Compendium Review: Reproductive System and Development and Aging

Reproductive System

Table of Contents

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


Human Life Cycle

The reproductive cycle in males and females differs greatly. Sexual maturity in females occurs between the ages of 11-13 and in males from 14-16. DNA is distributed among 46 chromosomes within the nucleus. Mitosis (duplication division) occurs in cells other than reproductive cells. The reproductive system uses mitosis (reduction division). Each reproductive cell contains 23 chromosomes rather than 46 in other cells.


http://courses.bio.psu.edu/fall2005/biol110/tutorials/tutorial2_files/fig_13_3.jpg


Male Reproductive System

The male reproductive system includes the following: testes, epididymides, vasa deferentia, seminal vesicles, prostate gland, urethra, bulbourethral, and the penis.


http://www.drstandley.com/images/male.gif




http://www.mhhe.com/socscience/sex/common/ibank/ibank/0053.jpg

The penis is the male organ of sexual intercourse. The penis has a long shaft and an enlarged tip called the glans penis, which at birth is covered by a layer of skin. Circumcision is the surgical removal of the penis foreskin.


http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/10223.jpg

Spongy, erectile tissue containing distensible blood spaces extends through the shaft of the penis. During arousal, autonomic nerves release nitric oxide (NO) This leads to the production of cGMP 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.


http://www.mhhe.com/socscience/sex/common/ibank/ibank/0045.jpg

The testes produce sperm and the male sex hormones. They lie outside the abdominal cavity within the scrotum. The seminiferous tubules are packed with cells undergoing spermatogenesis (production of sperm). Mature sperm has 3 distinct parts: a head, middle piece, and tail. Mitochondria in the middle piece provide energy for the tail movement.


http://www.ehponline.org/members/2006/114-11/sperm.jpg

Sex cells reproduce with meiosis as opposed to mitosis. Spermatogenesis occurs as follows:


http://umanitoba.ca/science/biological_sciences/lab14/images/Spermatogenesis.jpg

The hypothalamus has ultimate control of the testes' sexual function because it secretes a hormone called gonadotropin-releasing hormone (GnRH). There are 2 gonadotropic hormones: follicle-stimulating (FSH) and luteinizing hormone (LH), which are present in both males and females. In males, FSH promotes the production of sperm in the seminiferous tubules. LH controls the production of testosterone. Testosterone is the main sex hormone and essential for the normal development and functioning of the male organs.


http://www.dva.gov.au/health/menshealth/images/04_hormones.gif


Female Reproductive System

The female reproductive system includes the ovaries, oviducts, uterus, cervix, and vagina.


http://cache.eb.com/eb/image?id=55703&rendTypeId=4

The ovaries release one egg a month and fertilization occurs in the oviduct. Development occurs in the uterus. The vagina is the birth canal as well as the organ for sexual intercourse and outlet for menstrual flow. Development of the embryo and fetus takes place in the uterus.

The external organs of the female are known collectively as the vulva.


http://faculty.southwest.tn.edu/rburkett/repro_12.jpg

Upon sexual stimulation, the labia minora, the vaginal wall, and the clitoris become engorged with blood. The breasts also swell and the nipples become erect. The labia majora enlarge, redden, and spread away from the vaginal opening. Orgasm occurs the height of sexual response. Unlike males, females have no refractory period and can have multiple orgasms in a single sexual experience.


Female Hormone Levels

Female hormone levels cycle on a monthly basis and the ovarian cycle drives the uterine cycle. An ovary contains many follicles and each one contains an immature egg, called an oocyte. A female is born with as many as 2 million follicles, but is reduced to 300,000-400,000 by puberty. During oogenesis, a single follicle actually goes through all stages in one place within the ovary. As the follicle matures, layers of follicel cells surround a secondary oocyte. Eventually, the mature follicle ruptures, the secondary oocyte is released. The follicle then becomes the corpus luteum which eventually disintegrates.


http://www.tarleton.edu/~anatomy/oogenesis.jpg

The ovarian cycle:


http://scienceblogs.com/pharyngula/upload/2006/04/cycle_lg.jpg

Estrogen and progesterone affect not only the uterus, but other parts of the body as well. Estrogen is largely responsible for secondary sex characteristics in females. Menopause is a period in a woman's life where the ovarian cycle ceases. This occurs around 45-55 years of age.

