Human Sexual Reproduction PDF

Chromosomes -contain genetic information which carries unique inherited traits such as skin color or hair color. Each sex cell, which has 23 chromosomes, is a haploid, while the regular cell, which has 46 chromosomes, is a diploid.  After the fusion of the egg and the sperm, th...

Chromosomes -contain genetic information which carries unique inherited traits such as skin color or hair color. Each sex cell, which has 23 chromosomes, is a haploid, while the regular cell, which has 46 chromosomes, is a diploid.  After the fusion of the egg and the sperm, the resulting fertilized egg, known as the zygote, contains 46 chromosomes ❑In sexual reproduction, the diploid zygote is formed through fertilization from the fusion of the male (sperm cell) and female (egg cell) sex cells, which are both haploid. ❑This organ system produces sperm cells (male gametes) and delivers them inside the female reproductive system. In males, the primary reproductive organs are the testes.  Penis: the penis is the male organ for sexual intercourse. It has three parts: The root: This is the part of the penis that attaches to the wall of your abdomen. The body or shaft: Shaped like a tube or cylinder, the body of the penis is made up of three internal chambers. The glans: This is the cone-shaped end of the penis. The glans, which is also called the head of the penis, is covered with a loose layer of skin called foreskin. Scrotum The scrotum is the loose pouch-like sac of skin that hangs behind the penis. It holds the testicles (also called testes), as well as many nerves and blood vessels. Testicles (testes) The testes are oval organs about the size of very large olives that lie in the scrotum, secured at either end by a structure called the spermatic cord. Epididymis The epididymis is a long, coiled tube that rests on the backside of each testicle. It carries and stores sperm cells that are created in the testes.  You have several internal organs — also called accessory organs — that play a big part in the male reproductive system. These organs include:  Vas deferens: The vas deferens is a long, muscular tube that travels from the epididymis into the pelvic cavity, to just behind the bladder. The vas deferens transports mature sperm to the urethra in preparation for ejaculation.  Ejaculatory ducts: These ducts are formed by the fusion of the vas deferens and the seminal vesicles. The ejaculatory ducts empty into the urethra.  Urethra: The urethra is the tube that carries urine from the bladder to outside of your body. In males, it has the additional function of expelling (ejaculating) semen when you reach orgasm.  Seminal vesicles: The seminal vesicles are sac-like pouches that attach to the vas deferens near the base of the bladder. The seminal vesicles make a sugar-rich fluid (fructose) that provides sperm with a source of energy and helps with the sperms’ ability to move (motility).  Prostate gland: The prostate gland is a walnut-sized structure that’s located below the urinary bladder in front of the rectum. The prostate gland contributes additional fluid to the ejaculate.  Bulbourethral glands: The bulbourethral glands, or Cowper’s glands, are pea-sized structures located on the sides of the urethra, just below the prostate gland. These glands produce a clear, slippery fluid that empties directly into the urethra.  Male Hormones and their Functions To regulate the function of the testes, two hormones are secreted by the anterior pituitary gland found in the brain. The luteinizing hormone (LH) stimulates the secretion of the sex hormone testosterone.  Testosterone is produced by the Leydig cells found between the seminiferous tubules. It is responsible for the development of secondary male characteristics during puberty such as deepening of the voice, growth of facial hair, broadening of the shoulders, and the development of muscles.  MATURE SPERM IN EPIDIDYMIS At the onset of puberty, teenage boys start to produce sperm cell in their testes. Thereafter, an adult male produces several hundred million sperm cells each day. After being produced in the seminiferous tubules, the sperm mature and travel through a series of tubes. They then enter a long coiled tube called the epididymis.  OVARIES The ovaries are the female reproductive structures responsible for producing eggs. They are located inside the abdominal cavity located just slightly below the waist, with one ovary on each side of the body. Like the testes, the ovaries produce hormones. Estrogen, one of its hormones, triggers the development of secondary female characteristics such as widening of the hips and the enlargement of the breasts. The onset of mature egg cell production among females starts around the ages of 11 to 14 years, during the first discharge of blood from the vagina, called menarche. Thereafter, each month, a normal adult female releases a mature egg cell or female gamete in one of her ovaries. After the sperm has been deposited inside the female reproductive system during intercourse and after fertilization has occurred, the role of the male reproductive system is complete. The female reproductive system, on the other hand, will continue its role in nourishing and protecting the fertilized egg during nine months of development, or pregnancy.  