Biology: Reproductive System PDF

Lesson Overview The Reproductive System Lesson Overview 34.3 The Reproductive System Lesson Overview The Reproductive System Sexual Development...

Lesson Overview The Reproductive System Lesson Overview 34.3 The Reproductive System Lesson Overview The Reproductive System Sexual Development Growth of facial hair Increased muscular Testosterone development Deepening of the voice Breast development. Widening of the hips. Estrogen Lesson Overview The Reproductive System Sexual Development During the seventh week of development, male and female embryos start to develop differently. The male pattern of development is triggered by the production of testosterone in the embryo’s gonads. In female embryos, testosterone is absent and the female reproductive system develops under the influence of estrogens produced in the gonads. Lesson Overview The Reproductive System Puberty is a period of rapid growth and sexual maturation during which the reproductive system becomes fully functional. Lesson Overview The Reproductive System The Male Reproductive System When puberty is complete, the reproductive system is fully functional: the male can produce and release active sperm. Sperm LessonDevelopment Overview The Reproductive System 1. Just before birth (or just after) the testes descend from the abdomen into an external sac called the scrotum. 2. The temperature in the scrotum is a few degrees lower than the normal temperature of the body for proper sperm development. 3. Within each testis are clusters of hundreds of tiny tubules called seminiferous tubules where sperm develop. 4. After they are produced in the seminiferous tubules, sperm are moved into the epididymis, in which they mature and are stored. Lesson Overview The Reproductive System Sperm Development 5. From the epididymis, some sperm are moved into a tube called the vas deferens, which extends to the abdominal cavity and merges with the urethra. 6. Glands lining the reproductive tract—including the seminal vesicles, the prostate, and the bulbourethral glands—produce a nutrient-rich fluid called seminal fluid which nourishes the sperm and protects them from the acidity of the female reproductive tract. Lesson Overview The Reproductive System Sperm Development The combination of sperm and seminal fluid is known as semen. 1 milliliter of semen may contains 50 million and 130 million sperm. is packed with energy- releasing mitochondria highly condensed nucleus or flagellum, which propels the cell forward Lesson Overview The Reproductive System The Female Reproductive System The main function of the female reproductive system is to produce egg cells, or ova (singular: ovum). In addition, the system prepares the female’s body to nourish a developing embryo. Lesson Overview The Reproductive System Female Reproductive Structures 1. At puberty, each ovary contains up to 400,000 primary follicles. The follicles help an egg mature for release into the reproductive tract. About 400 eggs are released in a woman’s lifetime. One ovary usually produces and releases one mature ovum every 28 days or so. 1. The process of egg formation and release occurs as part of the menstrual cycle, a regular sequence of events involving the ovaries, the lining of the uterus, and the endocrine system. Lesson Overview The Reproductive System The Menstrual Cycle The menstrual cycle is regulated by hormones made by the hypothalamus, pituitary gland, and ovaries; it is controlled by internal feedback mechanisms. Lesson Overview The Reproductive System The Menstrual Cycle Menstrual cycle: an egg develops within a follicle and is released from an ovary. In addition, the uterus is prepared to receive a fertilized egg. If an egg is not fertilized, it is discharged, along with the lining of the uterus. If an egg is fertilized, embryonic development begins. The menstrual cycle stages: Follicular phase Ovulation Luteal phase Menstruation. Lesson Overview The Reproductive System Follicular Phase Ovulation When concentrations of estrogen reach FSH and LH stimulates the a certain level, the hypothalamus follicles (in ovaries) to mature. triggers a burst of LH and FSH. Estrogen cause the lining of the The follicle ruptures, resulting in uterus to thicken. ovulation (an egg is released from the ovary into one of the Fallopian tubes, and it’s push toward the uterus by micro cilia). Lesson Overview The Reproductive System Luteal Phase The ruptured follicle turns yellow (corpus luteum). This continues to release estrogens and begins to release progesterone which stimulates the growth and development of the blood supply and surrounding tissue in the uterine lining. Unless fertilization occurs and an embryo starts to develop, the corpus luteum degenerates. Lesson Overview The Reproductive System Menstruation Pregnancy The uterine wall along During the first two days of the with blood and the luteal phase, immediately unfertilized egg, are following ovulation, the chances discharged through that an egg will be fertilized are the vagina. the greatest. This is usually from 10 to 14 days after the The menstrual cycle completion of the last continues, on menstrual cycle. average, until a female is in her late 40’s to early 50’s, at which point the production of estrogens declines, and ovulation and menstruation stop (menopause). Lesson Overview Fertilization and Development Lesson Overview 34.4 Fertilization and Development Lesson Overview Fertilization and Development Fertilization and Early Development Fertilization is the fusion of a sperm and egg cell. Early development includes key events known as gastrulation, which produces the three cell layers of the embryo, and neurulation, which leads to the formation of the nervous system. Lesson Overview Fertilization and Development Fertilization Semen is generally released just below the cervix, the opening that connects the vagina to the uterus. Sperm swim actively through the uterus into the Fallopian tubes. If an egg is present in one of the Fallopian tubes, its chances of being fertilized are good. The fertilized egg is called a zygote. At this point the developing human can also be called an embryo. When a sperm enters the egg, the egg releases a material that coats preventing other sperm from attaching to, and entering, the egg. Lesson Overview Fertilization and Development Fertilization Multiple Embryos Fraternal Twins will result if two eggs are released during the same menstrual cycle and each is fertilized. They are not identical and may be different sexes. Identical Twins will result when a single zygote splits apart and produces two genetically identical embryos. Lesson Overview Fertilization and Development Implantation 1. While still in the Fallopian tube, the zygote begins to undergo mitosis. 