Human Reproduction and Development - Coursework Example

Human Reproduction, Growth, and Development Human Reproduction, Growth, and Development Explain the process of fertilization, implantation, and outline fetal development Midway through a female’s ovulation cycle, the ovary releases an oocyte that travels into the nearby fallopian tube in a process called ovulation. After vaginal intercourse, seminal fluid containing sperm is ejaculated into the female body through the vagina. The sperm cells swim up through the cervical cavity and the uterus into the fallopian tubes to arrive at the egg. Here, the sperm cell wiggles its way and penetrates the capsule of the oocyte. The sperm combines its DNA with that of the egg to form a zygote in a process called fertilization as displayed in the diagram below. (Diagram 1: Adopted from Berk, L, E., 2008. Infants, Children, and Adolescents, 6/E. Boston: Pearson Education/Allyn & Bacon) After fertilization, the zygote/ new embryo travels down the oviduct to the uterus in a process that takes about 24 hours in which the embryo simultaneously matures and sticks itself to the uterine wall. Implantation takes place when the embryo attaches itself to the wall of the uterus about 7 to 9 days after fertilization The development phases of pregnancy are called trimesters (three-month periods) because of the distinct transformations that take place during each phase The diagram displayed below shows a blastocyst that has burrowed itself into the uterine membrane between the 7th and the 9th days. (Diagram 1: Adopted from Berk, L, E., 2008. Infants, Children, and Adolescents, 6/E. Boston: Pearson Education/Allyn & Bacon) Implantation occurs during the second week of pregnancy and during this period, structures that feed and protect the developing fetus start to form. These include the amnion, yolk sac, chorion, placenta, and umbilical cord. After four weeks, the spinal cord and the primitive brain start to appear in the embryo. Heart, ribs, backbone, muscles, and the digestive tract begin to form. The embryo is about 6mm tall (1/4 inch). Many external features like the face, arms, and legs of the body begin to develop within 5 to 8 weeks of pregnancy when the embryo is 25cm tall (1 inch) and weighs 4 grams (1/7 ounce). The embryo begins to develop a sense of touch, and it can now move. Fast increase in body size begins between the 9th and 12th weeks of pregnancy. Organs, muscles, and nervous system become structured and connected. New behavioral abilities such as kicking, mouth opening, thumb sucking, and rehearsal of breathing begin to appear. External genitalia become well developed, and the sex of the fetus can be identified. The fetus now weighs about 28 grams (less than an ounce) and is about 7.6 cm tall (3 inches). Between the 13th and the 24th weeks (second trimester), the developing organism continues to grow fast, and the baby’s movements can be felt by the mother. Most of the brain’s neurons have been formed by week 24. The fetus’ eyes are sensitive to light, and he can now react to sound. The fetus is about 30 cm tall (12 inches) and weighs about 820 grams (1.8 pounds) (Barbara and Newman, 2012, p. 101). Between the 25th and 38th weeks (third trimester), the fetus size continues to grow and the lungs mature. Sensory and behavioral capacities enlarge because of rapid brain growth. Midway through this stage, a layer of fat is added under the fetus’ skin. Antibodies from the mother are transmitted to the fetus to protect him against diseases. The fetus rotates into an upside down position in readiness for birth. It is about 50 cm tall (20 inches) and weighs about 3,400 grams (7.5 pounds). The following diagram displays the sensitive areas in prenatal growth. Each developing organ has a sensitive phase during which each growth process may be disturbed. The blue bars indicate periods in the fetus development that are highly sensitive. The green bars show periods that are less sensitive although damage can still occur. (Adapted from: Barbara, N, M. & Newman, P., 2012. The Period of Pregnancy and Prenatal Development. Development through life: a psychosocial approach. (11th ed.). Belmont, CA: Wadsworth Cengage Learning). 