EGG PRODUCTION All females are born with all the approximately two million egg cells they will ever produce. About every 28 days, an ovum is released in an adult female body. Hairlike structures called cilia sweep the ovum from the ovary into either of the two fallopian tubes or oviducts. During sexual intercourse, sperm cells are deposited inside the vagina, a passage that leads from the outside of the female’s body to the entrance of the uterus, called cervix. If fertilization occurs, the fertilized ovum, now called zygote, travels down further and implants itself in a hollow, muscular organ about the size of a fist, called uterus. During a normal childbirth, a baby passes through the cervix and leaves the mother’s body through the vagina. The main external structures of the female reproductive system include: Labia majora: The labia majora (“large lips”) enclose and protect the other external reproductive organs.  Labia minora: The labia minora (“small lips”) can have a variety of sizes and shapes. They lie just inside the labia majora, and surround the openings to the vagina and urethra.  Bartholin’s glands: These glands are located next to the vaginal opening on each side 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 internal reproductive organs include: Vagina: The vagina is a canal that joins the cervix (the lower part of uterus) to the outside of the body.  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.  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 pathways for the ova (egg cells) to travel from the ovaries to the uterus. What happens during the menstrual cycle? Menstru means "monthly” – leading to the term menstrual cycle. The term menstruation refers to the periodic shedding of the uterine lining. Many women call the days that they notice vaginal bleeding their “period,” “menstrual” or cycle. The average menstrual cycle takes about 28 days and occurs in phases. These phases include: The follicular phase (development of the egg) The ovulatory phase (release of the egg) The luteal phase (hormone levels decrease if the egg does not implant) There are four major hormones (chemicals that stimulate or regulate the activity of cells or organs) involved in the menstrual cycle. These hormones include: Follicle-stimulating hormone Luteinizing hormone Estrogen Progesterone Women eventually stop menstruating, usually around the age of 45 to 55. After this event, called menopause, a woman can no longer ovulates and, therefore, is unable to bear a child.  Stages of Human Development Fertilization of the Ovum  A human develops from an egg that has been fertilized by a sperm. The process begin when a sperm are deposited in the vagina, and then move through the uterus into the fallopian tubes. Nearly 300 to 400 million sperm cells may have made the journey to the fallopian tubes, yet only of these sperm will fertilize the egg. The head of the sperm enters the ovum, and the nuclei of the ovum and the sperm fuse together to produce zygote, which will develop into a new organism.  EMBRYONIC DEVELOPMENT  The nine-month period is called pregnancy. Starting from implantation of the zygote to the uterine wall up to the first two months of pregnancy, the developing child is called an embryo. An umbilical cord forms and connects the placenta to the embryo. A thin membrane called the amniotic sac begins to form around the embryo. The amniotic sac becomes filled with a clear liquid called amniotic fluid, which helps cushion and protect the embryo. Fetal Development  During the third month of pregnancy, the developing embryo begins to look more human – the eyes, fingers, toes, arms, and legs have already developed and is now called a fetus.  By this time, too, all the major organs are present to some extent. The fetal heart can be heard beating, and the mother starts feeling the movement of the fetus within the uterus. The fetus also begins to suck its thumb. By the fourth month, the sex of the fetus can be determined by an ultrasound test. The fetus becomes more active as it moves around in the uterus. By the end of the seventh month of pregnancy, a layer of fat develops under the skin, and fetal bones begins to harden BIRTH  By the ninth month , the fetus has usually rotated to a head- down position inside the uterus. The time for birth has arrived. The birth process begins with the onset of labor, the muscular contractions of the uterus. As the contractions become stronger and in closer succession, the amniotic sac usually breaks and releases its fluid. Eventually, the contractions cause the opening of the uterus to widen so the baby can pass through the vagina and then out into the world, taking in his/ her first gasp of air.