Production of human?

• Fertilization


  Only one sperm cell will fertilize an ovum
• Capacitation


  1. Sperm undergo a final metabolic change as they swim through the fluid of the uterus and fallopian tube

  2. The acrosome becomes more fragile

  3. When sperm and egg make contact, the acrosomal enzymes will digest the layers of the cells and membrane around an ovum

  4. Once a sperm nucleus enters the ovum, changes in the egg cell membrane block the entry of other sperm
• Implantation


  1. Fertilization usually takes place within the fallopian tube, and the zygote begins to divide even as it is being swept toward the uterus

  2. The endometrium produces carbohydrate "docking" molecules toward the end of uterine cycle, and the blastocyst has a surface protein that fits the docking site

  3. The trophoblast secretes enzymes to digest the surface of the endometrium, creating a small crater into which blastocyst sinks

  4. The trophoblast will become the chorion, the embryonic membrane that will form the fetal portion of the placenta

  5. The inner cell mass will grow to become the embryo and other membranes
• Gastrulation


  An early developmental process in which an embryo transforms from a one-dimensional layer of epithelial cells (blastula) and reorganizes into a multilayered and multidimensional structure called the gastrula
• Structures derived from the three germ layers


  • Ectoderm: Epidermis; hair and nail follicles; sweat glands; Nervous system; pituitary gland; adrenal medulla; Lens and cornea; internal ear; Mucosa of oral and nasal cavities; salivary glands
  • Mesoderm: Dermis; bone and cartilage; Skeletal muscles; cardiac muscle; smooth muscle; Kidneys and adrenal cortex; Bone marrow and blood; lymphatic tissue, lining of blood vessels
  • Endoderm: Mucosa of esophagus, stomach, and intestines; Epithelium of respiratory tract, including lungs; Liver and mucosa of gallbladder; Thyroid gland; pancreas
• At 20 days, the embryonic membranes can be clearly distinguished from the embryo itself. As the embryo grows, the yolk sac membrane is incorporated into the umbilical cord.
• Yolk sac


  The site formation of the first blood cells and the cells that will become spermatogonia. In humans, the yolk sac is present during the early stages of pregnancy but typically decreases in size and function as the placenta takes over the role of providing nutrients to the growing fetus.
• Amniotic sac


  When the fetal kidneys becomes functional, they excrete urine into the amniotic fluid
• At about 4 to 5 weeks of development, the embryo shows definite form
• Placenta


  • Made of both fetal and maternal tissue, formed by the third month of gestation
  • The site of exchanges between maternal and fetal blood
  • Produces hormones to maintain pregnancy
• Umbilical cord


  • Connects the fetus to the placenta
  • Allows oxygen and nutrients to enter the fetal blood, and carbon dioxide and waste products to leave
• Afterbirth


  The delivery of the placenta
• Parturition


  1. Toward the end of gestation, the placental secretion of progesterone decreases while estrogen level remains high, and the myometrium begins to contract weakly at irregular intervals

  2. The fetus is often oriented head down within the uterus

  3. First stage: dilation of the cervix

  4. Second stage: delivery of the infant

  5. Third stage: delivery of the placenta (afterbirth)
• The average gestation period is 40 weeks, with a range of 37 weeks to 42 weeks
• There is some bleeding during the third stage of labor, but the uterus rapidly decreases in size, and the contractions compress the endometrium to close the ruptured blood vessels at the former site of the placenta. This is important to prevent severe maternal hemorrhage.