Humman gonad
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he gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes.
Regulation
The gonads are controlled hormonally by luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secreted by the anterior pituitary gland. This secretion in turn is controlled by the hypothalamus' gonadotropin-releasing hormone.
Development
Gonads start developing as a common anlage (an organ in the earliest stage of development), in the form of gonadal ridges, and only later are differentiated to male or female sex organs. The presence of the SRY gene, located on the Y chromosome and encoding the testis determining factor, determines male sexual differentiation. In the absence of the SRY gene from the Y chromosome, the female sex (ovaries instead of testis) will develop. The development of gonads is a part of the development of the urinary and reproductive organs
Human reproductive system
Human reproduction takes place as internal fertilization by sexual intercourse. During this process, the erect penis of the male is inserted into the female's vagina until the male ejaculates semen, which contains sperm, into the female's vagina. The sperm then travels through the vagina and cervix into the uterus or fallopian tubes for fertilization of the ovum. Upon successful fertilization and implantation, gestation of the foetus then occurs within the female's uterus for approximately nine months, this process is known as pregnancy in humans. Gestation ends with birth, the process of birth is known as labor. Labor consists of the muscles of the uterus contracting, the cervix dilating, and the baby passing out the vagina (the female genital organ). Human's babies and children are nearly helpless and require high levels of parental care for many years. One important type of parental care is the use of the mammary glands in the female breasts to nurse the baby.[8]
The female reproductive system has two functions: The first is to produce egg cells, and the second is to protect and nourish the offspring until birth. The male reproductive system has one function, and it is to produce and deposit sperm. Humans have a high level of sexual differentiation. In addition to differences in nearly every reproductive organ, numerous differences typically occur in secondary sexual characteristics.
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Female Reproductive System
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 system is designed to transport the ova to the site of fertilization. Conception, 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 implantation does not take place, the system is designed to menstruate (the monthly shedding of the uterine lining). In addition, the female reproductive system produces female sex hormones that maintain the reproductive cycle.
What Parts Make up the Female Anatomy?
The female reproductive anatomy includes parts inside and outside the body.
The function of the external female reproductive structures (the genitals) is twofold: To enable sperm to enter the body and to protect the internal genital organs from infectious organisms. The main external structures of the female reproductive system include:
· Labia majora: The labia majora enclose and protect the other external reproductive organs. Literally translated as "large lips," the labia majora are relatively large and fleshy, and are comparable to the scrotum in males. The labia majora contain sweat and oil-secreting glands. After puberty, the labia majora are covered with hair.
· Labia minora: Literally translated as "small lips," the labia minora can be very small or up to 2 inches wide. They lie just inside the labia majora, and surround the openings to the vagina (the canal that joins the lower part of the uterus to the outside of the body) and urethra (the tube that carries urine from the bladder to the outside of the body).
· Bartholin's glands: These glands are located beside the vaginal opening and produce a fluid (mucus) secretion.
· Clitoris: The two labia minora meet at the clitoris, a small, sensitive protrusion that is comparable to the penis in males. The clitoris is covered by a fold of skin, called the prepuce, which is similar to the foreskin at the end of the penis. Like the penis, the clitoris is very sensitive to stimulation and can become erect.
The internal reproductive organs in the female include:
· Vagina: The vagina is a canal that joins the cervix (the lower part of uterus) to the outside of the body. It also is known as the birth canal.
· Uterus (womb): The uterus is a hollow, pear-shaped organ that is the home to a developing fetus. The uterus is divided into two parts: the cervix, which is the lower part that opens into the vagina, and the main body of the uterus, called the corpus. The corpus can easily expand to hold a developing baby. A channel through the cervix allows sperm to enter and menstrual blood to exit.
· Ovaries: The ovaries are small, oval-shaped glands that are located on either side of the uterus. The ovaries produce eggs and hormones.
