43.3 Human Reproductive Anatomy and Gametogenesis

• The cells are released when the coelom is filled.
• Gonads that produce sperm and eggs are reproductive organs.
• The number of chromosomes in each reproductive cell was reduced by half and the number of cells increased through cell division.

• The reproductive systems of insects have separate sexes.
• The sperm are made in testes and travel through tubes to the epididymis.
• They travel to the uterus for fertilization after being released from the ovary.
• Fertilization can be done when the environment is optimal for offspring survival.

• There are a few differences between the structures of vertebrates.
• The cloaca openings are usually positioned opposite each other for transfer of sperm.
• There are openings for the female and uterus in mammals.
• Chimpanzees have a single uterus while species with two chambers produce large numbers of offspring at a time.

• The transfer of sperm from the male to the female can range from the release of the sperm into the watery environment for external fertilization to the development of a penis for direct delivery into the female's vagina in mammals.

• Specific organs and organ systems were developed as animals became more complex.

• The reproductive structures that evolved in land animals allow males and females to mate, fertilize internally, and support the growth and development of offspring.

• The reproductive tissues of male and female humans are the same until a low level of testosterone is released from male gonads.
• Testosterone creates male sexual organs.
• The female sexual tissues develop when testosterone is absent.
• Gonads become testes or ovaries.
• There are tissues that produce a penis in males and clitoris in females.
• The scrotum in a male is similar to the labia in a female.

• Seminiferous tubules are found in each wedge.

• The scrotum and penis are external to the body because they are immobile at body temperature.
• In mammals, the testes must be suspended outside the body at a lower temperature to produce sperm.
• Land mammals have testes that don't descend through the abdominals during fetal development.

• The human male's reproductive structures are shown.

• The sperm is carried from the testes to the penis.

• The walls of the seminiferous tubule are made up of sperm cells that are fully developed and less developed sperm at the center of the tubule.
• Sertoli cells protect the germ cells and promote their development when mixed with sperm cells.
• The Leydig cells are in the wall of the tubules.

• testosterone is produced by these cells when the male reaches adolescence.

• The site of sperm maturation is located along the top and bottom of the testes.
• The sperm leave the epididymis and enter the vas deferens, which carries the sperm behind the bladder and forms the ejaculatory duct.
• A section of the vas deferens is removed during a vasectomy in order to prevent fertilization.

• haploid cells are composed of a flagellum as a tail, a neck that contains the cell's energy- producing mitochondria, and a head that contains the genetic material.
• There is an acrosome at the top of the sperm's head.
• This structure contains lysosomal enzymes that can help sperm penetrate and fertilize the egg.
• The ejaculate will have between two and five liters of fluid and between 50 and 120 million sperm.

• Human sperm have a flagellum, neck, and head.

• The semen comes from the male reproductive system.
• The solution made by the glands is thick and alkaline.
• As sperm are only motile in an alkaline environment, a basic pH is important to reverse the acidity of the vaginal environment.
• The solution contains mucus, fructose, a coagulating enzyme, ascorbic acid, and local-acting hormones called prostaglandins.
• 60 percent of semen is accounted for by the seminal vesicle glands.

• There are three tubes of tissue in the penis.
• There are two tubes on the dorsal side and one tube on the ventral side.
• This tissue will become hard and engorged with blood in preparation for intercourse.
• The vagina has an ejaculation after the organ is inserted.
• The smooth muscle sphincters at the opening to the renal bladder prevent urine from entering the penis during intercourse.
• semen is expelled through the urethra during ejaculation and the orgasm is a two-stage process.
• The penis becomes flaccid after blood is drained from it.

• There are short ducts that connect to the urethra.
• Smooth muscle and glandular tissue make up the gland.
• The force needed for ejaculation is provided by the muscle.
• The glandular tissue makes a thin, milky fluid that contains citrate and PSA.
• The PSA helps to liquefy the ejaculate after it is released from the male.
• 30 percent of semen is made up of urine from the men's urethra.