Estrogen and progesterone have other functions, one affecting the endometrium causing the uterus to undergo a cyclical series of events known as the uterine cycle:


http://www.tarleton.edu/~anatomy/folliclecycle.jpg

Following unprotected sexual intercourse, many sperm will most likely make their way into the oviduct, where the egg is located following ovulation. Only one sperm fertilizes the egg and it becomes a zygote, which begins development as it travels down the oviduct to the uterus. The endometrium is now prepared to receive the developing embryo.


http://www.jillstanek.com/archives/fertilization.jpg


Control of Reproduction

Several methods are available to both dampen and enhance our reproductive potential. Birth control methods are used to regulate the number of children an individual or couple will have. Abstinence is the most reliable form of birth control and also prevents the transmission of STD's.
Other methods of birth control are as follows:


http://www.femcap.com/images/birth_control_methods.jpg


http://www.plannedparenthood.org/mar-monte/images/Mar%20Monte/bc_methods_english.gif

Sterilization is a surgical option that is relatively permanent as the success rate of fertility after reconnection is 50%.

Infertility is the failure of a couple to achieve pregnancy after one year of regular, unprotected intercourse. The most common cause of infertility in males is low sperm count and/or a large proportion of abnormal sperm. In women, body weight is the largest factor. The higher the weight, the less of a chance of conception.



Assisted reproductive technologies are available for infertile couples:

• Artificial Insemination by donor
  
• In Vitro Fertilization
• Gamete Intrafallopian Transfer
• Surrogate mothers
• Intracytoplasmic Sperm Injection

Sexually Transmitted Diseases

Sexually transmitted diseases are caused by viruses, bacteria, protists, fungi, and animals.

http://www.anselm.edu/homepage/jpitocch/genbio/stds.JPG

Genital human papillomavirus (HPV) is the most common sexually transmitted infection (STI). The virus infects the skin and mucous membranes. There are more than 40 HPV types that can infect the genital areas of men and women, including the skin of the penis, vulva (area outside the vagina), and anus, and the linings of the vagina, cervix, and rectum. You cannot see HPV. Most people who become infected with HPV do not even know they have it.


Development and Aging

Table of Contents

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


Fertilization

Fertilization is the union of a sperm and egg to a zygote. The acrosome of a sperm releases enzymes that digest a pathway for the sperm through the zona pellucida. The sperm nucleus enters the egg and fuses with the egg nucleus.


http://www.chariho.k12.ri.us/cms/library/images/reproduction/fertilization3.jpg

Pre-embryonic and Embryonic Development

Cleavage, growth, morphogenesis, and differentiation are the processes of development.


The extraembryonic membranes are not part of the embryo and fetus; instead they are outside the embryo. The extraembryonic membranes have the following functions:

• Chorion: develops into the fetal half of the placenta
• Allantois: accumulates the small amount of urine produced by fetal kidneys
• Yolk Sac: first embryonic membrane to appear which contains blood vessels
• Amnion: enlarges as the fetus enlarges and contains cushion to protect the embryo

http://img.tfd.com/dorland/thumbs/amnion.jpg

Development encompasses the events from fertilization to birth. Pre-embryonic development encompasses the events from the first week.


http://www.mhhe.com/biosci/esp/2002_general/Esp/folder_structure/re/m2/s2/assets/images/rem2s2_1.jpg

Embryonic development begins with the second week and lasts until the end of the second month. During implantation, the chorion secretes enzymes to digest away some of the tissue and blood vessels of the endometruim and uterus and begins to secrete human chorionic gonadotropin. The start of the major event called gastrulation turns the inner cell mass into the embryonic disk.

