Chapter 16- Reproductive System
16.1- Human Life Cycle
16.2- Male Reproductive System
16.3- Female Reproductive System
16.4- Female Hormone Levels
16.5- Control of Reproduction
16.6- Sexually Transmitted Diseases
16.1- Human Life Cycle
The reproductive system for males and females are very different. Puberty is known as a sequence of events that take place for females around the age of 11 and 13 and for males 14 and 16; this is when they become sexually competent young adults. The reproductive system is fully functioning, (ability to produce children) when puberty in complete. In the reproductive system males produce sperm in the testes while females produce their eggs in the ovaries, sperm is nurtured and transported in the ducts until exiting via the penis, females eggs are transported in the uterine tubes to the uterus. The penis delivers sperm to the vagina, which also transports menstrual fluid to the outside and serves as the birth canal. The uterus is where the fertilized egg develops and once the baby is born the breasts provide milk for the baby. The sex hormones are produced by the testes and the ovaries, these have a bug impact on the body; they bring masculinity to males and feminize females. All cells in the body have 46 chromosomes and when mitosis occurs the new cells normally have 46 chromosomes as well. Mitosis being duplication division takes place during growth and for tissue repair. Meiosis being reduction division occurs in the testes during sperm reproduction and in the ovaries for egg reproduction. For meiosis the 46 chromosomes reduce to 23 chromosomes the haploid or n number where as 46 chromosomes are diploid or 2n number. Sperm carries cells to the egg which provides the cytoplasm and chromosomes. The sperm has 23 chromosomes as does the egg, so the zygote which is the first cell of a new human has 46. Cells cannot function without meiosis.
16.2- Male Reproductive System
The scrotum holds the primary sex organs also known as the testes. The tightly coiled ducts known as epididymis is where sperm matures. The vas deferens is where matured sperm go to be stored. From here sperm goes to the ejaculatory ducts, these ducts enter the urethra. The urethra carries semen and urine at different times, therefore urine cannot escape during intercourse. Semen is a fluid containing sperm and secretions from the prostate gland, seminal vesicles and the bulbourethral glands. Semen includes sugar fructose which helps provide energy for the swimming sperm.
Male reproductive system is shown below:
The penis has a long shaft; the enlarged tip at the end is the glans penis. The layer of skin that covers the glans penis is the foreskin which can be surgically removed soon after birth, this is known as circumcision. Erectile tissue extends through the shaft. During sexual arousal the autonomic nerves release NO (nitric oxide); this leads to production of cGMP (cyclic guanosine monophosphate) this allows smooth muscles of the arterial walls to relax and lets erectile tissue fill with blood. The penis becomes erect when the veins become compressed taking blood away from the penis. If the erectile tissue is unable to expand enough for the veins to compress then erectile dysfunction or impotency can occur. Sperm enters the urethra once sexual stimulation intensifies, when the seminal fluid enters the urethra it is released by rhythmic muscle contractions causing it, this is part of the male orgasm. The psychological feeling is in the brain where as the physiological feeling involves the genital organs and body. There can be 400 million sperm in semen when ejaculated.
Sperm and male sex hormones are produced by the testes. During the last 2 months of fetal development the testes drop into the scrotum sacs from inside the abdominal cavity. The testis is made up of lobules- compartments that have 1 to 3 tightly coiled seminiferous tubules, this is packed with cells undergoing sperm production. Spermatogonia divide to make primary spermatocytes that move from the outer wall, get bigger and undergo meiosis I to make secondary spermatocytes. Secondary ones undergo meiosis II to make 4 spermatids, these then differentiate into sperm. Sertoli cells support, nourish and regulate the process of spermatogenesis. A head, middle piece and a tail make up a mature sperm. The middle piece has a mitochondria which gives energy for tail movement or the flagellum. A nucleus covered by the cap known as the acrosome is in the head, here is where enzymes are stored for penetration of the egg. Androgens are the male sex hormones secreted by cells that are between the seminiferous tubules, they are called interstitial cells. Testosterone is the most important androgen.
Testosterone is necessary for normal development and functioning of the sex organs. This brings and maintains the secondary sex characteristics. This provides hair on the face and chest of males. Also helps in greater muscle development.
