Reproductive system
From CreationWiki, the encyclopedia of creation science
The reproductive organs comprise the reproductive system. In the female, the organs include the uterus, uterine tubes, ovaries, vagina, and vulva. In the male, the organs include the testes, accessory ducts, accessory glands, and penis. The events leading to fertilization are contributed by the male and female reproductive systems. The female organs take responsibility for the developing human, birth, and nursing. The male and female gonads (testes and ovaries) produce sex cells (ova and sperm) and the hormones necessary for the proper development, maintenance, and functioning of the organs of reproduction and other organs and tissues.
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Male Reproductive Organs
Testes are suspended outside the abdominal cavity by the scrotum, a pouch of skin that keeps the testes close or far from the body at an optimal temperature for sperm development. About 250 meters of tubules are packed into each testis. Spermatocytes inside the tubules divide by meiosis to produce spermatids that in turn develop into mature sperm. Sperm production begins at puberty and continues throughout life. Several hundred million sperm produced each day. Once the sperm form, they are moved into the epididymis, where they mature and are stored. [1]
The anterior pituitary produces follicle-stimulating hones (FSH) and luteinizing hormones (LH). The action of LH is controlled by the gonadotropin-releasing hormone (GnRH). LH stimulates the cells in the seminiferous tubules to secrete testosterone. That has a role in sperm production and developing male secondary sex characteristics. FSH acts on cells to help in sperm maturation. Negative feedback by testosterone controls the actions of GnRH. Sperm passes through the vas deferens and connects to a short ejaculatory duct that connects to the urethra. The urethra passes through the penis and opens to the outside. Secretions from the seminal vesicles add fructose and prostaglandins to sperm as they pass. The prostate gland secretes a milky alkaline fluid. The bublourethral gland secretes a mucus-like fluid that provides lubrication for intercourse. Sperm and secretions make up semen. [2]
Female Reproductive Organs
The female reproductive system is designed to carry out several functions. It produces the female egg cells necessary for reproduction, called the ova or oocytes. The systed is designed to transport the ova to the site of fertilization. Concetion, the fertilization of an egg by a sperm, normally occurs in the fallopian tubes. The next step for the fertilized egg is to implant into the walls of the uterus, beginning the initial stages of pregnancy. If fertilization and/or implanation does not take place, the system is designed to mestruate (the monthly shedding of the uterine lining). In addition, the female reproductive system produces female sex hormones that maintain the reproductive cycle. During menopause the female reproductive system gradually stops making the female hormones necessary for the reproductive cycle to work. When the body no longer produces these hormones, a woman is considered to be menopausal.[3]
The follicular phase of the menstrual cycle starts on the first day of your period. During the phase, the following events occur:
- Two hormones, follicle stimulating hormone (FSH) and luteinizing hormone (LH) are released from the brain and travel in the blood to the ovaries.
- The hormones stimulate the growth of about 15-20 eggs in the ovaries, each in its own "shell," called a follicle.
- These hormones (FSH and LH) also trigger an increase in the production of the female hormone estrogen.
- As estrogen levels rise, like a switch, it turns off the production of follicle-stimulating hormone. This careful balance of hormones allows the body to limit the number of follicles that mature.
- As the follicular phase progresses, one follicle in one ovary becomes dominant and continues to mature. This dominant follicle suppresses all of the other follicles in the group. As a result, they stop growing and die. The dominant follicle continues to produce estrogen.
The ovulatory phase, or ovulation, starts about 14 days after the follicular phase started. The ovulatory phase is the midpoint of the menstrual cycle, with the next menstrual period starting about two weeks later. During the phase, the following events occur:
- The rise in estrogen from the dominant follicle triggers a surge in the amount of luteinizing hormone that is produced by the brain.
- This causes the dominant follicle to release its egg from the ovary.
- As the egg is released (a process called ovulation) it is captured by finger-like projections on the end of the fallopian tubes (fimbriae). The fimbriae sweep the egg into the tube.