· Fallopian tubes: These are narrow tubes that are attached to the upper part of the uterus and serve as tunnels for the ova (egg cells) to travel from the ovaries to the uterus. Conception, the fertilization of an egg by a sperm, normally occurs in the fallopian tubes. The fertilized egg then moves to the uterus, where it implants into the lining of the uterine wall.
Male reporoducyive system
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The male reproductive system is illustrated to the right. Sperm are produced in the testes located in the scrotum. Normal body temperature is too hot thus is lethal to sperm so the testes are outside of the abdominal cavity where the temperature is about 2° C (3.6° F) lower. Note also that a woman’s body temperature is lowest around the time of ovulation to help insure sperm live longer to reach the egg. If a man takes too many long, very hot baths, this can reduce his sperm count. Undescended testes (testes are supposed to descend before birth) will cause sterility because their environment is too warm for sperm viability unless the problem can be surgically corrected.
From there, sperm are transferred to the epididymis, coiled tubules also found within the scrotum, that store sperm and are the site of their final maturation.
In ejaculation, sperm are forced up into the vas deferens (plural = vasa deferentia). From the epididymis, the vas deferens goes up, around the front of, over the top of, and behind the bladder. A vasectomy is a fairly simple, outpatient operation that involves making a small slit in each scrotum, cutting the vasa deferentia near where they begin, and tying off the cut ends to prevent sperm from leaving the scrotum. Because this is a relatively non-invasive procedure (as compared to doing the same to a woman’s oviducts), this is a popular method of permanent birth control once a couple has had all the children they desire. Couples should carefully weigh their options, because this (and the corresponding female procedure) is not designed to be a reversible operation.
The ends of the vasa deferentia, behind and slightly under the bladder, are called the ejaculatory ducts. The seminal vesicles are also located behind the bladder. Their secretions are about 60% of the total volume of the semen (= sperm and associated fluid) and contain mucus, amino acids, fructose as the main energy source for the sperm, and prostaglandins to stimulate female uterine contractions to move the semen up into the uterus. The seminal vesicles empty into the ejaculatory ducts. The ejaculatory ducts then empty into the urethra (which, in males, also empties the urinary bladder).
The initial segment of the urethra is surrounded by the prostate gland (note spelling!). The prostate is the largest of the accessory glands and puts its secretions directly into the urethra. These secretions are alkaline to buffer any residual urine, which tends to be acidic, and the acidity of the woman’s vagina. The prostate needs a lot of zinc to function properly, and insufficient dietary zinc (as well as other causes) can lead to enlargement which potentially can constrict the urethra to the point of interferring with urination. Mild cases of prostate hypertrophy can often be treated by adding supplemental zinc to the man’s diet, but severe cases require surgical removal of portions of the prostate. This surgery, if not done very carefully can lead to problems with urination or sexual performance.
The bulbourethral glands or Cowper’s glands are the third of the accessory structures. These are a small pair of glands along the urethra below the prostate. Their fluid is secreted just before emission of the semen, thus it is thought that this fluid may serve as a lubricant for inserting the penis into the vagina, but because the volume of these secretions is very small, people are not totally sure of this function.
The urethra goes through the penis. In humans, the penis contains three cylinders of spongy, erectile tissue. During arousal, these become filled with blood from the arteries that supply them and the pressure seals off the veins that drain these areas causing an erection, which is necessary for insertion of the penis into the woman’s vagina. In a number of other animals, the penis also has a bone, the baculum, which helps to stiffen it. The head of the penis, the glans penis, is very sensitive to stimulation. In humans, as in other mammals, the glans is covered by the foreskin or prepuce, which may have been removed by circumcision. Medically, circumcision is not a necessity, but rather a cultural “tradition”. Males who have not been circumcised need to keep the area between the glans and the prepuce clean so bacteria and/or yeasts don’t start to grow on accumulated secretions, etc. there. There is some evidence that uncircumcised males who do not keep the glans/prepuce area clean are slightly more prone to penile cancer.
