9 months of pregnancy. 8 months 7 months 6 months
The baby is crouded and
usually head down.
5 months
4 months
3 months
2 months
This is at one month of pregnancy.
Embryonic development begins with the second week and lasts until the end of the second month of development. At the end of the first week the embryo usually begins the process of implanting itself in the wall of the uterus. The embryo is now the size of the period at the end of this sentence. As the week progresses the inner cell mass becomes the embryonic disk and two more extraembryonic membranes form. The yolk sac is the first site of blood cell formation. The amniotic cavity surrounds the embryo as it develops. At the third week two important organ systems make their appearance. The nervous system is the first organ system to be visually evident. A thickening appears along the entire posterior length of the embryo and then invagination occurs as neural folds appear. When the neural folds meet at the midline the neural tube which later develops into the brain and the spinal cord is formed. Development of the heart begins in the third week and continues into the fourth week. At four and five weeks a body stalk connects the embryo to the chorion which has treelike projections called chorionic villi. Once this process is complete the umbilical cord which connects the developing embryo to the placenta is fully formed. During the sixth through eight weeks of development the embryo changes to a form that is easily recognized as a human being. At the end of this period the embryo is about 38mm long and weighs no more than an aspirin tablet even though all organ systems have been established. At the third month the uterus is the size of a grapefruit. The fourth month fetal movement is felt by the mother. The fifth month the uterus reaches up to level of umbilicus and pregnancy is obvious. The sixth month the doctor can tell where the head is. The seventh month uterus reaches halfway between umbilicus and rib cage. The eighth month weight gain is about a pound a week. The ninth month sleeping becomes difficult and uterus is up to rib cage causing shortness of breath and heartburn.
There are many types of birth control. For example the birth control pill is a pill that you take orally at the same time everyday. There is an intrauterine device which is a small piece of molded plastic that is inserted into the uterus by a physician. These are believed to alter the environment of the uterus and oviducts so that fertilization probably will not occur but if it does occur implantation cannot take place. A diaphragm is a soft latex cup with a flexible rim that lodges behind the pubic bone and fits over the cervix. Each woman must be properly fitted by a physician. A female condom consists of a large polyurethane tube with a flexible ring that fits onto the cervix. A male condom is a latex sheath that fits over the erect penis. The ejaculate is trapped inside the sheath and does not enter the vagina. There are also vaccines that can be given as birth control.
This is pictures of birth control pills for a month and the vaginal ring and patch which are also means of birth control for women. Some birth control methods protect against std's but not all std's. They are mostly used as a means to not get pregnant.
The female gonads are paired ovaries that lie in shallow depressions one on each side of the upper pelvic cavity. The ovaries produce eggs and the female sex hormones, estrogen and progesterone. The oviducts extend from the uterus to the ovaries. They have finger like projections called fimbriae that sweep over the ovaries. When an egg bursts from an ovary during ovulation it usually is swept into an oviduct by the combined action of the fimbriae and the beating of cilia that line the oviducts. Once in the oviduct the egg is propelled slowly by ciliary movement and tubular muscle contraction toward the uterus. An egg lives approximately only 6-24 hours unless fertilization occurs. Fertizilation formation usually takes place in the oviduct. A developing embryo normally arrives at the uterus after several days and then implantation occurs and the embryo embeds in the uterine lining which has been prepared to recieve it. The uterus is a thick walled muscular organ about the size and shape of an inverted pear. It lies above and is tipped over the urinary bladder. The oviducts join the uterus at its upper end while at its lower end the cervix enters the vagina nearly at a right angle. The vagina is a tube that lies at a 45degree angle to the small of the back. The mucosal lining of the vagina lies in folds and can extend. This is specially important when the vagina serves as the birth canal and it facilitates sexual intercourse when the vagina recieves the penis. The vagina also acts as an exit for menstrual flow. Which is also called a period.
The male gonads or primary sex organs are paired testes which are suspended within the sacs of the scrotum. Sperm produced by rhe testes mature within the epididymis which is a tightly coiled duct lying just outside each testis. Maturation seems to be required in order for sperm to swim to the egg. When sperm leave an epididymis they enter a vas deferens where they may also be stored for a time. Each vas deferens passes into the abdominal cavity where it curves around the bladder and empties into an ejaculatory duct. The ejaculatory ducts enter the urethra. At the time of ejaculation sperm leave the penis in a fluid called semen. The seminal vesicles, the prostate gland, and the bulbourethral glands add secrections to seminal fluid. The pair of seminal vesicles lie at the base of the bladder and each has a duct that joins with a vas deferens. The prostate gland is a single donut shaped gland that surrounds the upper portion of the urethra just below the bladder. Bulbourethral glands are pea sized organs that lie posterior to the prostate on either side of the urethra. Their secretion makes the seminal fluid gelatinous. Each component of seminal fluid seems to have a particular function. Sperm are more viable in a basic solution and seminal fluid which is milky in appearance has a slightly basic pH. Swimming sperm require energy and serves as an energy source. Semen also contains prostaglandins chemicals that cause the uterus to contract. Some investigators believe that uterine contractions help propel the sperm toward the egg. The penis is the male organ of sexual intercourse. The penis has a long shaft and an enlarged tip calledthe glans penis. The glans penis is normally covered by a layer of skin called the foreskin. Spongy erectile tissue conyaining distensible blood spaces extends through the shaft of the penis. During sexual arousal autonomic nerves release nitric oxide. This stimulus leads to the production of cyclic guanosine monophosphate which causes the smooth muscle of incoming arterial walls to relax and the erectile tissue to fill with blood. The veins that take blood away from the penis are compressed and the penis becomes erect.
The human life cycle has two types of cell divisions- mitosis in which the chromosome number stays constant and meiosis in which the chromosome number is reduced. During growth or cell repair mitosis ensures that each new cell has 46 chrosomes. During production of sex cells the chrosome number is reduced from 46 to 23. Therefore an egg and a sperm each have 23 chrosomes so that when the sperm fertilizes the egg the new cell called a zygote has 46 chrosomes. The first cell of a new human being is called the zygote. Because a sperm has 23 chrosomes and the egg has 23 chrosomes the zygote has 46 chrosomes altogether. Without meiosis the chrosome number in each generation of human beings would double and the cells would no longer be able to function.