- Also during this phase, there is an increase in the amount and thickness of mucous produced by the cervix (lower part of the uterus). If a woman were to have intercourse during this time, the thick mucus captures the man's sperm, nourishes it, and helps it to move towards the egg for fertilization.
The luteal phase of the menstrual cycle begins right after ovulation and involves the following processes:
- Once it releases its egg, the empty follicle develops into a new structure called the corpus luteum.
- The corpus luteum secretes the hormone progesterone. Progesterone prepares the uterus for a fertilized egg to implant.
- If intercourse has taken place and a man's sperm has fertilized the egg (a process called conception), the fertilized egg (embryo) will travel through the fallopian tube to implant in the uterus. The woman is now considered pregnant.
- If the egg is not fertilized, it passes through the uterus. Not needed to support a pregnancy, the lining of the uterus breaks down and sheds, and the next menstrual period begins.
Growth
Growth hormone is a protein hormone of about 190 amino acids that is synthesized and secreted by cells called somatotrophs in the anterior pituitary. It is a major participant in control of several complex physiologic processes, including growth and metabolism. Growth hormone is also of considerable interest as a drug used in both humans and animals. Direct effects are the result of growth hormone binding its receptor on target cells. Fat cells (adipocytes), for example, have growth hormone receptors, and growth hormone stimulates them to break down triglyceride and supresses their ability to take up and accumulate circulating lipids. Indirect effects are mediated primarily by a insulin-like growth factor-I (IGF-I), a hormone that is secreted from the liver and other tissues in response to growth hormone. A majority of the growth promoting effects of growth hormone is actually due to IGF-I acting on its target cells.
Growth is a very complex process, and requires the coordinated action of several hormones. The major role of growth hormone in stimulating body growth is to stimulate the liver and other tissues to secrete IGF-I. IGF-I stimulates proliferation of chondrocytes (cartilage cells), resulting in bone growth. Growth hormone does seem to have a direct effect on bone growth in stimulating differentiation of chondrocytes. IGF-I also appears to be the key player in muscle growth. It stimulates both the differentiation and proliferation of myoblasts. It also stimulates amino acid uptake and protein synthesis in muscle and other tissues.
Production of growth hormone is modulated by many factors, including stress, exercise, nutrition, sleep and growth hormone itself. However, its primary controllers are two hypothalamic hormones and one hormone from the stomach:
- Growth hormone-releasing hormone (GHRH) is a hypothalamic peptide that stimulates both the synthesis and secretion of growth hormone.
- Somatostatin (SS) is a peptide produced by several tissues in the body, including the hypothalamus. Somatostatin inhibits growth hormone release in response to GHRH and to otherstimulatory factors such as low blood glucose concentration.
- Ghrelin is a peptide hormone secreted from the stomach. Ghrelin binds to receptors on somatotrophs and potently stimulates secretion of growth hormone.
Growth hormone secretion is also part of a negative feedback loop involving IGF-I. High blood levels of IGF-I lead to decreased secretion of growth hormone not only by directly suppressing the somatotroph, but by stimulating release of somatostatin from the hypothalamus. Growth hormone also feeds back to inhibit GHRH secretion and probably has a direct (autocrine) inhibitory effect on secretion from the somatotroph. Integration of all the factors that affect growth hormone synthesis and secretion lead to a pulsatile pattern of release. Basal concentrations of growth hormone in blood are very low. In children and young adults, the most intense period of growth hormone release is shortly after the onset of deep sleep.
