Human Reproduction PDF

Chapter 9 Human Reproductio n Male and Female Reproductive System  Humans begin their lives as a single cell. This single cell is formed by the fusion of two sex cells- an egg and a sperm- from the parents. As you reach adolescence, your sex organs undergo changes to be able t...

Chapter 9 Human Reproductio n Male and Female Reproductive System  Humans begin their lives as a single cell. This single cell is formed by the fusion of two sex cells- an egg and a sperm- from the parents. As you reach adolescence, your sex organs undergo changes to be able to produce sex cells needed to produce new individuals. These sex cells contains structures called chromosomes that contain genetic information which carries unique traits such as skin color or hair color.  Human sex cells contain only half the number of chromosomes of a regular body cell (somatic). Each sex cell which has 23 chromosomes, is a haploid (n), while the regular cell which has 46 chromosomes is a diploid (2n). After the fusion of the egg and the sperm, the resulting fertilized egg, known as a zygote, contains 46 chromosomes. 01 Male Reproductive System  The male reproductive system produces sperm cells (male gametes) and delivers them to the female reproductive system. In males the primary reproductive organs are the testes. Testes The testes are oval-shaped organs found inside a protective sac of skin called the scrotum. The location of the testes in the scrotum, which is outside the body is very important for the proper development of the sperm. Testes Since the scrotum lies outside the abdominal cavity, its temperature is one to two degrees lower than the internal body temperature (37˚C), making it ideal for sperm production, which requires lower temperatures. Since the scrotum lies outside the abdominal cavity, its temperature is one to two degrees lower than the internal body temperature (37˚C), making it ideal for sperm production, which requires lower temperatures. Sperm cells are produced in the linings of the seminiferous tubules through meiosis.  Male Hormones and Their Functions To regulate the functions of the testes, two hormones are secreted by the anterior pituitary gland found in the brain. 1. Luteinizing Hormone (LH) stimulates the secretion of the sex hormone testosterone. 2. Follicle-stimulating Hormone (FSH) along with testosterone, stimulates sperm production in the seminiferous tubules.  Male Hormones and Their Functions Testosterone is produced by the Ledwig cells between the seminiferous tubules. It is responsible for the development of secondary male characteristics during puberty. Mature Sperms in the Epididymis An adult male produces several hundred million sperms each day. After being produced in the seminiferous tubules, the sperms mature and travel through a series of tubes. They then enter a long coiled tube called epididymis, where they will mature until they are capable of swimming and moving.  Mature Sperms in the Epididymis The epididymis is also where most of the sperms are stored. Mature sperms will travel from the epididymis to vas deferens then exit the body through the urethra. The Human Sperm Cell A human sperm cell consists of three parts; a head that contains the chromosomes, a midpiece that contains the mitochondria, and a long tail that is responsible for movement.  The Human Sperm The head is made up of a nucleus covered by a cap called acrosome, which stores enzymes needed to penetrate an egg cell during penetration.  The midpiece contains the mitochondria that supply the energy needed to propel the sperm through the female reproductive tract. The tail of the sperm is a powerful flagellum that enable the sperm cell to move.  Transportation of the Sperm During their passage through the urethra, sperms mix with the fluids produced by neighboring glands- the prostate gland, seminal vesicles and the bulbourethral glands. The combined secretions of these glands, collectively called semen, which nourishes the sperm cells.  Transportation of the Sperm Gland Functions of Secretion Alkaline fluid that neutralizes the acids in the Prostate Gland female reproductive system. Fluids rich in sugars that sperm use for Seminal Vesicles energy. Alkaline fluid that neutralizes traces of acidic Bulbourethral Glands urine in the urethra.  Delivery of the Sperm The urethra leads the sperm cell through the penis, the male organ that deposits the sperm in the female reproductive system during sexual intercourse or copulation. During sexual excitation, blood rushes into the penis making it rigid or erect. Sperm exit the penis through ejaculation, the forceful expulsion of the sperm out of a male’s body. 02 Female Reproductive System Ovaries The ovaries are the female reproductive structures responsible for producing eggs.  They are located inside the abdominal cavity just slightly below the waist with one ovary on each side of the body. Estrogen, one of its hormones triggers the development of secondary female characteristics. Most importantly it stimulates egg development. The onset of mature egg cell production among females starts at around ages of 11 to 14 years, during the first discharge of blood from the vagina called menarche. Every month thereafter, a normal adult female releases a mature egg cell (female gamete) in from one of her ovaries. After the sperm has been deposited inside the female reproductive system during copulation and after fertilization has occurred, the role of the male reproductive system is complete. The female reproductive system, on the other hand will begin its role in nourishing and protecting the fertilized egg during nine months of development. This is called gestation or pregnancy.  