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An Overview of the Testes
The Importance of Testosterone
Testes Essentials
· The testes secrete testosterone, which is necessary for proper physical development in boys.
· In adulthood, testosterone maintains libido, muscle strength, and bone density.
· Disorders of the testes are caused by too little testosterone production.
The testes (or testicles) are a pair of sperm-producing organs that maintain the health of the male reproductive system. The testes, like their female counterpart the ovaries, are known as gonads. This simply means they are the primary reproductive organs.
In addition to their role in the male reproductive system, the testes also have the distinction of being an endocrine gland because they secrete testosterone—a hormone that is vital to the normal development of male physical characteristics.
Anatomy of the Testes
The testes are twin oval-shaped organs about the size of a large grape. They are located within the scrotum, which is the loose pouch of skin that hangs outside the body behind the penis. While this location makes the testes vulnerable to injury (they have no muscles or bones to shield them), it provides a cooler temperature for the organs. A cooler environment is necessary for healthy sperm production.
Testosterone: The Hormone of the Testes
Testosterone is necessary for proper physical development in boys. It is the primary androgen, which is the term for any substance that stimulates and/or maintains masculine development. During puberty, testosterone is involved in many of the processes that transition a boy to manhood, including:
· Healthy development of male sex organs
· Growth of facial and body hair
· Lowering of the voice
· Increase in height
· Increase in muscle mass
· Growth of the Adam’s apple
The importance of testosterone is not limited to puberty. Throughout adulthood, the hormone is integral in a variety of functions, such as:
· Maintaining libido
· Sperm production
· Maintaining muscle strength and mass
· Promoting healthy bone density
Testosterone Production
The hypothalamus and pituitary gland control how much testosterone the testes produce and secrete.
The hypothalamus sends a signal to the pituitary gland to release gonadotrophic substances (follicle stimulating hormone and luteinizing hormone). Luteinizing hormone (LH) stimulates testosterone production. If too much testosterone is produced, the hypothalamus alerts the pituitary gland to make less LH, which tells the testes to decrease testosterone levels.
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An Overview of the Ovaries
Estrogen, Progesterone, and Reproduction
· The ovaries maintain the health of the female reproductive system.
· They secrete two main hormones—estrogen and progesterone.
· Diseases associated with the ovaries include ovarian cysts, ovarian cancer, menstrual cycle disorders, and polycystic ovarian syndrome.
The ovaries are a pair of ova-producing organs (that is, they produce egg cells) that maintain the health of the female reproductive system. The ovaries, like their male counterpart, the testes, are known as gonads. This simply means they are the primary reproductive organs.
In addition to their role in producing ova, the ovaries also have the distinction of being an endocrine gland because they secrete hormones—primarily estrogen and progesterone—that are vital to normal reproductive development and fertility.
Anatomy of the Ovaries
The ovaries are oval shaped and about the size of a large grape. They are located on opposite ends of the pelvic wall, on either side of the uterus. The ovaries are each attached to the fimbria (tissue that connects the ovaries to the fallopian tube).
Hormones of the Ovaries
Ovaries produce and release two groups of sex hormones—progesterone and estrogen. There are actually three major estrogens, known as estradiol, estrone, and estriol. These substances work together to promote the healthy development of female sex characteristics during puberty and to ensure fertility.
Estrogen (estradiol, specifically) is instrumental in breast development, fat distribution in the hips, legs, and breasts, and the development of reproductive organs.
To a lesser extent, the ovaries release the hormone relaxin prior to giving birth. Another minor hormone is inhibin, which is important for signaling to the pituitary to inhibit follicle-stimulating hormone secretion.
.Menstruation and the menstrual cycle fact sheet
Menstruation (men-STRAY-shuhn) is a woman's monthly bleeding. When you menstruate, your body sheds the lining of the uterus (womb). Menstrual blood flows from the uterus through the small opening in the cervix and passes out of the body through the vagina (see how the menstrual cycle works below). Most menstrual periods last from 3 to 5 days.
