Development and Inheritance
Utilizing knowledge from your learning and assigned readings, respond to the following questions:
- What activity during oocyte activation prevents penetration by additional sperm?
- Outline the events that take place between exposure of the oocyte to spermatozoa and formation of the first blastomere pair.
- List and briefly characterize the three trimesters of gestation.
- Describe the events of embryonic development from conception until the fetal stage, including development of the primary germ layers.
- List and describe the three stages of labor.
Expert Solution Preview
Introduction:
In this assignment, we will discuss the process of development and inheritance. It is essential to understand the process of development and the various stages involved in reproduction. This knowledge is crucial for medical students to provide appropriate medical advice to their patients during pregnancy, childbirth, and child development. The following are the answers to the questions provided concerning development and inheritance.
1. What activity during oocyte activation prevents penetration by additional sperm?
The activity that prevents penetration by additional sperm during oocyte activation is known as the cortical reaction. This process involves the fusion of cortical granules from the oocyte with the plasma membrane, creating a fertilization envelope that surrounds the oocyte. This envelope makes the zona pellucida impenetrable to additional sperm, thus preventing polyspermy. The cortical reaction ensures that only one spermatozoon can enter and fertilize the oocyte.
2. Outline the events that take place between exposure of the oocyte to spermatozoa and formation of the first blastomere pair.
When the spermatozoon reaches the oocyte, it binds to the zona pellucida and undergoes the acrosome reaction to allow the spermatozoon’s head to penetrate the zona pellucida. The spermatozoon then binds to the oocyte membrane, and its contents enter the ooplasm. This triggers a rapid increase in intracellular calcium concentration, which leads to oocyte activation. The oocyte and spermatozoon nuclei fuse to form a diploid zygote, and a series of mitotic cell divisions lead to the formation of a two-cell stage embryo. The blastomeres divide further, and the first cell division plane is usually perpendicular to the long axis of the polar body. The first blastomere pair formation occurs after the second cleavage division.
3. List and briefly characterize the three trimesters of gestation.
The three trimesters of gestation are:
– First trimester: This trimester begins from conception and lasts for 12 weeks. During this period, the blastocyst implants in the uterus, and embryonic development occurs. The major organs and body systems start to form, and the fetus grows from around 0.16 inches to 3 inches.
– Second trimester: This trimester begins from the 13th week and lasts until the 28th week. This period is characterized by significant fetal growth and the development of body systems, including the central nervous system, the digestive system, and the respiratory system. The fetus grows to around 14 inches in length and becomes more active.
– Third trimester: This trimester starts from the 29th week and lasts until delivery. Fetal growth and maturation of organ systems continue during this period, and the fetus gains weight rapidly. The fetus undergoes lung maturation, kick counts, and position changes in preparation for childbirth.
4. Describe the events of embryonic development from conception until the fetal stage, including development of the primary germ layers.
Embryonic development starts from conception and lasts until the 8th week of gestation. The zygote undergoes a series of mitotic cell divisions, forming a blastocyst. The inner cell mass of the blastocyst differentiates into three primary germ layers: the ectoderm, mesoderm, and endoderm. The ectoderm produces the skin, hair, nails, and nervous system. The mesoderm produces the muscles, bones, blood vessels, and heart. The endoderm produces the digestive system and respiratory system. These germ layers then undergo further differentiation and development to form the entire body.
5. List and describe the three stages of labor.
The three stages of labor are:
– First stage: This stage begins with the onset of labor and ends with complete dilation of the cervix. This stage can last up to 20 hours and is characterized by uterine contractions and cervical dilation.
– Second stage: This stage starts with complete dilation of the cervix and ends with the delivery of the baby. This stage typically lasts between 20 minutes to 2 hours and involves the mother pushing the baby through the birth canal.
– Third stage: This stage starts right after the delivery of the baby and ends with the delivery of the placenta. This stage typically lasts between 5 to 30 minutes and involves contractions that help deliver the placenta.
