Unit IV: Compendium I

I. Reproductive System
A. The Life Cycle
B. Male Reproductive System
C.Female Reproductive System
D. Female Hormone Levels
E. Control of Reproduction
F. STDs


II. Development and Aging

A. Fertilization
B. Pre-embryonic/Embryonic Development
C. Fetal Development
D. Pregnancy and Birth
E. Development After Birth


A. The life cycle

Puberty is a sequence in which a person becomes sexually mature. Puberty is usually completed between 11 and 13 for girls and between 14 and 16 for boys. The reproductive system is the one system of the body that differs greatly between males and females. Male reproductive organs (testes) produce sperm. Female reproductive organs (ovaries) produce eggs. In men the sperm are transported through the penis. Females transport the eggs to the uterus. The penis delivers sperm to the vagina through intercourse. The vagina will also be the birth canal. The uterus holds the developing fertilized egg. Both the testes and the ovaries produce sex hormones. The respective hormones give masculine or feminine qualities.
Mitosis duplicates our 46 chromosomes before dividing. However, in meiosis, which only occurs in the testes and ovaries for reproduction, the diploid number of chromosomes is reduced to twenty three. This way when the sperm fertilizes the egg, the zygote (or new cell) has 46 chromosomes, instead of the number doubling each generation.

This zygote will one day be a full-
fledged human.

B. Male reproductive system
The testes are the main sex organ (gonads). They are paired and they found in the sacs of the scrotum. When sperm is produced it is stored for maturation in the epididymis. Once mature the sperm enters a vas deferens. They may be stored here for a time. The vas deferentia wrap around the bladder and empty into an ejaculatory duct. These empty into the urethra. Sperm leave the penis in semen during ejaculation. The semen carries secretions from the prostate, bulbourethral glands and the seminal vesicles. The seminal fluid contains nutrients, chemicals and sugars. All are important to sperm energy and transportation.
The penis is the organ of male intercourse. This consists of a shaft and a tip called the glans penis. Erectile tissue contains spaces for blood. This spongy tissue fills with blood when stimulated by NO (nitric oxide) and cGMP (cyclic guanosine monophosphate). The veins that take away the blood are compressed and the penis becomes erect. A sphincter closes off the bladder which keeps urine from entering the urethra. As stimulation increases seminal fluid enter the urethra and the glands inject secretions. Rhythmic muscle contractions push the seminal fluid out of the urethra. This is ejaculation. This is one aspect of the male orgasm (sensations, both physical and psychological that occur at the climax of sexual intercourse.) The penis becomes flaccid again after ejaculation or after loss of sexual arousal.
Testes descend into the scrotum from the abdominal cavity during puberty. This is important because the temperature of the abdominal cavity is too high to produce sperm. A testis is made up of compartments called lobules. Each contain one to three seminiferous tubules. Inside spermatogenesis (production of sperm) is occurring. The original sperm cell for spermatogenesis is the spermagonia. It divides into two primary spermocytes through mitosis. Te secondary spermocytes are the meiosis division of primary spermocytes. Each secondary spermocyte becomes two early spermatids. When these mature they become sperm. The process is nourished and regulated by sertoli cells. The process takes about 74 days. The parts of a mature sperm are the head, the middle piece and the tail. The head contains a nucleus and enzymes needed to penetrate the egg. The tail acts as a flagellum.
The hypothalamus is in control of hormone release and therefore testes' function. It secretes a hormone called gonadotropin-releasing hormone (GnRH.) This stimulates the petuitary gland to secrete the gonadotropic hormones FSH and LH. FSH promotes the production of sperm when found in males. LH controls testosterone production when found in males. Testosterone is essential for the development of the male reproductive organs. Testosterone also contributes to other distinctive characteristics of males (i.e. they tend to be taller, hairier and broader than females.)

This cross-section shows the male
reproductive system.

