The female and male reproductive systems are two homologous organ systems that developed from the same tissue embryologically speaking. Pregnancy involves anatomical and physiological changes in both the mother and the developing human that are driven by the nervous and endocrine systems. In this assignment, I will examine how hormones drive these anatomical and physiological changes.

 

• Describe anatomical and physiological changes that occur at the gross and histological levels during pregnancy and postpartum in the mother and developing human during the following stages:
• Fertilization
• Embryonic development
• Fetal development
• Birth
• Postpartum period
• Examine how hormones regulate the ovarian cycle, in utero development, and the process of labor and giving birth.
• Briefly discuss the similarities and differences in oogenesis vs. Spermatogenesis.

 

(i) Fertilization

A mature ovum is released into the mother's fallopian tube through the ovulation process. It remains active for approximately 48 hours. During this time, if a sperm reaches the ovum, fertilization occurs and a zygote is formed.

As ovulation occurs, the uterine wall becomes thick with tissues and blood vessels under the influence of estrogen and progesterone. This happens so that implantation of the embryo in the uterine wall can take place.

(ii) Embryonic development

During the first week after zygote formation, the zygote pronuclei is formed. The zygote divides repeatedly to form a ball of cells called the morula stage. By the end of 3rd week after fertilization, a blastocyst is formed with an inner and outer cell mass. By the end of the 5th week, there is the loss of zona pellucida and the blastocyst is free. By the end of the 6th week, the blastocyst attaches to the uterine wall.

Step-by-step explanation

(i) Fertilization

A mature ovum is released into the mother's fallopian tube through the ovulation process. It remains active for approximately 48 hours. During this time, if a sperm reaches the ovum, fertilization occurs and a zygote is formed.

As ovulation occurs, the uterine wall becomes thick with tissues and blood vessels under the influence of estrogen and progesterone. This happens so that implantation of the embryo in the uterine wall can take place.

(ii) Embryonic development

During the first week after zygote formation, the zygote pronuclei is formed. The zygote divides repeatedly to form a ball of cells called the morula stage. By the end of 3rd week after fertilization, a blastocyst is formed with an inner and outer cell mass. By the end of the 5th week, there is the loss of zona pellucida and the blastocyst is free. By the end of the 6th week, the blastocyst attaches to the uterine wall.

(iii) Fetal development

Once implantation occurs and the placenta develops, it begins to secrete the hormone HCG. Progesterone levels also rise and the fetus continues to develop. Fetal development is divided into three trimesters of three months each. The cell differentiation is almost complete and more important changes occur. The early body structures established during the embryonic stage continue to grow and develop. The neural tube develops into the brain and spinal cord and neurons continue to form and migrate to different locations.

Between the 9th and 12th week of gestation, reflexes start to appear and the fetus can move its arms and legs. During the second trimester, that is the 4th to 6th month of pregnancy, the heartbeat grows stronger, and other body structures develop further. Hair, nails, and eyelashes form. During the period from 7th to 9th months, the fetus continues to develop, grow in size and weight and the lungs begin to expand and contract, preparing the muscles for breathing.

(iv) Birth

Birth of the fetus, or parturition, occurs at the end of the 9th month of gestation. Hormones responsible for the entire process of parturition are oxytocin, endorphins, adrenaline, and prolactin. There are three stages of parturition - dilation of the cervix, contractions of the uterus and delivery of the fetus, and expulsion of the placenta.

(v) Postpartum period

The postpartum period begins just after childbirth. The mother's body, the hormone levels, and the uterus size return to the normal state. It normally includes the first six weeks after childbirth. During this time, the mammary glands begin to produce milk under the influence of prolactin, which is secreted during the gestation period too so as to prepare the milk glands for lactation.

(vi) Examine how hormones regulate the ovarian cycle, in utero development, and the process of labor and giving birth.

The hormones play a major role in ovulation because follicle-stimulating hormone stimulates the follicles of the ovary to produce Ovum. After fertilization, The menstrual cycle is maintained by the estrogen and progesterone hormones and during the delivery, oxytocin plays important role in the contraction of muscles for the expulsion of the baby.

(vii) Oogenesis and spermatogenesis

a. Similarities

• Both the processes occur in the reproductive organs.
• Haploid gametes are produced at the end of both spermatogenesis and oogenesis.
• Mitosis as well as meiosis is involved in the production of gametes.
• Both processes are meant to carry out the fertilization process.

b. Differences

• Spermatogenesis is the process of forming male gametes or sperms and the oogenesis is the process of forming female gametes or eggs. In spermatogenesis, four mature sperm cells are produced from a spermatogonium whereas, in oogenesis, one mature egg cell is produced from an oogonium.
• Sperms produced in spermatogenesis are motile but the ovum produced in oogenesis is non-motile.
• During spermatogenesis, equal cytokinesis occurs whereas, during oogenesis, unequal cytokinesis occurs which gives rise to four polar bodies along with an ovum.