2. Analyze characteristics of post natal growth and development. Development, however, does not stop at birth. Respiratory, gastrointestinal, homeostasis and cardiovascular systems are some of the systems that undergo major changes at birth and many other are yet to complete their development. The first year of infancy is characterized by continuous rapid physical growth. The weight of a healthy baby doubles in six months and triples by the end of the year. The head and the chest expand rapidly within this period allowing development of the lungs, heart, and brain. The bones, which are usually soft at birth, begin to harden at this stage and the soft parts of the new-born skull (fontanels) begin to calcify. The infant’s brain weight also increases rapidly reaching 75% of its adult weight by the end of the second year. The maturation process in childhood happens in an organized manner. The nervous system of the child becomes more mature at this stage and the child’s capacity to perform increasingly complex tasks (motor skills) expands. The large muscles in the body’s core, arms, and legs develop before the small muscles in the fingers and toes. Children learn to perform large motor skills like walking and running before they learn to perform small motor skills like writing and drawing. The core of the child’s body develops before the outer parts and development starts from the top down. As a result, babies learn to hold their head up before they learn to crawl. Growth in adolescents proceeds in the reverse direction. The arms, feet and legs develop first, followed by the upper body, which accounts for most of the young adults increase in height. Big differences in body proportions in girls and boys during adolescence is caused by the action of sex hormones on the skeleton. Girls’ hips begin to expand relative to the waist and shoulders while the boys’ shoulders widen relative to the hips. 3. Explain the key aspects of physical changes throughout life. For growing children to develop into adult men and women capable of reproducing, hormones are required to stimulate their bodies to change appropriately. In the pre-pubertal years, the hypothalamic pituitary gonadal system is maintained in a non-active stage by the central nervous system inhibition. During adolescence, the reproductive endocrine system becomes highly active. The brain releases gonadotropin-releasing hormone that targets the pituitary gland (hypophysis) to stimulate other endocrine glands to release of luteinizing hormone and follicle stimulating hormone. The attainment of sexual maturity is symbolized by production of spermatozoa in males and ovulation cycle characterized by the release of ova in females. Menopause is a naturally occurring phenomenon that takes place in all females when the number of ovarian follicles in the ovary are depleted. Estrogen and progesterone levels drop as a result and the luteinizing hormone and the follicle stimulating hormone increase in response. The changes in hormonal levels cause menopause. Menstruation occurs less regularly and eventually stops. 4. Evaluate the causes and effects of ageing. Aging is broadly believed to be caused by damage, either as a result of an inefficient defensive system or normal toxic waste released after metabolism accumulated throughout a person’s lifespan. The effects of aging range from a visibly wrinkled skin to fragile bones. The breakdown and wearing of elastic fibers cause the skin to stretch, sag, and lose its ability to snap back when pulled. Skin becomes rough and more transparent as are the result of thinning of the epidermis. Aging causes the muscles to shrink and lose mass. The size and number of muscles also reduce taking them longer to respond to motion. Joint movements become more limited, and flexibility reduces with age because of changes in ligaments and tendons. Also aging interferes with the balance between bone formation and absorption causing loss of bone tissue. The mineral composition of bones reduces so that the bones lose their thickness and become more delicate. Why the human body ages remain a large mystery and, as a result, many theories that explain the science of aging have been developed. The theories are categorized into two; the programmed theories and the error theories. Programmed theories state that the human body is meant to age, and there is a specific biological timeline that the body follows. The programmed theories include the programmed longevity, the endocrine theory, and the immunology theory. The error theories state that aging is a result of environmental damage on the human body over time that accumulates over time. References Barbara, N, M. & Newman, P., 2012. The Period of Pregnancy and Prenatal Development. Development through life: a psychosocial approach. (11th ed.). Belmont, CA: Wadsworth Cengage Learning. Berk, L, E., 2008. Infants, Children, and Adolescents, 6/E. Boston: Pearson Education/Allyn &Bacon. Larsen, W. J., 2001. Human embryology. Edinburgh: Churchill Livingstone. Moore K., & Persaud, T., 2003, Before We Are Born(6th ed.). Philadelphia: Saunders. Read More