C. Female reproductive system
The female gonads are the ovaries. They are also paired. They produce eggs. The oviducts, or fallopian tubes extend from the uterus to the ovaries. When an egg bursts from an ovary it is swept into the fallopian tube by its finger-like projections called fimbriae. The egg is then propelled by ciliary movement and muscle contraction to the uterus. An egg will generally live only 6-24 hours without being fertilized. Fertilization and zygote formation take place in the oviduct, normally. The developing embryo wil usually arrive at the uterus after several days. It will then embed in the uterine lining. The uterus is a muscular organ with thick walls. It is about the size and shape of a pear. The cervix, at the bottom of the uterus, joins almost a right angle. Development of the embryo and fetus takes place in the uterus. It starts at only about 5cm wide but can grow to 30cm for the development of a fetus.The endometrium, which lines the uterus, is essential to the formation of placenta, which nourishes the fetus. A small opening in the cervix leads to the vaginal canal. The vagina is a tube that is functional for intercourse (for fertilization) and as the birth canal. It also is the exit for menstrual flow.
The vulva is the term for the collective of external female genitalia. Two large, hair-covered fold of skin called the labia majora extend back from the mons pubis, a fatty area under the pubic hair. Two small folds lay just inside the labia majora called the labia minora. They extend from the vaginal opening to form a foreskin for the glans clitoris. The clitoris is contains erectile tissue that fills with blood when aroused. The cleft between the labia minora contains the urethra and the vaginal opening. The urinary and sexual systems, unlike in males, are separate.
The labia minora, vaginal wall and clitoris become engorged with blood during stimulation. The breasts also swell and the nipples become erect. The labia majora enlarge as well. The vagina is lubricated by glands that secrete mucus and fluid. The clitoris is what is actually stimulated in sexual intercourse and can swell to two to three times its normal size. Orgasms occur at the height of sexual response which causes the walls of the vagina and uterus to contract rhythmically. There is no refractory period for females after orgasms and can have many in one sexual experience.

D. Female hormone levels
An ovary has many follicles, each containing an immature egg called an oocyte. At puberty a female will have somewhere between 300,000-400,000 follicles. A very small number of these will ever mature. During the reproductive years a female will only produce one egg a month. The follicle goes through three different stages and then back, in what is called the ovarian cycle. The primary follicle (stage 1) contains epithelial cells that surround an oocyte. The secondary follicle (stage 2) surrounds the oocyte with follicular fluid and washes it. The vesicular follicle (stage 3) continues to fill with fluid until it balloons the ovary wall. When an oocyte goes through meiosis it reduces after the first stage into the secondary oocyte and the polar body, which simply holds the discarded chromosomes. If fertilize the 14th day of a 28 day cycle. If fertilization does not occur then a new cycle will begin with menstruation.
Estrogen is mainly responsible for secondary functions in women, such as fat distribution (curves and breasts) and, generally, less body hair than men. Progesterone is also involved in breast development and more hormones are also involved in milk production. Between the ages of 45 and 55 the ovarian cycle will, likely, cease. This is called menopause. The ovaries no longer produce estrogen or progesterone. Completion of menopause d the secondary oocyte will undergo meiosis 2. Before any of this occurs the oocyte is released from the ovary by bursting from the vesicular follicle. This is called ovulation. When the vesicular follicle has released the oocyte it becomes a corpus luteum which is a gland-like structure. If the egg is not fertilized the corpus luteum disinegrates. The ovary also produces the sex hormones. The corpus luteum will produce progesterone while the primary and secondary follicles produce estrogen. Like in males, females produce GnRH (hypothalamus), FSH ans LH (pituitary)The last two stimulate the ovarian cycle in females. Gonadotropic hormones occur intermittently throughout the cycle. Through the feedback process the hormone levels cause ovulation onis usually considered after a year with no menstruation period. The 28-day cycle, or uterine cycle, is marked by four definite stages. In the first the endometrium disintegrates and causes the blood vessels to rupture. Blood and tissue, called the menses, passes out of the vagina. This is known as menstruation. In the second stage the endometrium thickens with the increased production of estrogen. In the third, usually on day 14, ovulation occurs. The last period, increased production of progesterone causes the endometrium to double or triple in thickness. The endometrium is now ready to receive a developing embryo. If this does not happen, sex hormones will decrease and cause the endometrium to break down again.
During intercourse many dsperm will travel to the oviduct where the egg is. Only one will fertilize the egg. If it becomes a zygote it will begin to develop on its way down the oviduct to the uterus. It will attach to the endometrium and implant. Pregnancy has now begun. The placenta sustains the embryo. This is where exchange occurs between maternal and fetal tissue. The placenta will initially produce the hormone HCG. Detection of it in the bloodstream or urine signifies pregnancy. Increased production of progesterone will signal the ceasing of follicle beginning. The endometrium does not break down resulting in no menstruation.

See ovulation take place!