Hormonal control of testes is shown below:
16.3- Female Reproductive System
The pair of ovaries are female gonads. Eggs and the female sex hormones estrogen and progesterone are produced by the ovaries. From the uterus to the ovaries is the oviducts also known as the uterine or fallopian tubes. The oviducts are not attached to the ovaries, but there are some fimbriae that sweep over them. Fimbriae and cilia are what sweep an egg into the oviduct during ovulation. If an egg is not fertilized it will only live for 6-24 hours. Fertilization begins in the oviduct and goes to the uterus a few days later where implantation occurs and it is embedded in the uterine lining. The uterus is a thick-walled muscular organ. The oviducts are at the upper end while the cervix is at the lower end. Cervix cancer is common in women. A hysterectomy is the removal of uterus and the cervix. The womb is 5 cm wide but can stretch up to 30 cm wide. Formation of the placenta gets help from the lining of the uterus known as the endometrium. 2 layers make up the endometrium- the basal layer and an inner functional layer. When not pregnant the inner layer varies in thickness causing a monthly uterine cycle. The vaginal canal is located at the small opening in the cervix. The acidic environment in the vaginal canal is what protects from pathogenic bacteria.
Female reproductive system
The vulva is an external genital organ, the 2 folds of skin covered with hair included with the vulva are known as the labia majora, the labia minora lay insde the labia majora. The organ involved with sexual arousal is the glans clitoris. The cleft between the labia minora is where the opening to the urethra and the vagina. The hymen (a ring of tissue) is what keeps the vagina somewhat closed until sexual intercourse. When sexual stimulation occurs the labia minora, the vaginal wall and the clitoris become engorged with blood, the breasts swell and the nipples become erect. Also the labia majora enlarge, redden and spread away from the vaginal opening.
16.4- Female Hormone Levels
Ovaries have follicles and they contain immature eggs called oocyte. Females are born with as many as 2 million follicles and when we hit puberty we only have 300,000 to 400,000. Only about 400 follicles ever mature, only 1 egg per month during reproductive years. While the follicle matures it changes from a primary to a secondary to a vesicular follicle. Primary oocytes undergo meiosis I resulting in the cells being haploid with 23 chromosomes. One of these is a polar body which holds discarded chromosomes. If a secondary oocyte is fertilized by sperm it will undergo meiosis II, it not fertilized it won’t undergo anything and will die off. When ovulation occurs the vesicular follicle bursts letting the oocyte go surrounded by a clear membrane. Then the vesicular follicle turns into a corpus luteum, if no egg is fertilized this disintegrates. Primary follicles produce estrogen, secondary produce estrogen and some progesterone. Other progesterone is produced by corpus luteum. Hypothalamus
has control of the sexual function of the ovaries, it secretes gonadotropin releasing hormone.
Estrogen is responsible for secondary sex hormones More fat under the skin is what accounts for females having a more rounded appearance than males. Estrogen and progesterone are essential in breast development. The female pelvis tilting forward is why females tend to have a stomach bulge, protruding buttocks and more of a lower back curve than males. When the ovarian cycle stops it is known as menopause. Complete menopause is when the menstruation cycle is gone for a year. Estrogen and progesterone affect the endometrium which causes the uterus to undergo the cycle. The cycle consists of 28 days, days 1-5 tissue and blood pass through the vagina, days 6-13 the proliferative phase where the endometrium gets thick, on day 14 ovulation occurs. The secretory phase occurs during days 15-28 where the endometrium doubles or triples in thickness. And is now prepared to receive a developing embryo.
The placenta sustains the developing embryo and the fetus. At first the placenta produces human chorionic gonadotropin (HCG), this is what maintains the corpus luteum in the ovary. HCG is what a pregnancy test determines when pregnant. When pregnant the menstruation stops. With birth control pills are taken the active pills build of the uterine lining and when inactive pills are taken the lining sheds and ovulation doesn’t occur. The pills keep the sperm from getting into the uterus by thickening the cervical mucus.
