Understanding Fertilization and Embryonic Development

Fertilization and Embryonic Development

Fertilization is a chemical process by which the sperm penetrates the egg. There are two types of fertilization: internal and external.

  • Internal fertilization occurs when sexual intercourse takes place. In this case, millions of sperm are expelled and enter the vagina.
  • External fertilization occurs when sperm swim in the water to fertilize the eggs released by the female.

Segmentation

During this stage, the zygote undergoes a number of divisions that produce large quantities of cells called blastomeres. The egg, after many divisions, resembles a blackberry; this state is known as a morula. Subsequently, a central cavity called the blastocoel is formed in the inner cell mass; this stage is called a blastula. The segmentation rate depends on the amount of yolk in the egg: the fewer the yolk, the higher the rate of multiplication, and vice versa.

Gastrulation

During this stage, a series of processes occur that are aimed at the formation of the fundamental layers of the embryo: ectoderm, mesoderm, and endoderm. From these three layers, different organs and systems of each species will develop. Gastrulation occurs through different procedures, depending on the species: invagination, epiboly, immigration, and delamination.

Organogenesis

Organogenesis is the formation of organs in the embryo from the three embryonic layers. Before acquiring their final form, organs begin their development with an outline or rudimentary organ formation. Then, through differentiation and growth, they take their final form. All organs of the body derive from the three embryonic layers formed during gastrulation:

  • Ectoderm: Epidermis, attached glands, lens, nerve tissue, tooth enamel.
  • Mesoderm: Skeletal muscles, connective tissue, circulatory system, blood cells and lymph, kidneys, nephridium, conduits, etc.
  • Endoderm: Liver, pancreas, intestinal epithelium and glands, lungs, trachea, thyroid, etc.

The stage of organogenesis comprises two processes: differentiation and growth.

Delivery

Delivery begins with the expulsion of the placenta, umbilical cord, and membranes.

Gonorrhea

Symptoms

  • Urgency or increased urinary frequency
  • Urinary incontinence
  • Urethral discharge
  • Pain when urinating
  • Redness and itching of the opening of the penis (urethra)
  • Swollen testicles

Treatment

There are two aspects to be covered in sexually transmitted diseases (STDs), especially if it is as contagious as gonorrhea. The first is to cure the affected person. The second is to locate all sexual contacts to try to prevent further spread of the disease. During the Vietnam War, it was found that gonorrhea is resistant to penicillin and tetracycline. This resistance has increased in recent years. Therefore, new treatment guidelines have been designed for several types of last-generation, more powerful antibiotics:

  • Ceftriaxone 125 mg intramuscularly, once
  • Cefixime, 400 mg oral, once
  • Ciprofloxacin, 500 mg oral, once
  • Ofloxacin 400 mg oral, once
  • Spectinomycin, 2 g intramuscularly, once
  • Cefuroxime Axetil, 1 g orally once
  • Cefpodoxime proxetil 200 mg orally, once
  • Enoxacin, 400 mg oral, once
  • Erythromycin 500 mg orally four times a day for a week

It is important to follow up at 7 days after treatment with new cultures to confirm the cure of the infection.

Prevention

Sexual abstinence is the only absolutely safe method to avoid gonorrhea, but it is not practical or reasonable for many people. Safer sex behaviors can reduce risk. Sexual intercourse with one person free of any STD is currently the most acceptable preventive measure. The use of condoms for both sexes significantly decreases the likelihood of contracting an STD if used properly: the condom must be placed from the beginning to the end of sexual intercourse and should be used where sexual activity is practiced with a partner in which an STD is suspected. The treatment of both partners is essential to prevent reinfection, and it is one reason why this disease is notifiable. Gonorrhea is relatively easy to cure and eradicate, as the causative germ is found only in human mucus.