E. Control of reproduction

Birth control methods are used to decrease the likelihood of reproduction. The most reliable method is abstinence, or the refrain from sexual intercourse. It is also the most reliable inhibitor of sexually transmitted diseases (STDs.) There are a number of birth control methods and many used are contraceptives. These are devices or medications that inhibit pregnancy. Some are male and female condoms, birth control pills, implants (usually contain hormones), and many others.
Infertility is the inability to become pregnant after a year of intercourse. About 15% of all couple are infertile. The cause in 40% is the male. The cause in 40% is the female and the cause in 20% is both. Often infertility in males is due to low sperm count.When males are inactive the temperature in the testes can be too high for proper sperm production. Overweight females have trouble conceiving because small follicles and ovulation fails. Pelvic inflammation can cause blockage of the oviducts. Medical intervention can sometimes help infertile couple conceive. Sometimes females can be given fertility drugs. These may cause multiple ovulations and even multiple births. There are also assisted reproductive technologies that increase the chance of pregnancy. A woman can be artificially inseminated by a donor. Sperm are placed in the vagina by a physician. In males with low sperm counts their sperm can be collected over a time so that they can artificially inseminate their partners. Often a woman is artificially inseminated by a donor who is unknown to her. Sometimes the sperm are placed directly into the uterus. During in vitro fertilization immature eggs are collected from follicles. They will mature in glassware and concentrated sperm are added. Then the embryo(s) is transferred to the uterus. Sometimes women are contracted by infertile women to have a baby for her. The sperm and egg could be contributed by the contracting parents.

The process of in vitro fertilization

F. STDs
STDs are caused by viruses, bacteria, protists, fungi or animals. Some viral STDs are genital herpes and HIV/AIDS. AIDS is the last stage of an HIV infection. The primary host of HIV is a T lymphocyte. These are the cells that would normally trigger an immune response so the immune system is greatly impaired. In the early stage the symptoms are few but the individual is highly contagious. By the last stage the T lymphocyte count is very low and the person usually contracts a normally maintainable infection. The person will die from this opportunistic infection. Genital herpes is the herpes simplex virus type-2. Its symptoms include itching, blisters, fever, pain on urination, swollen groinal lymph nodes. These blisters will rupture and leave very painful ulcers. Pregnant women with herpes should have a C section because it prevents the possibility of the baby contracting the virus in the birth canal. Genital warts are another virus. They appear as lesions on the genitals. They are linked to cancer of the genitalia. Hepatitis is a virus that infects the liver. There are six different kinds. Four of these are sexually transmitted or can be.
Chlamydia (burning and discharge), gonorrhea (pain on urination and greenish discharge) and syphilis (chancre, rash, patches on the mucous membranes, possible gummas and aneurysms) are all bacterial STDs. Depending on the person these infections can be very mild to very severe.


II. Development and Aging

A. Fertilization
When a sperm and an egg unite they form a zygote. This is the first cell of a new individual. This process is called fertilization. The tail of a sperm is a flagellum, which allows it to swim toward the egg. The mitochondria necessary for energy are found in the middle section. The head is the nucleus and is the only part that will fuse with the egg nucleus. The plasma membrane of the egg is covered by the zona pellucida. The zona pellucida is surrounded by a few layers of follicular cells called the corona radiata. Several sperm will penetrate the corona radiata during fertilization and many will attempt to penetrate the zona pellucida. Only one will enter the egg. When a sperm touches the egg the membrane depolarizes and no other sperm can bind to the membrane.

Many sperm attempt, but only one
will enter the egg.

B. Pre-embryonic/ embryonic development

The processes of human development are: cleavage (early cell dvision), growth ( the daughter cells begin increasing in size), morphogenesis (certain cells move to certain areas and shaping occurs) and differentiation (cells take on specific structures and functions.)
The first week after fertilization is pre-embryonic. The zygote divides repeatedly immediately after fertilization. It travels during the oviduct while doing so. The embryonic cells become a blastocyst which is separated by the inner and outer cell mass. The inner will become the embryo. If the inner mass splits in two than identical twins can develop. From the second week to the end of the second month embryonic development occurs. The embryo will have just implanted into the uterus wall.The outer cells which became the chorion will secrete enzymes to digest some of the endometrium. It also secretes the HCG hormone. The inner cell mass becomes the embryonic disk throughout the second week. Two other membranes form: the yolk sac and the amniotic cavity. Its fluid insulates and absorbs shock. Gastrulation is the process where the embryonic disk separates into three layers of tissue. The first, ectoderm, will become the skin epithelial linin and the nervous system. The second, mesoderm, will become the skeleton, muscles, dermis of skin, cardiovascular system, reproductive system and urinary system. The third, endoderm, will become epithelial lining. After the third week the nervous system is visible. The heart begins to form. It will pump blood by the end of the fourth week. The body stalk that is evident in the fourth will be the umbilical cord by the end of the fifth week. Limb buds appear that will later be arms and legs. From the sixth to eighth week the embryo becomes shaped more like a human being. Even though all organ systems have been developed the embryo weighs no more than an aspirin.

