Biology 156: Compendium Review Unit 4 Topic One

Table of Contents

Reproductive System

Human Life Cycle
Male Reproductive System
Female Reproductive System
Female Hormone Levels
Control of Reproduction
Sexually Transmitted Diseases

Development and Aging

Fertilization
Pre-Embryonic and Embryonic Development
Fetal Development
Pregnancy and Birth
Development After Birth

Reproductive System

Human Life Cycle

The reproductive system is different between males and females. Puberty is when both males and females go from a child to a sexually competent young adult. The reproductive organs function to :

Produce sperm in the testes (male) and eggs in the ovaries (female)
Nurture and transport the sperm in ducts (male), transport eggs in uterine tubes to uterus (female)
Penis delivers sperm and vagina receives sperm and also transports menstrual fluid, and is the birth canal
The uterus is where a fertilized egg develops and the breast provide nourishment (milk) after birht
Testes and ovaries produce sex hormones that bring about masculinization and feminization and allow a pregnancy to continue

Mitosis is a duplication division while Meiosis is a reduction division. Meiosis takes place only in the testes in production of sperm and ovaries in the production of eggs. The chromosome number is reduced from 46 to 23 (haploid). Sperm carry only chromosomes while the egg provides the other half of chromosomes and cytoplasm for the new individual. The first cell of a new person is a zygote which has the total 46 chromosomes

Male Reproductive System

The primary sex organs of the male are paired testes suspended in the scrotum sacs. Sperm are produced in the testes and mature in the epididymis (tightly coiled duct outside of the testis). When the sperm leave the epididymis they enter the vas deferens. The vas deferens pass into the abdominal cavity, curving around the bladder and emptying into an ejaculatory duct which enters the utethra. When ejaculation occurs the sperm exit the penis in semen (made from secretions of the seminal vesicles, prostate gland, bulbourethral glands)

The male organ for sexual intercourse is the penis which is made of a long shaft and enlarged tip (glans penis). Circumcision is the surgical removal of the foreskin covering the glans penis. Spongy tissue that contains distensible blood spaces fills the shaft. In sexual arrousal, autonomic nerves release nitric oxide which leads to the production of cyclic guanosine monophosphate which causes the smooth muscle of incoming arterial walls to relax and allows the tissue to fill with blood. The veins taking blood away are compressed resulting in erection. Sperm enter the urethra and rythmic muscle contractions cause it to be expelled from the penis. There can be as many as 400 million sperm in 3.5 ml of semen expelled.

The testes start development in the abdominal cavity but descend into the scrotal sacs in the last two months of fetal development. The scrotum regulates the temperature of the testes by moving them closer or further away from the body. The testis is made up of compartments called lobules and each of these contain up to three coiled seminiferous tubules. These tubules are filled with cells undergoing spermatogenesis.

Spermatogonia divide into speratocytes that move away from the wall grow, and undergo meiosis 1 which results in spermatocytes with 23 chromosomes. These undergo meiosis 2 resulting in four spermatids which differentiate into sperm. Sertoli cells provide nourishment and support to this process which takes approximately 74 days. Mature sperm have a head, middle piece, and tail. The middle piece has mitochondria for energy to move the tail (flagellum). The head has the nucleus covered by an acrosome cap which has the enzymes needed to penetrate the egg. Sperm usually live no longer than 48 hours in the female genital tract.

Male sex hormones are androgens and are secreted by interstitial cells. The hypothalamus has ultimate control of the testes sexual function by secreting GnRH which stimulates the anterior pituitary to secrete the gonadotropic hormones (FSH and LH) Testosterone is essential for the normal developement and functioning in male sex organs. It brings about and maintains secondary sex characteristics.

Female Reproductive System

The female gonads are the ovaries, one on each side of the upper pelvic cavity. They produce eggs and estrogen and progesterone. Oviducts run from the uterus to the ovaries, but are not attatched to the ovaries. Fimbriae are projections that sweep over the ovaries. During ovulation, when an egg bursts from the ovary it is swept into the oviduct by the fimbriae and the cilia that line the oviducts. The egg then slowly moves towards the uterus where it can live for 6-24 hours without fertilization. Fertilization and the formation of a zygote usually happens in the oviducts and the embryo will arrive at the uterus several days later. Once in the uterus the embryo embeds into the uterine lining.

The uterus is a muscular organ that roughly resembles the size and shape of an inverted pear. The oviducts join the upper end , and at the lower end the cervix enters the vagina almost at a right angle. The uterus can stretch from 5cm wide to 30cm to accomadate a baby. Endometrium is the lining and helps in the formation of the placenta to supply nutrients for the embryonic and fetal development. There are two endometrial layers. The basal and inner functional layer. An opening in the cervix leads to the vaginal canal. The lining lies in folds and can extend which is important when it serves as the birth canal.

