Compendium Review #7

For chapters 16 & 17:

• Human Life Cycle

• Fertilization and Fetal Development

• Pregnancy, Birth, and Development


***HUMAN LIFE CYCLE***
From zygote to baby to adolescent to adult and back to the beginning again. The human life cycle deals with two different kinds of cell division-meiosis and mitosis: the gamete production and the growth and repair of tissues, respectively.



To state the obvious, there are males and females, each with a reproductive system unique to each. The males have external genitals such as the penis and the scrotum. They also havev sperm in the epididymides. These sperm move through the vasa deferentia to the urethra. Then the seminal vesicles, prostate gland, and bulbouretral glands add the fluid that flow with the sperm, carrying them, hopefully, to a successful journey in search for a woman's egg. This is call semen, and it takes it's part in a male's orgasm when the semen ejaculates our of the male's penis. The males have a testosterone level that is relatively maintained at a constant level.

Females are quite different. They have their reproductive system inside their body. There is usually one mature follicle produced a month by the oogenesis in the ovaries. (testies of a woman). The follicle balloons out of the ovary and bursts, releasing an egg that goes into the oviduct, which then goes to the uterus, where the growth and development, the whole she-bang of reproduction, takes place. The external genital rea of a woman includes the vagnal opening, the clitoris, the labia minora, and the labia majora. For females to orgasm, they culminate in uterine and receive oviduct contractions.



Women have to go through three main hormonal levels. There is the ovarian cycle and the uterine cyce, where the woman is not pregnant and there is the fertilization and pregnancy cycle, where the woman is pregnant. First off, the ovarian cycle which is under the hormonal control of the hypothalamus and the anterior pituitary. The first half of the cycle deals with the FSH coming from the anterir pituitary which causes maturation of afollcle thatseretes estrogen and some progesterone. After this half, the LH also from the anterior pituitary changes the follicle into the corpus luteum which secretes progesteron and some estrogen. During the uterine cycle, estrogen allows the endometrium to rebuild. Ovulation usually happens on the 14th day of a woman's typical 28 day cycle. The progesterone causes the endometrium to get thicker and become secretory; alow level of hormones causes this endometrium to break down. Menstruation is then the result.



During fertilization, the embryo is in the thckened endometrium where it will develop. The HCG production by the placenta keeps the corpus luteum around as well as the progesterone production. This cycle lasts 9 months for the baby to fully develop.

***FERTILIZATION AND FETAL DEVELOPMENT***



During fertilization, the sperm nucleus enters the egg and fuses with the egg nucleus. The processes of developmentinclude cleavage, growth, morphogenesis,and differentiation. In internal development, the extraembryonic membranes are at work. This is the pr-embryonic and embryonic development.



The nextstage is fetal development. This is where all the organ systems are established and the placenta is fully functioning. The umbilical arteries and vein exchange blood from the placenta. This also gives the fetus oxygen and nutrients and get rid ofcarbon dioxide and wastes. Fetal development takes place from the 3rd month all through the end of the cycle, at 9 months.



The third and fourth months is where the skeleton hardens from the cartilage it once was. The sex also becomes distinct and if the SRY gene is there, the testes and male genitals develop, but if not, then ovaries and female genitals develop. The 5th-9th months are set aside as mostly a growth and weight gaining stage for the baby. The lungs also develop.





***PREGNANCY, BIRTH, AND DEVELOPMENT***



Changes women go through during pregnancy may include: weight gain, constipation, heartburn, darkening of certain skin areas, and pregnancy-induced diabetes, all due to the placenta's addtitional hormones.



There are three stages for bith. Stage one consists of the parturition nd the cervix dialating. The next stage is the actually birth process and the presence of the baby. The last stage is where the afterbirth is expelled. In other words, the placenta is taken out. The life cycle, or development, starts at infancy, eads to childhood, then adolescence and finally adulthood.



The once-infant is then able to produce a baby of his or her own. Starting at age 20, an increased risk of infirmity, disease, and death steadily increase. Aging is still being researched but some hypotheses include that aging may have a genetic basis, that it may be due to the declining existance of hormones, or that it may be due to what we eat and how we exercise. This aging has a big effect on the body to where our organs are slowly deteriorating and not functioning as well.