• It protects the urethra from acid left over from urine.
• This usually accounts for a few drops of fluid in the ejaculate.
• The removal of the penis from the vagina may not work if sperm are present.
• The location and functions of the male reproductive organs are summarized.

• The female's body has a number of reproductive structures.
• Table 43.2 summarizes the location and functions of the female reproductive organs.
• The structures found in the inguinal area of women are associated with the vulva.
• The pubic symphysis overlies the mons pubis.
• The scrotum in a male is the same tissue that produces the labia majora.
• The vagina and urethra are protected by these labia.
• The labia minora is hairless and the mons pubis is covered with hair.
• At the sides of the vaginal opening, the greater vestibular glands are located.

• The human female's reproductive structures are shown.

• The breasts are made of fat.
• The size of the breast is determined by the amount of fat behind it.
• The nursing child gets milk from the ducts that are empty at the nipple, as well as the milk that is rich in vitamins and minerals.

• There is a system of ligaments that holds the ovaries in place.
• The cortex contains nerves and blood vessels that help it remove waste.
• The cortex contains the functional parts of the ovaries.
• The cortex is made up of cells that surround eggs.
• The eggs are prepared for release by a group of cells during the menstrual period.

• Oocytes are located in the ovary.
• The follicle matures at the beginning of the menstrual cycle.
• The egg is released at ovulation.
• The follicle becomes a luteum.
• There is an oocyte at the center of the light micrograph.
• The fimbrae help the nonmotile egg enter the uterus.
• The smooth muscle contracts in the same direction, moving the egg towards the uterus.
• The embryo is usually moved to the uterus for development after fertilization.
• It takes the embryo a week to travel through the oviduct.
• tubal ligation is similar to a vasectomy in that the oviducts are severed and sealed.

• The uterus is the size of a woman's fist.
• The endometrium is rich in blood vessels and mucus.
• The embryo and fetus are supported by the uterus.
• The wall of the uterus is made of smooth muscle.
• The smooth muscle in the uterus helps pass the baby through the vagina during labor.
• A portion of the lining of the uterus is torn off during each menstrual period, and then builds up again in preparation for an implant.
• The top of the vagina has a piece of the uterus in it.

• The menstrual flow can leave the body.
• It is the receptacle for the penis during intercourse and the vessel for the delivery of offspring.
• It is lined with cells to protect the underlying tissue.

• The sexual response in humans is both psychological and physical.
• There are four phases to the sexual response.
• During phase one of excitement, there is an increase in the amount of testosterone in both men and women.
• The nipples, clitoris, labia, and penis are enlarged with blood.
• Vaginal fluids are released to lubricate the vagina.
• During the second phase, stimulation continues, the outer third of the vaginal wall enlarges with blood, and breathing and heart rate increase.

• The muscles in both sexes contract during orgasm.
• In the male, semen is placed in the urethra and then the urethra expels it through the penis.
• The processes described in the first three phases return to their normal state during phase four.
• A man can't maintain an erection or ejaculate for a period of time ranging from minutes to hours.

• Sperm and eggs are produced through the process of meiosis.
• Two cell divisions separate the pairs of chromosomes in the nucleus and then separate the chromatids that were made during an earlier stage of the cell's life cycle.
• haploid cells have half of their chromosomes found in diploid cells.

• There are diploid, undifferentiated cells under the tubule.
• The stem cells, called spermatagonium, go through a process where one offspring goes on to differentiate into a sperm cell and the other into the next generation of sperm.

• A primary spermatocyte is what Meiosis starts with.
• A secondary spermatocyte is produced at the end of the first meiotic division.
• The cell is haploid and must go through another division.
• When the spermatid reaches the tubule and grows a flagellum, it is called a sperm cell.
• Four sperm result from each primary spermatocyte.

• Stem cells are present at birth but inactive through adolescence.

• This continues into old age.

• There is a link to learn about the process of spermatogenesis.

• Oogenesis begins with a germ cell, called an oogonium, which undergoes a process called mitosis to increase in number, eventually resulting in up to two million cells in the embryo.