16.5- Control of Reproduction
Not having sex is the most sure way to not get pregnant or to get sexually transmitted diseases. Medications and devices that reduce the chances of getting pregnant are contraceptives. Some forms of contraceptives are IUD- a piece of plastic put into the uterus by a doctor, diaphragm- soft latex cup that fits over the cervix, female condom- a polyurethane tube with a flexible ring that fits in the cervix, male condom- latex sheath that covers the penis. Vasectomy- cutting and sealing the vas deferens, this keeps sperm from reaching the seminal fluid. Tubal ligation- cuts and seals the oviducts which keeps eggs from passing through the oviducts. The morning after pill can be taken after unprotected sex if taken within a certain amount of time to be successful.
If after a year of regular unprotected sex a couple is still unable to become pregnant they are considered infertile. A big reason for males being infertile is due low sperm count or a large amount being abnormal. Smoking and alcohol can contribute to this. And if too much time is spent sitting around the temperature for the testes remains too high for adequate sperm production. In females the highest reason for infertility is body weight. Another cause is pelvic inflammatory disease and endometriosis. Assisted reproductive technologies (ART) are techniques that can help people to become pregnant. There is artificial insemination, where sperm is placed in the vagina by a doctor. In vitro fertilization (IVF) here conception occurs in laboratory glassware. Immature eggs are matured in glassware and then sperm is added, after a few days they are put in uterus and if successful a baby can be born. Gamete intrafallopian transfer- this is the same as the vitro process only this process puts sperm and eggs in the oviducts as soon as they are brought together. Surrogate mothers are being paid and are under contract to carry and have babies. Intracytoplasmic sperm injection is the process of putting a sperm directly in an egg.
16.6- Sexually Transmitted Diseases
Some STDs caused by viruses are HIV infections, genital warts, genital herpes and hepatitis. Genital warts are caused by human papillomaviruses and are associated cervical cancer, tumors of the vulva, anus and penis. Genital herpes are caused by the herpes simplex virus. Type I causes cold sores and fever blisters, type II causes genital herpes. Hepatitis infects the liver which can lead to liver failure, liver cancer and death. Some STDs caused by bacteria are known as chlamydia, gonorrhea and syphilis. Chlamydia can cause cervical ulcerations and have urinary tract infection symptoms. Gonorrhea can lead to pelvic inflammatory disease. Both gonorrhea and chlamydia can lead to infertility. Gonorrhea can spread to internal parts of the body causing heart damage or arthritis. Syphilis can affect the nervous system, a rash can occur and be seen of the bottoms of our hands and feet.
Chapter 17- Development and Aging
17.1- Fertilization
17.2- Pre-Embryonic and Embryonic Development
17.3- Fetal Development
17.4- Pregnancy and Birth
17.5- Development After Birth
17.1- Fertilization
Fertilization occurs when a sperm and an egg unite to form a zygote. The flagellum of a sperm swims to the egg. The zygote gets the cytoplasm and organelles from the mother. The eggs plasma membrane is surrounded by an extracellular matrix called zona pellucida. A few layers of adhering follicular cells known as corona radiata surround the zona pellucida. For fertilization SPERM PENETRATE THE CORONA RADIATA AND ATTEMPT TO PENETRATE THE ZONA PELLUCIDA AND ONLY ONE SPERM ENTERS THE EGG. THE SPERM IS ALLOWED TO PENETRATE THE ZONA PELLUCIDA WITH HELP FROM THE ACROSOME. The zona pelucida and changes in the eggs plasma membrane keep more than one sperm entering an egg. Once a sperm touches the egg the eggs plasma membrane depolarizes to keep other sperm out.
17.2- Pre- Embryonic and Embryonic Development
Cleavage, growth, morphogenesis and differentiation are all processes of development. Extraembryonic membranes are outside of the embryo, these are known as chorion- takes away waste and nourishes the fetus and embryo with oxygen, allantois- accumulates urine produced by fetal kidneys and its blood vessels become the umbilical blood vessels, yolk sac- 1st to appear and is the first site of blood cell formation, amnion- serves as a cushion to protect the embryo.