When periods (menstruations) come regularly, this is called the menstrual cycle. Having regular menstrual cycles is a sign that important parts of your body are working normally. The menstrual cycle provides important body chemicals, called hormones, to keep you healthy. It also prepares your body for pregnancy each month. A cycle is counted from the first day of 1 period to the first day of the next period. The average menstrual cycle is 28 days long. Cycles can range anywhere from 21 to 35 days in adults and from 21 to 45 days in young teens.
The rise and fall of levels of hormones during the month control the menstrual cycle.
In the first half of the cycle, levels of estrogen (the “female hormone”) start to rise. Estrogen plays an important role in keeping you healthy, especially by helping you to build strong bones and to help keep them strong as you get older. Estrogen also makes the lining of the uterus (womb) grow and thicken. This lining of the womb is a place that will nourish the embryo if a pregnancy occurs. At the same time the lining of the womb is growing, an egg, or ovum, in one of the ovaries starts to mature. At about day 14 of an average 28-day cycle, the egg leaves the ovary. This is called ovulation.
After the egg has left the ovary, it travels through the fallopian tube to the uterus. Hormone levels rise and help prepare the uterine lining for pregnancy. A woman is most likely to get pregnant during the 3 days before or on the day of ovulation. Keep in mind, women with cycles that are shorter or longer than average may ovulate before or after day 14.
A woman becomes pregnant if the egg is fertilized by a man’s sperm cell and attaches to the uterine wall. If the egg is not fertilized, it will break apart. Then, hormone levels drop, and the thickened lining of the uterus is shed during the menstrual period. During your period, you shed the thickened uterine lining and extra blood through the vagina. Your period may not be the same every month. It may also be different than other women's periods. Periods can be light, moderate, or heavy in terms of how much blood comes out of the vagina. This is called menstrual flow. The length of the period also varies. Most periods last from 3 to 5 days. But, anywhere from 2 to 7 days is normal. For the first few years after menstruation begins, longer cycles are common. A woman's cycle tends to shorten and become more regular with age. Most of the time, periods will be in the range of 21 to 35 days apart. Women can have a range of problems with their periods, including pain, heavy bleeding, and skipped periods.
· Amenorrhea (ay-men-uh-REE-uh) — the lack of a menstrual period. This term is used to describe the absence of a period in:
o Young women who haven't started menstruating by age 15
o Women and girls who haven't had a period for 90 days, even if they haven't been menstruating for long
Causes can include:
o Pregnancy
o Breastfeeding
o Extreme weight loss
o Eating disorders
o Excessive exercising
o Stress
o Serious medical conditions in need of treatment
As above, when your menstrual cycles come regularly, this means that important parts of your body are working normally. In some cases, not having menstrual periods can mean that your ovaries have stopped producing normal amounts of estrogen. Missing these hormones can have important effects on your overall health. Hormonal problems, such as those caused by polycystic ovary syndrome (PCOS) or serious problems with the reproductive organs, may be involved. It’s important to talk to a doctor if you have this problem.
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Dysmenorrhea (dis-men-uh-REE-uh)
— painful periods, including
severe cramps. Menstrual cramps in teens are caused by too much of a chemical
called prostaglandin (pros-tuh-GLAN-duhn). Most teens with dysmenorrhea do not
have a serious disease, even though the cramps can be severe. In older women,
the pain is sometimes caused by a disease or condition such as uterine
fibroids or endometriosis.
For some women, using a heating pad or taking a warm bath helps ease their
cramps. Some over-the-counter pain medicines can also help with these symptoms.
They include:
o Ibuprofen (eye-byu-PROH-fuhn) (for instance, Advil, Motrin, Midol Cramp)
o Ketoprofen (key-toh-PROH-fuhn) (for instance, Orudis KT)
o Naproxen (nuh-PROK-suhn) (for instance, Aleve)
If these medicines don’t relieve your pain or the pain interferes with work or school, you should see a doctor. Treatment depends on what’s causing the problem and how severe it is.