Egg Production All females are born with all the approximately two million egg cells they will produce in their lifetime. By the time a female reaches puberty, the number of egg cells would have gone down to about 400,000. During puberty, the increased production of hormones enables one immature egg to complete its development each month. In the lifetime of a female, out of 400,000 egg cells at the start of puberty only 300 to 500 will mature and are then called ova (ovum). Egg Production About every 28 days, an ovum is released in an adult female body. Hair-like structures called cilia sweep the ovum from the ovary into either of the fallopian tubes or oviducts. Each fallopian tube is a passageway through which an ovum moves from an ovary to the uterus. Egg Production It takes three to four days for ovum to travel inside the fallopian tube. If the ovum is not fertilized at this stage, it dies within 24 to 48 hours. 03 Female Reproductive Cycles  All females who have reach puberty will undergo monthly physiological cycles known as ovarian and menstrual cycle. 1. Ovarian cycle- involves the ovary, prepares the egg for maturation. 2. Menstrual cycle- involves the uterus, grooms the uterus for a possible implantation and, later on pregnancy.  The Ovarian Cycle The ovaries prepare the female body each month to make pregnancy possible. This series of events is collectively known as ovarian cycle. The monthly release of an ovum from the ovary is called ovulation. The released ovum is swept into the fallopian tube and begins to move toward the uterus to await fertilization. The ovarian cycle spans about 28 days, although it varies from female to female.  The Follicular Phase In an ovary, egg cells mature within follicles. A follicle is a cluster of cells that surrounds an immature egg cell and provides it with nutrients and protection. During the follicular phase of the ovarian cycle, hormones regulate the completion of an egg cell’s maturation.  The Follicular Phase (1-4). Anterior pituitary gland releases follicle- stimulating hormone (FSH) and luteinizing hormone (LH) into the bloodstream. These hormones cause the follicle to produce estrogen. Estrogen, is a sex hormone that aids the growth of the ovarian follicle. 5. When the follicle bursts, ovulation occurs.  The Luteal Phase (6-7). After ovulation luteal phase begins LH causes the ruptured follicle to grow and form corpus luteum. LH causes the corpus luteum to secrete both estrogen and progesterone. Progesterone is a sex hormone that signals the body to prepare for fertilization.  The Menstrual Cycle The normal menstrual cycle lasts for 28 days. The events in the menstrual cycle are controlled by the changing levels of estrogen and progesterone. Prior to and after ovulation increased level of estrogen and progesterone cause the lining of the uterus to thicken. If pregnancy does not occur, the levels of estrogen and progesterone decrease, causing the lining of the uterus to be shed, which marks the end of the menstrual cycle.  The Menstrual Cycle At the end of ovarian and menstrual cycles, neither estrogen or progesterone is being produced. This signals the pituitary gland to produce FSH and LH starting the cycles again. The production of estrogen and progesterone in women eventually declines around their mid 40s. This begins the transition to the menopausal stage. 04 Stages of Human Development Before Birth Fertilization of the Ovum The process begins when sperms are deposited in the vagina, and then move through the uterus into the fallopian tubes. If the sperm reach the fallopian tube within 36 hours during the female’s ovulation period, there will be an egg ready to be fertilized in one of the fallopian tubes. Fertilization of the Ovum During fertilization, a sperm cell penetrates an ovum and releases the enzymes stored in its acrosome. These enzymes break down the jellylike outer layers of the ovum. The head of the sperm enters the ovum. The nuclei of the sperm and ovum fuse to produce a zygote. Fertilization of the Ovum Cell division takes place as the zygote travels back down the oviduct toward the uterus. (6-7 days) The zygote becomes a small ball of cells that attaches itself to the uterine wall in the process called implantation. Embryonic Development Starting from the implantation of the zygote to the uterine wall up to the first two months of pregnancy, the developing child is called an embryo. Embryonic Development A part of the uterine wall produces the villi which constitute the placenta, along with other blood vessels and capillaries. An umbilical cord forms and connects the placenta to the embryo. Nutrients and oxygen in the mother’s blood are transported to the embryo through the veins in the umbilical cord. Embryonic Development Carbon dioxide and other wastes are carried away from the embryo through an artery in the umbilical cord to the mother’s bloodstream for disposal. During the 3rd week of pregnancy, a thin membrane called amniotic sac begins to form around the embryo. This is filled with amniotic fluid, which helps cushion and protect the embryo. Fetal Development 3rd month- the developing embryo becomes more human, the eyes, fingers, toes, arms and legs have already developed. -All major organs are present, the fetal heart can be heard beating. -The mother starts feeling the movement of fetus within the uterus. -The fetus begins to suck its thumb. Fetal Development 4th month- The sex of the fetus can be determined through an ultrasound test. -The fetus becomes more active as it moves around in the uterus. 7th month- a layer of fat develops under the skin, and fetal bones begins to harden.  Birth - In the ninth month of pregnancy, the fetus usually rotated to a head- down position inside the uterus, signaling that the time for birth has arrived.  Birth The birth process begins with the onset of labor, the muscular contractions of the uterus. As the contractions become stronger and in close succession the amniotic sac usually breaks down and releases its fluid.  Birth 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.