Fetal development begins in the third month and the uterus is the size of a grapefruit.


http://www.cerebralpalsychildren.com/CP1.jpg

	One Month Your baby is an embryo consisting of two layers of cells from which all her organs and body parts will develop. 4 weeks 5 weeks 6 weeks 7 weeks
	Two Months Your baby is now about the size of a kidney bean and is constantly moving. He has distinct, slightly webbed fingers. 8 weeks 9 weeks 10 weeks 11 weeks 12 weeks
	Three Months By now your baby is about 3 inches long and weighs nearly an ounce. Her tiny, unique fingerprints are now in place. 13 weeks 14 weeks 15 weeks 16 weeks
	Four Months Your baby is now about 5 inches long and weighs 5 ounces. His skeleton is starting to harden from rubbery cartilage to bone. 17 weeks 18 weeks 19 weeks 20 weeks
	Five Months Eyebrows and eyelids are now in place. Your baby would now be more than 10 inches long if you stretched out her legs. 21 weeks 22 weeks 23 weeks 24 weeks
	Six Months Your baby weighs about a pound and a half. His wrinkled skin is starting to smooth out as he puts on baby fat. 25 weeks 26 weeks 27 weeks 28 weeks 29 weeks
	Seven Months By now, your baby weighs about 3 pounds and is more than 15 inches long. She can open and close her eyes and follow a light. 30 weeks 31 weeks 32 weeks 33 weeks
	Eight Months Your baby now weighs about 4 3/4 pounds. His layers of fat are filling him out, making him rounder, and his lungs are well developed. 34 weeks 35 weeks 36 weeks 37 weeks
	Nine Months The average baby is more than 19 inches long and weighs nearly 7 pounds now, but babies vary widely in size at this stage 38 weeks 39 weeks 40 weeks 41 weeks

Development of Male and Female Genitals

The sex of an individual is determined at the moment of fertilization. Males have a pair of chromosomes designated XY and females have XX. During the first several weeks of development, it is impossible to tell the gender of an unborn child by external inspection.


http://www.mfi.ku.dk/PPaulev/chapter29/images/29-1.jpg


http://www.mhhe.com/socscience/sex/common/ibank/ibank/0058b.jpg

Sometimes, abnormalities in genital development occur. Some XY indivisuals develop into females and some XX individuals develop into males. In androgen insensitivity syndrome, the 3 types of hormones are produced by testes, but the individual develops as a female because the plasma membrane receptors for testosterone are ineffective. True gonadal hermaphroditism in which a person has both ovarian and testicular tissue is rare. However, about 1% of the population has psuedohermaproditism. The individual has testes, but appears to be a normal female until puberty.

Pregnancy and Birth

Major changes take place in the mother's body during pregnancy: energy levels fluctuate, the uterus relaxes, the pulmonary values increase, possible stress incontinence, edema, varicose veins, and of course, stretch marks. The uterus has contractions throughout the pregnancy. False labor contractions are called Braxton-Hicks contractions. Labor has 3 stages.


http://www.stewwebb.com/Amanda%20Birth.jpg

Development After Birth

Development does not cease once birth has occurred. Aging encompasses the progressive changes that contribute to an increased risk of infirmity, disease, and death. There are many hypotheses regarding aging: genetic, a whole body process, and/or other extrinsic factors. Aging affects our body systems in different ways: less elasticity in the skin, collagen fibers decrease, fewer sweat glands, fewer hair follicles, cardiovascular disorders, respiratory disorders, lower blood supply to various organs, constipation, heart burn, gastritis, cancer, neuron death due to a lack of O2 from reduced blood flow, loss of skeletal muscle mass, decline in bone density, arthritis, and hormone level decrease.


http://www.forpeaceofmind.com.au/Vol7/media/images/special_features-medicine_mismanagement-2.jpg

References:

Human Reproduction. (2008). www.biology.iupui.edu/biocourses/n100/2k4ch39repronotes.html

Mader, S. (2008). Reproductive System and Development and Aging. Human Biology 10th Ed. (p 319-352)

Sexual Development. (2008). www.themediaproject.com/facts/development/lifecycle.htm