All of the external genital organs are known as the vulva (labia majora, labia minora, glans clitoris, urethra, vagina) The labia minora, vaginal wall, and clitoris become engorged with blood upon sexual stimulation. The labia majora enlarge and move away from the vaginal opening. Blood vessels in the vaginal wall release droplets of fluid that lubricate.

Female Hormone Levels

Hormone levels cycle on a monthly basis with the ovarian cycle driving the uterine cycle. An ovary has multiple follicles containing oocytes (immature eggs). As the follicle matures in the ovarian cycle it changes from a primary to a secondary to a vesicular follicle. A primary oocyte undergoes meiosis 1 resulting in haploid cells. One cell is a polar body that holds discarded chromosomes. The secondary oocyte undergoes meiosis 2 only if the egg gets fertilized. When its time the vesicular follicle bursts releasing the oocyte surrounded by a clear membrane (this is ovulation). The follicle then turns into a corpus luteum that disinigrates if fertilization does not occur. The corpus luteum is also responsible for producing progesterone.

The hypothalamus has ultimate control of the ovaries sexual function by secreting GnRH (stimulates production of FSH and LH). During the follicular phase, FSH promotes the development of follicles that secrete estrogen. Positive feedback leads to GnRH secretion, and ovulation around the 14th day of cycle. Next the luteal phase begins LH promotes corpus luteum development to secrete progesterone. If pregnancy doesn't happen, then menstration begins.

Estrogen promotes secondary sex characteristics, such as body hair, fat distribution, breast development. Menopause is when the ovarian cycle ceases. Estrogen and progesterone have many functions affecting the endometrium in the uterine cycle.

If the egg is fertilized, it becomes a zygote and develops as it travels down to the uterus. The placenta is made from maternal and fetal tissue and is where molecules exchange from maternal and fetal blood. Rising amounts of HCG maintain corpus luteum to produce progesterone and no new follicles begin in the ovary. At some point the placent begins to produce progesterone and some estrogen on its own.

Control of Reproduction

Birth control methods are used to regulate the number of children couples or an individual will have. Methods include:

Abstinence- not engaging in any sexual intercourse
Contraceptives
Intrauterine Device- inserted into the uterus preventing fertilization and implantation
Diaphragm-fits over the cervix
Condoms- cover the penis or female condoms fit on the cervix and cover external genitals
Contraceptive Implants- disrupt the ovarian cycle by releasing progesterone
Contraceptive Injections-progesterone only
Contraceptive Vaccines
Vasectomy- vas deferens are cut and tied off
Tubal ligation-cutting and sealing the oviducts

Infertilty is failure to achieve pregnancy after one year of regular, unprotected intercourse. Most causes are from low sperm count, or large amounts of abnormal sperm (from smoking, alcohol combined with a sedentary lifestyle). In females, body weight is the most significant factor. Assisted reproductive technologies include

Artificial insemination by a donor-
In Vitro Fertilization-
Gamete Intrafallopian Transfer
Surrogate Mothers
Intracytoplasmic Sperm Injection

Sexually Transmitted Diseases

These diseases are caused by viruses, bacteria, protists, fungi and animals

Virus caused STDs

HIV
AIDS
Genital Warts-caused by HPV. These lesions can be removed by surgery, freezing, burning, lasers, or acids
Genital Herpes- caused by herpes simplex virus. Causes cold sores and fever blisters
Hepatitis- Infects the liver, and can cause cancer that leads to death. Six viruses (A-G) cause hepatitis

Bacteria caused STDs-can be cured with antibiotics, although many strains are becoming resistant

Chlamydia- can result in PID in women if untreated
Conorrhea-thick green, yellow urethral discharge in males. Can also spread to internal body parts
Syphilis-can be treated by penicillin. Has three stages

Development and Aging

Fertilization

This is the union of a sperm and egg that forms a zygote. The flagellum of the sperm enables it to swim towards the egg. The mitochondria in the middle give it energy and the head which contains the nucleus enables to fuse with the egg. The plasma membrane of the egg is surrounded by zona pellucida which is surrounded by follicular cells(corona radiata). The acrosome allows the sperm to penetrate the zona pellucida

Pre-Embryonic and Embryonic Development

The processes of development are as follows

Cleavage-first after fertilization, zygote divides exponentially. This is mitotic division
Growth- daughter cells also increase size
Morphogenesis- embryo begins to assume various shapes
Differentiation- Cells take on specific structure and function (nervous system is first)