2. As the embryo grows, a cavity forms in the center, until the embryo becomes a hollow ball of cells known as a blastocyst. 3. About six or seven days after fertilization, the blastocyst attaches to the wall of the uterus and begins to grow into the tissues of the mother (number 8 in figure.) Lesson Overview Fertilization and Development Implantation https://www.youtube.com/watch?v=UgT5rUQ9EmQ https://www.youtube.com/watch?v=dgPCDXmcQjM Lesson Overview Fertilization and Development Gastrulation The result of gastrulation is the formation of three cell layers called the ectoderm, mesoderm, and endoderm. The ectoderm and endoderm form first. The mesoderm is produced by a process of cell migration shown in the figure. Lesson Overview Fertilization and Development Gastrulation Skin and nervous Many internal system organs: Bones, Linings of organs of digestive, muscles, blood cells, respiratory, excretory system and gonads. Lesson Overview Fertilization and Development Neurulation * Neurulation is the first step in the development of the nervous system. A block of mesodermal tissue begins differentiate into the notochord. spinal cord & brain will develop Lesson Overview Fertilization and Development Neurulation If the neural tube does not close completely, a serious birth defect known as spina bifida can result. Studies show that folic acid, also known as vitamin B9, can prevent most cases of spina bifida. Because neurulation usually occurs before a woman is aware of pregnancy, folic acid is an important nutrient in any woman’s diet. Lesson Overview Fertilization and Development The Placenta The embryo is surrounded by the amnion, a sac filled with amniotic fluid that cushions and protects the developing embryo. Another sac, known as the chorion, forms just outside the amnion. The chorion makes direct contact with the tissues of the uterus. Near the end of the third week of development, chorionic villi form on the outer surface of the chorion and extend into the uterine lining. The chorionic villi and uterine lining form the placenta. The placenta is the connection between the mother and the embryo that acts as the embryo’s organ of respiration, nourishment, and excretion. Lesson Overview Fertilization and Development The Placenta After eight weeks of development, the embryo is called a fetus. By the end of three months, most of the major organs and tissues are fully formed. The muscular system is well developed. The fetus may begin to move and show signs of reflexes. The fetus is about 8 centimeters long and has a mass of about 28 grams. LATER DEVELOPMENT * During the fourth, fifth, and sixth months after fertilization, the tissues of the fetus become more complex and specialized, and begin to function. * During the last three months before birth, the organ systems of the fetus mature, and the fetus grows in size and mass. MONTHS 4–6 – The fetal heart becomes large enough so that it can be heard with a stethoscope. – Bone continues to replace the cartilage that forms the early skeleton. – A layer of soft hair grows over the skin of the fetus. – The mother begins to feel the fetus moving. MONTHS 7–9 – The fetus doubles in mass, and the lungs and other organs undergo a series of changes that prepare them for life outside the uterus. – The fetus is now able to regulate its body temperature. – The central nervous system and lungs complete their development. LATER DEVELOPMENT – On average, it takes nine months for a fetus to develop fully. – Babies born before eight months of development are called premature babies and often have severe breathing problems because of incomplete lung development. CHILDBIRTH – A complex set of factors triggers the birth process; one of these factors is the release of the hormone oxytocin from the mother’s posterior pituitary gland. – Oxytocin affects a group of large involuntary muscles in the uterine wall. As these muscles are stimulated, they begin a series of rhythmic contractions known as labor. – As labor progresses, the contractions become more frequent and more powerful. – The opening of the cervix expands until it is large enough for the head of the baby to pass through. – At some point, the amniotic sac breaks, and the fluid it contains rushes out of the vagina. CHILDBIRTH – As the baby meets the outside world, he or she may begin to cough or cry, a process that rids the lungs of fluid. – Breathing starts almost immediately, and the blood supply to the placenta begins to dry up. – The umbilical cord is clamped and cut, leaving a small piece attached to the baby that will soon dry and fall off, leaving a scar known as the navel—or, its more familiar term, the belly button. – In a final series of uterine contractions, the placenta and the empty amniotic sac are expelled from the uterus as the afterbirth. – Within a few hours after birth, the pituitary hormone prolactin stimulates the production of milk in the mother’s breasts. INFANT AND MATERNAL HEALTH – The virus that causes AIDS can infect the developing fetus, and the virus responsible for rubella (German measles) can cause birth defects. – Alcohol can permanently injure the nervous system, and drugs such as heroin and cocaine can cause drug addiction in newborn babies. – Smoking during pregnancy can double the risk of low weight at birth, leading to other severe health problems. INFANT AND MATERNAL HEALTH – From 1970 to 2000, the infant mortality rate in the United States decreased by about 65 percent. – Many factors contributed to this decrease. INFANT AND MATERNAL HEALTH – For example, in 1993 the U.S. Public Health Service recommended that women consume 4 mg of folic acid per day. Between 1996 and 1998, manufacturers of enriched grain products began to add folic acid to their products, which affected the incidence of spina bifida.