductive system, they gain fertilizing activity (for around 48h)
• Steps of Fertilization:

  1st step: sperm cell reaches the egg cell

  2nd step: Enzymes released from the acrosome melt egg cell membrane

  3rd step: The nucleus of the sperm cell enters the egg cell cytoplasm

  4th step: Egg cell releases chemicals that make the membrane thicker and not permeable for other sperm cells.

  5th step: The two nuclei from the nucleus of the first cell of the new organism (zygote)
• Embryo development:

  The embryo continues to grow and produces new cells that form tissues and organs.
• Inside the uterus the embryo becomes enclosed in a fluid-filled sac called the amnion, which protects it from damage.
• The fluid is called amniotic fluid.
• The oxygen and food needed to keep the embryo alive and growing are obtained from the mother’s blood by means of a structure called the placenta.
• The placenta becomes closely attached to the lining of the uterus and is attached to the embryo by an umbilical cord.
• Umbilical cord is made of:

  -an artery that brings O2, nutrients and hormones from the mother to the embryo

  -2 veins that carry CO2 and waste from the embryo to the mother

  -Placenta is a large, flat organ attached to the endometrium. Its a connection between the mother and the embryo
• Birth begins when the strong muscles in the wall of the uterus start to contract. The birth is triggered by the hormone oxytocin produced in the hypothalamus.
• Stage 1: Delivery

  • The muscular walls of the uterus start to contract, slowly stretching the opening of the cervix.   

  • The pressure breaks the amniotic sac, releasing the amniotic fluid. 

  • Contraction gradually becomes more frequent, pushing the baby down towards the cervix, which becomes dilated to allow the baby to pass through.

  • This stage of labor is the longest and can range from 12 to 20 hours for women having their first baby. 

  
• Stage 2: Expulsion

  •The expulsion stage begins when the cervix is fully dilated and ends when the baby is born. 

  •As pressure on the cervix increases, women may have the sensation of pelvic pressure and an urge to begin pushing.

  •In first labors, birth is usually completed within 3 hours. 

  
• Stage 3:Placenta delivery

  • This is the period from just after the fetus is expelled until just after the placenta is expelled.

  • Placental expulsion begins as a physiological separation from the wall of the uterus.

  •The average time from delivery of the baby until complete expulsion of the placenta is estimated to be 10–12 minutes.

  
• implantation: the zygote is dividing and traveling downward to the uterus. At around day 7-8 is implanting in the endometrium