· Abnormal uterine bleeding — vaginal bleeding that’s different from normal menstrual periods. It includes:
o Bleeding between periods
o Bleeding after sex
o Spotting anytime in the menstrual cycle
o Bleeding heavier or for more days than normal
o Bleeding after menopause
Abnormal
bleeding can have many causes. Your doctor may start by checking for problems
that are most common in your age group. Some of them are not serious and are
easy to treat. Others can be more serious. Treatment for abnormal bleeding
depends on the cause.
In both teens and women nearing menopause, hormonal changes can cause long
periods along with irregular cycles. Even if the cause is hormonal changes, you
may be able to get treatment. You should keep in mind that these changes can
occur with other serious health problems, such as uterine fibroids, polyps, or
even cancer. See your doctor if you have any abnormal bleeding.
Hormones Control the Menstrual Cycle
Hormones are involved at every stage of the menstrual cycle.
· The pituitary gland produces FSH which starts the development of one egg in a follicle in one of the ovaries.
· The ovary produces oestrogen which causes the repair of the lining of the uterus after the last menstruation.
· The pituitary now produces LH which causes ovulation and stimulates the empty follicle to produce progesterone.
· Progesterone causes the lining of the uterus to get thicker ready for the fertilised egg.
· If the egg is not fertilised, production of oestrogen and progesterone stops, the lining of the uterus breaks down and menstruation occurs.
FSH Follicle-stimulating hormone (FSH) is a glycoprotein gonadotropin secreted by the anterior pituitary in response to gonadotropin-releasing hormone (GnRH), which is released by the hypothalamus. The same pituitary cell also secretes luteinizing hormone (LH), another gonadotropin. FSH and LH are composed of alpha and beta subunits. The specific beta subunit confers the unique biologic activity. FSH and LH bind to receptors in the testis and ovary and regulate gonadal function by promoting sex steroid production and gametogenesis.[1]
In men, LH stimulates testosterone production from the interstitial cells of the testes (Leydig cells). FSH stimulates testicular growth and enhances the production of an androgen-binding protein by the Sertoli cells, which are a component of the testicular tubule necessary for sustaining the maturing sperm cell. This androgen-binding protein causes high local concentrations of testosterone near the sperm, an essential factor in the development of normal spermatogenesis. Sertoli cells, under the influence of androgens, also secrete inhibin, a polypeptide, which may help to locally regulate spermatogenesis. Hence, maturation of spermatozoa requires FSH and LH.
In women, LH stimulates estrogen and progesterone production from the ovary. A surge of LH in the midmenstrual cycle is responsible for ovulation, and continued LH secretion subsequently stimulates the corpus luteum to produce progesterone. Development of the ovarian follicle is largely under FSH control, and the secretion of estrogen from this follicle is dependent on FSH and LH. The granulosa cells of the ovary secrete inhibin, which plays a role in cellular differentiation.
FSH and LH secretion are affected by a negative feedback from sex steroids. Inhibin also has a negative feedback on FSH selectively. High-dose testosterone or estrogen therapy suppresses FSH and LH. Primary gonadal failure in men and women leads to high levels of FSH and LH, except in selective destruction of testicular tubules with subsequent elevation of only FSH, as in Sertoli-cell-only syndrome. Similarly, any process leading to a low FSH level also simultaneously results in a low LH level, except in rare instances of isolated FSH deficiency or isolated LH deficiency in fertile eunuch syndrome
Follicle-stimulating hormone ( FSH) abnormalities are divided into 2 major groups (low and high), depending on FSH levels. Group Work No 1.
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The reproduction of mankind is a great marvel and mystery. Had God consulted me in the matter, I should have advised him to continue the generation of the species by fashioning them of clay. T.Ejigu