Extraembryonic membranes are outside the membrane

Chorion- develops into the fetal half of the placenta. Provides nourishment and oxygen and takes away waste
Allantois- extends away from the embryo. Later turns into urinary bladder. Takes blood to and from fetus
Yolk sac-First embryonic membrane that appears. First site for blood cell formation
Amnion-contains fluid that protects and cushions the embryo

Development is all the events from fertilization to birth. Due date is usually calculated by adding 280 days to the date of the last know menstration. Pre-embryonic development occurs in the first week. The zygote divides and becomes a morula and then a blastocyst. The cells of a blastocyst arrange to form and inner cell mass surrounded by an outer layer. Inner becomes the embryo and outer the chorion. Each cell in inner layer can become any type of tissue

Embryonic development starts with the second week all the way to the end of the second month. Implantation occurs and HCG is secreted by the chorion. Inner cell mass turns into the embryonic disk. Amniotic cavity surrounds the embryo. The nervous system and heart begin to appear during the third week. In the fourth and fifth week the umbilical cord is formed along with a head tail and limb buds. Sense organs become more prominant. In the sixth through eighth weeks the embryo is easily seen, and the nervous system can enables reflex reactions.

Fetal Development

The placenta produces progesterone and estrogen which function to prevent any new follicles from maturing and also to maintain the endometrium. The placenta has a fetal side contributed by the chorion and a maternal side of uterine tissues. Carbon dioxide and wastes move from the fetal side to maternal side and nutrients and oxygen move from the maternal side to fetal side.

The umbilical cord is the lifeline for the fetus. Umbilical arteries carry oxygen poor blood to the placenta and umbilical veins carry nutrients and oxygen from the placenta to the fetus. The circulatory changes that happen at birth are: the blood returns to the left side of the heart and a flap covers the oval opening, the arterial duct closes and the remains of this duct turn into conective tissue

Fetal development is from the third month to the ninth. The fetus is easily seen as human. In the third and fourth months fingernails, nipples, eyelashes, eyebrows and hair appear. Cartilage is turning to bone and the skull is formed of 6 fontanels. Around the third month sex can be distinguished, and in the fourth month the fetal heartbeat can be heard. In the fifth through seven months movement can be felt. Vernix caseosa coats the fetus and protects the skin from amniotic fluid. At the end of 9 months, the fetus rotates to point its head down toward the cervix and is ready to be born.

Sex is determined at the moment of fertilization, but the gonads do not develop until the seventh week. This is when the indifferent tissue becomes testes or ovaries depending on hormones. If the SRY gene is present testes will develop.

Pregnancy and Birth

Changes in the mother's body during pregnancy are due to placental hormones. At first the woman may feel nausea and fatigued, however these go away and many women have increased levels of energy and general sense of well being. Weight gain is due to breast and uterine enlargement, fetus weight, amniotic fluid, and the mother's own increase in body fluid. Progesterone relaxes smooth muscle including artery walls leading to lower blood pressure, and an increase in blood volume which also increases red blood cells. When the size of the uterus increases it pushes the intestines, liver, stomach and diaphragm down and widens the thoracic cavity. Blood carbon dioxide levels fall and this favors the flow from fetal blood to maternal blood. These effects are good, however the enlarged uterus can lead to stress incontinence, edema and varicose veins. The placenta also produces peptide hormones resulting in pregnancy induced diabetes.

The uterus has contractions throughout the pregnancy but as birth nears they become more noticible and closer together. Uterine contractions push the fetus down, stretching the cervix. The cervical canal disappears as the lower uterus is pulled towards the baby's head. The amniotic membrane ruptures. When the cervix is completely dialated, this is the end of stage one. In stage two the contractions are every 1-2 minutes and last for one minute, the baby's head comes down into the vagina and then the rest of the baby is delivered. When the umbilical cord is clamped and cut this ends stage two. Stage three is 15 minutes later with the delivery of the placenta.

Development After Birth

Development continues all through life. Gerontology is the study of aging and the goal is not to increase life span, but to increase the quality of this life span. Hypothesis about the cause of aging include:

Genetic in Origin
Whole-Body Process
Extrinsic Factors

As we age skin becomes thinner, less elastic and looses adipose. Cardiovascular disorders increase along with respiratory disorders. Blood flow to the liver decreases along with the kidneys. Response time can be slower and skelatal muscle mass can decrease. Along with the effects listed there are many other adverse effects to aging, but these are all not inevitable. Successful old age begins with good healthy habits that should be developed when we are younger.

Works Cited

Mader, Sylvia. Human Biology 10th ed

Frolich Power Point

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