At three weeks this embryo has eyes and limb buds.

C. Fetal Development

The umbilical cord is the lifeline of the fetus. Its arteries carry O2 poor blood to the placenta and its veins bring nutrients and O2 rich blood to the heart of the fetus.

Between the the third and fourth months the eyes and ears are apparent. The head growth begins to slow and the rest of the increases in size. Skeleton forms as bones replace cartilage. Gender can be determined and fingernail, nipples, eyelashes and eyebrows are apparent. The heart beat can be heard at the end of the fourth month. Between the fifth and seventh months movement can be felt. The skin is coated with a protective substance, vernix caseosa. The fetus weighs about 3 pounds and is about a foot long at the end of this period. The baby could possibly survive if born at this time. Throughout the next two months the fetus continues to grow until it reaches about 7.5 pounds and is almost two feet long. Near the end of the nine months the fetus will rotate so the head is pointed toward the cervix. It is possible that it won't turn and breech birth, which is difficult and dangerous, is possible. Most likely a cesarean section would be performed to save the baby from asphyxiation. The sex of an individual is determined at fertilization. The gonads don't form, however until about the seventh week. The sex organs form according to hormone action. Some individuals with the XY (male) chromosome may become female because the Y chromosome is missing a piece. This missing piece may be present in some with XX (female) chromosomes. This causes them to have male genitalia. Those with Ambiguous Sex Determination develop as females even though they will have testes internally. This is because the plasma membrane receptors for testosterone are ineffective. About 1% of the population may have Psuedohermaphroditism. This is where an individual has testes, but appears female until puberty. At puberty male aspects become apparent as the body responds to testosterone. The clitoris will enlarge and look like a penis.

Breech birth may cause the child
to asphyxiate.

D. Pregnancy and Birth
Many changes take place in the woman's body during pregnancy. When first pregnant the woman may be nauseous and vomit. After this there might be an increase of energy. The woman will gain weight for many reasons: the breasts and uterus enlarge, There is the amniotic fluid as well as the storage of protein and fat. The woman may have lower blood pressure and retain water and sodium more. Then blood volume can increase 40%. Many will experience heartburn because smooth muscle relaxes much more. This may also cause constipation. Respiratory functions improve as the bronchial tubes relax and the uterus increases in size. The size increase causes the thoracic cavity to expand. The CO2 level drops about 20% which sends better blood to the fetus. Stress incontinence can be caused due to compression of the ureters and bladder.
Contractions happen throughout pregnancy.They are light at first but become stronger and more frequent at the end of pregnancy. Before parturition, or birth, the mucous plug will be expelled. During the first stage of birth the contractions occur so that the cervical canal disappears. Then the baby's head will open the cervix more so. The amniotic sac will rupture by this point if it had not already. In the second stage the contractions occur every 1-2 minutes and last about a minute each. The desire to push becomes greater as the baby's head enters the vagina. The baby descends head first. Then each shoulder comes. The rest follows easily. Then the umbilical cord is cut. The third stage is the after birth. The placenta is delivered. The contractions dislodge it as the uterus shrinks.

E. Development after birth

Development occurs throughout life and can be marked by four stages: infancy, childhood, adolescence and adulthood. Gerontology is the study of aging. This is of interest because there are more older people now than ever before. The human lifespan is expected to jump to 120 years maximum. There are three major hypotheses about the cause of aging. One is the genetic origin. Some genes may express the decrease of life span. Mitochondria can perhaps produce free radicals that will render cells dysfunctional. Another idea is that the decrease in hormonal activity affects the organs and immune system. It may not be the whole system that stops functioning but that a vital tissue decreases or changes. It is also possible that much of the aging process today is do to diet and exercise as well as other health habits.
There are many effects on the body as aging occurs. skin becomes thinner and less elastic.Sagging and wrinkling occur and the people feel colder as there is less adipose in the epithelial system. The skin dries since there is less oil glands. The arteries become more rigid and less effective. There is less elasticity in the lungs and breathing becomes more difficult. Blood flow to the liver and kidneys is reduced and they are less efficient. The digestive tract becomes less efficient. Short term memory may go. However, cognitive skill can remain unchanged without complications. hearing is more difficult as the ability to hear higher pitches goes. Glaucoma may develop as fluid builds up in the eye. Bone density is lost. Sometimes weight gain occurs because metabolism slows. The external genitals of females become less pronounced. The walls of the oviducts and vagina become thinner. Some sperm production occurs to death, but the number of sperm produced decreases gradually between 50 and 90 years of age. Though all these effects have been seen, they may be due to the health habits of the older generation. We won't know until we see the next generation come of age.