The extraembryonic membranes are shown below
Pre-embryonic development occurs in the first week. After fertilization the zygote divides over and over as it goes down the oviduct to the uterus. Morula is known as a compacted ball of embryonic cells which become a blastocyst. In this there is an inner cell mass which becomes the embryo, the inner cell mass is surrounded by outer cells which becomes the chorion. Embryonic development begins in the 2nd week lasting until the end of the 2nd month. Implantation is successful when the embryo implants itself in the wall of the uterus. An ectopic pregnancy occurs if the embryo implants itself elsewhere, which will result in an unsuccessful pregnancy. Amniotic fluid serves as an insulator against cold and heat and also absorbs shock. Gastrulation is a major event that moves cells to become tissue layers known as primary germ layers these layers are ectoderm, mesoderm and endoderm. During the 3rd week the nervous system and the heart are relevant. In the 5th week the head enlarges and its possible to make out the eyes, nose and ears. In the 6th-8th weeks the embryo can be recognized as a human, brain development occurs and the embryo is about 38mm long and weighs no more than an aspirin tablet.
17.3- Fetal Development
The placenta is the source of estrogen and progesterone during pregnancy, they have 2 functions- they prevent new follicles from maturing and they maintain the endometrium. The lifeline of the fetus is the umbilical cord, it has the arteries and vein. Fetal development occurs in the 3rd month lasting until the 9th month. In the 3rd and 4th months fingernails, eyebrows, eyelashes, and hair on the head appear. Cartilage is replaced by bone. It is the 3rd month when you can tell the sex of the baby. In the 4th month the heartbat can be heard with a stethoscope. In the 5th through 7th months the mom can feel more than a flutter sensation as the baby can kick and jab when moving around. The eyelids are fully open. At the 8th through 9th months the baby moves so that the head is pointed towards the cervix. If the baby ends up in a breech position (butt 1st) then a c-section may be needed.
The sex of the baby is determined at fertilization. Males have a pair of X and Y chromosomes while females have 2 X chromosomes. Gonads start developing at 7 weeks. Indifferent is what the tissue that gives rise to the gonads. It is called this because it can either be ovaries or testes. At 6 weeks the ducts are the same for males and females. If the SRY gene is present testes will develop and testosterone makes the ducts become male genital ducts. If the SRY gene is not present then ovaries will form instead. With estrogen present female ducts will form. At 14 weeks both the testes and the ovaries are deep inside the abdominal cavity, sperm and follicles are starting to form. The testes descend to the scrotal sac while the ovaries remain in the abdominal cavity.
17.4- Pregnancy and Birth
The energy of a pregnant woman may be lower at first but increase later in the pregnancy. There is a 40% rise in blood volume, with this cardiac output increases 20-30%. Blood flow to the kidneys, placenta, skin, and breasts rises significantly. The uterus pressing on the pelvic cavity can lead to incontinence. Also pregnancy can bring on varicose veins. Stretch marks and pregnancy induced diabetes are other side effects to pregnancy. Throughout pregnancy the uterus contracts lasting 20-30 seconds occurring every 15-20 minutes. Once they last about 40 seconds or longer and occur regularly every 15-20 minutes the woman is in labor. Contractions push the fetus down, stretching the cervix and this happens over and over until birth. In the 1st stage of birth The water breaks and the contractions make the cervical canal disappear as the uterus is pulled up towards the baby’s head. In stage 2 the contractions occur every 1-2 minutes lasting 1 minute each. With this comes the feeling to push as the baby’s head enters the vagina. Once the head and shoulders are out the rest is easy. After the baby is out and breathing ok the umbilical cord is cut and tied. During the 3rd stage the afterbirth is delivered.
17.5- Development After Birth
Infancy, childhood, adolescence and adulthood make up the stages of life. Menopause and andropause are a part of life for men and women. Diabetes type 2 is common in older adults. The immune system in older adults no longer performs as it use to. Some of the hypothesis of aging are that it may have a genetic basis, it may be due to changes that affect the whole body, and it may be due to diet and exercise. With age our skin becomes thinner and we lose some elasticity. Older people feel colder and their skin sags and wrinkles. The leading cause of death is due to cardiovascular disorders. Blood flow to the liver is reduced. The loss of teeth can happen in older adults but not because of aging more because of neglect. All the negativity of aging could be less dramatic if people take care of themselves with eating right and exercising regularly.
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