Development
The position and diameter of ovarian follicles 4 mm in diameter were recorded, the number of ovarian follicles 2 mm in diameter counted, and blood samples collected daily for periods of 18 days, starting at 2, 8, 14, 24 and 34 weeks of age in ten heifers. The mean age at first ovulation was 52.8 ± 1.6 weeks. At all ages ovarian follicular development occurred in a wave-like manner, as in mature cattle. The maximum diameter of the dominant and the largest subordinate follicles increased between 2 and 34 weeks of age; however, the greatest increase occurred between 2 and 8 weeks of age. There was a similar increase in the numbers of small and large ovarian follicles. The duration of detection of dominant follicles (number of days visible at a diameter of 4 mm) also increased between 2 and 34 weeks of age. The emergence of waves of follicular development was preceded by peaks in plasma FSH concentrations at 2 weeks of age but this was less clear at other ages. There was a rise in circulating concentrations of gonadotrophins between 4 and 14 weeks of age. We concluded that in heifer calves as young as 2 weeks of age ovarian follicles grew in a wave-like fashion, similar to those of adult cattle. We speculate that the early rise in gonadotrophin secretion stimulated the increase in numbers of follicles and follicle diameters observed, indicating an early critical step in reproductive development. [4]
Diseases
Like all complex organ systems the human reproductive system is affected by many diseases. There are four main categories of reproductive diseases in humans. They are: 1) genetic or congenital abnormalities, 2) cancers, 3) infections which are often sexually transmitted diseases, and 4) functional problems cause by environmental factors, physical damage, psychological issues, autoimmune disorders, or other causes. The best known type of functional problems include sexual dysfunction and infertility which are both broad terms relating to many disorders with many causes.
Specific reproductive diseases are often symptoms of other diseases and disorders, or have multiple, or unknown causes making them difficult to classify. Examples of unclassifiable disorders include Peyronie's disease in males and endometriosis in females. Many congenial conditions cause reproductive abnormalities but are better known for their other symptoms, these include: Turner syndrome, Klinefelter syndrome, Cystic fibrosis, and Bloom syndrome.
It is also known that disruption of the endocrine system by certain chemical adversely affects the development of the reproductive system and can cause vaginal cancer. Many other reproductive diseases have also been link to exposure to synthetic and environmental chemicals. Common chemicals with known links to reproductive disorders include: lead, dioxin, styrene, toluene, and pesticides.
Examples of congenital abnormalities
- Kallmann syndrome - Genetic disorder causing decreased functioning of the sex hormone-producing glands caused by a deficiency of a hormone.
- Cryptorchidism - Absence of one or both testes from the scrotum.
- Androgen insensitivity syndrome - A genetic disorder causing people who are genetically male (i.e. XY chromosome pair) to develop sexually as a female due to an inability to utilize androgen.
- Intersexuality - A person who has genitalia and/or other sexual traits which are not clearly male or female.
Examples of cancers
- Prostate cancer - Cancer of the prostate gland.
- Breast cancer - Cancer of the mammary gland.
- Ovarian cancer - Cancer of the ovary.
- Penile cancer - Cancer of penis.
- Uterine cancer - Cancer of the uterus.
- Testicular cancer - Cancer of the testicles.
- Cervical Cancer - Cancer of the cervix.
Examples of infections
- HIV - Infection by the retrovirus known as human immunodeficiency virus.
- Genital warts - Sexually transmitted infection caused by some sub-types of human papillomavirus (HPV).
- Herpes simplex - Sexually transmitted infection caused by a virus called herpes simplex virus (HSV) type 2.
- Gonorrhea - Common sexually transmitted disease caused by the Gram-negative bacterium Neisseria gonorrheae.
- Yeast infection - Infection of the vagina by any species of the fungus genus Candida.
- Pelvic inflammatory disease - Painful infection of the female uterus, fallopian tubes, and/or ovaries with associated scar formation and adhesions to nearby tissues and organs.
- Syphilis - Sexually transmitted infection caused by the bacterium Treponema pallidum.
- Pubic lice - Infection of the pubic hair by crab lice, Phthirius pubis.
- Trichomoniasis - Sexually transmitted infection by the single-celled protozoan parasite Trichomonas vaginalis.
Examples of functional problems
- Impotence - The inability of a male to produce or maintain an erection.
- Hypogonadism - A lack of function of the gonads, in regards to either hormones or gamete production.
- Ectopic pregnancy - When a fertilized ovum is implanted in any tissue other than the uterine wall.
- Hypoactive sexual desire disorder - A low level of sexual desire and interest.
- Female sexual arousal disorder - A condition of decreased, insufficient, or absent lubrication in females during sexual activity.
- Premature ejaculation - A lack of voluntary control over ejaculation.
References
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